Triple DES
In cryptography, Triple DES is a block cipher derived from the Data Encryption Standard (DES) cipher by using it three times. Triple DES is also known as TDES or, more standard, TDEA (Triple Data Encryption Algorithm [1]).
When it was discovered that a 56-bit key of DES is not enough to protect from brute force attacks, TDES was chosen as a simple way to enlarge the key space without a need to switch to a new algorithm. The use of three steps is essential to prevent meet-in-the-middle attacks that are effective against double DES encryption.
In general TDES with three different keys (3-key {k1, k2, k3} TDES) has a key length of 168 bits: three 56-bit DES keys (with parity bits 3-key TDES has the total storage length of 192 bits), but due to the meet-in-the-middle attack the effective security it provides is only 112 bits. A variant, called two-key TDES (2-key TDES), uses k1 = k3, thus reducing the key size to 112 bits and the storage length to 128 bits. However, this mode is susceptible to certain chosen-plaintext or known-plaintext attacks [2] [3] and thus it is designated by NIST to have only 80 bits of security [4].
By design, DES and therefore TDES, suffer from slow performance in software.[5] TDES is better suited to hardware implementations[5], and indeed where it is still used is likely to be within a hardware implementation.
TDES is slowly disappearing from use, largely replaced by the Advanced Encryption Standard (AES). One large-scale exception is within the electronic payments industry, which still uses 2TDES extensively and continues to develop and spread standards based upon it (e.g. EMV, the standard for inter-operation of IC cards; also called "Chip cards", and IC capable POS terminals and ATM's). This guarantees that TDES will remain an active cryptographic standard well into the future.
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References
- ↑ NIST, Recommendation for the Triple Data Encryption Algorithm (TDEA) Block Cipher (PDF), Special Publication 800-67.
- ↑ Ralph Merkle, Martin Hellman: On the Security of Multiple Encryption (PDF), Communications of the ACM, Vol 24, No 7, pp 465–467, July 1981.
- ↑ Paul van Oorschot, Michael J. Wiener, A known-plaintext attack on two-key triple encryption (PDF), EUROCRYPT'90, LNCS 473, 1990, pp 318–325.
- ↑ NIST, Recommendation for Key Management—Part 1: general (PDF), Special Publication 800-57.
- ↑ 5.0 5.1 Details of the Data Encryption Standard