Why we don’t write personal data to the blockchain
Blockchain is immutable; data-protection law grants a right to erasure. We reconcile the two by never putting personal data — not even its hash — on the chain.
Blockchain often brings to mind “writing everything to the chain.” In Tamga Network the opposite is true: personal data is never written to the chain. This is not a limitation we tolerate — it is a foundational rule.
The reason is simple but important: a blockchain is immutable, while data-protection law (GDPR/KVKK) grants individuals a right to erasure. Putting personal data on an immutable ledger conflicts directly with that right. Even an encrypted hash of the data is risky, because a hash can be correlated across contexts and used to re-identify a person.
So what is the chain for?
The chain holds only non-personal trust data: which institution is authorized to issue credentials, its public key, its accreditation and revocation status, schema records. The document itself — the diploma, the prescription, the bill of lading — stays in the holder’s wallet.
ON-CHAIN (public, non-personal) OFF-CHAIN (in the wallet) Root CA anchors the credential itself (SD-JWT) issuer public keys / category personal claims revocation status (StatusList) pairwise pseudonyms
A verifier checks a credential with three free, public read queries — is the issuer valid, is it recognized, is it revoked — without ever contacting the issuer and without any personal data being on the chain. Details: Architecture.