This paper presents an efficient fair document exchange protocol. The exchange of the documents will be between two parties. The protocol is based on the verifiable and recoverable encryption of a document’s key. This verifiable and recoverable encryption of the document’s key will allow one party to verify the encrypted key. It will also ensure this party that the Semi Trusted Third Party will be able to recover the key if the other party misbehaves. The protocol also incorporates the concept of enforcing the honesty of one party. The proposed protocol consists of only three messages and is more efficient than related protocols.
This document provides an overview of digital signatures, including:
- Digital signatures use asymmetric cryptography to authenticate digital messages and detect tampering.
- They employ key generation, signing, and verification algorithms.
- Direct digital signatures involve only the communicating parties, while arbitrated signatures use a trusted third party arbiter.
- Examples of arbitrated signature techniques include using symmetric encryption with a shared key between parties and arbiter, or public-key encryption so the arbiter cannot read messages.
This document proposes a token-based contract signing protocol using one-time private keys (OTPK) to provide secure authentication between parties. The protocol aims to solve issues with exchanging digital signatures for electronic contracts by ensuring fairness - that either both parties receive each other's signatures or neither does. It uses an offline trusted third party that is only involved if one party fails to send their signature. The key aspects are:
1) OTPK allows generation of a single-use private key for each authentication, improving security by preventing key storage.
2) The protocol simulates paper-based contract signing by exchanging digital signatures in a fair manner with or without a third party.
3) It aims to provide
The document discusses digital signatures, which provide authentication of electronic documents and messages. Digital signatures use public key cryptography, with each user having a unique private key and corresponding public key. To generate a digital signature, a document's hash value is encrypted with the sender's private key. Recipients can verify the signature by decrypting the hash with the sender's public key and comparing it to a newly generated hash of the received document. This allows confirmation of the sender's identity and ensures the document has not been altered. The document outlines the basic digital signature process and requirements for using digital signatures to authenticate electronic information.
Digital signatures provide authentication of digital documents through encryption with a private key. They offer advantages over physical signatures like non-repudiation and integrity verification by checking that the document contents have not changed. Digital signatures are created by running a hash function over a message to generate a message digest, then encrypting the digest with a private key. They can be used for a variety of applications including e-voting, online money transfers, and filing government forms electronically.
IRJET- A Review on Implementation Techniques of Blockchain Enabled Smart Cont...IRJET Journal
This document provides a summary of blockchain and smart contracts for document verification. It discusses how blockchain uses cryptography and smart contracts to allow for verification of digital documents like degrees in a decentralized manner. Blockchain provides trust, autonomy, and integrity for such a system by storing document hashes and details securely on the distributed ledger. Smart contracts can then enable functions for users to validate certificates and degrees stored on the blockchain to avoid fraud.
Digital signature is an electronic signature form used by an original signer to sign a specific
document. When the original signer is not in his office or when he/she travels outside, he/she delegates his
signing capability to a proxy signer and then the proxy signer generates a signing message on behalf of the
original signer.During the transmission of data between the sender and receiver, errors may occur frequently.
Therefore, the sender must re-transmit the data to the receiver in order to correct these errors, which makes the
system very feeble. The techniques of proxy signature and fault tolerance are two important issues in modern
communication.To communicate securelyover an unreliable public network, the two parties must be able to
authenticate one another and agree on a secret encryption key. Authenticated key agreement protocols have an
important role in building a secure communications network between the two parties. In this paper, we propose
a secure proxy signature scheme with fault tolerance over an efficient and secure authenticated key agreement
protocol based on factoring and the discrete logarithm problem.
This document defines electronic signatures and discusses how they work using public key infrastructure (PKI). It explains that electronic signatures involve hashing document contents, encrypting the hash with a private key, and including the encrypted hash and public key in a digital certificate. It describes risks like man-in-the-middle attacks and the role of certificate authorities in verifying identities and signatures. The document also outlines standard certificate formats, details the components of a certificate, and explains how improved signing procedures provide non-repudiation of signed documents.
This document provides an overview of digital signatures, including how they work and their legal aspects. It discusses how encryption scrambles messages and digital signatures verify authorship and document integrity. Digital signatures use public/private key pairs, where the private key is unique to the signer. To create a digital signature, a hash of the message and private key is computed. Verification involves recomputing the hash with the public key and signature to validate authenticity. Digital signatures provide evidence of authorship, represent a legal ceremony of approval, and make documents more efficient to process.
This document provides an overview of digital signatures, including:
- Digital signatures use asymmetric cryptography to authenticate digital messages and detect tampering.
- They employ key generation, signing, and verification algorithms.
- Direct digital signatures involve only the communicating parties, while arbitrated signatures use a trusted third party arbiter.
- Examples of arbitrated signature techniques include using symmetric encryption with a shared key between parties and arbiter, or public-key encryption so the arbiter cannot read messages.
This document proposes a token-based contract signing protocol using one-time private keys (OTPK) to provide secure authentication between parties. The protocol aims to solve issues with exchanging digital signatures for electronic contracts by ensuring fairness - that either both parties receive each other's signatures or neither does. It uses an offline trusted third party that is only involved if one party fails to send their signature. The key aspects are:
1) OTPK allows generation of a single-use private key for each authentication, improving security by preventing key storage.
2) The protocol simulates paper-based contract signing by exchanging digital signatures in a fair manner with or without a third party.
3) It aims to provide
The document discusses digital signatures, which provide authentication of electronic documents and messages. Digital signatures use public key cryptography, with each user having a unique private key and corresponding public key. To generate a digital signature, a document's hash value is encrypted with the sender's private key. Recipients can verify the signature by decrypting the hash with the sender's public key and comparing it to a newly generated hash of the received document. This allows confirmation of the sender's identity and ensures the document has not been altered. The document outlines the basic digital signature process and requirements for using digital signatures to authenticate electronic information.
Digital signatures provide authentication of digital documents through encryption with a private key. They offer advantages over physical signatures like non-repudiation and integrity verification by checking that the document contents have not changed. Digital signatures are created by running a hash function over a message to generate a message digest, then encrypting the digest with a private key. They can be used for a variety of applications including e-voting, online money transfers, and filing government forms electronically.
IRJET- A Review on Implementation Techniques of Blockchain Enabled Smart Cont...IRJET Journal
This document provides a summary of blockchain and smart contracts for document verification. It discusses how blockchain uses cryptography and smart contracts to allow for verification of digital documents like degrees in a decentralized manner. Blockchain provides trust, autonomy, and integrity for such a system by storing document hashes and details securely on the distributed ledger. Smart contracts can then enable functions for users to validate certificates and degrees stored on the blockchain to avoid fraud.
Digital signature is an electronic signature form used by an original signer to sign a specific
document. When the original signer is not in his office or when he/she travels outside, he/she delegates his
signing capability to a proxy signer and then the proxy signer generates a signing message on behalf of the
original signer.During the transmission of data between the sender and receiver, errors may occur frequently.
Therefore, the sender must re-transmit the data to the receiver in order to correct these errors, which makes the
system very feeble. The techniques of proxy signature and fault tolerance are two important issues in modern
communication.To communicate securelyover an unreliable public network, the two parties must be able to
authenticate one another and agree on a secret encryption key. Authenticated key agreement protocols have an
important role in building a secure communications network between the two parties. In this paper, we propose
a secure proxy signature scheme with fault tolerance over an efficient and secure authenticated key agreement
protocol based on factoring and the discrete logarithm problem.
This document defines electronic signatures and discusses how they work using public key infrastructure (PKI). It explains that electronic signatures involve hashing document contents, encrypting the hash with a private key, and including the encrypted hash and public key in a digital certificate. It describes risks like man-in-the-middle attacks and the role of certificate authorities in verifying identities and signatures. The document also outlines standard certificate formats, details the components of a certificate, and explains how improved signing procedures provide non-repudiation of signed documents.
This document provides an overview of digital signatures, including how they work and their legal aspects. It discusses how encryption scrambles messages and digital signatures verify authorship and document integrity. Digital signatures use public/private key pairs, where the private key is unique to the signer. To create a digital signature, a hash of the message and private key is computed. Verification involves recomputing the hash with the public key and signature to validate authenticity. Digital signatures provide evidence of authorship, represent a legal ceremony of approval, and make documents more efficient to process.
Privacy Preserving Reputation Calculation in P2P Systems with Homomorphic Enc...IJCNCJournal
This document discusses a method for privacy-preserving reputation calculation in peer-to-peer systems using homomorphic encryption. Specifically, it proposes:
1) Extending the EigenTrust reputation system to calculate node reputations in a distributed manner while preserving evaluator privacy. It does this by successively updating encrypted reputation values through calculation to reflect trust values without disclosing the original values.
