.NET Security and Cryptography

RSA Used as a Digital Signature Algorithm

The RSA algorithm can be used for both privacy and digital signing. In Chapter 4, we saw how RSA can be used for keeping secrets, and especially for sharing secret symmetric keys. In this chapter, we look at RSA digital signatures, which is the flip side of the coin. Whereas privacy is achieved by encrypting with the public key and decrypting with the associated private key, digital signing is achieved the other way around, by encrypting with the private key and decrypting with the matching public key.

For digital signatures, it turns out that it is not actually necessary to encrypt the entire original message. It is entirely sufficient, as well as much more efficient, to generate a hash of the original ...