mini_asn1_der.swift

//
//  mini_asn1_der.swift
//  miniasn1
//
//  Created by Ales Teska on 18.2.19.
//  Copyright © 2019 TeskaLabs. All rights reserved.
//

import Foundation

func asn1_int_to_bytes(x: UInt) -> [UInt8] {
    var l = x
    var d:[UInt8] = []
    while (l > 0) {
        d.append(UInt8(l & 0xFF))
        l = l >> 8
    }
    return d
}

func asn1_il(tag: UInt8, length: UInt) -> [UInt8] {
    if (length < 128) {
        return [tag, UInt8(length)]
    }
    let d = asn1_int_to_bytes(x:length)
    return [tag, 0x80 | UInt8(d.count)] + d
}

func asn1_SEQUENCE(elements: [[UInt8]?], implicit_tagging: Bool = true) -> [UInt8] {
    var d:[UInt8] = []
    
    var n: UInt8 = 0
    for e:[UInt8]? in elements {
        guard (e != nil)  else {
            n += 1
            continue
        }
        var identifier: UInt8 = e![0]
        if implicit_tagging {
            let e0 = e![0]
            if (((e0 & 0x1F) == 0x10) || ((e0 & 0x1F) == 0x11) || (e0 == 0xA0)) {
                // the element is constructed
                identifier = 0xA0
            } else {
                // the element is primitive
                identifier = 0x80
            }
        }
        else {
            identifier = e![0]
        }
        d.append(identifier + n)
        d += e![1..<e!.count]
        
        n += 1
    }
    
    return asn1_il(tag:0x30, length:UInt(d.count)) + d
}

func asn1_SEQUENCE_OF(elements: [[UInt8]?], implicit_tagging: Bool = true) -> [UInt8] {
    return asn1_SEQUENCE(elements: elements, implicit_tagging: false)
}

func asn1_INTEGER(value: UInt) -> [UInt8] {
    // TODO: Support for negative numbers
    if (value == 0) {
        return asn1_il(tag: 0x02, length: 1) + [0]
    }
    var b = asn1_int_to_bytes(x: value)
    if (b[0] & 0x80 == 0x80){
        b.insert(0, at: 0)
    }
    return asn1_il(tag: 0x02, length: UInt(b.count)) + b
}

func asn1_OCTEC_STRING(value: Data) -> [UInt8] {
    return asn1_il(tag:0x04, length:UInt(value.count)) + value
}

func asn1_IA5STRING(value: String) -> [UInt8] {
    let b = value.data(using: .ascii)!
    return asn1_il(tag:0x16, length:UInt(b.count)) + b
}

func asn1_BITSTRING(value: Data) -> [UInt8] {
    return asn1_il(tag:0x03, length:UInt(value.count)+1) + [0] + value
}

func asn1_UTF8String(value: String) -> [UInt8] {
    let b = value.data(using: .utf8)!
    return asn1_il(tag:12, length:UInt(b.count)) + b
}

func asn1_UTCTime(value: Date) -> [UInt8] {
    
    let formatter = DateFormatter()
    formatter.dateFormat = "yyMMddHHmmSS"
    let s = formatter.string(from: value) + "Z"
    let b = s.data(using: .ascii)!
    return asn1_il(tag: 23, length: UInt(b.count)) + b
}

func asn1_variable_length_quantity(value: Int) -> [UInt8] {
    // Break it up in groups of 7 bits starting from the lowest significant bit
    // For all the other groups of 7 bits than lowest one, set the MSB to 1

    var v = value
    var m: UInt8 = 0x00
    var output: [UInt8] = []
    while (v >= 0x80) {
        output.insert(UInt8(v & 0x7f) | m | m, at:0)
        v = v >> 7
        m = 0x80
    }
    output.insert(UInt8(v) | m, at:0)
    return output
}

func asn1_OBJECT_IDENTIFIER(value:String) -> [UInt8] {
    let a: [Int] = value.split(separator: ".").map { Int($0)! }
    var oid: [UInt8] = [UInt8(a[0]*40 + a[1])] // First two items are coded by a1*40+a2
    // A rest is Variable-length_quantity
    for n in a[2..<a.count] {
        oid += asn1_variable_length_quantity(value:n)
    }
    return asn1_il(tag: 0x06, length: UInt(oid.count)) + oid
}