Verifiable credentials

We have seen hashes, keys, signatures and certificates. Now we reach the thing that brings them all together: the verifiable credentialA digital document in which an institution signs information about a person and gives it to the person's wallet.. A diploma, a student certificate, a ticket, a professional licence, an identity credential: all can be issued this way.

What is inside?

• Issuer: which institution issued it (and its certificate).
• Type: whether it is a diploma or a ticket. In Tamga each type has a permanent name and rules.
• Claims: the actual content, such as name, programme, graduation date or seat number.
• Validity: when it was issued and until when it is valid.
• Status pointer: where to find out whether it has been revoked.
• Binding to the person: the wallet key the credential is bound to.
• Signature:the institution's digital signature over all of it.

Bound to the person: a credential that cannot be copied

Anyone can copy a PDF and forward it. A verifiable credential is bound, at issuance, to a key on the person's phone. When the credential is presented, the wallet signs one more small proof with that key: holder bindingBinding a credential to a key in the wallet, so that only the wallet holding that key can present it.. Even if a copy of the credential reaches someone else, it cannot be presented without that key.

How it differs from paper

• Software checks it, not a person; it takes seconds.
• A forged credential fails the signature check.
• Claims can be shown one by one; there is no need to hand over the whole document.
• When it is revoked, the verifier finds out immediately.