![]() Therefore, 2TDES has a key length of 112 bits. In other words, user encrypt plaintext blocks with key K 1, then decrypt with key K 2, and finally encrypt with K 1 again. Second variant of Triple DES (2TDES) is identical to 3TDES except that K 3is replaced by K 1. This provides backwards compatibility with DES. User first decrypt using K 3, then encrypt with K 2, and finally decrypt with K 1.ĭue to this design of Triple DES as an encrypt–decrypt–encrypt process, it is possible to use a 3TDES (hardware) implementation for single DES by setting K 1, K 2, and K 3 to be the same value. Now decrypt the output of step 1 using single DES with key K 2.įinally, encrypt the output of step 2 using single DES with key K 3.ĭecryption of a ciphertext is a reverse process. The encryption-decryption process is as follows −Įncrypt the plaintext blocks using single DES with key K 1. ![]() The encryption scheme is illustrated as follows − This means that the actual 3TDES key has length 3×56 = 168 bits. 3-KEY Triple DESīefore using 3TDES, user first generate and distribute a 3TDES key K, which consists of three different DES keys K 1, K 2 and K 3. Incidentally, there are two variants of Triple DES known as 3-key Triple DES (3TDES) and 2-key Triple DES (2TDES). This led to the modified schemes of Triple DES (sometimes known as 3DES). The pragmatic approach was not to abandon the DES completely, but to change the manner in which DES is used. However, users did not want to replace DES as it takes an enormous amount of time and money to change encryption algorithms that are widely adopted and embedded in large security architectures. The speed of exhaustive key searches against DES after 1990 began to cause discomfort amongst users of DES.
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