gistfile1.txt

import Foundation

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

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

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