Security in Computer Networks

8.4.3 Hash Function Algorithms
Home | Introduction | 8.1 What Is Network Security? | 8.2 Principles of Cryptography | 8.3 Authentication | 8.4 Integrity | 8.5 Key Distribution and Certification | 8.6 Access Control: Firewalls | 8.7 Attacks and Countermeasures | 8.8 Security in Many Layers: Case Studies

The MD5 message digest algorithm of Ron Rivest [RFE 1321] is in wide use today.  It computes a 128-bit message digest in a four-step process consisting of a padding step, an append step, an initialization of an accumulator, and a final looping step in which the messgae's 16-word blocks are processed in four rounds.  It is not known whether MD5 actually satisfies the requirements listed above.
 
The second major message digest algorithm in use today in the Secure Hash Algorithm (SHA-1) [FIPS 1995].  This algorithm is based on principles similar to those used in the design of MD4 [RFC 1320], the predecessor to MD5.  SHA-1, a US federal standard, is required for use whenever a secure message digest algorithm is needed for federal applications.  It produces a 160-bit message digest.  The longer output length makes SHA-1 more secure.