matrix-js-sdk/src/crypto/algorithms/olm.ts

/*
Copyright 2016 - 2021 The Matrix.org Foundation C.I.C.

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.
*/

/**
 * Defines m.olm encryption/decryption
 *
 * @module crypto/algorithms/olm
 */

import { logger } from '../../logger';
import * as olmlib from "../olmlib";
import { DeviceInfo } from "../deviceinfo";
import {
    DecryptionAlgorithm,
    DecryptionError,
    EncryptionAlgorithm,
    registerAlgorithm,
} from "./base";
import { Room } from '../../models/room';
import { MatrixEvent } from "../..";
import { IEventDecryptionResult } from "../index";

const DeviceVerification = DeviceInfo.DeviceVerification;

interface IMessage {
    type: number;
    body: string;
}

/**
 * Olm encryption implementation
 *
 * @constructor
 * @extends {module:crypto/algorithms/EncryptionAlgorithm}
 *
 * @param {object} params parameters, as per
 *     {@link module:crypto/algorithms/EncryptionAlgorithm}
 */
class OlmEncryption extends EncryptionAlgorithm {
    private sessionPrepared = false;
    private prepPromise: Promise<void> = null;

    /**
     * @private

     * @param {string[]} roomMembers list of currently-joined users in the room
     * @return {Promise} Promise which resolves when setup is complete
     */
    private ensureSession(roomMembers: string[]): Promise<void> {
        if (this.prepPromise) {
            // prep already in progress
            return this.prepPromise;
        }

        if (this.sessionPrepared) {
            // prep already done
            return Promise.resolve();
        }

        this.prepPromise = this.crypto.downloadKeys(roomMembers).then((res) => {
            return this.crypto.ensureOlmSessionsForUsers(roomMembers);
        }).then(() => {
            this.sessionPrepared = true;
        }).finally(() => {
            this.prepPromise = null;
        });

        return this.prepPromise;
    }

    /**
     * @inheritdoc
     *
     * @param {module:models/room} room
     * @param {string} eventType
     * @param {object} content plaintext event content
     *
     * @return {Promise} Promise which resolves to the new event body
     */
    public async encryptMessage(room: Room, eventType: string, content: object): Promise<object> {
        // pick the list of recipients based on the membership list.
        //
        // TODO: there is a race condition here! What if a new user turns up
        // just as you are sending a secret message?

        const members = await room.getEncryptionTargetMembers();

        const users = members.map(function(u) {
            return u.userId;
        });

        await this.ensureSession(users);

        const payloadFields = {
            room_id: room.roomId,
            type: eventType,
            content: content,
        };

        const encryptedContent = {
            algorithm: olmlib.OLM_ALGORITHM,
            sender_key: this.olmDevice.deviceCurve25519Key,
            ciphertext: {},
        };

        const promises = [];

        for (let i = 0; i < users.length; ++i) {
            const userId = users[i];
            const devices = this.crypto.getStoredDevicesForUser(userId);

            for (let j = 0; j < devices.length; ++j) {
                const deviceInfo = devices[j];
                const key = deviceInfo.getIdentityKey();
                if (key == this.olmDevice.deviceCurve25519Key) {
                    // don't bother sending to ourself
                    continue;
                }
                if (deviceInfo.verified == DeviceVerification.BLOCKED) {
                    // don't bother setting up sessions with blocked users
                    continue;
                }

                promises.push(
                    olmlib.encryptMessageForDevice(
                        encryptedContent.ciphertext,
                        this.userId, this.deviceId, this.olmDevice,
                        userId, deviceInfo, payloadFields,
                    ),
                );
            }
        }

        return await Promise.all(promises).then(() => encryptedContent);
    }
}

/**
 * Olm decryption implementation
 *
 * @constructor
 * @extends {module:crypto/algorithms/DecryptionAlgorithm}
 * @param {object} params parameters, as per
 *     {@link module:crypto/algorithms/DecryptionAlgorithm}
 */
class OlmDecryption extends DecryptionAlgorithm {
    /**
     * @inheritdoc
     *
     * @param {MatrixEvent} event
     *
     * returns a promise which resolves to a
     * {@link module:crypto~EventDecryptionResult} once we have finished
     * decrypting. Rejects with an `algorithms.DecryptionError` if there is a
     * problem decrypting the event.
     */
    public async decryptEvent(event: MatrixEvent): Promise<IEventDecryptionResult> {
        const content = event.getWireContent();
        const deviceKey = content.sender_key;
        const ciphertext = content.ciphertext;

        if (!ciphertext) {
            throw new DecryptionError(
                "OLM_MISSING_CIPHERTEXT",
                "Missing ciphertext",
            );
        }

        if (!(this.olmDevice.deviceCurve25519Key in ciphertext)) {
            throw new DecryptionError(
                "OLM_NOT_INCLUDED_IN_RECIPIENTS",
                "Not included in recipients",
            );
        }
        const message = ciphertext[this.olmDevice.deviceCurve25519Key];
        let payloadString;

        try {
            payloadString = await this.decryptMessage(deviceKey, message);
        } catch (e) {
            throw new DecryptionError(
                "OLM_BAD_ENCRYPTED_MESSAGE",
                "Bad Encrypted Message", {
                    sender: deviceKey,
                    err: e,
                },
            );
        }

        const payload = JSON.parse(payloadString);

