Public key encryption using Hash digest
Combining hashes with public key cryptography.
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Public key encryption with hash digest and digital signature
Sender hashes message, encrypts with recipient's public key, then signs with sender's private key.
To add authentication, nonrepudiation, and integrity to public key encryption, the sender first applies a hash function to the message to produce a fixed-length message digest. The sender then encrypts the digest and original message using the recipient's public key. Finally, the sender encrypts the result one more time using his or her own private key, producing a digital signature. The recipient authenticates with the sender's public key, decrypts with his or her private key, and re-applies the hash function to verify the message has not been altered.
Explanation: To add authentication, nonrepudiation, and integrity to public key encryption, the sender first applies a hash function to the message to produce a fixed-length message digest. The sender then encrypts the digest and original message using the recipient's public key. Finally, the sender encrypts the result one more time using his or her own private key, producing a digital signature. The recipient authenticates with the sender's public key, decrypts with his or her private key, and re-applies the hash function to verify the message has not been altered.