How to perform Stampery.com's Merkle Proof?

Question

I am using the Stampery API to anchor hashes into different Blockchains. I wanted to independently verify that my hash with the given Merkle Proof from Stampery. I tried to follow their Whitepaper but with no success.

What I've tried so far is the following:

Hash:
265D0E134C56080CBD9049427C39C5B6425FDC909FC16072FC4AA0D6957B7264

Merkle proof:
R 4C83C6F2C253CD8B44A3EDEB076B65877BEBA0DCA2B85497C3B7E74785EC5618 
R 9F016BF9C9CD4C4F55D171C211666B214C38C7FBDDCED9BC5D2D4239E6C7CE19
L 5461D61A21A6EF783737F328DA8BB8BF5D24804B8574F0E6CBEC076D026C2FBE
R FD894CD6289981AEEC0CE250C841257276FE56D2A003BFE482B2E669BA4A93AC

Merkle root:
16DA7D280DC9B527985F8749636DFB5E3C6B3856A4C7F7CB3E8BA6AEC9F33EB7

Code:

var mP = [
    "4C83C6F2C253CD8B44A3EDEB076B65877BEBA0DCA2B85497C3B7E74785EC5618",
    "9F016BF9C9CD4C4F55D171C211666B214C38C7FBDDCED9BC5D2D4239E6C7CE19",
    "5461D61A21A6EF783737F328DA8BB8BF5D24804B8574F0E6CBEC076D026C2FBE",
    "FD894CD6289981AEEC0CE250C841257276FE56D2A003BFE482B2E669BA4A93AC"
];

r = SHA3( SHA3( mP[2]+SHA3( SHA3(hash+mP[0]) +mP[1])) +mP[3] );

with $r \neq merkleRoot $. Here I simply applied the SHA3 (Keccak) algorithm (as mentioned in the paper) successive, taking into account the L and R from the Merkle Proof. I guess, that the Ls and Rs decide the order of the operands of the SHA3 function.

I am not sure what I am doing wrong and would be happy for any help!

---

Edit: With the help aesedepece I got a minimal node version running:

var crypto = require('crypto');

function SHA256(x) {
    var buf = new Buffer(x, 'hex');
    return crypto.createHash('sha256').update(buf).digest('hex');
}

var hash = "265D0E134C56080CBD9049427C39C5B6425FDC909FC16072FC4AA0D6957B7264";
var mP = [
    "4C83C6F2C253CD8B44A3EDEB076B65877BEBA0DCA2B85497C3B7E74785EC5618",
    "9F016BF9C9CD4C4F55D171C211666B214C38C7FBDDCED9BC5D2D4239E6C7CE19",
    "5461D61A21A6EF783737F328DA8BB8BF5D24804B8574F0E6CBEC076D026C2FBE",
    "FD894CD6289981AEEC0CE250C841257276FE56D2A003BFE482B2E669BA4A93AC"
];

var merkleRoot = "265D0E134C56080CBD9049427C39C5B6425FDC909FC16072FC4AA0D6957B7264";

var r = SHA256(SHA256(mP[2]+SHA256(SHA256(hash+mP[0])+mP[1]))+mP[3]);
console.log(r);

Answer 1

You seem to be doing everything right. The problem here is that you are using the verification process from BTA v5 on a proof generated by BTA v6 (the LTS version of our API). The v6 whitepaper is here.

Put simply: you'll need to use SHA256 instead of SHA3:

r = SHA256(SHA256(mP[2]+SHA256(SHA256(hash+mP[0])+mP[1]))+mP[3]);

Also make sure your hash functions operate on a byte level, not on the hexadecimal representation of the hash digests.

Please don't hesitate to ask for clarification!