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Public-Key Encryption Algorithms
Digital Signatures


Using cryptography for integrity checking and non-repudiation.

  • accomplished through the use of one-way hash functions and public-key algorithms.
  • Use a hash function to create a digest of a message with the following properties:
    • the digest is relatively short between 128 - 256 bits
    • given message it is easy to generate the hash value
    • given the hash value it is difficult to reconstruct the message
    • given the hash value, it is difficult to find a message which hashes to the same value
  • The most often used hash functions are:
    • MD5 - Message Digest 5 by Ron Rivest
    • SHA - Secure Hash Algorithm by NIST (National Institute of Science and Technology) and NSA
  • the process of digital signature works like this:
    1. Grean computes a digest of a message with a hash function and encrypts it with his private key. The encrypted digest is called the digital signature of the message
    2. The message and the digital signature are sent to Brandon.
    3. Brandon receives the message and the digital signature. The digital signature is decrypted using Grean's public key, and computes the digest with the original message. The computed digest is compared with the received digest, and if they are the same, then authentication is accomplished and Brandon is sure that the message was not altered during transmission and that Grean was the sender of the message.



Copyright 1997 by Slackers Union. Comments should go to any of the group members. Opinions reflected on this page are by no means opinions of UCSD. Go sue somebody else.

Last Modified: June 1, 1997