#PEcrypt - use a string key to encrypt/decrypt another string
# - Simon Peverett - January 2004
class PEcrypt:
"""
PEcrypt - very, very simple word key encryption system
uses cyclic XOR between the keyword character
bytes and the string to be encrypted/decrypted.
Therefore, the same function and keyword will
encrypt the string the first time and decrypt
it if called on the encrypted string.
"""
def __init__(self, aKey):
"""
Initialise the class with the key that
is used to encrypt/decrypt strings
"""
self.key = aKey
# CRC can be used to validate a key (very roughly)
# if you store the CRC from a previous keyword
# and then compare with a newly generated one and
# they are the same then chances are the keyword
# is correct - only a single byte so not that reliable
self.crc = 0
for x in self.key:
intX = ord(x)
self.crc = self.crc ^ intX
def Crypt(self, aString):
"""
Encrypt/Decrypt the passed string object and return
the encrypted string
"""
kIdx = 0
cryptStr = "" # empty 'crypted string to be returned
# loop through the string and XOR each byte with the keyword
# to get the 'crypted byte. Add the 'crypted byte to the
# 'crypted string
for x in range(len(aString)):
cryptStr = cryptStr + \
chr( ord(aString[x]) ^ ord(self.key[kIdx]))
# use the mod operator - % - to cyclically loop through
# the keyword
kIdx = (kIdx + 1) % len(self.key)
return cryptStr
if __name__ == "__main__":
def strToHex(aString):
hexStr = ""
for x in aString:
hexStr = hexStr + "%02X " % ord(x)
return hexStr
# self test routine
print "\nTesting PEcrypt!"
print "----------------\n"
keyStr = "This is a key"
testStr = "The quick brown fox jumps over the lazy dog!"
print "\nString : ", testStr
print "in hex : ", strToHex(testStr)
print "key : ", keyStr
pe = PEcrypt(keyStr) # generate the PEcrypt instance
print "\nPEcrypt CRC = %02X" % pe.crc
testStr = pe.Crypt(testStr)
print "\nEncrypted string"
print "Ascii : ", testStr
print "Hex : ", strToHex(testStr)
testStr = pe.Crypt(testStr)
print "\nDecrypted string"
print "Ascii : ", testStr
print "Hex : ", strToHex(testStr)
