Retrieve blog credentials using Windows Live Writer SDK. Source: blog comments here http://lozanotek.com/blog/archive/2007/07/22/Using_The_Windows_Live_Writer_API_To_Retrieve_Your_Blog_Password.aspx#27081

BlogCredentials.cs

  using System;
using Microsoft.Win32;

// Add a ref to C:\Program Files (x86)\Windows Live\Writer\WindowsLive.Writer.BlogClient.dll
using WindowsLive.Writer.BlogClient;

// Add a ref to C:\Program Files (x86)\Windows Live\Writer\WindowsLive.Writer.CoreServices.dll
using WindowsLive.Writer.CoreServices.Settings;
using WindowsLive.Writer.CoreServices;

namespace RecoverLiveWriterCredentials
{
    class Program
    {
        static void Main(string[] args)
        {
            ApplicationEnvironment.Initialize();

            RegistrySettingsPersister persister =
            new RegistrySettingsPersister(Registry.CurrentUser,
            @"Software\\Microsoft\\Windows Live\\Writer\\Weblogs");

            string[] names = persister.GetSubSettings();
            for (int i = 0; i < names.Length; i++)
            {
                ISettingsPersister blogPersister = persister.GetSubSettings(names[i]);
                SettingsPersisterHelper settings = new SettingsPersisterHelper(blogPersister);

                CredentialsDomain domain = new CredentialsDomain("name", "description", null, null);
                BlogCredentials creds = new BlogCredentials(settings, domain);

                Console.WriteLine("Blog: {0}", blogPersister.Get("BlogName"));
                Console.WriteLine("Username: {0}", creds.Username);
                Console.WriteLine("Password: {0}", creds.Password);
                Console.WriteLine();
            }
            Console.ReadLine();
        }
    }
}