Difference between revisions of "SHA-1"

From The ECRYPT Hash Function Website
(Claimed Security Margins)
(General Description)
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== General Description ==
 
== General Description ==
SHA-1 is an iterated hash function.  
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SHA-1 is an iterated hash function. It can be used to
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compute a 160-bit hash value for messages having a length of less
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than <amsmath>$2^{64}$</amsmath> bits, cf. [http://csrc.nist.gov/publications/fips/fips180-2/fips180-2.pdf  FIPS 180-2 Secure Hash Standard].
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As most iterated hash functions, SHA-1 applies MD strengthening.
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=== Compression Function ===
 
=== Compression Function ===
The compression function takes as input a 512-bit message block and a 160-bit chaining variable, and produces a 160-bit chaining value. The compression function is described as follows:
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The compression function processes input message blocks of 512 bits and
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produces a 160-bit chaining value. The compression function of
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SHA-1 basically consists of two parts: the message expansion and
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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
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illustrated in <!-- \nh{Figure}~\ref{fig:SHA1CompressionFunction}--!>.
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[[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 math 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 math (iv in the first iteration) is added to the output of the state update transformation (feed forward). This is graphically illustrated in