The document discusses network security principles such as cryptography, authentication, and message integrity. It explains symmetric key cryptography where senders and receivers share the same key, and public key cryptography where users have a public key for encrypting messages and a private key for decrypting. The document also outlines common attacks like eavesdropping, message insertion, and denial of service and how techniques like encryption, firewalls, and access control can help address security threats.
The document summarizes key concepts in network security including cryptography, authentication, integrity, and access control. It discusses principles like confidentiality, authentication, and integrity. It introduces common examples of Alice, Bob, and Trudy to illustrate security concepts and the need to protect against eavesdropping, impersonation, message alteration, and denial of service attacks. Symmetric and public key cryptography algorithms are overviewed including DES, AES, and RSA.
Generate an Encryption Key by using Biometric Cryptosystems to secure transfe...IOSR Journals
The document describes a proposed method for generating an encryption key from biometric cryptosystems to securely transfer data over a network. It involves extracting minutiae points from a fingerprint scan, generating a cryptographic key from the biometric template, and using an RSA encryption algorithm with the biometric-derived private key. A public key is also calculated based on ridge and furrow patterns in the fingerprint scan. The goal is to uniquely generate encryption keys for each individual using their biometric fingerprint information to add an extra layer of security beyond traditional encryption techniques.
This document discusses enhancing security in DNA-based cryptography. It describes how DNA can be used to store encrypted data by encoding messages in DNA strands using an alphabet of short DNA sequences. The document outlines several methods for DNA-based cryptography including DNA steganography systems that hide encrypted messages within collections of DNA strands. It also summarizes the RSA encryption algorithm and describes challenges in DNA-based cryptography systems like preventing unauthorized access and protecting against cryptanalysis. The document concludes that initial investigations show DNA cryptography methods can in principle be unbreakable but also discusses ways to improve security.
A brief discussion of network security and an introduction to cryptography. We end the presentation with a discussion of the RSA algorithm, and show how it works with a basic example.
The document provides an overview of cryptography concepts including encryption, decryption, symmetric cryptosystems, block ciphers, substitution ciphers, the one-time pad, and algorithms such as DES, Triple DES, AES, and others. Key points covered include Kerckhoffs's principle of keeping algorithms public and keys private, how symmetric encryption works between two parties with a shared key, methods of encrypting plaintext in blocks or as a bit stream, techniques like substitution and transposition ciphers, weaknesses of approaches like the Hill cipher, and the history and operation of standard block ciphers.
Ciphertext policy Attribute based Encryption with anonymous access policy ijp2p
In Ciphertext Policy Attribute based Encryption scheme, the encryptor can fix the policy, who can decrypt
the encrypted message. The policy can be formed with the help of attributes. In CP-ABE, access policy is
sent along with the ciphertext. We propose a method in which the access policy need not be sent along
with the ciphertext, by which we are able to preserve the privacy of the encryptor. The proposed
construction is provably secure under Decision Bilinear Diffe-Hellman assumption.
Cupdf.com public key-cryptography-569692953829ajsk1950
This document provides an overview of public key cryptography. It discusses how public key cryptography uses asymmetric key pairs, with one key used for encryption and the other for decryption. One key is public and accessible, while the other is private. It also discusses how digital signatures use public key cryptography to authenticate the sender of a message. The document provides examples to illustrate how public key encryption and digital signatures work. It discusses issues like key management and risks associated with public key cryptography.
The document summarizes key concepts in network security including cryptography, authentication, integrity, and access control. It discusses principles like confidentiality, authentication, and integrity. It introduces common examples of Alice, Bob, and Trudy to illustrate security concepts and the need to protect against eavesdropping, impersonation, message alteration, and denial of service attacks. Symmetric and public key cryptography algorithms are overviewed including DES, AES, and RSA.
Generate an Encryption Key by using Biometric Cryptosystems to secure transfe...IOSR Journals
The document describes a proposed method for generating an encryption key from biometric cryptosystems to securely transfer data over a network. It involves extracting minutiae points from a fingerprint scan, generating a cryptographic key from the biometric template, and using an RSA encryption algorithm with the biometric-derived private key. A public key is also calculated based on ridge and furrow patterns in the fingerprint scan. The goal is to uniquely generate encryption keys for each individual using their biometric fingerprint information to add an extra layer of security beyond traditional encryption techniques.
This document discusses enhancing security in DNA-based cryptography. It describes how DNA can be used to store encrypted data by encoding messages in DNA strands using an alphabet of short DNA sequences. The document outlines several methods for DNA-based cryptography including DNA steganography systems that hide encrypted messages within collections of DNA strands. It also summarizes the RSA encryption algorithm and describes challenges in DNA-based cryptography systems like preventing unauthorized access and protecting against cryptanalysis. The document concludes that initial investigations show DNA cryptography methods can in principle be unbreakable but also discusses ways to improve security.
A brief discussion of network security and an introduction to cryptography. We end the presentation with a discussion of the RSA algorithm, and show how it works with a basic example.
The document provides an overview of cryptography concepts including encryption, decryption, symmetric cryptosystems, block ciphers, substitution ciphers, the one-time pad, and algorithms such as DES, Triple DES, AES, and others. Key points covered include Kerckhoffs's principle of keeping algorithms public and keys private, how symmetric encryption works between two parties with a shared key, methods of encrypting plaintext in blocks or as a bit stream, techniques like substitution and transposition ciphers, weaknesses of approaches like the Hill cipher, and the history and operation of standard block ciphers.
Ciphertext policy Attribute based Encryption with anonymous access policy ijp2p
In Ciphertext Policy Attribute based Encryption scheme, the encryptor can fix the policy, who can decrypt
the encrypted message. The policy can be formed with the help of attributes. In CP-ABE, access policy is
sent along with the ciphertext. We propose a method in which the access policy need not be sent along
with the ciphertext, by which we are able to preserve the privacy of the encryptor. The proposed
construction is provably secure under Decision Bilinear Diffe-Hellman assumption.
Cupdf.com public key-cryptography-569692953829ajsk1950
This document provides an overview of public key cryptography. It discusses how public key cryptography uses asymmetric key pairs, with one key used for encryption and the other for decryption. One key is public and accessible, while the other is private. It also discusses how digital signatures use public key cryptography to authenticate the sender of a message. The document provides examples to illustrate how public key encryption and digital signatures work. It discusses issues like key management and risks associated with public key cryptography.
This document discusses the implementation of a hybrid cryptography algorithm combining DES and IDEA. It begins by providing background on encryption, key escrow schemes, and the need for stronger algorithms. It then separately describes DES and IDEA, including their structure, performance analysis, and types of cryptanalysis attacks they are susceptible to. The document proposes a new hybrid algorithm combining DES and IDEA to improve security and integrity.
Bluetooth technology is an emerging wireless networking standard, which is based on chip that provides short-range wireless frequency hopping communication. Now, Bluetooth technology is mainly applied to the communication between mobile terminal devices, such as palm computers, mobile phones, laptops and so on. However, the phenomenon of data-leaking frequently arises in using the Bluetooth technology for data transfer. To enhance the security of data transmission in Bluetooth communication, a hybrid encryption algorithm based on DES and RSA is proposed. The currently used encryption algorithm employed by the Bluetooth to protect the confidentiality of data during transport between two or more devices is a 128-bit symmetric stream cipher called E0. The proposed hybrid encryption algorithm, instead of the E0 encryption, DES algorithm is used for data transmission because of its higher efficiency in block encryption, and RSA algorithm is used for the encryption of the key of the DES because of its management advantages in key cipher. Under the dual protection with the DES algorithm and the RSA algorithm, the data transmission in the Bluetooth system will be more secure. This project is extended with triple des in place of des to enhance more security.
This document provides an overview of cryptography concepts and algorithms. It discusses symmetric and asymmetric encryption algorithms such as DES, AES, RSA. It also covers hashing algorithms like MD5 and SHA which are used to generate cryptographic checksums of documents. The key ideas are that encryption encodes information, decryption decodes it, symmetric algorithms use the same key for both, and asymmetric algorithms use different public/private keys for encryption and decryption respectively.
