Which is the correct process for Non-Repudiation?

Question

BlackTom AI · Accepted Answer

Non-repudiation is achieved by the sender digitally signing a message with their private key so that anyone can verify the signature with the sender’s public key, proving the sender cannot later deny having sent it.

1) Relevant knowledge points and concepts
- Hash function: produces a fixed-size digest H = Hash(data) that detects any change to the data.  
- Asymmetric keys: sender has a private key (kept secret) and a public key (widely known).  
- Digital signature: created by encrypting the hash (and optionally sender details) with the sender’s private key. Verification is done by decrypting that signature with the sender’s public key.  
- Non-repudiation: because only the sender has the private key, a valid signature proves authorship.

2) Step-by-step reasoning process
- Sender computes H = Hash(data).  
- Sender constructs a signature block Sig = Encrypt_privateSender(H || sender_details). This binds the hash and identity data to the sender.  
- Sender transmits the data and Sig to the receiver.  
- Receiver computes H' = Hash(received_data).  
- Receiver decrypts Sig using the sender’s public key: Decrypt_publicSender(Sig) → (H_dec || sender_details_dec).  
- Compare H' to H_dec and verify sender_details_dec. If they match, the data is intact and signed by the sender.

3) Intermediate symbolic steps
- H = Hash(data)  
- Sig = PrivSender_encrypt(H || details)  
- H' = Hash(received_data)  
- Decrypt_public(Sig) = H_dec || details_dec  
- Check: H' ?= H_dec and details_dec == expected_sender

4) Why the correct answer is correct
Encrypting the hash with the sender’s private key creates a signature that anyone can verify with the sender’s public key, proving origin and integrity. Hashing prevents signing large messages directly and ensures tamper detection.

5) Why other options are incorrect
- Encrypting with the sender’s public key: public key encryption does not provide non-repudiation because anyone can encrypt with the public key and it does not prove the sender’s authorship.  
- Using receiver’s keys (public or private): these bind the message to the receiver, not the sender, so they don’t prove sender origin.  
- Using a shared symmetric key: both parties share the key so either could have generated the MAC/signature; it cannot provide non-repudiation.

6) Conclusion
The described process (hash, sign with sender’s private key, receiver hash, verify with sender’s public key, compare) is correct for non-repudiation and matches the provided answer.

Which is the correct process for Non-Repudiation? 单项选择题

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