Kraken API "Invalid signature" error using Matlab - matlab

Question

I am trying to implement the API of the bitcoin exchange Kraken in MATLAB. Unfortunately I got stuck at trying to execute an authentication in order to retrieve private user data.
In particular, I was playing with the following Implementation: Kraken API MATLAB client invalid signature error. The documentation of Kraken's API is here: https://www.kraken.com/help/api
When connecting with the Private user data but I continuously run into the error: {"error":["EAPI:Invalid signature"]}. Could someone maybe have a quick look at the implementation below and look for flaws in the code? Or has someone successfully implemented the Kraken API for Matlab?
Many thanks!
% Private
uri = '0/private/Balance';
postdata='';
[response,status] = kraken_authenticated(uri,postdata)
% test uri='0/private/AddOrder'
% test postdata='&pair=XBTEUR&type=buy&ordertype=limit&price=345.214&volume=0.65412&leverage=1.5&oflags=post'
function [response,status]=kraken_authenticated(uri,postdata)
% Generate URL
url=['https://api.kraken.com/',uri];
% nonce
nonce = num2str(floor((now-datenum('1970', 'yyyy'))*8640000000));
key = ' '
secret = ' '
% 1st hash
Opt.Method = 'SHA-256';
Opt.Input = 'ascii';
sha256string = DataHash(['nonce=',nonce,postdata],Opt);
% 2nd hash
%sign = crypto([uri,sha256string], secret, 'HmacSHA512');
sign = crypto([uri,sha256string], base64decode(secret), 'HmacSHA512')
%sign = HMAC([uri,sha256string], base64decode(secret), 'SHA-512');
%header_0=http_createHeader('Content-Type','application/x-www-form-urlencoded');
header_1=http_createHeader('API-Key',key);
header_2=http_createHeader('API-Sign',char(sign));
header=[header_1 header_2];
[response,status] = urlread2(url,'POST',['nonce=',nonce,postdata],header);
end
function signStr = crypto(str, key, algorithm)
import java.net.*;
import javax.crypto.*;
import javax.crypto.spec.*;
import org.apache.commons.codec.binary.*
keyStr = java.lang.String(key);
key = SecretKeySpec(keyStr.getBytes('UTF-8'), algorithm);
%key = SecretKeySpec(keyStr.getBytes(), algorithm)
mac = Mac.getInstance(algorithm);
mac.init(key);
toSignStr = java.lang.String(str);
signStr = java.lang.String(Hex.encodeHex( mac.doFinal( toSignStr.getBytes('UTF-8'))))
%signStr = java.lang.String(Hex.encodeHex( mac.doFinal( toSignStr.getBytes())))
end
function header = http_createHeader(name,value)
header = struct('name',name,'value',value);
end

Answer 1

I'm actually trying to do my owm implementation in c++, and I was here for another error I get, but here is a possible cause I noticed in your code :
The first sha256 hash should be of a concatenation of nonce and postdata. As postdata is also containing the nonce, if the nonce value is 123456789, then you should do (pseudo-code) :
sha256("123456789nonce=123456789")
or in Matlab :
sha256string = DataHash([nonce,'nonce=',nonce],Opt);
I hope it helps.