How to sign a message using Bitcoin private key?

Question

How does one create a proper signature for a given message using Bitcoin private keys?

I have an input address of

5JeWZ1z6sRcLTJXdQEDdB986E6XfLAkj9CgNE4EHzr5GmjrVFpf

or

6d7f6815bd7927423a728db28c5f4ea4032a81ab8dbca06ec41476508de48a6d

I want to sign message:

test

I convert it to hex:

74657374

I feed it to a signing function of ECDSA library that uses secp256k1, and I get two outputs,

r = D16A44BF1095FB7D517C7C4DD6A51E3EFD29548C5CAD8CA4AB763946D02AE0E8 
s = 2AB3E674B788804B87CED50619A1EFA267E17D20C016D0779BC3203D40E8105D 

If I marshal it with DER/asn1 as a list of Big Integers, I get a result of:

MEUCIQDRakS/EJX7fVF8fE3WpR4+/SlUjFytjKSrdjlG0Crg6AIgKrPmdLeIgEuHztUGGaHvomfhfSDAFtB3m8MgPUDoEF0=

If I marshal them as a list of byte arrays, I get

MEQEINFqRL8Qlft9UXx8TdalHj79KVSMXK2MpKt2OUbQKuDoBCAqs+Z0t4iAS4fO1QYZoe+iZ+F9IMAW0HebwyA9QOgQXQ==

if I marshal them as one long byte array, I get 0WpEvxCV+31RfHxN1qUePv0pVIxcrYykq3Y5RtAq4Ogqs+Z0t4iAS4fO1QYZoe+iZ+F9IMAW0HebwyA9QOgQXQ==

None of them appear to work as signatures when I try to verify the message signature using tools like http://brainwallet.org/#verify .

How do I properly sign messages using Bitcoin private keys to be compatible with BitcoinQT?

Answer 1

Using bitcoind and bitcoin-cli you can do it as follows:

bitcoin-cli signmessage 1DiWX6p3FdHPZqN88vMeGVXSwAQ1h7BeVj 'Hello world!'

Answer 2

In Bitcoin-qt

Or you can do it in blockchain.info/wallet by clicking the menu above your addresses.

No need to do it manually.