What Is Whisper?
Also known as: Whisper Protocol, shh
In short
Whisper is a peer-to-peer (P2P) communication protocol designed in Ethereum's early days to let decentralized applications message each other with a focus on privacy. It fell out of use over time and was succeeded by protocols such as Waku.
In Ethereum's original vision, the decentralized web was built on three core components: the Ethereum blockchain for computation and state, Swarm for file storage and Whisper for messaging. Whisper ran on the devp2p network layer used by Ethereum nodes and delivered messages by broadcasting them among peers in the network without writing them to the blockchain. This way, messaging required no transaction fees and left no permanent record on-chain.
To hide the sender and recipient, the protocol distributed encrypted messages to a wide network using topic tags, and it required a small proof of work computation on each message to limit unwanted message load. However, this design struggled to scale; spreading messages to many nodes required high bandwidth. The Status messaging app, one of the few projects that used Whisper in practice, developed the protocol further and created Waku.
Support for Whisper was eventually removed from major Ethereum clients such as Geth. Today, the term is mostly mentioned in the context of Ethereum's history and the development of decentralized messaging protocols; it is not used in new applications.
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