SecSignVerifyTransform crashing in Swift with CSSM error Code=-2147415790 - macos

Question

I'm trying to obtain a digital signature for a XML string using a RSA private key using Swift as command-line script (to be called from FileMaker later).
The compiler kept crashing with "segmentation fault 11" and then "Illegal Instruction: 4" and I kept drilling down until I (think) I found the problem, but it's completely beyond me, so please, please help!! ;) :)
As the title says, when I invoke SecTransformExecute on my SecSignTransform, with a binary version of my String as input attribute, I get the following error message:
Error Domain=Internal CSSM error Code=-2147415790 "The operation
couldn’t be completed. (Internal CSSM error error -2147415790 -
Internal error #80010912 at __SignTransform_block_invoke_2
/SourceCache/Security/Security-57031.1.35/Security/libsecurity_transform/lib/SecSignVerifyTransform.c:279)" UserInfo=0x7fc620e23aa0 {NSDescription=Internal error #80010912 at
__SignTransform_block_invoke_2 /SourceCache/Security/Security-57031.1.35/Security/libsecurity_transform/lib/SecSignVerifyTransform.c:279,
Originating Transform=CoreFoundationObject}
Here is the relevant part of my code:
import Foundation
import CoreFoundation
import Security
var signer: SecTransformRef
var signedData, digestData: NSData
var error: Unmanaged<CFErrorRef>?
var status: OSStatus
var key: SecKey
var anyItem: Unmanaged<AnyObject>?
var keySearchDict: [String : AnyObject]
let keyMatch = "[*place search tag here*]" as String
// turns a string into a binary to sign
let str = "Hello World"
let uintData = [UInt8](str.utf8)
let sourceData = CFDataCreate(kCFAllocatorDefault, uintData, countElements(uintData))
// sets up keySearchDict to query Keychain
keySearchDict = [(kSecClass as String): (kSecClassKey as String), (kSecMatchSubjectContains as String): keyMatch, (kSecReturnRef as String): kCFBooleanTrue]
// gets private key using keySearchDict
status = SecItemCopyMatching(keySearchDict, &anyItem)
key = (anyItem!.takeRetainedValue() as SecKey)
if status != 0 { println("status is: \(SecCopyErrorMessageString(status, &error).takeRetainedValue())") }
// creates SecTransform object using key
signer = SecSignTransformCreate(key, &error).takeRetainedValue()
if error == nil { println("signer transform creation error == nil") } else { println(error) }
// signer to get data from sourceData
SecTransformSetAttribute(signer, kSecTransformInputAttributeName, sourceData!, &error)
if error == nil { println("signer attribute setting error == nil") } else { println(error) }
// execute the transform
//signedData = (SecTransformExecute(signer, &error) as NSData)
let anything = SecTransformExecute(signer, &error)
if error == nil { println("signer execute error == nil") } else { println("erro: \(error!.takeRetainedValue())"); println(CFErrorGetCode(error!.takeRetainedValue())) }
println("anything = \(anything)")
//println(signedData)
I'm not very familiar with objc and actually not quite a proper coder, so please forgive my poor coding style ;) Also, sorry if I'm posting too much of it, but I figured better more than less...
Maybe I'm doing something wrong when transforming the String to binary for signing? I tried it both using CFData and NSData (to make this self contained, I'm using "Hello World" as my String, but in my code I actually load a UTF8 encoded XML from a file using NSData(contentsOfFile:) yet both generate the same error...)
Thanks you so much for your help! It's being a great learning experience, but I've been at it for over a week full-time now, so I really can use a break!! ;) :D

Answer 1

I have found a solution. The code no longer crashes, and I connected to the web service successfully after it, and the XMLDSIG signature was accepted by it (see related Question on XMLDSIG if interested in details on canonicalization and xml reference).
The key I was using is not compatible with signing (not sure why or even what the key was, actually...)
I was looking into counter-authenticating with a server using a X509 certificate (for an unrelated part of my solution) when I came across the SecIdentity class, needed to create a SecCredential together with the certificate and authenticate with the server.
I saw Identities embed a private key, and thought if could work for me. And it did!
Here are the changes I made:
Changed the kSecClass to kSecClassIdentity in the search dictionary
Retrieved the SecIdentity using SecItemCopyMatching
After casting it accordingly, used SecIdentityCopyPrivateKey to retrieve the private key into a SecKeyRef
Used this key in SecSignTransform, and voilà!! It worked!
Here is the working code:
// ...
// get the SecIdentity (substitutes KeySearchDict etc)
idSearchDict = [(kSecClass as String): (kSecClassIdentity as String), (kSecMatchSubjectContains as String): keyMatch, (kSecReturnRef as String):
status = SecItemCopyMatching(idSearchDict, &anyItem)
id = (anyItem!.takeRetainedValue() as SecIdentity)
// Retrieve the private key from SecIdentity
var KeyRef: Unmanaged<SecKeyRef>?
SecIdentityCopyPrivateKey(id, &KeyRef)
priKey = (KeyRef!.takeRetainedValue() as SecKey)
// Create SecSign using the private key
signer = SecSignTransformCreate(priKey, &error).takeRetainedValue()
if error != nil { print("signer transform creation error: ") ; println(error) }
/ signer to get data from sourceData
// ...
I'll post another question with the difficulties I'm facing with XMLDSIG, and add it to the comments, in case anyone is interested. I've already solved that too, and the answer is there in case you need it.
Thanks to everyone who tried to help, and hope this saves someone a lot of time and headache in the future!!
PS: loving Swift, otherwise 😉 😃