How to get sha256 hash output as binary data instead of hex using powershell?

Question

Is there an in-built method to generate SHA256 as a binary data for a given string ? Basically, I am using below bash script to first generate a hash as a binary data and then do a base64 encoding. All I want to have is the exact thing in Powershell so that both the outputs are identical:

clearString="test"
payloadDigest=`echo -n "$clearString" | openssl dgst -binary -sha256 | openssl base64 `
echo ${payloadDigest}

In powershell, I can get the SHA256 in hex using the below script, but then struggling to get it as a binary data:

$ClearString= "test"
$hasher = [System.Security.Cryptography.HashAlgorithm]::Create('sha256')
$hash = $hasher.ComputeHash([System.Text.Encoding]::UTF8.GetBytes($ClearString))

$hashString = [System.BitConverter]::ToString($hash)
$256String= $hashString.Replace('-', '').ToLower()
$sha256String="(stdin)= "+$256String
$sha256String

I can then use [Convert]::ToBase64String($Bytes) to convert to base64 but in between how do I get a binary data similar to bash output before I pass it to base64 conversion.

$hasher.ComputeHash() returns a Byte[] array, so you can just do [Convert]::ToBase64String($hash) if I'm not mistaken. By doing [System.BitConverter]::ToString($hash) you are converting the binary data into a hex string. — Theo
– Theo, Commented Nov 12, 2019 at 9:50

Theo · Accepted Answer · 2019-11-12 10:24:35Z

7

I think you are over-doing this, since the ComputeHash method already returns a Byte[] array (binary data). To do what (I think) you are trying to achieve, don't convert the bytes to string, because that will result in a hexadecimal string.

$ClearString= "test"
$hasher = [System.Security.Cryptography.HashAlgorithm]::Create('sha256')
$hash = $hasher.ComputeHash([System.Text.Encoding]::UTF8.GetBytes($ClearString))
# $hash is a Byte[] array

# convert to Base64
[Convert]::ToBase64String($hash)

returns

n4bQgYhMfWWaL+qgxVrQFaO/TxsrC4Is0V1sFbDwCgg=

answered Nov 12, 2019 at 10:24

Theo

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1 Comment

aashleo Over a year ago

Thanks Theo, this was very helpful. I see where I went wrong now.

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