        // check that we were the intended recipient, to avoid unknown-key attack
        // https://github.com/vector-im/vector-web/issues/2483
        if (payload.recipient != this.userId) {
            throw new DecryptionError(
                "OLM_BAD_RECIPIENT",
                "Message was intented for " + payload.recipient,
            );
        }

        if (payload.recipient_keys.ed25519 != this.olmDevice.deviceEd25519Key) {
            throw new DecryptionError(
                "OLM_BAD_RECIPIENT_KEY",
                "Message not intended for this device", {
                    intended: payload.recipient_keys.ed25519,
                    our_key: this.olmDevice.deviceEd25519Key,
                },
            );
        }

        // check that the original sender matches what the homeserver told us, to
        // avoid people masquerading as others.
        // (this check is also provided via the sender's embedded ed25519 key,
        // which is checked elsewhere).
        if (payload.sender != event.getSender()) {
            throw new DecryptionError(
                "OLM_FORWARDED_MESSAGE",
                "Message forwarded from " + payload.sender, {
                    reported_sender: event.getSender(),
                },
            );
        }

        // Olm events intended for a room have a room_id.
        if (payload.room_id !== event.getRoomId()) {
            throw new DecryptionError(
                "OLM_BAD_ROOM",
                "Message intended for room " + payload.room_id, {
                    reported_room: event.getRoomId(),
                },
            );
        }

        const claimedKeys = payload.keys || {};

        return {
            clearEvent: payload,
            senderCurve25519Key: deviceKey,
            claimedEd25519Key: claimedKeys.ed25519 || null,
        };
    }

    /**
     * Attempt to decrypt an Olm message
     *
     * @param {string} theirDeviceIdentityKey  Curve25519 identity key of the sender
     * @param {object} message  message object, with 'type' and 'body' fields
     *
     * @return {string} payload, if decrypted successfully.
     */
    private async decryptMessage(theirDeviceIdentityKey: string, message: IMessage): Promise<string> {
        // This is a wrapper that serialises decryptions of prekey messages, because
        // otherwise we race between deciding we have no active sessions for the message
        // and creating a new one, which we can only do once because it removes the OTK.
        if (message.type !== 0) {
            // not a prekey message: we can safely just try & decrypt it
            return this.reallyDecryptMessage(theirDeviceIdentityKey, message);
        } else {
            const myPromise = this.olmDevice.olmPrekeyPromise.then(() => {
                return this.reallyDecryptMessage(theirDeviceIdentityKey, message);
            });
            // we want the error, but don't propagate it to the next decryption
            this.olmDevice.olmPrekeyPromise = myPromise.catch(() => {});
            return await myPromise;
        }
    }

    private async reallyDecryptMessage(theirDeviceIdentityKey: string, message: IMessage): Promise<string> {
        const sessionIds = await this.olmDevice.getSessionIdsForDevice(theirDeviceIdentityKey);

        // try each session in turn.
        const decryptionErrors: Record<string, string> = {};
        for (let i = 0; i < sessionIds.length; i++) {
            const sessionId = sessionIds[i];
            try {
                const payload = await this.olmDevice.decryptMessage(
                    theirDeviceIdentityKey, sessionId, message.type, message.body,
                );
                logger.log(
                    "Decrypted Olm message from " + theirDeviceIdentityKey +
                    " with session " + sessionId,
                );
                return payload;
            } catch (e) {
                const foundSession = await this.olmDevice.matchesSession(
                    theirDeviceIdentityKey, sessionId, message.type, message.body,
                );

                if (foundSession) {
                    // decryption failed, but it was a prekey message matching this
                    // session, so it should have worked.
                    throw new Error(
                        "Error decrypting prekey message with existing session id " +
                        sessionId + ": " + e.message,
                    );
                }

                // otherwise it's probably a message for another session; carry on, but
                // keep a record of the error
                decryptionErrors[sessionId] = e.message;
            }
        }

        if (message.type !== 0) {
            // not a prekey message, so it should have matched an existing session, but it
            // didn't work.

            if (sessionIds.length === 0) {
                throw new Error("No existing sessions");
            }

            throw new Error(
                "Error decrypting non-prekey message with existing sessions: " +
                JSON.stringify(decryptionErrors),
            );
        }

        // prekey message which doesn't match any existing sessions: make a new
        // session.

        let res;
        try {
            res = await this.olmDevice.createInboundSession(
                theirDeviceIdentityKey, message.type, message.body,
            );
        } catch (e) {
            decryptionErrors["(new)"] = e.message;
            throw new Error(
                "Error decrypting prekey message: " +
                JSON.stringify(decryptionErrors),
            );
        }

        logger.log(
            "created new inbound Olm session ID " +
            res.session_id + " with " + theirDeviceIdentityKey,
        );
        return res.payload;
    }
}

registerAlgorithm(olmlib.OLM_ALGORITHM, OlmEncryption, OlmDecryption);