A method includes receiving a first message that includes a first relational key element based on a first group element, and a second relational key element based on the first group element and raised to the power of a first plaintext value. The method also includes receiving a second message that includes a third relational key element based on a second group element, and a fourth relational key element based on the second group element and raised to the power of a second plaintext value. The method additionally includes comparing the first message to the second message without decryption of the first or second messages and, based on the comparison, determining that the first plaintext value and the second plaintext value are the same.