# What could be the keylength of a DES encryption?

What could be the keylength of the DES encryption if we have an output of 64 bytes?

DES has a 56-bit key in 8-bytes. The length of the output depends on the length of the input, mode and padding, not the key.

Note: The LSb (least significant bit) of each key byte is reserved for parity, depending on the DES implementation parity may or not be checked.

• Note that I have seen DES being used as synonym for 2 key or 3 key triple DES (which one is chosen during key configuration). That's of course not a correct use of the DES acronym (as there are other schemes based on DES), but I think it may be interesting for real world scenarios. Sep 16, 2017 at 14:21

DES is the block cipher with the

• fixed key length of 56 bits, and
• the fixed block size of 64 bits.

It is co called cryptographic primitive (something as building block for constructing real ciphers).

To cipher some message it must be first divided / padded to the integer number of 64-bits blocks.

So the key length must be 56-bits.

BTW., DES is now considered not be safe (mainly because of that short key length). Triple DES (3DES) is now (relatively simple) substitution for it (with the 3 times longer, i. e. 168-bits key).

• 1. CTR mode does not require padding. 2. There is also a lot of 2TDEA with a 112 bit key and that has been deprecated. 3. 3DES provides is only 112 bits of security due to a meet-in-the-middle attack. 4. Arguably a better upgrade for DES is AES.
– zaph
Sep 15, 2017 at 23:30