Over the past few years many hotels have begun transitioning from older MIFARE Classic 1K key cards to newer, more secure cards — AES cards (such as MIFARE Ultralight AES or MIFARE Plus) and ULC cards (MIFARE Ultralight C, which uses 3DES). The change improves security, but it can also create confusion when properties try to use these cards in systems originally configured for older technology.
If your property recently switched to AES or ULC cards and is experiencing encoding issues or door lock errors, understanding the differences between these card types can help resolve most problems quickly.
The Difference Between 1K Cards and Newer Secure Cards
For many years, hotels relied on MIFARE Classic 1K RFID cards. These cards use a legacy encryption method (Crypto1) and a memory structure that most hotel lock systems were designed around.
Newer cards use stronger, standard encryption: 128-bit AES on chips such as MIFARE Ultralight AES and MIFARE Plus, or 3DES on ULC (MIFARE Ultralight C) cards. Both are far harder to clone or duplicate than MIFARE Classic.
Because these cards use different encryption and authentication methods, the way hotel systems communicate with them is different.
Key Differences
Encryption
1K cards use older proprietary encryption (Crypto1), which has been publicly broken.
AES cards use the Advanced Encryption Standard (AES); ULC cards use 3DES. Both are far more secure.
Card Authentication
1K cards authenticate quickly with older readers.
AES and ULC cards require secure mutual authentication before data is read or written.
Memory Structure
1K cards have a fixed sector-and-block memory layout.
Ultralight-family cards (ULC, Ultralight AES) use a smaller page-based memory, and MIFARE Plus supports multiple security levels.
Because of this, a system configured for 1K cards may not automatically recognize or encode AES or ULC cards.
Common Problems Hotels Encounter
When hotels transition to AES or ULC cards, they often see a few predictable issues.
Cards Will Not Encode
The most common problem occurs when the encoder is still configured for 1K cards. The encoder may detect the card but fail to write data.
Solution:
Verify the encoder supports your new card type.
Update encoder firmware if required.
Confirm the card profile in the PMS or lock software matches the new card type.
Cards Encode But Doors Won’t Open
This typically means the door locks are still operating in legacy mode.
New card types often require the lock firmware to support the new authentication method.
Solution:
Update lock firmware.
Ensure locks are configured for the new card type.
Confirm the correct key set is programmed.
Slow Encoding or Delayed Reads
Secure authentication requires additional steps. If readers or encoders are outdated, communication can appear slower.
Solution:
Verify reader and encoder compatibility with the new card type.
Update reader firmware if available.
Why Hotels Are Moving Away From 1K Cards
Despite the learning curve, newer secure cards offer major benefits.
Much Stronger Security
MIFARE Classic cards can be read and cloned with inexpensive tools. NXP, the chip maker, no longer recommends MIFARE Classic for security-relevant applications. AES and ULC cards make unauthorized cloning far more difficult.
Required Security Upgrades
Some lock manufacturers now require the move. After the 2024 “Unsaflok” vulnerability disclosure, dormakaba’s Saflok fix involves upgraded locks, software and encoders, plus reissuing keycards — upgraded properties use MIFARE Ultralight C cards instead of MIFARE Classic.
Brand Standards
Many large hotel brands are requiring stronger key card security to protect guests and reduce fraud.
Best Practices When Switching Card Types
If your hotel is upgrading from 1K cards to AES or ULC cards, a few steps can make the transition smoother.
Confirm your encoder supports the new card type.
Verify lock firmware compatibility.
Update the key card profile in your hotel system software.
Test cards on multiple doors before placing large orders.
Working with a supplier who understands hotel access systems can also help avoid many of these headaches.
Final Thoughts
AES and ULC cards represent the next generation of hotel key card technology. While they behave differently than traditional 1K cards, the added security makes them an important upgrade for modern properties.
If your property is experiencing issues with new cards, the solution is usually a configuration or firmware adjustment rather than a defective card.
Understanding the differences between card types can save hotel teams time, reduce frustration at the front desk, and ensure guests continue to enjoy smooth and secure access to their rooms.
Sources & further reading
- MIFARE Plus EV2 fact sheet (security levels and migration from MIFARE Classic) — NXP Semiconductors
- MIFARE Ultralight AES product data sheet — NXP Semiconductors
- MIFARE Ultralight C product page — NXP Semiconductors
- Security Statement on Crypto1 Implementations — NXP / MIFARE
- Dismantling MIFARE Classic (ESORICS 2008) — Radboud University Nijmegen
- Saflok Lock Vulnerability Can Be Exploited to Open Millions of Doors — SecurityWeek