A comparative study of symmetric key algorithm des, aes and blowfish for vide...pankaj kumari
Cryptography means storing and transmitting data or information in a particular form that allow to be kept secret.
Symmetric key cryptography:- Both sender and receiver share the secret key.The symmetric key is kept private.both parties use the same key for encryption and decryption.
Asymmetric key cryptography:- Asymmetric key cryptography uses public or private key for encryption and decryption.Public key is kept by publically and private is kept secret.sender use the public key to send message and receiver use the private or secret key to decrypt the message.
Advanced Encryption Standard (AES) Implementaion using JavaSunil Kumar R
The document describes a project report on the implementation of the AES encryption algorithm. It was submitted by two students, Sunil Kumar R and Shreekant, in partial fulfillment of the requirements for a Bachelor of Engineering degree in computer science. The project was carried out under the guidance of three faculty members at R.V. College of Engineering in Bangalore. It includes a certificate signed by the faculty confirming the students' satisfactory completion of the project.
A RSA- DWT Based Visual Cryptographic Steganogrphy Technique by Mohit GoelMohit Goel
1) The document presents a technique for visual cryptographic steganography that uses RSA encryption and discrete wavelet transform (DWT) for data security.
2) In the proposed method, data is first encrypted using RSA encryption and then embedded in an image using Haar-DWT based steganography.
3) Experimental results on 100 images show the proposed technique achieves higher PSNR values compared to other techniques like LSB and LSB-DCT steganography, indicating better image quality and security of the hidden data.
iaetsd Secured multiple keyword ranked search over encrypted databasesIaetsd Iaetsd
This document proposes a Robust Key-Aggregate Cryptosystem (RKAC) that allows flexible and efficient assignment of decryption rights for encrypted data stored in cloud storage. The RKAC produces constant-sized ciphertexts such that a constant-sized aggregate decryption key can decrypt any subset of ciphertexts. This allows the data owner to share access to selected encrypted files by sending a single small aggregate key to authorized users, without decrypting the files themselves or distributing individual keys. The RKAC is described as providing a secure and flexible method for sharing encrypted data stored in the cloud.
In cryptography, encryption is the process of encoding a message or information in such a way that only authorized parties can access it and those who are not authorized cannot. Encryption does not itself prevent interference, but denies the intelligible content to a would-be interceptor.
This paper presents an efficient implementation of the RSA encryption algorithm using the GNU MP Library. It describes generating RSA keys with primes of 1024 bits, encrypting and decrypting files by processing characters in groups, and analyzing encryption and decryption times with varying group sizes. It finds that encryption and decryption times decrease when more characters are processed together. A GUI for the RSA implementation is also described and screenshots are provided.
This document proposes a hybrid encryption-decryption algorithm combining AES and DES. It implements the algorithm in VHDL using a Modelsim platform. The hybrid algorithm integrates AES into each iteration of DES's Feistel network, using AES operations like substitution and key addition. This increases computational complexity compared to the individual standards. The VHDL implementation includes modules for AES encryption/decryption and the hybrid algorithm. Simulations validate the code works correctly. Future work could increase iterations to suit different security levels or implement a 128-bit AES variant. The hybrid approach strengthens AES security against attacks.
The document discusses various methods of authentication in wireless networks, including standards like 802.11 and 802.16, as well as encryption methods such as Diffie-Hellman key exchange, RSA, RC4, and TripleDES. It also examines network types like TTP and describes how clients can connect to a trusted third party server or directly connect to another client with encryption. The objectives are to investigate authentication methods, implement one in Java, and document the implementation.
“SECURITY” in this contemporary scenarios has become a more sensible issue either it may be in the “REAL WORLD” or in the “CYBER WORLD”. In the real world as opposed to the cyber world information gathering often precedes an attack. Today the illicit activities of the hackers are growing by leaps and bounds. However; fortunately, the antagonists reacted promptly and resurrected the internet world from the brink of prostration. Tersely quoting some security ditherers - hijackers, Eavesdropping, hacking, mapping, packet sniffing, spoofing, etc.
This document describes an audio cryptography system project that embeds encrypted messages within audio files. The system has two main modules: a GUI module built using AWT, Swing components; and an encryption/decryption module. Messages are encrypted before being embedded in audio files using LSB coding and encryption algorithms. The encrypted audio files can then be transmitted and decrypted at the recipient end to extract the original message. The system aims to provide security, confidentiality and integrity to transmitted messages.
Android based message encryption decryption using matrixeSAT Journals
Abstract
In this paper we are going to encrypt plain text to encrypted text. Message encryption is character value based encryption in which 3D message character matrix is replaced with 2D encryption value matrix. It can also know by some kind of message masking which work on upper level to provide maximum security. Password protection increases encrypted message file security.
Keywords – Matrix, ASCII Offset Value, DES, 3D Message Masking, and 2D.
Encryption is a process that converts plain text into ciphertext through the use of cryptographic algorithms and encryption keys. There are two main types of encryption: symmetric encryption which uses the same key for encryption and decryption, and asymmetric encryption which uses a public key for encryption and a private key for decryption. Common symmetric encryption algorithms discussed include DES, Triple DES, AES, Blowfish and Twofish. Asymmetric algorithms include RSA. Other algorithms mentioned are IDEA, MD5, and FPE. The document also discusses how encryption keys are used and changed in Magento.
This document analyzes and compares the performance of various cryptography algorithms. It discusses symmetric key algorithms like DES, AES, Blowfish and IDEA as well as asymmetric algorithms like RSA and Diffie-Hellman. The performance is evaluated based on parameters like encryption/decryption time, memory usage and throughput. Experiments show that Blowfish has better performance than AES for encrypting audio files, with lower average encryption and decryption times. In conclusion, cryptography is important for network security and Blowfish performs encryption/decryption more efficiently than AES for audio files.
This document describes a proposed technique for information security that uses a hybrid of DES and RSA encryption along with LSB steganography. The message is first encrypted with DES, then the DES keys are encrypted with RSA. The hybrid encrypted result is then embedded into an image file using LSB steganography. This combines the strengths of cryptography and steganography for improved security of transmitted data. The encryption time is faster than previous techniques and brute force attacks on this technique would be very difficult.
Module 6
Advanced Networking
Security problems with internet architecture, Introduction to Software defined networking, Working of SDN, SDN in data centre, SDN applications, Data centre networking, IoT.
The document discusses network security and introduces concepts like cryptography, authentication, and message integrity. It notes that network security aims to ensure confidentiality, authentication, and access for legitimate users while preventing attacks from unauthorized parties. The chapter will cover principles of cryptography, security protocols for different layers, and operational security measures like firewalls and intrusion detection systems. Users are asked to cite the source if using the slides and to respect the authors' copyright.
This document discusses the use and sharing of PowerPoint slides from a textbook on computer networking. It allows the slides to be modified and used for educational purposes with only two requirements: 1) Cite the source if using the slides substantially unaltered, and 2) Note the copyright if posting slides substantially unaltered online. The document is copyrighted by the authors of the textbook from 1996-2007.
The document discusses network security and introduces concepts like cryptography, authentication, and message integrity. It notes that network security aims to ensure confidentiality, authentication, and access to services. Cryptography uses techniques like encryption, digital signatures, and hash functions to provide these security properties. The document provides examples to illustrate symmetric and public key cryptography, including how algorithms like DES, AES, RSA and hash functions work. It also introduces common network security examples like Alice, Bob and the intruder Trudy.
This document discusses the implementation of a hybrid cryptography algorithm combining DES and IDEA. It begins by providing background on encryption, key escrow schemes, and the need for stronger algorithms. It then separately describes DES and IDEA, including their structure, performance analysis, and types of cryptanalysis attacks they are susceptible to. The document proposes a new hybrid algorithm combining DES and IDEA to improve security and integrity.
