RFC002 Authentication token
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Nuts foundation
W.M. Slakhorst
Request for Comments: 002
Nedap
S. van der Vegt
Nedap
September 2020
todo
This document describes a Nuts standards protocol.
This document is released under the Attribution-ShareAlike 4.0 International (CC BY-SA 4.0) license.
This document describes the concept of a token which can be used to authenticate a user. The token is a result of an authentication process. Several identification methods can be used, as long as the method of use is capable of creating a digital signature which can be verified by all network participants.
The token proves the relationship between the user and the service provider. This RFC is a specification for §6.5 from the Nuts Start Architecture.
The token is the result of signing a login contract. The login contract is a different way of authentication than normally used. Normally a user discloses something only that user knows and the service provider compares this with the information it knows. The login contract is more of a mandate given by the user to the service provider allowing it to do digital requests on behalf of the user. The mandate is signed by the user by means of a digital signature. The digital signature is created with a private key where the public key has been validated by a trusted third party. This is extremely important for the network. Whereas normal disclosure is only of value between the user and service provider, by adding a signature, the resulting token can be used for requests over the network by the service provider.
todo
The user will be a care professional or patient. The user has a need to process data across care providers. It is the party that needs to be authenticated and authorized. It either is the subject and therefore automatically has certain rights to process data or it is a care professional which also has a relation with a care organization.
The issuer is the trusted third party. Trusting the correct Issuers is a manual configuration task for the service provider. Since trust within Nuts has to be cryptographically proven, this can only be in the form of configuring trusted certificates or public keys. A distributed network of service providers will only work if each party trusts the same set of issuers. To further improve the security and robustness of the network, each proof of a relation between the real world and virtual domain needs to be rooted to a different trusted third party.
The service provider is the party that offers software services that provides the user with access to the virtual domain. The service provider is responsible for implementing all the specifications in software.
The verifier is a service provider that, in the context of this RFC, verifies a token. It could also be the party that holds the desired data for the user. It is responsible for authentication and presumably also the authorization.
The login contract must be human-readable so the user can make a conscious decision about what it’s agreeing to.
The login contract must also be machine-readable. This means that the variation in different contracts must be limited. A fixed set of contracts provides an easy fix.
A verifier must be able to verify the token without contacting external services. Contacting an external service would give that service too much information about care professionals, care organizations and service providers.
The token must hold the correct attributes on the user identity for the specific scope the token is to be used for. This data is shared with a different legal context (eg: different organization) and is therefore subject to legislation.
The token holds a digital signature binding the identity attributes to the login contract. This also makes the token tamper-proof.
The token is only valid during a limited time. This period of validity must be visible in the login contract so the user is aware of the validity period.
A token is limited to a single care organization. The name of the care organization must therefore be displayed in the login contract.
A token can only be used by service providers that provide service for the same care organization stated in the login contract.
A login contract must state a version number. This will allow service providers to update versions independently.
A login contract should be able to support multiple languages.
A mandate usually consists of two parties: the party giving the mandate and the party receiving the mandate. It’s limited in time and limited in scope. The scope for the login contract consists of the care organization the user works for and a custom scope which could limit the use of the contract for data retrieval, single-sign-on or something else.
The following template is to be used to create a token for a care professional:
Or the Dutch version:
Various placeholders are placed between double curly-braces:
service_provider: as defined in this document.
care_organisation: the care organisation the user works for.
valid_from: a specific ISO formatted date time value. The token is not valid before this moment.
valid_to: a specific ISO formatted date time value. The token is not valid after this moment.
A complete example presented to the user would look like:
The time layout used is constructed as: Monday, 2 January 2006 15:04:05 The name of the service provider must match the name that has been registered for this service provider. The name of the care organization must match the name within the proof that has been published by the service provider. The signature must be made by cryptographic means which can be connected to the user.
The Authentication Token MUST be signed by the user. See section 7 for more detail on supported means. In order to support several signing means, the signed token MUST be encapsulated by a Container. As a container specification we use the W3C Verifiable Presentation specification 1.0.
It is recommended to reuse existing specifications for Verifiable Presentations (VP). If no existing specification exists, the type of the VP MUST be prepended with Nuts. This indicates that the VP SHOULD be specified within this RFC.
This specification uses the JSON-LD format for VPs since the JWT format isn't usable for all type of proofs. See the linked data proofs section for more detail.
Future means will be added when available.
IRMA, which stands for “I reveal my attributes” is the name of an app that implements the idemix cryptographic protocol suite. It provides strong authentication as well as privacy-preserving features such as anonymity, the ability to transact without revealing the identity of the transactor, and unlinkability, the ability of a single identity to send multiple transactions without revealing that the transactions were sent by the same identity. More information can be found on the website of the Privacy by Design foundation.
IRMA works by having the service provider show a challenge which can be cryptographically proven by a user, using their mobile. There are three types of challenges IRMA supports:
Loading attributes
Disclosing attributes
Signing
The loading of attributes is required to get the right attributes in the user’s mobile phone. These attributes can later be disclosed to a service provider or can be used to sign data. IRMA supports both desktop and mobile flows. If the user is browsing a website on a desktop, the challenging service provider will show a QR-code to the user. The IRMA app is capable of scanning this QR-code which connects the service provider session to the IRMA app. When browsing a website on the same mobile device, it’s possible to use the IRMA app directly without showing a QR code.
