Authentication after a read failure of a MIFARE card - arduino

Question

An arduino and a mfrc522 rfid reader are easy to use to read and write mifare card.
My aim is to use the both key of the card in a sector, some blocks are readable with key A, and some are only readable by key B.
Setting properly the access bits allow this behaviour. So as to try it on the second sector (blocks 4 5 6 7), I set the access bits g0 [0 0 0], g1 [1 0 1], g2 [0 0 0], g3 [1 0 1] by writting the block 7 with {,0xF5,0xA5,0xA0,0x38,} cf. §8.7 of https://www.nxp.com/docs/en/data-sheet/MF1S50YYX_V1.pdf. Now the block 5 is not readable with keyA but with keyB (g1), and keyB is no more readable (g3). So when I authenticate with keyA an attempt to read the block 5 lead to an error. At this time the others authentications fail, and it is not possible to read the others blocks, though the access bits allow it.
I tried to read the second sector with key B for block 5 and keyA for the others code, it is working. But if I try to read with key A then with keyB in case of failure it is not working.
Extract of the code :
// The sector of interest is the second one : blocks 4 5 6 7
Serial.println("\nAuthenticate block 0x05 with key B");
for (i = 4; i < 8; i++) {
// Block 5 is readable with key B
status = readblock(i==5?MF1_AUTHENT1B:MF1_AUTHENT1A, i, i==5?keyB:keyA, serial);
if ( status == MI_ERR) {
Serial.print(" - Unable to read block nb. 0x");
Serial.println(i, HEX);
}
}
Serial.println("\nAuthenticate with key A then key B if failed");
for (i = 4; i < 8; i++) {
// Try to authenticate each block first with the A key.
status = readblock(MF1_AUTHENT1A, i, keyA, serial);
if ( status == MI_ERR) {
Serial.print(" - Try keyB - ");
status = readblock(MF1_AUTHENT1B, i, keyB, serial);
if ( status == MI_ERR) {
Serial.print(" - Unable to read block nb. 0x");
Serial.println(i, HEX);
}
}
}
readblock function (authentication and read)
byte readblock(byte mode, byte block, byte *key, byte *serial)
{
int j;
byte data[MAX_LEN];
byte status = MI_ERR;
// Try to authenticate the block first
status = nfc.authenticate(mode, block, key, serial);
if ( status == MI_OK) {
Serial.print("Authenticated block nb. 0x");
Serial.print(block, HEX);
// Reading block i from the tag into data.
status = nfc.readFromTag(block, data);
if (status == MI_OK) {
// If there was no error when reading; print all the hex
// values in the data.
Serial.print(" : ");
for (j = 0; j < 15; j++) {
Serial.print(data[j], HEX);
Serial.print(", ");
}
Serial.println(data[15], HEX);
} else
Serial.print(" - Read failed");
} else {
Serial.print("Failed authentication block nb. 0x");
Serial.print(block, HEX);
}
return status;
}
The result is
Authenticate block 0x05 with key B
Authenticated block nb. 0x4 : 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0
Authenticated block nb. 0x5 : AB, CD, EF, 1, 23, 45, 67, 89, 98, 76, 54, 1A, 10, FE, DC, BA
Authenticated block nb. 0x6 : 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0
Authenticated block nb. 0x7 : 0, 0, 0, 0, 0, 0, F5, A5, A0, 38, 0, 0, 0, 0, 0, 0
Authenticate with key A then key B if failed
Authenticated block nb. 0x4 : 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0
Authenticated block nb. 0x5 - Read failed - Try keyB - Failed authentication block nb. 0x5 - Unable to read block nb. 0x5
Failed authentication block nb. 0x6 - Try keyB - Failed authentication block nb. 0x6 - Unable to read block nb. 0x6
Failed authentication block nb. 0x7 - Try keyB - Failed authentication block nb. 0x7 - Unable to read block nb. 0x7
So I would like to know if it is possible to attempt to read a block with the bad key and then go on reading the block with the othe rkey, and so on.

Answer 1

An explanation can be found in https://www.nxp.com/docs/en/application-note/AN1304.pdf p.24
Each time an Authentication operation, a Read operation or a Write operation fails, the MIFARE Classic or MIFARE Plus remains silent and it does not respond anymore to any commands. In this situation in order to continue the NDEF Detection Procedure the MIFARE Classic or MIFARE Plus needs to be re-activated and selected.
So you have to re-activate and select after failure, by adding these lines to your code for instance :
Serial.println("\nAuthenticate with key A then key B if failed");
for (i = 4; i < 8; i++) {
// Try to authenticate each block first with the A key.
status = readblock(MF1_AUTHENT1A, i, keyA, serial);
if ( status == MI_ERR) {
Serial.print(" - Try keyB - ");
/** RE ACTIVATE AND SELECT ------------------------------- **/
nfc.haltTag();
status = nfc.requestTag(MF1_REQIDL, data);
if (status == MI_OK) {
status = nfc.antiCollision(data);
memcpy(serial, data, 5);
nfc.selectTag(serial);
}
/** ------------------------------------------------------ **/
status = readblock(MF1_AUTHENT1B, i, keyB, serial);
if ( status == MI_ERR) {
Serial.print(" - Unable to read block nb. 0x");
Serial.println(i, HEX);
}
}
}