2) Improving calculation efficiency by offloading parts of the task to participating nodes and using different public keys during calculation to improve robustness against node churn.
3) Evaluating the performance of the proposed method, finding it reduces maximum circulation time for aggregating multiplication results by half, reducing computation time per round. The privacy preservation cost scales
1. The document discusses the history and development of electronic signatures, from encoding messages to modern cryptography. It describes how asymmetric cryptography and public/private key pairs enabled electronic signatures by verifying the identity of the sender.
2. An example is given of obtaining a cryptographic USB key from a Trusted Third Party to digitally sign documents and emails. Integrity is ensured as signatures cannot be altered without invalidating the signature.
3. Examples of using electronic signatures include signing contracts between call centers and offshore companies, signing sales proposals from banks to customers, and signing insurance contracts online with time stamping and IP address verification. Electronic signatures provide security, proof of origin, and increase conversion rates.
A digital signature provides authentication of the sender, integrity of the document, and non-repudiation by using public key cryptography. It consists of a signing process, where the document is hashed and the hash is encrypted with the private key and attached to the original document. In verification, the signature is decrypted with the public key and compared to a newly generated hash of the document to validate authenticity. Digital signatures are commonly used for legally binding electronic documents and communications to establish trust between parties.
A PROXY SIGNATURE SCHEME BASED ON NEW SECURE AUTHENTICATED KEY AGREEMENT PROT...csandit
Proxy signature scheme permits an original signer to delegate his/her signing capability to a
proxy signer and then the proxy signer generates a signing message on behalf of the original
signer. So far, the proxy signature scheme is only applied in a special duration, when the
original signer is not in his office or when he travels outside. The two parties must be able to
authenticate one another and agree on a secret encryption key, in order to communicate
securely over an unreliable public network. Authenticated key agreement protocols have an
important role in building a secure communications network between the two parties. In this
paper, we propose a secure proxy signature scheme over an efficient and secure authenticated
key agreement protocol based on RSA cryptosystem.
Elliptic curve cryptography (ECC) is an approach to public-key cryptography that uses elliptic curves over finite fields. It provides the same level of security as other cryptosystems but with smaller key sizes. ECC is used for encryption, digital signatures, and other tasks. It is based on the algebraic structure of elliptic curves and points on those curves forming an Abelian group. The U.S. has endorsed ECC algorithms for key exchange and digital signatures.
BLOCKCHAIN-BASED SMART CONTRACTS : A SYSTEMATIC MAPPING STUDY csandit
An appealing feature of blockchain technology is smart contracts. A smart contract is
executable code that runs on top of the blockchain to facilitate, execute and enforce an
agreement between untrusted parties without the involvement of a trusted third party. In this
paper, we conduct a systematic mapping study to collect all research that is relevant to smart
contracts from a technical perspective. The aim of doing so is to identify current research topics
and open challenges for future studies in smart contract research. We extract 24 papers from
different scientific databases. The results show that about two thirds of the papers focus on
identifying and tackling smart contract issues. Four key issues are identified, namely, codifying,
security, privacy and performance issues. The rest of the papers focuses on smart contract
applications or other smart contract related topics. Research gaps that need to be addressed in
future studies are provided.
AN EFFICIENT GROUP AUTHENTICATION FOR GROUP COMMUNICATIONSIJNSA Journal
- The document proposes a new type of authentication called group authentication that authenticates all users in a group at once, rather than authenticating users individually.
- A group manager is responsible for registering users and issuing unique tokens to each user based on a secret polynomial. During authentication, users present their tokens to prove they belong to the same group without revealing their identities.
- Two group authentication protocols are proposed: a basic one-time protocol where tokens are revealed, and an improved protocol that protects tokens by having each user generate shares of a random polynomial for others and releasing the sum of their token and shares received. This allows for authentication without revealing tokens or the secret.
This document discusses cyber or online contracts. It defines a cyber-contract as one created through communications over computer networks, whether entirely through email exchanges showing offer and acceptance, or a combination of electronic and other means. The key elements of a valid contract - offer, acceptance, consideration, and consent - still apply to online contracts. Digital signatures can verify the identity of parties to an online contract by encrypting messages with public and private keys. This allows confirmation that a message has not been altered and verifies the sender. Overall, the document outlines how traditional contract law elements can be applied to agreements made electronically.
1) Electronic contracts are standard form contracts with non-negotiable terms formulated by one party like a manufacturer or service provider. The Information Technology Act, 2000 recognizes the validity of e-contracts.
2) E-contracts can be formed via email exchanges or through websites using clickwrap, browsewrap, or shrinkwrap agreements. However, e-contracts raise issues around jurisdiction, capacity to contract, consent, and meeting of minds.
3) The Information Technology Act and Indian Evidence Act provide for the validity and evidentiary value of e-contracts in India if they meet requirements for identification of parties, subject matter, signatures. However, the laws do not address all aspects of online contracts.
A SYSTEMATIC MAPPING STUDY ON CURRENT RESEARCH TOPICS IN SMART CONTRACTSijcsit
The document summarizes the results of a systematic mapping study on current research topics related to smart contracts. The study identified 24 relevant papers from scientific databases. Two-thirds of the papers focused on identifying and addressing issues with smart contracts, such as coding, security, privacy and performance issues. The remaining papers examined smart contract applications or other topics. The study aims to map current research areas and identify gaps to guide future work on smart contracts.
This document analyzes and summarizes the cryptanalysis of a recent two-factor authentication scheme proposed by Wang and Ma. The analysis points out some issues with the scheme. Specifically, while the scheme claims passwords are not stored on the server, identities are stored in a table on the server without cryptographic protection. The analysis also shows that an adversary could break the scheme by determining a user's identity from their compromised smart card, even though the paper does not explicitly give the adversary this capability. Through capturing a smart card, determining the user's identity, and running an offline password guessing attack, the entire scheme can be compromised if either factor is obtained.
This document discusses the definition, essential elements, and validity of e-contracts under Indian law. It defines an e-contract as any contract formed through electronic means like email. The key points are:
1. The Indian Contract Act and Information Technology Act recognize the validity of e-contracts and electronic communications/records as legally binding.
2. Essential elements of a valid contract like offer, acceptance, consideration must be present in e-contracts for them to be enforceable.
3. E-contracts can be formed via websites through clickwrap/browsewrap/shrinkwrap agreements or via email exchange. The postal rule of acceptance applies to email.
4. Electronic records and digital signatures have evidentiary
Game Theory Approach for Identity Crime DetectionIOSR Journals
This document discusses using game theory to detect identity crimes related to credit card fraud. It proposes a two-layered detection system using communal detection and spike detection algorithms. Communal detection uses a whitelist approach to reduce false positives, while spike detection identifies attributes that detect fraud spikes to increase true positives. It also discusses using dynamic time warping to minimize detection times. The paper evaluates the approach on real credit application data, finding it achieves lower identity variation frequencies, fraudulent identities, and verification times compared to existing detection methods.
This document discusses e-commerce and e-contracts. It begins by defining e-commerce as commerce conducted electronically, including buying and selling of goods and services online. It then discusses different types of e-commerce like business-to-business, business-to-consumer, consumer-to-business, and consumer-to-consumer. The document also summarizes the Bhagwandas Kedia case, which established that contracts formed through telephone conversations are considered formed at the location where the acceptance is received, opening the door for e-contracts to be recognized.
This document discusses e-contracts, comparing them to traditional contracts. It defines e-contracts as contracts formed online through email or other electronic means. E-contracts are legally binding under Indian law if they meet the requirements of a valid contract. Common types of e-contracts include shrinkwrap, clickwrap, and browsewrap agreements. The document analyzes several cases related to the validity of different e-contract types and notes some limitations, such as lack of clear notice for browsewrap agreements. It concludes that e-contracts will continue growing with advances in technology but notes Indian law does not fully cover all online contract aspects.
An e-contract is any contract formed through electronic means such as email, websites, or software. The Uniform Computer Information Transactions Act provides rules for forming, governing, and setting basic terms of e-contracts. E-contracts can be formed through processes like exchanging emails containing offers and acceptances, completing web forms, or clicking to agree to online terms. There are different types of e-contracts like employment contracts, shrinkwrap contracts governing software licenses, and source code escrow agreements. Forming e-contracts involves information, intention, agreement, and settlement phases with various legal considerations around elements, signatures, and international guidelines.
A fair exchange & customer anonymity protocolIJNSA Journal
The rapid development of technology and the reach of such technologies at affordable costs has made it
possible for all people across the world to make purchases at a click of the mouse and at their
convenience.Electronic commerce technologies and protocols facilitate the processing of online
transactions. Trust plays a major role in e-commerce transactions and various protocols help establishing
this trust by providing fair exchange and anonymity.
