removed cryptojs from requirements

static/js/modules/interface/main.js

@@ -49,7 +49,10 @@ document.addEventListener("DOMContentLoaded", () => {
             let sig = BigInt(packet.sig);
             // decrypt and compare signature
             let dehash = sender.rsaPubKey.encrypt(sig);
-            let hash = BigInt("0x" + CryptoJS.SHA3(JSON.stringify(data)).toString());
+
+            let hasher = new jsSHA("SHA3-256", "TEXT");
+            hasher.update(JSON.stringify(data));
+            let hash = BigInt("0x" + hasher.getHash("HEX"));
             if (dehash !== hash) {
                 window.console.error(`Signature invalid! Ignoring packet ${data.id}.`);
                 return;

static/js/modules/interface/packet.js

@@ -12,16 +12,12 @@ export class Packet {
 
     static _sign(data) {
         // compute hash of data
-        let hash = CryptoJS.SHA3(JSON.stringify(data));
+        let hasher = new jsSHA("SHA3-256", "TEXT");
-        let res = 0n;
+        hasher.update(JSON.stringify(data));
-        for (let word32 of hash.words) {
+        let hash = BigInt("0x" + hasher.getHash("HEX"));
-            // remove any sign
-            let bi = BigInt.asUintN(32, BigInt(word32));
-            res = (res << 32n) | bi;
-        }
 
         // sign hash
-        let sig = window.rsa.privKey.decrypt(res);
+        let sig = window.rsa.privKey.decrypt(hash);
 
         // return new packet
         return {
@@ -54,22 +50,23 @@ export class Packet {
         });
     }
 
-    static createRandomCyphertext(sessionId, range, cipherText) {
+    static createRandomHMAC(sessionId, range, hmac, key) {
         return this._sign({
             ...this._createBase("RANDOM"),
             session: sessionId,
             range: range,
-            stage: "CIPHERTEXT",
+            stage: "COMMIT",
-            cipherText: cipherText,
+            hmac: hmac,
+            key: key,
         });
     }
 
-    static createRandomKey(sessionId, key) {
+    static createRandomNoise(sessionId, noise) {
         return this._sign({
             ...this._createBase("RANDOM"),
             session: sessionId,
-            stage: "DECRYPT",
+            stage: "REVEAL",
-            cipherKey: key,
+            noise: noise,
         });
     }
 

static/js/modules/interface/random.js

@@ -1,19 +1,24 @@
 import { socket, game } from "./main.js";
 import { Packet } from "./packet.js";
+import { cryptoRandom } from "../crypto/random_primes.js";
 
 class RandomSession {
     constructor(range) {
         this.range = range;
-        this.cipherTexts = {};
+        this.hmacs = {};
-        this.cipherKeys = {};
+        this.keys = {};
-        this.ourKey = CryptoJS.lib.WordArray.random(32).toString();
+        this.noises = {};
-        this.ourNoise = CryptoJS.lib.WordArray.random(8);
+        this.ourKey = cryptoRandom(1024).toString(16);
+        this.ourNoise = cryptoRandom(64);
         this.finalValue = null;
         this.resolvers = [];
     }
 
-    cipherText() {
+    hmac() {
-        return CryptoJS.AES.encrypt(this.ourNoise, this.ourKey).toString();
+        let hasher = new jsSHA("SHA3-256", "HEX");
+        hasher.update(this.ourKey);
+        hasher.update(this.ourNoise.toString(16));
+        return hasher.getHash("HEX");
     }
 }
 
@@ -58,7 +63,7 @@ export class Random {
 
         socket.emit(
             "message",
-            Packet.createRandomCyphertext(sessionId, n, session.cipherText())
+            Packet.createRandomHMAC(sessionId, n, session.hmac(), session.ourKey)
         );
 
         return session;
@@ -78,41 +83,49 @@ export class Random {
             session = this.initialiseSession(data.range, data.session);
         }
 
-        if (stage === "CIPHERTEXT") {
+        if (stage === "COMMIT") {
-            session.cipherTexts[data.author] = data.cipherText;
+            session.hmacs[data.author] = data.hmac;
+            session.keys[data.author] = data.key;
 
             if (
-                Object.keys(session.cipherTexts).length ===
+                Object.keys(session.hmacs).length ===
                 Object.keys(game.players).length - 1
             ) {
                 // Step 3: release our key once all players have sent a ciphertext
                 socket.emit(
                     "message",
-                    Packet.createRandomKey(data.session, session.ourKey)
+                    Packet.createRandomNoise(
+                        data.session,
+                        "0x" + session.ourNoise.toString(16)
+                    )
                 );
             }
-        } else if (stage === "DECRYPT") {
+        } else if (stage === "REVEAL") {
-            session.cipherKeys[data.author] = data.cipherKey;
+            // Check HMAC
+            let noise = BigInt(data.noise) % 2n ** 64n;
+            let hasher = new jsSHA("SHA3-256", "HEX");
+            hasher.update(session.keys[data.author]);
+            hasher.update(noise.toString(16));
+            let hash = hasher.getHash("HEX");
+
+            if (hash === session.hmacs[data.author]) {
+                session.noises[data.author] = noise;
+            }
 
