1.加密：
pyDes.des(key, [mode], [IV], [pad], [padmode])
pyDes.triple_des(key, [mode], [IV], [pad], [padmode])key -> Bytes containing the encryption key. 8 bytes for DES, 16 or 24 bytes
for Triple DES
mode -> Optional argument for encryption type, can be either
pyDes.ECB (Electronic Code Book) or pyDes.CBC (Cypher Block Chaining)
IV -> Optional Initial Value bytes, must be supplied if using CBC mode.
Length must be 8 bytes.
pad -> Optional argument, set the pad character (PAD_NORMAL) to use during
all encrypt/decrpt operations done with this instance.
padmode -> Optional argument, set the padding mode (PAD_NORMAL or PAD_PKCS5)
to use during all encrypt/decrpt operations done with this instance.
实例：
Example
-------
from pyDes import *data = "Please encrypt my data"
k = des("DESCRYPT", CBC, "\0\0\0\0\0\0\0\0", pad=None, padmode=PAD_PKCS5)
# For Python3, you'll need to use bytes, i.e.:
# data = b"Please encrypt my data"
# k = des(b"DESCRYPT", CBC, b"\0\0\0\0\0\0\0\0", pad=None, padmode=PAD_PKCS5)
d = k.encrypt(data)
print "Encrypted: %r" % d
print "Decrypted: %r" % k.decrypt(d)
assert k.decrypt(d, padmode=PAD_PKCS5) == data
