refactor utils service to utils

src/services/crypto.service.ts

@@ -355,6 +355,42 @@ export class CryptoService implements CryptoServiceAbstraction {
             macBytes != null ? macBytes.buffer : null, key);
     }
 
+    // EFForg/OpenWireless
+    // ref https://github.com/EFForg/OpenWireless/blob/master/app/js/diceware.js
+    async randomNumber(min: number, max: number): Promise<number> {
+        let rval = 0;
+        const range = max - min + 1;
+        const bitsNeeded = Math.ceil(Math.log2(range));
+        if (bitsNeeded > 53) {
+            throw new Error('We cannot generate numbers larger than 53 bits.');
+        }
+
+        const bytesNeeded = Math.ceil(bitsNeeded / 8);
+        const mask = Math.pow(2, bitsNeeded) - 1;
+        // 7776 -> (2^13 = 8192) -1 == 8191 or 0x00001111 11111111
+
+        // Fill a byte array with N random numbers
+        const byteArray = new Uint8Array(await this.cryptoFunctionService.randomBytes(bytesNeeded));
+
+        let p = (bytesNeeded - 1) * 8;
+        for (let i = 0; i < bytesNeeded; i++) {
+            rval += byteArray[i] * Math.pow(2, p);
+            p -= 8;
+        }
+
+        // Use & to apply the mask and reduce the number of recursive lookups
+        // tslint:disable-next-line
+        rval = rval & mask;
+
+        if (rval >= range) {
+            // Integer out of acceptable range
+            return this.randomNumber(min, max);
+        }
+
+        // Return an integer that falls within the range
+        return min + rval;
+    }
+
     // Helpers
 
     private async aesEncrypt(plainValue: ArrayBuffer, key: SymmetricCryptoKey): Promise<EncryptedObject> {