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Cryptographic signature scheme From Wikipedia, the free encyclopedia
In cryptography, the Full Domain Hash (FDH) is an RSA-based signature scheme that follows the hash-and-sign paradigm. It is provably secure (i.e., is existentially unforgeable under adaptive chosen-message attacks) in the random oracle model. FDH involves hashing a message using a function whose image size equals the size of the RSA modulus, and then raising the result to the secret RSA exponent.
In the random oracle model, if RSA is -secure, then the full domain hash RSA signature scheme is -secure where,
For large this reduces to .
This means that if there exists an algorithm that can forge a new FDH signature that runs in time t, computes at most hashes, asks for at most signatures and succeeds with probability , then there must also exist an algorithm that breaks RSA with probability in time .
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