The research aims at designing and developing a protocol that provides both fair exchange and anonymity,
thus avoiding the need to have manual dispute resolution. It takes into account the technical flaws
researched and overcomes those by implementing methods to ensure that confidentiality and integrity of the
messages are maintained by making sure that the Trusted Third Party does not have the authority to view
or modify the messages but can only verify the authenticity of the other two parties.
A Fair Exchange & Customer Anonymity Protocol Using A Trusted Third Party for...IJNSA Journal
The rapid development of technology and the reach of such technologies at affordable costs has made it possible for all people across the world to make purchases at a click of the mouse and at their convenience.Electronic commerce technologies and protocols facilitate the processing of online transactions. Trust plays a major role in e-commerce transactions and various protocols help establishing this trust by providing fair exchange and anonymity.
The research aims at designing and developing a protocol that provides both fair exchange and anonymity, thus avoiding the need to have manual dispute resolution. It takes into account the technical flaws researched and overcomes those by implementing methods to ensure that confidentiality and integrity of the messages are maintained by making sure that the Trusted Third Party does not have the authority to view or modify the messages but can only verify the authenticity of the other two parties.
DESIGN AND EVALUATION OF A NEW FAIR EXCHANGE PROTOCOL BASED ON AN ONLINE TTP IJNSA Journal
Security protocols in e-commerce are required to manage the transactions between buyers and sellers. In order to engage customers in e-commerce, these protocols should be well formulated and secured; they should protect both parties from fraudulent users and subsequently promote the growth of e-commerce. There are some protocols, known as fair exchange protocols, in e-commerce that are designed to guarantee fairness between the customer and the merchant so that neither party gains any advantage over the other. Therefore, in this paper, we introduce a new fair exchange protocol for trading products online between a buyer and a seller. The items to be exchanged in this protocol are a digital product and a payment. The following are the characteristics of this new protocol: (1) Dependency on a trusted third party is greatly reduced; further, the protocol also overcomes increased communication overheads and risks, hence leading to substantial improvement in the efficiency and practicality of the protocol. (2) The
protocol ensures fairness for all parties and provides an internal dispute resolution mechanism, thereby guaranteeing that none of the parties involved in the transaction suffer unfairly in case one of the entities disappears before the transaction is formalized. (3) The protocol consists of three messages exchanged between the buyer (customer) and the seller (merchant).
A Novel Fair Anonymous Contract Signing Protocol for E-Commerce Applications IJNSA Journal
With the economy developing and popular Internet, the general concept of contract signing has changed. In the past, people usually sign a contract at the same time and same place face to face, but actually each party involved in contract may live in different part of earth, they want to sign something for business or some other things in economic, efficient, secure and fairway. A fair contract signing protocol allows two potentially mis-trusted parities to exchange their commitments (i.e., digital signatures) to an agreed contract over the Internet in a fair way, so that either each of them obtains the other’s signature, or neither party does. Based on the LUCAS signature scheme, a new digital anonymous contract signing protocol is proposed in this paper. Like the existing LUCAS-based solutions for the same problem, our protocol is fair, anonymous and optimistic. Furthermore, the proposed protocol satisfied a new
property, i.e., it is abuse-free. That is, if the protocol is executed unsuccessfully, either of the two parties can not show the validity of intermediate results to others.
E mail security using Certified Electronic Mail (CEM)Pankaj Bhambhani
The document discusses certified electronic mail (CEM) and its properties like non-repudiation, fairness, use of a trusted third party, and timeliness. It also summarizes the S/MIME protocol and proposes adding non-repudiation of receipt to S/MIME to improve its security. Finally, it outlines a key chain based CEM protocol that uses a transparent trusted third party and satisfies properties like non-repudiation of origin and receipt as well as fairness.
Privacy Preserving Reputation Calculation in P2P Systems with Homomorphic Enc...IJCNCJournal
This document discusses a method for privacy-preserving reputation calculation in peer-to-peer systems using homomorphic encryption. Specifically, it proposes:
1) Extending the EigenTrust reputation system to calculate node reputations in a distributed manner while preserving evaluator privacy. It does this by successively updating encrypted reputation values through calculation to reflect trust values without disclosing the original values.
2) Improving calculation efficiency by offloading parts of the task to participating nodes and using different public keys during calculation to improve robustness against node churn.
3) Evaluating the performance of the proposed method, finding it reduces maximum circulation time for aggregating multiplication results by half, reducing computation time per round. The privacy preservation cost scales
1. The document discusses the history and development of electronic signatures, from encoding messages to modern cryptography. It describes how asymmetric cryptography and public/private key pairs enabled electronic signatures by verifying the identity of the sender.
2. An example is given of obtaining a cryptographic USB key from a Trusted Third Party to digitally sign documents and emails. Integrity is ensured as signatures cannot be altered without invalidating the signature.
3. Examples of using electronic signatures include signing contracts between call centers and offshore companies, signing sales proposals from banks to customers, and signing insurance contracts online with time stamping and IP address verification. Electronic signatures provide security, proof of origin, and increase conversion rates.
A digital signature provides authentication of the sender, integrity of the document, and non-repudiation by using public key cryptography. It consists of a signing process, where the document is hashed and the hash is encrypted with the private key and attached to the original document. In verification, the signature is decrypted with the public key and compared to a newly generated hash of the document to validate authenticity. Digital signatures are commonly used for legally binding electronic documents and communications to establish trust between parties.
A PROXY SIGNATURE SCHEME BASED ON NEW SECURE AUTHENTICATED KEY AGREEMENT PROT...csandit
Proxy signature scheme permits an original signer to delegate his/her signing capability to a
proxy signer and then the proxy signer generates a signing message on behalf of the original
signer. So far, the proxy signature scheme is only applied in a special duration, when the
original signer is not in his office or when he travels outside. The two parties must be able to
authenticate one another and agree on a secret encryption key, in order to communicate
securely over an unreliable public network. Authenticated key agreement protocols have an
important role in building a secure communications network between the two parties. In this
paper, we propose a secure proxy signature scheme over an efficient and secure authenticated
key agreement protocol based on RSA cryptosystem.
Elliptic curve cryptography (ECC) is an approach to public-key cryptography that uses elliptic curves over finite fields. It provides the same level of security as other cryptosystems but with smaller key sizes. ECC is used for encryption, digital signatures, and other tasks. It is based on the algebraic structure of elliptic curves and points on those curves forming an Abelian group. The U.S. has endorsed ECC algorithms for key exchange and digital signatures.
BLOCKCHAIN-BASED SMART CONTRACTS : A SYSTEMATIC MAPPING STUDY csandit
An appealing feature of blockchain technology is smart contracts. A smart contract is
executable code that runs on top of the blockchain to facilitate, execute and enforce an
agreement between untrusted parties without the involvement of a trusted third party. In this
paper, we conduct a systematic mapping study to collect all research that is relevant to smart
contracts from a technical perspective. The aim of doing so is to identify current research topics
and open challenges for future studies in smart contract research. We extract 24 papers from
different scientific databases. The results show that about two thirds of the papers focus on
identifying and tackling smart contract issues. Four key issues are identified, namely, codifying,
security, privacy and performance issues. The rest of the papers focuses on smart contract
applications or other smart contract related topics. Research gaps that need to be addressed in
future studies are provided.
AN EFFICIENT GROUP AUTHENTICATION FOR GROUP COMMUNICATIONSIJNSA Journal
- The document proposes a new type of authentication called group authentication that authenticates all users in a group at once, rather than authenticating users individually.
- A group manager is responsible for registering users and issuing unique tokens to each user based on a secret polynomial. During authentication, users present their tokens to prove they belong to the same group without revealing their identities.
- Two group authentication protocols are proposed: a basic one-time protocol where tokens are revealed, and an improved protocol that protects tokens by having each user generate shares of a random polynomial for others and releasing the sum of their token and shares received. This allows for authentication without revealing tokens or the secret.
This document discusses cyber or online contracts. It defines a cyber-contract as one created through communications over computer networks, whether entirely through email exchanges showing offer and acceptance, or a combination of electronic and other means. The key elements of a valid contract - offer, acceptance, consideration, and consent - still apply to online contracts. Digital signatures can verify the identity of parties to an online contract by encrypting messages with public and private keys. This allows confirmation that a message has not been altered and verifies the sender. Overall, the document outlines how traditional contract law elements can be applied to agreements made electronically.
1) Electronic contracts are standard form contracts with non-negotiable terms formulated by one party like a manufacturer or service provider. The Information Technology Act, 2000 recognizes the validity of e-contracts.
