Convert From Base64 With Powershell Script

1. steps

• capture the encoded string in fiddler
• pass that into the command decode-base64 -data <$string>
• get the result as encoded `json`
• this is what echo $string | jq '.' is doing in bash

2. demo

• decoding aGVsbG8gd29ybGQ= into hello world

3. script

function decode-base64 {
    [CmdletBinding()]
    param (
        [Parameter(Mandatory = $true)]    
        [string]$data
    )
begin {
        $intro = @"
  _____     
 / _T_ \   presents..
/ / E \ \  ..BASE64 STRING DECODER
\ \_I_/ /  ....just pass the string with the cmdlet / function call
 \__N__/   ....results in clipboard & file
"@
        Write-Host $intro -ForegroundColor cyan
        $outputFile = "$env:USERPROFILE\documents\decoded.json"
    }
    process {
        $convertedData = [Convert]::FromBase64String($data)
        $stringData = [System.Text.Encoding]::UTF8.GetString($convertedData)
    }
    
    end {
        Write-Host "~~~~~~~~~~~~~~~~~~~~~~~~~~~" -ForegroundColor cyan
        Write-Host "decoded string:" -ForegroundColor cyan
        Write-Host "~~~~~~~~~~~~~~~~~~~~~~~~~~~" -ForegroundColor cyan
        Write-Host $stringData 
        Write-Host "~~~~~~~~~~~~~~~~~~~~~~~~~~~" -ForegroundColor cyan
        Write-Host "copied to clipboard & to $outputFile"
        Write-Host "~~~~~~~~~~~~~~~~~~~~~~~~~~~" -ForegroundColor cyan
        $stringData | Out-File $outputFile  -Force 
        $stringData | clip
        Pause
        ii $outputFile
    }
}

Originally published at http://pavol.kutaj.com on October 18, 2020.