I am developing financial software and need to keep customer data and other secrets secure against OS compromise. Servers will have keys stored in a hardware ta

I am developing financial software and need to keep customer data and other secrets secure against OS compromise. Servers will have keys stored in a hardware tamper-proof USB. All such data will be strongly encrypted. When possible, the data will be used in its encrypted format, and if required to decrypt, the plain text will be transient within the program. What am I missing?