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.