Bluetooth technology is an emerging wireless networking standard, which is based on chip that provides short-range wireless frequency hopping communication. Now, Bluetooth technology is mainly applied to the communication between mobile terminal devices, such as palm computers, mobile phones, laptops and so on. However, the phenomenon of data-leaking frequently arises in using the Bluetooth technology for data transfer. To enhance the security of data transmission in Bluetooth communication, a hybrid encryption algorithm based on DES and RSA is proposed. The currently used encryption algorithm employed by the Bluetooth to protect the confidentiality of data during transport between two or more devices is a 128-bit symmetric stream cipher called E0. The proposed hybrid encryption algorithm, instead of the E0 encryption, DES algorithm is used for data transmission because of its higher efficiency in block encryption, and RSA algorithm is used for the encryption of the key of the DES because of its management advantages in key cipher. Under the dual protection with the DES algorithm and the RSA algorithm, the data transmission in the Bluetooth system will be more secure. This project is extended with triple des in place of des to enhance more security.
This document provides an overview of cryptography concepts and algorithms. It discusses symmetric and asymmetric encryption algorithms such as DES, AES, RSA. It also covers hashing algorithms like MD5 and SHA which are used to generate cryptographic checksums of documents. The key ideas are that encryption encodes information, decryption decodes it, symmetric algorithms use the same key for both, and asymmetric algorithms use different public/private keys for encryption and decryption respectively.
A comparative study of symmetric key algorithm des, aes and blowfish for vide...pankaj kumari
Cryptography means storing and transmitting data or information in a particular form that allow to be kept secret.
Symmetric key cryptography:- Both sender and receiver share the secret key.The symmetric key is kept private.both parties use the same key for encryption and decryption.
Asymmetric key cryptography:- Asymmetric key cryptography uses public or private key for encryption and decryption.Public key is kept by publically and private is kept secret.sender use the public key to send message and receiver use the private or secret key to decrypt the message.
Advanced Encryption Standard (AES) Implementaion using JavaSunil Kumar R
The document describes a project report on the implementation of the AES encryption algorithm. It was submitted by two students, Sunil Kumar R and Shreekant, in partial fulfillment of the requirements for a Bachelor of Engineering degree in computer science. The project was carried out under the guidance of three faculty members at R.V. College of Engineering in Bangalore. It includes a certificate signed by the faculty confirming the students' satisfactory completion of the project.
A RSA- DWT Based Visual Cryptographic Steganogrphy Technique by Mohit GoelMohit Goel
1) The document presents a technique for visual cryptographic steganography that uses RSA encryption and discrete wavelet transform (DWT) for data security.
2) In the proposed method, data is first encrypted using RSA encryption and then embedded in an image using Haar-DWT based steganography.
3) Experimental results on 100 images show the proposed technique achieves higher PSNR values compared to other techniques like LSB and LSB-DCT steganography, indicating better image quality and security of the hidden data.
iaetsd Secured multiple keyword ranked search over encrypted databasesIaetsd Iaetsd
This document proposes a Robust Key-Aggregate Cryptosystem (RKAC) that allows flexible and efficient assignment of decryption rights for encrypted data stored in cloud storage. The RKAC produces constant-sized ciphertexts such that a constant-sized aggregate decryption key can decrypt any subset of ciphertexts. This allows the data owner to share access to selected encrypted files by sending a single small aggregate key to authorized users, without decrypting the files themselves or distributing individual keys. The RKAC is described as providing a secure and flexible method for sharing encrypted data stored in the cloud.
In cryptography, encryption is the process of encoding a message or information in such a way that only authorized parties can access it and those who are not authorized cannot. Encryption does not itself prevent interference, but denies the intelligible content to a would-be interceptor.
This paper presents an efficient implementation of the RSA encryption algorithm using the GNU MP Library. It describes generating RSA keys with primes of 1024 bits, encrypting and decrypting files by processing characters in groups, and analyzing encryption and decryption times with varying group sizes. It finds that encryption and decryption times decrease when more characters are processed together. A GUI for the RSA implementation is also described and screenshots are provided.
This document proposes a hybrid encryption-decryption algorithm combining AES and DES. It implements the algorithm in VHDL using a Modelsim platform. The hybrid algorithm integrates AES into each iteration of DES's Feistel network, using AES operations like substitution and key addition. This increases computational complexity compared to the individual standards. The VHDL implementation includes modules for AES encryption/decryption and the hybrid algorithm. Simulations validate the code works correctly. Future work could increase iterations to suit different security levels or implement a 128-bit AES variant. The hybrid approach strengthens AES security against attacks.
The document discusses various methods of authentication in wireless networks, including standards like 802.11 and 802.16, as well as encryption methods such as Diffie-Hellman key exchange, RSA, RC4, and TripleDES. It also examines network types like TTP and describes how clients can connect to a trusted third party server or directly connect to another client with encryption. The objectives are to investigate authentication methods, implement one in Java, and document the implementation.
“SECURITY” in this contemporary scenarios has become a more sensible issue either it may be in the “REAL WORLD” or in the “CYBER WORLD”. In the real world as opposed to the cyber world information gathering often precedes an attack. Today the illicit activities of the hackers are growing by leaps and bounds. However; fortunately, the antagonists reacted promptly and resurrected the internet world from the brink of prostration. Tersely quoting some security ditherers - hijackers, Eavesdropping, hacking, mapping, packet sniffing, spoofing, etc.
This document describes an audio cryptography system project that embeds encrypted messages within audio files. The system has two main modules: a GUI module built using AWT, Swing components; and an encryption/decryption module. Messages are encrypted before being embedded in audio files using LSB coding and encryption algorithms. The encrypted audio files can then be transmitted and decrypted at the recipient end to extract the original message. The system aims to provide security, confidentiality and integrity to transmitted messages.
Android based message encryption decryption using matrixeSAT Journals
Abstract
In this paper we are going to encrypt plain text to encrypted text. Message encryption is character value based encryption in which 3D message character matrix is replaced with 2D encryption value matrix. It can also know by some kind of message masking which work on upper level to provide maximum security. Password protection increases encrypted message file security.
Keywords – Matrix, ASCII Offset Value, DES, 3D Message Masking, and 2D.
Encryption is a process that converts plain text into ciphertext through the use of cryptographic algorithms and encryption keys. There are two main types of encryption: symmetric encryption which uses the same key for encryption and decryption, and asymmetric encryption which uses a public key for encryption and a private key for decryption. Common symmetric encryption algorithms discussed include DES, Triple DES, AES, Blowfish and Twofish. Asymmetric algorithms include RSA. Other algorithms mentioned are IDEA, MD5, and FPE. The document also discusses how encryption keys are used and changed in Magento.
This document analyzes and compares the performance of various cryptography algorithms. It discusses symmetric key algorithms like DES, AES, Blowfish and IDEA as well as asymmetric algorithms like RSA and Diffie-Hellman. The performance is evaluated based on parameters like encryption/decryption time, memory usage and throughput. Experiments show that Blowfish has better performance than AES for encrypting audio files, with lower average encryption and decryption times. In conclusion, cryptography is important for network security and Blowfish performs encryption/decryption more efficiently than AES for audio files.
This document describes a proposed technique for information security that uses a hybrid of DES and RSA encryption along with LSB steganography. The message is first encrypted with DES, then the DES keys are encrypted with RSA. The hybrid encrypted result is then embedded into an image file using LSB steganography. This combines the strengths of cryptography and steganography for improved security of transmitted data. The encryption time is faster than previous techniques and brute force attacks on this technique would be very difficult.
Module 6
Advanced Networking
Security problems with internet architecture, Introduction to Software defined networking, Working of SDN, SDN in data centre, SDN applications, Data centre networking, IoT.
The document discusses network security and introduces concepts like cryptography, authentication, and message integrity. It notes that network security aims to ensure confidentiality, authentication, and access for legitimate users while preventing attacks from unauthorized parties. The chapter will cover principles of cryptography, security protocols for different layers, and operational security measures like firewalls and intrusion detection systems. Users are asked to cite the source if using the slides and to respect the authors' copyright.
This document discusses the use and sharing of PowerPoint slides from a textbook on computer networking. It allows the slides to be modified and used for educational purposes with only two requirements: 1) Cite the source if using the slides substantially unaltered, and 2) Note the copyright if posting slides substantially unaltered online. The document is copyrighted by the authors of the textbook from 1996-2007.
