Question

I thank you in advance for sharing your knowledge. Here is my question:
By default, SQL Azure connections are encrypted. so what is the significance of checking the ‘encrypt connection’ checkbox in the connection properties while connecting to SQL Azure from SSMS? Does it make any difference?

Answer 1

Paras,

When the client library first attempts a connection to SQL Server / SQL Azure, it sends an initial connection request. Consider this a “pre-pre-connection” request. At this point the client does not know if SSL/Encryption is required and waits an answer from SQL Server/SQL Azure to determine if SSL is indeed required throughout the session (not just the login sequence, the entire connection session). A bit is set on the response indicating so. Then the client library disconnects and reconnects armed with this information.

Consider a proxy sitting between the client and SQL Azure (or SQL Server). The client talks to the proxy, and the proxy talks to SQL Azure/Sql Server. If you do not force the encryption bit on the client, you leave it to the proxy to encrypt or not the session. The proxy could encrypt the connection on the backend (it would have to for SQL Azure) but not on the client-side of the connection, hence accessing all your sensitive data. So checking the encryption box bypasses the “pre-pre-connection” request which prevents any proxy from turning off the encryption bit in question on the client side of the proxy, hence avoiding the man-in-the-middle attack.

Hopefully that makes sense… 🙂 If you download Wireshark and watch what happens with the pre-pre-login packets, you will see what I mean. Checking the box changes the pre-login handshake mechanism to avoid the man-in-the-middle attack I described.