I'm trying to construct the message verification signature of bitcoin qt in python. I'm able to compute the couple (r,s) of the signature, but, even I'm not able to find the correct way to encode it to find the correct base64 encoded string that bitcoin-qt use.

Here is my example :

My test bitcoin addresse : "1BBwZVdBjoPxotHfrKLpHJBSy7vmc2pjex" Private Key : 18 (the integer 18 in base 10) Message : "Hello World"

When I sign, I use an integer k (specified in the ECDSA) which is 1 (just an example). I get (r,s)=(55066263022277343669578718895168534326250603453777594175500187360389116729240, 23952895512439370531107719399796920806315532907434078350311186283065887977941) in base 10.

How do I construct the signature string generated by bitcoin-qt from these r and s ?

Thank you very much for your help.