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Triple DES
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Triple DES

In cryptography, Triple DES (also 3DES) is a block cipher formed from the Data Encryption Standard (DES) cipher. It was developed by Walter Tuchman (the leader of the DES development team at IBM) and is specified in FIPS Pub 46-3. There are several ways to use DES three times; not all are Triple-DES and not all are as secure.

Triple-DES is defined as performing a DES encryption, then a DES decryption, and then a DES encryption again.

C = DESk3(DES-1k2(DESk1(P))).
with
P — plaintext.
C — ciphertext.
k1, k2, k3 — 56-bit DES keys.
DESk — DES encryption with key k.
DES-1k — DES decryption with key k.

Triple-DES has a key length of 168-bits (three 56-bit DES keyss), but because of an attack it has an effective key size of 112 bits. A variant uses k1 = k3, thus reducing the key size to 112 bits. This mode is susceptible to some attacks, though.

DES is not a group; if it were one, the Triple-DES construction would be equivalent to a single DES operation and no more secure.

When k1 = k2 or k2 = k3, Triple DES is reduced to single DES, and this is often used to provide backward compatibility. The use of three steps is essential to prevent meet-in-the-middle attacks; double DES would have serious vulnerabilities. The choice of decryption for the middle step (as opposed to encryption) does not affect the security of the algorithm but instead lets tools that implement triple DES interoperate with legacy single DES tools.

See also

External links


Block ciphers
Algorithms: 3-Way | AES | Blowfish | Camellia | CAST-128 | CAST-256 | CMEA | DEAL | DES | DES-X | FEAL | G-DES | GOST | IDEA | Iraqi | KASUMI | KHAZAD | Khufu and Khafre; | LOKI89/91 | LOKI97 | Lucifer | MacGuffin | Madryga | MAGENTA | MARS | MISTY1 | MMB | NewDES | RC2 | RC5 | RC6 | Red Pike; | S-1 | SAFER | Serpent | SHARK | Skipjack | Square | TEA | Triple DES; | Twofish | XTEA
Design: Feistel network; | Key schedule; | Product cipher; | S-box | SPN   Attacks: Brute force; | Linear / Differential cryptanalysis | Mod n; | XSL   Standardisation: AES process; | CRYPTREC | NESSIE   Misc: Avalanche effect | Block size; | IV | Key size; | Modes of operation; | Piling-up lemma; | Weak key;