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3.2.0 • Public • Published

ASN.1 TypeScript Library

This library was based off of my D ASN.1 Library.

What is ASN.1?

ASN.1 stands for Abstract Syntax Notation. ASN.1 was first specified in X.680 - Abstract Syntax Notation One (ASN.1), by the International Telecommunications Union. ASN.1 messages can be encoded in one of several encoding/decoding standards. It provides a system of types that are extensible, and can presumably describe every protocol. You can think of it as a protocol for describing other protocols as well as a family of standards for encoding and decoding said protocols. It is similar to Google's Protocol Buffers, or Sun Microsystems' External Data Representation (XDR).

For more information on what ASN.1 is, see documentation/asn1.md.

Why Use This Library?

I believe this library is the first complete implementation of ASN.1, meaning that it implements all data types defined in the specification, and encodes and decodes exactly as specified.

I have never seen any implementation of ASN.1 elsewhere that supports all data types; in fact, most just implement the ten or so most common types. Several implementations I have seen do not support things that are supported by the specification, such as constructed strings.

This library is fully compliant to the specification. If I am wrong, please write up an issue and I will correct it.

Why Not Use This Library?

This library is meant to be fully compliant to the specification, not lightweight. If you need a web application that encodes and decodes very simple ASN.1 data and loads lightning-fast, this may not be the library for you.


You can build this library by running npm run build. The outputs will all be in dist.

  • dist/index.js is the root for usage in NodeJS.
  • dist/asn1.min.js is the entire ASN.1 library for the web browser, which is minified, and accessible under the variable asn1.

Library Usage

For each codec in the library, usage entails instantiating the class, then using that class' properties to get and set the encoded value. For all classes, the empty constructor creates an END OF CONTENT element. The remaining constructors will be codec-specific.

Here is a TypeScript example of encoding with Basic Encoding Rules, using the BERElement class.

let el : BERElement = new BERElement();
el.typeTag = ASN1UniversalType.integer;
el.integer = 1433; // Now the data is encoded.
console.log(el.integer); // Logs '1433'

... and here is how you would decode that same element:

let encodedData : Uint8Array = el.toBytes();
let el2 : BERElement = new BERElement();
console.log(el2.integer); // Logs '1433'

Tests under the test directory can also serve as examples.

Future Development

  • Implement a function for ITU X.690, Section 11.6.
  • Implement these codecs:
    • Octet Encoding Rules (This is used by Simple Transportation Management Protocol (STMP) and DATEX-ASN.)
    • Canonical Octet Encoding Rules
    • NTCIP Encoding Rules (This is used by Simple Transportation Management Protocol (STMP) and DATEX-ASN.)
    • JSON Encoding Rules (May require changes to ASN1Element, or a separate element.)
    • Lightweight Encoding Rules (I cannot find a standard anywhere for this.)
    • BACNet Encoding Rules
    • Packed Encoding Rules
      • Basic Aligned Packed Encoding Rules (PER) (This is used by MCS / T.125, which is used by RDP. I believe it is also used by J2735 / DSRC.)
      • Make a separate RDPER (Remoted Desktop Protocol Encoding Rules)
      • Basic Unaligned Packed Encoding Rules (UPER) (May require changes to ASN1Element) (Used by 3GPP RRC)
      • Canonical Aligned Packed Encoding Rules (CPER)
      • Canonical Unaligned Packed Encoding Rules (CUPER) (May require changes to ASN1Element)
  • Internationalized strings
  • Serverless Functions (May be done in a different repo.)

See Also


npm i asn1-ts

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