Where does SecKeyCreateSignature get the key name for Keychain signing authorization dialog? - swift

Question

I have noticed a difference between certain keys in the Keychain with respect to how they appear in the Keychain signing dialog, and I cannot figure out why some are displayed a certain way while others are not.
Here is some test code to use identities in the Keychain to sign a sample bit of data.
func testCreateSignature() throws {
let query: [String: Any] = [kSecClass as String: kSecClassIdentity,
kSecMatchLimit as String: kSecMatchLimitAll,
kSecReturnAttributes as String: false,
kSecReturnRef as String: true,
kSecReturnData as String: true]
var resultsRef: CFTypeRef?
let status = SecItemCopyMatching(query as CFDictionary, &resultsRef)
guard status == errSecSuccess else { throw SecurityError.unhandledError(status: status) }
guard let results = resultsRef as? [[String:Any]] else {
throw SecurityError.unexpectedCertificateData
}
let data = Data([0xDE, 0xAD, 0xBE, 0xEF])
var privateKey: SecKey!
for result in results {
let secIdentity = result[kSecValueRef as String] as! SecIdentity
try SecIdentityCopyPrivateKey(secIdentity, &privateKey).check()
var error: Unmanaged<CFError>?
let signature = SecKeyCreateSignature(privateKey, .rsaSignatureMessagePKCS1v15SHA1, data as CFData, &error)!
if let error = error {
throw error.takeRetainedValue()
}
print(signature)
}
}
When the code attempts to use one of the keys that Xcode installed for code signing, the resulting dialog looks like the following:
However, when the code attempts to use a key that I've installed, no matter what the label on the key in the Keychain is, it always looks like this:
When my app attempts to use a key to sign, I would like the user to see the name of the key the app wants to use, instead of just generic "privateKey", but I cannot find where this information might be stored on the key.
I have checked the kSecAttrLabel and kSecAttrApplicationLabel attributes of both identities and the private keys and cannot find the text that appears in the dialogs.

Answer 1

I found it. It is a property of the Access Control List of a Keychain item. See 'descriptor' param for SecAccessCreate.
If you do not specify a custom ACL when importing a key, it will default to "privateKey".
I was using SecPKCS12Import to import a .pfx file. I attempted to set the kSecImportExportAccess key in the options parameter to a custom SecAccess object, but it would always import with a default ACL.
I ended up refactoring the code to use SecItemImport instead to import the .pfx file and supplied a custom SecAccess instance:
static func importIdentity(contentsOf url: URL, password: String) throws {
let data = try Data.init(contentsOf: url)
var access: SecAccess!
try SecAccessCreate("License Key" as CFString, nil, &access).check()
var keychain: SecKeychain!
var outItems: CFArray?
let filename: CFString? = url.isFileURL ? url.lastPathComponent as CFString : nil
var inputFormat: SecExternalFormat = .formatPKCS12
var itemType: SecExternalItemType = .itemTypeAggregate
let unmanagedPassword = Unmanaged<AnyObject>.passRetained(password as AnyObject)
let unmanagedAccess = Unmanaged<SecAccess>.passRetained(access)
var params: SecItemImportExportKeyParameters = SecItemImportExportKeyParameters(version: UInt32(SEC_KEY_IMPORT_EXPORT_PARAMS_VERSION),
flags: .importOnlyOne,
passphrase: unmanagedPassword,
alertTitle: nil,
alertPrompt: nil,
accessRef: unmanagedAccess,
keyUsage: nil,
keyAttributes: nil)
try SecKeychainCopyDefault(&keychain).check()
try SecItemImport(data as CFData, filename, &inputFormat, &itemType, [], &params, keychain, &outItems).check()
}
Importing the identity as above will result in "License Key" being shown in the signing dialog rather than "privateKey".