3.3.3 Symmetric Encryption Facts

Symmetric-key encryption

(also known as secret-key encryption, pre-shared key, or private-key encryption) uses only one key to encrypt and decrypt data.

Symmetric-key encryption

A form of cryptography that provides confidentiality with a weak form of authentication or integrity.

Twofish

A symmetric block cipher permits a wide variety of tradeoffs between speed, software size, key setup time, and memory. Twofish: Uses 128-bit blocks and variable key lengths (128-, 192-, or 256-bits). Uses up to 16 rounds of substitution and transposition. Twofish was the runner up to Rijndael in the selection of the algorithm of AES.

Triple DES (3DES)

Applies DES three times. Uses a 168-bit key. Used in IPSec as its strongest and slowest encipherment. Encrypting large amounts of data tends to create patterns in the cipher text. There are two implementations of 3DES used to create strong cipher text by using multiple keys: EDE2 encrypts with key1, then decrypts with key2, and finally encrypts again with key1. EEE3 encrypts with key1, then encrypts with key2, and finally encrypts with key3.

DES

Data Encryption Standard

Block Cipher

Transpose plain text to cipher text in chunks

Stream Cipher

Transpose plain text to cipher text one bit at a time

Stream ciphers

Use a sequence of bits known as a keystream, which is the key used for encryption. The encryption is performed on each bit within the stream in real time. Common uses for symmetric-key stream ciphers include ATM card PINs and smart cards.

International Data Encryption Algorithm (IDEA)

Uses 64-bit blocks with 128-bit keys. Is used by Pretty Good Privacy (PGP) e-mail encryption. Is an optional algorithm in OpenPGP. Does not support variable block size.

Symmetric encryption

Well suited for bulk encryption of less sensitive data because it is less CPU-intensive than other encryption methods.

Blowfish

a keyed, symmetric block cipher that was intended to be free of the problems associated with other algorithms and replace DES. Blowfish: Uses 64-bit blocks and key lengths anywhere from 32 to 448 bits. Has no effective known cryptanalysis currently.

Ron's Cipher v2 or Ron's Code v2 (RC2)

a variable key-sized block cipher which was designed to replace DES. RC2 was produced by RSA Security, Inc. RC2: - Uses 64 bit blocks. - Uses 8 to 128-bit keys in 8 bit increments. - Uses salt, which is used to modify a password hash by using a random string of data to prohibit password hash matching types of attacks.

SkipJack

Created by the National Security Agency (NSA). Encrypts 64-bit blocks of data with an 80-bit key. Uses in the Clipper chip (Very Large Scale Integration) device with an ARM (Advanced RISC Machine). Became unpopular when a back door was discovered that allowed the NSA to decrypt all messages produced by the Clipper chip.

Advanced Encryption Standard (AES)

an iterative symmetric-key block cipher that was developed as a replacement to DES in 2001. AES: Uses the Rijndael Block Cipher which is resistant to all known attacks. Uses a variable-length block and key length (128-, 192-, or 256-bit keys). Is stronger and faster than 3DES when implemented with a large key size (256-bits). Was selected as the method to replace DES.

Block ciphers

encrypt by transposing plain text to cipher text in chunks (block-by-block) * Are fast. * Can process large amounts of data. They do not process small amounts of data well. * Are typically implemented in software. * Use a substitution and transposition function. * Apply several alternating rounds of substitution and transposition. A round refers to data going through one substitution and transposition process. * May being to show patterns in the cipher when processing large amounts of data. * Can be strengthened by implementing an Initialization Vector (IV) at the start of the encryption process