christophhagen/cryptokit25519

A Swift module for Curve25519 functions and AES-GCM encryption (compatible with Apple CryptoKit)

I'm a passionate programmer/engineer/scientist who likes to try new things, currently based in Munich, Germany.

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• 🚀 Space science and technology
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You can find some of my other projects on my website christophhagen.de

Repositories

Most of my repositories are written in/for Swift, because it's a very modern, safe, and versatile language.

• BinaryCodable is a binary encoder/decoder for Swift Codable types
• HealthKitExtensions makes it easier to work with Apple HealthKit
• HealthDB is an interface to the Health database from an iOS Backup (healthdb_secure.sqlite)
• Clairvoyant is a simple metrics system for logging and remote monitoring
• SwiftSerial allows using a Linux serial port in Swift
• Daly-Swift, NextcloudStatus and Growatt-Swift are interfaces to devices

There are many more repositories, also in C++ for my embedded projects.

And who doesn't enjoy a few statistics?

cryptokit25519's Issues

Crashes when generating keys

Hello, I tried to include CryptoKit25519 in a project that needs to support iOS 11+, but it seems to (randomly) crash whenever I generate keys (at least on iOS 13.4 where I am testing).
Here is the simplest sample project I could think of to reproduce the issue (using SwiftUI to be quicker):

import SwiftUI
import CryptoKit25519

struct ContentView: View {
    
    @State var privateKeyString = "n/a"
    @State var publicKeyString = "n/a"
    
    var body: some View {
        VStack {
            Text("Private key: \(privateKeyString)")
            Text("Public key: \(publicKeyString)")
            Button("Generate keys") {
                self.generateKeys()
            }
        }
    }
    
    func generateKeys() {
        let privateKey = try! Curve25519.Signing.PrivateKey()
        let privateData = privateKey.rawRepresentation
        privateKeyString = privateData.base64EncodedString()
        
        let publicKey = privateKey.publicKey
        let publicData = publicKey.rawRepresentation
        publicKeyString = publicData.base64EncodedString()
    }
    
}

Sometimes (usually - but not always - on the first try), keys are generated and displayed. But most often (almost always as of the second try) the app crashes. Unfortunately the error displayed is not always the same nor is very descriptive.

• Sometimes I get something like

Thread 1: EXC_BREAKPOINT (code=1, subcode=0x1e378bfa4)

on the row return Data(bytes) in the rawRepresentation variable in PrivateKey.swift

• Other times I get:

Thread 3: EXC_BAD_ACCESS (code=1, address=0xf5d65481e50b506b)

on the queue CA DispatchGroup

• When I am "luckiest" I get an EXC_BREAKPOINT exception on the declaration of the AppDelegate class together with the most descriptive error:

CryptoTest(589,0x1050ae040) malloc: Heap corruption detected, free list is damaged at 0x2834a8d40
*** Incorrect guard value: 11272132526359900924
CryptoTest(589,0x1050ae040) malloc: *** set a breakpoint in malloc_error_break to debug

which would indicate something like... a memory leak perhaps?

There seem to be no discernible pattern among the various kinds of errors. Also, the situation is the same if I remove the part on the publicKey and just generate the privateKey.

Do you perhaps know what could be going on here? Thanks a lot!

Cannot recover the correct public key from private keys

Hi, I have been testing around with this library and found that the public key could not be correctly computed from the private keys.

import CryptoKit25519

let k1 = try! Curve25519.KeyAgreement.PrivateKey(rawRepresentation: Data([
  75, 157, 102, 134, 12, 57, 222, 49, 73, 43, 219, 59, 9, 5, 39, 191,
  102, 239, 30, 167, 95, 16, 91, 182, 248, 115, 40, 223, 187, 159, 227, 55]))
print("actual  ", Array(k1.publicKey.rawRepresentation))
print("expected", [30, 222, 35, 48, 128, 169, 48, 95, 101, 138, 236, 237, 7, 239, 4, 206, 211, 112, 181, 241, 187, 160, 153, 179, 171, 195, 158, 199, 180, 245, 168, 63])
// actual   [24, 233, 101, 77, 124, 166, 123, 38, 231, 73, 205, 242, 13, 207, 115, 34, 178, 98, 195, 39, 109, 223, 183, 78, 35, 64, 1, 165, 74, 213, 89, 46]
// expected [30, 222, 35, 48, 128, 169, 48, 95, 101, 138, 236, 237, 7, 239, 4, 206, 211, 112, 181, 241, 187, 160, 153, 179, 171, 195, 158, 199, 180, 245, 168, 63]

let k2 = try! Curve25519.KeyAgreement.PrivateKey(rawRepresentation: Data([
  0xc8, 0x06, 0x43, 0x9d, 0xc9, 0xd2, 0xc4, 0x76, 0xff, 0xed, 0x8f, 0x25, 0x80, 0xc0, 0x88, 0x8d,
  0x58, 0xab, 0x40, 0x6b, 0xf7, 0xae, 0x36, 0x98, 0x87, 0x90, 0x21, 0xb9, 0x6b, 0xb4, 0xbf, 0x59]))
print("actual  ", Array(k2.publicKey.rawRepresentation))
print("expected", [
  0x1b, 0xb7, 0x59, 0x66, 0xf2, 0xe9, 0x3a, 0x36, 0x91, 0xdf, 0xff, 0x94, 0x2b, 0xb2, 0xa4, 0x66,
  0xa1, 0xc0, 0x8b, 0x8d, 0x78, 0xca, 0x3f, 0x4d, 0x6d, 0xf8, 0xb8, 0xbf, 0xa2, 0xe4, 0xee, 0x28])
// actual   [27, 183, 89, 102, 242, 233, 58, 54, 145, 223, 255, 148, 43, 178, 164, 102, 161, 192, 139, 141, 120, 202, 63, 77, 109, 248, 184, 191, 162, 228, 238, 40]
// expected [27, 183, 89, 102, 242, 233, 58, 54, 145, 223, 255, 148, 43, 178, 164, 102, 161, 192, 139, 141, 120, 202, 63, 77, 109, 248, 184, 191, 162, 228, 238, 40]

The two test vectors are, respectively, extracted from test vector from Noise protocol, and the test case given in Curve25519 package.

(First test vector)
Private key: 4b9d66860c39de31492bdb3b090527bf66ef1ea75f105bb6f87328dfbb9fe337
Public key:  1ede233080a9305f658aeced07ef04ced370b5f1bba099b3abc39ec7b4f5a83f

The cause is, some of the bits in the secret key must be unset (and some otherwise need to be set) before computation:

func normalize(secretKey: [UInt8]) -> [UInt8] {
  var newSecretKey = secretKey
  newSecretKey[0] &= 0xf8
  newSecretKey[31] &= 0x3f
  newSecretKey[31] |= 0x40
  return newSecretKey
}