The term was introduced by Adam Young and Moti Yung in the Proceedings of Advances in Cryptology – Crypto '96.
[1] Kleptography is a subfield of cryptovirology and is a natural extension of the theory of subliminal channels that was pioneered by Gus Simmons while at Sandia National Laboratory.
This is reminiscent of, but not the same as steganography that studies covert communications through graphics, video, digital audio data, and so forth.
In this case, even if the reverse engineer was well-funded and gained complete knowledge of the backdoor, it would remain useless for them to extract the plaintext without the attacker's private key.
[13] The algebraic nature of the attack follows the structure of the repeated Dlog Kleptogram in the work of Young and Yung.