The document discusses network security and introduces concepts like cryptography, authentication, and message integrity. It notes that network security aims to ensure confidentiality, authentication, and access to services. Cryptography uses techniques like encryption, digital signatures, and hash functions to provide these security properties. The document provides examples to illustrate symmetric and public key cryptography, including how algorithms like DES, AES, RSA and hash functions work. It also introduces common network security examples like Alice, Bob and the intruder Trudy.
The document discusses various topics related to network security including encryption, authentication, and protocols. It provides an overview of symmetric and public key cryptography, algorithms like DES and RSA, digital signatures, protocols like SSL and IPsec, and applications like PGP. Common security threats like packet sniffing, IP spoofing, and denial of service attacks are also summarized.
This document discusses network security concepts including encryption, authentication, and threats. It introduces common network security scenarios involving friends (Alice and Bob) communicating securely while an intruder (Trudy) may intercept or alter messages. Examples of real systems that require security are also given such as web browsers, online banking, and network routers. Common network attacks are then outlined like eavesdropping, spoofing, and denial of service attacks. The document proceeds to explain approaches to network security including symmetric and public key encryption methods. Specific encryption algorithms are described like DES and RSA public key encryption.
This document provides an overview of network security principles including cryptography, authentication, message integrity, and key distribution. It begins with an introduction to network security concepts and then outlines the topics that will be covered, which include principles of cryptography, authentication, integrity, key distribution, access control using firewalls, common attacks, and security at different layers. Examples are provided to illustrate authentication protocols and their vulnerabilities. Digital signatures and message digests are introduced as techniques for authentication and integrity. Symmetric and public key encryption algorithms like DES, AES, RSA are briefly described. The need for trusted intermediaries like key distribution centers and certification authorities is also noted.
This document provides an introduction to symmetric and asymmetric cryptography. Symmetric cryptography uses the same key for encryption and decryption, while asymmetric cryptography uses public and private key pairs. Symmetric cryptography is faster but requires secure key exchange, while asymmetric cryptography allows secure communication between parties who have not previously shared a key. Examples of symmetric algorithms discussed include AES and DES, while asymmetric or public key cryptography is illustrated using Diffie-Hellman key exchange. Both types are still widely used with increasingly large key sizes providing greater security.
Cryptography for Developers provides an overview of cryptography concepts for developers. It defines cryptography as the encryption of plaintext into ciphertext and back again. It discusses symmetric and asymmetric cryptography, including examples like the Caesar cipher. It covers hashing of passwords for storage and discusses popular algorithms like MD5 and SHA-2. The document also summarizes public key cryptography techniques like RSA and references materials for further learning.
Chapter 8SecurityComputer Networking A Top Down Approach .docxrusselldayna
Chapter 8
Security
Computer Networking: A Top Down Approach
6th edition
Jim Kurose, Keith Ross
Addison-Wesley
March 2012
A note on the use of these ppt slides:
We’re making these slides freely available to all (faculty, students, readers). They’re in PowerPoint form so you see the animations; and can add, modify, and delete slides (including this one) and slide content to suit your needs. They obviously represent a lot of work on our part. In return for use, we only ask the following:
If you use these slides (e.g., in a class) that you mention their source (after all, we’d like people to use our book!)
If you post any slides on a www site, that you note that they are adapted from (or perhaps identical to) our slides, and note our copyright of this material.
Thanks and enjoy! JFK/KWR
All material copyright 1996-2012
J.F Kurose and K.W. Ross, All Rights Reserved
Network Security
Chapter 8: Network Security
Chapter goals:
understand principles of network security:
cryptography and its many uses beyond “confidentiality”
authentication
message integrity
security in practice:
firewalls and intrusion detection systems
security in application, transport, network, link layers
2
Network Security
Chapter 8 roadmap
8.1 What is network security?
8.2 Principles of cryptography
8.3 Message integrity, authentication
8.4 Securing e-mail
8.5 Securing TCP connections: SSL
8.6 Network layer security: IPsec
8.7 Securing wireless LANs
8.8 Operational security: firewalls and IDS
3
Network Security
What is network security?
confidentiality: only sender, intended receiver should “understand” message contents
sender encrypts message
receiver decrypts message
authentication: sender, receiver want to confirm identity of each other
message integrity: sender, receiver want to ensure message not altered (in transit, or afterwards) without detection
access and availability: services must be accessible and available to users
4
Network Security
Friends and enemies: Alice, Bob, Trudy
well-known in network security world
Bob, Alice (lovers!) want to communicate “securely”
Trudy (intruder) may intercept, delete, add messages
5
Network Security
Who might Bob, Alice be?
… well, real-life Bobs and Alices!
Web browser/server for electronic transactions (e.g., on-line purchases)
on-line banking client/server
DNS servers
routers exchanging routing table updates
other examples?
6
Network Security
There are bad guys (and girls) out there!
Q: What can a “bad guy” do?
A: A lot! See section 1.6
eavesdrop: intercept messages
actively insert messages into connection
impersonation: can fake (spoof) source address in packet (or any field in packet)
hijacking: “take over” ongoing connection by removing sender or receiver, inserting himself in place
denial of service: prevent service from being used by others (e.g., by overloading resources)
7
Network Security
Chapter 8 roadmap
8.1 What is network security?
8.2 Principles of cryptograph ...
Asymmetric key cryptography uses two keys - a public key that can be shared publicly and a private key that is kept secret. This allows two parties who have never shared secrets before, like Alice and Bob, to communicate securely by encrypting messages with each other's public keys. Common asymmetric algorithms discussed are RSA, which uses prime number factorization, and ECC, which is based on elliptic curve discrete logarithms. A public key infrastructure (PKI) with certificate authorities (CAs) is required to authenticate users and manage public keys.
Asymmetric key cryptography uses two keys - a public key that can be shared publicly and a private key that is kept secret. This allows two parties who have never shared secrets before, like Alice and Bob, to communicate securely by encrypting messages with each other's public keys. Common asymmetric algorithms include RSA, which uses prime number factorization, and ECC, which is based on elliptic curve discrete logarithms. Certificate authorities issue digital certificates that bind public keys to identities to facilitate trust in public key infrastructures.
This document provides an introduction to security and cryptography. It begins with an overview of security goals like confidentiality, authenticity, integrity, and non-repudiation. It then discusses symmetric cryptography algorithms like DES and AES, and how they provide confidentiality. Asymmetric cryptography algorithms like RSA and ECC are introduced for providing authentication, non-repudiation through digital signatures, and facilitating key exchange. Hash functions are described for providing integrity and digital signatures. Modes of operation for block ciphers like CBC are covered. Popular algorithms and their application to security goals are summarized.
This document provides an overview of security and cryptography topics including:
- The basics of security including confidentiality, authenticity, integrity, and non-repudiation goals and how symmetric and asymmetric cryptography help achieve them.
- Symmetric cryptography algorithms like DES, Triple DES, and AES as well as modes of operation like CBC.
- Asymmetric cryptography concepts like public/private key pairs, digital signatures, and how RSA works.
- Other cryptographic tools like hash functions, message authentication codes, and key exchange methods like Diffie-Hellman.
- The role of public key infrastructure and certificates in authenticating public keys.
- Attacks on cryptographic algorithms and their implementations are also briefly discussed.
This document provides an overview of security and cryptography topics including:
- The basics of security including confidentiality, authenticity, integrity, and non-repudiation goals and how symmetric and asymmetric cryptography help achieve them.
- Symmetric cryptography algorithms like DES, Triple DES, and AES along with modes of operation like CBC.
- Asymmetric cryptography including key exchange with Diffie-Hellman and digital signatures with RSA and ECC.
- Cryptographic hash functions like SHA and their properties. Message authentication codes (MACs) that provide integrity.
- Public key infrastructure with certificates and how they establish authenticity of public keys.
- Attacks on algorithms, implementations, and protocols and the need for unpredictable
This document provides an overview of security and cryptography topics including:
- The basics of security including confidentiality, authenticity, integrity, and non-repudiation goals and how symmetric and asymmetric cryptography help achieve them.
