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Definition

A hash function HH maps input of variable size to an output of fixed size.

H():{0,1}*{0,1}kH(\cdot): \{0,1\}^* \rightarrow \{0,1\}^k

with hash function HH, an input bit stream {0,1}*\{0,1\}^* and output digest {0,1}k\{0,1\}^k of kk bit.

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Properties

Cryptographic Hash Functions

Attributes

Algorithms

Crypto Hash Output bits Security bits Block size bits
MD5 128 < 64 512
SHA-1 160 < 63 512
SHA-256 256 128 512
SHA3-256 256 128 1088

Cryptographic hashes often divide the input in fixed length blocks mim_i and iteratively compute hi=f(hi1,mi)h_i = f(h_{i-1}, m_i)

Attacks