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Encyclopedia > Triple DES

Triple DES
Three successive invocations of DES
General
Designer(s): IBM
First published: 1978
Derived from: DES
Cipher detail
Key size(s): 112 (2TDES) or 168 bits (3TDES)
Block size(s): 64 bits
Structure: Feistel network
Rounds: 48 DES-equivalent rounds
Best public cryptanalysis
Lucks: 232 known plaintexts, 2113 operations including 290 DES encryptions, 288 memory; Biham: find one of 228 target keys with a handful of chosen plaintexts per key and 284 encryptions

In cryptography, Triple DES is a block cipher formed from the Data Encryption Standard (DES) cipher by using it three times. Image File history File links Download high resolution version (1177x1116, 70 KB) Triple DES- overall view of ciphering. ... IBM redirects here. ... Year 1978 (MCMLXXVIII) was a common year starting on Sunday (link displays the 1978 Gregorian calendar). ... The Data Encryption Standard (DES) is a cipher (a method for encrypting information) selected as an official Federal Information Processing Standard (FIPS) for the United States in 1976, and which has subsequently enjoyed widespread use internationally. ... In cryptography, the key size (alternatively key length) is the size of the digits used to create an encrypted text; it is therefore also a measure of the number of possible keys which can be used in a cipher, and the number of keys which must be tested to break... In modern cryptography, symmetric key ciphers are generally divided into stream ciphers and block ciphers. ... In cryptography, a Feistel cipher is a block cipher with a particular structure, named after IBM cryptographer Horst Feistel; it is also commonly known as a Feistel network. ... Cryptanalysis (from the Greek kryptós, hidden, and analýein, to loosen or to untie) is the study of methods for obtaining the meaning of encrypted information, without access to the secret information which is normally required to do so. ... The German Lorenz cipher machine, used in World War II for encryption of very high-level general staff messages Cryptography (or cryptology; derived from Greek κρυπτός kryptós hidden, and the verb γράφω gráfo write or λεγειν legein to speak) is the study of message secrecy. ... Encryption Decryption In cryptography, a block cipher is a symmetric key cipher which operates on fixed-length groups of bits, termed blocks, with an unvarying transformation. ... The Data Encryption Standard (DES) is a cipher (a method for encrypting information) selected as an official Federal Information Processing Standard (FIPS) for the United States in 1976, and which has subsequently enjoyed widespread use internationally. ... This article is about algorithms for encryption and decryption. ...

Contents

Acronyms

Triple DES is also known as TDES, 3DES or, more standard, TDEA (Triple Data Encryption Algorithm [1]). 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 standard abbreviation 3DES is used.


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; if it were one, the TDES construction would be equivalent to a single DES operation and no more secure. The Meet-in-the-middle attack is a cryptographic attack which, like the Birthday attack, makes use of a space-time tradeoff. ... This picture illustrates how the hours on a clock form a group under modular addition. ...


The simplest variant of TDES operates as follows: DES(k3;DES(k2;DES(k1;M))), where M is the message block to be encrypted and k1, k2, and k3 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): DES(k3;DES − 1(k2;DES(k1;M))) and so a single DES encryption with key k can be represented as TDES-EDE with k1 = k2 = k3 = 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 (3TDES) has a key length of 168 bits: three 56-bit DES keys (with parity bits 3TDES 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 (2TDES), 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 officially [4] designated to have only 80-bits of security. In cryptography, the key size (alternatively key length) is a measure of the number of possible keys which can be used in a cipher. ... A key is a piece of information that controls the operation of a cryptography algorithm. ... The Meet-in-the-middle attack is a cryptographic attack which, like the Birthday attack, makes use of a space-time tradeoff. ... A chosen plaintext attack is any form of cryptanalysis which presumes that the attacker has the capability to choose arbitrary plaintexts to be encrypted and obtain the corresponding ciphertexts. ... The known-plaintext attack (KPA) is an attack model for cryptanalytic where the attacker has samples of both the plaintext and its encrypted version (ciphertext) and is at liberty to make use of them to reveal further secret information; typically this is the secret key. ...


As of 2005, the best attack known on 3TDES requires around 232 known plaintexts, 2113 steps, 290 single DES encryptions, and 288 memory[5] (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 operations[6]. 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. 2005 is a common year starting on Saturday of the Gregorian calendar. ...


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. In cryptography, the Advanced Encryption Standard (AES), also known as Rijndael, is a block cipher adopted as an encryption standard by the U.S. government. ... It has been suggested that Chip and PIN be merged into this article or section. ...


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. A Virtual Private Network, or VPN, is a private communications network usually used within a company, or by several different companies or organizations, communicating over a public network. ... Sprint Nextel Corporation (NYSE: S), headquartered in Reston, Virginia, is one of the largest telecommunications companies in the United States. ...


See also

In cryptography, DES-X (or DESX) is a variant on the DES (Data Encryption Standard) block cipher intended to increase the complexity of a brute force attack using a technique called key whitening. ... Walter Tuchman led the Data Encryption Standard development team at IBM. He was also responsible for the development of Triple DES. Horst Feistel ‹The stub template below is included via a redirect that has been proposed for deletion. ... Horst Feistel (30 January 1915(1)–14 November 1990) was a cryptographer who worked on the design of ciphers at IBM, initiating research that would culminate in the development of the Data Encryption Standard (DES) in the 1970s. ... The Data Encryption Standard (DES) is a cipher (a method for encrypting information) selected as an official Federal Information Processing Standard (FIPS) for the United States in 1976, and which has subsequently enjoyed widespread use internationally. ... In cryptography, the Advanced Encryption Standard (AES), also known as Rijndael, is a block cipher adopted as an encryption standard by the U.S. government. ...

References

  1. ^ NIST, Recommendation for the Triple Data Encryption Algorithm (TDEA) Block Cipher (PDF), Special Publication 800-67.
  2. ^ Ralph Merkle, Martin Hellman: On the Security of Multiple Encryption (PDF), Communications of the ACM, Vol 24, No 7, pp 465–467, July 1981.
  3. ^ Paul van Oorschot, Michael J. Wiener , A known-plaintext attack on two-key triple encryption, EUROCRYPT'90, LNCS 473, 1990, pp 318–325.
  4. ^ NIST, Recommendation for Key Management — Part 1: general (PDF), Special Publication 800-57.
  5. ^ Stefan Lucks: Attacking Triple Encryption (PDF), Fast Software Encryption 1998, pp 239–253.
  6. ^ Eli Biham: How to Forge DES-Encrypted Messages in 228 Steps (PostScript), 1996.

  Results from FactBites:
 
Cryptographic Algorithms : Triple DES (373 words)
DES (the Data Encryption Standard) is a symmetric block cipher developed by IBM.
DES is the most widely used symmetric algorithm in the world, despite claims that the key length is too short.
Assuming that the only feasible attack on DES is to try each key in turn until the right one is found, then 1,000,000 machines each capable of testing 1,000,000 keys per second would find (on average) one key every 12 hours.
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