http-message-signatures

HTTP Message Signatures

This library provides a way to perform HTTP message signing as per the HTTP Working Group draft specification for HTTP Message Signatures.

HTTP Message Signatures are designed to provide a way to verify the authenticity and integrity of parts of an HTTP message by performing a deterministic serialisation of components of an HTTP Message. More details can be found in the specifications.

Specifications

Two specifications are supported by this library:

1. HTTP Working Group spec
2. Network Working Group spec

Approach

As the Network WG specification is now expired and superseded by the HTTP WG one. This library takes a "HTTP WG" approach. This means that most support and maintenance will go into the HTTP WG implementation and syntax. The syntax is then back-ported to the legacy specification as much as possible.

Caveats

The specifications are in draft and are liable to change over time, introducing new features and removing existing ones. The aim is to support the latest version of the specification and not to try to support each version in isolation. However, this library was last updated against revision 13 of the HTTP WG specification.

Limitations in compliance with the specification

As with many libraries and environments, HTTP Requests and Responses are abstracted away from the developer. This fact is noted in the specification. As such (in compliance with the specification), consumers of this library should take care to make sure that they are processing signatures that only cover fields/components whose values can be reliably resolved. Below is a list of limitations that you should be aware of when selecting a list of parameters to sign or accept.

Derived component limitations

Many of the derived components are expected to be sourced from what are effectively http2 pseudo headers. However, if the application is not running in http2 mode or the message being signed is not being built as a http2 message, then some of these pseudo headers will not be available to the application and must be derived from a URL.

@request-target

The @request-target component is intended to be the equivalent to the "request target portion of the request line". See the specification for examples of what this means. In Node.js, this line in requests is automatically constructed for consumers, so it's not possible to know for certainty what this will be. For incoming requests, it is possible to extract, but for simplicity’s sake this library does not process the raw headers for the incoming request and, as such, cannot calculate this value with certainty. It is recommended that this component is avoided.

Multiple message component contexts

As described in section 7.4.4 it is deemed that complex message context resolution is outside the scope of this library.

This means that it is the responsibility of the consumer of this library to construct the equivalent message context for signatures that need to be reinterpreted based on other signer contexts.

Padding attacks

As described in section 7.5.7 it is expected that the Node.js application has taken steps to ensure that headers are valid and not "garbage". For this library to take on that obligation would be to widen the scope of the library to a complete HTTP Message validator.

Examples

NB: These examples show the "minimal" signature implementation. That is, they provider a proof of possession of the key by the sender, but don't provide any integrity over the message. To do that, you must add HTTP fields / components to the signing object. Please see the tests for further examples, or the type definitions.

Signing a request (Node.js)

This library has built-in signers/verifiers for Node.js using the native cryto package to perform all the required cryptographic operations. However, this is designed to be easily replaced with any other crypto library/runtime including SubtleCrypto or even a hosted KMS (Key Management Service).

const { httpbis: { signMessage }, createSigner } = require('http-message-signatures');

(async () => {
    // create a signing key using Node's built in crypto engine.
    // you can supply RSA kets, ECDSA, or ED25519 keys.
    const key = createSigner('sharedsecret', 'hmac-sha256', 'my-key-id');
    // minimal signing of a request - more aspects of the request can be signed by providing additional
    // parameters to the first argument of signMessage.
    const signedRequest = await signMessage({
        key,
    }, {
        method: 'POST',
        url: 'https://example.com',
        headers: {
            'content-type': 'application/json',
            'content-digest': 'sha-512=:YMAam51Jz/jOATT6/zvHrLVgOYTGFy1d6GJiOHTohq4yP+pgk4vf2aCsyRZOtw8MjkM7iw7yZ/WkppmM44T3qg==:',
            'content-length': '19',
        },
        body: '{"hello": "world"}\n',
    });
    // signedRequest now has the `Signature` and `Signature-Input` headers
    console.log(signedRequest);
})().catch(console.error);

This will output the following object (note the new Signature and Signature-Input headers):

{
  method: 'POST',
  url: 'https://example.com',
  headers: {
    'content-type': 'application/json',
    'content-digest': 'sha-512=:YMAam51Jz/jOATT6/zvHrLVgOYTGFy1d6GJiOHTohq4yP+pgk4vf2aCsyRZOtw8MjkM7iw7yZ/WkppmM44T3qg==:',
    'content-length': '19',
    'Signature': 'sig=:RkplfaUzQ4xIkSVP9hT+Y55yAYX9VwSeHmjS5X7d0fE=:',
    'Signature-Input': 'sig=();keyid="my-key-id";alg="hmac-sha256";created=1700669009;expires=1700669309'
  },
  body: '{"hello": "world"}\n'
}

Signing with your own signer

It's possible to provide your own signer (this is useful if you're using a secure enclave or key management service). To do so, you must create an object that conforms to the SigningKey interface.

For example, using SubtleCrypto:

const { webcrypto: crypto } = require('node:crypto');

function createMySigner() {
    return {
        id: 'my-key-id',
        alg: 'hmac-sha256',
        async sign(data) {
            const key = await crypto.subtle.importKey('raw', Buffer.from('sharedsecret'), {
                name: 'HMAC',
                hash: 'SHA-256',
            }, true, ['sign', 'verify']);
            return Buffer.from(await crypto.subtle.sign('HMAC', key, data));
        },
    };
}

Verifying a request

Verifying a message requires that there is a key-store that can be used to look-up keys based on the signature parameters, for example via the signatures keyid.

const { httpbis: { verifyMessage }, createVerifier } = require('http-message-signatures');

