PGP for securing my database?

I have considered TDE and cell level encryption mechanism for securing my database, however these two cannot fully satisfy my requirements. I've found that PGP may help me, but it is mainly used for mail services. What is the technical feasibility for implementing PGP for my SQL server database, is there any possibilities for that? TDE does not satisfy my requirements because it only protects data-at-rest. I need to protect the data from an attacker who has access to the database while it is running on the server containing the encryption certificate, as well as the data contained within backups. I'd also like to have some users able to see the decrypted values, while some other users cannot ever see the decrypted values. 1. I have implemented master-slave Replication, and need to enable security without affecting the replication. 2. Approximately 80% of coding has been completed, so its really hard to change the queries and stored procedures. 3. I need to enable security for selected tables only (payments, customer details, password, etc.) 4. I need to secure data from injection.