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How to test digital signature

hello this is Sun welcome back today my topic is digital signature a [Music] detail signature is equivalent to a handwritten signature it is an electronic verification of the sender a digital signature serves three purposes one authentication a digital signature gives the receiver reason to believe the message was created and assigned by the claimed sender two now repudiation with a digital signature the center cannot deny having sent the message later on three integrity a digital signature ensures that the message was not altered intended digital signatures are commonly used for software distribution financial transaction and other kisses with important detect forgery and a temporary digital signatures are very popular with email users let me demonstrate how digital signature works here is the scenario Bob is ascending a memo to Alice with his digital signature keep in mind digital signature uses a symmetric cryptography which means public key algorithm is employed first Bob generates two kids public key and a private key Bob keeps the private key and give Alice the receiver the public key after creating a memo Bob generates a digest by a hash in his mammal using some hash on rhythm table then encrypts the digest with his primary key this encrypted digest is the digital signature for the mammal Bob sends both of the memo and a digital signature to Alice notice here the memo is not encrypted we only focus on digital signature we Alice receives them she will do two things one Alice decrypts the digital signature using Bob's public key and she gets a digest if she cannot decrypt the digital signature then she knows it did not come from Bob because only Bob's public key is able to decrypt the digests generated with his primary key - once Alice gets the digest she will check the integrity of the memo here is what she does Alice hashes the memo with the same hash algorithm Bob used and computes the result to the digest she received if the are equal Alice can be confident that the memo has not changed since Bob signed the memo if the digest are not equal Alice will know the memo has changed in transit last I want to point out one common confusion about the digital signature using digital signature does not equipped the message itself in this example both is ascending in the plaintiffs mammal to Alice if he wanted to encrypt his memo he would have to use Alice's public key which is another story in another video thank you very much and see you next time [Music]