The Triple DES is basically three times the DES algorithm which is applied for each data block. TDES was an easy way to improve the security of the DES algorithm by increasing the key size from 56-bits to 168-bits (three times 56-bits). It is also defined in the same FIPS 46-3 publication as DES standard. It can either use one, two or three distinct keys. The one key mode corresponds to the DES itself, so it is not secure, two-key mode (key size is 112 bits) is also considered to be insecure. Only the three-key mode is considered to be appropriate until 2030.