Chapter 7: One-Time Pad or “Vernam Cipher”:

• Invented by Gilbert Vernam in 1917, considered a perfect encryption scheme because it is considered unbreakable if implemented properly.
• This cipher uses a pad made up of random values, the plaintext message that needs to be encrypted get converted into bits, and the one-time pad is made up of random bits.
• The encryption process uses a binary mathematical function called exclusive-OR (XOR).
•  XOR is an operation that is applied to two bits and is a function commonly used in binary mathematics and encryption methods.
• When combining the bits, if both values are the same, the results is 0 ( 1 XOR 1 = 0), but if the bits are different from each other, the result is 1 (1 XOR 0 = 1).
•  Example:

                                    Message stream 1001010111

                                    Keystream 0011101010

                                    Ciphertext stream 1010111101

• For the one-time pad encryption scheme to be unbreakable the follow has to be true about the implementation process:
• The pad must be used only one time, if not it can introduce patterns.
• The pad must be as long as the message, if it’s not as long as the message the pad will be reused to cover the whole message and that would be the same as using the pad more than once.
• The pad must be securely distributed and protected as its destination, the pads are usually individual pieces of paper that need to be delivered by a secure courier and properly guarded at each destination.
• The pad must be made up of truly random values.