2) E-contracts can be formed via email exchanges or through websites using clickwrap, browsewrap, or shrinkwrap agreements. However, e-contracts raise issues around jurisdiction, capacity to contract, consent, and meeting of minds.
3) The Information Technology Act and Indian Evidence Act provide for the validity and evidentiary value of e-contracts in India if they meet requirements for identification of parties, subject matter, signatures. However, the laws do not address all aspects of online contracts.
A SYSTEMATIC MAPPING STUDY ON CURRENT RESEARCH TOPICS IN SMART CONTRACTSijcsit
The document summarizes the results of a systematic mapping study on current research topics related to smart contracts. The study identified 24 relevant papers from scientific databases. Two-thirds of the papers focused on identifying and addressing issues with smart contracts, such as coding, security, privacy and performance issues. The remaining papers examined smart contract applications or other topics. The study aims to map current research areas and identify gaps to guide future work on smart contracts.
This document analyzes and summarizes the cryptanalysis of a recent two-factor authentication scheme proposed by Wang and Ma. The analysis points out some issues with the scheme. Specifically, while the scheme claims passwords are not stored on the server, identities are stored in a table on the server without cryptographic protection. The analysis also shows that an adversary could break the scheme by determining a user's identity from their compromised smart card, even though the paper does not explicitly give the adversary this capability. Through capturing a smart card, determining the user's identity, and running an offline password guessing attack, the entire scheme can be compromised if either factor is obtained.
This document discusses the definition, essential elements, and validity of e-contracts under Indian law. It defines an e-contract as any contract formed through electronic means like email. The key points are:
1. The Indian Contract Act and Information Technology Act recognize the validity of e-contracts and electronic communications/records as legally binding.
2. Essential elements of a valid contract like offer, acceptance, consideration must be present in e-contracts for them to be enforceable.
3. E-contracts can be formed via websites through clickwrap/browsewrap/shrinkwrap agreements or via email exchange. The postal rule of acceptance applies to email.
4. Electronic records and digital signatures have evidentiary
Game Theory Approach for Identity Crime DetectionIOSR Journals
This document discusses using game theory to detect identity crimes related to credit card fraud. It proposes a two-layered detection system using communal detection and spike detection algorithms. Communal detection uses a whitelist approach to reduce false positives, while spike detection identifies attributes that detect fraud spikes to increase true positives. It also discusses using dynamic time warping to minimize detection times. The paper evaluates the approach on real credit application data, finding it achieves lower identity variation frequencies, fraudulent identities, and verification times compared to existing detection methods.
This document discusses e-commerce and e-contracts. It begins by defining e-commerce as commerce conducted electronically, including buying and selling of goods and services online. It then discusses different types of e-commerce like business-to-business, business-to-consumer, consumer-to-business, and consumer-to-consumer. The document also summarizes the Bhagwandas Kedia case, which established that contracts formed through telephone conversations are considered formed at the location where the acceptance is received, opening the door for e-contracts to be recognized.
This document discusses e-contracts, comparing them to traditional contracts. It defines e-contracts as contracts formed online through email or other electronic means. E-contracts are legally binding under Indian law if they meet the requirements of a valid contract. Common types of e-contracts include shrinkwrap, clickwrap, and browsewrap agreements. The document analyzes several cases related to the validity of different e-contract types and notes some limitations, such as lack of clear notice for browsewrap agreements. It concludes that e-contracts will continue growing with advances in technology but notes Indian law does not fully cover all online contract aspects.
An e-contract is any contract formed through electronic means such as email, websites, or software. The Uniform Computer Information Transactions Act provides rules for forming, governing, and setting basic terms of e-contracts. E-contracts can be formed through processes like exchanging emails containing offers and acceptances, completing web forms, or clicking to agree to online terms. There are different types of e-contracts like employment contracts, shrinkwrap contracts governing software licenses, and source code escrow agreements. Forming e-contracts involves information, intention, agreement, and settlement phases with various legal considerations around elements, signatures, and international guidelines.
A fair exchange & customer anonymity protocolIJNSA Journal
The rapid development of technology and the reach of such technologies at affordable costs has made it
possible for all people across the world to make purchases at a click of the mouse and at their
convenience.Electronic commerce technologies and protocols facilitate the processing of online
transactions. Trust plays a major role in e-commerce transactions and various protocols help establishing
this trust by providing fair exchange and anonymity.
The research aims at designing and developing a protocol that provides both fair exchange and anonymity,
thus avoiding the need to have manual dispute resolution. It takes into account the technical flaws
researched and overcomes those by implementing methods to ensure that confidentiality and integrity of the
messages are maintained by making sure that the Trusted Third Party does not have the authority to view
or modify the messages but can only verify the authenticity of the other two parties.
A Fair Exchange & Customer Anonymity Protocol Using A Trusted Third Party for...IJNSA Journal
The rapid development of technology and the reach of such technologies at affordable costs has made it possible for all people across the world to make purchases at a click of the mouse and at their convenience.Electronic commerce technologies and protocols facilitate the processing of online transactions. Trust plays a major role in e-commerce transactions and various protocols help establishing this trust by providing fair exchange and anonymity.
The research aims at designing and developing a protocol that provides both fair exchange and anonymity, thus avoiding the need to have manual dispute resolution. It takes into account the technical flaws researched and overcomes those by implementing methods to ensure that confidentiality and integrity of the messages are maintained by making sure that the Trusted Third Party does not have the authority to view or modify the messages but can only verify the authenticity of the other two parties.
DESIGN AND EVALUATION OF A NEW FAIR EXCHANGE PROTOCOL BASED ON AN ONLINE TTP IJNSA Journal
Security protocols in e-commerce are required to manage the transactions between buyers and sellers. In order to engage customers in e-commerce, these protocols should be well formulated and secured; they should protect both parties from fraudulent users and subsequently promote the growth of e-commerce. There are some protocols, known as fair exchange protocols, in e-commerce that are designed to guarantee fairness between the customer and the merchant so that neither party gains any advantage over the other. Therefore, in this paper, we introduce a new fair exchange protocol for trading products online between a buyer and a seller. The items to be exchanged in this protocol are a digital product and a payment. The following are the characteristics of this new protocol: (1) Dependency on a trusted third party is greatly reduced; further, the protocol also overcomes increased communication overheads and risks, hence leading to substantial improvement in the efficiency and practicality of the protocol. (2) The
protocol ensures fairness for all parties and provides an internal dispute resolution mechanism, thereby guaranteeing that none of the parties involved in the transaction suffer unfairly in case one of the entities disappears before the transaction is formalized. (3) The protocol consists of three messages exchanged between the buyer (customer) and the seller (merchant).
A Novel Fair Anonymous Contract Signing Protocol for E-Commerce Applications IJNSA Journal
With the economy developing and popular Internet, the general concept of contract signing has changed. In the past, people usually sign a contract at the same time and same place face to face, but actually each party involved in contract may live in different part of earth, they want to sign something for business or some other things in economic, efficient, secure and fairway. A fair contract signing protocol allows two potentially mis-trusted parities to exchange their commitments (i.e., digital signatures) to an agreed contract over the Internet in a fair way, so that either each of them obtains the other’s signature, or neither party does. Based on the LUCAS signature scheme, a new digital anonymous contract signing protocol is proposed in this paper. Like the existing LUCAS-based solutions for the same problem, our protocol is fair, anonymous and optimistic. Furthermore, the proposed protocol satisfied a new
property, i.e., it is abuse-free. That is, if the protocol is executed unsuccessfully, either of the two parties can not show the validity of intermediate results to others.
E mail security using Certified Electronic Mail (CEM)Pankaj Bhambhani
The document discusses certified electronic mail (CEM) and its properties like non-repudiation, fairness, use of a trusted third party, and timeliness. It also summarizes the S/MIME protocol and proposes adding non-repudiation of receipt to S/MIME to improve its security. Finally, it outlines a key chain based CEM protocol that uses a transparent trusted third party and satisfies properties like non-repudiation of origin and receipt as well as fairness.
International Journal of Engineering Research and Applications (IJERA) is an open access online peer reviewed international journal that publishes research and review articles in the fields of Computer Science, Neural Networks, Electrical Engineering, Software Engineering, Information Technology, Mechanical Engineering, Chemical Engineering, Plastic Engineering, Food Technology, Textile Engineering, Nano Technology & science, Power Electronics, Electronics & Communication Engineering, Computational mathematics, Image processing, Civil Engineering, Structural Engineering, Environmental Engineering, VLSI Testing & Low Power VLSI Design etc.
