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{{Infobox block cipher| name = Triple DES| image = | caption = Three successive invocations of DES| designers = IBM| derived from = [Data Encryption Standard| derived to =| key size = 112 (2TDES) or 168 bits (3TDES)| block size = 64 bits| structure = Feistel network, Triple DES is a [block cipher formed from the Data Encryption Standard (DES) cipher by using it three times.

Acronyms Triple DES is also known as TDES or, more standard, TDEA (Triple Data Encryption Algorithm NIST, Recommendation for the Triple Data Encryption Algorithm (TDEA) Block Cipher (PDF), Special Publication 800-67.). The non-standard convention to use DES (standard) when we actually mean DEA (algorithm) is so widespread that in order to avoid confusion we use it in this article. On the other hand, since there are variations of TDES which use two different keys (2TDES) and three different keys (3TDES) the non-standard abbreviation 3DES is confusing and should be avoided.

Algorithm When it was found that a 56-bit key of DES is not enough to guard against 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. Note that DES is not a group (mathematics); if it were one, the TDES construction would be equivalent to a single DES operation and no more secure.

The simplest variant of TDES operates as follows: \textrm{DES}(k_3;\textrm{DES}(k_2;\textrm{DES}(k_1; M))), where M is the message block to be encrypted and k_1, k_2, and k_3 are DES keys. This variant is commonly known as EEE because all three DES operations are encryptions. In order to simplify interoperability between DES and TDES the middle step is usually replaced with decryption (EDE mode): \textrm{DES}(k_3;\textrm{DES}^{-1}(k_2;\textrm{DES}(k_1; M))) and so a single DES encryption with key k can be represented as TDES-EDE with k_1 = k_2 = k_3 = k. The choice of decryption for the middle step does not affect the security of the algorithm.

Security In general TDES with three different keys (3-key TDES) has a key length of 168 bits: three 56-bit DES key (cryptography)s (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 attack or known-plaintext attack attacks 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, EUROCRYPT'90, LNCS 473, 1990, pp 318–325. and thus it is officially NIST, Recommendation for Key Management — Part 1: general (PDF), Special Publication 800-57. designated to have only 80-bits of security.

As of 2005, the best attack known on 3-key TDES requires around 232 known plaintexts, 2113 steps, 290 single DES encryptions, and 288 memoryStefan Lucks: Attacking Triple Encryption (PDF), Fast Software Encryption 1998, pp 239–253. (the paper presents other tradeoffs between time and memory). This is not currently practical. If the attacker seeks to discover any one of many cryptographic keys, there is a memory-efficient attack which will discover one of 228 keys, given a handful of chosen plaintexts per key and around 284 encryption operationsEli Biham: How to Forge DES-Encrypted Messages in 228 Steps (PostScript), 1996.. This attack is highly parallelizable and verges on the practical, given billion-dollar budgets and years to mount the attack, though the circumstances in which it would be useful are limited.

Usage TDES is slowly disappearing from use, largely replaced by its natural successor, 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 promulgate standards based upon it (e.g. EMV). This guarantees that TDES will remain an active cryptographic standard well into the future.

By design, DES and therefore TDES, suffer from slow performance in software; on modern processors, AES tends to be around six times faster. TDES is better suited to hardware implementations, and indeed where it is still used it tends to be with a hardware implementation (e.g., VPN appliances and the Nextel cellular and data network), but even there AES outperforms it. Finally, AES offers markedly higher security margins: a larger block size, potentially longer keys, and as of 2007, no known public cryptanalytic attacks.

See also

• DES-X
• Walter Tuchman
• Horst Feistel
• Data Encryption Standard (DES)
• Advanced Encryption Standard (AES)

References

triple DES from FOLDOC
triple DES < cryptography > A product cipher which, like DES, operates on 64-bit data blocks. There are several forms, each of which uses the DES cipher 3 times.

Triple DES - Wikipedia, the free encyclopedia
In cryptography, Triple DES is a block cipher formed from the Data Encryption Standard (DES) cipher by using it three times.

Triple DES, 3DES, DES Encryption - The Cryptography Specialists
If you are considering deployment of cryptography using the DES algorithm (including triple DES, 3DES), you have found the right site.

3des & triple des encryption
3des & triple des - Where to find 3des & triple des encryption software

Triple DES Encryption
Triple DES Encryption Overview. The Data Encryption Standard (DES) was developed by an IBM team around 1974 and adopted as a national standard in 1977.

triple DES
The Free Online Dictionary of Computing (http://foldoc.doc.ic.ac.uk/) is edited by Denis Howe < dbh@doc.ic.ac.uk >. Previous: Trilogy Next: tri state

Triple DES Encryption - Thales Esecurity
Triple DES Encryption from Thales Esecurity ... Maximising the benefits of a security upgrade - Triple DES Encryption

Triple-DES - Definition at Your Dictionary
A cipher that, as does DES, operates on 64-bit data blocks. There are several variants, each of which applies the basic DES algorithm three times.

Triple DES definition of Triple DES in the Free Online Encyclopedia.
See DES. (cryptography) triple DES - A product cipher which, like DES, operates on 64-bit data blocks. There are several forms, each of which uses the DES cipher 3 times.

Triple DES - Wikipedia, la enciclopedia libre
En criptografía el Triple DES se llama al algoritmo que hace triple cifrado del DES. También es conocido como TDES o 3DES, fue desarrollado por IBM en 1978.