How to securely store passwords for remote services?

Question

How can I securely store login credentials for remote service in my web applications database?

I have to allow web applications administrator to set the username/password for remote Exchange server. I believe I cannot use hashing since I need the exact password to authenticate to the remote service. I am wondering what is the most secure way to handle this?

Answer 1

There are several options I believe:

• encryption by passphrase: http://technet.microsoft.com/en-us/library/ms190357.aspx
• asymetric key: http://technet.microsoft.com/en-us/library/ms186950.aspx
• certificate: http://technet.microsoft.com/en-us/library/ms188061.aspx
• symetric key: http://technet.microsoft.com/en-us/library/ms174361.aspx