LF Legacy 
EM4100 / EM4200
For older 125 kHz access control systems and key fobs.
Security None
Memory 64–128 bit ROM
HITAG® S: Technical Data, Security and Use
HITAG S is an LF RFID product family from NXP Semiconductors for contactless identification applications. The passive transponders operate in the frequency range of 100 to 150 kHz and are available as HITAG S256 with 256 bits and as HITAG S2048 with 2,048 bits of EEPROM. Both variants use the same protocol and support anti-collision.
HITAG S is aimed primarily at industrial identification and legacy applications as well as existing HITAG infrastructures. NXP names animal identification, laundry automation and the logistics of kegs and gas cylinders, among others. For authentication, a proprietary method with a secret 48-bit key is available. The current NXP product page now labels HITAG S as “Not Recommended for New Designs”.
| Feature | Value |
|---|---|
| Manufacturer | NXP Semiconductors |
| Product family | HITAG S |
| Variants | HITAG S256 / HITAG S2048 |
| Type designation | HTSICH56 / HTSICH48 |
| RFID class | LF |
| Frequency range | 100–150 kHz |
| Standards | ISO 11784/85; designed for ISO 14223 and ISO 18000-2 infrastructure |
| Data rate reader → transponder | 5.2 kbit/s |
| Data rate transponder → reader | 2 / 4 / 8 kbit/s |
| EEPROM / total memory | 256 bits (32 bytes) or 2,048 bits (256 bytes) |
| Memory structure S2048 | 64 pages of 4 bytes each; 16 blocks of 4 pages each |
| Authentication | Encrypted challenge authentication with a secret 48-bit key |
| Data encryption | No encryption of data transmission after successful authentication |
| UID | 32 bits |
| Anti-collision | Yes; fast anti-collision protocol |
| Operating modes | Reader Talks First; optional Transponder Talks First |
| Memory protection | Secure Memory Lock |
| Write cycles | Up to 100,000 erase/write cycles |
| Data retention | At least 10 years at ambient temperature ≤ 55 °C according to the data sheet |
| Smartphone NFC | No, not directly via the NFC module of normal smartphones |
| Product status at NXP | Not Recommended for New Designs |
| Typical media | RFID card and application-specific LF special transponders |
| Security rating | Legacy / 48-bit authentication |
| Recommendation | Mainly for existing HITAG S infrastructure and specialized LF applications |
HITAG S works as more than just a simple LF identifier carrier. The product family offers read/write memory, anti-collision, Reader Talks First and optionally Transponder Talks First as well as a Secure Memory Lock function. The S2048 variant organizes its 2,048 bits in 64 pages of four bytes each. Authentication protects access, but according to the data sheet, the subsequent data transmission itself is not encrypted.
Typical Applications
HITAG S was developed by NXP for LF applications that require writable memory, the detection of multiple transponders and integration into existing HITAG infrastructure.
Typical applications are:
- Animal identification according to ISO 11784/85
- Laundry automation
- Logistics and identification of beer kegs
- Logistics and identification of gas cylinders
- Pigeon racing and corresponding identification systems
- Brand protection applications
NXP offers the IC as a wafer, chip card module and HVSON2 component, among others. For customer-specific RFID media, depending on the reader, antenna design and operating environment, options include RFID cards or robust special transponders, for example.
Security
Security level: Legacy / proprietary 48-bit authentication
HITAG S can operate in authentication mode with a secret 48-bit key. During challenge authentication, the reader sends a 32-bit random number and a secret data stream generated from it. The transponder checks this and, if authentication is successful, responds with a secret 32-bit response.
This function must not be confused with AES. The current NXP data sheet explicitly states “48 bit secret key based encrypted authentication”, not AES. After successful authentication, read and write access is possible; according to the data sheet, the actual data transmission is unencrypted even in authentication mode.
For existing HITAG S systems, authentication can continue to be part of the existing security concept. For new applications with higher requirements for modern cryptography and encrypted communication, on the other hand, a more up-to-date system should be considered.
