Ensure bit length of randomly generated numbers are fine

static/js/modules/crypto/paillier.js

@@ -1,14 +1,15 @@
-import { random2048, generate_prime } from "./random_primes.js";
+import { cryptoRandom, generate_prime } from "./random_primes.js";
 import { mod_exp } from "./math.js";
 
 class Cyphertext {
-    constructor(key, plainText) {
-        // Compute g^m r^n mod n^2
-        let r = random2048();
+    constructor(key, plainText, r) {
+        if (r === undefined) {
+            r = cryptoRandom(4096);
 
-        // Resample to avoid modulo bias.
-        while (r >= key.n) {
-            r = random2048();
+            // Resample to avoid modulo bias.
+            while (r >= key.n) {
+                r = cryptoRandom(4096);
+            }
         }
 
         // Compute g^m by binomial theorem.
@@ -21,13 +22,11 @@ class Cyphertext {
         this.plainText = plainText;
 
         this.readOnly = false;
-
-        this.rp = null;
     }
 
     update(c) {
-        this.cyphertext *= c.cyphertext;
-        this.r *= c.r;
+        this.cyphertext = (this.cyphertext * c.cyphertext) % this.pubKey.n ** 2n;
+        this.r = (this.r * c.r) % this.pubKey.n ** 2n;
         this.plainText += c.plainText;
     }
 
@@ -48,9 +47,9 @@ class ProofSessionProver {
     constructor(cipherText) {
         this.cipherText = cipherText;
 
-        this.rp = random2048();
+        this.rp = cryptoRandom(4096);
         while (this.rp >= this.cipherText.pubKey.n) {
-            this.rp = random2048();
+            this.rp = cryptoRandom(4096);
         }
     }
 
@@ -59,12 +58,17 @@ class ProofSessionProver {
     }
 
     prove(challenge) {
-        return {
-            proof:
-                ((this.rp % this.cipherText.pubKey.n) *
-                    mod_exp(this.cipherText.r, challenge, this.cipherText.pubKey.n)) %
-                this.cipherText.pubKey.n,
-        };
+        return (
+            ((this.rp % this.cipherText.pubKey.n) *
+                mod_exp(this.cipherText.r, challenge, this.cipherText.pubKey.n)) %
+            this.cipherText.pubKey.n
+        );
+    }
+
+    asVerifier() {
+        return this.cipherText
+            .asReadOnlyCyphertext()
+            .prove(this.cipherText.plainText, this.noise());
     }
 }
 
@@ -76,24 +80,23 @@ export class ReadOnlyCyphertext {
         this.pubKey = key;
 
         this.readOnly = true;
-
-        this.proofPromise = null;
     }
 
     update(c) {
-        this.cyphertext *= c.cyphertext;
+        this.cyphertext = (this.cyphertext * c.cyphertext) % this.pubKey.n ** 2n;
     }
 
-    async prove() {
-        // request a proof
-        let promise = new Promise((res) => (this.proofPromise = res));
+    prove(plainText, a) {
+        return new ProofSessionVerifier(this, plainText, a);
     }
 }
 
 class ProofSessionVerifier {
-    constructor(cipherText, a) {
+    constructor(cipherText, plainText, a) {
         this.cipherText = cipherText;
-        this.challenge = random2048();
+        this.cipherText.update(this.cipherText.pubKey.encrypt(-1n * plainText, 1n));
+        // Shift the challenge down by 1 to ensure it is smaller than either prime factor.
+        this.challenge = cryptoRandom(2048) << 1n;
         this.a = a;
     }
 
@@ -126,8 +129,8 @@ export class PaillierPubKey {
         this.g = this.n + 1n;
     }
 
-    encrypt(m) {
-        return new Cyphertext(this, m);
+    encrypt(m, r) {
+        return new Cyphertext(this, m, r);
     }
 
     toJSON() {

static/js/modules/crypto/paillier_proof.js

@@ -1,28 +0,0 @@
-import { random2048 } from "./random_primes.js";
-import { mod_exp } from "./math";
-
-class PlaintextVerifier {
-    constructor(cyphertext, value, pub_key) {
-        this.proving =
-            (cyphertext * mod_exp(pub_key.g, value, pub_key.n ** 2)) % pub_key.n ** 2;
-        this.challenge = random2048();
-    }
-
-    verify(response) {}
-}
-
-class PlaintextProver {
-    constructor(cyphertext, pub_key, priv_key) {
-        this.value = priv_key.decrypt(cyphertext.text);
-        this.mixin = random2048();
-
-        this.pubKey = pub_key;
-    }
-
-    handleChallenge(challenge) {
-        return (
-            (this.mixin * mod_exp(cyphertext.mixin, challenge, this.pubKey.n)) %
-            this.pubKey.n
-        );
-    }
-}

static/js/modules/crypto/random_primes.js

@@ -1,7 +1,12 @@
 import { mod_exp } from "./math.js";
 
-export function random2048() {
-    const byteArray = new BigUint64Array(32);
+export function cryptoRandom(bits) {
+    if (bits === undefined) {
+        bits = 2048;
+    }
+    let length = bits / 64;
+
+    const byteArray = new BigUint64Array(length);
     window.crypto.getRandomValues(byteArray);
     let intRepr = 0n;
     for (let int of byteArray) {
@@ -18,7 +23,7 @@ export function random2048() {
  * We generate between 2^2047 and 2^2048 - 1 by adding differences.
  */
 function generate_bigint() {
-    let intRepr = random2048();
+    let intRepr = cryptoRandom();
 
     // Drop the MSB to force into range from above
     intRepr >>= 1n;
@@ -56,7 +61,7 @@ function miller_rabin(n, k) {
     }
 
     for (; k > 0; k--) {
-        let a = random2048();
+        let a = cryptoRandom();
         let x = mod_exp(a, d, n);
 
         if (x === 1n || x === n - 1n) {