DecryptByCert performance

I have bunch of encrypted rows in the table and have stored procedure to select those rows.
It looks like this
SELECT CAST(DecryptByCert(Cert_ID('CertId'), field1) AS VARCHAR) AS f1,
CAST(DecryptByCert(Cert_ID('CertId'), field2) AS VARCHAR) AS f2,
CAST(DecryptByCert(Cert_ID('CertId'), field3) AS VARCHAR(255)) AS f3
FROM [table]

This stored procedure takes really long time even with hundreds of rows, so I suspect that I do something wrong. Is there any way to optimize this stored procedure?

Encryption/decryption by an asymmetric key (i.e. certificate) is much slower than when using a symmetric key.The recommended way to encrypt data is by using a symmetric key (or set of keys if you prefer) for protecting the data (i.e. AES or 3DES key), and protect these key using the certificate.

Another limitation you should consider is that asymmetric key encryption in SQL Server 2005 is limited to only one block of data. This means that the maximum amount of plaintext you can encrypt is limited by the modulus of the private key. In the case of RSA 1024 (in case you are using SQL Server 2005-generated certificates), the maximum plaintext is 117 bytes.

I am also including an additional thread from this forum that talk about this topic:

http://forums.microsoft.com/MSDN/ShowPost.aspx?PostID=114314&SiteID=1

Thanks a lot,

-Raul Garcia

SDE/T

SQL Server Engine