JSContact Cryptographic Key Extensions

1.1. Linking Keys to Services

JSContact allows a card to specify online services and cryptographic keys but does not provide a means of specifying which key is to be used for which purpose. This is a particular problem with key formats used to support a wide range of applications, an OpenPGP key may be used to sign email or sign a repository commit.¶

The EmailAddress object and OnlineService object are extended to add a keys property which MAY be used to specify the key identifiers of the related keys.¶

For example, Alice has an email address entry that has keys for signing and encrypting emails using S/MIME and OpenPGP.¶

{
    "@type":"Card",
    ...
    "emails" : $$$$ Empty $$$$,
    ...
    }

1.2. Enhanced specification of cryptographic credentials

The JSContact cryptokeys property allows a card to specify cryptographic credentials as URIs but not their intended uses. A data URI containing an X.509v3 certificate might be intended for use with S/MIME, for code signing or some entirely unrelated purpose. Best design practice encourages the use of common cryptographic infrastructures to support a wide range of applications but best use practices encourage limiting the use of particular cryptographic keys to a single application.¶

The use of the JSON Web Key (JWK) format provides a much richer format for describing cryptographic keys and their properties than a URI and a media type.¶

For example, Bob is trying to send an encrypted email to Alice, her contact card lists two keys but only one is an encryption key with the JWK use parameter enc:¶

[NB: This example is showing presentation as a JWK raw key alone, we would probably want to present the certificate as well, this has been left open so we can have a full discussion before fixing a scheme.]¶

{
    "@type":"Card",
    ...
    "cryptoKeys" : {
...
}

1.3. Groups

It is often convenient to organize related email addresses and online services used for a common purpose into groups.¶

For example, Alice might create separate sets of SSH, repository commit signing and code signing keys for code development:¶

{
    "@type":"Card",
    ...
    "groups" : $$$$ Empty $$$$,
    ...
    }

Each group identifier is specified as an online service:¶

{
    "@type":"Card",
    ...
    "onlineServices" : {
...
}

1.4. Authenticated Locators

The features described in this document are designed to support but not require the exchange of JSContact data by means of an Encrypted Authenticated Resource Locator (EARL) [draft-hallambaker-earl]. An EARL is a URI form that contains a multi-purpose key that MAY be used to locate, decrypt and authenticate an associated ciphertext package.¶

For example, Alice's JSContact information might be retrievable from the EARL:¶

jscontact://example.com/eio5-53ip-ct6i-x7c7-mm6a-65jg-34pw

Alice might publish her EARL on her business card either as text or as a machine readable code such as a QR code. Alternatively, Alice might publish the information as a prefixed DNS TXT record in the domain she uses as her DNS handle:¶

_jscontact.alice.example.com TXT "jscontact=jscontact://example.com/e
    io5-53ip-ct6i-x7c7-mm6a-65jg-34pw"

1.5. Authenticated Updates

The authenticated locator mechanisms described above are intended to be used to establish a 'first contact' between the parties preserving the maximum possible degree of trust from the context.¶

Once the initial contact exchange has been achieved, the credentials exchanged in that first contact SHOULD be used to obtain and authenticate future updates.¶

Contact cards that support updates MUST include a UID property. Updates to contact cards MUST specify the same UID value.¶

The updates property provides an open framework for describing the update mechanisms supported. The mechanisms provided to update the contact MAY be different from the mechanism originally used to distribute it.¶

For example, Alice publishes her current contact card by means of a DNS TXT record containing an EARL and a QR code encoding the same EARL on the business card she presents when meeting people in person. Applications MAY update the card by polling the URI specified in the updates entry and verifying the signature on the plaintext enveloped data returned.¶

{
    "@type":"Card",
    ...
    "updates" : {
"update1" : {
  "@type": "Update",
  "uri": "https://contacts.example.com/NCZD-QRTK-J44L-DB4T-4GY6-B35
B-3OWI",
  "cryptoKeyIds": {
    "MDJ2-HOZA-LLSB-ETKS-4HTO-T2DG-6XOP": "sign"}}}
    ...
    "cryptoKeys" : {
"MDJ2-HOZA-LLSB-ETKS-4HTO-T2DG-6XOP" : {
  "@type": "JsonWebKeySet",
  "jsonWebKeys": [{
      "kty": "OKP",
      "kid": "MDJ2-HOZA-LLSB-ETKS-4HTO-T2DG-6XOP",
      "crv": "Ed448",
      "x": "MP4ugyKPz-2lfMCVDqRHPryM5KLQ5MR85lgzQQS-BlmWmB2Oxau8Mj7
SBg3gb1VIJdmxVE8vrOoA"}
    ]}}
    ...
    }

Since it is easier to update information on a Web site than in DNS or on a business card, it is likely that some users will prefer to use these mechanisms to distribute pro-forma contact information consisting of basic contact information and update information alone. Therefore, contact applications SHOULD attempt to update contact cards providing update information on receipt.¶

Retrieving a plaintext signed contact assertion via HTTPS provides a simple but limited update mechanism providing end-to-end integrity but not confidentiality. While the contact information is delivered over an encrypted transport, the contact card is stored unencrypted on the server which may not be acceptable in certain applications. Another limitation is that the relying party is required to poll the contact service for updates. A more sophisticated updates protocol might provide update notifications. Such considerations are outside the scope of this document and left for future work.¶

