Fix less than ideal random digits generator. Closes #34

lib/index.js

@@ -26,10 +26,21 @@ exports.randomString = function (size) {
 
 exports.randomDigits = function (size) {
 
-    const buffer = exports.randomBits(size * 8);
     const digits = [];
-    for (let i = 0; i < buffer.length; ++i) {
-        digits.push(Math.floor(buffer[i] / 25.6));
+
+    let buffer = internals.random(size * 2);            // Provision twice the amount of bytes needed to increase chance of single pass
+    let pos = 0;
+
+    while (digits.length < size) {
+        if (pos >= buffer.length) {
+            buffer = internals.random(size * 2);
+            pos = 0;
+        }
+
+        if (buffer[pos] < 250) {
+            digits.push(buffer[pos] % 10);
+        }
+        ++pos;
     }
 
     return digits.join('');
@@ -47,21 +58,27 @@ exports.randomBits = function (bits) {
     }
 
     const bytes = Math.ceil(bits / 8);
+    return internals.random(bytes);
+};
+
+
+exports.fixedTimeComparison = function (a, b) {
+
     try {
-        return Crypto.randomBytes(bytes);
+        return Crypto.timingSafeEqual(Buffer.from(a), Buffer.from(b));
     }
     catch (err) {
-        throw Boom.internal('Failed generating random bits: ' + err.message);
+        return false;
     }
 };
 
 
-exports.fixedTimeComparison = function (a, b) {
+internals.random = function (bytes) {
 
     try {
-        return Crypto.timingSafeEqual(Buffer.from(a), Buffer.from(b));
+        return Crypto.randomBytes(bytes);
     }
     catch (err) {
-        return false;
+        throw Boom.internal('Failed generating random bits: ' + err.message);
     }
 };

test/index.js

@@ -48,6 +48,18 @@ describe('randomDigits()', () => {
 
         expect(() => Cryptiles.randomDigits(99999999999999999999)).to.throw(/Failed generating random bits/);
     });
+
+    it('generates equal digits distribution', () => {
+
+        const digits = { 0: 0, 1: 0, 2: 0, 3: 0, 4: 0, 5: 0, 6: 0, 7: 0, 8: 0, 9: 0 };
+        for (let i = 0; i < 1000000; ++i) {
+            digits[Cryptiles.randomDigits(1)] += 1;
+        }
+
+        for (const digit in digits) {
+            expect(digits[digit]).to.be.between(99000, 101000);
+        }
+    });
 });
 
 describe('randomBits()', () => {