Triple DES (3DES)
Triple DES (3DES) is a symmetric block cipher that applies DES 3 consecutive times, or rounds, to encrypt each 64-bit block.
- was created as an interim solution after DES was determined to not be secure
- uses 3 different or identical keys
- uses a key bundle of keys
, , and - each key is a standard 56-bit DES key
- how it works
- DES encrypt with
- DES decrypt with
- DES encrypt with
- DES encrypt with
- 3 options for keys
- all three keys are independent and different
- 3 x 56-bit keys = 168 independent key bits
and are identical - two independent 56-bit keys = 112 independent key bits
- all keys are the same
- one 56-bit key
- all three keys are independent and different
- option 1 is most secure, 3 is least secure
- using 1 key is considered insecure and equivalent to just DES
Vulnerability
- Birthday paradox
- with a block length of 64 bits, a ciphertext collision will likely occur when about
plaintext blocks are encrypted with the same key
- with a block length of 64 bits, a ciphertext collision will likely occur when about