Abstract—In developing countries there is a number of commodities and services which are financially supported by the
government as financial aid to their citizens. Such commodities
as bread, cooking gas and car fuel, all that commodities and
services follow a same systematic manual distribution process.
This typical and manual process is time and effort consumed for
the government, it also weak in term of control and monitoring,
so that the middle non-governmental entities can smuggle these
commodities outside the legal channels for double profit seeking
or intentional political reasons. In all cases, this will lead
to unsatisfactory situation within citizens and open doors for
corruption and chaos. This paper introduces model for solving
this problem by increasing the control for whole process and
thus decreasing the smuggling and wasting rates. The proposed
model is based on Identity-based Cryptography, so it provides the same security features and services as traditional PKI without the overhead of key management when the number of users in the system gets large.
International Journal of Computer Science and Information Security,IJCSIS ISSN 1947-5500, Pittsburgh, PA, USA
Email: ijcsiseditor@gmail.com
http://sites.google.com/site/ijcsis/
https://google.academia.edu/JournalofComputerScience
https://www.linkedin.com/in/ijcsis-research-publications-8b916516/
http://www.researcherid.com/rid/E-1319-2016
Protocols and Practices in Using Encryption Chapter 4AfiqEfendy Zaen
The document discusses various protocols for using encryption, including:
- Arbitrated protocols which use a trusted third party to ensure fairness
- Adjudicated protocols which use a third party to judge disputes after they occur
- Self-enforcing protocols which guarantee fairness without an outside party
It also describes key distribution protocols like using symmetric keys exchanged through a server, asymmetric keys exchanged between two parties, and digital signatures to authenticate identities. The document emphasizes that proper key management is important for encryption and different protocols have advantages and disadvantages related to efficiency, trust, and implementation.
Different types of Authentications described in different scenarios. Basically a survey paper on Different kinds of authentications in different scenarios.
An Improvement To The Set Protocol Based On Signcryptionijcisjournal
The document summarizes an improvement to the SET payment protocol based on using signcryption. The SET protocol ensures security for online credit card transactions but has some disadvantages. Signcryption allows simultaneous encryption and signature verification in one step, providing better performance than separate signature and encryption. The proposed improvement uses identity-based signcryption in the SET protocol to reduce the number of encryption/decryption operations and make it less time consuming compared to signature-then-encryption. It details the setup phase and modified protocol steps using signcryption for order and payment messages between the customer, merchant and payment gateway.
Law & Emerging Technology - The Model Law on E-Commerce (Unit 2).pptxssuser32bd0c
The document discusses the Model Law on Electronic Commerce (MLEC) adopted by UNCITRAL in 1996. It summarizes the key principles and provisions of the MLEC, including non-discrimination, technological neutrality, functional equivalence. It provides examples of how countries have incorporated the MLEC into their laws governing e-commerce and discusses some relevant case laws. It also discusses electronic contracts and signatures under Indian law, particularly the Information Technology Act, 2000.
The techniques of proxy signature and fault tolerance are two important issues in modern
communication.Proxy signature scheme permits an original signer to delegate his/her signing capability to a
proxy signer, and then the proxy signer generates a signing message on behalf of the original signer. To
communicate securelyover an unreliable public network, the two parties must be able to authenticate one
another and agree on a secret encryption key. Authenticated key agreement protocols have an important role in
building a secure communications network between the two parties. In this paper, we propose a secure proxy
signature scheme with fault tolerance over an efficient and secure authenticated key agreement protocol based
on the discrete logarithm problem.The scheme does not require any extra mechanism, such as checkpoints, to
achieve the property of fault tolerance.
Literature review of Digital SignatureAsim Neupane
The document discusses digital signatures and how they work. It explains that a digital signature is an electronic signature that authenticates the identity of the sender and ensures the message has not been altered. It is generated by encrypting a message digest of the document with the sender's private key. This allows the recipient to decrypt the signature with the public key and verify that the message matches the original. The document then discusses how digital signatures can be made more efficient through the use of message digests, which provide a fingerprint of the data through a hash function. This allows signing just the digest rather than the entire message.
The document proposes a secure payment scheme for multihop wireless networks using a trusted node identification method. It improves an existing report-based payment scheme by assigning trust values to nodes based on their past performance. The proposed scheme has 5 phases: 1) communication through high trust nodes, 2) classifying reports as fair or cheating, 3) identifying cheaters by requesting evidence, 4) updating credit accounts, and 5) updating trust values. It aims to increase performance by reducing message drops through trusted nodes and limiting overhead through lightweight report-based payments instead of receipts with signatures. The experimental results suggest it improves throughput and packet delivery ratio compared to other schemes.
A secure payment scheme in multihop wireless network by trusted node identifi...prjpublications
The document proposes a secure payment scheme for multihop wireless networks using a trusted node identification method. It improves an existing report-based payment scheme by assigning trust values to nodes based on their past performance. The proposed scheme has 5 phases: 1) communication through high trust nodes, 2) report classification, 3) cheater identification, 4) credit account updates, 5) trust value updates. It aims to increase performance by reducing dropped packets through trusted nodes and minimizing overhead in the report-based scheme through limited cryptographic operations. The experimental results suggest it improves throughput and delivery ratio compared to other schemes.
The document discusses security issues and methods for e-commerce, including Pretty Good Privacy (PGP). PGP provides encryption methods for authentication and confidentiality of electronic messages and files. It uses public/private key encryption along with hashing and digital signatures. The document also discusses other methods for e-commerce security including privacy policies, cryptography (symmetric and asymmetric keys), and digital certificates. Secure Socket Layer (SSL) and public key infrastructure help ensure secure transmission of data and authentication of parties engaging in e-commerce transactions over the internet.
This document provides a legal and practical analysis of TradeTrust-enabled electronic bills of lading (TT eBLs). It addresses the lack of interoperability between existing electronic bill of lading platforms, which has hindered wider adoption. TradeTrust provides a solution by enabling any party to issue TT eBLs using blockchain technology, allowing them to function similarly to paper bills of lading. This achieves both technical and potential legal interoperability without requiring all parties to use the same platform. The document analyzes how TT eBLs comply with the Model Law on Electronic Transferable Records and the laws of Singapore, England, and several US states. It provides guidance to industry on using TT eBLs and addresses considerations
This presentation covers:
What is Digital Signature ?
How does digital signature work?
Advantages and Shortcomings of Digital Signatures
What is e-Commerce
How does e-commerce work?
Advantages and Disadvantages of e-commerce
Industrial revolution and notions of technology .pptxVishweshSingh16
The document discusses the United Nations Commission on International Trade Law's (UNCITRAL) Model Law on Electronic Commerce (MLEC) from 1996. The MLEC aims to facilitate electronic commerce by establishing principles of non-discrimination of electronic documents, technological neutrality, and functional equivalence of electronic and paper documents. It sets rules for electronic contracting, digital signatures, and attribution of electronic messages. The MLEC has been influential as many states have based domestic e-commerce laws on it, helping unify international standards in the area. It also establishes that electronic documents cannot be denied validity solely due to their electronic form.
Similar to OPTIMIZING ONE FAIR DOCUMENT EXCHANGE PROTOCOL (20)
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1. International Journal of Network Security & Its Applications (IJNSA), Vol.4, No.1, January 2012
DOI : 10.5121/ijnsa.2012.4101 1
OPTIMIZING ONE FAIR DOCUMENT EXCHANGE
PROTOCOL
Abdullah M. Alaraj
Department of IT, Computer College, Qassim University, Saudi Arabia
arj@qu.edu.sa
ABSTRACT
This paper presents an efficient fair document exchange protocol. The exchange of the documents will
be between two parties. The protocol is based on the verifiable and recoverable encryption of a
document’s key. This verifiable and recoverable encryption of the document’s key will allow one party
to verify the encrypted key. It will also ensure this party that the Semi Trusted Third Party will be able to
recover the key if the other party misbehaves. The protocol also incorporates the concept of enforcing
the honesty of one party. The proposed protocol consists of only three messages and is more efficient
than related protocols.
KEYWORDS
Fair Document Exchange, Fair Exchange Protocols, e-Commerce, Security, Protocols
1. INTRODUCTION
Individuals and businesses are relying on the Internet for conducting different types of
transactions. One of these transactions is the exchange of valuable documents (such as
electronic payment and products) between the parties. That is, party A will exchange its
valuable document for party B’s valuable document. As an example of such an exchange, party
A would like to buy an electronic product (e-product such as computer game) from party B. As
parties using communication networks, they cannot send their documents at the same time.
Rather, one party sends its document at a time. After receiving the document of the first party,
the second party sends its document.
