- One-Time Pad is an unbreakable cryptosystem developed by Gilbert Vernam and Joseph Mauborgne 1918
- Key is a random sequence of 0,1 same length as the message and are added together with XOR aka exclusive or
- Example
- plaintext 00101001
- key 10101100
- ciphertext 10000101
- Decryption uses the same key, add teh key onto the ciphertext to return the plaintext
- If used on the alphabet, the key is a random sequence of shifts between 0 to 25
- unbreakable for ciphertext only attack
- if we only have a piece of plaintext, the random generation means we know nothing about the rest of the key
- Issues
- truly random generation
- trusted courier
- key is very long, dangerous to reuse
- Trivia
- hotline between washington and USSR was thought to be a one-time pad
- Variation of one time pad
- satellite produce and broadcast several random sequences of bits at a rate fast enough that no computer can store more than a very small faction of the outputs
- Alice wants to send message to bob
- use RSA to agree on a method to sample bits from the random bit streams, use these bits to generate a key for a one time pad
- Attacker Eve cannot decrypt because by the time she knows about the message the stream has disappeared

## Wednesday, September 11, 2013

### Notes - One-Time Pads

The following are notes from Introduction to Cryptography with Coding Theory.

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