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I recommend that you use SHA-2, it's FIPS approved: http://csrc.nist.gov/publications/fips/fips180-2/fips180-2.pdf

SHA-1 will be fased out by the NIST by 2010, to be replaced by SHA-2 (SHA-224, SHA-256, SHA-384, and SHA-512).

So stick with SHA-2.

Most open source OS's have an implementation of SHA-2. E.g. Openbsd: http://fxr.watson.org/fxr/source/crypto/sha2.c?v=OPENBSD and http://fxr.watson.org/fxr/source/crypto/sha2.h?v=OPENBSD

J.