             // Step 4: get final random value
             if (
-                Object.keys(session.cipherKeys).length ===
+                Object.keys(session.noises).length ===
                 Object.keys(game.players).length - 1
             ) {
                 // Lock out wait calls as they may resolve to never-ending promises.
                 await navigator.locks.request(`random-${data.session}`, () => {
-                    let total = BigInt("0x" + session.ourNoise.toString());
+                    let total = session.ourNoise;
 
-                    for (let participant of Object.keys(session.cipherKeys)) {
+                    for (let noise of Object.values(session.noises)) {
-                        let decrypted = CryptoJS.AES.decrypt(
+                        total += noise;
-                            session.cipherTexts[participant],
-                            session.cipherKeys[participant]
-                        ).toString();
-
-                        total += BigInt("0x" + decrypted);
                     }
 
-                    // Find first good block of bits to avoid modular bias
+                    // Find first good block of bits
                     let blockSize = BigInt(Math.ceil(Math.log2(session.range)));
                     let blockMask = 2n ** blockSize - 1n;
 

templates/index.html

@@ -6,7 +6,6 @@
     <link href="{{ url_for('static', filename='css/style.css') }}" rel="stylesheet">
 
     <script src="https://cdn.socket.io/4.5.4/socket.io.min.js"></script>
-    <script src="https://cdnjs.cloudflare.com/ajax/libs/crypto-js/4.1.1/crypto-js.min.js"></script>
     <script src="{{ url_for('static', filename='js/lz-string.min.js') }}"></script>
     <script src="{{ url_for('static', filename='js/sha3.js') }}"></script>
     <script src="{{ url_for('static', filename='js/modules/interface/main.js') }}" type="module"></script>

whitepaper/Dissertation.bib

@@ -286,7 +286,7 @@ howpublished = {\url{https://zcash.readthedocs.io/en/latest/rtd_pages/basics.htm
 }
 
 @misc{jssha,
-    author = {Caligatio},
+    author = {Brian Turek},
     title = {{jsSHA: A JavaScript/TypeScript implementation of the complete Secure Hash Standard (SHA) family}},
     year = {2022},
     publisher = {GitHub},
@@ -522,3 +522,5 @@ author = {"Nir"},
 title = {Frequently Asked Questions | Soulseek},
 howpublished = {\url{http://www.soulseekqt.net/news/faq-page#t10n606}}
 }
+
+@

whitepaper/Dissertation.tex

@@ -83,6 +83,7 @@ We present a modern implementation of the Paillier cryptosystem for the browser,
 		$\lambda(k)$ & Carmichael's totient function \\
 		$H(\dots)$ & Ideal cryptographic hash function \\
 		$\in_R$ & Selection at random \\
+        $A \mathbin\Vert B$ & Concatenation of $A$ and $B$ \\
 		\bottomrule
 	\end{tabularx}
 \end{table}
@@ -598,17 +599,19 @@ This is achieved with a standard application of bit-commitment, and properties o
         \node[draw=blue!50,rectangle,thick,text width=4cm] (NoiseA) at (0,-1.5) {Generate random noise $N_A$, random key $k_A$};
         \node[draw=blue!50,rectangle,thick,text width=4cm] (NoiseB) at (6,-1.5) {Generate random noise $N_B$, random key $k_B$};
 
-        \draw [->,very thick] (0,-3)--node [auto] {$E_{k_A}(N_A)$}++(6,0);
+        \draw [->,very thick] (0,-3)--node [auto] {$H(k_A \mathbin\Vert N_A), k_A$}++(6,0);
-        \draw [<-,very thick] (0,-4)--node [auto] {$E_{k_B}(N_B)$}++(6,0);
+        \draw [<-,very thick] (0,-4)--node [auto] {$H(k_B \mathbin\Vert N_B), k_B$}++(6,0);
 
-        \draw [->,very thick] (0,-5)--node [auto] {$k_A$}++(6,0);
+        \draw [->,very thick] (0,-5)--node [auto] {$N_A$}++(6,0);
-        \draw [<-,very thick] (0,-6)--node [auto] {$k_B$}++(6,0);
+        \draw [<-,very thick] (0,-6)--node [auto] {$N_B$}++(6,0);
 
