There is no such thing as ''sha2''. The title is intended to cover the family of hashing algorithms ''beyond [sha1]''.

The [sha1] secure hash algorithm produces a digest of 160 bits. This provides 80 bits of security against collisions
given the birthday attack (ref). An update document from NIST [http://csrc.nist.gov/cryptval/shs/sha256-384-512.pdf]
specifies a new family of secure hashing algorithms with longer digest lengths, specifically 
SHA-256, SHA-384, and SHA-512. An additional update also specifies SHA-224 [http://csrc.nist.gov/publications/fips/fips180-2/fips180-2withchangenotice.pdf].

[tcllib] now includes a pure-tcl implementation of SHA-224 and SHA-256. For comparison, here are some timing
data for the pure-Tcl implementation of all the digests in [tcllib]
 md4    time: 248 microseconds per iteration using tcl
 md5    time: 275 microseconds per iteration using tcl
 sha1   time: 409 microseconds per iteration using tcl
 rmd128 time: 410 microseconds per iteration using tcl
 rmd160 time: 679 microseconds per iteration using tcl
 sha224 time: 880 microseconds per iteration using tcl
 sha256 time: 894 microseconds per iteration using tcl
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[RLH] - I have the latest ActiveTcl 8.4.9 and I do not see anything about SHA-256/384/512 in the docs. Were those added after the 8.4.9 release? addendum: I installed 8.5 and no sign in the docs about the other SHA stuff.

[PT] 22-Feb-2005: When I say 'now' above I actually mean today - 22 Feb 2005. You can grab the CVS sources
from 
  cvs -d:pserver:anonymous@cvs.sourceforge.net:/cvsroot/tcllib co tcllib/modules/sha1
until we create a new release.

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[LV] 2007 Jan 31
In the latest tcllib, I see a file called tcllib/modules/sha2/sha256.tcl . The top of the page talks about sha1, and the code appears to implement the 224 and 256 bit algorithms. The longer codes don't appear to be there yet. I also don't see anything in the doc pages. Of course, right now, a competition for sha3 is in the works, so perhaps someone stopped because the older stuff have been challenged.


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See also [sha1], [md4], [md5], [ripemd], [cryptkit]
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See http://code.wikia.com/wiki/SHA_checksum for a place where a Tcl enthusist might consider adding an example of the use of the tcllib module to calculate a sha checksum.


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