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  SQL Server Tips by Gama and Naughter

Asymmetric Encryption / Decryption

Asymmetric Cryptography or Public Key Cryptography uses a pair of different keys: a so called public key and a private key. The sender of the message as its name suggests keeps the private key confidential while the public key can be distributed to anyone who wants it. If you encrypt a message with one key of the pair, then only the other key can successfully decrypt the message. Public Key Cryptography is 2 to 3 orders of magnitude slower than symmetric algorithms, so normally it should not be used to encrypt bulk data. Instead it is normally used to encrypt session keys for symmetric algorithms.


RSA is a public key algorithm developed and named after its three inventors: Ron Rivest, Adi Shamir, and Leonard Adleman. It was originally devised in 1978 and is the most popular public key algorithm in use. XP_CRYPTOAPI provides XP_RSA_ENCRYPT and XP_RSA_DECRYPT for encryption / decryption using RSA. The basic layout of the encryption and decryption algorithms is very similar to their symmetric counterparts. Rather than creating a hash of the password and deriving a session key from this, the key is directly accessed from the CSPís container (described later).


The National Institute of Standards and Technology (NIST) developed the Digital Signature Algorithm as part of a proposal in 1991 for use in their Digital Signature Standard (DSS). DSA is only meant to be using for signatures and as such no XPís are provided to perform encryption / decryption of user data.

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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