(async () => {
    // an example keystore for looking up keys by ID
    const keys = new Map();
    keys.set('my-key-id', {
        id: 'my-key-id',
        algs: ['hmac-sha256'],
        // as with signing, you can provide your own verifier here instead of using the built-in helpers
        verify: createVerifier('sharedsecret', 'hmac-sha256'),
    });
    // minimal verification
    const verified = await verifyMessage({
        // logic for finding a key based on the signature parameters
        async keyLookup(params) {
            const keyId = params.keyid;
            // lookup and return key - note, we could also lookup using the alg too (`params.alg`)
            // if there is no key, `verifyMessage()` will throw an error
            return keys.get(keyId);
        },
    }, {
        method: 'POST',
        url: 'https://example.com',
        headers: {
            'content-type': 'application/json',
            'content-digest': 'sha-512=:YMAam51Jz/jOATT6/zvHrLVgOYTGFy1d6GJiOHTohq4yP+pgk4vf2aCsyRZOtw8MjkM7iw7yZ/WkppmM44T3qg==:',
            'content-length': '19',
            'signature': 'sig=:RkplfaUzQ4xIkSVP9hT+Y55yAYX9VwSeHmjS5X7d0fE=:',
            'signature-input': 'sig=();keyid="my-key-id";alg="hmac-sha256";created=1700669009;expires=1700669309',
        },
    });
    console.log(verified);
})().catch(console.error);

Verifying a response with request components

The HTTP Message Signatures specification allows for responses to reference parts of the request and incorporate them within the signature, tightly binding the response to the request. If you expect that request bound signatures will be used, you can provide the request as an optional parameter to the verifyMessage() method:

const { httpbis: { verifyMessage }, createVerifier } = require('http-message-signatures');

(async () => {
    // an example keystore for looking up keys by ID
    const keys = new Map();
    keys.set('my-key-id', {
        id: 'my-key-id',
        alg: 'hmac-sha256',
        // as with signing, you can provide your own verifier here instead of using the built-in helpers
        verify: createVerifier('sharedsecret', 'hmac-sha256'),
    });
    // minimal verification
    const verified = await verifyMessage({
        // logic for finding a key based on the signature parameters
        async keyLookup(params) {
            const keyId = params.keyid;
            // lookup and return key - note, we could also lookup using the alg too (`params.alg`)
            // if there is no key, `verifyMessage()` will throw an error
            return keys.get(keyId);
        },
    }, {
        // the response
        status: 200,
        headers: {
            'content-type': 'application/json',
            'content-digest': 'sha-512=:YMAam51Jz/jOATT6/zvHrLVgOYTGFy1d6GJiOHTohq4yP+pgk4vf2aCsyRZOtw8MjkM7iw7yZ/WkppmM44T3qg==:',
            'content-length': '19',
            'signature': 'sig=:RkplfaUzQ4xIkSVP9hT+Y55yAYX9VwSeHmjS5X7d0fE=:',
            'signature-input': 'sig=();keyid="my-key-id";alg="hmac-sha256";created=1700669009;expires=1700669309',
        },
    }, {
        // the request
        method: 'POST',
        url: 'https://example.com',
        headers: {
            'content-type': 'application/json',
            'content-digest': 'sha-512=:YMAam51Jz/jOATT6/zvHrLVgOYTGFy1d6GJiOHTohq4yP+pgk4vf2aCsyRZOtw8MjkM7iw7yZ/WkppmM44T3qg==:',
            'content-length': '19',
            'signature': 'sig=:RkplfaUzQ4xIkSVP9hT+Y55yAYX9VwSeHmjS5X7d0fE=:',
            'signature-input': 'sig=();keyid="my-key-id";alg="hmac-sha256";created=1700669009;expires=1700669309',
        },
    });
    console.log(verified);
})().catch(console.error);

Verifying with your own verifier

As with signing, it's possible to provide your own verifier (this is useful if you're running in an environment that may not have access to Node.js' native crypto package). To do so, you must create an object that conforms to the VerifyingKey interface.

For example, using SubtleCrypto:

const { webcrypto: crypto } = require('node:crypto');
const { httpbis: { verifyMessage } } = require('http-message-signatures');

(async () => {
    // an example keystore for looking up keys by ID
    const keys = new Map();
    keys.set('my-key-id', {
        id: 'my-key-id',
        alg: 'hmac-sha256',
        // provide a custom verify function
        async verify(data, signature, parameters) {
            const key = await crypto.subtle.importKey('raw', Buffer.from('sharedsecret'), {
                name: 'HMAC',
                hash: 'SHA-256',
            }, true, ['sign', 'verify']);
            return crypto.subtle.verify('HMAC', key, signature, data);
        },
    });
    // minimal verification
    const verified = await verifyMessage({
        // logic for finding a key based on the signature parameters
        async keyLookup(params) {
            const keyId = params.keyid;
            // lookup and return key - note, we could also lookup using the alg too (`params.alg`)
            // if there is no key, `verifyMessage()` will throw an error
            return keys.get(keyId);
        },
    }, {
        // the request
        method: 'POST',
        url: 'https://example.com',
        headers: {
            'content-type': 'application/json',
            'content-digest': 'sha-512=:YMAam51Jz/jOATT6/zvHrLVgOYTGFy1d6GJiOHTohq4yP+pgk4vf2aCsyRZOtw8MjkM7iw7yZ/WkppmM44T3qg==:',
            'content-length': '19',
            'signature': 'sig=:RkplfaUzQ4xIkSVP9hT+Y55yAYX9VwSeHmjS5X7d0fE=:',
            'signature-input': 'sig=();keyid="my-key-id";alg="hmac-sha256";created=1700669009;expires=1700669309',
        },
    });
    console.log(verified);
})().catch(console.error);

Changelog

1.0.4 (2024-01-16)

Bug Fixes

• never sign empty set of fields (fc9ff1f)