Implementing-cryptography-using-python

58 Chapter 2 ■ Cryptographic Protocols and Perfect Secrecy
realMsg = hexlify(realMessage)
decoyMsg = hexlify(decoyMessage)
realKey = int(realMsg, 16) ^ msg
decoyKey = int(decoyMsg, 16) ^ msg
print ("The secret message is: ", msg)
print ("The real key is: ", realKey)
print ("The decoy key is: ", decoyKey)
print ()
# choose either the decoy key or the real key
key = realKey
plain = otpDec(msg, key)
print (plain)
print ()
key = decoyKey
plain = otpDec(msg, key)
print ()
print (plain)
The output using the keys should resemble the following:
The secret message is: 27865585609579580086126129250694423149352332105546
The real key is: 167190391575317824697301565359800501773353221186411
The decoy key is: 142430497120678699528160795125823853486446056338465
attackthematmidnight!
retreatanddonotattack
Once you use the same key more than once, you open the key to vulnerabilities
as now the same key will convert more than one ciphertext to plaintext.
Since there is most likely only one key that will decrypt two different messages,
the key would be compromised. Using the real key in the preceding example
again would tip the advisories of your encryption methods.
One-Way Hashes
You were briefly introduced to hashes in the previous chapter. As a reminder,
a hash function is an algorithm that changes the input or changes the data of an
arbitrary or random length into a fixed-sized output.
In our previous example, you saw passwords that were hashed using the
SHA-512 algorithm. Storing passwords as hashes provides a level of security
in the event that the password storage database is compromised. Hashes can
be used as a more advanced version of checksums. When we move a file from
one drive to another, we have a checksum on frames called a Frame Check