Cryptography Reference
In-Depth Information
Chapter 11
Hash Functions
Hash functions are an important cryptographic primitive and are widely used in
protocols. They compute a digest of a message which is a short, fixed-length bit-
string. For a particular message, the message digest, or hash value , can be seen as
the fingerprint of a message, i.e., a unique representation of a message. Unlike all
other crypto algorithms introduced so far in this topic, hash functions do not have
a key. The use of hash functions in cryptography is manifold: Hash functions are
an essential part of digital signature schemes and message authentication codes, as
discussed in Chapter 12. Hash functions are also widely used for other cryptographic
applications, e.g., for storing of password hashes or key derivation.
In this chapter you will learn:
Why hash functions are required in digital signature schemes
Important properties of hash functions
A security analysis of hash functions, including an introduction to the birthday
paradox
An overview of different families of hash functions
How the popular hash function SHA-1 works
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