- Symmetric cryptography algorithms like DES, Triple DES, and AES and how they operate using symmetric keys for encryption and decryption.
- Cryptographic hashing and message authentication codes (MACs) and how they provide integrity and authentication.
- Asymmetric (public key) cryptography like RSA and ECC using key pairs for encryption, signatures, and key exchange without pre-shared secrets.
- Key exchange methods like Diffie-Hellman and how public key infrastructure (PKI) uses digital
This document provides an overview of security and cryptography topics including:
- The basics of security including confidentiality, authenticity, integrity, and non-repudiation goals and how symmetric and asymmetric cryptography help achieve them.
- Symmetric cryptography algorithms like DES, Triple DES, and AES and how they operate using symmetric keys for encryption and decryption.
- Cryptographic hashing and message authentication codes (MACs) and how they provide integrity and authentication.
- Asymmetric (public key) cryptography like RSA and ECC using key pairs for encryption, signatures, and key exchange without pre-shared secrets.
- Key exchange methods like Diffie-Hellman and how public key infrastructure (PKI) uses digital
This document provides an overview of security and cryptography topics including:
- The basics of security including confidentiality, authenticity, integrity, and non-repudiation goals and how symmetric and asymmetric cryptography, hashes, signatures, and MACs address them.
- Symmetric block ciphers like DES and AES including modes of operation like CBC.
- Asymmetric cryptography concepts like key exchange using Diffie-Hellman and digital signatures using RSA.
- Cryptographic hash functions like SHA and their properties.
- Public key infrastructure concepts like certificates and how they establish authenticity of public keys.
This document provides an overview of security and cryptography topics including:
- The basics of security including confidentiality, authenticity, integrity, and non-repudiation goals and how symmetric and asymmetric cryptography help achieve them.
- Symmetric cryptography algorithms like DES, Triple DES, and AES and how they operate using symmetric keys for encryption and decryption.
- Cryptographic hashing and message authentication codes (MACs) and how they provide integrity and authentication.
- Asymmetric (public key) cryptography like RSA and ECC using key pairs for encryption, signatures, and key exchange without pre-shared secrets.
- Key exchange methods like Diffie-Hellman and how public key infrastructure (PKI) uses digital
This document discusses public key cryptography and the RSA algorithm. RSA allows two parties to communicate securely without having to share a secret key beforehand. It works by having each party generate both a public and private key. The public key can be used to encrypt messages, while only the private key can decrypt them. RSA relies on the difficulty of factoring large numbers to be secure. The document provides an example of how RSA key generation and encryption/decryption work in practice.
1. Chapter 7
Network Security
A note on the use of these ppt slides:
We’re making these slides freely available to all (faculty, students, readers). Computer Networking:
They’re in powerpoint form so you can add, modify, and delete slides
(including this one) and slide content to suit your needs. They obviously A Top Down Approach
represent a lot of work on our part. In return for use, we only ask the Featuring the Internet,
following:
If you use these slides (e.g., in a class) in substantially unaltered form,
that you mention their source (after all, we’d like people to use our book!) 2nd edition.
Jim Kurose, Keith Ross
If you post any slides in substantially unaltered form on a www site, that
you note that they are adapted from (or perhaps identical to) our slides, and
note our copyright of this material. Addison-Wesley, July
Thanks and enjoy! JFK/KWR 2002.
All material copyright 1996-2002
J.F Kurose and K.W. Ross, All Rights Reserved
Network Security 7-1
2. Chapter 7: Network Security
Chapter goals:
understand principles of network security:
cryptography and its many uses beyond
“confidentiality”
authentication
message integrity
key distribution
security in practice:
firewalls
security in application, transport, network, link
layers
Network Security 7-2
3. Chapter 7 roadmap
7.1 What is network security?
7.2 Principles of cryptography
7.3 Authentication
7.4 Integrity
7.5 Key Distribution and certification
7.6 Access control: firewalls
7.7 Attacks and counter measures
7.8 Security in many layers
Network Security 7-3
4. What is network security?
Confidentiality: only sender, intended receiver
should “understand” message contents
sender encrypts message
receiver decrypts message
Authentication: sender, receiver want to confirm
identity of each other
Message Integrity: sender, receiver want to ensure
message not altered (in transit, or afterwards)
without detection
Access and Availability: services must be accessible
and available to users
Network Security 7-4
5. Friends and enemies: Alice, Bob, Trudy
well-known in network security world
Bob, Alice (lovers!) want to communicate “securely”
Trudy (intruder) may intercept, delete, add messages
Alice Bob
data, control
channel
messages
data secure secure data
sender receiver
Trudy
Network Security 7-5
6. Who might Bob, Alice be?
… well, real-life Bobs and Alices!
Web browser/server for electronic
transactions (e.g., on-line purchases)
on-line banking client/server
DNS servers
routers exchanging routing table updates
other examples?
Network Security 7-6
7. There are bad guys (and girls) out there!
Q: What can a “bad guy” do?
A: a lot!
eavesdrop: intercept messages
actively insert messages into connection
impersonation: can fake (spoof) source address
in packet (or any field in packet)
hijacking: “take over” ongoing connection by
removing sender or receiver, inserting himself
in place
denial of service: prevent service from being
used by others (e.g., by overloading resources)
more on this later ……
Network Security 7-7
8. Chapter 7 roadmap
7.1 What is network security?
7.2 Principles of cryptography
7.3 Authentication
7.4 Integrity
7.5 Key Distribution and certification
7.6 Access control: firewalls
7.7 Attacks and counter measures
7.8 Security in many layers
Network Security 7-8
9. The language of cryptography
Alice’s Bob’s
K encryption K decryption
A
key B key
plaintext encryption ciphertext decryption plaintext
algorithm algorithm
symmetric key crypto: sender, receiver keys identical
public-key crypto: encryption key public, decryption key
secret (private)
Network Security 7-9
10. Symmetric key cryptography
substitution cipher: substituting one thing for another
monoalphabetic cipher: substitute one letter for another
plaintext: abcdefghijklmnopqrstuvwxyz
ciphertext: mnbvcxzasdfghjklpoiuytrewq
E.g.: Plaintext: bob. i love you. alice
ciphertext: nkn. s gktc wky. mgsbc
Q: How hard to break this simple cipher?:
brute force (how hard?)
other?
Network Security 7-
11. Symmetric key cryptography
KA-B KA-B
plaintext encryption ciphertext decryption plaintext
message, m algorithm algorithm
K (m)
A-B
m=K ( K (m) )
A-B A-B
symmetric key crypto: Bob and Alice share know same
(symmetric) key: K
A-B
e.g., key is knowing substitution pattern in mono
alphabetic substitution cipher
Q: how do Bob and Alice agree on key value?
Network Security 7-
12. Symmetric key crypto: DES
DES: Data Encryption Standard
US encryption standard [NIST 1993]
56-bit symmetric key, 64-bit plaintext input
How secure is DES?
DES Challenge: 56-bit-key-encrypted phrase
(“Strong cryptography makes the world a safer
place”) decrypted (brute force) in 4 months
no known “backdoor” decryption approach
making DES more secure:
use three keys sequentially (3-DES) on each datum
use cipher-block chaining
Network Security 7-
13. Symmetric key
crypto: DES
DES operation
initial permutation
16 identical “rounds” of
function application,
each using different
48 bits of key
final permutation
Network Security 7-
14. AES: Advanced Encryption Standard
new (Nov. 2001) symmetric-key NIST
standard, replacing DES
processes data in 128 bit blocks
128, 192, or 256 bit keys
brute force decryption (try each key)
taking 1 sec on DES, takes 149 trillion
years for AES
Network Security 7-
15. Public Key Cryptography
symmetric key crypto public key cryptography
requires sender, radically different
receiver know shared approach [Diffie-
secret key Hellman76, RSA78]
Q: how to agree on key sender, receiver do
in first place not share secret key
(particularly if never public encryption key
“met”)? known to all
private decryption
key known only to
receiver
Network Security 7-
16. Public key cryptography
+ Bob’s public
K
B key
- Bob’s private
K
B key
plaintext encryption ciphertext decryption plaintext
message, m algorithm + algorithm message
K (m) - +
B m = K B(K (m))
B
Network Security 7-
17. Public key encryption algorithms
Requirements:
+ .
