$Path = "$env:temp\secret.txt"
$Secret = 'Hello World!'
$Passphrase = 'Some secret key'
 
$key = [Byte[]]($Passphrase.PadRight(24).Substring(0,24).ToCharArray())
 
$Secret |
 ConvertTo-SecureString -AsPlainText -Force |
 ConvertFrom-SecureString -Key $key |
 Out-File -FilePath $Path
 
notepad $Path

$Passphrase = Read-Host 'Enter the secret pass phrase'
 
$Path = "$env:temp\secret.txt"
 
$key = [Byte[]]($Passphrase.PadRight(24).Substring(0,24).ToCharArray())
 
try
{
 $decryptedTextSecureString = Get-Content -Path $Path -Raw |
 ConvertTo-SecureString -Key $key -ErrorAction Stop
 
 $cred = New-Object -TypeName System.Management.Automation.PSCredential('dummy', $decryptedTextSecureString)
 $decryptedText = $cred.GetNetworkCredential().Password
}
catch
{
 $decryptedText = '(wrong key)'
}
"The decrypted secret text: $decryptedText"