X-Git-Url: http://cvs.zerfleddert.de/cgi-bin/gitweb.cgi/proxmark3-svn/blobdiff_plain/c2d2a5a6b580670724e68a86f46adfa2946a45b9..42c235e7efdac01da7e7ef3e4e442557fe50198d:/armsrc/crapto1.c

diff --git a/armsrc/crapto1.c b/armsrc/crapto1.c
index 87213757..e2058651 100644
--- a/armsrc/crapto1.c
+++ b/armsrc/crapto1.c
@@ -15,7 +15,7 @@
     Foundation, Inc., 51 Franklin Street, Fifth Floor,
     Boston, MA  02110-1301, US$
 
-    Copyright (C) 2008-2008 bla <blapost@gmail.com>
+    Copyright (C) 2008-2014 bla <blapost@gmail.com>
 */
 #include "crapto1.h"
 #include <stdlib.h>
@@ -24,17 +24,16 @@
 static uint8_t filterlut[1 << 20];
 static void __attribute__((constructor)) fill_lut()
 {
-        uint32_t i;
-        for(i = 0; i < 1 << 20; ++i)
-                filterlut[i] = filter(i);
+	uint32_t i;
+	for(i = 0; i < 1 << 20; ++i)
+			filterlut[i] = filter(i);
 }
 #define filter(x) (filterlut[(x) & 0xfffff])
 #endif
 
 static void quicksort(uint32_t* const start, uint32_t* const stop)
 {
-	uint32_t *it = start + 1, *rit = stop;
-	uint32_t tmp;
+	uint32_t *it = start + 1, *rit = stop, t;
 
 	if(it > rit)
 		return;
@@ -44,19 +43,13 @@ static void quicksort(uint32_t* const start, uint32_t* const stop)
 			++it;
 		else if(*rit > *start)
 			--rit;
-		else {
-			tmp = *it;
-			*it = *rit;
-			*rit = tmp;
-		}
+		else
+			t = *it,  *it = *rit, *rit = t;
 
 	if(*rit >= *start)
 		--rit;
-	if(rit != start) {
-		tmp = *rit;
-		*rit = *start;
-		*start = tmp;
-	}
+	if(rit != start)
+		t = *rit,  *rit = *start, *start = t;
 
 	quicksort(start, rit - 1);
 	quicksort(rit + 1, stop);
@@ -92,7 +85,8 @@ update_contribution(uint32_t *item, const uint32_t mask1, const uint32_t mask2)
 /** extend_table
  * using a bit of the keystream extend the table of possible lfsr states
  */
-static inline void extend_table(uint32_t *tbl, uint32_t **end, int bit, int m1, int m2, uint32_t in)
+static inline void
+extend_table(uint32_t *tbl, uint32_t **end, int bit, int m1, int m2, uint32_t in)
 {
 	in <<= 24;
 	for(*tbl <<= 1; tbl <= *end; *++tbl <<= 1)
@@ -190,6 +184,7 @@ struct Crypto1State* lfsr_recovery32(uint32_t ks2, uint32_t in)
 	uint32_t *even_head = 0, *even_tail = 0, eks = 0;
 	int i;
 
+	// split the keystream into an odd and even part
 	for(i = 31; i >= 0; i -= 2)
 		oks = oks << 1 | BEBIT(ks2, i);
 	for(i = 30; i >= 0; i -= 2)
@@ -206,6 +201,7 @@ struct Crypto1State* lfsr_recovery32(uint32_t ks2, uint32_t in)
 
 	statelist->odd = statelist->even = 0;
 
+	// initialize statelists: add all possible states which would result into the rightmost 2 bits of the keystream
 	for(i = 1 << 20; i >= 0; --i) {
 		if(filter(i) == (oks & 1))
 			*++odd_tail = i;
@@ -213,11 +209,15 @@ struct Crypto1State* lfsr_recovery32(uint32_t ks2, uint32_t in)
 			*++even_tail = i;
 	}
 
+	// extend the statelists. Look at the next 8 Bits of the keystream (4 Bit each odd and even):
 	for(i = 0; i < 4; i++) {
 		extend_table_simple(odd_head,  &odd_tail, (oks >>= 1) & 1);
 		extend_table_simple(even_head, &even_tail, (eks >>= 1) & 1);
 	}
 
+	// the statelists now contain all states which could have generated the last 10 Bits of the keystream.
+	// 22 bits to go to recover 32 bits in total. From now on, we need to take the "in"
+	// parameter into account.
 	in = (in >> 16 & 0xff) | (in << 16) | (in & 0xff00);
 	recover(odd_head, odd_tail, oks,
 		even_head, even_tail, eks, 11, statelist, in << 1);
@@ -325,12 +325,10 @@ uint8_t lfsr_rollback_bit(struct Crypto1State *s, uint32_t in, int fb)
 {
 	int out;
 	uint8_t ret;
-	uint32_t tmp;
+	uint32_t t;
 
 	s->odd &= 0xffffff;
-	tmp = s->odd;
-	s->odd = s->even;
-	s->even = tmp;
+	t = s->odd, s->odd = s->even, s->even = t;
 
