What is Triple DES?
[[Image:3des-overall-view.png|200px|thumbnail|The operation of the '''Triple DES''' where M is the [[Plaintext]], C is the [[Ciphertext]] and {k<sub>1</sub>, k<sub>2</sub>, k<sub>3</sub>} is the set of the [[Key (cryptography)|three encryption keys]].]] In [[cryptography]], '''Triple DES''' is a [[block cipher]] created 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 <ref>NIST, [http://csrc.nist.gov/publications/drafts/800-67r2/sp800-67r2-draft.pdf Recommendation for the Triple Data Encryption Algorithm (TDEA) Block Cipher] ([[PDF]]), Special Publication 800-67.</ref>). When it was discovered that a 56-bit key of DES is not enough to protect from [[brute force attack]]s, 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 attack]]s that are effective against double DES encryption. In general TDES with three different keys (3-key {k<sub>1</sub>, k<sub>2</sub>, k<sub>3</sub>} TDES) has a [[Key size|key length]] of 168 bits: three 56-bit DES [[key (cryptography)|key]]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. Another version, called two-key TDES (2-key TDES), uses k<sub>1</sub> = k<sub>3</sub>, thus reducing the key size to 112 bits and the storage length to 128 bits. However, this mode can be taken advantage of through certain [[Chosen-plaintext attack|chosen-plaintext]] or [[Known-plaintext attack|known-plaintext]] attacks <ref>[[Ralph Merkle]], [[Martin Hellman]]: [http://www.cs.purdue.edu/homes/ninghui/courses/Spring04/homeworks/p465-merkle.pdf On the Security of Multiple Encryption] {{Webarchive|url=https://web.archive.org/web/20110927011526/http://www.cs.purdue.edu/homes/ninghui/courses/Spring04/homeworks/p465-merkle.pdf |date=2011-0