Notes - Computer Security MT24, Example hash functions

Created: January 10, 2025
Updated: January 10, 2025

Flashcards

LM (Lan Manager)

@Define the components of the LM hash in terms of its:

  • Input
  • Output
  • Operation
  • Input: Maximum of 14 characters of printable ASCII
  • Output: 128 bit hash
  • Operation:
    • Null-pad the password to 14 characters
    • Force any lowercase letters to upper case
    • Split into 7-byte halves, each of which makes a 56-bit DES key
    • Use the DES key to encrypt a certain, fixed 64-bit block
    • Concatenate the two DES encryptions to make a 128 bit hash.

scrypt

How does the scrypt algorithm slow down brute-force attacks on its hashes?

The algorithm uses a lot of memory, by creating many pseudorandom blocks and then combining them in a pseudorandom order.

MD4

@Define the components of the MD4 hash in terms of its:

  • Inputs
  • Outputs
  • Construction (summary)
  • Inputs: 512 bits (16 words of 32 bits)
  • Output: 128 bits
  • Construction: Iterating a compression function and using MD padding

MD5

  • Successor to MD4, was also insecure.

SHA-1

  • Also insecure, designed by the NSA.

SHA-2

  • Larger output compared to MD4, MD5, SHA-1 and also bigger input blocks.
  • Used in Bitcoin.

SHA-3

  • Different construction compared to SHA-2.
  • NSA-free!
  • Allows arbitrary-length input and output.
  • Has adjustable security parameters.


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