Full Domain Hash
From CryptoDox, The Online Encyclopedia on Cryptography and Information Security
Full Domain Hash (FDH) is an RSA-based signature scheme that follows the hash-and-decrypt paradigm. FDH involves hashing a message using a function whose image size equals the size of the RSA modulus, and then raising it to the secret RSA exponent. Thus hashing and padding are combined into a single step. It is roughly the digital signature analogue of RSA-OAEP.