RSA Security 5.2.2 manual Public-Key Operations

Chapter 7

Public-Key Operations

In public-key cryptography, two associated keys are necessary: one to encrypt, and the other to decrypt. The sender encrypts a message using the recipient’s public key. Once a message is encrypted, it can be decrypted only with the recipient’s private key. This is in contrast to algorithms like DES and the RC2, RC4, and RC5 algorithms, which are called symmetric-key encryption algorithms because the key used to encrypt is the same key needed to decrypt.

In public-key cryptography, it is also possible to encrypt using a private key. In this case, the sender takes the plaintext input and the private key and follows the same steps needed to decrypt an encrypted file. This creates a ciphertext that can be read using the public key. To read it, the recipient follows the same steps needed to encrypt with the public key and restores it to the plaintext. Private-key encryption with public-key decryption is used for digital signatures and verification. See “RSA Digital Signatures” on page 233 and “DSA Signatures” on page 243 for more information.

Crypto-C supplies a number of public-key algorithms. These include:

•RSA encryption and decryption

•DSA signatures

•Diffie-Hellman key agreement

•Elliptic curve public-key operations

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