From 46fb86265c1a450eecdb05e0f1f49dcf54339535 Mon Sep 17 00:00:00 2001
From: AloneLiberty <111039319+AloneLiberty@users.noreply.github.com>
Date: Thu, 2 Feb 2023 15:18:39 +0000
Subject: [PATCH] NFC: fix creating MF Classic tags from "Add Manually" menu
 (BCC calulation and ATQA/SAK writing) (#2342)

* NFC: fix creating MF Classic cards from "Add Manually" menu (BCC calculation and AQTA/SAK writing)
* NFC: Fix BCC/SAK/ATQA in unit_tests and SAK in nfc_generate_mf_classic

Co-authored-by: gornekich <n.gorbadey@gmail.com>
---
 applications/debug/unit_tests/nfc/nfc_test.c | 28 +++++++++++++--
 lib/nfc/helpers/nfc_generators.c             | 36 +++++++++++++++++---
 2 files changed, 57 insertions(+), 7 deletions(-)

diff --git a/applications/debug/unit_tests/nfc/nfc_test.c b/applications/debug/unit_tests/nfc/nfc_test.c
index d613be2b..54bdd590 100644
--- a/applications/debug/unit_tests/nfc/nfc_test.c
+++ b/applications/debug/unit_tests/nfc/nfc_test.c
@@ -348,13 +348,37 @@ static void mf_classic_generator_test(uint8_t uid_len, MfClassicType type) {
     memcpy(atqa, nfc_dev->dev_data.nfc_data.atqa, 2);
 
     MfClassicData* mf_data = &nfc_dev->dev_data.mf_classic_data;
-    // Check the manufacturer block (should be uid[uid_len] + 0xFF[rest])
+    // Check the manufacturer block (should be uid[uid_len] + BCC (for 4byte only) + SAK + ATQA0 + ATQA1 + 0xFF[rest])
     uint8_t manufacturer_block[16] = {0};
     memcpy(manufacturer_block, nfc_dev->dev_data.mf_classic_data.block[0].value, 16);
     mu_assert(
         memcmp(manufacturer_block, uid, uid_len) == 0,
         "manufacturer_block uid doesn't match the file\r\n");
-    for(uint8_t i = uid_len; i < 16; i++) {
+
+    uint8_t position = 0;
+    if(uid_len == 4) {
+        position = uid_len;
+
+        uint8_t bcc = 0;
+
+        for(int i = 0; i < uid_len; i++) {
+            bcc ^= uid[i];
+        }
+
+        mu_assert(manufacturer_block[position] == bcc, "manufacturer_block bcc assert failed\r\n");
+    } else {
+        position = uid_len - 1;
+    }
+
+    mu_assert(manufacturer_block[position + 1] == sak, "manufacturer_block sak assert failed\r\n");
+
+    mu_assert(
+        manufacturer_block[position + 2] == atqa[0], "manufacturer_block atqa0 assert failed\r\n");
+
+    mu_assert(
+        manufacturer_block[position + 3] == atqa[1], "manufacturer_block atqa1 assert failed\r\n");
+
+    for(uint8_t i = position + 4; i < 16; i++) {
         mu_assert(
             manufacturer_block[i] == 0xFF, "manufacturer_block[i] == 0xFF assert failed\r\n");
     }
diff --git a/lib/nfc/helpers/nfc_generators.c b/lib/nfc/helpers/nfc_generators.c
index 590ff4d5..50c89aba 100644
--- a/lib/nfc/helpers/nfc_generators.c
+++ b/lib/nfc/helpers/nfc_generators.c
@@ -30,12 +30,32 @@ static void nfc_generate_mf_classic_uid(uint8_t* uid, uint8_t length) {
     furi_hal_random_fill_buf(&uid[1], length - 1);
 }
 
-static void nfc_generate_mf_classic_block_0(uint8_t* block, uint8_t uid_len) {
+static void nfc_generate_mf_classic_block_0(
+    uint8_t* block,
+    uint8_t uid_len,
+    uint8_t sak,
+    uint8_t atqa0,
+    uint8_t atqa1) {
     // Block length is always 16 bytes, and the UID can be either 4 or 7 bytes
     furi_assert(uid_len == 4 || uid_len == 7);
     furi_assert(block);
-    nfc_generate_mf_classic_uid(block, uid_len);
-    for(int i = uid_len; i < 16; i++) {
+
+    if(uid_len == 4) {
+        // Calculate BCC
+        block[uid_len] = 0;
+
+        for(int i = 0; i < uid_len; i++) {
+            block[uid_len] ^= block[i];
+        }
+    } else {
+        uid_len -= 1;
+    }
+
+    block[uid_len + 1] = sak;
+    block[uid_len + 2] = atqa0;
+    block[uid_len + 3] = atqa1;
+
+    for(int i = uid_len + 4; i < 16; i++) {
         block[i] = 0xFF;
     }
 }
@@ -74,7 +94,6 @@ static void
     data->nfc_data.type = FuriHalNfcTypeA;
     data->nfc_data.interface = FuriHalNfcInterfaceRf;
     data->nfc_data.uid_len = uid_len;
-    nfc_generate_mf_classic_block_0(data->mf_classic_data.block[0].value, uid_len);
     data->nfc_data.atqa[0] = 0x44;
     data->nfc_data.atqa[1] = 0x00;
     data->nfc_data.sak = 0x08;
@@ -316,6 +335,7 @@ static void nfc_generate_ntag_i2c_plus_2k(NfcDeviceData* data) {
 
 void nfc_generate_mf_classic(NfcDeviceData* data, uint8_t uid_len, MfClassicType type) {
     nfc_generate_common_start(data);
+    nfc_generate_mf_classic_uid(data->mf_classic_data.block[0].value, uid_len);
     nfc_generate_mf_classic_common(data, uid_len, type);
 
     // Set the UID
@@ -339,7 +359,6 @@ void nfc_generate_mf_classic(NfcDeviceData* data, uint8_t uid_len, MfClassicType
         }
         // Set SAK to 18
         data->nfc_data.sak = 0x18;
-
     } else if(type == MfClassicType1k) {
         // Set every block to 0xFF
         for(uint16_t i = 1; i < MF_CLASSIC_1K_TOTAL_SECTORS_NUM * 4; i += 1) {
@@ -366,6 +385,13 @@ void nfc_generate_mf_classic(NfcDeviceData* data, uint8_t uid_len, MfClassicType
         data->nfc_data.sak = 0x09;
     }
 
+    nfc_generate_mf_classic_block_0(
+        data->mf_classic_data.block[0].value,
+        uid_len,
+        data->nfc_data.sak,
+        data->nfc_data.atqa[0],
+        data->nfc_data.atqa[1]);
+
     mfc->type = type;
 }