http://i2p-javadocs.i2p/net/i2p/crypto/SHA1.html
References: NIST FIPS PUB 180-2, "Secure Hash Signature Standard (SHS) with
change notice", National Institute of Standards and Technology (NIST),
2002 August 1, and U.S. Department of Commerce, August 26. http://csrc.ncsl.nist.gov/CryptoToolkit/Hash.html NIST FIPS PUB 180-1, "Secure Hash Standard",
U.S.