Saving credentials for reuse by powershell and error ConvertTo-SecureString : Key not valid for use in specified state

Question

I was doing something like described in this post to save credentials in a secured file so our automated process can use that to run remote PS scripts via Invoke-command: http://blogs.technet.com/b/robcost/archive/2008/05/01/powershell-tip-storing-and-using-password-credentials.aspx

This works great when I run this under my account - password is read from encrypted file, passed to Invoke-command and everything is fine.

Today, when my script was ready for its prime time, I tried to run it under windows account that will be used by automated process and got this error below while my script was trying to read secured password from a file:

ConvertTo-SecureString : Key not valid for use in specified state.
At \\remoted\script.ps1:210 char:87
+ $password = get-content $PathToFolderWithCredentials\pass.txt | convertto-sec
urestring <<<<
    + CategoryInfo          : InvalidArgument: (:) [ConvertTo-SecureString], C
   ryptographicException
    + FullyQualifiedErrorId : ImportSecureString_InvalidArgument_Cryptographic
   Error,Microsoft.PowerShell.Commands.ConvertToSecureStringCommand

Asked my workmate to run under his account and he got the same error.

This is the code I am using to save credentials:

$PathToFolderWithCredentials = "\\path\removed"

write-host "Enter login as domain\login:"
read-host | out-file $PathToFolderWithCredentials\login.txt

write-host "Enter password:"
read-host -assecurestring | convertfrom-securestring | out-file $PathToFolderWithCredentials\pass.txt

write-host "*** Credentials have been saved to $pathtofolder ***"

This is the code in the script to run by automated process to read them to use in Invoke-command:

$login= get-content $PathToFolderWithCredentials\login.txt
$password = get-content $PathToFolderWithCredentials\pass.txt | convertto-securestring
$credentials = new-object -typename System.Management.Automation.PSCredential -argumentlist $login,$password

Error happens on line $password = get-content $PathToFolderWithCredentials\pass.txt | convertto-securestring

Any ideas?

Answer 1

ConvertFrom-SecureString takes a Key ( and SecureKey) parameter. You can specify the key to save the encrypted standard string and then use the key again in ConvertTo-SecureString to get back the secure string, irrespective of the user account.

http://technet.microsoft.com/en-us/library/dd315356.aspx

In a project, I have implemented asymmetric encryption, whereby people encrypt the password using the public key and the automation process has the private key to decrypt passwords: Handling passwords in production config for automated deployment

Answer 2

You have to create the password string on the same computer and with the same login that you will use to run it.

Answer 3

The below will allow credentials to be saved as a file, then those credentials to be used by another script being run by a different user, remotely.

The code was taken from a great article produced by David Lee, with only some minor adjustments from myself https://blog.kloud.com.au/2016/04/21/using-saved-credentials-securely-in-powershell-scripts/

First step is to save a a secure password to a file using AES. The below will run as a stand alone script:

            # Prompt you to enter the username and password
            $credObject = Get-Credential

            # The credObject now holds the password in a ‘securestring’ format
            $passwordSecureString = $credObject.password

            # Define a location to store the AESKey
            $AESKeyFilePath = “aeskey.txt”
            # Define a location to store the file that hosts the encrypted password
            $credentialFilePath = “credpassword.txt”

            # Generate a random AES Encryption Key.
            $AESKey = New-Object Byte[] 32
            [Security.Cryptography.RNGCryptoServiceProvider]::Create().GetBytes($AESKey)

            # Store the AESKey into a file. This file should be protected! (e.g. ACL on the file to allow only select people to read)

            Set-Content $AESKeyFilePath $AESKey # Any existing AES Key file will be overwritten

            $password = $passwordSecureString | ConvertFrom-SecureString -Key $AESKey

            Add-Content $credentialFilePath $password

Then in your script where you need to use credentials use the following:

            #set up path and user variables
            $AESKeyFilePath = “aeskey.txt” # location of the AESKey                
            $SecurePwdFilePath = “credpassword.txt” # location of the file that hosts the encrypted password                
            $userUPN = "domain\userName" # User account login 

            #use key and password to create local secure password
            $AESKey = Get-Content -Path $AESKeyFilePath 
            $pwdTxt = Get-Content -Path $SecurePwdFilePath
            $securePass = $pwdTxt | ConvertTo-SecureString -Key $AESKey

            #crete a new psCredential object with required username and password
            $adminCreds = New-Object System.Management.Automation.PSCredential($userUPN, $securePass)

            #use the $adminCreds for some task
            some-Task-that-needs-credentials -Credential $adminCreds

Please be aware that if the user can get access to the password file and the key file, they can decrypt the password for the user.

Answer 4

Another approach would be to protect the data using scope 'LocalMachine' instead of 'CurrentUser' which is the one used by ConvertFrom-SecureString.

public static string Protect(SecureString input, DataProtectionScope dataProtectionScope = DataProtectionScope.CurrentUser, byte[] optionalEntropy = null)
{
    byte[] data = SecureStringToByteArray(input);
    byte[] data2 = ProtectedData.Protect(data, optionalEntropy, dataProtectionScope);
    for (int i = 0; i < data.Length; i++)
    {
        data[i] = 0;
    }

    return ByteArrayToString(data2);
}
private static byte[] SecureStringToByteArray(SecureString s)
{
    var array = new byte[s.Length * 2];
    if (s.Length > 0)
    {
        IntPtr intPtr = Marshal.SecureStringToGlobalAllocUnicode(s);
        try
        {
            Marshal.Copy(intPtr, array, 0, array.Length);
        }
        finally
        {
            Marshal.FreeHGlobal(intPtr);
        }
    }

    return array;
}
private static string ByteArrayToString(byte[] data)
{
    var stringBuilder = new StringBuilder();
    for (int i = 0; i < data.Length; i++)
    {
        stringBuilder.Append(data[i].ToString("x2", CultureInfo.InvariantCulture));
    }

    return stringBuilder.ToString();
}

The encrypted string can be used by ConvertTo-SecureString which is using scope 'CurrentUser'.

Answer 5

Assuming you have a known list of N users who will use the credentials (e.g. one developer userMe and a system/service user userSys) you can just (get those users to) make N copies of the pass.txt file: one for each user.

So the password of userX will result in e.g. 2 *.pass.txt files:

• userX.userMe.pass.txt
• userX.userSys.pass.txt

When userMe wants the creds he/she reads userX.userMe.pass.txt etc.