ASN1Codable

ASN1Codable is a Swift library for encoding and decoding ASN.1 data, designed to integrate with Swift's Codable protocol.

What is ASN.1 and DER Encoding?

ASN.1 (Abstract Syntax Notation One) is a standard interface description language used to define data structures for representing, encoding, transmitting, and decoding data. It’s widely used in telecommunications, cryptography, and various file formats.

DER (Distinguished Encoding Rules) is a subset of ASN.1 encoding rules designed to produce unambiguous binary representations of data structures, ensuring compatibility across systems.

Common Uses of ASN.1 and DER Encoding

• Public Key Infrastructure (PKI): Encoding certificates (e.g., X.509), certificate signing requests (CSRs), and other cryptographic data.
• Cryptographic Protocols: Encoding keys and digital signatures.
• Mac App Store Receipts: Representing purchase and subscription information for app validation.
• Telecommunications Protocols: Encoding signaling messages in mobile networks.

Features

• Simplified parsing and encoding of ASN.1 DER and BER data.
• Support for common ASN.1 types, including integers, strings, and sequences.
• Easy integration with Swift's Codable for type-safe data manipulation.
• Initial support for PKI certificates and certificate signing requests.
• New Feature: Decoding of Mac App Store receipts.
• Fully open source and available under the MIT license.

Installation

You can add ASN1Codable to your project using the Swift Package Manager (SPM).

1. In Xcode, go to File > Add Packages....
2. Enter the repository URL:

   https://github.com/w8wjb/ASN1Codable
   

3. Choose a version or branch and add the package to your project.

Alternatively, update your Package.swift:

dependencies: [
    .package(url: "https://github.com/w8wjb/ASN1Codable", from: "1.0.0")
]

Getting Started

Basic Usage

Decoding an SSL Certificate

let certPath = "path/to/der/certificate"
let certData = try Data(contentsOf: URL(fileURLWithPath: certPath))

let decoder = DERDecoder()
let cert = try decoder.decode(Certificate.self, from: certData)

Generating a self-signed certificate

let privateKeyPath = "path/to/private.key"
let keyData = try Data(contentsOf: URL(fileURLWithPath: privateKeyPath))

let attributes: [CFString : Any] = [
    kSecAttrKeyType: kSecAttrKeyTypeRSA,
    kSecAttrKeyClass: kSecAttrKeyClassPrivate,
    kSecAttrKeySizeInBits: 1024
]


var error: Unmanaged<CFError>?
let privateKey: SecKey = SecKeyCreateWithData(keyData as CFData, attributes as CFDictionary, &error)
if let error = error {
    throw error.takeRetainedValue()
}

let publicKey: SecKey = SecKeyCopyPublicKey(privateKey)


let dn = DistinguishedName((.C, "US"),
                            (.L, "Orbit City"),
                            (.O, "Spacely Sprockets"))

let tbs = TBSCertificate(serialNumber: BInt(1234),
                            issuer: dn,
                            notBefore: Date(),
                            notAfter: Date().addingTimeInterval(126227702), // 4 years from now
                            subject: dn,
                            publicKey: publicKey)

var cert = Certificate(tbsCertificate: tbs)


try cert.sign(privateKey: privateKey, algorithm: .rsaSignatureMessagePKCS1v15SHA1)

Decoding custom ASN.1 Data

Here’s an example of decoding an ASN.1-encoded sequence:

import ASN1Codable

struct Certificate: Codable {
    let version: Int
    let serialNumber: String
    let issuer: String
    let subject: String
}

let derData: Data = ... // ASN.1 DER-encoded data
do {
    let decoder = ASN1Decoder()
    let certificate = try decoder.decode(Certificate.self, from: derData)
    print("Issuer: \(certificate.issuer)")
} catch {
    print("Failed to decode: \(error)")
}

Encoding custom ASN.1 Data

import ASN1Codable

let certificate = Certificate(version: 2, serialNumber: "12345", issuer: "CA Inc.", subject: "John Doe")
do {
    let encoder = ASN1Encoder()
    let derData = try encoder.encode(certificate)
    print("Encoded DER data: \(derData)")
} catch {
    print("Failed to encode: \(error)")
}

Documentation

For a detailed guide on supported ASN.1 types and custom configuration options, visit the Wiki.

Contributing

We welcome contributions from the community! To contribute:

1. Fork the repository.
2. Create a feature branch.
3. Submit a pull request.

License

ASN1Codable is distributed under the MIT license. See LICENSE for more information.