[Remark: Addition of a JOSE based encryption scheme would be straightforward. This would require extension of the envelope specification and to pass a decryption key to the parties the contact is passed to.]¶

A contact card MAY specify multiple update mechanisms providing a degree of resilience in the case that a publication service stops providing service.¶

For example, Alice might choose three independent contact directory services publishing her contact information on all three ensuring that the people she has shared her contact information with can remain in contact years or even decades after the initial contact exchange.¶

2.1. Requirements Language

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [RFC2119].¶

2.2. Defined Terms

TBS¶

2.3. Related Specifications

JSContact: A JSON Representation of Contact Data [RFC9553].

Describes the format used for contact data interchange.¶

JSON Web Key (JWK) [RFC7517].

Describes publishing public keys in JSON format.¶

Encrypted Authenticated Resource Locator [draft-hallambaker-earl].

Describes a URI form that provides means of retrieving, decrypting and authenticating an associated ciphertext.¶

2.4. Implementation Status

Reference code under the MIT Open-Source license has been developed to demonstrate all the features described in this document.¶

3.1. Additional Card Properties

The following properties are added to the Card object specified in [RFC9553].¶

"updates": {
  "update1": {
    "@type": "Update",
    "uri": "https://contacts.example.com/NCZD-QRTK-J44L-DB4T-4GY6-B35
        B-3OWI",
    "cryptoKeyIds": {
      "MDJ2-HOZA-LLSB-ETKS-4HTO-T2DG-6XOP": "sign"}}}

"serviceGroups":

3.2. Extended Objects

The following objects specified in [RFC9553] are extended to add the specified properties.¶

3.3. New Objects

The following object is defined:¶

4.1. S/MIME

S/MIME (Secure/Multipurpose Internet Mail Extensions) provides a consistent way to send and receive secure MIME data over SMTP and other messaging transports.¶

Certificates issued for use with S/MIME are commonly used for other purposes, for example TLS client authentication. For the purposes of this discussion, our focus is strictly limited to the use of the certificate for messaging.¶

If the messaging protocol is SMTP, the service is specified as an EmailAddress, otherwise the OnlineService structure is used with the appropriate service specifier.¶

Strawman proposal:¶

• Use a single JWK entry with an x5c to specify the encryption key cert, signature key cert and cert path.¶
• Specify the JWK in the keys section of the corresponding EmailAddress or OnlineService with the key identifier of the corresponding JWK and the 'smime' use.¶

{
    "@type":"Card",
    ...
    "cryptoKeys" : {
...
}

4.2. OpenPGP

OpenPGP provides encryption with public key or symmetric cryptographic algorithms, digital signatures, compression, and key management.¶

OpenPGP key management is commonly used for many purposes including signing repository commits. For the purposes of this section, our focus is strictly limited to the use of keys for messaging.¶

If the messaging protocol is SMTP, the service is specified as an EmailAddress, otherwise the OnlineService structure is used with the appropriate service specifier.¶

Strawman proposal:¶

• User specifies their OpenPGP primary key as an OnlineService with service type 'openpgp'. This is also the place any key server information would be placed.¶
• The first key in the keys entry of the service is the key identifier of the primary key¶
• The sub keys are the following keys¶
• The corresponding key entries are of type JsonWebKey¶
• The key data is specified as a binary data property¶
• Other services specify the subkeys that they use.¶

{
    "@type":"Card",
    ...
    "cryptoKeys" : {
...
}

4.3. SSH

Although the SSH protocol does support certificates these are not currently widely used on the client side and it is not clear that the use case of a single user specifying multiple SSH client keys for use on multiple devices has been fully distinguished from the use case of a corporation certifying keys for multiple employees.¶

If the user only has a client single key for a given use, this can be specified as JWK public key parameters.¶

If the user is making use of client side SSH certificates to provision each device with separate SSH credentials, the contact card should specify the SSH certificate.¶

{
    "@type":"Card",
    ...
    "onlineServices" : {}

{
    "@type":"Card",
    ...
    "cryptoKeys" : {}

4.4. Code Signing

Code signing typically makes use of PKIX certificates. While a single certificate could in practice be used for multiple platforms, each code signing program tends to have their own requirements and set of recognized CAs.¶

It is however useful for a user to specify their own personal hierarchy with a personal root for testing and development purposes.¶

A developer may have multiple code signing keys for the same platform. For example, separate signing keys for each development machine.¶

Some mechanism is required to allow development and production keys to be distinguished.¶

{
    "@type":"Card",
    ...
    "onlineServices" : {}

{
    "@type":"Card",
    ...
    "cryptoKeys" : {}

4.5. Commit Signing

OpenPGP key management is commonly used for signing repository commits.¶

This use is specified by means of an OnlineService with the service type 'commit' with key entries for the set of authorized signing keys.¶

{
    "@type":"Card",
    ...
    "onlineServices" : {}

{
    "@type":"Card",
    ...
    "cryptoKeys" : {}