/**
* Constructor
*
* @param string $data DER encoded data
* @throws DecodeException If data does not adhere to DER
*/
public function __construct($data)
{
$this->_identifier = Identifier::fromDER($data, $this->_contentOffset);
Length::expectFromDER($data, $this->_contentOffset);
$this->_der = $data;
$this->_typeTag = intval($this->_identifier->tag());
}
/**
* Decode element from DER data.
*
* @param string $data DER encoded data
* @param int|null $offset Reference to the variable that contains offset
* into the data where to start parsing. Variable is updated to
* the offset next to the parsed element. If null, start from offset
* 0.
* @throws DecodeException If decoding fails
* @throws \UnexpectedValueException If called in the context of an expected
* type, but decoding yields another type
* @return self
*/
public static function fromDER($data, &$offset = null)
{
assert('is_string($data)', "got " . gettype($data));
// decode identifier
$idx = $offset ? $offset : 0;
$identifier = Identifier::fromDER($data, $idx);
// determine class that implements type specific decoding
$cls = self::_determineImplClass($identifier);
try {
// decode remaining element
$element = $cls::_decodeFromDER($identifier, $data, $idx);
} catch (\LogicException $e) {
// rethrow as a RuntimeException for unified exception handling
throw new DecodeException("Error while decoding " . self::tagToName($identifier->tag()) . ".", 0, $e);
}
// if called in the context of a concrete class, check
// that decoded type matches the type of a calling class
$called_class = get_called_class();
if (__CLASS__ != $called_class) {
if (!$element instanceof $called_class) {
throw new \UnexpectedValueException("{$called_class} expected, got " . get_class($element) . ".");
}
}
// update offset for the caller
if (isset($offset)) {
$offset = $idx;
}
return $element;
}
/**
* Explode DER structure to DER encoded components that it contains.
*
* @param string $data
* @throws DecodeException
* @return string[]
*/
public static function explodeDER($data)
{
$offset = 0;
$identifier = Identifier::fromDER($data, $offset);
if (!$identifier->isConstructed()) {
throw new DecodeException("Element is not constructed.");
}
$length = Length::expectFromDER($data, $offset);
$end = $offset + $length->length();
$parts = array();
while ($offset < $end) {
// start of the element
$idx = $offset;
// skip identifier
Identifier::fromDER($data, $offset);
// decode element length
$length = Length::expectFromDER($data, $offset);
// extract der encoding of the element
$parts[] = substr($data, $idx, $offset - $idx + $length->length());
// update offset over content
$offset += $length->length();
}
return $parts;
}
