Is it possible to update a Keychain item's kSecAttrAccessible value?

Question

Is it possible to update the value of the attribute kSecAttrAccessible of existing items in the Keychain? It seems that it cannot be changed after the item was

Answer 1

After opening a support incident at Apple Developer Technical Support (ADTS), I received a reply that answers this question. SecItemUpdate() requires the Keychain item's data via the attribute kSecValueData to perform the update of the attribute kSecAttrAccessible. According to ADTS, this constraint is currently not documented in the reference documentation.

NSData *encodedIdentifier = [@"BUNDLE_IDENTIFIER" 
                             dataUsingEncoding:NSUTF8StringEncoding];
NSDictionary *query = [NSDictionary dictionaryWithObjectsAndKeys:
                       kSecClassGenericPassword, kSecClass,
                       encodedIdentifier, kSecAttrGeneric,
                       encodedIdentifier, kSecAttrService,
                       nil];

// Obtain the Keychain item's data via SecItemCopyMatching()
NSData *itemData = ...;

NSDictionary *updatedAttributes = 
    [NSDictionary dictionaryWithObjectsAndKeys:
        kSecAttrAccessibleAfterFirstUnlock, kSecAttrAccessible,
        (CFDataRef)itemData, kSecValueData,
        nil];

OSStatus updateItemStatus = SecItemUpdate((CFDictionaryRef)query, 
                                          (CFDictionaryRef)updatedAttributes);

// updateItemStatus should have the value errSecSuccess