It's admittedly a very general question, but I've heard "Whisper" mentioned in several places when reading about certain DApps.

I understand it allows peer-to-peer messaging of some kind, but what are the purposes of these messages, and who is it that they're passing between? Is it a way for DApps or contracts to communicate, or something else?

up vote 35 down vote accepted

Whisper is a part of the Ethereum P2P protocol suite that allows for messaging between users via the same network that the blockchain runs on.

There are many uses, some of which are listed on the wiki

The protocol is seperate from the blockchain, so smart contracts do not have access.

Whisper has existed in a sort of alpha, working-prototype state for some time now. It can be enabled by using the -shh flag in geth, but nodes do not relay the messages by default, so chances are that messages won't get through unless you are directly connected to the recipient. API documentation can be found on github.

  • Is this statement still true: "nodes do not relay messages... chances are that messages won't get through unless directly connected" ? – Saad Malik Jul 6 at 2:35
  • Whisper is still not turned on by default, AFAIK, but enough nodes may hev it enabled that it is practical to use. You'd have to test it out and/or ask in gitter.im/ethereum/whisper – Tjaden Hess Jul 6 at 16:46

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