Cryptography · Unit 4 · 8 hrs
Cryptographic Hash Functions and Digital Signatures
Exam-focused notes for Cryptographic Hash Functions and Digital Signatures (Cryptography, CSC327): what the TU syllabus asks and how it has actually been tested, with 12 solved past questions from this unit.
What this unit covers
- Message Authentication
- Message Authentication Functions
- Message Authentication Codes
- Hash Functions
- Properties of Hash functions
- Applications of Hash Functions
- Message Digests: MD4 and MD5
- Secure Hash Algorithms: SHA-1 and SHA-2
- Digital Signatures: Direct Digital Signatures, Arbitrated Digital Signature
- Digital Signature Standard: The DSS Approach, Digital Signature Algorithm
- Digital Signature Standard: The RSA Approach
Properties of Hash functions
Describe the properties of hash functions. Discuss how hash value is generated using SHA-1 algorithm.[10]
A hash function is a function that maps a message of any length into a fixed-length hash value, which serves as the authenticator. Cryptographic hash functions play a fundamental role in efficient and secure information processing. Property Description ----...
Full solved answer →Write short notes on (any two) a. Totient value of any positive integer. b. Properties of hash function. c. Virus or Worms. [5]
--- Definition: Euler's Totient Function, denoted by φ(n), is defined as the number of positive integers less than n that are relatively prime (coprime) to n. Two numbers are relatively prime if their greatest common divisor (GCD) is 1. Special Property: If...
Full solved answer →Describe the properties of hash functions. Discuss how hash value is generated using SHA-1 algorithm.[10]
A hash function is a function that maps a message of any length into a fixed-length hash value, which serves as an authenticator. Cryptographic hash functions are a fundamental tool of cryptography for efficient and secure information processing. Property D...
Full solved answer →List the properties of hash function. Discuss the first pass of MD4. [5]
A hash function maps a message of any length into a fixed-length hash value, which serves as an authenticator. The key properties are: 1. One-way property (Pre-image resistance): It is computationally hard to find the input (message) from the output (hash v...
Full solved answer →Digital Signature Standard
Describe the working mechanism of digital signature algorithm. [5]
A Digital Signature is a cryptographic mechanism where content is digitally signed with an individual's private key and verified using the individual's public key. It provides authentication, integrity, and non-repudiation. --- - Signing Algorithm -- used b...
Full solved answer →Define digital signature. Describe the approaches of DSS. [5]
A digital signature is an electronic signature that can be used to authenticate the identity of the sender of a message and to ensure that the original content of the message or document that has been sent is unchanged. Content is digitally signed with an i...
Full solved answer →Message Authentication Codes
What is Message Authentication Code? List the operation of computing digest value in different passes of MD4. Describe about Needhom-Schroeder protocol.[10]
--- Definition: A Message Authentication Code (MAC) is a function of the message and a secret key that produces a fixed-length value that serves as the authenticator. Working Principle: - This technique assumes that the sender and receiver share a common se...
Full solved answer →Write down any two limitations of MAC. What do policy and mechanism mean in cryptography? Describe with a scenario. [5]
--- 1. No Non-repudiation: Since both the sender and receiver share the same secret key (symmetric key) to generate and verify the MAC, either party can forge a message. The sender can later deny sending a message, and there is no way to prove otherwise. A ...
Full solved answer →Applications of Hash Functions
What are the applications of hash functions? Discuss how SHA-1 algorithm generates hash value from a given message.[10]
--- A hash function maps a message of any length into a fixed-length hash value, which serves as an authenticator. Hash functions are fundamental tools in cryptography and play a vital role in secure information processing. - One-way property: Computational...
Full solved answer →Digital Signatures
How direct digital signature different from arbitrated digital signature? How digital signature generation and verification is done using RSA. [5]
--- - Involves only two parties: the sender and the receiver. - The sender signs the message using their private key. - The receiver verifies the signature using the sender's public key. - No third party is involved in the process. - Weakness: The sender ca...
Full solved answer →Explain the generic model of digital signature process. Consider the two prime numbers 7 and 19. Select 29 as public key and 41 as private key. Encrypt the plaintext 4 and decrypt the cipher text 3 using RSA.[10]
A digital signature uses asymmetric (public key) cryptography to provide authentication, integrity, and non-repudiation. The sender signs using their private key; the receiver verifies using the sender's public key. Sender side: 1. Message: Sender has the o...
Full solved answer →Secure Hash Algorithms
Compare the SHA parameters between SHA-1 and SHA-2 families. Decrypt the cipher text DRIJ with the key $$\begin{pmatrix} 7 & 8 \ 11 & 11 \end{pmatrix}$$ using the Hill cipher. [10]
--- Parameter SHA-1 SHA-224 SHA-256 SHA-384 SHA-512 ------------------ Message Digest Size (bits) 160 224 256 384 512 Max Message Size (bits) $<2^{64}$ $<2^{64}$ $<2^{64}$ $<2^{128}$ $<2^{128}$ Block Size (bits) 512 512 512 1024 1024 Word Size (bits) 32 32 ...
Full solved answer →Make Unit 4 stick
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