Digital signature

Digital signatures are used to ensure the authenticity of message received. It uses asymmetric encryption.

Sender:

1. The message to be send is put through a hash function to produce a digest.

A message digest is a numeric representation of the content of a message

1. The digest is encrypted with sender's private key to create the digital signature
2. The message and the encrypted digest are sent to the recipient

Recipient:

1. The received encrypted digest is decrypted with sender's public key.
2. The received message is put through the hash algorithm to get a digest
3. The decrypted digest is compared to the recalculated digest
4. If they are the same, the identity of the sender of this message is verified.

About hash function:

1. One-way: it is impossible to revers the function, i.e., it is impossible to get the original message from the digest
2. No same digest for 2 different messages