When encrypting data the encrypted text must differ for same values

This is part of the Semicolon&Sons Code Diary - consisting of lessons learned on the job. You're in the security category.

Last Updated: 2021-05-16

I was storing medical test data in the Project S database. The test was either positive or negative. My first instinct was to encrypt the result. But I realized just in time that a simple encrypt(result) call would cause all positive items to have the same encrypted text. Thus if you knew one patient's result was positive, you knew them all.

I got around this by adding another field that varied with each record, such that there would be no discernible pattern in the encrypted text: encrypt(result, uuid)