HMAC sha256 returning different values in c# than python

Question

I need to port some python code into c# and I'm having some trouble with this line:

Python

hmac.new(key, message,digestmod=hashlib.sha256).digest()

C#

HMACSHA256 hm = new HMACSHA256(key);
byte[] result = hm.ComputeHash(enc.GetBytes(message));

Why am I getting a different result in C# when key and message are the same (checked byte-by-byte) ?

Roland · Accepted Answer · 2015-10-23 11:55:36Z

5

You can get different hashes for the same message if you use different encodings when converting the message into a byte array. It is not clear which encoding you are using, but the point is that they should match.

For example:

hmac.new("mykey", "mymessage",digestmod=hashlib.sha256).digest()

gTM3eMvH4WsjwCGzp4gZNV5a62dEcWw/gjTMPngjJpQ=

In C# you get different results depending on your 'enc' variable.

Encoding enc = Encoding.GetEncoding("ASCII");

gTM3eMvH4WsjwCGzp4gZNV5a62dEcWw/gjTMPngjJpQ=

Encoding enc = Encoding.GetEncoding("Unicode");

2wqHPyE5oiI3ukxOaKo9ao6AN8fcwjgdDInBHTXTwGQ=

answered Oct 23, 2015 at 11:55

Roland

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1 Comment

Adrian Buzea Over a year ago

Thanks. I still can't figure out which encoding the python function uses. I have tried chardet and it detects it as windows-1251 but it's not that one. I have tried UTF 7,8,16,32 and Unicode but it doesn't seem to be one of those.

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