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  SQL Server Tips by Gama and Naughter

MS CryptoAPI based Signing / Verification Implementations

Similar to asymmetric encryption, a public key must first exist to perform signing. Once the CSP handle is acquired, and similar to the hashing XP’s, a hash is created of the data to sign using “CryptCreateHash”, and “CryptHashData”. Then the “CryptSignHash” function is called which signs the hash. Parameters to this function include the hash object, a handle to the public key to use to create the signature and a buffer to container the resultant signature. The resulting signature is then returned as an output parameter in the XP.

For signature verification, the procedure is quite similar to the signing step. The received message is hashed using “CryptCreateHash” and CryptHashData”. Then the “CryptVerifyHash” function is called. This takes the signature, the computed hash object, the signature and the public key to use. This function decrypts the signature with the public key, and compares the result with the computed hash of the received data. The result of this function is a boolean value that is returned as an output parameter in the XP.

The above book excerpt is from:

Super SQL Server Systems
Turbocharge Database Performance with C++ External Procedures

ISBN: 0-9761573-2-2
Joseph Gama, P. J. Naughter  


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