There are risks associated with such exchange. One of the most important risks is the case
where party A sends its document to party B but the later either disappears before sending its
document to party A or sends an incorrect document. Therefore, party A will be the loser in
this scenario because the party who sends its document first will be at risk. This problem is
known as the fairness problem. The fairness problem is solved using fair exchange protocols
that ensure the fair exchange of documents between the parties involved. That is, fair exchange
protocols will ensure that either both parties get each other's item or none do.
The contribution of this paper is that it applies the concept of enforcing the honesty of one
party to the verifiable and recoverable encryption of a document’s key proposed by Zhang et al
[12]. The result of this application is a new optimized fair document exchange protocol as will
be shown in the comparison in section 5.
The paper is organized as follows. Section 2 will be discussing the literature survey. Section 3
will present the new protocol. The analysis of the proposed protocol and comparison will be
discussed in sections 4 and 5, respectively.
2. International Journal of Network Security & Its Applications (IJNSA), Vol.4, No.1, January 2012
2
2. LITERATURE SURVEY
A number of fair exchange protocols have been proposed in the literature
[1,2,3,4,7,9,10,11,12,14, 19]. These protocols are either based on a Trusted Third Party (TTP)
or gradual exchange protocols. The gradual exchange protocols [10] allow the parties to
exchange their items without involvement of any other party. The TTP-based protocols require
a TTP to be involved. The involvement of the TTP can be either online such as in [7, 9, 17] or
offline such as in [1, 2, 3, 4, 11, 12, 19]. The online TTP must be available during the
exchange of items between parties because one of the parties (or all of the parties involved)
will use it either for verification purposes or downloading items. The offline TTP will not be
involved during the exchange of items between parties. Rather, it will be contacted in case one
party misbehaves.
The fair exchange protocols can be used to exchange any two items between two (or more)
parties. The items can be valuable documents, a document and payment, two digital signatures
on a contract, and an email with a receipt. The focus in this paper is on fair exchange protocols
that are for the exchange of two valuable documents between two parties.
Zhang et al [12] proposed a fair document exchange protocol between two parties A and B.
The protocol is based on the verifiable and recoverable encryption of keys. Parties A and B
will first exchange their encrypted documents in the first two messages. Then, the parties will
exchange the decryption keys to decrypt the encrypted documents. If one party misbehaves,
the offline STTP (Semi Trusted Third Party that will not collude with any party but may
misbehave by itself) can be contacted to recover the key. To start the protocol, party A will
send its encrypted document to party B. Party B will then verify the correctness of the
encrypted document. If it is correct, then party B will send the following to party A: (a) its
encrypted document, (b) verifiable and recoverable encryption of the key that encrypts the
document, and (c) the authorization token. Party A will then verify the correctness of the
encrypted document, authorization token and the encrypted key. If these verifications are
correct, then it is safe for party A to send its decryption key to party B. Finally, once party B
decrypted the document, it sends its decryption key to party A. If party B misbehaves by either
sending an incorrect decryption key or not sending the decryption key to party A, then party A
can contact the STTP to recover the decryption key.
Ray et al [7] proposed a fair exchange protocol for the exchange of documents (e.g. digital
products and payments between customers and merchants). The protocol is based on cross
validation theorem that states [7] “if a message is encrypted with the product key of two
compatible keys and another message is encrypted with either of the two compatible keys and
the two encrypted messages compare, then the two original unencrypted messages must also
compare”.
In the protocol, a merchant M exchanges a digital product for a payment from a customer C.
Before the protocol starts, the merchant (M) needs to register with a trusted third party (TTP).
The TTP generates the key pair KM1 and KM1
-1
. The TTP then provides M with KM1 and
keeps KM1
-1
with itself. C needs to have an account in a bank. The bank generates the key
pairs KC1 and KC1
-1
. The bank then provides C with KC1 and keeps KC1
-1
with itself. M needs
to send the digital product, its description and its price to the TTP. The TTP encrypts the
digital product using the key KM1 and then advertises it on its website. C needs to download
the encrypted digital product from the TTP.
The exchange part of Ray et al protocol [7] consists of four messages. C sends to M the first
message that includes the purchase order and the payment that is encrypted with the product
key of (KC1 x KC2). Then, M sends the second message to C. The second message includes the
digital product that is encrypted with the product key of (KM1 x KM2). On receiving the
second message, C compares the hash value of the encrypted digital product that was
3. International Journal of Network Security & Its Applications (IJNSA), Vol.4, No.1, January 2012
3
downloaded from the TTP with the hash value of the encrypted digital product that is included
in the second message. If the two hash values are matched then C can be sure that the
unencrypted digital products will be matched as well. After verifying that the two hashes are
compared, C sends the third message to M. The third message includes the decryption key for
the encrypted payment. Finally, M sends the fourth message to C which includes the
decryption key of the encrypted digital product. If M misbehaves, C contacts the TTP for the
recovery of the decryption key of the digital product.
Alaraj and Munro [1] proposed a fair exchange protocol for the exchange of two documents
(the two documents can be a digital product and payment) between a customer and a merchant.
Alaraj and Munro proposed a new design approach for the exchange. They call it enforcing the
customer to be honest. The protocol works as follows. The merchant starts the protocol by
sending the first message to the customer. The first message includes the merchant’s document
encrypted with a key. This key is also encrypted using a shared public key between the
merchant and the TTP. On receiving the first message, the customer will verify the encrypted
document and the encrypted key. If they are correctly verified then the customer will send the
second message to the merchant. The second message includes the customer’s document
encrypted with a key that was sent to the customer by the merchant in the first message. On
receiving the second message, the merchant will use the key that it already has to decrypt the
customer’s document. When the document is decrypted correctly, the merchant will send the
decryption key to the customer. If the merchant refuses to send the decryption key, the
customer can contact the TTP to send the decryption key to the customer. This approach is
called enforcing the customer to be honest because the customer can not cheat by sending an
incorrect document because they are going to encrypt their document using a key that the
merchant already has. Using this approach, Alaraj and Munro [1] were able to propose a fair
exchange protocol using only three messages.
Alaraj and Munro [3] proposed a protocol that is similar to the protocol in [1]. The difference
is that the merchant is the one who is enforced to be honest in [3].
The design approach of most of the protocols proposed in the literature, apart from Alaraj and
Munro [1, 3], is to include at least four messages in the exchange protocol. The first two
messages are for the exchange of the encrypted items between the participating parties. The
last two messages are for the exchange of decryption keys to decrypt the items received in the
first two messages. The design approach of Alaraj and Munro [1, 3] is to have only three
messages in the protocol. The first message includes the encrypted item of the first party. The
other party will be able to verify it and if it is correctly verified then they will send the second
message to the first party. The second message includes the encrypted item of the second party
but the first party will be able to decrypt it as it is encrypted with a key that the first party
already has. Therefore, the second party has to send a correct item in order to receive the
decryption key of the first party’s item in the third message. Therefore, the design approach of
Alaraj and Munro protocols [1, 3] is based on the exchange of an item (i.e. that is included in
the second message) for a decryption key (i.e. that is included in the third message). The result
is to have more efficient protocol that includes only three messages.
The proposed protocol in this paper uses the concept of having one party to be enforced to be
honest to reduce the number of messages. Moreover, the concept of verifiable and recoverable
encryption of keys is also used. Therefore, more efficient protocol is proposed.
3. THE DOCUMENT EXCHANGE PROTOCOL
3.1 Notations
The following represents the notations used in the proposed protocol:
4. International Journal of Network Security & Its Applications (IJNSA), Vol.4, No.1, January 2012
4
• Pa: party a
• Pb: party b
• STTP: Semi Trusted Third Party is a party neither Pa nor Pb. STTP will not collude with
any other party but may misbehave by itself
• h(X): a strong-collision-resistant one-way hash function, such as SHA-1 [13]
• pkx = (ex, nx): RSA Public Key [16] of the party x, where nx is a public RSA modulus and
ex is a public exponent
• skx = (dx, nx): RSA Private Key [16] of the party x, where nx is a public RSA modulus and
dx is a private exponent
• Dx: the document of party x
• kx: a symmetric key that will be used for encryption and decryption of a document
• C.bt: the certificate for the shared public key between Pb and the STTP. C.bt is issued by
the STTP. A standard X.509 certificate [15] can be used to implement C.bt
• enc.pkx(Y): an RSA [16] encryption of Y using the public key pkx (ex, nx). The encryption
of Y is computed as follows. enc.pkx(Y) = Yex
mod nx
• enc.skx(Z): an RSA [16] decryption of Z using the private key skx (dx, nx). The decryption
of Z is computed as follows. enc.skx(Z) = Zdx
mod nx
• enc.kx(Y) : encryption of Y using a symmetric key kx (kx can be used for decrypting
enc.kx(Y))
• Sig.a (X): the RSA digital signature [16] of the party a on X. The digital signature of party
a on X is computed by encrypting the hash value of X using the private key ska (da, na).
