Practical Message Authentication Schemes

Use of encryption algorithms in message authentication is replaced by secure hash functions which are often faster than encryption algorithms. Tsudik 14] has proposed three methods on message authentication which are only based on one-way hash functions and use some keys to make them secure. In this paper, we give a set of practical methods, each of which uses a fast collision free hash function (such as MD5) and provides secure message authentication. The idea of the proposed methods is almost similar to that of Tsudik's, but we are able to reduce the key length eight times compared to the Tsudik's constructions, while maintaining the same security. In our methods, the secret key is added using exclusive-or or assign operators (instead of concatenation) to make them faster. We also have proved that our methods belong to the Secure Keyed One-Way Hash Function (SKOWHF) group, if the underlying hash function is secure.