How does a digital signature works?

Hi moonflash,

This is what i know about digital signatures.

First of all as you must be knowing that digital signatures are used when you want that person who send you some message can't say that he has not sent that message.It is normally used to sign important documents.

How does it work ? ( i suppose it is based on working of assymetric key cryptography where algorithm is public & uses two keys encryption key which is public & decryption key which is private)

So first of all md5 hash value of our orignal document is calculated than we calculate D(md5) at sender site here D is the private decryption key that only sender know & public encryption/decryption algorithm.

Now whole document and the D(md5) value is sent to reciever.

At recievers site.

Reciever again calculates md5 hash value of document which will be same if document is recieved without any error.

Now reciever calculates E(D(md5)) i.e use public encryption key of sender & use it for encryption of D(md5) send by sender now as encryption & decryption operations are reverse process. the value that we get after E(D(md5)) should be again plain md5.

Now this md5 value is compared with the md5 value calculated previously on recieved document so if both match than we can say that given sender has only sent the message conditioned that no one know's his privated decryption key.

please correct me if i am wrong.

Hi faizaan,

thanks for your information. It makes me clear what a digital signature is. if possible give me some links regarding which makes me clear with the concept with diagrams.

Can someone explain the same in layman's language?