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<?php |
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declare(strict_types = 1); |
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namespace Sop\ASN1\Type\Primitive; |
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use Sop\ASN1\Component\Identifier; |
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use Sop\ASN1\Component\Length; |
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use Sop\ASN1\Exception\DecodeException; |
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use Sop\ASN1\Feature\ElementBase; |
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use Sop\ASN1\Type\BaseString; |
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use Sop\ASN1\Type\PrimitiveType; |
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use Sop\ASN1\Type\UniversalClass; |
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/** |
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* Implements *BIT STRING* type. |
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*/ |
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class BitString extends BaseString |
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{ |
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use UniversalClass; |
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use PrimitiveType; |
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/** |
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* Number of unused bits in the last octet. |
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* |
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* @var int |
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*/ |
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protected $_unusedBits; |
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/** |
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* Constructor. |
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* |
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* @param string $string Content octets |
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* @param int $unused_bits Number of unused bits in the last octet |
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*/ |
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public function __construct(string $string, int $unused_bits = 0) |
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{ |
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$this->_typeTag = self::TYPE_BIT_STRING; |
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parent::__construct($string); |
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$this->_unusedBits = $unused_bits; |
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} |
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/** |
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* Get the number of bits in the string. |
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*/ |
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public function numBits(): int |
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{ |
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return strlen($this->_string) * 8 - $this->_unusedBits; |
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} |
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/** |
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* Get the number of unused bits in the last octet of the string. |
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*/ |
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public function unusedBits(): int |
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{ |
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return $this->_unusedBits; |
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} |
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/** |
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* Test whether bit is set. |
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* |
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* @param int $idx Bit index. Most significant bit of the first octet is index 0. |
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*/ |
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public function testBit(int $idx): bool |
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{ |
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// octet index |
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$oi = (int) floor($idx / 8); |
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// if octet is outside range |
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if ($oi < 0 || $oi >= strlen($this->_string)) { |
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1 |
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throw new \OutOfBoundsException('Index is out of bounds.'); |
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} |
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// bit index |
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$bi = $idx % 8; |
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// if tested bit is last octet's unused bit |
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if ($oi === strlen($this->_string) - 1) { |
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if ($bi >= 8 - $this->_unusedBits) { |
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throw new \OutOfBoundsException('Index refers to an unused bit.'); |
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} |
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} |
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$byte = $this->_string[$oi]; |
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// index 0 is the most significant bit in byte |
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$mask = 0x01 << (7 - $bi); |
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return (ord($byte) & $mask) > 0; |
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} |
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/** |
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* Get range of bits. |
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* |
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* @param int $start Index of first bit |
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* @param int $length Number of bits in range |
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* |
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* @throws \OutOfBoundsException |
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* |
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* @return string Integer of $length bits |
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*/ |
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public function range(int $start, int $length): string |
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{ |
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if (!$length) { |
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return '0'; |
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} |
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if ($start + $length > $this->numBits()) { |
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throw new \OutOfBoundsException('Not enough bits.'); |
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} |
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$bits = gmp_init(0); |
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$idx = $start; |
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$end = $start + $length; |
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while (true) { |
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$bit = $this->testBit($idx) ? 1 : 0; |
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$bits |= $bit; |
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if (++$idx >= $end) { |
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break; |
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} |
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$bits <<= 1; |
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} |
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return gmp_strval($bits, 10); |
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} |
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/** |
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* Get a copy of the bit string with trailing zeroes removed. |
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*/ |
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public function withoutTrailingZeroes(): self |
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{ |
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// if bit string was empty |
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if (!strlen($this->_string)) { |
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return new self(''); |
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} |
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$bits = $this->_string; |
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// count number of empty trailing octets |
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$unused_octets = 0; |
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for ($idx = strlen($bits) - 1; $idx >= 0; --$idx, ++$unused_octets) { |
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if ("\x0" !== $bits[$idx]) { |
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break; |
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} |
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} |
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// strip trailing octets |
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if ($unused_octets) { |
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$bits = substr($bits, 0, -$unused_octets); |
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} |
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// if bit string was full of zeroes |
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if (!strlen($bits)) { |
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return new self(''); |
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} |
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// count number of trailing zeroes in the last octet |
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$unused_bits = 0; |
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$byte = ord($bits[strlen($bits) - 1]); |
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while (!($byte & 0x01)) { |
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++$unused_bits; |
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$byte >>= 1; |
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} |
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return new self($bits, $unused_bits); |
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} |
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/** |
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* {@inheritdoc} |
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*/ |
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protected function _encodedContentDER(): string |
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{ |
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$der = chr($this->_unusedBits); |
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$der .= $this->_string; |
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if ($this->_unusedBits) { |
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$octet = $der[strlen($der) - 1]; |
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// set unused bits to zero |
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$octet &= chr(0xff & ~((1 << $this->_unusedBits) - 1)); |
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$der[strlen($der) - 1] = $octet; |
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} |
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return $der; |
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} |
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/** |
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* {@inheritdoc} |
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*/ |
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protected static function _decodeFromDER(Identifier $identifier, |
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string $data, int &$offset): ElementBase |
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{ |
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$idx = $offset; |
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$length = Length::expectFromDER($data, $idx); |
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if ($length->intLength() < 1) { |
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throw new DecodeException('Bit string length must be at least 1.'); |
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} |
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$unused_bits = ord($data[$idx++]); |
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if ($unused_bits > 7) { |
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throw new DecodeException( |
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'Unused bits in a bit string must be less than 8.'); |
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} |
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$str_len = $length->intLength() - 1; |
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if ($str_len) { |
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$str = substr($data, $idx, $str_len); |
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if ($unused_bits) { |
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$mask = (1 << $unused_bits) - 1; |
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if (ord($str[strlen($str) - 1]) & $mask) { |
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throw new DecodeException( |
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'DER encoded bit string must have zero padding.'); |
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} |
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} |
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} else { |
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$str = ''; |
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} |
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$offset = $idx + $str_len; |
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return new self($str, $unused_bits); |
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} |
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} |
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sop /
asn1
