README

A PHP library for X.690 Abstract Syntax Notation One (ASN.1) Distinguished Encoding Rules (DER) encoding and decoding.

Requirements

• PHP >=7.2
• gmp
• mbstring

Installation

This library is available on Packagist.

composer require sop/asn1

Usage

The general idea is that each ASN.1 type has its corresponding PHP class, that knows the details of encoding and decoding the specific type.

To decode DER data, use fromDER static method of the expected type. To encode object to DER, use toDER instance method.

Many methods return an UnspecifiedType object, that works as an intermediate wrapper with accessor methods ensuring type safety.

All objects are immutable and method chaining is promoted for the fluency of the API. Exception shall be thrown on errors.

Code Examples

Here are some simple usage examples. Namespaces are omitted for brevity.

Encode

Encode a sequence containing a UTF-8 string, an integer and an explicitly tagged object identifier, conforming to the following ASN.1 specification:

Example ::= SEQUENCE {
    greeting    UTF8String,
    answer      INTEGER,
    type    [1] EXPLICIT OBJECT IDENTIFIER
}

$seq = new Sequence(
    new UTF8String('Hello'),
    new Integer(42),
    new ExplicitlyTaggedType(
        1, new ObjectIdentifier('1.3.6.1.3'))
);
$der = $seq->toDER();

Decode

Decode DER encoding from above.

$seq = UnspecifiedType::fromDER($der)->asSequence();
$greeting = $seq->at(0)->asUTF8String()->string();
$answer = $seq->at(1)->asInteger()->intNumber();
$type = $seq->at(2)->asTagged()->asExplicit()->asObjectIdentifier()->oid();

Real-World Examples

See the following for more practical real-world usage examples.

• EC Private Key
  • Decode
  • Encode
• X.501 Attribute
  • Decode
  • Encode
• X.509 Certificate (TBSCertificate sequence)
  • Decode
  • Encode

ASN.1 References

• ITU-T X.690 07/2002
• ITU-T X.690 08/2015
• Hosted by OSS Nokalva
  • ASN.1 — Communication Between Heterogeneous Systems by Olivier Dubuisson
  • ASN.1 Complete by Professor John Larmouth

License

This project is licensed under the MIT License.