Riskless/static/js/random.js

class RandomSession {
    constructor(range) {
        this.range = range;
        this.cipherTexts = {};
        this.cipherKeys = {};
        this.ourKey = CryptoJS.lib.WordArray.random(32).toString();
        // 32-bit as JavaScript does funny stuff at 64-bit levels.
        this.ourNoise = CryptoJS.lib.WordArray.random(4).toString();
        this.finalValue = null;
        this.resolvers = [];
    }

    cipherText() {
        return CryptoJS.AES.encrypt(this.ourNoise, this.ourKey).toString();
    }
}

class Random {
    constructor() {
        this.locked = false;
        this.sessions = {};
    }

    get(sessionId) {
        // Spin until lock frees.
        while (this.locked);

        if (this.sessions[sessionId].finalValue === null) {
            let session = this.sessions[sessionId];
            let resolver;
            let promise = new Promise((resolve) => {
                resolver = resolve;
            });
            session.resolvers.push(resolver);
            return promise;
        } else {
            return new Promise((resolve) => {
                resolve(this.sessions[sessionId].finalValue);
            });
        }
    }

    /**
     * Start a cooperative random session.
     */
    coopRandom(n, sessionId) {
        let session = new RandomSession(n);
        if (sessionId === undefined) {
            sessionId = window.crypto.randomUUID();
        }

        this.sessions[sessionId] = session;

        socket.emit("message", {
            type: "RANDOM",
            author: ID,
            session: sessionId,
            range: n,
            stage: "CIPHERTEXT",
            cipherText: session.cipherText(),
        });

        return sessionId;
    }

    /**
     * Process cooperative random protocol.
     *
     * @param data Packet received
     */
    processCooperativeRandom(data) {
        // Step 0: extract relevant information from data
        let session = this.sessions[data.session];
        const stage = data.stage;

        if (session === undefined) {
            // Step 1: generate and encrypt our random value. 8 bytes = 64 bit integer
            const noise = CryptoJS.lib.WordArray.random(8).toString();
            console.log(`our noise: ${noise}`);

            session = new RandomSession(data.range);
            this.sessions[data.session] = session;

            // Step 2: send our random value and wait for all responses
            socket.emit("message", {
                type: "RANDOM",
                author: ID,
                session: data.session,
                stage: "CIPHERTEXT",
                range: data.range,
                cipherText: session.cipherText(),
            });
        }

        if (stage === "CIPHERTEXT") {
            session.cipherTexts[data.author] = data.cipherText;

            if (
                Object.keys(session.cipherTexts).length ===
                Object.keys(players).length - 1
            ) {
                // Step 3: release our key once all players have sent a ciphertext
                socket.emit("message", {
                    type: "RANDOM",
                    author: ID,
                    session: data.session,
                    stage: "DECRYPT",
                    cipherKey: session.ourKey,
                });
            }
        } else if (stage === "DECRYPT") {
            session.cipherKeys[data.author] = data.cipherKey;

            // Step 4: get final random value
            if (
                Object.keys(session.cipherKeys).length ===
                Object.keys(players).length - 1
            ) {
                // Lock out wait calls as they may resolve to never-ending promises.
                this.locked = true;

                let total = 0;

                for (let participant of Object.keys(session.cipherKeys)) {
                    total += CryptoJS.AES.decrypt(
                        session.cipherTexts[participant],
                        session.cipherKeys[participant]
                    );
                }

                session.finalValue = total % session.range;

                this.resolve(data.session);

                this.locked = false;
            }
        }
    }

    /**
     * Resolve a session by calling any callbacks associated with the session and then deleting it.
     *
     * @param sessionId
     */
    resolve(sessionId) {
        const session = this.sessions[sessionId];
        for (let resolve of session.resolvers) {
            resolve(session.finalValue);
        }
    }
}