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Short note: Digital signature

Short answer

A digital signature provides authentication, integrity, and non-repudiation by hashing the message and encrypting the digest with the sender's private key. The receiver verifies by decrypting with the sender's public key and comparing with a fresh hash of the received message. Algorithms include RSA, DSA, and ECDSA. Digital certificates bind public keys to identities. Signing does not provide confidentiality; the message can be encrypted separately.

Write a short note on Digital signature.

A digital signature is the electronic equivalent of a handwritten signature. It is a value created from a message and the signer's private key, which allows anyone to verify, with the signer's public key, that the message came from the signer and was not changed.

Services provided

Authentication (identity of signer), message integrity, and non-repudiation (signer cannot deny).

Working (hash then sign)

Sender:  M --hash--> H(M) --encrypt with sender's private key--> signature S
         send M + S
Receiver: decrypt S with sender's public key -> H1
          hash received M -> H2
          H1 == H2 ?  valid : rejected
  1. The sender computes the message digest with a hash function (SHA-256).
  2. The digest is encrypted with the sender's private key; this is the signature.
  3. The message and signature are sent.
  4. The receiver decrypts the signature with the sender's public key and compares it with a fresh hash of the received message. If they match, the signature is valid.

Signing the short digest is faster than signing the full message. Algorithms: RSA, DSA (DSS), ECDSA. A digital certificate (X.509) issued by a certification authority binds a public key to its owner. Signing alone does not give confidentiality; the message can also be encrypted.

✓ Answer checked by Claude Opus 5.5 (high effort)

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