This is computed as follows. Sig.a (X) = (h(x))da
mod na
• A → B: X: A sends message X to B
• X + Y: concatenation of X and Y
• heDx: hash value of encrypted Dx using kx
3.2 Assumptions
The following represents the assumptions made for the proposed protocol:
• Each party (Pb, Pa and STTP) has its own public and private keys.
o The STTP’s public key is denoted as pkt = (et, nt) and its corresponding private
key is denoted as skt = (dt, nt).
o Pb’s public key is denoted as pkb = (eb, nb) and its corresponding private key is
denoted as skb = (db, nb).
o Pa’s public key is denoted as pka = (ea, na) and its corresponding private key is
denoted as ska = (da, na).
• Pb has a RSA-based public-key certificate C.bt = (Pb, pkbt, Wbt, Sig.t) issued by STTP
[12]. The content of C.bt is described as follows.
o Pb in C.bt is Pb’s identity to make C.bt valid only for Pb.
o The public key pkbt and its associated private key skbt are denoted as pkbt =
(ebt, nbt) and skbt = (dbt, nbt), respectively, where nbt is a product of two distinct
large primes chosen randomly by STTP. This pair of keys needs to be
produced in relation to Pb’s public key pkb = (eb, nb) so that ebt = eb and nbt > nb
[12]. STTP does not allow any other party, including Pb, to know skbt, and it
sends only C.bt to Pb. One C.bt certificate will be issued for Pb, and Pb can use
C.bt for as many document exchanges as Pb wishes [12]
o Wbt in C.bt is defined as Wbt = (h(skt + pkbt) -1
* dbt) mod nbt, where skt is
STTP’s private key, and h(skt + pkbt) -1
is the multiplicative inverse of h(skt +
pkbt) modulo nbt,
i.e. h(skt + pkbt) -1
h(skt + pkbt) mod nbt = 1.
5. International Journal of Network Security & Its Applications (IJNSA), Vol.4, No.1, January 2012
5
Wbt is included in C.bt in order to eliminate the need for STTP to store and
safe-keep private key skbt [12]. Therefore, STTP will compute it from Wbt, i.e.
dbt = (h(skt + pkbt) Wbt) mod nbt
o Sig.t in C.bt is STTP’s RSA signature on h(Pb, pkbt, Wbt), i.e. Sig.t=enc.skt(h(Pb
+ pkbt + Wbt))
• The following is known to Pb before the exchange protocol is executed:
o heDa = h(enc.ka(Da)) which is the hash value of encrypted Da with ka
• The following is known to Pa before the exchange protocol is executed:
o ekb = enc.pkb(kb) which is the encryption of kb with the public key of Pb
3.3 Protocol description
Semi Trusted Third Party (STTP) will be used in the proposed protocol. The STTP may
misbehave but it will not collude with any other party involved in the exchange [18].
The idea of the proposed protocol is to have one party (Pb) sends its first message to the other
party (Pa). The first message includes the encrypted document, verifiable and recoverable
encryption of Pb’s key (this key is used to encrypt Pb’s document) and the authorization token.
The verifiable and recoverable encryption of Pb’s key allows Pa to verify it and if it is correct
then Pa can be sure that STTP will be able to recover the key in case Pb does not sends it i.e. if
Pb misbehaves. So, when Pa verifies this verifiable and recoverable encryption correctly then Pa
will send its message that contains its encrypted document using a key that was sent to Pa by
Pb. Then, Pa will wait for the third message from Pb that includes the decryption key for the
encrypted document received in the first message. If Pb did not send the third message then Pa
will contact STTP to recover the key. The STTP will verify the authorization token generated
by Pb to make sure that Pa provided what Pb wants.
Therefore, for Pb to produce this verifiable and recoverable encryption of Pb’s key kb, Pb
chooses a large prime rb relatively prime to nb in Pb’s public key pkb=(eb, nb) and then
computes the following [12]:
Xb= rb*kb, where chosen rb needs to ensure that xb <nb
Yb= rb
eb
mod (nb * nbt), with key pkbt =(ebt, nbt) and nb<nbt
Zb= kb
eb
mod (nb * nbt)
Xb, Yb and Zb form the verifiable and recoverable encryption of Pb’s key kb. Note that Yb can
be decrypted using either skb or skbt [7]. Therefore, either Pb or STTP can recover rb.
The Pb’s authorization token will be defined by Pb. Pb’s authorization token represents Pb’s
RSA signature on h(C.bt+Yb+Ya+Pa) [12]. That is, Sb= skb(h(C.bt + Yb + Ya + Pa)),where:
Ya = h(enc.ka(Da)), this Ya is specified by Pb.
The authorization Sb represents Pb’s conditional authorization stating that STTP can recover rb
from Yb (which will enable Pa to derive kb from Xb) if and only if Pa provides an item “i.e.
enc.ka(Da)” for STTP such that h(enc.ka(Da))=Ya. STTP will verify this Sb and if it is correct
then STTP can be sure that this “enc.ka(Da)” is the one that Pb is looking for.
Therefore, the verifiable and recoverable encryption of key “kb” will be generated by Pb, it will
be verified by Pa, and it will be recovered by STTP.
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3.4 Exchange Protocol
Figure 1: Exchange phase of the protocol
Pb will start the exchange protocol by sending the first message E-M1 to Pa. The contents of E-
M1 are as follows:
E-M1: Pb → Pa: enc.kb(Db) + C.bt + enc.pka(Xb + Zb) + Yb + Sb + enc.pka(ka)
The description of the contents of E-M1 is as follows:
• enc.kb(Db) is the encryption of Pb’s document Db using kb
• C.bt is RSA-based public-key certificate that is discussed in section 3.2
• enc.pka(Xb + Zb) is the encryption of Xb and Zb using Pa’s public key pka.
• Yb
• Sb
• enc.pka(ka) is the encryption of ka using the public key of Pa. ka will later be used by Pa
to encrypt its document Da. ka is chosen by Pb and will be sent to Pa to use it for
encrypting its document Da
On receiving the first message (E-M1), Pa will make the following verifications [12]:
1. Verifying the correctness of Sb. This is done by decrypting Sb using Pb’ public key pkb
to get the hash value included in the signature. Then, computing the hash value of
(C.bt+Yb+Ya+Pa). If the two hash values match then Sb is correct.
2. Verifying the correctness of C.bt = (Pb, pkbt, Wbt, Sig.t) by decrypting Sig.t using
STTP’s public key pkt to get the hash value included in the signature. Then,
computing the hash value of (Pb, pkbt, Wbt). If the two hash values match then C.bt is
correct.
3. Compute the hash value of enc.kb(Db) and then compare it with heDb. If the two hash
values match then Pa is sure that the encrypted Db is the one that Pa is looking for
4. Confirm that Xb < nb, and Zb mod nb= enc.pkb(kb). It is assumed that enc.pkb(kb) is
known to Pa (section 3.2)
5. Confirm that Xb
eb
mod nb = (Yb * enc.pkb(kb)) mod nb
6. Confirm that Xb
eb
mod nbt = (Yb * Zb) mod nbt
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If all verifications above are correct then it is secure for Pa to send its document Da that is
encrypted with a key that Pb already has. Otherwise, Pa terminated the protocol. So, if all
verifications are correct then Pa will send the second message (E-M2) to Pb as follows:
E-M2: Pa → Pb: enc.ka(Da)
The description of the contents of E-M2 is as follows:
• enc.ka(Da) is the encryption of Pa’s document using ka. ka was sent to Pa in E-M1
On receiving E-M2, Pb will do the following:
• Compute the hash value of enc.ka(Da) then compare it with heDa (it is assumed that
heDa is known to Pb , section 3.2)
If the above verification is correct then Pb will decrypt Da using ka (note that, ka is already
known to Pb). Then, Pb will send E-M3 to Pa as follows:
E-M3: Pb → Pa: rb
On receiving E-M3, Pa will compute kb as follows:
kb = Xb/rb
Then, Pa will use the key kb to decrypt enc.kb(Db) to retrieve Db.
At this step, both Pa and Pb have each other’s documents i.e. they have fairly exchanged their
documents.
3.5 Dispute Resolution Protocol (Key recovery protocol)
Figure 2: Dispute Resolution Phase of the Protocol
In the case of dispute (where Pb misbehaves by either sending incorrect E-M3 or not sending
E-M3 at all), Pa will initiate the dispute resolution protocol by sending the message DR-M1 to
the STTP as follows.
