# UID Changeable RFID Cards ## What Are UID Changeable RFID Cards? UID changeable RFID cards represent a specialized category of contactless smart cards where the Unique Identifier (UID) stored in the card's chip can be rewritten or cloned by the user. Unlike standard **UID changeable RFID cards** issued by institutions which have a factory-locked, permanent UID, these cards feature chips that allow the UID to be modified using specific hardware and software. In my experience working with access control systems, discovering these cards opened up a new realm of testing and development possibilities, though it also highlighted significant security considerations. ### Personal Experience and Perspective My first encounter with a **UID changeable RFID card** was during a security audit for a small office building. We were testing the vulnerability of their 125kHz RFID door entry system. I had a natural aptitude for understanding RF protocols and electronics, which I honed through years of hobbyist projects. This skill allowed me to quickly grasp how these cards function. I successfully cloned an authorized card's UID onto a blank changeable card, demonstrating a critical flaw in their system. This hands-on experience solidified my opinion: while **UID changeable RFID cards** are powerful tools for penetration testers, developers, and hobbyists, their existence necessitates that organizations implement systems with encryption and mutual authentication, not just UID matching. ## Technical Specifications and Parameters For developers and integrators, here are the detailed technical specifications for a common type of **UID changeable RFID card**. *Please note: These technical parameters are for reference data. For precise specifications, you need to contact the backend management.* * **Chip Model:** NXP MF1 IC S50 (Clone Variant) * **Operating Frequency:** 13.56 MHz * **Communication Protocol:** ISO 14443A * **Memory Capacity:** 1KB EEPROM * **Memory Structure:** 16 sectors, 4 blocks per sector (64 blocks total). Each block is 16 bytes. * **UID Storage:** Stored in Block 0. Typically