Simple_CBC_DES.sagews

from sage.crypto.util import ascii_integer
from sage.crypto.block_cipher.sdes import SimplifiedDES
bin = BinaryStrings();

def encrypt(m, k):
    ct = [];
    iv = ZZ.random_element(256);
    n = 0;
    for a in m:
        if n==0:
            pt = bin.encoding(chr(int(str(bin.encoding(a)), 2)^^iv));
        else:
            pt = bin.encoding(chr(int(str(bin.encoding(a)), 2)^^int(ct[n-1],2)));
        c = sdes.encrypt(list(pt), k);
        ct.append(''.join(str(i) for i in c));
        n = n + 1;
    return [format(iv, '08b')] + ct;

def decrypt(ct, k):
    pt = '';
    n = 0;
    iv = int(str(ct[0]), 2);
    for c in ct[1:]:
        p = sdes.decrypt(list(bin(c)), k);
        if n==0:
            p = chr(int(''.join(str(i) for i in p), 2) ^^ iv);
        else:
            p = chr(int(''.join(str(i) for i in p), 2) ^^ int(ct[n], 2));
        pt += p;
        n = n + 1;
    return pt;

sdes = SimplifiedDES();
k = [0, 0, 0, 0, 0, 1, 1, 1, 1, 1];
m = 'Top Secret';
print "Message = ", m;
ct = encrypt(m, k);
print "IV = ", ct[0];
print "Ciphertext = ", ct[1:];
pt = decrypt(ct, k);
print "Plaintext = ", pt;

Message = Top Secret IV = 11111001 Ciphertext = ['10010110', '01100001', '00010101', '11111000', '01011001', '10001011', '11010011', '10111000', '00101100', '11010010'] Plaintext = Top Secret