old_contents: /**
  * @license Apache-2.0
  *
  * Copyright (c) 2018 The Stdlib Authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
  * You may obtain a copy of the License at
  *
  *    http://www.apache.org/licenses/LICENSE-2.0
  *
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS,
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
  
  'use strict';
  
  // MODULES //
  
  var isString = require( '@stdlib/assert/is-string' ).isPrimitive;
  var fromCodePoint = require( '@stdlib/string/from-code-point' );
  var ksa = require( './ksa.js' );
  var prga = require( './prga.js' );
  
  
  // MAIN //
  
  /**
  * Returns an (alleged) RC4 stream cipher.
  *
  *
  * @param {string} key - cipher key
  * @returns {Function} stream cipher
  *
  * @example
  * var encrypt = arc4( 'pwd12' );
  * var out = encrypt( 'beep boop bop' );
  * // returns '...'
  *
  * var decrypt = arc4( 'pwd12' );
  * var str = decrypt( out );
  * // returns 'beep boop bop'
  */
  function arc4( key ) {
  	var getByte;
  	var state;
  	if ( !isString( key ) ) {
  		throw new TypeError( 'invalid input argument. Must provide a string primitive. Value: `' + key + '`.' );
  	}
  	// Initialize the cipher state:
  	state = ksa( key );
  
  	// Generate a pseudorandom generation function:
  	getByte = prga( state );
  
  	return cipher;
  
  	/**
  	* Encrypts a provided string.
  	*
  	* @param {string} str - string to encrypt
  	* @returns {string} encrypted string
  	*
  	* @example
  	* var out = cipher( 'beep boop bop' );
  	* // returns '...'
  	*/
  	function cipher( str ) {
  		var out;
  		var b1;
  		var b2;
  		var ch;
  		var i;
  		if ( !isString( str ) ) {
  			throw new TypeError( 'invalid input argument. Must provide a string primitive. Value: `' + str + '`.' );
  		}
  		out = '';
  		for ( i = 0; i < str.length; i++ ) {
  			// Get a Unicode code point from the provided string:
  			b1 = str.charCodeAt( i );
  
  			// Generate a pseudorandom byte:
  			b2 = getByte();
  
  			// Generate a new character code point:
  			ch = (b1 ^ b2); // bitwise XOR
  
  			// Update the cipher text:
  			out += fromCodePoint( ch );
  		}
  		return out;
  	}
  }
  
  
  // EXPORTS //
  
  module.exports = arc4;
  
new_contents: /**
  * @license Apache-2.0
  *
  * Copyright (c) 2018 The Stdlib Authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
  * You may obtain a copy of the License at
  *
  *    http://www.apache.org/licenses/LICENSE-2.0
  *
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS,
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
  
  'use strict';
  
  // MODULES //
  
  var isString = require( '@stdlib/assert/is-string' ).isPrimitive;
  var fromCodePoint = require( '@stdlib/string/from-code-point' );
  var ksa = require( './ksa.js' );
  var prga = require( './prga.js' );
  
  
  // MAIN //
  
  /**
  * Returns an (alleged) RC4 stream cipher.
  *
  *
  * @param {string} key - cipher key
  * @returns {Function} stream cipher
  *
  * @example
  * var encrypt = arc4( 'pwd12' );
  * var out = encrypt( 'beep boop bop' );
  * // returns '...'
  *
  * var decrypt = arc4( 'pwd12' );
  * var str = decrypt( out );
  * // returns 'beep boop bop'
  */
  function arc4( key ) {
  	var getByte;
  	var state;
  	if ( !isString( key ) ) {
  		throw new TypeError( 'invalid input argument. Must provide a string primitive. Value: `' + key + '`.' );
  	}
  	// Initialize the cipher state:
  	state = ksa( key );
  
  	// Generate a pseudorandom generation function:
  	getByte = prga( state );
  
  	return cipher;
  
  	/**
  	* Encrypts a provided string.
  	*
  	* @private
  	* @param {string} str - string to encrypt
  	* @returns {string} encrypted string
  	*
  	* @example
  	* var out = cipher( 'beep boop bop' );
  	* // returns '...'
  	*/
  	function cipher( str ) {
  		var out;
  		var b1;
  		var b2;
  		var ch;
  		var i;
  		if ( !isString( str ) ) {
  			throw new TypeError( 'invalid input argument. Must provide a string primitive. Value: `' + str + '`.' );
  		}
  		out = '';
  		for ( i = 0; i < str.length; i++ ) {
  			// Get a Unicode code point from the provided string:
  			b1 = str.charCodeAt( i );
  
  			// Generate a pseudorandom byte:
  			b2 = getByte();
  
  			// Generate a new character code point:
  			ch = (b1 ^ b2); // bitwise XOR
  
  			// Update the cipher text:
  			out += fromCodePoint( ch );
  		}
  		return out;
  	}
  }
  
  
  // EXPORTS //
  
  module.exports = arc4;
  
subject: Add private annotation