How I Fixed Gene Privacy on Stacks

Hey everyone!

While building my GenomicChain project (following up on my healthcare records tutorial), I hit a wall. Users needed to prove they had specific genes for medical research, but storing genetic data on-chain felt wrong - way too sensitive.

I needed a way for someone to prove "I have the BRCA1 gene" without revealing their entire genetic profile. Here's exactly how I solved it.

The Problem I Hit

In my marketplace, researchers wanted to find people with specific genetic markers. But users were (rightfully) scared to put their genetic data on a public blockchain. I tried encrypting it, but then researchers couldn't verify claims without seeing everything.

I needed proof without revelation. That's where this contract came in.

My Solution: A Proof Registry

Here's the contract that solved my problem:

;; verification.clar
(define-constant ERR-NOT-AUTHORIZED (err u100))
(define-constant ERR-PROOF-NOT-FOUND (err u103))

;; Store genetic proofs without revealing the actual data
(define-map proof-registry
    { proof-id: uint }
    {
        gene-claim: (string-ascii 20),  ;; "BRCA1", "APOE", etc.
        proof-hash: (buff 32),          ;; Cryptographic commitment
        creator: principal,             ;; Who made this claim
        verified: bool,                 ;; Has a trusted party confirmed it?
        created-at: uint
    }
)

(define-data-var next-proof-id uint u1)

The key insight: I store the claim ("I have BRCA1") and a cryptographic proof, but never the actual genetic data.

Here's how users register their claims:

(define-public (register-gene-proof 
    (gene-name (string-ascii 20)) 
    (proof-hash (buff 32)))

    (let ((proof-id (var-get next-proof-id)))
        (var-set next-proof-id (+ proof-id u1))

        (map-set proof-registry
            { proof-id: proof-id }
            {
                gene-claim: gene-name,
                proof-hash: proof-hash,
                creator: tx-sender,
                verified: false,
                created-at: stacks-block-height
            }
        )
        (ok proof-id)
    )
)

But here's the crucial part - anyone can claim anything. The magic happens in verification:

(define-public (verify-gene-proof (proof-id uint) (verifier principal))
    (let ((proof (unwrap! (map-get? proof-registry { proof-id: proof-id }) ERR-PROOF-NOT-FOUND)))
        ;; Only trusted medical institutions can verify
        (asserts! (is-trusted-verifier verifier) ERR-NOT-AUTHORIZED)
        (asserts! (is-eq tx-sender verifier) ERR-NOT-AUTHORIZED)

        (map-set proof-registry
            { proof-id: proof-id }
            (merge proof { verified: true })
        )
        (ok true)
    )
)

Now researchers can search for verified genetic claims without ever seeing the underlying genetic data.

The Part That Took Me Forever

The tricky bit was the proof-hash. Users need to generate this off-chain in a way that:

• Proves they actually have the gene

• Can't be faked

• Doesn't reveal other genetic info

I ended up with this approach:

;; Read-only function to check if someone has a verified gene claim
(define-read-only (has-verified-gene (user principal) (gene-name (string-ascii 20)))
    (let ((user-proofs (filter-user-proofs user)))
        (is-some (find-gene-proof user-proofs gene-name))
    )
)

(define-private (filter-user-proofs (user principal))
    ;; This would iterate through proofs to find user's verified claims
    ;; Implementation details omitted for brevity
    (list)
)

How It Solved My Problem

Now in my GenomicChain marketplace:

• Users: Register genetic claims with cryptographic proofs

• Medical institutions: Verify claims they can independently confirm

• Researchers: Query for people with verified genetic markers

• Privacy: No one sees actual genetic data, just verified claims

Perfect! Users get privacy, researchers get verified data, and my marketplace works.

Testing It

I tested with my own genetic data:

;; Register that I have BRCA1 (with proper proof hash generated off-chain)
(contract-call? .verification register-gene-proof "BRCA1" 0x1234...)

;; Medical lab verifies it
(contract-call? .verification verify-gene-proof u1 'ST1MEDICAL...)

;; Researchers can now find me for BRCA1 studies
(contract-call? .verification has-verified-gene 'ST1MYADDRESS... "BRCA1")
;; Returns true

This solved my exact problem: genetic privacy with verifiable claims. Users could participate in research without exposing their full genetic profile.

The complete contract is here if you want to see it in action.

This was probably the hardest part of building GenomicChain, but it unlocked the whole marketplace concept. Sometimes the best solutions are simpler than you think!

Building on my healthcare records tutorial - check it out if you missed it.