25/09/2019
How does a Digital Signature Work?
Digital signatures are based on Public Key infrastructure. By this mechanism, two keys are generated, a Public Key and Private Key. The private key is kept by the signer and it should be kept securely. On the other hand, the receiver must have the public key to decrypt the message.
For example, a person named Charlie wants to send an encrypted message to Lisbon. As stated above, Charlie must have a private key to sign the message digitally.
Before encrypting the message using the private key, an algorithm named ‘MD algorithm’ encrypts the message to be sent by Charlie into a 128/256-bit format known as a hash value. Then Charlie’s private key encrypts this hash value. On completion of both the processes, Charlie’s message is said to be digitally signed.
On the side of Lisbon, the digitally signed message is decrypted with the help of the signer’s public key. The public key decrypts the message and converts it into another hash value. Then the program which is used to open the message (e.g., MS Word, Adobe Reader etc.) compares this hash value to the original hash value which was generated on Charlie’s side. If the hash value on Lisbon’s side matches with the hash value generated on Charlie’s side, then the program will allow the message to open up and displays the message “The document has not been modified since this signature was applied.” The program will not allow the document to open if both the hash values don’t match.
