ParagonIE_Sodium_Core_ChaCha20_Ctx::__construct( string $key = '', string $iv = '', string $counter = '' )

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    }