Unable to create Private keys from Data in iOS 16.1

Question

I am using Elliptic Curve keys generated using SecKeyCreateRandomKey from the Security framework for performing Diffe Helman Key exchange in my app. After generating the key pair I am converting the Private key into data using SecKeyCopyExternalRepresentation(<myPrivateKey>,&error) and then store the base64 encoded string of this in the Keystore. To convert the Private key back I am using the following code

 let priKeyData = Data(base64Encoded: priKeyStr)
if(priKeyData != nil) {

       guard let dataPtr = CFDataCreate(kCFAllocatorDefault, UnsafePointer<UInt8>(Array(priKeyData!)), priKeyData!.count)
          else {return (nil) }
guard let priKey = SecKeyCreateWithData(dataPtr as CFData,attributes as CFDictionary,&error)
          else {return (nil)}
}

This works totally fine on iOS version prior 16.1. But in devices with iOS 16.1 the conversion from data to SecKey is failing with the following error:

Swift.Unmanaged<__C.CFErrorRef>(_value: Error Domain=NSOSStatusErrorDomain Code=-50 "EC private key creation from data failed" UserInfo={numberOfErrorsDeep=0, NSDescription=EC private key creation from data failed}))

What could be the reason for this? is there any other way to store SecKey in the Keystore without doing the conversions?

Security

689

Posted by

admiral_ank

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Answer 1

When I plug your code into Xcode 14.1 it flags an Initialization of 'UnsafePointer<UInt8>' results in a dangling pointer warning on your CFDataCreate line. For more background on that problem, see The Peril of the Ampersand.

In this case, however, the solution is very direct. You have a Data value and you want a CFData value, so add an as coercion:

guard
    let priKeyData = Data(base64Encoded: priKeyStr),
    let priKey = SecKeyCreateWithData(priKeyData as CFData, attributes as CFDictionary, &error)
else {
    return nil
}
return priKey

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—
Quinn “The Eskimo!” @ Developer Technical Support @ Apple
let myEmail = "eskimo" + "1" + "@" + "apple.com"

Posted by

eskimo

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Answer 2

When I plug your code into Xcode 14.1 it flags an Initialization of 'UnsafePointer<UInt8>' results in a dangling pointer warning on your CFDataCreate line. For more background on that problem, see The Peril of the Ampersand.

In this case, however, the solution is very direct. You have a Data value and you want a CFData value, so add an as coercion:

guard
    let priKeyData = Data(base64Encoded: priKeyStr),
    let priKey = SecKeyCreateWithData(priKeyData as CFData, attributes as CFDictionary, &error)
else {
    return nil
}
return priKey

Share and Enjoy
—
Quinn “The Eskimo!” @ Developer Technical Support @ Apple
let myEmail = "eskimo" + "1" + "@" + "apple.com"

Posted by

eskimo

Add a Comment

Answer 3

For more background on that problem, see The Peril of the Ampersand.

This is super useful.

Thank you for your quick response and the informative Thread on Ampersand

Posted by

admiral_ank

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Unable to create Private keys from Data in iOS 16.1

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