Advantages and Disadvantages of HITAG S
| Advantages | Disadvantages |
|---|---|
| 256-bit and 2,048-bit variants with the same protocol | No longer recommended by NXP for new designs |
| Writable EEPROM instead of a pure fixed identifier | Proprietary 48-bit authentication instead of current AES cryptography |
| Anti-collision for multiple transponders in the reader field | Data transmission not encrypted after authentication |
| Secure Memory Lock for protecting memory areas | No direct smartphone NFC support |
| Designed for existing HITAG infrastructure | Maximum of 256 bytes of total memory |
Alternatives to HITAG S
Depending on the existing reader infrastructure, security requirements and required memory, other chip types may be better suited. However, switching from LF to HF is not a direct chip replacement and may require new readers or a changed system architecture.
HF / NFC Recommendation 
MIFARE DESFire EV3
For new access control, ID card and multi-application systems.
Security AES-128
Memory 2 / 4 / 8 / 16 KB
HF Recommendation 
LEGIC advant
For secure access control and multi-application solutions.
Security 3DES / AES
Memory 4 KB
Frequently Asked Questions about HITAG S
Which variants of HITAG S are available?
NXP distinguishes two memory sizes: HITAG S256 has a total of 256 bits of read/write memory, HITAG S2048 a total of 2,048 bits. Both variants work with the same HITAG S protocol. The S2048 version provides the memory in 64 pages of four bytes each, or 16 blocks of four pages each.
Does HITAG S have 2 KB of memory?
No. The specification “2 KB” would be technically incorrect. HITAG S2048 has 2,048 bits, i.e. 256 bytes of total memory. HITAG S256 has 256 bits or 32 bytes.
Does HITAG S use AES?
No. For HITAG S, the NXP data sheet describes encrypted authentication based on a secret 48-bit key. AES is not mentioned for HITAG S in the data sheet.
Is data transmitted in encrypted form with HITAG S?
Not after the transponder has been successfully selected. In authentication mode, an encrypted challenge sequence is carried out first. After successful authentication, the transponder switches to the selected state. NXP explicitly points out that the subsequent data transmission is not encrypted, even in authentication mode.
Can HITAG S detect multiple transponders at the same time?
HITAG S has an anti-collision method. If there are several transponders in the field, the reader can determine their UIDs step by step and then select a specific transponder. For the fast anti-collision protocol, NXP specifies a performance of detecting 100 tags in 3.2 seconds. The performance actually achievable depends on the reader and the respective application.
Can HITAG S be read with a smartphone?
Not directly with a smartphone's usual NFC module. HITAG S operates in the LF range of 100 to 150 kHz, while smartphone NFC operates at 13.56 MHz. HITAG S therefore requires a dedicated LF reader.
Which readers support HITAG S?
A reader must support the HITAG S protocol and the corresponding LF frequency range. NXP developed HITAG S as an extension of the existing HITAG infrastructure and refers to the use of existing reader infrastructure. For a replacement or reorder, the specific reader and system support should nevertheless be checked instead of inferring compatibility from the frequency alone.
Can the memory of HITAG S be locked?
Yes. NXP mentions a “Secure Memory Lock functionality”. The memory organization contains configuration and access parameters that can be used to protect memory areas. A permanent lock should therefore only be applied once the encoding and data structure are finalized.
Is HITAG S still intended for new projects?
NXP still lists HITAG S on its product website, but currently labels the product family as “Not Recommended for New Designs”. For existing HITAG S systems, the chip may still be relevant for compatible additions or replacement needs. For a new system architecture, on the other hand, current alternatives should be evaluated based on reader compatibility, security needs and application.
Request RFID Media with HITAG S
Do you need RFID media with HITAG S for an existing system?
For the review, the desired media format and quantity, the existing reader or system used, and the required HITAG S variant and encoding are particularly helpful. For existing installations, an existing transponder or the exact reader designation should ideally also be known.
Technical sources
Data as of: September 2026
The technical information is based on the NXP data sheet „HITAG® S transponder IC – HTSICH56; HTSICH48“, Rev. 3.1 dated 11 December 2014, and the current NXP product page for the HITAG S family. Among other things, the data sheet describes the HITAG S256 and HITAG S2048 variants, memory organization, data rates, anti-collision, supported standards and the 48-bit key-based authentication.
Trademark notice
HITAG is a trademark of NXP B.V.