RSA Algorithm for Signing Messages: Explained | CCIE Security Exam

# RSA Algorithm for Signing Messages

### Question

When the RSA algorithm is used for signing a message from Alice to Bob, which statement best describes that operation?

### Explanations

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A. B. C. D. E. F.

A.

The correct answer is F: Alice signs the message with her private key, and Bob verifies that signature with his public key.

The RSA algorithm is a widely used public-key cryptographic algorithm that can be used for encryption, decryption, and digital signature generation. In the case of signing a message from Alice to Bob, the following steps occur:

1. Alice generates a pair of public and private keys using the RSA algorithm. The public key is made available to anyone who wants to send her a message, while the private key is kept secret.

2. Alice signs the message with her private key. To do this, she applies a mathematical function to the message that produces a unique digital signature.

3. Alice sends the message and digital signature to Bob.

4. Bob receives the message and digital signature and uses Alice's public key to verify the signature. He applies a mathematical function to the message and the signature using Alice's public key, and if the result matches the original message, he knows that the signature is authentic and that the message came from Alice.

The reason why Alice uses her private key to sign the message is that only she should have access to her private key. If she used her public key to sign the message, anyone could verify the signature with her public key, and the signature would not provide any assurance that the message came from Alice.

Therefore, the correct answer is F: Alice signs the message with her private key, and Bob verifies that signature with his public key.