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Using Powershell -encodedcommand to Pass Parameters

I'm trying to find an elegant way to pass parameters in a powershell script, where a string can contain any number of special characters that will need to be escaped. For example, a complex password with special characters.

I looked at the -encodedcommand option, but it looks like it is only intended to pass an encoded script block, not an encoded version of the parameters.

For example, consider the following script:

param(
[Parameter()][Alias("un")][string]$Username,
[Parameter()][Alias("pw")][string]$Password
)

Write-Host "Username: $Username"
Write-Host "Password: $Password"

The string '-un testuser -pw testpw' is encoded by base64 as follows: LQB1AG4AIAB0AGUAcwB0AHUAcwBlAHIAIAAtAHAAdwAgAHQAZQBzAHQAcAB3AA ==

I tried to call the script as a .ps1 file and pass a -coded code with the line above, but I got the error "Parameter A could not be found, which matches the parameter name" encodedcommand "

So great, this should be a call to powershell.exe directly.

Also tried the following: powershell.exe -encodedcommand LQB1AG4AIAB0AGUAcwB0AHUAcwBlAHIAIAAtAHAAdwAgAHQAZQBzAHQAcAB3AA == -file Base64ParamTest.ps1

This ran the script, but the parameters did not matter.

This behaves the way I expected, but not the way I hope. Is there a way to pass my parameters on their own as safely encoded strings?

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1 answer

You should include a script call as part of the command, for example:

PS> $command = "& '$pwd\login.ps1' -un testuser -pw testpw"
PS> $bytes = [Text.Encoding]::Unicode.GetBytes($command)
PS> $encodedCommand = [Convert]::ToBase64String($bytes)
PS> powershell.exe -noprofile -encodedCommand $encodedCommand
Username: testuser
Password: testpw

, , :

###########################################################
#
# Stashing passwords to avoid interactive password prompting
#

# NOT RECOMMENDED BUT IF PASSWORD IS DYNAMIC OR WIDELY KNOWN

$passwd = ConvertTo-SecureString "Not Very Secret Password" -AsPlainText -Force

# Need a way to prompt for password and use clear text password for use with net use
$cred = Get-Credential
$cred.GetNetworkCredential().UserName 
$cred.GetNetworkCredential().Password

#
# SAFE BUT NOT NECESSARILY PORTABLE APPROACH 
# Depends on how DPAPI works with roaming profiles
#

# Capture once and store to file
$passwd = Read-Host "Enter password" -AsSecureString
$encpwd = ConvertFrom-SecureString $passwd
$encpwd
$encpwd > $path\password.bin

# Later pull this in and restore to a secure string
$encpwd = Get-Content $path\password.bin
$passwd = ConvertTo-SecureString $encpwd

# Let see if the rehydrate worked?
$bstr = [System.Runtime.InteropServices.Marshal]::SecureStringToBSTR($passwd)
$str =  [System.Runtime.InteropServices.Marshal]::PtrToStringBSTR($bstr)
[System.Runtime.InteropServices.Marshal]::ZeroFreeBSTR($bstr)
$str

$cred = new-object System.Management.Automation.PSCredential 'john',$passwd
$cred

# NOTE: The "secret" required to rehyrdate correctly is stored in DPAPI - consequence:
#       You can only rehydrate on the same machine that did the ConvertFrom-SecureString


#
# PORTABLE BUT NOT NECESSARILY SAFE APPROACH
#

# Let do this so that it will work on multiple machines:

$key = 1..32 | ForEach-Object { Get-Random -Maximum 256 }
$passwd = Read-Host "Enter password" -AsSecureString
$encpwd = ConvertFrom-SecureString $passwd -Key $key
$encpwd
# Could easily modify this to store username also
$record = new-object psobject -Property @{Key = $key; EncryptedPassword = $encpwd}
$record
$record | Export-Clixml $path\portablePassword.bin

# Later pull this in and restore to a secure string
$record = Import-Clixml $path\portablePassword.bin
$passwd = ConvertTo-SecureString $record.EncryptedPassword -Key $record.Key

# Let see if the rehydrate worked?
$bstr = [System.Runtime.InteropServices.Marshal]::SecureStringToBSTR($passwd)
$str =  [System.Runtime.InteropServices.Marshal]::PtrToStringBSTR($bstr)
[System.Runtime.InteropServices.Marshal]::ZeroFreeBSTR($bstr)
$str

$cred = new-object System.Management.Automation.PSCredential 'john',$passwd
$cred

Start-Process powershell.exe -Credential $cred -NoNewWindow

# Portable is better BUT the secret (Key) is shared (stored with the password file)
# Can be reversed to original password - still much better than clear-text password
# stored in your script.
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