lecture45.pptx
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Stream ciphers encrypt symbols one at a time using a keystream, while block ciphers encrypt fixed-length blocks. Stream ciphers are faster but more susceptible to tampering, while block ciphers are slower but provide greater security against tampering. Modern encryption algorithms mostly use block ciphers like AES, which encrypt 128-bit blocks. The lecture discusses the differences between stream and block ciphers and the concept of malleability in encryption.
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Answer die following questions with short answers Explain the d.pdf
Answer die following questions with short answers: Explain the difference between stream
ciphers and block cipher. Explain the difference between passive and active attacks. Describe
the difference between authentication and non-repudiation Explain the difference between a
MAC and message digest. Give one advantage and one disadvantage of public-key cryptography
over symmetric-key cryptogra Why is CBC mode considered preferable to ECB mode?
Solution
a)
stream cipher and block cipher differ in whitch the plain text is encoded and decoded.
the basic difference is how the logic used for the encryption and decryption. the idea of block
cipher is partition the plain text into relatively larger blocks and further each block will be
encoded.
and same key is used for both encryption and decryption.example DES,IDEA
the idea of stream cipher is plain text is encrypted and transfered bit by bit.but key property of
stream cipher is different key is generated for each block or bit.example -ISAAC,FISH
b)
passive attack is indirect attack.the attacked host is completely unaware about the attack.
hence it is called passive attack like some body listens the packet transformation or observing
the host in network.
active attack is direct attack.its nothing but the attacked one gets aware of the attack.
like somebody listens the id and password and stop the services(denial of service) or logic
bomb.
both are harmful.
c)
authentication and non repudiation are two different things.
authentication verifies the who you are(user-id).where the non-repudiation verifies the what you
did(messages).
authentication is done through a central instance where non repudiation can done by anyone
d)
message digest is a hash of a message.its output of a cryptographic hash function appilied to
input data it refered to as message.
mac is a piece of information that proves the integrity of a message.
message digest is take only single input and produces a message digest(aka hash) if the message
change it produce different hash code.
mac (message authentication code) is take input and security code to check the integrity of
message. HMAC is one of this kind.
e)
advantage of public key cryptography over the symmetric key cryptography is increased
security and convenience.
and no need of key distribution(transmitted to anyone).and it provide digital signatures that
cannot be repudiated.
the disadvantage of public key cryptography over symmetric cryptography is speed.they are
many symmetic key methods runs faster than the public key cryptography.
f)
the reason why cbc is considered better than ecb has nothing to do with situations involving
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This document provides an overview of cryptographic algorithms and their uses. It begins with symmetric encryption, which uses a single secret key to encrypt and decrypt data, providing confidentiality. The most common symmetric algorithms are the Data Encryption Standard (DES) and the Advanced Encryption Standard (AES), which are block ciphers that encrypt data in fixed-size blocks. It also discusses stream ciphers, which encrypt data one element at a time. The document then covers secure hash functions, public-key encryption, digital signatures, and key management before concluding with an example application of encrypting stored data.
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Answer die following questions with short answers: Explain the difference between stream
ciphers and block cipher. Explain the difference between passive and active attacks. Describe
the difference between authentication and non-repudiation Explain the difference between a
MAC and message digest. Give one advantage and one disadvantage of public-key cryptography
over symmetric-key cryptogra Why is CBC mode considered preferable to ECB mode?
