Decoding a base64 encoded field in a csv with powershell

Question

Apologies if this a stupid question or I'm asking it in the wrong place.

I have a .csv file with a bunch of network logs in the following format sourceIP,port,destinationIP,port,packetdata. The "packetdata" field contains ASCII information which has been base64 encoded. I need to import the CSV file, convert that single field from base64 back to the original and then export the whole file without touching the other rows.

I know I need to use import-csv to get the data in and I know there's a FromBase64String conversion method but I'm kind of lost.

This is what I have at the moment, which is pretty much hacked together from other code and doesn't actually complete when I try and run it...

import-csv c:\testbase64.csv|foreach-object {$_.packetdata =  [text.encoding]::utf8.getstring([convert]::FromBase64String($_.packetdata))|Export-Csv -Path "C:\outputtest.csv" -NoTypeInformation

[text.encoding]::utf8.getstring([convert]::FromBase64String($variable)) does work if run seperately on the commandline with a standard variable with base64 data in as the data source

I'd appreciate any help anyone can give on this, it would make reading these files much less painful.

Answer 1

Save this as import.ps1 and use as follows: .\import.ps1 C:\test.csv. It will output a CSV in the current directory called Output.csv.

You'll also need to change the Port columns so one is SourcePort and one is DestPort - you can't have 2 columns with the same name when using Import-Csv.

$csv = Import-Csv $args[0]

$csv | ForEach-Object { $_.PacketData = [text.encoding]::utf8.getstring([convert]::FromBase64String($_.PacketData)) }

$csv | Export-Csv "Output.csv" -NoTypeInformation