From 755be05603dbe28948af4cf26a08bcd42c2c5ceb Mon Sep 17 00:00:00 2001
From: Tau <tau@nowhere>
Date: Mon, 17 Dec 2018 17:09:56 -0500
Subject: [PATCH] board/sg-nfc.c: Use non-hardcoded UID

Turns out this does in fact vary between cards, even though its
actual value is unimportant.
---
 board/sg-nfc.c    | 24 ++++++++++++++++--------
 board/sg-nfc.h    |  2 +-
 cardhook/_com12.c | 12 ++++++++++--
 3 files changed, 27 insertions(+), 11 deletions(-)

diff --git a/board/sg-nfc.c b/board/sg-nfc.c
index 0afd1b0..9936879 100644
--- a/board/sg-nfc.c
+++ b/board/sg-nfc.c
@@ -215,21 +215,29 @@ static HRESULT sg_nfc_cmd_mifare_poll(
         const struct sg_req_header *req,
         struct sg_nfc_resp_mifare_poll *resp)
 {
+    uint32_t uid;
     HRESULT hr;
 
-    hr = nfc->ops->mifare_poll(nfc->ops_ctx);
+    uid = 0;
+    hr = nfc->ops->mifare_poll(nfc->ops_ctx, &uid);
 
     if (hr == S_OK) {
+        if (uid == 0 || uid == -1) {
+            sg_nfc_dprintf(nfc, "nfc->ops->mifare_poll returned bad uid\n");
+
+            return E_UNEXPECTED;
+        }
+
         sg_nfc_dprintf(nfc, "Mifare card is present\n");
 
         sg_resp_init(&resp->resp, req, sizeof(resp->payload.some));
-        resp->payload.some[0] = 0x01;   /* Chunk size? */
-        resp->payload.some[1] = 0x10;   /* Unknown */
-        resp->payload.some[2] = 0x04;   /* Chunk size? */
-        resp->payload.some[3] = 0x52;   /* UID byte 0 */
-        resp->payload.some[4] = 0xCC;   /* UID byte 1 */
-        resp->payload.some[5] = 0x55;   /* UID byte 2 */
-        resp->payload.some[6] = 0x25;   /* UID byte 3 */
+        resp->payload.some[0] = 0x01;       /* Chunk size? */
+        resp->payload.some[1] = 0x10;       /* Unknown */
+        resp->payload.some[2] = 0x04;       /* Chunk size? */
+        resp->payload.some[3] = uid >> 24;  /* UID byte 0 */
+        resp->payload.some[4] = uid >> 16;  /* UID byte 1 */
+        resp->payload.some[5] = uid >>  8;  /* UID byte 2 */
+        resp->payload.some[6] = uid      ;  /* UID byte 3 */
 
         return S_OK;
     } else if (hr == S_FALSE) {
diff --git a/board/sg-nfc.h b/board/sg-nfc.h
index 507c6a8..9d91cd2 100644
--- a/board/sg-nfc.h
+++ b/board/sg-nfc.h
@@ -8,7 +8,7 @@
 #include "hook/iobuf.h"
 
 struct sg_nfc_ops {
-    HRESULT (*mifare_poll)(void *ctx);
+    HRESULT (*mifare_poll)(void *ctx, uint32_t *uid);
     HRESULT (*mifare_read_luid)(void *ctx, uint8_t *luid, size_t nbytes);
 };
 
diff --git a/cardhook/_com12.c b/cardhook/_com12.c
index a87f14b..78aefe1 100644
--- a/cardhook/_com12.c
+++ b/cardhook/_com12.c
@@ -13,13 +13,14 @@
 
 #include "hooklib/uart.h"
 
+#include "util/crc.h"
 #include "util/dprintf.h"
 #include "util/dump.h"
 
 static HRESULT com12_handle_irp(struct irp *irp);
 static HRESULT com12_handle_irp_locked(struct irp *irp);
 
-static HRESULT com12_mifare_poll(void *ctx);
+static HRESULT com12_mifare_poll(void *ctx, uint32_t *uid);
 static HRESULT com12_mifare_read_luid(void *ctx, uint8_t *luid, size_t nbytes);
 static HRESULT com12_led_set_color(void *ctx, uint8_t r, uint8_t g, uint8_t b);
 
@@ -117,7 +118,7 @@ static HRESULT com12_handle_irp_locked(struct irp *irp)
     return hr;
 }
 
-static HRESULT com12_mifare_poll(void *ctx)
+static HRESULT com12_mifare_poll(void *ctx, uint32_t *uid)
 {
     HRESULT hr;
     FILE *f;
@@ -152,6 +153,13 @@ static HRESULT com12_mifare_poll(void *ctx)
         com12_aime_luid[i] = byte;
     }
 
+    /* NOTE: We are just arbitrarily using the CRC32 of the LUID here, real
+       cards do not work like this! However, neither the application code nor
+       the network protocol care what the UID is, it just has to be a stable
+       unique identifier for over-the-air NFC communications. */
+
+    *uid = crc32(com12_aime_luid, sizeof(com12_aime_luid), 0);
+
     hr = S_OK;
 
 end: