functions/Backup-DbaDbMasterKey.ps1

function Backup-DbaDbMasterKey {
    <#
.SYNOPSIS
Backs up specified database master key.
 
.DESCRIPTION
Backs up specified database master key.
 
.PARAMETER SqlInstance
The target SQL Server instance.
 
.PARAMETER SqlCredential
Allows you to login to SQL Server using alternative credentials.
 
.PARAMETER Database
Backup master key from specific database(s).
 
.PARAMETER ExcludeDatabase
The database(s) to exclude - this list is auto-populated from the server.
 
.PARAMETER Path
The directory to export the key. If no path is specified, the default backup directory for the instance will be used.
 
.PARAMETER Credential
Pass a credential object for the password
     
.PARAMETER Password
The password to encrypt the exported key. This must be a SecureString.
 
.PARAMETER InputObject
Database object piped in from Get-DbaDatabase
  
.PARAMETER EnableException
        By default, when something goes wrong we try to catch it, interpret it and give you a friendly warning message.
        This avoids overwhelming you with "sea of red" exceptions, but is inconvenient because it basically disables advanced scripting.
        Using this switch turns this "nice by default" feature off and enables you to catch exceptions with your own try/catch.
 
.NOTES
Tags: Certificate, Database
Author: Chrissy LeMaire (@cl), netnerds.net
Website: https://dbatools.io
Copyright: (C) Chrissy LeMaire, clemaire@gmail.com
License: MIT https://opensource.org/licenses/MIT
 
.EXAMPLE
Backup-DbaDbMasterKey -SqlInstance server1\sql2016
 
Prompts for export password, then logs into server1\sql2016 with Windows credentials then backs up all database keys to the default backup directory.
 
ComputerName : SERVER1
InstanceName : SQL2016
SqlInstance : SERVER1\SQL2016
Database : master
Filename : E:\MSSQL13.SQL2016\MSSQL\Backup\server1$sql2016-master-20170614162311.key
Status : Success
 
.EXAMPLE
Backup-DbaDbMasterKey -SqlInstance Server1 -Database db1 -Path \\nas\sqlbackups\keys
 
Logs into sql2016 with Windows credentials then backs up db1's keys to the \\nas\sqlbackups\keys directory.
 
#>

    [CmdletBinding()]
    param (
        [parameter(Mandatory, ValueFromPipeline)]
        [Alias("ServerInstance", "SqlServer")]
        [DbaInstanceParameter[]]$SqlInstance,
        [PSCredential]$SqlCredential,
        [PSCredential]$Credential,
        [string[]]$Database,
        [string[]]$ExcludeDatabase,
        [Security.SecureString]$Password,
        [string]$Path,
        [Microsoft.SqlServer.Management.Smo.Database[]]$InputObject,
        [Alias('Silent')]
        [switch]$EnableException
    )
    begin {
        if ($Credential) {
            $Password = $Credential.Password
        }
    }
    process {
        foreach ($instance in $SqlInstance) {
            $InputObject += Get-DbaDatabase -SqlInstance $SqlInstance -SqlCredential $SqlCredential -Database $Database -ExcludeDatabase $ExcludeDatabase
        }
        
        foreach ($db in $InputObject) {
            $server = $db.Parent
            if (Test-Bound -ParameterName Path -Not) {
                $Path = $server.BackupDirectory
            }
            
            if (!$Path) {
                Stop-Function -Message "Path discovery failed. Please explicitly specify -Path" -Target $server -Continue
            }
            
            if (!(Test-DbaPath -SqlInstance $server -Path $Path)) {
                Stop-Function -Message "$instance cannot access $Path" -Target $server -ErrorRecord $_ -Continue
            }
            
            if (!$db.IsAccessible) {
                Write-Message -Level Warning -Message "Database $db is not accessible. Skipping."
                continue
            }
            
            $masterkey = $db.MasterKey
            
            if (!$masterkey) {
                Write-Message -Message "No master key exists in the $db database on $instance" -Target $db -Level Verbose
                continue
            }
            
            # If you pass a password param, then you will not be prompted for each database, but it wouldn't be a good idea to build in insecurity
            if ((Test-Bound -ParameterName Password -Not) -and (Test-Bound -ParameterName Credential -Not)) {
                $password = Read-Host -AsSecureString -Prompt "You must enter Service Key password for $instance"
                $password2 = Read-Host -AsSecureString -Prompt "Type the password again"
                
                if (([System.Runtime.InteropServices.marshal]::PtrToStringAuto([System.Runtime.InteropServices.marshal]::SecureStringToBSTR($password))) -ne ([System.Runtime.InteropServices.marshal]::PtrToStringAuto([System.Runtime.InteropServices.marshal]::SecureStringToBSTR($password2)))) {
                    Stop-Function -Message "Passwords do not match" -Continue
                }
            }
            
            $time = (Get-Date -Format yyyMMddHHmmss)
            $dbname = $db.name
            $Path = $Path.TrimEnd("\")
            $fileinstance = $instance.ToString().Replace('\', '$')
            $filename = "$Path\$fileinstance-$dbname-$time.key"
            
            try {
                $masterkey.Export($filename, [System.Runtime.InteropServices.marshal]::PtrToStringAuto([System.Runtime.InteropServices.marshal]::SecureStringToBSTR($password)))
                $status = "Success"
            }
            catch {
                $status = "Failure"
                Write-Message -Level Warning -Message "Backup failure: $($_.Exception.InnerException)"
            }
            
            Add-Member -Force -InputObject $masterkey -MemberType NoteProperty -Name ComputerName -value $server.ComputerName
            Add-Member -Force -InputObject $masterkey -MemberType NoteProperty -Name InstanceName -value $server.ServiceName
            Add-Member -Force -InputObject $masterkey -MemberType NoteProperty -Name SqlInstance -value $server.DomainInstanceName
            Add-Member -Force -InputObject $masterkey -MemberType NoteProperty -Name Database -value $dbname
            Add-Member -Force -InputObject $masterkey -MemberType NoteProperty -Name Filename -value $filename
            Add-Member -Force -InputObject $masterkey -MemberType NoteProperty -Name Status -value $status
            
            Select-DefaultView -InputObject $masterkey -Property ComputerName, InstanceName, SqlInstance, Database, 'Filename as Path', Status
        }
    }
    end {
        Test-DbaDeprecation -DeprecatedOn "1.0.0" -EnableException:$false -Alias Backup-DbaDatabaseMasterKey
    }
}