From a7f39a1b79f3800960de69db948ebb0b83ed4134 Mon Sep 17 00:00:00 2001
From: merlokk <807634+merlokk@users.noreply.github.com>
Date: Fri, 9 Jul 2021 13:09:59 +0300
Subject: [PATCH] move crc search function to desfirecrypto

---
 client/src/mifare/desfirecrypto.c     | 44 +++++++++++++++++++++++++++
 client/src/mifare/desfirecrypto.h     |  1 +
 client/src/mifare/desfiresecurechan.c | 39 +++---------------------
 3 files changed, 50 insertions(+), 34 deletions(-)

diff --git a/client/src/mifare/desfirecrypto.c b/client/src/mifare/desfirecrypto.c
index b65512b23..246545e9e 100644
--- a/client/src/mifare/desfirecrypto.c
+++ b/client/src/mifare/desfirecrypto.c
@@ -109,6 +109,50 @@ size_t DesfireGetMACLength(DesfireContext *ctx) {
     return mac_length;
 }
 
+size_t DesfireSearchCRCPos(uint8_t *data, size_t datalen, uint8_t respcode, uint8_t crclen) {
+    size_t crcpos = datalen - 1;
+    while (crcpos > 0)
+        if (data[crcpos] == 0)
+            crcpos--;
+        else
+            break;
+    crcpos++; // crc may be 0x00000000 or 0x0000
+    PrintAndLogEx(INFO, "crcpos: %d", crcpos);
+    if (crcpos < crclen) {
+        PrintAndLogEx(WARNING, "No space for crc. pos: %d", crcpos);
+        return 0;
+    }
+
+    uint8_t crcdata[1024] = {0};
+    bool crcok = false;
+    for (int i = 0; i < crclen + 1; i++) {
+    PrintAndLogEx(INFO, "--crcpos: %d", crcpos - i);
+        if (crcpos - i == 0)
+            break;
+        if (crcpos - i + crclen > datalen)
+            continue;
+    PrintAndLogEx(INFO, "--crcposcheck: %d", crcpos - i);
+        
+        memcpy(crcdata, data, crcpos - i);
+        crcdata[crcpos - i] = respcode;
+        bool res;
+        if (crclen == 4)
+            res = desfire_crc32_check(crcdata, crcpos - i + 1, &data[crcpos - i]);
+        else
+            res = iso14443a_crc_check(crcdata, crcpos - i + 1, &data[crcpos - i]);
+        if (res) {
+    PrintAndLogEx(INFO, "--crc OK pos: %d", crcpos - i);
+            crcpos -= i;
+            crcok = true;
+            break;
+        }
+    }
+    if (!crcok)
+        crcpos = 0;
+    
+    return crcpos;
+}
+
 static void DesfireCryptoEncDecSingleBlock(uint8_t *key, DesfireCryptoAlgorythm keyType, uint8_t *data, uint8_t *dstdata, uint8_t *ivect, bool dir_to_send, bool encode) {
     size_t block_size = desfire_get_key_block_length(keyType);
     uint8_t sdata[MAX_CRYPTO_BLOCK_SIZE] = {0};
diff --git a/client/src/mifare/desfirecrypto.h b/client/src/mifare/desfirecrypto.h
index ff12335e6..824225b39 100644
--- a/client/src/mifare/desfirecrypto.h
+++ b/client/src/mifare/desfirecrypto.h
@@ -95,6 +95,7 @@ void DesfireSetKdf(DesfireContext *ctx, uint8_t kdfAlgo, uint8_t *kdfInput, uint
 bool DesfireIsAuthenticated(DesfireContext *dctx);
 size_t DesfireGetMACLength(DesfireContext *ctx);
 
+size_t DesfireSearchCRCPos(uint8_t *data, size_t datalen, uint8_t respcode, uint8_t crclen);
 
 void DesfireCryptoEncDec(DesfireContext *ctx, bool use_session_key, uint8_t *srcdata, size_t srcdatalen, uint8_t *dstdata, bool encode);
 void DesfireCryptoEncDecEx(DesfireContext *ctx, bool use_session_key, uint8_t *srcdata, size_t srcdatalen, uint8_t *dstdata, bool encode, uint8_t *iv);
diff --git a/client/src/mifare/desfiresecurechan.c b/client/src/mifare/desfiresecurechan.c
index 5f9fec5a9..b62a0a056 100644
--- a/client/src/mifare/desfiresecurechan.c
+++ b/client/src/mifare/desfiresecurechan.c
@@ -161,41 +161,12 @@ static void DesfireSecureChannelDecodeEV1(DesfireContext *ctx, uint8_t *srcdata,
             DesfireCryptoEncDec(ctx, true, srcdata, srcdatalen, dstdata, false);
             PrintAndLogEx(INFO, "decoded[%d]: %s", srcdatalen, sprint_hex(dstdata, srcdatalen));
             
-            size_t crcpos = srcdatalen - 1;
-            while (crcpos > 0)
-                if (dstdata[crcpos] == 0)
-                    crcpos--;
-                else
-                    break;
-            crcpos++; // crc may be 0x00000000
-            *dstdatalen = crcpos;
-            PrintAndLogEx(INFO, "crcpos: %d", crcpos);
-            if (crcpos < 4) {
-                PrintAndLogEx(WARNING, "No space for crc. pos: %d", crcpos);
-                return;
-            }
-            
-            uint8_t crcdata[1024] = {0};
-            bool crcok = false;
-            for (int i = 0; i < 5; i++) {
-                if (crcpos == 0)
-                    break;
-                if (crcpos - i + 4 > srcdatalen)
-                    continue;
-                
-                memcpy(crcdata, dstdata, crcpos - i);
-                crcdata[crcpos - i] = respcode;
-                if (desfire_crc32_check(crcdata, crcpos - i + 1, &dstdata[crcpos - i])) {
-                    crcpos -= i;
-                    crcok = true;
-                    break;
-                }
-           }
-            
-            if (crcok) {
-                *dstdatalen = crcpos;
+            size_t puredatalen = DesfireSearchCRCPos(dstdata, srcdatalen, respcode, 4);
+            if (puredatalen != 0) {
+                *dstdatalen = puredatalen;
             } else {
-                PrintAndLogEx(WARNING, "CRC32 error. pos: %d", crcpos);
+                PrintAndLogEx(WARNING, "CRC32 error.");
+                *dstdatalen = srcdatalen;
             }
             
     } else {