1. A method for generating a key-specific decryption engine, the method comprising: providing, to a sending computer, a reference implementation of a decryption engine configured to perform a decryption operation of a symmetric cryptographic technique, the reference implementation of the decryption engine configured to accept a symmetric key as a first input and an encrypted message as a second input, wherein the encrypted message is an encrypted version of an original message that was previously encrypted using the symmetric key; determining, by the sending computer using the reference implementation, expected outputs corresponding to different values specified for the second input, wherein the expected outputs include the original message that corresponds to the encrypted message as a corresponding one of the different values; determining, by the sending computer, one or more boolean functions configured for generating the expected outputs including the original message based on the symmetric key as the first input and the different values including the encrypted message as the second input; generating, by the sending computer and based on the determinings, the key-specific decryption engine including the one or more boolean functions; and providing, by the sending computer to a receiving computer, the generated key-specific decryption engine, wherein the receiving computer including the provided key-specific decryption engine is configured for decrypting the encrypted message without requiring the symmetric key as an input to the provided key-specific decryption engine for the decrypting.