Just one quesrtion: why on Earth? What's this good for? Why doing two roundrips for nothing? There is absolutely no use enctrypting values with symmetric encryption in a web application. Use https and encrypt the traffic, or forget it. Why? Because you neet to send the key also. And at that point the whole encryption is useless.
On the other hand, if you send encrypted data to the client, than you send it beack to the server just to decrypt it, and to send it back unencrypted... well, I prefere not to make any statement about this scenario.
But let's suppose for a second, that for some reason this obscrubtion (as it is not cryptography, just because you use a cryptographic function) is useful. You wrote, that on server side the sql server is encrypting the data with AES (I would never put such a functionality in the datastore tier), and you send this chipertext to the client via an asp.net application. Than you have have a client with a browser where you have javascript also. So why don't you decrypt in javascript? AES is just AES. Just use this for example:
https://code.google.com/p/crypto-js/[
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