Solution
a)
stream cipher and block cipher differ in whitch the plain text is encoded and decoded.
the basic difference is how the logic used for the encryption and decryption. the idea of block
cipher is partition the plain text into relatively larger blocks and further each block will be
encoded.
and same key is used for both encryption and decryption.example DES,IDEA
the idea of stream cipher is plain text is encrypted and transfered bit by bit.but key property of
stream cipher is different key is generated for each block or bit.example -ISAAC,FISH
b)
passive attack is indirect attack.the attacked host is completely unaware about the attack.
hence it is called passive attack like some body listens the packet transformation or observing
the host in network.
active attack is direct attack.its nothing but the attacked one gets aware of the attack.
like somebody listens the id and password and stop the services(denial of service) or logic
bomb.
both are harmful.
c)
authentication and non repudiation are two different things.
authentication verifies the who you are(user-id).where the non-repudiation verifies the what you
did(messages).
authentication is done through a central instance where non repudiation can done by anyone
d)
message digest is a hash of a message.its output of a cryptographic hash function appilied to
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mac is a piece of information that proves the integrity of a message.
message digest is take only single input and produces a message digest(aka hash) if the message
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mac (message authentication code) is take input and security code to check the integrity of
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e)
advantage of public key cryptography over the symmetric key cryptography is increased
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the disadvantage of public key cryptography over symmetric cryptography is speed.they are
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This document proposes a unified operation structure (UOS) that combines existing block cipher modes of operation to allow for multi-mode functionality. The UOS uses three buffers to store feedback information from the previous encryption block, overcoming the typical need for separate buffers for each mode. This provides a common solution for supporting multiple modes of operation with low memory requirements, making it suitable for ubiquitous computing devices. The UOS can integrate encryption modes like ECB, CBC, CFB and OFB as well as authentication modes like CBC-MAC to provide both confidentiality and integrity.
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Modern Internet protocols support several modes of operation in encryption tasks for data confidentiality
to keep up with varied environments and provide the various choices, such as multi-mode IPSec support.
To begin with we will provide a brief background on the modes of operation for symmetric-key block
ciphers. Different block cipher modes of operation have distinct characteristics. For example, the cipher
block chaining (CBC) mode is suitable for operating environments that require self-synchronizing
capabilities, and the output feedback (OFB) mode requires encryption modules only. When using
symmetric-key block cipher algorithms such as the Advanced Encryption Standard (AES), users
performing information encryption often encounter difficulties selecting a suitable mode of operation.
This paper describes a structure for analyzing the block operation mode combination. This unified
operation structure (UOS) combines existing common and popular block modes of operation. UOS does
multi-mode of operation with most existing popular symmetric-key block ciphers and do not only consist
of encryption mode such as electronic codebook (ECB) mode, cipher block chaining (CBC) mode, cipher
feedback (CFB) mode and output feedback (OFB) mode, that provides confidentiality but also message
authentication mode such as the cipher block chaining message authentication code (CBC-MAC) in
cryptography. In Cloud Computing, information exchange frequently via the Internet and on-demand.
This research provides an overview and information useful for approaching low-resource hardware
implementation, which is proper to ubiquitous computing devices such as a sensor mote or an RFID tag.
The use of the method is discussed and an example is given. This provides a common solution for multimode and this is very suitable for ubiquitous computing with several resources and environments. This
study indicates a more effectively organized structure for symmetric-key block ciphers to improve their
application scenarios. We can get that it is flexible in modern communication applications.
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In today’s digital communication era sharing of information is increasing significantly. The information being transmitted is vulnerable to various passive and active attacks. Therefore, the information security is one of the most challenging aspects of communication. Cryptography is the one of the main categories of computer security that converts information from its normal form into an unreadable form by using Encryption and Decryption Techniques. The two main characteristics that identify and differentiate one encryption algorithm from another are its ability to secure the protected data against attacks and its speed and efficiency in doing so. There are basically two techniques of cryptography Symmetric and Asymmetric. This paper presents a detailed study of the symmetric encryption techniques.
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It has been shown that the encrypted information or ciphertext produced by symmetric-key block ciphers
with Electronic codebook mode is vulnerable to ciphertext searching, replay, insertion and deletion
because it encrypts each block independently. To compensate for this, each block of the encrypted
information should be encrypted dependently. The encrypted information should be operated with a
special mode. The operation mode should be changed. This paper analysis what an operational mode of
block ciphers needs to feedback exactly and proposes a simple real-time changing operation mode
technique that extends the existing mode changing opportunity. The new change operation mode
technique considers the sign differences between the intra-feedback information and the public-feedback
information, and then adaptively determines the corresponding change operation mode factor for each
data block. This mode hopping technique for mobile streaming security is highly suitable for recent block
computing in future various environments.