Supported attributes are listed in a so-called scheme. The contents are maintained by the Privacy by design foundation. They ultimately decide if a certain issuer is allowed to join the scheme. This does not mean they control the private keys for each issuer.
Although the IRMA protocol is open, the best way to support IRMA as service provider is to use the available open-source IRMA Go server. The server implementation has been validated and since it contains a lot of complex cryptographical math, it’s better to not build your own implementation.
Since the goal is to identify the user, the selection of attributes used to sign the login contract is crucial. The combination of attributes must be globally unique and must have been obtained at a high level. The list below shows the selection of attributes required together with their issuer. A complete list of supported attributes can be found on the IRMA website.
pbdf.gemeente.personalData.initials
pbdf.gemeente.personalData.familyname
pbdf.gemeente.personalData.dateofbirth
pbdf.gemeente.personalData.digidlevel
pbdf.sidn-pbdf.email.email
The first 3 identify the user but are possibly not unique, therefore the email attribute is added to make the set of attributes unique. The digidlevel is added to assure the attributes were obtained using the correct security level.
When the service provider is using the open-source IRMA Go server the following request must be sent to the correct endpoint:
The message field must have the full login contract as specified in chapter 6. The server will respond with some data that has to be converted into a QR code or a link that will activate the IRMA app on mobile. The response also contains a token that can be used for polling an endpoint for status changes. Interactions on the mobile phone will trigger certain status changes. When the operation is successful the result can be fetched from an endpoint, see the next paragraph. The IRMA javascript library can help in this process.
Below is the response of a successful IRMA signature challenge
The response is quite lengthy and contains tons of information. Luckily the IRMA Go library has functionality to check the signature using information of the well-known IRMA schemes. This will give you information about the validity, the used attributes, the value of the disclosed attributes and at which point in time the signature was created.
The response is used as part of the authorization token in the OAuth flow.
Below is a complete example of how an Irma proof can be embedded in a VP:
Beside the mandatory VP fields, the following applies:
The type field MUST contain the following values ["VerifiablePresentation", "NutsIrmaPresentation"].
The proof field MUST be a singular object.
The proof.type field MUST equal NutsIrmaSignedContract.
The proof.proofValue field MUST be the base64 encoded JSON response from §7.1.3
UZI is a Dutch abbriviation for "Unieke Zorgverlener Identificatienummer" and translates to Unique Care-professional Identification number. The number is issued by the CIBG authority, an organization implementing Dutch government policies related to care professions.
The number is coupled to the BIG register, a Dutch authority which registers the competence of a care professional, based on education and training.
For more detailed information it is recommended to read the Certification Practice Statement, UZI-register v10.0 (UZI CPS from now on).
The UZI number can be used to uniquely identify a care giver. The means to do this is by using a smart card. This card contains 2 or 3 certificates and keypairs. Personal cards have a certificate which can be used to sign data on behalf of the care professional.
Certificates on the card follow a known chain: The certificates descent from the Dutch PKI root Staat der Nederlanden Root CA - G3. The full tree can be found here. Every signature can be verified by validating the chain and checking for revoked cards.
The certificate contains the following attributes which can be used to identify the care giver and optionally their organization. These fields are included here for clarity. More information can be found in the the UZI CPS, section 7.1.5:
oidCa The OID that Identifies the certificates CA. Different CAs are used for different card types.
cardType A single character to represent the card type:
Z: Health care professional (Zorgverlener)
N: Employee registred (Medewerker op naam)
M: Anonymous employee (Medewerker niet op naam)
S: Server
orgID Number to identify the care organization
roleCodeIndicates the profession of the care professional and their specialism.
uziNr The actual identifying number.
givenName First names of certificate holder.
surname Prefix and birthname of certificate holder.
A convenient way of packaging data with its signature is the form of a JWS [RFC7515].
A JWS consists of a header, payload and signature. The header MUST contain the the typ , x5cand alg fields. The type depends on the content of the payload, the x5c field MUST contain the certificate from the UZI card used to sign the JWS. The alg MUST contain the value RS256 value. The payload can be any set of bytes.
The header SHOULD NOT contain any other fields.
The signature MUST be a RS256 signature of ASCII(BASE64URL(UTF8(JWS Protected Header)) || '.' || BASE64URL(JWS Payload))
To use the UZI card to sign an authentication token, the form of a JWT MUST be used. The header typ field MUST contain the value JWT, the payload MUST be an encoded JSON object and MUST have the fields iat set to the issuence time as described in [RFC7519] and the message field set to a valid login contract. The payload JSON object SHOULD NOT contain any other fields.
In order to validate an UZI signed JWS, the validator MUST perform the following checks:
The alg value MUST be equal to RS256
The signature MUST be correct and created with the certificate from the x5c header field
The certificate MUST descend from the known CA tree
The certificate MUST have the repudiation bit set
The certificate MUST NOT be revoked
If the typ is a JWT and the JSON payload contains an iat, the certificate chain MUST be valid at the given date
The following snippets contain examples of an UZI signed JWT with a login contract.
Below is a complete example of how an UZI proof can be embedded in a VP:
Beside the mandatory VP fields, the following applies:
The type field MUST be set to the value ["VerifiablePresentation", "NutsUziPresentation"].
The proof field MUST be a singular object.
The proof.type field MUST equal NutsUziSignedContract.
The proof.proofValue field MUST contain the JWT in its compact serialization form as described in [RFC7515 section 3.1].
