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.

See: Data Encryption Standard.