From fe6bf3c58c939bfa076f06034e7963ec27080ef0 Mon Sep 17 00:00:00 2001
From: Oleg Moiseenko <olegmsn@gmail.com>
Date: Wed, 1 Nov 2017 18:48:59 +0200
Subject: [PATCH] improve `hf 14a info` (#457)

* added validate_prng_nonce from iceman1001 fork
* added DetectClassicPrng from iceman1001 fork
---
 client/cmdhf14a.c        | 15 +++++++++
 client/mifarehost.c      | 69 ++++++++++++++++++++++++++++++++++++++++
 client/mifarehost.h      |  1 +
 common/crapto1/crapto1.c |  1 -
 4 files changed, 85 insertions(+), 1 deletion(-)

diff --git a/client/cmdhf14a.c b/client/cmdhf14a.c
index 3f103f5f..928864a1 100644
--- a/client/cmdhf14a.c
+++ b/client/cmdhf14a.c
@@ -244,8 +244,10 @@ int CmdHF14AInfo(const char *Cmd)
 	PrintAndLog("ATQA : %02x %02x", card.atqa[1], card.atqa[0]);
 	PrintAndLog(" SAK : %02x [%d]", card.sak, resp.arg[0]);
 
+	bool isMifareClassic = true;
 	switch (card.sak) {
 		case 0x00: 
+			isMifareClassic = false;
 
 			//***************************************test****************
 			// disconnect
@@ -480,6 +482,19 @@ int CmdHF14AInfo(const char *Cmd)
 	// try to see if card responses to "chinese magic backdoor" commands.
 	mfCIdentify();
 	
+	if (isMifareClassic) {		
+		switch(DetectClassicPrng()) {
+		case 0:
+			PrintAndLog("Prng detection: HARDEND (hardnested)");		
+			break;
+		case 1:
+			PrintAndLog("Prng detection: WEAK");
+			break;
+		default:
+			PrintAndLog("Prng detection error.");		
+		}
+	}
+	
 	return select_status;
 }
 
diff --git a/client/mifarehost.c b/client/mifarehost.c
index fe1a8edb..67277b59 100644
--- a/client/mifarehost.c
+++ b/client/mifarehost.c
@@ -903,3 +903,72 @@ int tryDecryptWord(uint32_t nt, uint32_t ar_enc, uint32_t at_enc, uint8_t *data,
 	return 0;
 }
 
+/** validate_prng_nonce
+ * Determine if nonce is deterministic. ie: Suspectable to Darkside attack.
+ * returns
+ *   true = weak prng
+ *   false = hardend prng
+ */
+bool validate_prng_nonce(uint32_t nonce) {
+	uint16_t *dist = 0;
+	uint16_t x, i;
+
+	dist = malloc(2 << 16);
+	if(!dist)
+		return -1;
+
+	// init prng table:
+	for (x = i = 1; i; ++i) {
+		dist[(x & 0xff) << 8 | x >> 8] = i;
+		x = x >> 1 | (x ^ x >> 2 ^ x >> 3 ^ x >> 5) << 15;
+	}
+	
+	uint32_t res = (65535 - dist[nonce >> 16] + dist[nonce & 0xffff]) % 65535;
+	
+	free(dist);	
+	return (res == 16);
+}
+
+/* Detect Tag Prng, 
+* function performs a partial AUTH,  where it tries to authenticate against block0, key A, but only collects tag nonce.
+* the tag nonce is check to see if it has a predictable PRNG.
+* @returns 
+*	TRUE if tag uses WEAK prng (ie Now the NACK bug also needs to be present for Darkside attack)
+*   FALSE is tag uses HARDEND prng (ie hardnested attack possible, with known key)
+*/
+int DetectClassicPrng(void){
+
+	UsbCommand resp, respA;	
+	uint8_t cmd[] = {0x60, 0x00}; // MIFARE_AUTH_KEYA
+	uint32_t flags = ISO14A_CONNECT | ISO14A_RAW | ISO14A_APPEND_CRC | ISO14A_NO_RATS;
+	
+	UsbCommand c = {CMD_READER_ISO_14443a, {flags, sizeof(cmd), 0}};
+	memcpy(c.d.asBytes, cmd, sizeof(cmd));
+
+	clearCommandBuffer();
+	SendCommand(&c);
+	if (!WaitForResponseTimeout(CMD_ACK, &resp, 2000)) {
+        PrintAndLog("PRNG UID: Reply timeout.");
+		return -1;
+	}
+	
+	// if select tag failed.
+	if (resp.arg[0] == 0) {
+		PrintAndLog("PRNG error: selecting tag failed, can't detect prng.");
+		return -1;
+	}
+	
+	if (!WaitForResponseTimeout(CMD_ACK, &respA, 5000)) {
+        PrintAndLog("PRNG data: Reply timeout.");
+		return -1;
+	}
+
+	// check respA
+	if (respA.arg[0] != 4) {
+		PrintAndLog("PRNG data error: Wrong length: %d", respA.arg[0]);
+		return -1;
+	}
+
+	uint32_t nonce = bytes_to_num(respA.d.asBytes, respA.arg[0]);
+	return validate_prng_nonce(nonce);
+}
diff --git a/client/mifarehost.h b/client/mifarehost.h
index 118d55cc..031dac1b 100644
--- a/client/mifarehost.h
+++ b/client/mifarehost.h
@@ -60,5 +60,6 @@ extern int saveTraceCard(void);
 extern int tryDecryptWord(uint32_t nt, uint32_t ar_enc, uint32_t at_enc, uint8_t *data, int len);
 
 extern int mfCIdentify();
+extern int DetectClassicPrng(void);
 
 #endif
diff --git a/common/crapto1/crapto1.c b/common/crapto1/crapto1.c
index 9398a1f3..1edfca1b 100644
--- a/common/crapto1/crapto1.c
+++ b/common/crapto1/crapto1.c
@@ -426,7 +426,6 @@ int nonce_distance(uint32_t from, uint32_t to)
 	return (65535 + dist[to >> 16] - dist[from >> 16]) % 65535;
 }
 
-
 static uint32_t fastfwd[2][8] = {
 	{ 0, 0x4BC53, 0xECB1, 0x450E2, 0x25E29, 0x6E27A, 0x2B298, 0x60ECB},
 	{ 0, 0x1D962, 0x4BC53, 0x56531, 0xECB1, 0x135D3, 0x450E2, 0x58980}};
-- 
2.39.5