Performance of Encryption algorithms

I am in the stage of design for an application that uses SQL server 2005. We intended to encrypt some sensitve data using the encryption features in SQL server 2005. we will use symmetric key encryption. The question here is which symmetric encryption algorithm has the best performance? how much does the key size affect the perfromance? the data to be encrypted will be some lines of text equal to a word document.
any ideas?

Hi Muhammad,

We don't have explicit numbers for the performance of different algorithms/key lengths yet but from what we have seen there is no significant difference. The biggest performance impact is how the data is stored (i.e. storing encrypted data across very many rows in lots of columns and then selecting every column and every row is much more expensive than selectively retrieving a small set of rows/columns).

If you would like more details, please let me know,

Sung