Exporting SecKey from iOS to watchOS - ios

Question

I am trying to sync up private asymmetric keys between my iOS app and its watchOS equivalent. I have tried using SecKeyCopyExternalRepresentation to export it out as CFData and then send it to the watch using WatchConnectivity. However when it gets to the watch I have no way of converting the Data back into a SecKey. I tried using SecKeyCreateWithData in an attempt to recreate it, but it seems that that only works with symmetric keys, for when I tried it it crashed the watch app. Any ideas?
iOS Code:
func sendSharedKeyPair(keyPair: (publicKey: SecKey, privateKey: SecKey)) {
var error: Unmanaged<CFError>?
let publicKeyData = SecKeyCopyExternalRepresentation(keyPair.publicKey, &error)
if let error = error {
return print("Error sending shared key: \(error)")
}
let privateKeyData = SecKeyCopyExternalRepresentation(keyPair.privateKey, &error)
if let error = error {
return print("Error sending shared key: \(error)")
}
if let publicKeyData = publicKeyData, let privateKeyData = privateKeyData {
session.sendMessage(["requestedCommand": WatchControllerCommands.sendSharedKeyPair.rawValue, "keyPair": ["publicKey": publicKeyData, "privateKey": privateKeyData]], replyHandler: nil, errorHandler: { error in
print(error)
})
}
}
watchOS Code:
func session(_ session: WCSession, didReceiveMessage message: [String : Any]) {
guard let requestedCommand = (message["requestedCommand"] as? String).flatMap({ WatchControllerCommands(rawValue: $0) }), requestedCommand == .sendSharedKeyPair else { return }
guard let publicKeyData = (message["keyPair"] as? [String: Any])?["publicKey"].flatMap({ $0 as? Data }), let privateKeyData = (message["keyPair"] as? [String: Any])?["privateKey"].flatMap({ $0 as? Data }) else { return print("Couldn't parse keys") }
let publicTag = "myAppTag"
let privateTag = publicTag + ".private"
let privateAttributes = [String(kSecAttrIsPermanent): true,
String(kSecAttrApplicationTag): privateTag] as [String : Any]
let publicAttributes = [String(kSecAttrIsPermanent): true,
String(kSecAttrApplicationTag): publicTag] as [String : Any]
var error: Unmanaged<CFError>?
let publicCFData = publicKeyData as CFData
let privateCFData = privateKeyData as CFData
let publicCFDict = publicAttributes as CFDictionary
let privateCFDict = privateAttributes as CFDictionary
SecKeyCreateWithData(publicCFData, publicCFDict, &error)
if let error = error {
print(error)
}
SecKeyCreateWithData(privateCFData, privateCFDict, &error)
if let error = error {
print(error)
}
}

Answer 1

From headerdocs around SecKeyCreateWithData:
#param attributes Dictionary containing attributes describing the key
to be imported. The keys in this dictionary are kSecAttr* constants
from SecItem.h. Mandatory attributes are: * kSecAttrKeyType *
kSecAttrKeyClass * kSecAttrKeySizeInBits
Your code only defines kSecAttrIsPermanent and kSecAttrApplicationTag attributes.