Why does encrypting HMAC-SHA1 in exactly the same code in C# and PowerShell show different results?

Question

I've been trying to encrypt a Amazon S3-like authorization key with HMAC-SHA1 in PowerShell with the following code:

$str="PUT\n\napplication/x-zip-compressed\nThu, 09 Feb 2017 08:59:43 GMT\n/test-bucket/test-key"
$secret="c334da95a6734ff4a04abd99efca450f"
$sha = [System.Security.Cryptography.KeyedHashAlgorithm]::Create("HMACSHA1")
$sha.Key = [System.Text.Encoding]::UTF8.Getbytes($secret)
$sign = [Convert]::Tobase64String($sha.ComputeHash([System.Text.Encoding]::UTF8.Getbytes(${str})))
echo $sign

This code outputs NcJQ1MapHbyRwC2FzvABYyte5uY=, which is incorrect according to our service provider's suggestion.

Then I tried to use exactly the same classes in C# code:

static void Main(string[] args)
{
    var str = "PUT\n\napplication/x-zip-compressed\nThu, 09 Feb 2017 08:59:43 GMT\n/test-bucket/test-key";
    var secret = "c334da95a6734ff4a04abd99efca450f";

    var sha = System.Security.Cryptography.KeyedHashAlgorithm.Create("HMACSHA1");
    sha.Key = System.Text.Encoding.UTF8.GetBytes(secret);
    Console.WriteLine(Convert.ToBase64String(sha.ComputeHash(System.Text.Encoding.UTF8.GetBytes(str)))); //1S+/P9zgcCCyjwUK1bPKaKeya7A=
    Console.Read();
}

Oddly enough, this time, the result is correct: 1S+/P9zgcCCyjwUK1bPKaKeya7A=

I also tried Python, and it vindicated the C# code. Why did PowerShell run into an incorrect answer even though the inputs, classes and the methods are exactly the same with those which are called in C# code?

Do you have a repo with the full solution? I keep getting AccessDenied :( — Dini
– Dini, Commented Apr 9, 2021 at 12:35

Peter Mortensen · Accepted Answer · 2017-02-10 11:08:00Z

22

It's because the escape character in PowerShell is ` while the one in C# is \.

$str = "PUT`n`napplication/x-zip-compressed`nThu, 09 Feb 2017 08:59:43 GMT`n/test-bucket/test-key"

Should yield the expected result.

edited Feb 10, 2017 at 11:08

Peter Mortensen

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answered Feb 10, 2017 at 2:29

Igor

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5 Comments

Dan Field Over a year ago

That's what i thought too, but when I test it that way I still don't get the expected result.

Eric Over a year ago

Tested with powershell it does return 1S+/P9zgcCCyjwUK1bPKaKeya7A=

Dan Field Over a year ago

The original question had a different expected result. This answer is correct. I didn't bother to check the C# version...

Aries Over a year ago

Thanks @Igor , you are right, I got the correct result.

Aries Over a year ago

Sorry @DanField, since I changed the key, I forgot to update the output.

Peter L · Accepted Answer · 2022-03-23 22:49:19Z

0

The post from @Igor was useful however I also had to create my HMACSHA1 instance like this:

$sha = New-Object System.Security.Cryptography.HMACSHA1

answered Mar 23, 2022 at 22:49

Peter L

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