cmdwiegand: add option to brute-force hex input length

Author: jkramarz

client/src/cmdwiegand.c

@@ -165,6 +165,7 @@ int CmdWiegandDecode(const char *Cmd) {
         arg_str0("r", "raw", "<hex>", "raw hex to be decoded"),
         arg_str0("b", "bin", "<bin>", "binary string to be decoded"),
         arg_str0("n", "new", "<hex>", "new padded pacs as raw hex to be decoded"),
+        arg_lit0("f", "force", "skip preabmle checking, brute force all possible lengths for raw hex input"),
         arg_param_end
     };
     CLIExecWithReturn(ctx, Cmd, argtable, false);
@@ -180,6 +181,8 @@ int CmdWiegandDecode(const char *Cmd) {
     uint8_t phex[8] = {0};
     res = CLIParamHexToBuf(arg_get_str(ctx, 3), phex, sizeof(phex), &plen);
 
+    bool no_preamble = arg_get_lit(ctx, 4);
+
     CLIParserFree(ctx);
 
     if (res) {
@@ -195,6 +198,12 @@ int CmdWiegandDecode(const char *Cmd) {
             PrintAndLogEx(ERR, "Hex string contains none hex chars");
             return PM3_EINVARG;
         }
+
+        if(no_preamble){
+            // pass hex input length as is and brute force all possible lengths
+            blen = -hlen;
+        }
+
     } else if (blen) {
         int n = binarray_to_u96(&top, &mid, &bot, binarr, blen);
         if (n != blen) {

client/src/wiegand_formats.c

@@ -1716,8 +1716,28 @@ bool decode_wiegand(uint32_t top, uint32_t mid, uint32_t bot, int n) {
     if (n > 0) {
         wiegand_message_t packed = initialize_message_object(top, mid, bot, n);
         res = HIDTryUnpack(&packed);
+    } else if(n < 0) {
+        PrintAndLogEx(INFO, "Brute forcing all possible lengths...");
+        int scan_end = (-n)*4;
+        int scan_start = scan_end-3;
+
+        wiegand_message_t packed = initialize_message_object(top, mid, bot, scan_end);
+ 
+        // find the first bit set in the first nibble
+        for(int i = 0; i < 4; i++) {
+            if (get_bit_by_position(&packed, i) == 1) {
+                scan_start = scan_end-i;
+                break;
+            }
+        }
+
+        PrintAndLogEx(INFO, "Scanning from bit %d to %d...", scan_start, scan_end);
+        for(int i = scan_start; i <= scan_end; i++) {
+            packed.Length = i;
+            res |= HIDTryUnpack(&packed);
+        }
     } else {
-        wiegand_message_t packed = initialize_message_object(top, mid, bot, n); // 26-37 bits
+        wiegand_message_t packed = initialize_message_object(top, mid, bot, 0); // 26-37 bits
         res = HIDTryUnpack(&packed);
 
         PrintAndLogEx(INFO, "Trying with a preamble bit...");