The types

Every universal type of X.690 has a class under SpomkyLabs\Pki\ASN1\Type. Each is built with create(), each knows its tag, and each is immutable.

Primitive types

ASN.1 type	Class	Built from	Read with
BOOLEAN	Primitive\Boolean	bool	value(): bool
INTEGER	Primitive\Integer	int, numeric string, BigInteger	number(): string, intNumber(): int, getValue(): BigInteger
ENUMERATED	Primitive\Enumerated	as Integer	as Integer
BIT STRING	Primitive\BitString	string and a count of unused bits	string(), numBits(), testBit(), range()
OCTET STRING	Primitive\OctetString	string	string()
NULL	Primitive\NullType	nothing	—
OBJECT IDENTIFIER	Primitive\ObjectIdentifier	dotted string	oid(): string
RELATIVE-OID	Primitive\RelativeOID	dotted string	oid(): string
ObjectDescriptor	Primitive\ObjectDescriptor	string	descriptor(): string
REAL	Primitive\Real	fromFloat(), fromString()	floatVal(), mantissa(), exponent(), base()
EOC	Primitive\EOC	nothing	—

An INTEGER never comes back as a PHP integer unless you ask for one. A serial number or an RSA modulus does not fit, so number() returns a decimal string and getValue() a brick/math BigInteger. intNumber() throws when the value does not fit in a PHP integer.

String types

Each carries the character set its tag promises, and refuses a string outside it.

ASN.1 type	Class
UTF8String	Primitive\UTF8String
PrintableString	Primitive\PrintableString
NumericString	Primitive\NumericString
IA5String	Primitive\IA5String
VisibleString	Primitive\VisibleString
GeneralString	Primitive\GeneralString
GraphicString	Primitive\GraphicString
BMPString	Primitive\BMPString
UniversalString	Primitive\UniversalString
T61String	Primitive\T61String
VideotexString	Primitive\VideotexString
CharacterString	Primitive\CharacterString

They all extend BaseString, so string() gives the value and (string) works. The StringType interface marks them, and the time types with them, for a signature that takes any of them.

use SpomkyLabs\Pki\ASN1\Type\Primitive\PrintableString;

$string = PrintableString::create('FR');
echo $string->string();    // FR
echo $string;              // FR

A PrintableString built from a value its character set forbids throws rather than encode something a peer would read differently.

Time types

ASN.1 type	Class
UTCTime	Primitive\UTCTime
GeneralizedTime	Primitive\GeneralizedTime

Both extend BaseTime: create(DateTimeImmutable) in, dateTime(): DateTimeImmutable out, and fromString() for the ASN.1 spelling.

use SpomkyLabs\Pki\ASN1\Type\Primitive\GeneralizedTime;

$time = GeneralizedTime::create(new DateTimeImmutable('2030-01-01 12:00:00', new DateTimeZone('UTC')));
echo $time->string();     // 20300101120000Z

UTCTime writes a two-digit year, which is why RFC 5280 asks for it only before 2050 and GeneralizedTime after. UTCTime::CENTURY_PIVOT is where the library splits the two centuries when it reads one. Time in the X.509 layer picks the right one for you.

Constructed types

ASN.1 type	Class
SEQUENCE, SEQUENCE OF	Constructed\Sequence
SET, SET OF	Constructed\Set
a string in constructed form	Constructed\ConstructedString

use SpomkyLabs\Pki\ASN1\Type\Constructed\Set;
use SpomkyLabs\Pki\ASN1\Type\Primitive\Integer;

$set = Set::create(Integer::create(3), Integer::create(1));
$set = $set->sortedSetOf();   // DER requires the members of a SET OF to be sorted

ConstructedString is a string encoded as a sequence of fragments, which BER allows and DER does not. The library reads one and gives you strings(), the fragments, or string(), the whole value.

Pseudotypes

Three tags are not ASN.1 types but expectations you can pass to expectType():

Constant	Matches
Element::TYPE_STRING	any string type
Element::TYPE_TIME	UTCTime or GeneralizedTime
Element::TYPE_CONSTRUCTED_STRING	a string in constructed form

$element->expectType(Element::TYPE_STRING);

Bit flags

A BIT STRING that carries named flags — keyUsage, for one — is easier to read through Flags:

use SpomkyLabs\Pki\ASN1\Util\Flags;

$flags = Flags::fromBitString($bitString, 9);
$flags->test(0);           // the first bit, as the specification numbers them
echo $flags->string();     // the bits as a byte string

The extensions that carry flags already do this for you: see KeyUsageExtension.