How do you decrypt securestring in powershell

A security warning first:

Converting a secure string to a regular [string] instance defeats the very purpose of using [securestring] (System.Security.SecureString) to begin with: you'll end up with a plain-text representation of your sensitive data in your process' memory whose lifetime you cannot control.

Also, note that secure strings are generally not recommended for use in new code anymore: they offer only limited protection on Windows, and virtually none on Unix-like platforms, where they aren't even encrypted.

PowerShell v7+ now offers ConvertFrom-SecureString -AsPlainText to convert a secure string to its - unsecured - plain-text representation:

# PowerShell 7.0 or higher.
$password = Read-Host "Enter password" -AsSecureString
$plainTextPassword = ConvertFrom-SecureString -AsPlainText $password

In PowerShell v6- (including Windows PowerShell), you can use the following:

$password = Read-Host "Enter password" -AsSecureString
$plainTextPassword = [Net.NetworkCredential]::new('', $password).Password

$password = Read-Host "Enter password" -AsSecureString
$password = [Runtime.InteropServices.Marshal]::SecureStringToBSTR($password)
$password = [Runtime.InteropServices.Marshal]::PtrToStringBSTR($password)
echo $password
pause

To convert Read-Host SecureStrings to normal strings, you use

$NewVaraible = [Runtime.InteropServices.Marshal]::SecureStringToBSTR($ReadVariable)
$NewNewVariable = [Runtime.InteropServices.Marshal]::PtrToStringBSTR($NewVariable)

Or you could just update the existing variable:

$ReadVaraible = [Runtime.InteropServices.Marshal]::SecureStringToBSTR($ReadVariable)
$ReadVariable = [Runtime.InteropServices.Marshal]::PtrToStringBSTR($ReadVariable)