-        \node[draw=blue!50,rectangle,thick] (CA) at (0,-7) {Compute $N_A + N_B$};
+        \node[draw=blue!50,rectangle,thick] (ChA) at (0,-7) {Check $H(k_B \mathbin\Vert N_B)$};
-        \node[draw=blue!50,rectangle,thick] (CB) at (6,-7) {Compute $N_A + N_B$};
+        \node[draw=blue!50,rectangle,thick] (ChB) at (6,-7) {Check $H(k_A \mathbin\Vert N_A)$};
+        \node[draw=blue!50,rectangle,thick] (CA) at (0,-8) {Compute $N_A + N_B$};
+        \node[draw=blue!50,rectangle,thick] (CB) at (6,-8) {Compute $N_A + N_B$};
 
-        \draw [very thick] (A)-- (NoiseA)-- (CA)-- (0,-7);
+        \draw [very thick] (A)-- (NoiseA)-- (ChA)-- (CA)-- (0,-8);
-        \draw [very thick] (B)-- (NoiseB)-- (CB)-- (6,-7);
+        \draw [very thick] (B)-- (NoiseB)-- (ChB)-- (CB)-- (6,-8);
     \end{tikzpicture}
 \end{center}
 \end{protocol}
@@ -617,7 +620,7 @@ To generalise this to $n$ peers, we ensure that each peer waits to receive all e
 
 Depending on how $N_A + N_B$ is then moved into the required range, this system may be manipulated by an attacker who has some knowledge of how participants are generating their noise. As an example, suppose a random value within range is generated by taking $N_A + N_B \mod 3$, and participants are producing 2-bit noises. An attacker could submit a 3-bit noise with the most-significant bit set, in which case the probability of the final result being a 1 is significantly higher than the probability of a 0 or a 2. This is a typical example of modular bias. To avoid this problem, peers should agree beforehand on the number of bits to transmit, and compute the final value as $N_A \oplus N_B$.
 
-The encryption function used must also guarantee the integrity of decrypted ciphertexts. Otherwise, a malicious party could create a ciphertext which decrypts to multiple valid values by using different keys.
+The hash function used must also be resistant to length-extension attacks for the presented protocol. In general, a hash-based message authentication code can be used.
 
 \begin{proposition}
     With the above considerations, the scheme shown is not manipulable by a single cheater.
@@ -626,13 +629,13 @@ The encryption function used must also guarantee the integrity of decrypted ciph
 \begin{proof}
     Suppose $P_1, \dots, P_{n-1}$ are honest participants, and $P_n$ is a cheater with a desired outcome.
 
-    In step 1, each participant $P_i$ commits $E_{k_i}(N_i)$. The cheater $P_n$ commits a constructed noise $E_{k_n}(N_n)$.
+    In step 1, each participant $P_i$ commits $H(k_i \mathbin\Vert N_i)$. The cheater $P_n$ commits  $H(k_n \mathbin\Vert N_n)$.
 
-    The encryption function $E_k$ holds the confidentiality property: that is, without $k$, $P_i$ cannot retrieve $m$ given $E_k(m)$. So $P_n$'s choice of $N_n$ cannot be directed by other commitments.
+    The hash function $H$ holds the preimage resistance property: that is, $P_i$ cannot find $m$ given $H(m)$. So $P_n$'s choice of $N_n$ cannot be directed by other commitments.
 
     The final value is dictated by the sum of all decrypted values. $P_n$ is therefore left in a position of choosing $N_n$ to control the outcome of $a + N_n$, where $a$ is selected uniformly at random from the abelian group $\mathbb{Z}_{2^\ell}$ for $\ell$ the agreed upon bit length.
 
-    As every element of this group is of order $2^\ell$, the distribution of $a + N_n$ is identical regardless of the choice of $N_n$. So $P_n$ maintains no control over the outcome of $a + N_n$.
+    As every element of this group is of order $2^\ell$, the distribution of $a + N_n$ is identical regardless of the choice of $N_n$. As $P_n$ cannot reasonably find a collision for $H(k_n \mathbin\Vert N_n)$, $P_n$ must reveal $N_n$. So $P_n$ maintains no control over the outcome of $a + N_n$.
 \end{proof}
 
 This extends inductively to support $n-1$ cheating participants, even if colluding. Finally, we must consider how to reduce random noise to useful values.
@@ -652,6 +655,8 @@ Random values are used in two places. \begin{itemize}
 
 As this protocol must run many times during a game, we consider each operation of the protocol as a "session", each of which has a unique name that is derived from the context. A benefit of this is that the unique name can be used with the Web Locks API to prevent race conditions that may occur due to this protocol running asynchronously.
 
+To achieve bit-commitment, we use SHA-3 \cite{FIPS202}, as implemented by jsSHA \cite{jssha}. SHA-3 is resistant to length-extension attacks, and is considered secure, so it is reasonable to assume that a malicious player will not be able to find a collision.
+
 \section{Proof system}
 
 Players should prove a number of properties of their game state to each other to ensure fair play. These are as follows. \begin{enumerate}