The key and initialization vector strings are to be taken as ASCII, suppressing the special interpretation given to leading "0X", "0x", "0B", and "0b" characters. This flag applies to both the key and initialization vector.
-b
Use ECB mode.
-d
Decrypt the input.
-F N
Use N -bit alternative CFB mode. Currently N must be a multiple of 7 between 7 and 56 inclusive (this does not conform to the alternative CFB mode specification).
-f N
Use N -bit CFB mode. Currently N must be a multiple of 8 between 8 and 64 inclusive (this does not conform to the standard CFB mode specification).
-k key
Use key as the cryptographic key.
-m N
Compute a message authentication code (MAC) of N bits on the input. The value of N must be between 1 and 64 inclusive; if N is not a multiple of 8, enough 0 bits will be added to pad the MAC length to the nearest multiple of 8. Only the MAC is output. MACs are only available in CBC mode or in CFB mode.
-o N
Use N -bit ouput feedback (OFB) mode. Currently N must be a multiple of 8 between 8 and 64 inclusive (this does not conform to the OFB mode specification).
-p
Disable the resetting of the parity bit. This flag forces the parity bit of the key to be used as typed, rather than making each character be of odd parity. It is used only if the key is given in ASCII.
-v vector
Set the initialization vector to vector; the vector is interpreted in the same way as the key. The vector is ignored in ECB mode.
The key and initialization vector are taken as sequences of ASCII characters which are then mapped into their bit representations. If either begins with "0X" or "0x", that one is taken as a sequence of hexadecimal digits indicating the bit pattern; if either begins with "0B" or "0b", that one is taken as a sequence of binary digits indicating the bit pattern. In either case, only the leading 64 bits of the key or initialization vector are used, and if fewer than 64 bits are provided, enough 0 bits are appended to pad the key to 64 bits.
According to the DES standard, the low-order bit of each character in the key string is deleted. Since most ASCII representations set the high-order bit to 0, simply deleting the low-order bit effectively reduces the size of the key space from 2^56 to 2^48 keys. To prevent this, the high-order bit must be a function depending in part upon the low-order bit; so, the high-order bit is set to whatever value gives odd parity. This preserves the key space size. Note this resetting of the parity bit is not done if the key is given in binary or hex, and can be disabled for ASCII keys as well.
The DES is considered a very strong cryptosystem, and other than table lookup attacks, key search attacks, and Hellman’s time-memory tradeoff (all of which are very expensive and time-consuming), no cryptanalytic methods for breaking the DES are known in the open literature. No doubt the choice of keys and key security are the most vulnerable aspect of bdes.