1 need K B( ) and K - ( ) such that
B
.
- +
K (K (m)) = m
B B
+
given public key K , it should be impossible to compute private key K
2 B
-
B
RSA: Rivest, Shamir, Adelson algorithm
Network Security 7-
18. RSA: Choosing keys
1. Choose two large prime numbers p, q.
(e.g., 1024 bits each)
2. Compute n = pq, z = (p-1)(q-1)
3. Choose e (with e<n) that has no common factors
with z. (e, z are “relatively prime”).
4. Choose d such that ed-1 is exactly divisible by z.
(in other words: ed mod z = 1 ).
5. Public key is (n,e). Private key is (n,d).
+ -
KB KB
Network Security 7-
19. RSA: Encryption, decryption
0. Given (n,e) and (n,d) as computed above
1. To encrypt bit pattern, m, compute
e
c = m e mod n (i.e., remainder when m is divided by n)
2. To decrypt received bit pattern, c, compute
d
m = c d mod n (i.e., remainder when c is divided by n)
Magic d
m = (m e mod n) mod n
happens!
c
Network Security 7-
20. RSA example:
Bob chooses p=5, q=7. Then n=35, z=24.
e=5 (so e, z relatively prime).
d=29 (so ed-1 exactly divisible by z.
letter m me c = me mod n
encrypt:
l 12 1524832 17
d
decrypt:
c c m = cd mod n letter
17 481968572106750915091411825223071697 12 l
Network Security 7-
21. RSA: Why is that d
m = (m e mod n) mod n
Useful number theory result: If p,q prime and
n = pq, then: y y mod (p-1)(q-1)
x mod n = x mod n
e
(m mod n) d mod n = med mod n
ed mod (p-1)(q-1)
= m mod n
(using number theory result above)
1
= m mod n
(since we chose ed to be divisible by
(p-1)(q-1) with remainder 1 )
= m
Network Security 7-
22. RSA: another important property
The following property will be very useful later:
- + + -
K (K (m)) = m = K (K (m))
B B B B
use public key use private key
first, followed first, followed
by private key by public key
Result is the same!
Network Security 7-
23. Chapter 7 roadmap
7.1 What is network security?
7.2 Principles of cryptography
7.3 Authentication
7.4 Integrity
7.5 Key Distribution and certification
7.6 Access control: firewalls
7.7 Attacks and counter measures
7.8 Security in many layers
Network Security 7-
24. Authentication
Goal: Bob wants Alice to “prove” her identity
to him
Protocol ap1.0: Alice says “I am Alice”
“I am Alice”
Failure scenario??
Network Security 7-
25. Authentication
Goal: Bob wants Alice to “prove” her identity
to him
Protocol ap1.0: Alice says “I am Alice”
in a network,
Bob can not “see”
Alice, so Trudy simply
“I am Alice” declares
herself to be Alice
Network Security 7-
26. Authentication: another try
Protocol ap2.0: Alice says “I am Alice” in an IP packet
containing her source IP address
Alice’s
IP address
“I am Alice”
Failure scenario??
Network Security 7-
27. Authentication: another try
Protocol ap2.0: Alice says “I am Alice” in an IP packet
containing her source IP address
Trudy can create
a packet
Alice’s
“spoofing”
IP address
“I am Alice” Alice’s address
Network Security 7-
28. Authentication: another try
Protocol ap3.0: Alice says “I am Alice” and sends her
secret password to “prove” it.
Alice’s Alice’s
“I’m Alice”
IP addr password
Alice’s Failure scenario??
OK
IP addr
Network Security 7-
29. Authentication: another try
Protocol ap3.0: Alice says “I am Alice” and sends her
secret password to “prove” it.
Alice’s Alice’s
“I’m Alice”
IP addr password
playback attack: Trudy
Alice’s records Alice’s packet
OK
IP addr and later
plays it back to Bob
Alice’s Alice’s
“I’m Alice”
IP addr password
Network Security 7-
30. Authentication: yet another try
Protocol ap3.1: Alice says “I am Alice” and sends her
encrypted secret password to “prove” it.
Alice’s encrypted
“I’m Alice”
IP addr password
Alice’s Failure scenario??
OK
IP addr
Network Security 7-
31. Authentication: another try
Protocol ap3.1: Alice says “I am Alice” and sends her
encrypted secret password to “prove” it.
Alice’s encryppted
IP addr password
“I’m Alice” record
and
Alice’s
OK playback
IP addr
still works!
Alice’s encrypted
“I’m Alice”
IP addr password
Network Security 7-
32. Authentication: yet another try
Goal: avoid playback attack
Nonce: number (R) used only once –in-a-lifetime
ap4.0: to prove Alice “live”, Bob sends Alice nonce, R.
Alice
must return R, encrypted with shared secret key
“I am Alice”
R
KA-B(R) Alice is live, and
only Alice knows
key to encrypt
nonce, so it must
Failures, drawbacks? be Alice!
Network Security 7-
33. Authentication: ap5.0
ap4.0 requires shared symmetric key
can we authenticate using public key techniques?
ap5.0: use nonce, public key cryptography
“I am Alice”
Bob computes
R + -
- KA(KA (R)) = R
K A (R) and knows only Alice
“send me your public key”
could have the private
+ key, that encrypted R
KA such that
+ -
K (K (R)) = R
A A
Network Security 7-
34. ap5.0: security hole
Man (woman) in the middle attack: Trudy poses as
Alice (to Bob) and as Bob (to Alice)
I am Alice I am Alice
R -
K (R)
T
R - Send me your public key
K (R) +
A K
T
Send me your public key
+
K
A +
K (m)
Trudy gets T
- +
+ m = K (K (m))
K (m)
A sends T to Alice
m T
- + ennrypted with
m = K (K (m))
A A Alice’s public key
Network Security 7-
35. ap5.0: security hole
Man (woman) in the middle attack: Trudy poses as
Alice (to Bob) and as Bob (to Alice)
Difficult to detect:
Bob receives everything that Alice sends, and vice
versa. (e.g., so Bob, Alice can meet one week later and
recall conversation)
problem is that Trudy receives all messages as well!
Network Security 7-
36. Chapter 7 roadmap
7.1 What is network security?
7.2 Principles of cryptography
7.3 Authentication
7.4 Message integrity
7.5 Key Distribution and certification
7.6 Access control: firewalls
7.7 Attacks and counter measures
7.8 Security in many layers
Network Security 7-
37. Digital Signatures
Cryptographic technique analogous to hand-
written signatures.
sender (Bob) digitally signs document,
establishing he is document owner/creator.
verifiable, nonforgeable: recipient (Alice) can
prove to someone that Bob, and no one else
(including Alice), must have signed document
Network Security 7-
38. Digital Signatures
Simple digital signature for message m:
Bob signs m by encrypting with his private key
- -
KB, creating “signed” message, KB(m)
-
Bob’s message, m K B Bob’s private -
K B(m)
key
Dear Alice
Bob’s message,
Oh, how I have missed Public key m, signed
you. I think of you all the
time! …(blah blah blah) encryption (encrypted) with
algorithm his private key
Bob
Network Security 7-
39. Digital Signatures (more)
-
Suppose Alice receives msg m, digital signature KB(m)
Alice verifies m signed by Bob by applying Bob’s
-
+ + -
public key KB to KB(m) then checks KB(KB(m) ) = m.
+ -
If KB(KB(m) ) = m, whoever signed m must have used
Bob’s private key.
Alice thus verifies that:
Bob signed m.
No one else signed m.
Bob signed m and not m’.
Non-repudiation:
-
Alice can take m, and signature KB(m) to
court and prove that Bob signed m.
