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 = DES_{k3}(DES^{-1}_{k2}(DES_{k1}(P))).
- P — plaintext.
- C — ciphertext.
- k_{1}, k_{2}, k_{3} — 56-bit DES keys.
- DES_{k} — DES encryption with key k.
- DES^{-1}_{k} — DES decryption with key k.
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 k_{1} = k_{2} or k_{2} = k_{3}, 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
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