||SQL Server Tips by Gama and Naughter
Hash Message Authentication Code
A Hash Message Authentication Code (HMAC) is
a one-way function, which is also dependent on a shared secret key.
It can be used to determine whether a message sent over an insecure
channel has been tampered with. The sender computes the HMAC for the
data to send and sends both the data and HMAC to the receiver. The
receiver then regenerates the HMAC and compares it to the received
HMAC. Any change to the received data or HMAC will cause the
calculated and received HMAC values to differ. XPCrypt includes
support for MD2, MD4, MD5 and SHA1 HMACís.
Each HMAC implemented in this chapter uses
the syntax ďXP_AlgorithmName_HMACí
The above book excerpt is from:
Turbocharge Database Performance with C++ External Procedures
Joseph Gama, P. J. Naughter