Network Security 7-
40. Message Digests large
H: Hash
message
Function
m
Computationally expensive
to public-key-encrypt
H(m)
long messages
Goal: fixed-length, easy- Hash function properties:
to-compute digital many-to-1
“fingerprint”
produces fixed-size msg
apply hash function H digest (fingerprint)
to m, get fixed size
given message digest x,
message digest, H(m).
computationally
infeasible to find m such
that x = H(m)
Network Security 7-
41. Internet checksum: poor crypto hash
function
Internet checksum has some properties of hash function:
produces fixed length digest (16-bit sum) of message
is many-to-one
But given message with given hash value, it is easy to find
another message with same hash value:
message ASCII format message ASCII format
I O U 1 49 4F 55 31 I O U 9 49 4F 55 39
0 0 . 9 30 30 2E 39 0 0 . 1 30 30 2E 31
9 B O B 39 42 D2 42 9 B O B 39 42 D2 42
B2 C1 D2 AC different messages B2 C1 D2 AC
but identical checksums!
Network Security 7-
42. Digital signature = signed message digest
Alice verifies signature and
Bob sends digitally signed integrity of digitally signed
message: message:
large
message H: Hash encrypted
m function H(m)
msg digest
-
KB(H(m))
Bob’s digital large
private signature message
- Bob’s
key KB (encrypt) m digital
public
+ signature
key KB
encrypted H: Hash (decrypt)
msg digest function
-
+ KB(H(m))
H(m) H(m)
equal
?
Network Security 7-
43. Hash Function Algorithms
MD5 hash function widely used (RFC 1321)
computes 128-bit message digest in 4-step
process.
arbitrary 128-bit string x, appears difficult to
construct msg m whose MD5 hash is equal to x.
SHA-1 is also used.
US standard [NIST, FIPS PUB 180-1]
160-bit message digest
Network Security 7-
44. Chapter 7 roadmap
7.1 What is network security?
7.2 Principles of cryptography
7.3 Authentication
7.4 Integrity
7.5 Key distribution and certification
7.6 Access control: firewalls
7.7 Attacks and counter measures
7.8 Security in many layers
Network Security 7-
45. Trusted Intermediaries
Symmetric key problem: Public key problem:
How do two entities When Alice obtains
establish shared secret Bob’s public key (from
key over network? web site, e-mail,
Solution: diskette), how does she
know it is Bob’s public
trusted key distribution key, not Trudy’s?
center (KDC) acting as
intermediary between Solution:
entities trusted certification
authority (CA)
Network Security 7-
46. Key Distribution Center (KDC)
Alice, Bob need shared symmetric key.
KDC: server shares different secret key with each
registered user (many users)
Alice, Bob know own symmetric keys, KA-KDC KB-KDC , for
communicating with KDC.
KDC
KA-KDC KP-KDC
KX-KDC
KP-KDC KB-KDC
KY-KDC
KZ-KDC
KA-KDC KB-KDC
Network Security 7-
47. Key Distribution Center (KDC)
Q: How does KDC allow Bob, Alice to determine shared
symmetric secret key to communicate with each other?
KDC
generates
KA-KDC(A,B)
R1
Alice KA-KDC(R1, KB-KDC(A,R1) )
Bob knows to
knows use R1 to
R1 KB-KDC(A,R1) communicate
with Alice
Alice and Bob communicate: using R1 as
session key for shared symmetric encryption
Network Security 7-
48. Certification Authorities
Certification authority (CA): binds public key to
particular entity, E.
E (person, router) registers its public key with CA.
E provides “proof of identity” to CA.
CA creates certificate binding E to its public key.
certificate containing E’s public key digitally signed by CA
– CA says “this is E’s public key”
Bob’s digital
+
public +
signature KB
key KB (encrypt)
CA
certificate for
K-
Bob’s private
identifying key CA Bob’s public key,
information signed by CA
Network Security 7-
49. Certification Authorities
When Alice wants Bob’s public key:
gets Bob’s certificate (Bob or elsewhere).
apply CA’s public key to Bob’s certificate, get
Bob’s public key
+ digital Bob’s
KB signature public
+
(decrypt) K B key
CA
public +
K CA
key
Network Security 7-
50. A certificate contains:
Serial number (unique to issuer)
info about certificate owner, including algorithm
and key value itself (not shown) info about certificate issuer
valid dates
digital signature by issuer
Network Security 7-
51. Chapter 7 roadmap
7.1 What is network security?
7.2 Principles of cryptography
7.3 Authentication
7.4 Integrity
7.5 Key Distribution and certification
7.6 Access control: firewalls
7.7 Attacks and counter measures
7.8 Security in many layers
Network Security 7-
53. Firewalls: Why
prevent denial of service attacks:
SYN flooding: attacker establishes many bogus TCP
connections, no resources left for “real” connections.
prevent illegal modification/access of internal data.
e.g., attacker replaces CIA’s homepage with
something else
allow only authorized access to inside network (set of
authenticated users/hosts)
two types of firewalls:
application-level
packet-filtering
Network Security 7-
54. Should arriving
Packet Filtering packet be allowed
in? Departing packet
let out?
internal network connected to Internet via
router firewall
router filters packet-by-packet, decision to
forward/drop packet based on:
source IP address, destination IP address
TCP/UDP source and destination port numbers
ICMP message type
TCP SYN and ACK bits
Network Security 7-
55. Packet Filtering
Example 1: block incoming and outgoing
datagrams with IP protocol field = 17 and with
either source or dest port = 23.
All incoming and outgoing UDP flows and telnet
connections are blocked.
Example 2: Block inbound TCP segments with
ACK=0.
Prevents external clients from making TCP
connections with internal clients, but allows
internal clients to connect to outside.
Network Security 7-
56. Application gateways gateway-to-remote
host telnet session
host-to-gateway
telnet session
Filters packets on
application data as well application
gateway
router and filter
as on IP/TCP/UDP fields.
Example: allow select
internal users to telnet
outside.
1. Require all telnet users to telnet through gateway.
2. For authorized users, gateway sets up telnet connection to
dest host. Gateway relays data between 2 connections
3. Router filter blocks all telnet connections not originating
from gateway.
Network Security 7-
57. Limitations of firewalls and gateways
IP spoofing: router filters often use all or
can’t know if data nothing policy for UDP.
“really” comes from tradeoff: degree of
claimed source communication with
if multiple app’s. need outside world, level of
special treatment, each security
has own app. gateway. many highly protected
client software must sites still suffer from
know how to contact attacks.
gateway.
e.g., must set IP address
of proxy in Web
browser
Network Security 7-
58. Chapter 7 roadmap
7.1 What is network security?
7.2 Principles of cryptography
7.3 Authentication
7.4 Integrity
7.5 Key Distribution and certification
7.6 Access control: firewalls
7.7 Attacks and counter measures
7.8 Security in many layers
Network Security 7-
59. Internet security threats
Mapping:
before attacking: “case the joint” – find out
what services are implemented on network
Use ping to determine what hosts have
addresses on network
Port-scanning: try to establish TCP connection
to each port in sequence (see what happens)
nmap (http://www.insecure.org/nmap/) mapper:
“network exploration and security auditing”
Countermeasures?
Network Security 7-
60. Internet security threats
Mapping: countermeasures
record traffic entering network
look for suspicious activity (IP addresses, pots
being scanned sequentially)
Network Security 7-
61. Internet security threats
Packet sniffing:
broadcast media
promiscuous NIC reads all packets passing by
can read all unencrypted data (e.g. passwords)
e.g.: C sniffs B’s packets
A C
src:B dest:A payload
B
Countermeasures?
Network Security 7-
62. Internet security threats
Packet sniffing: countermeasures
all hosts in orgnization run software that
checks periodically if host interface in
promiscuous mode.
one host per segment of broadcast media
(switched Ethernet at hub)
A C
src:B dest:A payload
B
Network Security 7-
63. Internet security threats
IP Spoofing:
can generate “raw” IP packets directly from
application, putting any value into IP source
address field
receiver can’t tell if source is spoofed
e.g.: C pretends to be B
A C
src:B dest:A payload
B
Countermeasures?
