Cryptography: Hash Functions, Public Key, SSL, and PGP

Posted by on Jan 30, 2025 in Information Consulting and Management | 0 comments

Hash Function Algorithms

MD5: A widely used hash function (RFC 1321) that computes a 128-bit message digest in a 4-step process. For any arbitrary 128-bit string x, it appears difficult to construct a message m whose MD5 hash is equal to x.

SHA-1: Another hash function in use. It is a US standard [NIST, FIPS PUB 180-1] and produces a 160-bit message digest.

Public-Key Certification

Motivation: Trudy plays a pizza prank on Bob.

  1. Trudy creates an e-mail order: “Dear Pizza Store, Please deliver to me four
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Message Authentication Codes (MAC) and Hash Functions in Cryptography

Posted by on Jan 27, 2025 in Information Consulting and Management | 0 comments

Message Authentication Codes (MAC)

An alternative authentication technique involves the use of a secret key to generate a small fixed-size block of data, known as a cryptographic checksum or MAC, that is appended to the message.

  • Condenses a variable-length message using a secret key to a fixed-size authenticator.
  • This technique assumes that two communicating parties, say A and B, share a common secret key.
  • When A has a message to send to B, it calculates the MAC as a function of the message and key:
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Cryptography Concepts and Security Analysis

Posted by on Jan 22, 2025 in Information Consulting and Management | 0 comments

1. Consider the mono-alphabetic substitution cipher (Lecture 1, slide 20). What is the size of its key space? -26!

2. Consider the poly-alphabetic substitution cipher (Lecture 1, slide 22). What is the size of its key space? -26^t (that is, 26 to the power of t)

3. You know that a meaningful plaintext in a language with an x-letter alphabet is encrypted using either the mono-alphabetic substitution cipher or the poly-alphabetic substitution cipher (with a key of t random numbers in [1,x], for a known

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Cryptography: Concepts, Algorithms, and Security

Posted by on Jan 11, 2025 in Information Consulting and Management | 0 comments

Prime Numbers, GCD, and Congruence

Prime Numbers: Numbers > 1 with no divisors other than 1 & itself.

GCD: Largest positive integer dividing 2 numbers without a remainder.

Congruence: 2 numbers are congruent modulo N if they have the same remainder when divided by N (A ≡ B mod N).

Classical vs. Modern Cryptography

Classical Cryptography:

  1. Based on secrecy of the encryption algorithm.
  2. Key distribution was physical & therefore not as secure.
  3. Encryptions like the Caesar cipher were susceptible
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