| 0,0 → 1,75 |
|---|
| """ crypto.cipher.arc4 |
| |
| A Stream Cipher Encryption Algorithm 'Arcfour' |
| |
| A few lines of code/ideas borrowed from [PING] |
| [PING] CipherSaber implementation by Ka-Ping Yee <ping@lfw.org>, 5 May 2000. |
| |
| Some documentation text and test vectors taken from [IDARC4] |
| [IDARCH4] K.Kaukonen, R.Thayer, "A Stream Cipher Encryption Algorithm 'Arcfour'", |
| ftp://ietf.org/draft-kaukonen-cipher-arcfour-03.txt |
| Generally munged to map to crypto.cipher calling conventions |
| |
| Copyright © (c) 2002 by Paul A. Lambert |
| Read LICENSE.txt for license information. |
| |
| November 5, 2002 |
| """ |
| |
| class ARC4: |
| """ ARC4 Stream Cipher Algorithm |
| """ |
| def __init__(self,key=None): |
| """ key -> octet string for key """ |
| self.name = 'ARC4' |
| self.strength = None # depends on keySize |
| self.blockSize = 1 # blockSize is in bytes |
| |
| if key != None: |
| self.setKey(key) |
| |
| def setKey(self, key): |
| """ Set initial state from key. Never use the same key more than once! |
| """ |
| self.keySize = len(key) |
| self.strength = self.keySize # this does not include subtracting IV size :-( |
| i, j, self.state = 0, 0, range(256) |
| for i in range(256): |
| j = (j + self.state[i] + ord(key[i % len(key)])) % 256 |
| self.state[i], self.state[j] = self.state[j], self.state[i] |
| self.keyReady = 1 # Ready |
| |
| def encrypt(self, plainText, more = None): |
| """ Encrypt a string and return a binary string |
| multiple sequential calls can be made using more =1, |
| this continues the encryption |
| New sessions of encrypt can NOT be called twice with the same key!!!! |
| """ |
| if self.keyReady != 1 : raise 'Error, ARC4 key already used once!' |
| if more != 1: |
| self.keyReady = None |
| cipherText = arcfourBlock(self.state, plainText) |
| return cipherText |
| |
| |
| def decrypt(self, cipherText, more = None): |
| """ Decrypt a string and return a string """ |
| if self.keyReady != 1 : |
| raise 'set for decryption required' |
| if more != 1: |
| self.keyReady = None |
| plainText = arcfourBlock(self.state, cipherText) |
| return plainText |
| |
| |
| def arcfourBlock(state, input): |
| """ Use state to encrypt input string, returns string """ |
| i, j, output = 0, 0, [] |
| for byte in input: |
| i = (i + 1) % 256 |
| j = (j + state[i]) % 256 |
| state[i], state[j] = state[j], state[i] |
| n = (state[i] + state[j]) % 256 |
| output.append(chr(ord(byte) ^ state[n])) |
| output = ''.join(output) # convert to string |
| return output |