TA0347 Technical article

Transcription

1 Technical article Key features and benefits of STMicroelectronics short-range contactless memory ICs Introduction STMicroelectronics has a broad range offer of short-range contactless memory ICs. All devices are based on the ISO14443 type B standard. They are accessible through a MHz carrier frequency and allow a data transfer rate of 106 kbit/s in both reception and emission modes. They all include the anticollision mechanism that allows detecting and selecting tags present at the same time within range of the reader. Three series are currently available: SRI2K and SRI4K short-range ICs with 2048 to 4096 bits of user EEPROM SRI512 and SRT512 featuring 512 bits of user EEPROM SRIX4K short-range IC with 4096 bits of user EEPROM and anti-clone function. The memory can be read and written at 32-bit bock level. It is organized into three areas: A reloadable 32-bit one time programmable (OTP) area which can be used as a counter (available on all SRIxx devices) Two 32-bit binary countdown counter(s) with anti-tearing logic EEPROM user area, that can be write protected at block level ROM area containing the 64-bit device unique identifier. The memory features a 5 ms programming time at 32-bit level, an endurance of 1million read/write cycles, and 40 years of data retention. The objective of this technical article is to provide a detailed description of the ST shortrange contactless memory IC key features linked to end-applications such as mass transit. August 2012 Doc ID Rev 2 1/9

2 Contents TA0347 Contents 1 Key features Reloadable 32-bit OTP area bit binary counters Overview of anti-tearing mechanism Debit and reloading Passive security and anti-clone proprietary function Passive security Anti-clone function Benefits of ST short-range contactless memory ICs for mass transit applications Revision history /9 Doc ID Rev 2

3 Key features 1 Key features The key features of ST short-range contactless ICs as the following: Reloadable 32-bit OTP area Two binary counters protected by anti-tearing logic allowing debit and reloading Passive security and anti-clone proprietary function A detailed description of each key feature is given in the following sections. 1.1 Reloadable 32-bit OTP area The bits of the OTP area can only be programmed from 1 to 0. The OTP area can be delivered with all bits initialized to 1 or its content pre-programmed with customer data (personalization). Typical applications are the storage of abacus, certificates, and application data. Example The value stored in the OTP area is 0xBB corresponding to b, and the new value programmed is 0xAA ( b). If a write error occurs, the possible new values can be: 0xBB -> b initial value 0xBA -> b intermediate lower value 0xAB -> b intermediate lower value 0xAA -> b final value As a result, the updated value is always lower or equal than the initial value if a power-down occurs bit binary counters All ST short-range devices feature two 32-bit countdown counters (C 1 and C 2 ) protected with automated anti-tearing logic Overview of anti-tearing mechanism This feature allows the values stored in each counter to be protected if a power-down occurs during the programming cycle. In this case, the counter value is not updated and the previous value is retained. The anti-tearing algorithm is based on the following principle: The counter retains the active value. A non-volatile register (C A ) is erased, while the other register (C B ) is programmed with the new counter value. Doc ID Rev 2 3/9

4 Key features TA Debit and reloading A typical application of the binary counters is the e-purse which is pre-programmed with a determined amount. This amount can be decremented each time a purchase operation is performed or reloaded at point-of-sales. In e-purse applications, C 1 can be used for debit and C 2 for credit, each counter being protected by the anti-tearing logic. The e-purse amount, E, is defined by: E = C 1 C 2 By design, the counter values cannot be increased and once they have reached zero they remain at zero. The potential reload is defined at personalization (initial value). The validity of each transaction can be followed and controlled by anti-clone (SRiX4K). Example The e-purse is loaded with a maximum of 250 units, in 2 reloading steps. 1. Initial value at personalization: C 1 = 250, C 2 = 250. E = 0 unit. 2. Loading of 100 units: C 1 = 250, C 2 = 150. E = 100 units. 3. Debit of 35 units for an intra- zone trip: C 1 = 215, C 2 = 150. E = 65 units. 4. Debit of 65 units for a 3 zones trip: C 1 = 150, C 2 = 150. E = 0 unit. 5. Reloading of 150 units (last reload): C 1 = 150, C 2 = 0. E = 150 units. 1.3 Passive security and anti-clone proprietary function Passive security Read access to short-range contactless memory content can be performed by any ISO14443 reader while write access depends on memory protection status and data location in the memory area. The following areas are available depending on the products: EEPROM user area organized into blocks which can be individually write-protected. Reloaded OTP area (see Section 1.1: Reloadable 32-bit OTP area), 32-bit counters (see Section 1.2: 32-bit binary counters) ROM area: once an EEPROM user block has been protected, it can no longer be unprotected and behaved like ROM. A first level of data security can be ensured by the application itself, by using the adequate memory area to store data. To enhance data protection, the application can encrypt the memory content using the adequate cryptography engines and the unique device identifier (UID) as a key. All ST short range contactless devices feature a 64-bit UID which allows supporting any powerful algorithm. The system remains open, flexible and evolutive since data security is fully controlled by the application without any link to the silicon product. Refer to Figure 1 for a comparison between ST and competition encryption schemes. 4/9 Doc ID Rev 2

5 Key features Figure 1. Comparison between ST and competition encryption sche Doc ID Rev 2 5/9

6 Key features TA Anti-clone function Figure 2. The anti-clone function is only available on the SRiX4K. It complements the passive security. A certificate is generated to authentify the device. This is not a password since data is accessible whatever the anti-clone status. The authenticate process can be launched as often as needed. Refer to Figure 1 for a description of the anti-clone process. Comparison between ST and competition anti-clone schemes 6/9 Doc ID Rev 2

7 Benefits of ST short-range contactless memory ICs for mass transit applications 2 Benefits of ST short-range contactless memory ICs for mass transit applications SRT512 and SRI512 contactless memory ICs are ideal solutions for mass transit applications since they offer the following features: Two 32-bit countdown counters Protected by anti-tearing logic 2 32 transport units or cash equivalent 32 additional counts compared to competitor products Prevention of play twice fraud by copying the content of the first counter into the second one. The 2 counters that can be split into four 16-bit counters (LSB, MSB) Unique true 512-bit contactless memory IC on the market without taking into account the two 32-bit counters Compared to products deprived of counters, this also saving up to 50% of memory space. This memory space benefit is crucial since it leads to overall system improvement: Enhanced security since the memory can store bigger security certificates Better customer satisfaction thanks to better data protection against anti-tearing Fare management: better trip follow-up granularity These technological benefits result in financial profits for the operator since fraud and customer claims are reduced while the value stored on the ticket and the fare granularity are increased. SRI2K, SRI4K, and SRIX4K are good candidates for applications requiring more memory space or enhanced security. Doc ID Rev 2 7/9

8 Revision history TA Revision history Table 1. Document revision history Date Revision Changes 28-Aug Initial release. 30-Aug Removed all mentions of Mifare. Updated Figure 1: Comparison between ST and competition encryption sche and Figure 2: Comparison between ST and competition anti-clone schemes. 8/9 Doc ID Rev 2

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