dendrite/vendor/src/github.com/matrix-org/gomatrixserverlib/eventcrypto.go

/* Copyright 2016-2017 Vector Creations Ltd
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package gomatrixserverlib

import (
	"bytes"
	"crypto/sha256"
	"encoding/json"
	"fmt"
	"golang.org/x/crypto/ed25519"
)

// addContentHashesToEvent sets the "hashes" key of the event with a SHA-256 hash of the unredacted event content.
// This hash is used to detect whether the unredacted content of the event is valid.
// Returns the event JSON with a "hashes" key added to it.
func addContentHashesToEvent(eventJSON []byte) ([]byte, error) {
	var event map[string]rawJSON

	if err := json.Unmarshal(eventJSON, &event); err != nil {
		return nil, err
	}

	unsignedJSON := event["unsigned"]

	delete(event, "unsigned")
	delete(event, "hashes")

	hashableEventJSON, err := json.Marshal(event)
	if err != nil {
		return nil, err
	}

	hashableEventJSON, err = CanonicalJSON(hashableEventJSON)
	if err != nil {
		return nil, err
	}

	sha256Hash := sha256.Sum256(hashableEventJSON)
	hashes := struct {
		Sha256 Base64String `json:"sha256"`
	}{Base64String(sha256Hash[:])}
	hashesJSON, err := json.Marshal(&hashes)
	if err != nil {
		return nil, err
	}

	if len(unsignedJSON) > 0 {
		event["unsigned"] = unsignedJSON
	}
	event["hashes"] = rawJSON(hashesJSON)

	return json.Marshal(event)
}

// checkEventContentHash checks if the unredacted content of the event matches the SHA-256 hash under the "hashes" key.
func checkEventContentHash(eventJSON []byte) error {
	var event map[string]rawJSON

	if err := json.Unmarshal(eventJSON, &event); err != nil {
		return err
	}

	hashesJSON := event["hashes"]

	delete(event, "signatures")
	delete(event, "unsigned")
	delete(event, "hashes")

	var hashes struct {
		Sha256 Base64String `json:"sha256"`
	}
	if err := json.Unmarshal(hashesJSON, &hashes); err != nil {
		return err
	}

	hashableEventJSON, err := json.Marshal(event)
	if err != nil {
		return err
	}

	hashableEventJSON, err = CanonicalJSON(hashableEventJSON)
	if err != nil {
		return err
	}

	sha256Hash := sha256.Sum256(hashableEventJSON)

	if bytes.Compare(sha256Hash[:], []byte(hashes.Sha256)) != 0 {
		return fmt.Errorf("Invalid Sha256 content hash: %v != %v", sha256Hash[:], []byte(hashes.Sha256))
	}

	return nil
}

// ReferenceSha256HashOfEvent returns the SHA-256 hash of the redacted event content.
// This is used when referring to this event from other events.
func referenceOfEvent(eventJSON []byte) (EventReference, error) {
	redactedJSON, err := redactEvent(eventJSON)
	if err != nil {
		return EventReference{}, err
	}

	var event map[string]rawJSON
	if err = json.Unmarshal(redactedJSON, &event); err != nil {
		return EventReference{}, err
	}

	delete(event, "signatures")
	delete(event, "unsigned")

	hashableEventJSON, err := json.Marshal(event)
	if err != nil {
		return EventReference{}, err
	}

	hashableEventJSON, err = CanonicalJSON(hashableEventJSON)
	if err != nil {
		return EventReference{}, err
	}

	sha256Hash := sha256.Sum256(hashableEventJSON)

	var eventID string
	if err = json.Unmarshal(event["event_id"], &eventID); err != nil {
		return EventReference{}, err
	}

	return EventReference{eventID, sha256Hash[:]}, nil
}

// SignEvent adds a ED25519 signature to the event for the given key.
func signEvent(signingName, keyID string, privateKey ed25519.PrivateKey, eventJSON []byte) ([]byte, error) {

	// Redact the event before signing so signature that will remain valid even if the event is redacted.
	redactedJSON, err := redactEvent(eventJSON)
	if err != nil {
		return nil, err
	}

	// Sign the JSON, this adds a "signatures" key to the redacted event.
	// TODO: Make an internal version of SignJSON that returns just the signatures so that we don't have to parse it out of the JSON.
	signedJSON, err := SignJSON(signingName, keyID, privateKey, redactedJSON)
	if err != nil {
		return nil, err
	}

	var signedEvent struct {
		Signatures rawJSON `json:"signatures"`
	}
	if err := json.Unmarshal(signedJSON, &signedEvent); err != nil {
		return nil, err
	}

	// Unmarshal the event JSON so that we can replace the signatures key.
	var event map[string]rawJSON
	if err := json.Unmarshal(eventJSON, &event); err != nil {
		return nil, err
	}

	event["signatures"] = signedEvent.Signatures

	return json.Marshal(event)
}

// VerifyEventSignature checks if the event has been signed by the given ED25519 key.
func verifyEventSignature(signingName, keyID string, publicKey ed25519.PublicKey, eventJSON []byte) error {
	redactedJSON, err := redactEvent(eventJSON)
	if err != nil {
		return err
	}

	return VerifyJSON(signingName, keyID, publicKey, redactedJSON)
}