1<?php
2
3/**
4 * PHP Class for handling Google Authenticator 2-factor authentication
5 *
6 * @author Michael Kliewe
7 * @copyright 2012 Michael Kliewe
8 * @license http://www.opensource.org/licenses/bsd-license.php BSD License
9 * @link http://www.phpgangsta.de/
10 */
11
12class PHPGangsta_GoogleAuthenticator
13{
14    protected $_codeLength = 6;
15
16    /**
17     * Create new secret.
18     * 16 characters, randomly chosen from the allowed base32 characters.
19     *
20     * @param int $secretLength
21     * @return string
22     */
23    public function createSecret($secretLength = 16)
24    {
25        $validChars = $this->_getBase32LookupTable();
26        unset($validChars[32]);
27
28        $secret = '';
29        for ($i = 0; $i < $secretLength; $i++) {
30            $secret .= $validChars[array_rand($validChars)];
31        }
32        return $secret;
33    }
34
35    /**
36     * Calculate the code, with given secret and point in time
37     *
38     * @param string $secret
39     * @param int|null $timeSlice
40     * @return string
41     */
42    public function getCode($secret, $timeSlice = null)
43    {
44        if ($timeSlice === null) {
45            $timeSlice = floor(time() / 30);
46        }
47
48        $secretkey = $this->_base32Decode($secret);
49
50        // Pack time into binary string
51        $time = chr(0).chr(0).chr(0).chr(0).pack('N*', $timeSlice);
52        // Hash it with users secret key
53        $hm = hash_hmac('SHA1', $time, $secretkey, true);
54        // Use last nipple of result as index/offset
55        $offset = ord(substr($hm, -1)) & 0x0F;
56        // grab 4 bytes of the result
57        $hashpart = substr($hm, $offset, 4);
58
59        // Unpak binary value
60        $value = unpack('N', $hashpart);
61        $value = $value[1];
62        // Only 32 bits
63        $value = $value & 0x7FFFFFFF;
64
65        $modulo = pow(10, $this->_codeLength);
66        return str_pad($value % $modulo, $this->_codeLength, '0', STR_PAD_LEFT);
67    }
68
69    /**
70     * Get QR-Code URL for image, from google charts
71     *
72     * @param string $name
73     * @param string $secret
74     * @return string
75     */
76    public function getQRCodeGoogleUrl($name, $secret) {
77        $urlencoded = urlencode('otpauth://totp/'.rawurlencode($name).'?secret='.$secret.'');
78        return 'https://chart.googleapis.com/chart?chs=200x200&chld=M|0&cht=qr&chl='.$urlencoded.'';
79    }
80
81    /**
82     * Check if the code is correct. This will accept codes starting from $discrepancy*30sec ago to $discrepancy*30sec from now
83     *
84     * @param string $secret
85     * @param string $code
86     * @param int $discrepancy This is the allowed time drift in 30 second units (8 means 4 minutes before or after)
87     * @return bool
88     */
89    public function verifyCode($secret, $code, $discrepancy = 1)
90    {
91        $currentTimeSlice = floor(time() / 30);
92
93        for ($i = -$discrepancy; $i <= $discrepancy; $i++) {
94            $calculatedCode = $this->getCode($secret, $currentTimeSlice + $i);
95            if ($calculatedCode == $code ) {
96                return true;
97            }
98        }
99
100        return false;
101    }
102
103    /**
104     * Set the code length, should be >=6
105     *
106     * @param int $length
107     * @return PHPGangsta_GoogleAuthenticator
108     */
109    public function setCodeLength($length)
110    {
111        $this->_codeLength = $length;
112        return $this;
113    }
114
115    /**
116     * Helper class to decode base32
117     *
118     * @param $secret
119     * @return bool|string
120     */
121    protected function _base32Decode($secret)
122    {
123        if (empty($secret)) return '';
124
125        $base32chars = $this->_getBase32LookupTable();
126        $base32charsFlipped = array_flip($base32chars);
127
128        $paddingCharCount = substr_count($secret, $base32chars[32]);
129        $allowedValues = array(6, 4, 3, 1, 0);
130        if (!in_array($paddingCharCount, $allowedValues)) return false;
131        for ($i = 0; $i < 4; $i++){
132            if ($paddingCharCount == $allowedValues[$i] &&
133                substr($secret, -($allowedValues[$i])) != str_repeat($base32chars[32], $allowedValues[$i])) return false;
134        }
135        $secret = str_replace('=','', $secret);
136        $secret = str_split($secret);
137        $binaryString = "";
138        for ($i = 0; $i < count($secret); $i = $i+8) {
139            $x = "";
140            if (!in_array($secret[$i], $base32chars)) return false;
141            for ($j = 0; $j < 8; $j++) {
142                $x .= str_pad(base_convert(@$base32charsFlipped[@$secret[$i + $j]], 10, 2), 5, '0', STR_PAD_LEFT);
143            }
144            $eightBits = str_split($x, 8);
145            for ($z = 0; $z < count($eightBits); $z++) {
146                $binaryString .= ( ($y = chr(base_convert($eightBits[$z], 2, 10))) || ord($y) == 48 ) ? $y:"";
147            }
148        }
149        return $binaryString;
150    }
151
152    /**
153     * Helper class to encode base32
154     *
155     * @param string $secret
156     * @param bool $padding
157     * @return string
158     */
159    protected function _base32Encode($secret, $padding = true)
160    {
161        if (empty($secret)) return '';
162
163        $base32chars = $this->_getBase32LookupTable();
164
165        $secret = str_split($secret);
166        $binaryString = "";
167        for ($i = 0; $i < count($secret); $i++) {
168            $binaryString .= str_pad(base_convert(ord($secret[$i]), 10, 2), 8, '0', STR_PAD_LEFT);
169        }
170        $fiveBitBinaryArray = str_split($binaryString, 5);
171        $base32 = "";
172        $i = 0;
173        while ($i < count($fiveBitBinaryArray)) {
174            $base32 .= $base32chars[base_convert(str_pad($fiveBitBinaryArray[$i], 5, '0'), 2, 10)];
175            $i++;
176        }
177        if ($padding && ($x = strlen($binaryString) % 40) != 0) {
178            if ($x == 8) $base32 .= str_repeat($base32chars[32], 6);
179            elseif ($x == 16) $base32 .= str_repeat($base32chars[32], 4);
180            elseif ($x == 24) $base32 .= str_repeat($base32chars[32], 3);
181            elseif ($x == 32) $base32 .= $base32chars[32];
182        }
183        return $base32;
184    }
185
186    /**
187     * Get array with all 32 characters for decoding from/encoding to base32
188     *
189     * @return array
190     */
191    protected function _getBase32LookupTable()
192    {
193        return array(
194            'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', //  7
195            'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', // 15
196            'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', // 23
197            'Y', 'Z', '2', '3', '4', '5', '6', '7', // 31
198            '='  // padding char
199        );
200    }
201}
202