Digital Signature

• Digital Signature (Recap)

  Symmetric: owners of a shared key can decrypt/encrypt with the same key

  Asymmetric: the mathematically related keys used to decrypt/encrypt
• Security Services

  • Data confidentiality
  • Data integrity
  • Anti-replay
  • Authentication
  • Non-repudiation
• Data confidentiality


  Ensures that nobody else except A and B can view/read the data
• Data integrity


  Ensures that the message is not changed in the way
• Authentication


  Ensures the identity of the other person
• Non-repudiation


  Proof of origin

  Proof of delivery
• Public Key Cryptography


  Sender can use their private key or receiver's public key to encrypt/decrypt
• Digital Signature


  Signing: Encryption with Private Key

  Verifying: Decryption with Public Key
• Key Generation


  • Choose 2 prime numbers p and q

  Choose integer e that is relative prime to (p-1)(q-1): Public Key PU = {e, pq}

  Find d, such that de = 1 mod (p-1)(q-1): Private Key PR = {d, pq}
• Digital Signature Process


  Alice Signing Algorithm

  Message and Signature

  Verifying Bob Algorithm
• Signing/Verifying using key in digital signature process: