Best patterns for encrypting database columns/tables in SQL Azure
I think that your problem can be solved with the MS framework called "Trust Services".
Buck Woody explains in this article how you can use it to solve problems of encrypted data with SQL Azure. From his article, a short description about how to use Trust Services:


  "With the new Trust Services service, the basic process is that you
  use a Portal to create a Trust Server using policies and other
  controls. You place a X.509 Certificate you create or procure in that
  server. Using the Software development Kit (SDK), the developer has
  access to an Application Layer Encryption Framework to set fields of
  data they want to encrypt. From there, the data can be stored in SQL
  Azure as a standard field – only it is encrypted before it ever
  arrives."


Further reference:


Learn More about Microsoft Codename "Trust Services"
Using Certificate-Based Encryption in Windows Azure Applications
Crypto Services and Data Security in Windows Azure
SQL Azure: Securing SQL Azure