IssueTracker

We noticed an error in the function used (in all Android versions and for all Android NFC devices) to check the presence of a tag, "RW_T4tPresenceCheck" in file rw_t4t.c (see https://android.googlesource.com/platform/external/libnfc-nci/+/85b7e84f6cc61506c94e98844cac9ce50bbbe9dc/src/nfc/tags/rw_t4t.c for example).

This error generates transaction failures in many NFC transactions.

Indeed, at line 1353 of this file (if (rw_t4t_read_file (0, 1, FALSE))), the presence of a tag is checked by sending a "Read Binary" command (ISO/IEC 7816-4 APDU) to the card.

This method is forbidden by the ISO/IEC 14443-4 standard which prescribes in its section 7.5.5 only two methods to check the PICC presence:

"
7.5.5 PICC presence check

The following methods may be used to check the presence of a PICC at any time including before any I-block exchange.

(...)

7.5.5.1 Method 1

The PCD may send an empty I-block and expect to receive an I-block from the PICC.

7.5.5.2 Method 2

Before the first I-block exchange, the PCD may send an R(NAK) block (with block number 0) and expect to receive an R(ACK) (with block number 1) block from the PICC (rule 12).

After the first I-block exchange, the PCD may either a) send an R(NAK) block (with current block number) and expect to receive an R(ACK) block from the PICC (rule 12), in which case the PCD should not retransmit its last I-block as mentioned in the note in rule 6,

or

b) toggle its block number then send an R(NAK) block and expect to receive the last I-block from the PICC (rule 11).
"

Both methods do not interfere with the ISO/IEC 7816-4 APDU management layer of the PCD and of the PICC, unlike the presence check with the Read Binary command which is currently implemented in Android.

The Android presence check implementation is a major problem which prevents from using Android NFC devices in all applications using a security mechanism requiring that the control of all the APDUs exchanged with the card.

There are millions of such cards, used nationwide in several major countries (e.g. Canada, Mexico, Israel, France, Italy, Belgium, Portugal, etc.).

A fix should be very urgently distributed since presently no one can release an Android application securely accessing these cards.

For information we work are Spirtech, an engineering company, expert in the fields of smart cards, cryptography and contactless technology (ISO 14443) which is currently developing several applications on Android, using its NFC features, for major public transport companies in Europe and in the world.