One-Time Pad | (Vernam Cipher) :)
The One-Time Pad
is one of the very few that can be mathematically proven secure encryption method !
• The security of almost ALL other procedures is based on unproven assumptions
• How does the one-time pad work:
The message is linked to a key using XOR that is just as long like the message is
- The key must be formed from real random values
- Each key may only be used once
• If one of these three requirements is violated, the one- time pad is no more safe
Example: let the plaintext P and key K each be a bit sequence of length n: P, K∈ {0,1} n
Then the ciphertext C is calculated using C = P ⊕ K.
What happens if the key K is used multiple times:
Obviously,for C1 = P1 ⊕ K and C2 = P2 ⊕ K:
C1 ⊕ C2 = P1 ⊕ K ⊕ P2 ⊕ K = P1 ⊕P2 ⊕ K ⊕K = P1 ⊕P2
If P1 and P2 are voice messages, both can largely be restored.
This is even possible (with restrictions) for more than two superpositions P1⊕ P2 ⊕ P3⊕ …
The decisive factor here is the entropy of the pi.
