Riley sent a secret message to Louis. Before sending the message, Riley digitally signed the message using his private key. Louis received the message, verified the digital signature using the corresponding key to ensure that the message was not tampered during transit. Which of the following keys did Louis use to verify the digital signature in the above scenario?

In asymmetric (public-key) cryptography, digital signatures are utilized to provide non-repudiation, authenticity, and integrity. The sender (Riley) creates the digital signature by hashing the message and encrypting that hash with their own private key. To verify the authenticity and integrity of the message, the recipient (Louis) must decrypt the signature using the sender's corresponding public key (Riley's public key). If the decryption is successful and the resulting hash matches the hash of the received message, it mathematically proves that the message originated from Riley and was not tampered with during transit.

B. Louis's public key: The recipient's public key is used by a sender to encrypt a confidential message intended for the recipient, not to verify a digital signature created by the sender.
C. Riley's private key: A private key is kept strictly secret by its owner (Riley) and is never shared with or used by the recipient (Louis) for signature verification.
D. Louis's private key: The recipient's private key is used to decrypt confidential messages sent to them, not to verify the sender's digital signature.

1. NIST FIPS 186-4, "Digital Signature Standard (DSS)," Section 4 (Digital Signature Algorithm).

2. EC-Council Certified Cybersecurity Technician (CCT) Official Courseware, Module: Cryptography.