Ensuring Digital Signature Lawfulness for Applications

How to eSign a document: digital signature lawfulness for applications

the whole concept of digital signature is something like the signature that we use in our day-to-day life as you know signature provides some level of assurance of signers identity so digital signature provides the highest level of assurance of assigners identity in previous video i talked about asymmetric encryption algorithm and i said we have a pair of keys so if you use one key for encryption then you need to use the other key for decryption now these keys have names we have private key and public key so when a person wants to use asymmetric algorithm that person generates a pair of key and these pair of keys are basically private and public keys the private one remains with the person who generated the key and the public one can be shared with the public let's say alice has a pair of public and private key and she wants to exchange some data with bob so she provides bob with her public key and asks bob to encrypt the message using her public key and send it back to her so bob has a clear takes a plain text and he uses alice's public key encrypts the message and then forwards it to alice now this message that has been encrypted with alice's public key can only be decrypted with alice's private key remember i said if you encrypt the message with one key you can decrypt it with the other key only and not any other keys so even if the whole crowd has the alice's public key they cannot decrypt the message that was encrypted with alice's public key so alice is the only one who has the private key she can decrypt her message using her private key and see the content of the message now what if alice encrypt the message using her private key so when she encrypts the message using her private key and forwards it to bob who can decrypt that message well bob can use alice's public key and decrypt the crypto message so can the rest of the public so what's the point of encrypting that message if everyone can decrypt that message and see the content of the message if someone encrypt a message using their private key the whole concern is not the confidentiality of the message so the concern is not really encrypting the message so that no one can see the message the concern is to make sure the message came from that person from the right person so in this case if bob asked alex to encrypt the message using alice's private key that means bob doesn't really care that anybody sees the content of the message what he cares here is that the message came from alice and no one else the whole concept is something like when you sign a check and you give it someone to take it to the bank and cash it bank doesn't really care how many people have seen that check and the content of the check and how much the value of that check is what they care is that the signature on the check matches the signature that they have on their file and if those signatures match then the bank says okay the right person signed this this check so when alice encrypts a message using her private key the only key that can decrypt that message is alice's public key so if bob can decrypt the message then bob knows that that message came from alice for sure now if tom who is a bad guy decides that to get his hand on the message and decrypt the message using alice's public key and see the content of the message and change the message then when he encrypt the message using any key including alice's public key and forwards it to bob then bob cannot open that message using alice's public key because that message was not encrypted by alice's private key so in this case bob knows that oh this message has been tampered with or this message didn't come from alice so bob knows that the real sender of the message is not alice and then he gets rid of the message so that's the concept of digital signature meaning encrypting a message using someone's private key and sending it out and asking someone else to decrypt it using that person's public key now we have an algorithm which is digital signature algorithm but that's the topic of another lesson but for now i just want you to understand the concept of digital signature all right that's it for now and i'll see you in another video