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<?php
declare(strict_types=1);
namespace SpomkyLabs\Pki\ASN1\Component;
use Brick\Math\BigInteger;
use SpomkyLabs\Pki\ASN1\Exception\DecodeException;
use SpomkyLabs\Pki\ASN1\Feature\Encodable;
use SpomkyLabs\Pki\ASN1\Util\BigInt;
use function array_key_exists;
use function mb_strlen;
use function ord;
/**
* Class to represent BER/DER identifier octets.
* @see \SpomkyLabs\Pki\Test\ASN1\Component\IdentifierTest
*/
final class Identifier implements Encodable
{
// Type class enumerations
final public const CLASS_UNIVERSAL = 0b00;
final public const CLASS_APPLICATION = 0b01;
final public const CLASS_CONTEXT_SPECIFIC = 0b10;
final public const CLASS_PRIVATE = 0b11;
// P/C enumerations
final public const PRIMITIVE = 0b0;
final public const CONSTRUCTED = 0b1;
/**
* Mapping from type class to human readable name.
*
* @internal
*
* @var array<int, string>
*/
private const MAP_CLASS_TO_NAME = [
self::CLASS_UNIVERSAL => 'UNIVERSAL',
self::CLASS_APPLICATION => 'APPLICATION',
self::CLASS_CONTEXT_SPECIFIC => 'CONTEXT SPECIFIC',
self::CLASS_PRIVATE => 'PRIVATE',
];
/**
* Type class.
*/
private int $_class;
/**
* Primitive or Constructed.
*/
private readonly int $_pc;
/**
* Content type tag.
*/
private BigInt $_tag;
/**
* @param int $class Type class
* @param int $pc Primitive / Constructed
* @param BigInteger|int $tag Type tag number
*/
private function __construct(int $class, int $pc, BigInteger|int $tag)
{
$this->_class = 0b11 & $class;
$this->_pc = 0b1 & $pc;
$this->_tag = BigInt::create($tag);
}
public static function create(int $class, int $pc, BigInteger|int $tag): self
{
return new self($class, $pc, $tag);
}
/**
* Decode identifier component from DER data.
*
* @param string $data DER encoded data
* @param null|int $offset Reference to the variable that contains offset
* into the data where to start parsing.
* Variable is updated to the offset next to the
* parsed identifier. If null, start from offset 0.
*/
public static function fromDER(string $data, int &$offset = null): self
{
$idx = $offset ?? 0;
$datalen = mb_strlen($data, '8bit');
if ($idx >= $datalen) {
throw new DecodeException('Invalid offset.');
}
$byte = ord($data[$idx++]);
// bits 8 and 7 (class)
// 0 = universal, 1 = application, 2 = context-specific, 3 = private
$class = (0b11000000 & $byte) >> 6;
// bit 6 (0 = primitive / 1 = constructed)
$pc = (0b00100000 & $byte) >> 5;
// bits 5 to 1 (tag number)
$tag = (0b00011111 & $byte);
// long-form identifier
if ($tag === 0x1f) {
$tag = self::decodeLongFormTag($data, $idx);
}
if (isset($offset)) {
$offset = $idx;
}
return self::create($class, $pc, $tag);
}
public function toDER(): string
{
$bytes = [];
$byte = $this->_class << 6 | $this->_pc << 5;
$tag = $this->_tag->getValue();
if ($tag->isLessThan(0x1f)) {
$bytes[] = $byte | $tag->toInt();
} // long-form identifier
else {
$bytes[] = $byte | 0x1f;
$octets = [];
for (; $tag->isGreaterThan(0); $tag = $tag->shiftedRight(7)) {
$octets[] = 0x80 | $tag->and(0x7f)->toInt();
}
// last octet has bit 8 set to zero
$octets[0] &= 0x7f;
foreach (array_reverse($octets) as $octet) {
$bytes[] = $octet;
}
}
return pack('C*', ...$bytes);
}
/**
* Get class of the type.
*/
public function typeClass(): int
{
return $this->_class;
}
public function pc(): int
{
return $this->_pc;
}
/**
* Get the tag number.
*
* @return string Base 10 integer string
*/
public function tag(): string
{
return $this->_tag->base10();
}
/**
* Get the tag as an integer.
*/
public function intTag(): int
{
return $this->_tag->toInt();
}
/**
* Check whether type is of an universal class.
*/
public function isUniversal(): bool
{
return $this->_class === self::CLASS_UNIVERSAL;
}
/**
* Check whether type is of an application class.
*/
public function isApplication(): bool
{
return $this->_class === self::CLASS_APPLICATION;
}
/**
* Check whether type is of a context specific class.
*/
public function isContextSpecific(): bool
{
return $this->_class === self::CLASS_CONTEXT_SPECIFIC;
}
/**
* Check whether type is of a private class.
*/
public function isPrivate(): bool
{
return $this->_class === self::CLASS_PRIVATE;
}
/**
* Check whether content is primitive type.
*/
public function isPrimitive(): bool
{
return $this->_pc === self::PRIMITIVE;
}
/**
* Check hether content is constructed type.
*/
public function isConstructed(): bool
{
return $this->_pc === self::CONSTRUCTED;
}
/**
* Get self with given type class.
*
* @param int $class One of `CLASS_*` enumerations
*/
public function withClass(int $class): self
{
$obj = clone $this;
$obj->_class = 0b11 & $class;
return $obj;
}
/**
* Get self with given type tag.
*
* @param int $tag Tag number
*/
public function withTag(int $tag): self
{
$obj = clone $this;
$obj->_tag = BigInt::create($tag);
return $obj;
}
/**
* Get human readable name of the type class.
*/
public static function classToName(int $class): string
{
if (! array_key_exists($class, self::MAP_CLASS_TO_NAME)) {
return "CLASS {$class}";
}
return self::MAP_CLASS_TO_NAME[$class];
}
/**
* Parse long form tag.
*
* @param string $data DER data
* @param int $offset Reference to the variable containing offset to data
*
* @return BigInteger Tag number
*/
private static function decodeLongFormTag(string $data, int &$offset): BigInteger
{
$datalen = mb_strlen($data, '8bit');
$tag = BigInteger::of(0);
while (true) {
if ($offset >= $datalen) {
throw new DecodeException('Unexpected end of data while decoding long form identifier.');
}
$byte = ord($data[$offset++]);
$tag = $tag->shiftedLeft(7);
$tag = $tag->or(0x7f & $byte);
// last byte has bit 8 set to zero
if ((0x80 & $byte) === 0) {
break;
}
}
return $tag;
}
}