# Difference between revisions of "SHA-1"

From The ECRYPT Hash Function Website

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== General Description == | == General Description == | ||

− | SHA-1 is an iterated hash function. | + | |

+ | SHA-1 is an iterated hash function. It can be used to | ||

+ | compute a 160-bit hash value for messages having a length of less | ||

+ | than <amsmath>$2^{64}$</amsmath> bits, cf. [http://csrc.nist.gov/publications/fips/fips180-2/fips180-2.pdf FIPS 180-2 Secure Hash Standard]. | ||

+ | As most iterated hash functions, SHA-1 applies MD strengthening. | ||

+ | |||

=== Compression Function === | === Compression Function === | ||

− | The compression function | + | The compression function processes input message blocks of 512 bits and |

+ | produces a 160-bit chaining value. The compression function of | ||

+ | SHA-1 basically consists of two parts: the message expansion and | ||

+ | the state update transformation. The chaining variable <amsmath>$h_{i-1}$</amsmath> (''iv'' in the first iteration) is added to the output of the state update transformation (feed forward). This is graphically | ||

+ | illustrated in <!-- \nh{Figure}~\ref{fig:SHA1CompressionFunction}--!>. | ||

+ | |||

+ | [[image:SHA1CompressionFunction.png|right|thumb|250px|The SHA-1 compression function]] | ||

==== Message Expansion ==== | ==== Message Expansion ==== |

## Revision as of 10:30, 12 October 2006

## 1 General Description

SHA-1 is an iterated hash function. It can be used to compute a 160-bit hash value for messages having a length of less than bits, cf. FIPS 180-2 Secure Hash Standard. As most iterated hash functions, SHA-1 applies MD strengthening.

### 1.1 Compression Function

The compression function processes input message blocks of 512 bits and
produces a 160-bit chaining value. The compression function of
SHA-1 basically consists of two parts: the message expansion and
the state update transformation. The chaining variable (*iv* in the first iteration) is added to the output of the state update transformation (feed forward). This is graphically
illustrated in