MATLAB: The encryption doesn’t work correctly? (SHA-256, HMAC-SHA-512)

Question

Here is the desription of what I need to do: https://cryptofacilities.zendesk.com/hc/en-us/articles/360000642493-Sign-Challenge-Web-Socket-API-

1) We have determined input:

challenge = 'c100b894-1729-464d-ace1-52dbce11db42';
apiSecret = '7zxMEF5p/Z8l2p2U7Ghv6x14Af+Fx+92tPgUdVQ748FOIrEoT9bgT+bTRfXc5pz8na+hL/QdrCVG7bh9KpT0eMTm';

2) We need to receive an expected output:

signed_output = '4JEpF3ix66GA2B+ooK128Ift4XQVtc137N9yeg4Kqsn9PI0Kpzbysl9M1IeCEdjg0zl00wkVqcsnG4bmnlMb3A==';

3) Here are steps of how we should encrypt it:

1. Hash the challenge with the SHA-256 algorithm
2. Base64-decode your api_secret
3. Use the result of step 2 to hash the result of step 1 with the HMAC-SHA-512 algorithm
4. Base64-encode the result of step 3

My code:

import matlab.net.*
 
% 1. Hash the challenge with the SHA-256 algorithm
hash_digest = DataHash(challenge, struct('Method','SHA-256'));
 
% 2. Base64-decode your api_secret
secret_decoded = base64decode(apiSecret);
 
% 3. Use the result of step 2 to hash the result of step 1 with the HMAC-SHA-512 algorithm
hmac_digest = HMAC(secret_decoded,hash_digest,'SHA-512');
 
% 4. Base64-encode the result of step 3
signed_output = base64encode(hmac_digest);

I am using these functions:

• DataHash
• HMAC Hash Message Authentication Code Function

The result is wrong. Could you please help me to fix it?

Answer 1

Your call of DataHash creates the hash considering the class of the obejct. You want to get the hash for the values only.

challenge = 'c100b894-1729-464d-ace1-52dbce11db42';
Opt.Method  = 'SHA-256';
Opt.Input   = 'ascii';   % Use the contents only and only 8 bits
hash_digest = DataHash(challenge, Opt)
% Compare with:
DataHash(challenge, struct('Method','SHA-256'))
% Note that this considers the class and dimensions of the input also:
DataHash(challenge.', struct('Method','SHA-256'))
%                 ^^ other result for transposed input!!!

By the way, DataHash is an overkill here. Leaner:

Engine = java.security.MessageDigest.getInstance('SHA-256');
Engine.update(uint8(challenge(:)));
Hash   = typecast(Engine.digest, 'uint8')

And for HMAC:

BlockSize         = 128;         % 64 for: MD5, SHA-1, SHA-256
KeySize           = numel(Key);
Key               = uint8(Key);  % Hash it if it is longer than BlockSize
ipad(1:BlockSize) = uint8(54);   % 0x36
ipad(1:KeySize)   = bitxor(uint8(54), Key);
opad(1:BlockSize) = uint8(92);   % 0x5c
opad(1:KeySize)   = bitxor(uint8(92), Key);
Engine2 = java.security.MessageDigest.getInstance('SHA-512');
Engine2.update(ipad);
Engine2.update(uint8(Msg));
iHash = typecast(Engine2.digest, 'uint8');
Engine2.update(opad);
Engine2.update(iHash);
HMAC = typecast(Engine2.digest, 'uint8');