A method that returns the message being signed

[tian000]

Expose a public method that returns the message being signed - so that users can verify the signature.

This method would look like

createPrefixedMessage(message, messagePrefix) {
  messagePrefix = messagePrefix || '\u0018Bitcoin Signed Message:\n'
  if (!Buffer.isBuffer(messagePrefix)) {
    messagePrefix = Buffer.from(messagePrefix, 'utf8')
  }
  if (!Buffer.isBuffer(message)) {
    message = Buffer.from(message, 'utf8')
  }
  const messageVISize = varuint.encodingLength(message.length)
  const buffer = Buffer.allocUnsafe(
    messagePrefix.length + messageVISize + message.length
  )
  messagePrefix.copy(buffer, 0)
  varuint.encode(message.length, buffer, messagePrefix.length)
  message.copy(buffer, messagePrefix.length + messageVISize)
  return message;
}

[junderw]

The message format is an implementation detail and not standardized, so it is inappropriate to expose it from the public interface.

[tian000]

How can I verify the message using my own cryptography libraries if I don't have access to the raw message that this library is signing?

[junderw]

In general, you have two options that you could choose from, one being focused on your individual app, and the other is focused on the public API of this library:

1. Fork the library to expose the internals for your individual use case. (Probably easiest for you, since it doesn't involve consideration for the public API exposed to 40k weekly downloads.)
2. Make the crypto parts modular. (ie. the library returns a class that needs to be constructed with a crypto library with a specific interface that is used within the code) (This is probably harder, will require a lot of review, and will require a major version increment before publishing)

[junderw]

I would recommend the first option... since Bitcoin Core has removed the signing and verifying functions that this library is based on... so we should really deprecate this library and halt its maintenance.

See #39

[tian000]

Got it! Thank you for the insights - I made a fork for my use-case here: https://github.com/bitcoinjs/bitcoinjs-message/compare/master...phantom:bitcoinjs-message:master