ADD; added some more descriptions of what the legic prng imp does.

[proxmark3-svn] / common / lfdemod.c

diff --git a/common/lfdemod.c b/common/lfdemod.c
index 8b31f1a4c10a751cd447d2667aa89f7a57a7e22e..ff80b8b341e538a17780756541268f497dce106e 100644 (file)
--- a/common/lfdemod.c
+++ b/common/lfdemod.c
@@ -84,7 +84,9 @@ size_t removeParity(uint8_t *BitStream, size_t startIdx, uint8_t pLen, uint8_t p
                        case 3: if (BitStream[j]==1) return 0; break; //should be 0 spacer bit
                        case 2: if (BitStream[j]==0) return 0; break; //should be 1 spacer bit
                        default: //test parity
-                               if (parityTest(parityWd, pLen, pType) == 0) return 0; break;
+                               if (parityTest(parityWd, pLen, pType) == 0) 
+                                       return 0; 
+                               break;
                }
                bitCnt+=(pLen-1);
                parityWd = 0;
@@ -148,8 +150,11 @@ uint32_t bytebits_to_byteLSBF(uint8_t *src, size_t numbits)
 //search for given preamble in given BitStream and return success=1 or fail=0 and startIndex and length
 uint8_t preambleSearch(uint8_t *BitStream, uint8_t *preamble, size_t pLen, size_t *size, size_t *startIdx)
 {
-       uint8_t foundCnt=0;
-       for (int idx=0; idx < *size - pLen; idx++){
+       // Sanity check.  If preamble length is bigger than bitstream length.
+       if ( *size <= pLen ) return 0;
+       
+       uint8_t foundCnt = 0;
+       for (int idx = 0; idx < *size - pLen; idx++){
                if (memcmp(BitStream+idx, preamble, pLen) == 0){
                        //first index found
                        foundCnt++;
@@ -723,6 +728,39 @@ int FDXBdemodBI(uint8_t *dest, size_t *size)
        return (int)startIdx;
 }
 
+// ASK/Diphase fc/64 (inverted Biphase)
+// Note: this i s not a demod, this is only a detection
+// the parameter *dest needs to be demoded before call
+int JablotronDemod(uint8_t *dest, size_t *size){
+       //make sure buffer has enough data
+       if (*size < 64) return -1;
+
+       size_t startIdx = 0;
+       // 0xFFFF preamble, 64bits
+       uint8_t preamble[] = {
+                       1,1,1,1,
+                   1,1,1,1,
+                               1,1,1,1,
+                               1,1,1,1,
+                               0
+               };
+
+       uint8_t errChk = preambleSearch(dest, preamble, sizeof(preamble), size, &startIdx);
+       if (errChk == 0) return -4; //preamble not found
+       if (*size != 64) return -3;
+       
+       uint8_t checkchksum = 0;
+       for (int i=16; i < 56; i += 8) {
+               checkchksum += bytebits_to_byte(dest+startIdx+i,8);
+       }
+       checkchksum ^= 0x3A;
+
+       uint8_t crc = bytebits_to_byte(dest+startIdx+56, 8);
+       
+       if ( checkchksum != crc ) return -5;    
+       return (int)startIdx;
+}
+
 // by marshmellow
 // FSK Demod then try to locate an AWID ID
 int AWIDdemodFSK(uint8_t *dest, size_t *size)