Single DES — PyCryptodome 3.210b0 documentation (2024)

DES (Data Encryption Standard) is a symmetric block cipher standardizedin FIPS 46-3(now withdrawn).It has a fixed data block size of 8 bytes.

Its keys are 64 bits long, even though 8 bits were used for integrity (now theyare ignored) and do not contribute to security. The effective key length istherefore 56 bits only.

DES was never cryptographically broken, but its key length is too short by nowadaysstandards and it could be brute forced with some effort.

As an example, encryption can be done as follows:

>>> from Crypto.Cipher import DES>>>>>> key = b'-8B key-'>>> cipher = DES.new(key, DES.MODE_OFB)>>> plaintext = b'sona si latine loqueris '>>> msg = cipher.iv + cipher.encrypt(plaintext)

Module’s constants for the modes of operation supported with Single DES:

var MODE_ECB:

Electronic Code Book (ECB)

var MODE_CBC:

Cipher-Block Chaining (CBC)

var MODE_CFB:

Cipher FeedBack (CFB)

var MODE_OFB:

Output FeedBack (OFB)

var MODE_CTR:

CounTer Mode (CTR)

var MODE_OPENPGP:

OpenPGP Mode

var MODE_EAX:

EAX Mode

Crypto.Cipher.DES.new(key, mode, *args, **kwargs)¶

Create a new DES cipher.

Parameters:

• key (bytes/bytearray/memoryview) – The secret key to use in the symmetric cipher.It must be 8 byte long. The parity bits will be ignored.

• mode (One of the supported MODE_* constants) – The chaining mode to use for encryption or decryption.

Keyword Arguments:

• iv (byte string) –(Only applicable for MODE_CBC, MODE_CFB, MODE_OFB,and MODE_OPENPGP modes).

  The initialization vector to use for encryption or decryption.

  For MODE_CBC, MODE_CFB, and MODE_OFB it must be 8 bytes long.

  For MODE_OPENPGP mode only,it must be 8 bytes long for encryptionand 10 bytes for decryption (in the latter case, it isactually the encrypted IV which was prefixed to the ciphertext).

  If not provided, a random byte string is generated (you must thenread its value with the iv attribute).

• nonce (byte string) –(Only applicable for MODE_EAX and MODE_CTR).

  A value that must never be reused for any other encryption donewith this key.

  For MODE_EAX there are norestrictions on its length (recommended: 16 bytes).

  For MODE_CTR, its length must be in the range [0..7].

  If not provided for MODE_EAX, a random byte string is generated (youcan read it back via the nonce attribute).

• segment_size (integer) –(Only MODE_CFB).The number of bits the plaintext and ciphertextare segmented in. It must be a multiple of 8.If not specified, it will be assumed to be 8.

• mac_len : (integer) –(Only MODE_EAX)Length of the authentication tag, in bytes.It must be no longer than 8 (default).

• initial_value : (integer) –(Only MODE_CTR). The initial value for the counter withinthe counter block. By default it is 0.

Return:

a DES object, of the applicable mode.