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
            PS C:\> Backup-DbaDbMasterKey -SqlInstance server1\sql2016
 
            ComputerName : SERVER1
            InstanceName : SQL2016
            SqlInstance : SERVER1\SQL2016
            Database : master
            Filename : E:\MSSQL13.SQL2016\MSSQL\Backup\server1$sql2016-master-20170614162311.key
            Status : Success
 
            Prompts for export password, then logs into server1\sql2016 with Windows credentials then backs up all database keys to the default backup directory.
 
        .EXAMPLE
            PS C:\> 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
    }
}