Adds random nonce (r) option to hf mf sim.

This makes the PM3 generate pseudo-random nonces rather than sequential
nonces, to make it act a bit more like a "real" MFC card.  A reader would
otherwise be able to detect the PM3 probing based on the predictable nonces
and throw different authentication challenges (or refuse to authenticate at
all).

The code includes an implementation of a rand-like function (prand), similar
to the one from libc, which is seeded automatically based on the time it
takes between the PM3 starting up and the first call to the RNG.

This isn't cryptographically random, but should be "good enough" to be able
to evade basic detection.

armsrc/iso14443a.c

@@ -2329,6 +2329,7 @@ typedef struct {
   * FLAG_7B_UID_IN_DATA - means that there is a 7-byte UID in the data-section, we're expected to use that
   * FLAG_10B_UID_IN_DATA	- use 10-byte UID in the data-section not finished
   *	FLAG_NR_AR_ATTACK  - means we should collect NR_AR responses for bruteforcing later
+  * FLAG_RANDOM_NONCE - means we should generate some pseudo-random nonce data
   *@param exitAfterNReads, exit simulation after n blocks have been read, 0 is infinite ...
   * (unless reader attack mode enabled then it runs util it gets enough nonces to recover all keys attmpted)
   */
@@ -2387,7 +2388,12 @@ void Mifare1ksim(uint8_t flags, uint8_t exitAfterNReads, uint8_t arg2, uint8_t *
 	uint8_t	mM = 0; //moebius_modifier for collection storage
 
 	// Authenticate response - nonce
-	uint32_t nonce = bytes_to_num(rAUTH_NT, 4);
+	uint32_t nonce;
+	if (flags & FLAG_RANDOM_NONCE) {
+		nonce = prand();
+	} else {
+		nonce = bytes_to_num(rAUTH_NT, 4);
+	}
 	
 	//-- Determine the UID
 	// Can be set from emulator memory, incoming data
@@ -2535,6 +2541,11 @@ void Mifare1ksim(uint8_t flags, uint8_t exitAfterNReads, uint8_t arg2, uint8_t *
 			LED_C_OFF();
 			crypto1_destroy(pcs);
 			cardAUTHKEY = 0xff;
+			if (flags & FLAG_RANDOM_NONCE) {
+				nonce = prand();
+			} else {
+				nonce++;
+			}
 			continue;
 		}
 		
@@ -2656,7 +2667,11 @@ void Mifare1ksim(uint8_t flags, uint8_t exitAfterNReads, uint8_t arg2, uint8_t *
 												// switch to moebius collection
 												gettingMoebius = true;
 												mM = ATTACK_KEY_COUNT;
+												if (flags & FLAG_RANDOM_NONCE) {
+													nonce = prand();
+												} else {
 													nonce = nonce*7;
+												}
 												break;
 											}
 										} else {

armsrc/util.c

@@ -431,3 +431,19 @@ uint32_t RAMFUNC GetCountSspClk(){
 	}
 }
 
+static uint64_t next_random = 1;
+
+/* Generates a (non-cryptographically secure) 32-bit random number.
+ *
+ * We don't have an implementation of the "rand" function or a clock to seed it
+ * with, so we just call GetTickCount the first time to seed ourselves.
+ */
+uint32_t prand() {
+	if (next_random == 1) {
+		next_random = GetTickCount();
+	}
+
+	next_random = next_random * 6364136223846793005 + 1;
+	return (uint32_t)(next_random >> 32) % 0xffffffff;
+}
+

armsrc/util.h

@@ -54,4 +54,6 @@ uint32_t RAMFUNC GetDeltaCountUS();
 void StartCountSspClk();
 uint32_t RAMFUNC GetCountSspClk();
 
+uint32_t prand();
+
 #endif

client/cmdhfmf.c

@@ -1100,6 +1100,7 @@ int usage_hf14_mf1ksim(void) {
 	PrintAndLog("      x    (Optional) Crack, performs the 'reader attack', nr/ar attack against a legitimate reader, fishes out the key(s)");
 	PrintAndLog("      e    (Optional) set keys found from 'reader attack' to emulator memory (implies x and i)");
 	PrintAndLog("      f    (Optional) get UIDs to use for 'reader attack' from file 'f <filename.txt>' (implies x and i)");
+	PrintAndLog("      r    (Optional) Generate random nonces instead of sequential nonces.");
 	PrintAndLog("samples:");
 	PrintAndLog("           hf mf sim u 0a0a0a0a");
 	PrintAndLog("           hf mf sim u 11223344556677");
@@ -1164,6 +1165,11 @@ int CmdHF14AMf1kSim(const char *Cmd) {
 			exitAfterNReads = param_get8(Cmd, pnr+1);
 			cmdp += 2;
 			break;
+		case 'r':
+		case 'R':
+			flags |= FLAG_RANDOM_NONCE;
+			cmdp++;
+			break;
 		case 'u':
 		case 'U':
 			param_gethex_ex(Cmd, cmdp+1, uid, &uidlen);

include/usb_cmd.h

@@ -217,6 +217,7 @@ typedef struct{
 #define FLAG_7B_UID_IN_DATA   0x04
 #define FLAG_10B_UID_IN_DATA  0x08
 #define FLAG_NR_AR_ATTACK     0x10
+#define FLAG_RANDOM_NONCE     0x20
 
 
 //Iclass reader flags