I read about 3DES encryption but I don't understand exactly what the specific meaning of key size is. For example I found that 3DES supports 64, 128, 192, and 256 bits key size. What are all the possible key sizes supported by 3DES? Is there any function to determine if a key is valid for 3DES or not? The KCV is the 'Key Check Value' for the key, calculated by assuming the key/components are 3DES keys, and encrypting a string of binary zeroes. The KCV is the first six hex digits of the resulting ciphertext. As mentioned above, a triple DES key is a bundle of three DES keys. A DES key is 64 bits long, but only 56 bits of these are used in the encryption process. A triple DES key is therefore 3 x 64 = 192 bits long, but the keyspace is only 3 x 56 = 168 bits. Note that if your 'triple DES' key is not exactly 192-bits long - i.e. Exactly 24 bytes. The Data Encryption Standard encryption algorithm on which Triple DES is based was first published in 1975. Over the years, as computers grew faster, the block cipher with a simple 56-bit key.

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The speed of exhaustive key searches against DES after 1990 began to cause discomfort amongst users of DES. 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 pragmatic approach was not to abandon the DES completely, but to change the manner in which DES is used. This led to the modified schemes of Triple DES (sometimes known as 3DES).

Incidentally, there are two variants of Triple DES known as 3-key Triple DES (3TDES) and 2-key Triple DES (2TDES).

3-KEY Triple DES

Before using 3TDES, user first generate and distribute a 3TDES key K, which consists of three different DES keys K₁, K₂ and K₃. This means that the actual 3TDES key has length 3×56 = 168 bits. The encryption scheme is illustrated as follows −

The encryption-decryption process is as follows −

• Encrypt the plaintext blocks using single DES with key K₁.

• Now decrypt the output of step 1 using single DES with key K₂.

• Finally, encrypt the output of step 2 using single DES with key K₃.

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• The output of step 3 is the ciphertext.

• Decryption of a ciphertext is a reverse process. User first decrypt using K_3, then encrypt with K_2, and finally decrypt with K₁.

Due 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 K₃ to be the same value. This provides backwards compatibility with DES.

Triple Des Encryption Key Generator Download

Second variant of Triple DES (2TDES) is identical to 3TDES except that K₃is replaced by K₁. In other words, user encrypt plaintext blocks with key K_1, then decrypt with key K_2, and finally encrypt with K₁ again. Therefore, 2TDES has a key length of 112 bits.

Triple Des Encryption Example

Triple DES systems are significantly more secure than single DES, but these are clearly a much slower process than encryption using single DES.