Wireless Mobile Internet Security, 2nd Edition

Chapter 5

Hash Function, Message Digest, and Message Authentication Code

As digital signature technology becomes more widely understood and utilized, many countries worldwide are competitively developing their own signature standards for their use and applications.

Some electronic applications utilizing digital signatures in electronic commerce (e-commerce) include e-mail and financial transactions. E-mail may need to be digitally signed, where sensitive information is being transmitted and security services such as sender authentication, message integrity, and nonrepudiation are desired. Financial transactions, in which money is being transferred directly or in exchange for services and goods, could also benefit from the use of digital signatures. Signing the message digest rather than the message often improves the efficiency of the process because the message digest is usually much smaller than the message.

In e-commerce, it is often necessary for communication parties to verify each other's identity. One practical way to do this is with the use of cryptographic authentication protocols employing a one-way hash function. Division into fixed-bit blocks can be accomplished by mapping the variable-length message onto the suitable-bit value by padding with all zeros, including 1-bit flag and the original message length in hex. Appropriate padding is needed to force the message to divide conveniently into certain fixed lengths. Several algorithms are introduced in order to compute ...