A digital signature is a mathematical function that can demonstrate that a digital message or file is authentic or from a particular person.
- Alice selects the file to be digitally signed or clicks on ‘sign’ in her email application
- The hash value of the file content or the message is calculated by Alice’s computer
- This hash value is encrypted with Alice’s Signing Key (which is a Private Key) to create the Digital Signature.
- Now, the original file or email message along with its Digital Signature are sent to Bob.
- After Bob receives the signed message, the associated application (such as email application) identifies that the message has been signed. Bob’s computer then proceeds to:
- Decrypt the Digital Signature using Alice’s Public Key
- Calculate the hash of the original message
- Compare the (a) hash it has computed from the received message with the (b) decrypted hash received with Alice’s message.
- Any difference in the hash values would reveal tampering of the message
Digital signatures are very handy for sending encrypted messages that prove a person’s ownership of a message or identity.