Network Security 7-
64. Internet security threats
IP Spoofing: ingress filtering
routers should not forward outgoing packets
with invalid source addresses (e.g., datagram
source address not in router’s network)
great, but ingress filtering can not be mandated
for all networks
A C
src:B dest:A payload
B
Network Security 7-
65. Internet security threats
Denial of service (DOS):
flood of maliciously generated packets “swamp”
receiver
Distributed DOS (DDOS): multiple coordinated
sources swamp receiver
e.g., C and remote host SYN-attack A
A C
SYN
SYN
SYN SYN SYN
B
SYN
Countermeasures? SYN
Network Security 7-
66. Internet security threats
Denial of service (DOS): countermeasures
filter out flooded packets (e.g., SYN) before
reaaching host: throw out good with bad
traceback to source of floods (most likely an
innocent, compromised machine)
A C
SYN
SYN
SYN SYN SYN
B
SYN
SYN
Network Security 7-
67. Chapter 7 roadmap
7.1 What is network security?
7.2 Principles of cryptography
7.3 Authentication
7.4 Integrity
7.5 Key Distribution and certification
7.6 Access control: firewalls
7.7 Attacks and counter measures
7.8 Security in many layers
7.8.1. Secure email
7.8.2. Secure sockets
7.8.3. IPsec
8.8.4. 802.11 WEP
Network Security 7-
68. Secure e-mail
Alice wants to send confidential e-mail, m, to Bob.
KS
m K (.
S )
KS(m ) KS(m )
KS( ) . m
+ Internet - KS
KS
+.
K ()
B + +
- .
KB ( )
KB(KS ) KB(KS )
+ -
KB
KB
Alice:
generates random symmetric private key, KS.
encrypts message with KS (for efficiency)
also encrypts KS with Bob’s public key.
sends both KS(m) and KB(KS) to Bob.
Network Security 7-
69. Secure e-mail
Alice wants to send confidential e-mail, m, to Bob.
KS
m K (.
S )
KS(m ) KS(m )
KS( ) . m
+ Internet - KS
KS
+.
K ()
B + +
- .
KB ( )
KB(KS ) KB(KS )
+ -
KB
KB
Bob:
uses his private key to decrypt and recover KS
uses KS to decrypt KS(m) to recover m
Network Security 7-
70. Secure e-mail (continued)
• Alice wants to provide sender authentication
message integrity.
- KA
+
KA
- -
m .
H( )
-.
K ()
A
KA(H(m)) KA(H(m)) +
KA( )
. H(m )
+ Internet - compare
m H( ). H(m )
m
• Alice digitally signs message.
• sends both message (in the clear) and digital signature.
Network Security 7-
71. Secure e-mail (continued)
• Alice wants to provide secrecy, sender authentication,
message integrity.
-
KA
-
m .
H( )
-
KA( )
. KA(H(m))
KS
+ KS( ) .
m + Internet
KS
+
KB ( )
. +
KB(KS )
+
KB
Alice uses three keys: her private key, Bob’s public
key, newly created symmetric key
Network Security 7-
72. Pretty good privacy (PGP)
Internet e-mail encryption A PGP signed message:
scheme, de-facto standard.
---BEGIN PGP SIGNED MESSAGE---
uses symmetric key Hash: SHA1
cryptography, public key
cryptography, hash Bob:My husband is out of town
tonight.Passionately yours,
function, and digital Alice
signature as described.
provides secrecy, sender ---BEGIN PGP SIGNATURE---
Version: PGP 5.0
authentication, integrity. Charset: noconv
inventor, Phil Zimmerman, yhHJRHhGJGhgg/12EpJ+lo8gE4vB3mqJh
was target of 3-year FEvZP9t6n7G6m5Gw2
---END PGP SIGNATURE---
federal investigation.
Network Security 7-
73. Secure sockets layer (SSL)
transport layer server authentication:
SSL-enabled browser
security to any TCP- includes public keys for
based app using SSL trusted CAs.
services. Browser requests
server certificate,
used between Web issued by trusted CA.
browsers, servers for Browser uses CA’s
e-commerce (shttp). public key to extract
server’s public key from
security services: certificate.
server authentication
check your browser’s
data encryption security menu to see
client authentication its trusted CAs.
(optional)
Network Security 7-
74. SSL (continued)
Encrypted SSL session: SSL: basis of IETF
Browser generates Transport Layer
symmetric session key, Security (TLS).
encrypts it with server’s SSL can be used for
public key, sends non-Web applications,
encrypted key to server. e.g., IMAP.
Using private key, server Client authentication
decrypts session key. can be done with client
Browser, server know certificates.
session key
All data sent into TCP
socket (by client or server)
encrypted with session key.
Network Security 7-
75. IPsec: Network Layer Security
Network-layer secrecy:
For both AH and ESP, source,
sending host encrypts the
destination handshake:
data in IP datagram
create network-layer
TCP and UDP segments;
logical channel called a
ICMP and SNMP
security association (SA)
messages.
Each SA unidirectional.
Network-layer authentication
Uniquely determined by:
destination host can
authenticate source IP security protocol (AH or
address ESP)
Two principle protocols: source IP address
authentication header 32-bit connection ID
(AH) protocol
encapsulation security
payload (ESP) protocol
Network Security 7-
76. Authentication Header (AH) Protocol
provides source AH header includes:
authentication, data connection identifier
integrity, no authentication data:
confidentiality source- signed message
AH header inserted digest calculated over
between IP header, original IP datagram.
data field. next header field:
protocol field: 51 specifies type of data
intermediate routers (e.g., TCP, UDP, ICMP)
process datagrams as
usual
IP header AH header data (e.g., TCP, UDP segment)
Network Security 7-
77. ESP Protocol
provides secrecy, host ESP authentication
authentication, data field is similar to AH
integrity. authentication field.
data, ESP trailer Protocol = 50.
encrypted.
next header field is in ESP
trailer.
authenticated
encrypted
ESP ESP ESP
IP header TCP/UDP segment
header trailer authent.
Network Security 7-
78. IEEE 802.11 security
War-driving: drive around Bay area, see what 802.11
networks available?
More than 9000 accessible from public roadways
85% use no encryption/authentication
packet-sniffing and various attacks easy!
Wired Equivalent Privacy (WEP): authentication as in
protocol ap4.0
host requests authentication from access point
access point sends 128 bit nonce
host encrypts nonce using shared symmetric key
access point decrypts nonce, authenticates host
Network Security 7-
79. IEEE 802.11 security
Wired Equivalent Privacy (WEP): data encryption
Host/AP share 40 bit symmetric key (semi-
permanent)
Host appends 24-bit initialization vector (IV) to
create 64-bit key
64 bit key used to generate stream of keys, kiIV
kiIV used to encrypt ith byte, di, in frame:
ci = di XOR kiIV
IV and encrypted bytes, ci sent in frame
Network Security 7-
80. 802.11 WEP encryption
IV
(per frame)
KS: 40-bit key sequence generator
secret ( for given KS, IV)
symmetric
k1IV k2IV k3IV … kNIV kN+1IV… kN+1IV 802.11 WEP-encrypted data
key IV
header plus CRC
plaintext
frame data d1 d2 d3 … dN CRC1 … CRC4
plus CRC
c1 c2 c3 … cN cN+1 … cN+4
Sender-side WEP encryption
Figure 7.8-new1: 802.11 WEP protocol
Network Security 7-
81. Breaking 802.11 WEP encryption
Security hole:
24-bit IV, one IV per frame, -> IV’s eventually reused
IV transmitted in plaintext -> IV reuse detected
Attack:
Trudy causes Alice to encrypt known plaintext d1 d2 d3
d4 …
Trudy sees: ci = di XOR kiIV
Trudy knows ci di, so can compute kiIV
Trudy knows encrypting key sequence k1IV k2IV k3IV …
Next time IV is used, Trudy can decrypt!
Network Security 7-
82. Network Security (summary)
Basic techniques…...
cryptography (symmetric and public)
authentication
message integrity
key distribution
…. used in many different security scenarios
secure email
secure transport (SSL)
IP sec
802.11 WEP
Network Security 7-