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The Use of NMACA Approach in Building a Secure Message Authentication Code

Integrity and authentication of long-term stored information are important issues that should be considered in secure storage systems. Digital archived information may include different types of objects with different representation, such as, documents, images and database tables. Authenticity of such information should be verified, especially when it transferred through communication channels. Authentication verification techniques are used to verify that information in the archive is authentic and has not been unintentionally or maliciously altered. In addition to detecting malicious attacks, integrity checks also identify data corrupted information. Message authentication code (MAC) algorithms are keyed hash functions whose specific purpose is message authentication. In most cases, MAC techniques use iterated hash functions, and those techniques are called iterated MACs. Such techniques usually use a MAC key that is used as an input to the compression function, and is involved in the compression function f at every stage. A wide range of authentication techniques use un- keyed hash functions, which are known as modification detection codes (MDCs). MD4, MD5, SHA-1 and RIPEMD-160 are some of many. Recently, powerful new attacks on hash functions such MD5 and SHA-1, among others, suggest introducing more secure hash functions. In this paper, we propose a new MAC methodology that uses an input MAC key on the compression function, to permute the order of message words and shifting operation in the compression function. The new methodology can be used in conjunction with a wide range of modification detection code techniques. Using MD5 algorithm as a model, a new MD5-MAC algorithm is presented. The MD5-MAC algorithm uses the MAC key in building the hash functions by defining the order for accessing source words and defining the number of bit positions for circular left shifts.