triple data encryption algorithm (TDEA)
An encryption algorithm whose key consists of three DES (Data Encryption Standard) keys, which is also referred to as a key bundle.
Note 1: A DES key consists of 64 binary digits (“0″s or “1”s) of which 56 bits are randomly generated and used directly by the algorithm. (The other 8 bits, which are not used by the algorithm, may be used for error detection. )
Note 2: Each TDEA encryption/decryption operation (as specified in ANSI X9.52) is a compound operation of DES encryption and decryption operations. Let EK(I) and DK(I) represent the DES encryption and decryption of I using DES key K respectively. The following operations are TDEA encryption operation: the transformation of a 64-bit block I into a 64-bit block O that is defined as follows:
O = EK3(DK2(EK1(I))).
TDEA decryption operation: the transformation of a 64-bit block I into a 64-bit block O that is defined as follows:
O = DK1(EK2(DK3(I))).
The standard specifies the following keying options for bundle (K1, K2, K3)
Keying Option 1: K1, K2, and K3 are independent keys;
Keying Option 2: K1 and K2 are independent keys and K3 = K1;
Keying Option 3: K1 = K2 = K3.