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Digital Signatures

Overview​

Digital signatures make use of public key cryptography to provide a way for the recipient to verify the authenticity of a document.

Anyone with muy public key can quickly verify that I did indeed sign a message.

They satisfy three useful claims:

  1. Authenticity: This could've only been signed by the sender.
  2. Integrity: This data wasn't forged or tampered with.
  3. Non-repudiation: The sender can't deny having sent the data.

Digitally signing a document​

  1. Unencrypted plaintext data is hashed (prevents tampering).
  2. The hash is encrypted using the private key.
  3. We attach (concatenate) the encrypted hash to the data.

Verifying the authenticity of a document​

  1. Remove signature from document
  2. Hash the document, get hash h.
  3. Decrypt signature using signer's public key.
  4. Verify that the hash h matches the decrypted signature.