ASN1Kit

ASN.1 Decoder for Swift

API Documentation

Generated API docs are available at https://gematik.github.io/ASN1Kit.

License

Licensed under the Apache License, Version 2.0.

Overview

This library can be used for ASN.1 (Abstract Syntax Notation One) encoding/decoding using distinguished encoding rules (DER) according to the ITU-T X.690

For more info, please find the complete X.690-0207.pdf specification.

Getting Started

ASN1Kit requires Swift 5.1.

Setup for integration

• Carthage: Put this in your Cartfile:

  github "gematik/ASN1Kit" ~> 1.0
  

Setup for development

You will need Bundler, XcodeGen and fastlane to conveniently use the established development environment.

1. Update ruby gems necessary for build commands

   $ bundle install --path vendor/gems
   

2. Checkout (and build) dependencies and generate the xcodeproject

   $ bundle exec fastlane setup
   

3. Build the project

   $ bundle exec fastlane build_all [build_mac, build_ios]
   

Code Samples

Use ASN1Decoder.decode(asn1:) to decode serialized data and String(from:) to get a hex representation of it:

let expected = "0A3B5F291CD"
let serialized = Data([0x23, 0xc, 0x3, 0x3, 0x0, 0x0A, 0x3B, 0x3, 0x5, 0x4, 0x5F, 0x29, 0x1C, 0xD0])

expect {
    let asn1 = try ASN1Decoder.decode(asn1: serialized)
    return try String(from: asn1)
} == expected

Construct an ASN1Object of your choice and serialize it:

let data = Data([0x0, 0x1, 0x2, 0x4]) as ASN1EncodableType
let data2 = Data([0x4, 0x3, 0x2, 0x1]) as ASN1EncodableType
let array = [data, data2]

let expected = Data([0x30, 0xc, 0x4, 0x4, 0x0, 0x1, 0x2, 0x4, 0x4, 0x4, 0x4, 0x3, 0x2, 0x1])
expect {
    try array.asn1encode().serialize()
} == expected

ASN.1-encode Swift primitives and extract the encoded value(s):

//0x0080 = 128
let expected = Data([0x00, 0x80])
expect {
    try 128.asn1encode(tag: nil).data.primitive
} == expected

Extract the tag of the first element of a constructed ASN1Object:

let data = Data([0x1, 0x2, 0x3, 0x4, 0x8])
let tag1 = ASN1Primitive(data: .primitive(data), tag: .taggedTag(3)) // context-specific class tag
let tag2 = ASN1Primitive(data: .primitive(data), tag: .universal(ASN1Tag.octetString))
let implicitTag = ASN1Primitive(data: .constructed([tag1, tag2]), tag: .taggedTag(83))

expect {
    implicitTag.data.items?.first?.tag
} == .taggedTag(3)