# Proving that a value has been extracted from a witness

**URL:** <https://community.zkproof.org/t/proving-that-a-value-has-been-extracted-from-a-witness/803>\
**Category:** Miscellaneous\
**Created:** [October 23, 2023, 11:26pm UTC](https://community.zkproof.org/t/proving-that-a-value-has-been-extracted-from-a-witness/803 "2023-10-23T23:26:13Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![harpocrates](https://avatars.discourse-cdn.com/v4/letter/h/b4bc9f/32.png) [@harpocrates](https://community.zkproof.org/u/harpocrates)\
**Post date:** [October 23, 2023, 11:26pm UTC](https://community.zkproof.org/t/proving-that-a-value-has-been-extracted-from-a-witness/803/1 "2023-10-23T23:26:14Z")

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Hey, I’m not new to zk proofs but never coded anything before. I have in mind to do some processing on encrypted data using FHE and return it to my user. I think I can figure out this part. However when they receive the encrypted message they need to send me back something they would extract from the decrypted message (which I would never see) and I need them to prove me that it’s been extracted from it. How could I achieve something like that ? Of course that would be extracted using a certain function they would run on it.

Thanks