Friday, December 14, 2012

How Digital Signatures Work

Similarly to handwritten signatures, digital signatures ensure the authenticity of a message.

Authenticity is concerned with 2 aspects:
  1. The message was sent by the actual sender (not an imposter).
  2. Message was not altered after sender sent it.
Usually, to achieve this, a hash value (which is also called a 'digest') will be computed using a hashing algorithm (e.g. SHA-1) and then this value will be encrypted using the senders private key (this talks about encryption). Resulting value will be sent along with the message.

When this message is received by the intended party, they will try to decrypt it with the senders public key (which was transmitted to the receiver beforehand). If the decryption is successful it indicates that the message was from the actual sender...not by an imposter!

Then the receiving party will calculate the hash value of the message using the same hashing algorithm used by the sender. If the computed value and the value sent encrypted by the private key is equal, it ensures that the message wasn't altered en route.

Ref:
[1] http://computer.howstuffworks.com/digital-signature.htm
[2] http://www.productivity501.com/digital-signatures-encryption/4710/

1 comment:

Tee Chess said...

PDF signature
You have explained the complete process of how digital signature works in a very simple way. With the help of this article I have also understood how all the things work out. Thanks.