Cryptography - Uses for hashes

Hash

Creating a hash value is a basic function of cryptography. The input is processed by a hashing function and the output is the hash value or message digest. Ciampa (2009) describes a hashing algorithm as the most basic cryptographic algorithm. A characteristic of a good hashing function is that no two different messages will produce the same hash value and the hash value cannot be reversed in order to find the original message. Additionally regardless of the input message length the output hash value length will be a fixed number of characters.

Standard Hash Algorithms

MD5 – Message digest algorithm version 5
SHA – Secure hashing algorithm
Whirlpool - Whirlpool hashing algothirm

Uses of hashes

Client authentication by a server is a good scenario for using hash values. As an example Ciampa (2009) describes how ATMs use hash values to validate user’s entered password hashed against the hashed password stored on the card.
This avoids the need to transmit passwords over the network, more efficient, more secure.

A message can be verified as the original with the use of a hash value.
The creator of the message generates a hash value also known as a message digest. The recipient can generate the hash value and compare with the original hash to verify the message content is original and has not been modified. However this technique does not provide confidentiality of the message.

Stallings(2005)describes three alternative ways in which the above technique can be used to obtain authenticity as well as confidentiality.

• Using conventional encryption
• Using public-key encryption
• Using secret value

Another use of hash function is message integrity check which is a digital signature found in secure email according to Pfleeger and Pfleeger (2007)

References

Ciampa, M, 2009, Security+ guide to network security fundamentals,

Pfleeger, C, Pfleeger, S, 2007, Security in computing, Prentice hall

Stallings, W, 2005, Business data communications, Prentice hall