I have previously discussed securing credentials using Windows Powershell atPowershell: Securing credentials using the PSCredential class. In this article, I will discuss a number of cmdlets I have created to secure credentials using a Advanced Encryption Standard (AES) encryption key to retrieve the content from a encrypted standard string.
As I am using an encryption key and storing the information in a content file, I will be using ACLs on the NTFS filesytem to control access. Alternative methods could be to store the encryption key in a database or use a certificate to control access to the item. Also, in practice I will store the encryption key on a remote file server.
Firstly, we need to create the encryption key using the ‘New-EncryptionKey’ cmdlet to which we use the RNGCryptoServiceProvider class to generate a random byte array for the encryption length. By default, the cmdlet using a 32-byte array to support the AES 256-bit encryption length. The cmdlet also supports using 128-bit and 192-bit encryption lengths which a 16-byte and 24-byte array. The random byte array for the specified encryption length is generated and sends the output to a file which will be the encryption key content.
Once the content has sent to the output file, the content of random byte array is then removed from the current session.
# Creates an AES 256-bit encryption key at the location D:\Output\Keys\mykey.key New-EncryptionKey -Output D:\Output\Keys\mykey.key # Creates an AES 192-bit encryption key at the location D:\Output\Keys\mykey.key New-EncryptionKey -Bytes 24 -Output D:\Output\Keys\mykey.key
We have now created an encryption key so that we may now convert the secure string for a credential object password using the specified encryption key and sends the output to a password file using the ‘New-EncryptedString’ cmdlet. The cmdlet will retrieve the content of the specified file containing the encryption key and from the stored credential objects convert the secure string of the password to an encrypted standard string and send the output to a file and clear the content of the stored encryption key from the current session.
New-EncryptedString -KeyFile D:\Output\Keys\mykey.key -PasswordFile D:\Output\Passwords\mypassword.txt
Finally we want to retrieve the credential object to use as a variable to pass to a subsequent cmdlet which will require authentication. The content of the password file is retrieved and converted to a secure string using the content of the encryption key and stored as a password variable and passed to the PSCredential class to represent a set of security credentials and return the object. For subsequent cmdlets I can use the ‘$Password.GetNetworkCredential().Password’ property value for authentication from the PSCredential object.
$Password = Get-PSCredentialObject -Username administrator -KeyFile D:\Output\Keys\mykey.key -PasswordFile D:\Output\Passwords\mypassword.txt
The cmdlets are available from the below:
New-EncryptionKey – https://github.com/dean1609/PowerShell/blob/master/Functions/New-EncryptionKey.ps1
New-EncryptedString – https://github.com/dean1609/PowerShell/blob/master/Functions/New-EncryptedString.ps1
Get-PSCredentialObject – https://github.com/dean1609/PowerShell/blob/master/Functions/Get-PSCredentialObject.ps1
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