iOS 7 Programming Cookbook

8.3. Finding Values in the Keychain

Problem

You want to query the keychain to find an existing item.

Solution

Use the SecItemCopyMatching function. Follow these steps:

1. Construct a dictionary to pass to the aforementioned function. Add the kSecClass key to the dictionary. Set the key’s value to reflect the type of item that you are looking for. Usually the value should be kSecClassGenericPassword.

2. Add the kSecAttrService key to the dictionary. Set the key’s value to the service string of the item you are looking for. In this chapter, for service names, we use our app’s bundle identifier and we are setting the bundle identifiers of all our apps to the same string, so that one can write to the keychain, another can read the same data, etc.

3. Add the kSecAttrAccount key to the dictionary and set its value to the actual key of the value that you previously stored in the keychain. If you followed the example that we wrote in Recipe 8.2, the account name in this case would be the string “Full Name.”

4. Add the kSecReturnAttributes attribute to the dictionary and set its value to kCFBooleanTrue if you want to retrieve the attributes, such as the creation and modification date, of the existing value in the keychain. If you want to retrieve the actual value of the item you stored in the keychain, instead of the kSecReturnAttributes key, add the kSecReturnData key to your dictionary and set its value to kCFBooleanTrue.

Once your dictionary is ready, you can pass it as the first parameter to the SecItemCopyMatching ...