The first recorded use of the term was in by Johannes Trithemius in his Steganographia , a treatise on cryptography and steganography, disguised as a book on magic. Generally, the hidden messages appear to be or to be part of something else: images, articles, shopping lists, or some other cover text. For example, the hidden message may be in invisible ink between the visible lines of a private letter. Some implementations of steganography that lack a shared secret are forms of security through obscurity , and key-dependent steganographic schemes adhere to Kerckhoffs's principle.
Trust on first use
Bellare - Research papers in cryptography
Trust on first use TOFU , or trust upon first use TUFU , is an authentication scheme  used by client software which needs to establish a trust relationship with an unknown or not-yet-trusted endpoint. In a TOFU model, the client will try to look up the endpoint's identifier, usually either the public identity key of the endpoint, or the fingerprint of said identity key, in its local trust database. If no identifier exists yet for the endpoint, the client software will either prompt the user to confirm they have verified the purported identifier is authentic, or if manual verification is not assumed to be possible in the protocol, the client will simply trust the identifier which was given and record the trust relationship into its trust database. If in a subsequent connection a different identifier is received from the opposing endpoint, the client software will consider it to be untrusted. In the SSH protocol, most client software though not all  will, upon connecting to a not-yet-trusted server, display the server's public key fingerprint, and prompt the user to verify they have indeed authenticated it using an authenticated channel. The client will then record the trust relationship into its trust database.
Kobalos – A complex Linux threat to high performance computing infrastructure
SSH Secure Shell is a network protocol that allows users to remotely login to a computer in order to perform tasks such as executing commands and transferring files. It was designed in as a means to replace less secure protocols like rlogin and telnet. SSH addresses this issue by encrypting traffic sent.
ESET researchers have analyzed malware that has been targeting high performance computing HPC clusters, among other high-profile targets. We have named this malware Kobalos for its tiny code size and many tricks; in Greek mythology, a Kobalos is a small, mischievous creature. Perhaps unrelated to the events involving Kobalos, there were multiple security incidents involving HPC clusters in the past year. Press articles also mention Archer, a breached UK-based supercomputer where SSH credentials were stolen, but do not contain details about which malware was used, if any.