Powershell script for hash - file

Question

I have a CSV file (Comma Separated Values)
The file looks like this:
20171108,120909470,SO1244,12,101
20171109,122715740,AG415757,11,101
I need to obscure the data in (for example) columns 3 and, without affecting any of the other entries in the file.
I want to do this using a hashing algorithm like SHA1 or MD5, so that the same strings will resove to the same hash values anywhere they are encountered.
I need to send data to a third party, and certain columns contain sensitive information (e.g. customer names). I need the file to be complete, and where a string is replaced, I need it to be done in the same way every time it is encountered (so that any mapping or grouping remains). It does not need military encryption, just to be difficult to reverse. As I need to to this intermittently, a scripted solution would be ideal.
What is the easiest way to achieve this using a command line tool or script?
By preference, I would like a PowerShell script, since that does not require any additional software to achieve...
This question seems like a duplicate of I need to hash (obfuscate) a column of data in a CSV file. Script preferred but the proposed solution didn't resolve my problem and throws the following error
You cannot call a method on a null-valued expression.
At C:\Users\mey\Hashr.ps1:4 char:5
+ $_.column3 = $_.column3.gethashcode()
The script is the following
(Import-Csv .\results.csv -delimiter ',' ) | ForEach-Object{
$_.column3 = $_.column3.gethashcode()
$_
} | Export-Csv .\myobfuscated.csv -NoTypeInformation -delimiter ','
Update:
Here's the program i am running and that has been proposed by #BaconBits:
param (
[Parameter(Mandatory = $true, ValueFromPipeline = $true, Position = 0)]
[String[]]
$String,
[Parameter(Position = 1)]
[ValidateSet('SHA1', 'MD5', 'SHA256', 'SHA384', 'SHA512')]
[String]
$HashName = 'SHA256'
)
process {
$StringBuilder = [System.Text.StringBuilder]::new(128)
[System.Security.Cryptography.HashAlgorithm]::Create($HashName).ComputeHash([System.Text.Encoding]::UTF8.GetBytes($String)) | ForEach-Object {
[Void]$StringBuilder.Append($_.ToString("x2"))
}
$StringBuilder.ToString()
}
}
$csv = Import-Csv .\results.csv -delimiter ','
foreach ($line in $csv) {
$line.column1 = Get-StringHash $line.column1
}
$csv | Export-Csv .\myobfuscated.csv -NoTypeInformation -delimiter ','
The csv file i am importing is an output from another java program i made and it creates no header, it just fill the csv file with values
I am getting this error
Get-StringHash : Cannot bind argument to parameter 'String' because it is null.

Answer 1

Based on the doc, you're not going to want to use GetHashCode() this way:
A hash code is intended for efficient insertion and lookup in
collections that are based on a hash table. A hash code is not a
permanent value. For this reason:
Do not serialize hash code values or store them in databases.
Do not use the hash code as the key to retrieve an object from a keyed collection.
Do not send hash codes across application domains or processes. In some cases, hash codes may be computed on a per-process or
per-application domain basis.
Do not use the hash code instead of a value returned by a cryptographic hashing function if you need a cryptographically strong
hash. For cryptographic hashes, use a class derived from the
System.Security.Cryptography.HashAlgorithm or
System.Security.Cryptography.KeyedHashAlgorithm class.
Do not test for equality of hash codes to determine whether two objects are equal. (Unequal objects can have identical hash codes.) To
test for equality, call the ReferenceEquals or Equals method.
Bullet point 4 is the main problem. There's no guarantee that the hashing isn't reversible. The hashing function used is an implementation detail, not a secure cryptographic function like SHA.
I'd use a function like this one:
function Get-StringHash {
[CmdletBinding()]
param (
[Parameter(Mandatory = $true, ValueFromPipeline = $true, Position = 0)]
[String[]]
$String,
[Parameter(Position = 1)]
[ValidateSet('SHA1', 'MD5', 'SHA256', 'SHA384', 'SHA512')]
[String]
$HashName = 'SHA256'
)
process {
$StringBuilder = [System.Text.StringBuilder]::new(128)
[System.Security.Cryptography.HashAlgorithm]::Create($HashName).ComputeHash([System.Text.Encoding]::UTF8.GetBytes($String)) | ForEach-Object {
[Void]$StringBuilder.Append($_.ToString("x2"))
}
$StringBuilder.ToString()
}
}
$csv = Import-Csv .\results.csv -delimiter ',' -Header column1,column2,column3,column4,column5
foreach ($line in $csv) {
$line.column3 = Get-StringHash $line.column3
}
$csv | Export-Csv .\myobfuscated.csv -NoTypeInformation -delimiter ','
I believe I based that function off of this one, but it's been awhile since I've written it.
Edit by LotPings to show results of hash
"column1","column2","column3","column4","column5"
"20171108","120909470","0cdd3c3acdb7cfa107286565c044c5a0f1e58268f6f10e7e3415ff84942e577d","12","101 "
"20171109","122715740","0a7fb9f6bb7a180f2fd9429b0fbd1e7b0a83597b6a64aa6a123cef3e84700fe3","11","101"

Answer 2

Bacon Bits appears to have the correct methodology minus one part. The ForEach loop in your original example does not modify the original variable. Also, it appears the column you want to modify is not 'Column3', but 'Column #2' as the headers begin at zero. I'll repeat the function provided in Bacon Bits's suggestion.
function Get-StringHash {
[CmdletBinding()]
param (
[Parameter(Mandatory = $true, ValueFromPipeline = $true, Position = 0)]
[String[]]
$String,
[Parameter(Position = 1)]
[ValidateSet('SHA1', 'MD5', 'SHA256', 'SHA384', 'SHA512')]
[String]
$HashName = 'SHA256'
)
process {
$StringBuilder = [System.Text.StringBuilder]::new(128)
[System.Security.Cryptography.HashAlgorithm]::Create($HashName).ComputeHash([System.Text.Encoding]::UTF8.GetBytes($String)) | ForEach-Object {
[Void]$StringBuilder.Append($_.ToString("x2"))
}
$StringBuilder.ToString()
}
}
I would suggest for the substitution:
$csv = Import-Csv .\results.csv | Select-Object *,#{n='Column #2';e={Get-StringHash $_.'Column #2'}} -ExcludeProperty 'Column #2'
$CSV | Export-Csv .\myobfuscated.csv -NoTypeInformation
This will put the 'Column #2' last in the CSV. You can simply list them explicitly if you need it to appear in the same order, e.g.:
Select-Object 'Column #0','Column #1',#{n='Column #2';e={Get-StringHash $_.'Column #2'}},'Column #3'