Introduction to Hash Functions – Part 1/2

Digital Signatures (e.g. RSA Signatures) are great because they achieve data integrity, message authentication and non-repudiation. However, they have few problems especially when the message (x) is long. In another word (How do we sign a message (x) greater than the modulus n?). The following figure shows an alternative solution, which split the message into blocks and sign each block individually.

rsa-signature

This technique (the figure above) works perfectly, but will face some problems:

  1. Computational load: Public-Key operations are time-consuming.
  2. Transmission or storage overhead: Signature is as long as the message itself.
  3. Security: Similar problems to ECB mode of operation (remove individual blocks, inject old blocks).

 

The solution to solve this problem is very simple, which is by having a shorter “representation” of a message, so that we can (sign) that instead of the message itself. This solution is known as (hash function produce representation); and also it is called hash or message digest, or digital fingerprint.

hash-functions

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