Creating a UserDefined CLR function in .Net
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using Microsoft.SqlServer.Server;
using System.Data.SqlTypes;
using Microsoft.SqlServer.Types;

    namespace ClassLibrary1
    {
        public partial class Class1
        {
            [Microsoft.SqlServer.Server.SqlFunction]
            public static SqlString GetPassword(SqlString Value)
            {
                return Value;
            }
        }
    }

CREATE ASSEMBLY ASSEM
authorization dbo
FROM 'E:NBM Sitestvt.stage.asentechdev1.comClassLibrary1.dll' WITH PERMISSION_SET = SAFE;

CREATE FUNCTION SampleFunc
(
    @value nvarchar(max)
)
RETURNS nvarchar(max) with execute as caller
AS
    External Name ASSEM.Class1.GetPassword
GO

Could not find Type 'Class1' in assembly 'ClassLibrary1'.

CREATE FUNCTION SampleFunc
(
  @value nvarchar(max)
)
RETURNS nvarchar(max) with execute as caller
AS
  External Name [ASSEM].[ClassLibrary1.Class1].[GetPassword]
GO