posts-go/posts/2023-08-23-real-world-crypto.md

Real World Crypto 101

My notes when reading Real-World Cryptography

Hash function convert from input to digest:

• Pre-image resistance: Given digest, can not find input
• Second pre-image resistance: Given input, digest, can not find another input produce same digest. Small change to input make digest big change.
• Collision resistance: Can not find 2 input produce same digest.

MAC aka Message Authentication Code produce from key, message to authentication tag. HMAC is MAC using hash.

• A send B message with MAC (generate from message and A key).
• B double check message with MAC (generate from receive message and B key).
• A and B use same key.

sequenceDiagram
    participant alice
    participant bob

    alice ->> bob: send username, password
    bob -->> alice: return alice|mac(private_key, alice)
    alice ->> bob: send alice|mac(private_key, alice)
    bob -->> alice: return OK
    alice ->> bob: send bob|mac(private_key, alice)
    bob -->> alice: return ERROR