DR-M1: Pa → STTP: C.bt + enc.ka(Da) + Yb + Sb
On receiving the message DR-M1 from Pa, STTP will do the following verifications:
8. International Journal of Network Security & Its Applications (IJNSA), Vol.4, No.1, January 2012
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1. Verifying the correctness of Sb. This is done by decrypting Sb using Pb’ public key pkb
to get the hash value included in the signature. Then, computing the hash value of
(C.bt+Yb+Ya+Pa). If the two hash values match then Sb is correct.
2. Verifying the correctness of C.bt = (Pb, pkbt, Wbt, Sig.t) by decrypting Sig.t using
STTP’s public key pkt to get the hash value included in the signature. Then,
computing the hash value of (Pb, pkbt, Wbt). If the two hash values match then C.bt is
correct
3. Compute the hash value of enc.ka(Da) and then compare it with Ya (Ya includes the
hash value of enc.ka(Da)).
If any of the verifications above is incorrect then STTP will send an error message to Pa.
Otherwise, if all verifications are correct then STTP will calculate rb from Yb. Therefore, STTP
needs to decrypt Yb using the shared private key i.e. skbt. So, STTP needs first to retrieve skbt
from C.bt as discussed in section 3.2. After decrypting Yb and getting rb from it, STTP will send
the following two messages.
DR-M2: STTP → Pb: enc.ka(Da)
On receiving DR-M2 from STTP, Pb will compute the hash value of enc.ka(Da) then compare it
with heDa. If the two hash values match then Pb will get Da by decrypting enc.ka(Da) using ka
that Pb already has.
DR-M3: STTP → Pa: rb
On receiving DR-M3 from STTP, Pa will compute kb as follows:
kb = Xb/rb
Then, Pa will use the key kb to decrypt enc.kb(Db) to retrieve Db.
At this step, both Pa and Pb have each other’s items and hence the fairness is ensured.
4. ANALYSIS
The analysis of the security of the verifiable and recoverable encryption of Pb’s key kb is the
same analysis conducted in [12]. Therefore, readers are referred to Zhang et al [12].
The following discusses all scenarios of the protocol’s messages E-M1, EM2, E-M3 and DR-
M1.
All possible scenarios of E-M1 will be studied as follows.
• Pb sends incorrect E-M1 to Pa. If so, Pa will find that E-M1 is incorrect when Pa makes
the verifications (these verifications discussed in sections 3.4). So, if E-M1 is incorrect
then Pa will not send E-M2 to Pb.
• Pb sends correct E-M1 to Pa. After Pa makes sure that E-M1 is correct by applying the
verifications (these verifications discussed in sections 3.4) it is Pa’s choice to complete
the exchange by sending E-M2 to Pb. However, if Pa decides to complete the exchange
then Pa is enforced to be honest i.e. Pa has to send correct E-M2 to be able to receive
E-M3 from Pb.
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All possible scenarios of E-M2 will be studied as follows.
• Pa sends to Pb in E-M2: enc.ka(Da) where ka used is the key sent to Pa by Pb in E-M1.
So, Pb will first decrypt the message to get Da and then send rb to Pa in E-M3
• Pa sends to Pb in E-M2: enc.k(Da)where k used is not the one sent to Pa in E-M1. So, Pb
will not send E-M3 to Pa i.e. Pb will not send rb
• Pa does not send E-M2 to Pb at all. So, Pb will not send E-M3 to Pa i.e. Pb will not send
rb
• Pa sends incorrect Da encrypted with ka. So, Pb will not send E-M3 to Pa i.e. Pb will not
send rb
• Pa sends incorrect Da encrypted with k i.e. incorrect key. So, Pb will not send E-M3 to
Pa i.e. Pb will not send rb
All scenarios of E-M3 will be studied as follows.
• Pb sends correct rb. So, Pa will use it to decrypt Pb’s document and the exchange
protocol will be completed fairly.
• Pb sends incorrect rb. So, Pa will contact the STTP to recover rb.
• Pb did not send rb at all i.e. Pb received correct E-M2 but did not send E-M3. So, Pa
will contact the STTP to recover rb.
Therefore, from the previous scenarios it is clear that the fairness is ensued for both Pa and Pb
either through the exchange phase of the protocol or through the dispute resolution phase.
All scenarios of DR-M1 will be studied as follows.
• Pa sends correct DR-M1 to STTP. So, STTP will make the necessary verifications (i.e.
verifications discussed in section 3.5) then STTP will send DR-M2 to Pb and DR-M3
to Pa
• Pa sends incorrect DR-M1 to STTP. So, STTP will make the necessary verifications
(i.e. verifications discussed in section 3.5) then STTP will send an abort message to Pa.
Therefore, if Pb misbehaves by not sending E-M3 or by sending incorrect E-M3 then the
fairness can be ensured by allowing Pa to send a correct DR-M1 to STTP. STTP will then
ensure fairness for both Pb and Pa by sending DR-M2 and DR-M3, respectively.
If Pa misbehaves by contacting STTP (i.e. by sending DR-M1) after receiving E-M1 i.e. before
sending E-M2 to Pb, then STTP will verify Pa’s request. If STTP finds that DR-M1 is not
correct then STTP will reject Pa’s request. If however STTP finds that DR-M1 is correct then
STTP will send DR-M2 to Pb and DR-M3 to Pa to ensure fairness for both parties. Therefore,
Pa will not gain any advantage over Pb.
STTP is not able to get the documents Da and Db because an encrypted Da will be sent to it in
DR-M1. STTP does not have the key to decrypt it. Rather, STTP will use it to verify if Pa sent
what Pb is looking for. Db is not sent to STTP at all. Therefore, STTP will not be able to get Da
and Db. Hence, it is Semi Trusted Third Party.
Non-repudiation can be assured in the proposed protocol by having the signatures of parties Pb
and Pa on their items to be included in messages E-M1 and E-M2.
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5. COMPARISONS
In this section, the proposed protocol will be compared against the relevant protocols in the
literature. That is, the proposed protocol will be compared against protocols in the literature,
which are for the exchange of two documents (two documents or a document and payment)
and involve an off-line or on-line TTP or STTP. The proposed protocol will be compared
against Zhang et al protocol [12], Ray et al protocol [7], Alaraj and Munro protocol [1].
The protocols will be compared against the following criteria: number of messages in the
exchange phase, number of messages in dispute phase, number of encryptions and decryptions
in the exchange phase, number of symmetric encryptions in the exchange phase, and whether
both parties involved in dispute resolution phase i.e. does the STTP need to contact both
parties to verify the dispute request.
The number of messages in the exchange phase of ECH protocol and our protocol is 3 whereas
it is 4 messages in both Zhang and Ray protocols. The number of messages in the dispute
resolution phase is almost the same for all protocols. The number of RSA encryptions and
decryptions for our protocol is 13 whereas it is 16 for Zhang et al protocol [12]. This shows
how the idea of enforcing the honesty of one party introduced in ECH protocol helped in
reducing the number of messages and the number of RSA encryptions and decryptions of
Zhang et al protocol [12]. The application of enforcing the honesty of a party to Zhang et al
protocol [12] is the main focus of this paper.
It is worth mentioning that Zhang et al’s protocol [12] is better in that it does not require the
document of party Pa to be sent to the STTP in the dispute resolution phase whereas our
protocol requires the party Pa to send its encrypted document “enc.ka(Da)” to the STTP in the
dispute resolution phase. However, this does not mean that the STTP will be able to decrypt
the document because STTP does not have the key ka. Rather, it uses it for the verification
purposes.
Table 1 presents all the comparisons between our protocol and other relevant protocols in the
literature.
Table 1: Comparison between our protocol and other protocols
Zhang
[12]
Ray
[7]
ECH
[1]
Our
Protocol
Number of messages in exchange
phase
4 4 3 3
Number of messages in dispute phase 3 3 to
5
3 3
Number of RSA encryptions and
decryptions in exchange phase
16 27 12 13
Number of symmetric encryptions and
decryptions in exchange phase
4 0 4 4
Both parties are involved
in dispute resolution
No Yes No No
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6. CONCLUSION
We have proposed an improved protocol for fairly exchanging two valuable documents
between two parties. The proposed protocol uses offline Semi Trusted Third Party (STTP) that
will only be contacted if one party misbehaved. The protocol is based on applying the idea of
enforcing the honesty of one party to the method of verifiable and recoverable encryption of
keys. The outcome of this application is a more efficient fair document exchange protocol.
Only three messages are required to exchange the valuable documents between the two parties.
Additionally, the number of modular exponentiations is less in our protocol compared to the
protocols based on verifiable and recoverable encryption of keys.
A future work will include formally evaluating the protocol and implementing it.
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