diff --git a/README.md b/README.md
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+# random-number-csprng
+
+A CommonJS module for generating cryptographically secure pseudo-random numbers.
+
+Works in Node.js, and should work in the browser as well, using Webpack or Browserify.
+
+This module is based on code [originally written](https://gist.github.com/sarciszewski/88a7ed143204d17c3e42) by [Scott Arciszewski](https://github.com/sarciszewski), released under the WTFPL / CC0 / ZAP.
+
+## License
+
+[WTFPL](http://www.wtfpl.net/txt/copying/) or [CC0](https://creativecommons.org/publicdomain/zero/1.0/), whichever you prefer. A donation and/or attribution are appreciated, but not required.
+
+## Donate
+
+My income consists largely of donations for my projects. If this module is useful to you, consider [making a donation](http://cryto.net/~joepie91/donate.html)!
+
+You can donate using Bitcoin, PayPal, Flattr, cash-in-mail, SEPA transfers, and pretty much anything else.
+
+## Contributing
+
+Pull requests welcome. Please make sure your modifications are in line with the overall code style, and ensure that you're editing the files in `src/`, not those in `lib/`.
+
+Build tool of choice is `gulp`; simply run `gulp` while developing, and it will watch for changes.
+
+Be aware that by making a pull request, you agree to release your modifications under the licenses stated above.
+
+## Usage
+
+This module will return the result asynchronously - this is necessary to avoid blocking your entire application while generating a number.
+
+An example:
+
+```javascript
+var Promise = require("bluebird");
+var randomNumber = require("random-number-csprng");
+
+Promise.try(function() {
+	return randomNumber(10, 30);
+}).then(function(number) {
+	console.log("Your random number:", number);
+}).catch({code: "RandomGenerationError"}, function(err) {
+	console.log("Something went wrong!");
+});
+```
+
+## API
+
+### randomNumber(minimum, maximum, [cb])
+
+Returns a Promise that resolves to a random number within the specified range.
+
+Note that the range is __inclusive__, and both numbers __must be integer values__. It is not possible to securely generate a random value for floating point numbers, so if you are working with fractional numbers (eg. `1.24`), you will have to decide on a fixed 'precision' and turn them into integer values (eg. `124`).
+
+* __minimum__: The lowest possible value in the range.
+* __maximum__: The highest possible value in the range. Inclusive.
+
+Optionally also accepts a nodeback as `cb`, but seriously, you should be using [Promises](https://gist.github.com/joepie91/791640557e3e5fd80861).
+
+### randomNumber.RandomGenerationError
+
+Any errors that occur during the random number generation process will be of this type. The error object will also have a `code` property, set to the string `"RandomGenerationError"`.
+
+The error message will provide more information, but this kind of error will generally mean that the arguments you've specified are somehow invalid.
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diff --git a/gulpfile.js b/gulpfile.js
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+++ b/gulpfile.js
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+var gulp = require('gulp');
+
+/* CoffeeScript compile deps */
+var gutil = require('gulp-util');
+var babel = require('gulp-babel');
+var cache = require('gulp-cached');
+var remember = require('gulp-remember');
+var plumber = require('gulp-plumber');
+
+var source = ["src/**/*.js"]
+
+gulp.task('babel', function() {
+	return gulp.src(source)
+		.pipe(plumber())
+		.pipe(cache("babel"))
+		.pipe(babel({presets: ["es2015"]}).on('error', gutil.log)).on('data', gutil.log)
+		.pipe(remember("babel"))
+		.pipe(gulp.dest("lib/"));
+});
+
+gulp.task('watch', function () {
+	gulp.watch(source, ['babel']);
+});
+
+gulp.task('default', ['babel', 'watch']);
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diff --git a/index.js b/index.js
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+++ b/index.js
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+'use strict';
+
+module.exports = require("./lib");
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diff --git a/lib/index.js b/lib/index.js
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--- /dev/null
+++ b/lib/index.js
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+'use strict';
+
+var Promise = require("bluebird");
+var crypto = Promise.promisifyAll(require("crypto"));
+var createError = require("create-error");
+
+var RandomGenerationError = createError("RandomGenerationError", {
+	code: "RandomGenerationError"
+});
+
+function calculateParameters(range) {
+	/* This does the equivalent of:
+  * 
+  *    bitsNeeded = Math.ceil(Math.log2(range));
+  *    bytesNeeded = Math.ceil(bitsNeeded / 8);
+  *    mask = Math.pow(2, bitsNeeded) - 1;
+  * 
+  * ... however, it implements it as bitwise operations, to sidestep any
+  * possible implementation errors regarding floating point numbers in
+  * JavaScript runtimes. This is an easier solution than assessing each
+  * runtime and architecture individually.
