A Survey of Key Technologies for Constructing Network Covert Channel

Table 6

Blockchain-based covert communication systems.

	Zombiecoin [10]	Botchain [29]	Chainchannels [30]
Message embedding method	Directly embedded	Directly embedded	Subliminal channel
The field to embed messages	OP_RETURN	OP_RETURN	Digital signature
Label embedding method	Directly embedded	Directly embedded	Directly embedded
The field to embed labels	Public key	Wallet addresses	Public key
Platform^†	Bitcoin only	Bitcoin only	All blockchain networks

^†The virtual currency the system is suitable for.