Hash functions are used to produce the message digests which are then encrypted with a private key to get:

The correct answer is Digital signature

Key Points

• Digital Signature:
  • ​A digital signature is a cryptographic technique used to ensure the authenticity and integrity of a message or document.
  • It involves taking a hash (message digest) of the content and encrypting it with the sender's private key.
  • The recipient can use the sender's public key to decrypt the signature and verify that the message hasn't been tampered with and was indeed signed by the sender.

Additional Information

• Public Key: In public-key cryptography, there are two keys: a public key and a private key. The public key is used for encryption and is shared with others, while the private key is kept secret and used for decryption. Messages encrypted with the public key can only be decrypted by the corresponding private key. However, the process you described doesn't directly involve producing public keys from message digests.
• Cipher Text: Cipher text is the output of the encryption process. When you encrypt a message, it turns into cipher text, which is the unreadable form of the original message. This process typically involves using a symmetric or asymmetric key algorithm to transform the message into a secure, coded format.
• Data Encryption Standard (DES): DES is a symmetric-key algorithm for data encryption. It uses a single key for both encryption and decryption. The process involves multiple rounds of permutation and substitution. While DES is a classic encryption algorithm, it's considered outdated and has been largely replaced by more secure algorithms like AES (Advanced Encryption Standard).