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The different computer networks whether wired or wireless are becoming more popular with its high
security aspect. Different security algorithms and technique are using to avoid any aforementioned attacks.
One of these technique is a cryptography technique that makes the data as unreadable during the transfer
hence; there is no chance to reclaim the information. Presently, most of the users are using various media
types and internet to transfer the data but, it has the chance to retrieve the data by using these media types.
The perfect solution for this problem is to provide security on time-to-time basis; this stage is always
significant to the security related community discussions. This paper explains the comparison between the
run time of three different encryption algorithms which are DES, AES and Blowfish The compression
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Unconditional& computational security,
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this presentation is on block cipher modes which are used for encryption and decryption to any message.That are Defined by the National Institute of Standards and Technology . Block cipher modes of operation are part of symmetric key encryption algorithm.
i hope you may like this.
A Survey on Generation and Evolution of Various Cryptographic Techniques
This document summarizes previous research that has surveyed and compared various symmetric key cryptographic techniques. Several studies analyzed the performance of algorithms like DES, 3DES, AES, Blowfish, RC4 in terms of encryption/decryption time, memory usage, power consumption, throughput, and security against attacks. Most found that Blowfish had among the best performance overall, being fast and requiring few resources while maintaining strong security. AES generally required more processing power and time than alternatives like DES or RC4. The performance of algorithms could also vary based on file/data type, size, and the computing platform or operating system used.
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lecture45.pptx
- 1. Foundations of Computer Security Lecture 45: Stream and Block Encryption Dr. Bill Young Department of Computer Sciences University of Texas at Austin Lecture 45: 1 Stream and Block Encryption
- 2. Stream and Block Ciphers An important distinction in symmetric cryptographic algorithms is between stream and block ciphers. Stream ciphers convert one symbol of plaintext directly into a symbol of ciphertext. Block ciphers encrypt a group of plaintext symbols as one block. Simple substitution is an example of a stream cipher. Columnar transposition is a block cipher. Most modern symmetric encryption algorithms are block ciphers. Block sizes vary (64 bits for DES, 128 bits for AES, etc.). Lecture 45: 2 Stream and Block Encryption
- 3. Stream Encryption Advantages: Speed of transformation: algorithms are linear in time and constant in space. Low error propogation: an error in encrypting one symbol likely will not affect subsequent symbols. Disadvantages: Low diffusion: all information of a plaintext symbol is contained in a single ciphertext symbol. Susceptibility to insertions/ modifications: an active interceptor who breaks the algorithm might insert spurious text that looks authentic. Lecture 45: 3 Stream and Block Encryption
- 4. Block Encryption Advantages: High diffusion: information from one plaintext symbol is diffused into several ciphertext symbols. Immunity to tampering: difficult to insert symbols without detection. Disadvantages: Slowness of encryption: an entire block must be accumulated before encryption / decryption can begin. Error propogation: An error in one symbol may corrupt the entire block. Lecture 45: 4 Stream and Block Encryption
- 5. Malleability An encryption algorithm is said to be malleable if transformations on the ciphertext produce meaningful changes in the plaintext. That is, given a plaintext P and the corresponding ciphertext C = E (P ), it is possible to generate C1 = f(C ) so that D (C1) = P1 = f′ (P ) with arbitrary , but known, functions f and f′ . Most modern block-structured ciphers are non-malleable. Lecture 45: 5 Stream and Block Encryption
- 6. Lessons An important distinction is between stream and block ciphers. Each has distinct strengths and weaknesses. Malleability means being able to manipulate ciphertext with predictable effects on plaintext. Next lecture: Advanced Encryption Standard Lecture 45: 6 Stream and Block Encryption