# Can the person who decrypts a homomorphically encrypted value know what operations were run?

I'm looking at the SEAL library but I'm trying to figure out what happens in a certain use case.

For example:

1. Alice encrypts the number 123456 homomorphically and sends it to Bob.

2. Bob adds 25 and does 3 left rotations on the value. He then sends it back.

3. Alice decrypts the value and gets 481123.

Following Step (3), is there a way for Alice to find out what operations Bob ran besides just guessing?

Maybe I'm not just confused about how the noise thing works.

• Are you asking about a specific scheme? The property you're asking about is called circuit privacy and not all homomorphic encryption schemes are circuit private. – Maeher Jul 29 '19 at 20:19
• I don't think I am not asking about a specific scheme but maybe I am. The circuit, which I've only briefly looked at before responding to you, is meant to be a secret from Alice. Bob can know it. I'm just trying to find out whether Alice can ever discover what the circuit did when she receives the result of the computation. I guess specifically, would the SEAL library accomplish this? – Lfod Jul 29 '19 at 20:26

No, not with SEAL at least. The noise is basically a measure of how much uncertainty there is after the operations are performed. Past a certain point there is simply too much and the decryption may be affected by it (the noise does not "round off" correctly), after which decryption may result in incorrect values. Because of this the "noise budget" is used in the library (invariant_noise_budget). Your results can safely be decrypted as long as the noise budget is positive.