Question

Suppose you receive a digital certificate that contains M and [h(M)]_CA , where M = (Alice, Alice's public key) and "CA" is a Certificate Authority.

How do you verify the Signature?

Remember that:

[X]_Bob indicates encryption via Bob's private key to X (signature)

h(X) indicates the cryptographic hash function applied to X

Group of answer choices

You decrypt the encrypted message using the CA's public key, then you compute the hash of [h(M)]_CA, finally you compare the two hashes

You decrypt the encrypted message using the CA's private key, then you compute the hash of [h(M)]_CA, finally you compare the two hashes

You decrypt the encrypted message using the CA's private key, then you compute the hash of M, finally you compare the two hashes

You decrypt the encrypted message using the CA's public key, then you compute the hash of M, finally you compare the two hashes

Answer 1

ans) the correct answer is the last one ---------- " You decrypt the encrypted message using the CA's public key, then you compute the hash of M, finally you compare the two hashes "

Explanation :

the steps of working : digital signature [ from alice to bob ]

1. Alice first creates a digest of the message, if the message is changed then digest is different ( hashing )

( digest is another name for HASHING made on input message )

2. Encrypts the digest/hash with her private key. now this encrypted digest act as a digital signature

3. Encrypted digest is send towards BOB along with the message ( append with message ).

4. At the receiver side, Bob receives the message, and decrypt the message digest using ALICE public key

5. Bob also creates a digest for the message using the same function as alice used before. ( h(M) )

6. Now compare the both digest ( of ALICE AND BOB ), If the digests match, then bob can assure that it comes securely from alice, and not tampered or modified by anyone else.