Message Signatures and Signature Verification

To apply a digital signature to a piece of data, a secure hash function is used to build a hash (digest) of the data (for example, a 160-bit hash value). This hash is then encrypted with the private key of the signer. Other users can then check the authenticity of the signature by reconstructing the hash value, and checking it against the decryption of the digital signature data. Microsoft® CryptoAPI abstracts the actual method of doing the signature, so that application developers need not be aware of the details of the signature mechanics.