What type of encryption should a security analyst use to ensure message authenticity?

To ensure message authenticity, the most suitable encryption method is asymmetric encryption. This type of encryption utilizes a pair of keys: a public key and a private key. The sender can use the private key to sign a message, creating a digital signature that verifies both the message's origin and integrity. Anyone with access to the corresponding public key can easily verify this signature, thus confirming that the message was indeed sent by the holder of the private key and has not been altered in transit.

Asymmetric encryption is particularly valuable in scenarios where secure key exchange and verification of identity are critical, such as in email communications or secure web transactions. This method allows for strong authentication mechanisms and ensures that messages are not only confidential but also authentic and unaltered.

In contrast, symmetric encryption uses a single key for both encryption and decryption, which does not provide the means to verify the origin of a message since anyone with the key can decrypt it. Small-scale encryption is not a standard term used in the context of encryption types, and while hashing is useful for integrity checks, it does not provide confidentiality or authenticity since it does not involve encryption keys. Therefore, asymmetric encryption is the key choice for ensuring message authenticity in secure communications.