Add API commands to sign & verify arbitrary messages

[dariuskramer]

Fixes #1496

End to End tests

Sign by -> Verified by

• Eclair -> Eclair
• Eclair -> Lnd
• Eclair -> C-lightning
• Lnd -> Eclair
• C-lightning -> Eclair

How to use the signmessage command

$> eclair-cli signmessage --msg=$(echo -n 'hello, world' | base64)
{
  "nodeId": "02ca7361934233f6d4defd4d792fb2ce2cd0b50c7605e6c5cd16006bcd5be2bf70",
  "message": "aGVsbG8gd29ybGQK",
  "signature": "1f730dce842c31b692dc041c2d0f00423d2a2a67b0c63c1a905d500f09652a5b1a036763a1603333fa589ae92d1f7963428ff170e976d0966a113f4b9f9d0efc7f"
}

How to use the verifymessage command

$> eclair-clir verifymessage --msg=$(echo -n 'hello, world' | base64) --sig=1f730dce842c31b692dc041c2d0f00423d2a2a67b0c63c1a905d500f09652a5b1a036763a1603333fa589ae92d1f7963428ff170e976d0966a113f4b9f9d0efc7f
{
  "valid": true,
  "publicKey": "02ca7361934233f6d4defd4d792fb2ce2cd0b50c7605e6c5cd16006bcd5be2bf70"
}

Signature format conversion

The signature we return are in hexadecimal format. Lnd & C-lightning use a zbase32 format. To convert from and to zbase32 you can use zbase32 and some basics Unix tools.

Hexadecimal to zbase32

echo -n "${eclair_signature}" | xxd -revert -plain | zbase32-encode

zbase32 to Hexadecimal

zbase32-decode "${zbase32_signature}" | xxd -cols 256 -plain

Message format

We expect the msg argument, for both commands, to be a valid base64 string, to avoid issues with charset and encoding:

$> eclair-cli signmessage --msg=0123456789-invalid
The form field 'msg' was malformed:
Invalid base 64 character '-' at index 10

[t-bast]

LGTM! 🚀