1<?php
  2
  3if (class_exists('ParagonIE_Sodium_Core_ChaCha20_Ctx', false)) {
  4    return;
  5}
  6
  7/**
  8 * Class ParagonIE_Sodium_Core_ChaCha20_Ctx
  9 */
 10class ParagonIE_Sodium_Core_ChaCha20_Ctx extends ParagonIE_Sodium_Core_Util implements ArrayAccess
 11{
 12    /**
 13     * @var SplFixedArray internally, <int, int>
 14     */
 15    protected $container;
 16
 17    /**
 18     * ParagonIE_Sodium_Core_ChaCha20_Ctx constructor.
 19     *
 20     * @internal You should not use this directly from another application
 21     *
 22     * @param string $key     ChaCha20 key.
 23     * @param string $iv      Initialization Vector (a.k.a. nonce).
 24     * @param string $counter The initial counter value.
 25     *                        Defaults to 8 0x00 bytes.
 26     * @throws InvalidArgumentException
 27     * @throws TypeError
 28     */
 29    public function __construct($key = '', $iv = '', $counter = '')
 30    {
 31        if (self::strlen($key) !== 32) {
 32            throw new InvalidArgumentException('ChaCha20 expects a 256-bit key.');
 33        }
 34        if (self::strlen($iv) !== 8) {
 35            throw new InvalidArgumentException('ChaCha20 expects a 64-bit nonce.');
 36        }
 37        $this->container = new SplFixedArray(16);
 38
 39        /* "expand 32-byte k" as per ChaCha20 spec */
 40        $this->container[0]  = 0x61707865;
 41        $this->container[1]  = 0x3320646e;
 42        $this->container[2]  = 0x79622d32;
 43        $this->container[3]  = 0x6b206574;
 44        $this->container[4]  = self::load_4(self::substr($key, 0, 4));
 45        $this->container[5]  = self::load_4(self::substr($key, 4, 4));
 46        $this->container[6]  = self::load_4(self::substr($key, 8, 4));
 47        $this->container[7]  = self::load_4(self::substr($key, 12, 4));
 48        $this->container[8]  = self::load_4(self::substr($key, 16, 4));
 49        $this->container[9]  = self::load_4(self::substr($key, 20, 4));
 50        $this->container[10] = self::load_4(self::substr($key, 24, 4));
 51        $this->container[11] = self::load_4(self::substr($key, 28, 4));
 52
 53        $counter = $this->initCounter($counter);
 54        $this->container[12] = self::load_4(self::substr($counter, 0, 4));
 55        $this->container[13] = self::load_4(self::substr($counter, 4, 4));
 56        $this->container[14] = self::load_4(self::substr($iv, 0, 4));
 57        $this->container[15] = self::load_4(self::substr($iv, 4, 4));
 58    }
 59
 60    /**
 61     * @internal You should not use this directly from another application
 62     *
 63     * @param int $offset
 64     * @param int $value
 65     * @return void
 66     * @psalm-suppress MixedArrayOffset
 67     */
 68    #[ReturnTypeWillChange]
 69    public function offsetSet($offset, $value)
 70    {
 71        if (!is_int($offset)) {
 72            throw new InvalidArgumentException('Expected an integer');
 73        }
 74        if (!is_int($value)) {
 75            throw new InvalidArgumentException('Expected an integer');
 76        }
 77        $this->container[$offset] = $value;
 78    }
 79
 80    /**
 81     * @internal You should not use this directly from another application
 82     *
 83     * @param int $offset
 84     * @return bool
 85     */
 86    #[ReturnTypeWillChange]
 87    public function offsetExists($offset)
 88    {
 89        return isset($this->container[$offset]);
 90    }
 91
 92    /**
 93     * @internal You should not use this directly from another application
 94     *
 95     * @param int $offset
 96     * @return void
 97     * @psalm-suppress MixedArrayOffset
 98     */
 99    #[ReturnTypeWillChange]
100    public function offsetUnset($offset)
101    {
102        unset($this->container[$offset]);
103    }
104
105    /**
106     * @internal You should not use this directly from another application
107     *
108     * @param int $offset
109     * @return mixed|null
110     * @psalm-suppress MixedArrayOffset
111     */
112    #[ReturnTypeWillChange]
113    public function offsetGet($offset)
114    {
115        return isset($this->container[$offset])
116            ? $this->container[$offset]
117            : null;
118    }
119
120    /**
121     * Initialize (pad) a counter value.
122     * @throws SodiumException
123     *
124     * @param string $ctr
125     * @return string
126     */
127    public function initCounter(
128        #[SensitiveParameter]
129        $ctr
130    ) {
131        $len = self::strlen($ctr);
132        if ($len === 0) {
133            return str_repeat("\0", 8);
134        }
135        if ($len < 8) {
136            return $ctr . str_repeat("\0", 8 - $len);
137        }
138        if ($len > 8) {
139            throw new SodiumException("counter cannot be more than 8 bytes");
140        }
141        return $ctr;
142    }
143}
144