 	out = s->even & 1;
 	out ^= LF_POLY_EVEN & (s->even >>= 1);
@@ -346,7 +344,8 @@ uint8_t lfsr_rollback_bit(struct Crypto1State *s, uint32_t in, int fb)
  */
 uint8_t lfsr_rollback_byte(struct Crypto1State *s, uint32_t in, int fb)
 {
-/*	int i, ret = 0;
+	/*
+	int i, ret = 0;
 	for (i = 7; i >= 0; --i)
 		ret |= lfsr_rollback_bit(s, BIT(in, i), fb) << i;
 */
@@ -367,7 +366,8 @@ uint8_t lfsr_rollback_byte(struct Crypto1State *s, uint32_t in, int fb)
  */
 uint32_t lfsr_rollback_word(struct Crypto1State *s, uint32_t in, int fb)
 {
-/*	int i;
+	/*
+	int i;
 	uint32_t ret = 0;
 	for (i = 31; i >= 0; --i)
 		ret |= lfsr_rollback_bit(s, BEBIT(in, i), fb) << (i ^ 24);
@@ -419,10 +419,11 @@ static uint16_t *dist = 0;
 int nonce_distance(uint32_t from, uint32_t to)
 {
 	uint16_t x, i;
-	if(!dist) {
+	// generate distance lookup table
+	if (!dist) {
 		dist = malloc(2 << 16);
-		if(!dist)
-			return -1;
+		if (!dist) return -1;
+		
 		for (x = i = 1; i; ++i) {
 			dist[(x & 0xff) << 8 | x >> 8] = i;
 			x = x >> 1 | (x ^ x >> 2 ^ x >> 3 ^ x >> 5) << 15;
@@ -435,6 +436,8 @@ int nonce_distance(uint32_t from, uint32_t to)
 static uint32_t fastfwd[2][8] = {
 	{ 0, 0x4BC53, 0xECB1, 0x450E2, 0x25E29, 0x6E27A, 0x2B298, 0x60ECB},
 	{ 0, 0x1D962, 0x4BC53, 0x56531, 0xECB1, 0x135D3, 0x450E2, 0x58980}};
+
+
 /** lfsr_prefix_ks
  *
  * Is an exported helper function from the common prefix attack
@@ -444,13 +447,13 @@ static uint32_t fastfwd[2][8] = {
  * encrypt the NACK which is observed when varying only the 3 last bits of Nr
  * only correct iff [NR_3] ^ NR_3 does not depend on Nr_3
  */
-uint32_t *lfsr_prefix_ks(uint8_t ks[8], int isodd)
+uint32_t* lfsr_prefix_ks(uint8_t ks[8], int isodd)
 {
-	uint32_t c, entry, *candidates = malloc(4 << 10);
-	int i, size = 0, good;
-
-	if(!candidates)
-		return 0;
+	uint32_t *candidates = malloc(4 << 10);
+	if(!candidates) return 0;
+	
+	uint32_t c,  entry;
+	int size = 0, i, good;
 
 	for(i = 0; i < 1 << 21; ++i) {
 		for(c = 0, good = 1; good && c < 8; ++c) {
@@ -470,9 +473,7 @@ uint32_t *lfsr_prefix_ks(uint8_t ks[8], int isodd)
 /** check_pfx_parity
  * helper function which eliminates possible secret states using parity bits
  */
-static struct Crypto1State*
-check_pfx_parity(uint32_t prefix, uint32_t rresp, uint8_t parities[8][8],
-          	uint32_t odd, uint32_t even, struct Crypto1State* sl)
+static struct Crypto1State* check_pfx_parity(uint32_t prefix, uint32_t rresp, uint8_t parities[8][8], uint32_t odd, uint32_t even, struct Crypto1State* sl)
 {
 	uint32_t ks1, nr, ks2, rr, ks3, c, good = 1;
 
@@ -500,12 +501,16 @@ check_pfx_parity(uint32_t prefix, uint32_t rresp, uint8_t parities[8][8],
 	return sl + good;
 }
 
-
 /** lfsr_common_prefix
  * Implentation of the common prefix attack.
+ * Requires the 28 bit constant prefix used as reader nonce (pfx)
+ * The reader response used (rr)
+ * The keystream used to encrypt the observed NACK's (ks)
+ * The parity bits (par)
+ * It returns a zero terminated list of possible cipher states after the
+ * tag nonce was fed in
  */
-struct Crypto1State*
-lfsr_common_prefix(uint32_t pfx, uint32_t rr, uint8_t ks[8], uint8_t par[8][8])
+struct Crypto1State* lfsr_common_prefix(uint32_t pfx, uint32_t rr, uint8_t ks[8], uint8_t par[8][8])
 {
 	struct Crypto1State *statelist, *s;
 	uint32_t *odd, *even, *o, *e, top;
@@ -513,7 +518,7 @@ lfsr_common_prefix(uint32_t pfx, uint32_t rr, uint8_t ks[8], uint8_t par[8][8])
 	odd = lfsr_prefix_ks(ks, 1);
 	even = lfsr_prefix_ks(ks, 0);
 	
-	s = statelist = malloc((sizeof *statelist) << 20);
+	s = statelist = malloc((sizeof *statelist) << 21);
 	if(!s || !odd || !even) {
 		free(statelist);
 		statelist = 0;
@@ -533,4 +538,4 @@ out:
 	free(odd);
 	free(even);
 	return statelist;
-}
+}
\ No newline at end of file