subject-property-value relationships . As an example , a claim about the subject “ Jane Doe ” can have the property “ alumni of ” with the value “ University A ”. Lastly , credentials hold proofs , which typically holds information about the cryptographic signatures of the issuer . In our simple example , the issuer would be “ University A ”. Therefore , the credential would be signed by the private key of the issuer , which can be verified by the issuer ’ s public key .
There are three different parties involved in the VC data model , which is presented by W3C ( see Figure 1 ) [ 4 ]. These are the issuer , holder , and verifier . A holder is a role an entity might perform by possessing one or more verifiable credentials and generating verifiable presentations from them . Examples of holders include students , employees , and customers . An issuer is a role an entity performs by asserting claims about one or more subjects , creating a verifiable credential from these claims , and transmitting the verifiable credential to a holder . Examples of issuers include corporations , non-profit organizations , trade associations , governments , and individuals . A verifier is a role an entity performs by receiving one or more verifiable credentials , optionally inside a verifiable presentation , for processing . Examples of verifiers include employers , security personnel , and websites .
A verifiable data registry is a role a system might perform by mediating the creation and verification of identifiers , keys , and other relevant data , such as verifiable credential schemas , revocation information , issuer public keys , and so on , which might be required to use verifiable credentials .
2.2 PUBLIC KEY CRYPTOGRAPHY ( PKC )
To digest the concept of TSX for PCF , it is important to get an overview over the concept of PKC [ 6 ]. PKC is the branch of cryptography that enables entities to sign digital documents or issue certificates to other entities asserting attributes about them . The digital signatures and the author of a certificate can be verified through mathematical algorithms .
PKCs create two keys as core components that belong to an entity . These keys are essentially large numbers that enable the signing and verification process of signatures . One of the keys is known as the public key the other is known as the private ( or secret ) key . As the name suggests , the private key is stored in a secure location , whereas the public one is placed in an area that is publicly accessible to everyone .
An entity uses its private key to sign a digital document , which is then sent to a requesting party , depending on the requirement of the application . The party holding the digitally signed document can present the document to a verifying party that considers the contents and then proceeds to verify the signature placed on the document by applying the public key . Thereby , the integrity of the document is ensured by a mathematical process and authenticates that the document was issued by a trusted entity . The verifier achieves this knowledge by getting the public key of the issuer through a trusted source , the so-called verifiable data registry , and then runs verification algorithms to achieve trust in the presented document .
No other public key can verify the integrity and authenticity of a document other than the mathematical pair of that private key . It is evident that the security of the private key storage is
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