http://i2p-javadocs.i2p/net/i2p/crypto/SHA1.html
A "SHS change notice" adds a SHA-224 algorithm for interoperability,
which, like SHA-1 and SHA-256, operates on 512-bit blocks and 32-bit words,
but truncates the final digest and uses distinct initialization values. 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.