In cryptography, the one-time pad (OTP) is a type of encryption which has been proven to be impossible to crack if used correctly. Each bit or character from the plaintext is encrypted by a modular addition with a bit or character from a secret random key (or pad) of the same length as the plaintext, resulting in a ciphertext.
The "pad" part of the name comes from early implementations where the key
material was distributed as a pad of paper, so the top sheet could be
easily torn off and destroyed after use. For easy concealment, the pad
was sometimes reduced to such a small size that a powerful magnifying glass was required to use it. Photos show captured KGB pads that fit in the palm of one's hand, or in a walnut shell. To increase security, one-time pads were sometimes printed onto sheets of highly flammable nitrocellulose.
Here the code, a brief implementation in python:
1.- The random key is generated.
2.- That key is used for encrypt the message.
3.- The same key and the ciphertext are used for decrypt the message.
from random import *
def create_key(message):
abc = "abcdefghijklmnopqrstuvwxyz0123456789;.:-_/@\&$%!?()[]#+^"
key = []
for char in message:
key += abc[randint(0,55)]
return key
def encrypt(message, key):
res = ""
for i in range(len(message)):
messagechar = ord(message[i]) - ord(start)
keychar = ord(key[i]) - ord(start)
calcuchar = (messagechar + keychar) % modulo
convertchar = chr(calcuchar + ord(start))
res += convertchar
return res
def decrypt(message, key):
res = ""
for i in range(len(message)):
messagechar = ord(message[i]) - ord(start)
keychar = ord(key[i]) - ord(start)
calcuchar = (messagechar - keychar) % modulo
convertchar = chr(calcuchar + ord(start))
res += convertchar
return res
#main
start = ' '
end = '~'
modulo = ord(end) - ord(start)
message = "this message is only a test to show a small implemetation of otp"
#key = "AKebnbl5fFWXTXYkfd=I_XujRdvgULghs;ucO_YeyVc"
key = create_key()
encryp = encrypt(message, key)
decryp = decrypt(encryp, key)
#print modulo
print ""
print "Message : ", message
print ""
print "Encrypted:", encryp
print ""
print "Decrypted:", decryp
print ""
print "Key : ", key
Here a capture of the script running:
Sorry if the SyntaxHighlighter fails.
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References
