@peculiar/asn1-schema

This package uses ES2015 decorators to simplify working with ASN.1 creation and parsing.

Introduction

Abstract Syntax Notation One (ASN.1) is a standard interface description language for defining data structures that can be serialized and deserialized in a cross-platform way. Working with ASN.1 can be complicated as there are many ways to represent the same data and many solutions handcraft, incorrectly, the ASN.1 representation of the data.

asn1-schema addresses this by using decorators to make both serialization and parsing of ASN.1 possible via a simple class that handles these problems for you.

This is important because validating input data before its use is important to do because all input data is evil.

Installation

Installation is handled via npm:

$ npm install @peculiar/asn1-schema

TypeScript examples

Node.js:

ASN.1 schema

Extension  ::=  SEQUENCE  {
  extnID      OBJECT IDENTIFIER,
  critical    BOOLEAN DEFAULT FALSE,
  extnValue   OCTET STRING
              -- contains the DER encoding of an ASN.1 value
              -- corresponding to the extension type identified
              -- by extnID
}

id-ce-basicConstraints OBJECT IDENTIFIER ::=  { id-ce 19 }

BasicConstraints ::= SEQUENCE {
  cA                      BOOLEAN DEFAULT FALSE,
  pathLenConstraint       INTEGER (0..MAX) OPTIONAL 
}

ASN.1 schema declaration in TypeScript project

import { Asn1Prop, Asn1PropTypes, Asn1Serializer } from "@peculiar/asn1-schema";

class Extension {

  public static CRITICAL = false;

  @AsnProp({ type: Asn1PropTypes.ObjectIdentifier })
  public extnID: string = "";

  @AsnProp({
    type: Asn1PropTypes.Boolean,
    defaultValue: Extension.CRITICAL,
  })
  public critical = Extension.CRITICAL;

  @AsnProp({ type: Asn1PropTypes.OctetString })
  public extnValue: ArrayBuffer = new ArrayBuffer(0);

}

class BasicConstraints {
  @AsnProp({ type: Asn1PropTypes.Boolean, defaultValue: false })
  public ca = false;

  @AsnProp({ type: Asn1PropTypes.Integer, optional: true })
  public pathLenConstraint?: number;
}

Encoding ASN.1 data

const basicConstraints = new BasicConstraints();
basicConstraints.ca = true;
basicConstraints.pathLenConstraint = 1;

const extension = new Extension();
extension.critical = true;
extension.extnID = "2.5.29.19";
extension.extnValue = AsnSerializer.serialize(basicConstraints);

console.log(Buffer.from(AsnSerializer.serialize(extension)).toString("hex")); // 30120603551d130101ff040830060101ff020101

ASN.1 encoded data

Decoding ASN.1 data

const extension = AsnParser.parse(Buffer.from("30120603551d130101ff040830060101ff020101", "hex"), Extension);
console.log("Extension ID:", extension.extnID); // Extension ID: 2.5.29.19
console.log("Critical:", extension.critical); // Critical: true

const basicConstraints = AsnParser.parse(extension.extnValue, BasicConstraints);
console.log("CA:", basicConstraints.ca); // CA: true
console.log("Path length:", basicConstraints.pathLenConstraint); // Path length: 1