RSA Security 5.2.2 manual Cryptography Overview, Symmetric-Key Cryptography, Ciphers

Cryptography Overview

Cryptography Overview

Symmetric-Key Cryptography

In symmetric-key cryptography, as Figure 3-1 shows, the encrypting key is the same as the decrypting key. Using any other key to decrypt will produce incorrect results. Symmetric-key cryptography is also sometimes called secret-key cryptography, because the key used to both encrypt and decrypt must be kept secret.

Ciphers

There are two categories of symmetric encryption algorithms, block ciphers and stream ciphers. As the name implies, a block cipher processes data in blocks. A stream cipher, on the other hand, processes a unit of data at a time, where a unit is generally a bit or byte. This allows a stream cipher to take in a variable length stream of data, encrypt it, and output a stream of ciphertext the same length as the input. Crypto-C offers the following block ciphers: DES, Triple DES, DESX, the RC2 cipher, the RC5, the RC6 cipher, and theAES cipher. Crypto-C offers the following stream cipher: the RC4 cipher.

	Encryption Operation
Original	Encryption	Encrypted
Message	Algorithm	Message
	Key
	Key Data
	Key
Encrypted	Decryption	Decrypted
Message	Algorithm	Message
	Decryption Operation

Figure 3-1Symmetric-Key Encryption and Decryption

3 6 R S A B S A F E C r y p t o - C D e v e l o p e r ’s G u i d e