How to encrypt only one field (Credit Card field)

Hello PI guru

We are using SAP PI 7.4 (Single Stack). I have a requirement where in I am getting PGP encrypted CSV file which I have to decrypt

and then do the mapping and send it to the target.

Each record will have a credit card number field which should be encrypted before being sent to the target system (SAP)

Without using UDF, is there a good way of achieving this?

Some limitations are

1. The source can't encrypt it.

2. For many reasons (including java resource) we don't want to use UDF.

Any comment or feedback will be highly appreciated.

Thanks in advance
Ram