Question at position 1 Alice signs a file before sending it to Kali. What is the main purpose of this process?To change file ownershipTo encrypt the file with a stronger cipherTo reduce file sizeTo ensure file authenticity and integrityClear my selection

Question

Question at position 1 Alice signs a file before sending it to Kali. What is the main purpose of this process?To change file ownershipTo encrypt the file with a stronger cipherTo reduce file sizeTo ensure file authenticity and integrityClear my selection

BlackTom AI · Accepted Answer

Digital signing uses the sender’s private key to produce a small cryptographic value tied to the file’s content, so the correct purpose is to ensure the file’s authenticity and integrity.

1) Relevant knowledge points and concepts
- Digital signature: a cryptographic operation that binds a signer’s identity (private key) to specific data.
- Hash function: produces a fixed-size digest representing file content; tiny changes in the file change the hash.
- Public/private key pair: private key signs, public key verifies.
- Authenticity: the receiver can be confident who created or signed the file.
- Integrity: the receiver can be confident the file wasn’t altered in transit.

2) Step-by-step reasoning process
- Step 1: Sender computes a cryptographic hash H = HASH(file). This condenses the file into a fixed-length digest.
- Step 2: Sender uses their private key to compute the signature S = Sign_private(H) (using RSA, ECDSA, etc.).
- Step 3: Sender transmits the file together with S (or attaches S to a message).
- Step 4: Receiver computes H’ = HASH(received file).
- Step 5: Receiver uses sender’s public key to verify the signature: Verify_public(S, H’). If verification succeeds, H’ matches the original H and the signer’s private key produced S.
- Conclusion from steps: successful verification proves the file came from the claimed signer (authenticity) and that the contents were not changed (integrity).

3) Intermediate details
- Hashing is deterministic; tiny file changes yield a different hash.
- Signature verification uses public-key math; only the private key could have produced a valid signature for that hash.
- The process does not encrypt file contents—signature is separate from confidentiality.

4) Why the correct answer is correct
Because signing binds the sender’s identity to the file’s content and allows the receiver to detect any tampering, ensuring both authenticity and integrity.

5) Why other options are incorrect
- Change file ownership: signing does not modify ownership metadata; it only attests origin.
- Encrypt with stronger cipher: encryption hides contents; signing does not encrypt (though you can sign then encrypt).
- Reduce file size: signing typically adds a signature, so it does not reduce size.

Final confirmation: The correct answer is "To ensure file authenticity and integrity," matching the provided answer.

Question at position 1 Alice signs a file before sending it to Kali. What is the main purpose of this process?To change file ownershipTo encrypt the file with a stronger cipherTo reduce file sizeTo ensure file authenticity and integrityClear my selection单项选择题

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