I have been trying to work with HMAC-SHA1 for oAuth, as it is the base requirement for generating the oAuth Signature.
According to the definition http://en.wikipedia.org/wiki/Hash-based_message_authentication_code
Definition (from RFC 2104)
HMAC (K,m) = H ((K ^ opad) || H ((K ^ ipad) || m))
H is a cryptographic hash function,
K is a secret key padded to the right with extra zeros to the input block size of the hash function, or the has