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opmsg contrib

This document covers opcoin. For opmux please refer to the MUA chapter inside the main README.md.

This is experimental stuff for experts. If you just want to send/receive encrypted messages, refer to the README. opcoins are not necessary to do that.

opcoin

Note: Do not use BTC addresses where you hold a lot of unspent outputs. Rather just import private keys from your wallet with little amount of money on it, to reduce damage after potential compromise. Your opmsg keys (and so your BTC imported opcoin keys) will be stored unencrypted on disk. I am assuming you are using FDE anyways, to protect your keystore. So again, do not use BTC addresses which own much money. After all, this is an experimentel feature, driving on the bitcoin network as a web-of-trust. At best, create a fresh BTC address for opcoins. You may still use them to proof ownership with micro transactions.

  1. Importing pubkeys

Bitcoins use ECC with curve secp256k1. As ECC is used, its easy for opmsg to work with it and to import it into the keystore and to en/decrypt messages, using bitcoin keys.

You can use opcoin to import public bitcoin keys by using the --public switch. As argument to --public you have to pass the hex encoded public portion of a bitcoin key, which either starts with 02, 03 (compressed format) or 04 (uncompressed).

These public keys may be found inside any bitcoin Pay-to-Public-Key-Hash (P2PKH) transaction, more specifically inside its locking script (sometimes called input script). Keep looking for hex strings starting with 02, 03 or 04. Bitcoin addresses for P2PKH transactions start with a 1. During import, you have to add the --name parameter, pointing to the bitcoin address. This makes sure that you dont accidently import a wrong key. Check that the bitcoin address (name) matches the string that you actually want to import. The bitcoin address becomes the name of that opmsg persona and opmsg -l will later list it as name, so you immediately see where it is coming from.

If the transaction is evaluated as valid by the bitcoin network and becomes part of the blockchain, you have (very) strong evidence that your peer holds the private key. You can tell your peer to transfer some small amounts of BTC to your address from the address you imported, to check that you are talking to the right person.

After import, link this opcoin persona to the source persona you want to use for op messenging.

  1. Importing private keys

You have to export/dump the bitcoin key in question out of your (unlocked) wallet. This will give you a WIF encoded string - starting with K, L (compressed) or 5 (uncompressed) - consisting of your private key. It is not necessary to add a --public key, as this is derived from the WIF string which you directly add to the --private switch. Again this time, the address has to be given via --name in order to validate you were refering to the right BTC address.

opcoin personas are imported using persona hash algo of sha256. Thats the same algo that is used by bitcoin itself.

Thats basically it. You can now use the opcoin personas as any other personas with opmsg. The main idea behind it is to use the public ledger with some micro transactions as a proof that a certain persona holds a key (proving it by sending you some satoshis of secret amount to your account).