+  */
+
+	var bitsNeeded = 0;
+	var bytesNeeded = 0;
+	var mask = 1;
+
+	while (range > 0) {
+		if (bitsNeeded % 8 === 0) {
+			bytesNeeded += 1;
+		}
+
+		bitsNeeded += 1;
+		mask = mask << 1 | 1; /* 0x00001111 -> 0x00011111 */
+		range = range >> 1; /* 0x01000000 -> 0x00100000 */
+	}
+
+	return { bitsNeeded: bitsNeeded, bytesNeeded: bytesNeeded, mask: mask };
+}
+
+module.exports = function secureRandomNumber(minimum, maximum, cb) {
+	return Promise.try(function () {
+		if (crypto == null || crypto.randomBytesAsync == null) {
+			throw new RandomGenerationError("No suitable random number generator available. Ensure that your runtime is linked against OpenSSL (or an equivalent) correctly.");
+		}
+
+		if (minimum == null) {
+			throw new RandomGenerationError("You must specify a minimum value.");
+		}
+
+		if (maximum == null) {
+			throw new RandomGenerationError("You must specify a maximum value.");
+		}
+
+		if (minimum % 1 !== 0) {
+			throw new RandomGenerationError("The minimum value must be an integer.");
+		}
+
+		if (maximum % 1 !== 0) {
+			throw new RandomGenerationError("The maximum value must be an integer.");
+		}
+
+		if (!(maximum > minimum)) {
+			throw new RandomGenerationError("The maximum value must be higher than the minimum value.");
+		}
+
+		var range = maximum - minimum;
+
+		var _calculateParameters = calculateParameters(range);
+
+		var bitsNeeded = _calculateParameters.bitsNeeded;
+		var bytesNeeded = _calculateParameters.bytesNeeded;
+		var mask = _calculateParameters.mask;
+
+
+		if (bitsNeeded > 53) {
+			throw new RandomGenerationError("Cannot generate numbers larger than 53 bits.");
+		}
+
+		return Promise.try(function () {
+			return crypto.randomBytesAsync(bytesNeeded);
+		}).then(function (randomBytes) {
+			var randomValue = 0;
+
+			/* Turn the random bytes into an integer, using bitwise operations. */
+			for (var i = 0; i < bytesNeeded; i++) {
+				randomValue |= randomBytes[i] << 8 * i;
+			}
+
+			/* We apply the mask to reduce the amount of attempts we might need
+    * to make to get a number that is in range. This is somewhat like
+    * the commonly used 'modulo trick', but without the bias:
+    * 
+    *   "Let's say you invoke secure_rand(0, 60). When the other code 
+    *    generates a random integer, you might get 243. If you take
+    *    (243 & 63)-- noting that the mask is 63-- you get 51. Since
+    *    51 is less than 60, we can return this without bias. If we
+    *    got 255, then 255 & 63 is 63. 63 > 60, so we try again.
+    * 
+    *    The purpose of the mask is to reduce the number of random
+    *    numbers discarded for the sake of ensuring an unbiased
+    *    distribution. In the example above, 243 would discard, but
+    *    (243 & 63) is in the range of 0 and 60."
+    * 
+    *   (Source: Scott Arciszewski)
+    */
+			randomValue = randomValue & mask;
+
+			if (randomValue <= range) {
+				/* We've been working with 0 as a starting point, so we need to
+     * add the `minimum` here. */
+				return minimum + randomValue;
+			} else {
+				/* Outside of the acceptable range, throw it away and try again.
+     * We don't try any modulo tricks, as this would introduce bias. */
+				return secureRandomNumber(minimum, maximum);
+			}
+		});
+	}).nodeify(cb);
+};
+
+module.exports.RandomGenerationError = RandomGenerationError;
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diff --git a/lib/random-bytes.js b/lib/random-bytes.js
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--- /dev/null
+++ b/lib/random-bytes.js
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+"use strict";
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diff --git a/package.json b/package.json
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--- /dev/null
+++ b/package.json
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+{
+  "name": "random-number-csprng",
+  "version": "1.0.0",
+  "description": "A cryptographically secure generator for random numbers in a range.",
+  "main": "index.js",
+  "scripts": {
+    "test": "echo \"Error: no test specified\" && exit 1"
+  },
+  "repository": {
+    "type": "git",
+    "url": "git://github.com/joepie91/node-random-number-csprng"
+  },
+  "keywords": [
+    "csprng",
+    "random",
+    "number",
+    "crypto"
+  ],
+  "author": "Sven Slootweg",
+  "license": "WTFPL",
+  "dependencies": {
+    "bluebird": "^3.3.3",
+    "create-error": "^0.3.1"
+  },
+  "devDependencies": {
+    "babel-preset-es2015": "^6.6.0",
+    "gulp": "^3.9.1",
+    "gulp-babel": "^6.1.2",
+    "gulp-cached": "^1.1.0",
+    "gulp-plumber": "^1.1.0",
+    "gulp-remember": "^0.3.0",
+    "gulp-util": "^3.0.7"
+  }
+}
diff --git a/src/index.js b/src/index.js
new file mode 100644
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--- /dev/null
+++ b/src/index.js
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+'use strict';
+
+const Promise = require("bluebird");
+const crypto = Promise.promisifyAll(require("crypto"));
+const createError = require("create-error");
+
+const RandomGenerationError = createError("RandomGenerationError", {
+	code: "RandomGenerationError"
+});
+
+function calculateParameters(range) {
+	/* This does the equivalent of:
+	 * 
+	 *    bitsNeeded = Math.ceil(Math.log2(range));
+	 *    bytesNeeded = Math.ceil(bitsNeeded / 8);
+	 *    mask = Math.pow(2, bitsNeeded) - 1;
+	 * 
+	 * ... however, it implements it as bitwise operations, to sidestep any
+	 * possible implementation errors regarding floating point numbers in
+	 * JavaScript runtimes. This is an easier solution than assessing each
+	 * runtime and architecture individually.
