Reference no: EM133397725

Question

Alice wants to send an email saying "I have job openings." to Bob, with a digital signature of the hash of the message. The hash function that Alice uses is SHA-256, which generates a fixed size 256-bit (32-byte) hash. Alice uses her own private key for the signature. Bob has the corresponding public key. The key pair is a 2048-bit RSA key. Charlie is Alice's secretary, and is malicious. Charlie wants to change the message to "I do not have job openings" while fooling Bob into believing that's what Alice said.

Alice writes an email and ask Charlie to edit it. Charlie sends the edited email to Alice for final approval. Alice then computes the hash of the approved email and signs the hash. Then Alice gives the signature to Charlie, and asks him to send the email with the signature to Bob. What does Charlie need to do to have more than a 50% chance of succeeding in fooling Bob into believing that Alice's message is that she does not have job openings? (you do not need to produce a concrete number).