Public key operations

• private key is used for signing = the transferred content is unchanged
• public key encryption = the content is encrypted
• creating signature is slow - can be sped up by using hash function
  • instead of signing the whole message only the hash of the message is used for signing

Message authentication code (MAC)

• integrity and authentication
• hard to bruteforce correct tag

HMAC

• RFC2014

• HMAC_k = Hash[(K+ XOR opad) ++ Hash[(K+ XOR ipad) ++ M]]

• overhead only 3 hashes

• use different keys for encryption and authentication!

  • Law get request decryption of message that was sent to us