+	 */
+	
+	let bitsNeeded = 0;
+	let bytesNeeded = 0;
+	let mask = 1;
+	
+	while (range > 0) {
+		if (bitsNeeded % 8 === 0) {
+			bytesNeeded += 1;
+		}
+		
+		bitsNeeded += 1;
+		mask = mask << 1 | 1; /* 0x00001111 -> 0x00011111 */
+		range = range >> 1;   /* 0x01000000 -> 0x00100000 */
+	}
+	
+	return {bitsNeeded, bytesNeeded, mask};
+}
+
+module.exports = function secureRandomNumber(minimum, maximum, cb) {
+	return Promise.try(() => {
+		if (crypto == null || crypto.randomBytesAsync == null) {
+			throw new RandomGenerationError("No suitable random number generator available. Ensure that your runtime is linked against OpenSSL (or an equivalent) correctly.");
+		}
+		
+		if (minimum == null) {
+			throw new RandomGenerationError("You must specify a minimum value.");
+		}
+		
+		if (maximum == null) {
+			throw new RandomGenerationError("You must specify a maximum value.");
+		}
+		
+		if (minimum % 1 !== 0) {
+			throw new RandomGenerationError("The minimum value must be an integer.");
+		}
+		
+		if (maximum % 1 !== 0) {
+			throw new RandomGenerationError("The maximum value must be an integer.");
+		}
+		
+		if (!(maximum > minimum)) {
+			throw new RandomGenerationError("The maximum value must be higher than the minimum value.")
+		}
+		
+		let range = maximum - minimum;
+		let {bitsNeeded, bytesNeeded, mask} = calculateParameters(range);
+		
+		if (bitsNeeded > 53) {
+			throw new RandomGenerationError("Cannot generate numbers larger than 53 bits.");
+		}
+		
+		return Promise.try(() => {
+			return crypto.randomBytesAsync(bytesNeeded);
+		}).then((randomBytes) => {
+			var randomValue = 0;
+			
+			/* Turn the random bytes into an integer, using bitwise operations. */
+			for (let i = 0; i < bytesNeeded; i++) {
+				randomValue |= (randomBytes[i] << (8 * i));
+			}
+			
+			/* We apply the mask to reduce the amount of attempts we might need
+			 * to make to get a number that is in range. This is somewhat like
+			 * the commonly used 'modulo trick', but without the bias:
+			 * 
+			 *   "Let's say you invoke secure_rand(0, 60). When the other code 
+			 *    generates a random integer, you might get 243. If you take
+			 *    (243 & 63)-- noting that the mask is 63-- you get 51. Since
+			 *    51 is less than 60, we can return this without bias. If we
+			 *    got 255, then 255 & 63 is 63. 63 > 60, so we try again.
+			 * 
+			 *    The purpose of the mask is to reduce the number of random
+			 *    numbers discarded for the sake of ensuring an unbiased
+			 *    distribution. In the example above, 243 would discard, but
+			 *    (243 & 63) is in the range of 0 and 60."
+			 * 
+			 *   (Source: Scott Arciszewski)
+			 */
+			randomValue = randomValue & mask;
+			
+			if (randomValue <= range) {
+				/* We've been working with 0 as a starting point, so we need to
+				 * add the `minimum` here. */
+				return minimum + randomValue;
+			} else {
+				/* Outside of the acceptable range, throw it away and try again.
+				 * We don't try any modulo tricks, as this would introduce bias. */
+				return secureRandomNumber(minimum, maximum);
+			}
+		});
+	}).nodeify(cb);
+}
+
+module.exports.RandomGenerationError = RandomGenerationError;
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diff --git a/test-distribution.js b/test-distribution.js
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+++ b/test-distribution.js
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+const randomNumber = require("./");
+const Promise = require("bluebird");
+
+Promise.map((new Array(2000000)), () => {
+	return randomNumber(10, 30);
+}).reduce((stats, number) => {
+	if (stats[number] == null) {
+		stats[number] = 0;
+	}
+	
+	stats[number] += 1;
+	return stats;
+}, {}).then((stats) => {
+	console.log(stats);
+});
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