Swift 4 Keychain SecItemUpdate Error status code -50 - ios

Question

I'm trying to use some keychain code to securely and persistently store some sensitive data. I have functions to save and read data which work fine but I cannot seem to get the update one to work.
let kSecClassValue = NSString(format: kSecClass)
let kSecAttrAccountValue = NSString(format: kSecAttrAccount)
let kSecValueDataValue = NSString(format: kSecValueData)
let kSecClassGenericPasswordValue = NSString(format: kSecClassGenericPassword)
let kSecAttrServiceValue = NSString(format: kSecAttrService)
let kSecMatchLimitValue = NSString(format: kSecMatchLimit)
let kSecReturnDataValue = NSString(format: kSecReturnData)
let kSecMatchLimitOneValue = NSString(format: kSecMatchLimitOne)
public class KeychainService: NSObject {
class func updatePassword(service: String, account:String, data: String) {
if let dataFromString: Data = data.data(using: String.Encoding.utf8, allowLossyConversion: false) {
// Instantiate a new default keychain query
let keychainQuery: NSMutableDictionary = NSMutableDictionary(objects: [kSecClassGenericPasswordValue, service, account, kCFBooleanTrue, kSecMatchLimitOneValue], forKeys: [kSecClassValue, kSecAttrServiceValue, kSecAttrAccountValue, kSecReturnDataValue, kSecMatchLimitValue])
let status = SecItemUpdate(keychainQuery as CFDictionary, [kSecValueDataValue:dataFromString] as CFDictionary)
if (status != errSecSuccess) {
if let err = SecCopyErrorMessageString(status, nil) {
print("Read failed: \(err)")
print("status: \(status)")
}
}
}
}
...
I am constantly getting error status -50 indicating one or more parameters passed to the function were not valid. I tried reading through the docs but couldn't come up with anything that worked.
Thank you in advance!

Answer 1

It turned out that I had to remove the last two keys from the keychainQuery dictionary so it looks like this:
public class KeychainService: NSObject {
class func updatePassword(service: String, account:String, data: String) {
if let dataFromString: Data = data.data(using: String.Encoding.utf8, allowLossyConversion: false) {
// Instantiate a new default keychain query
let keychainQuery: NSMutableDictionary = NSMutableDictionary(objects: [kSecClassGenericPasswordValue, service, account], forKeys: [kSecClassValue, kSecAttrServiceValue, kSecAttrAccountValue])
let status = SecItemUpdate(keychainQuery as CFDictionary, [kSecValueDataValue:dataFromString] as CFDictionary)
if (status != errSecSuccess) {
if let err = SecCopyErrorMessageString(status, nil) {
print("Read failed: \(err)")
print("status: \(status)")
}
}
}
}
...