CHG: syntax suger

[proxmark3-svn] / armsrc / crapto1.c

diff --git a/armsrc/crapto1.c b/armsrc/crapto1.c
index 4b4e240ed7bd44d63076e5277629357e728c0ecd..fcfd0b4da996ee9d2bc9cd98a4b828d223182e82 100644 (file)
--- a/armsrc/crapto1.c
+++ b/armsrc/crapto1.c
@@ -15,7 +15,7 @@
     Foundation, Inc., 51 Franklin Street, Fifth Floor,\r
     Boston, MA  02110-1301, US$\r
 \r
-    Copyright (C) 2008-2008 bla <blapost@gmail.com>\r
+    Copyright (C) 2008-2014 bla <blapost@gmail.com>\r
 */\r
 #include "crapto1.h"\r
 #include <stdlib.h>\r
@@ -24,9 +24,9 @@
 static uint8_t filterlut[1 << 20];\r
 static void __attribute__((constructor)) fill_lut()\r
 {\r
-        uint32_t i;\r
-        for(i = 0; i < 1 << 20; ++i)\r
-                filterlut[i] = filter(i);\r
+       uint32_t i;\r
+       for(i = 0; i < 1 << 20; ++i)\r
+                       filterlut[i] = filter(i);\r
 }\r
 #define filter(x) (filterlut[(x) & 0xfffff])\r
 #endif\r
@@ -85,7 +85,8 @@ update_contribution(uint32_t *item, const uint32_t mask1, const uint32_t mask2)
 /** extend_table\r
  * using a bit of the keystream extend the table of possible lfsr states\r
  */\r
-static inline void extend_table(uint32_t *tbl, uint32_t **end, int bit, int m1, int m2, uint32_t in)\r
+static inline void\r
+extend_table(uint32_t *tbl, uint32_t **end, int bit, int m1, int m2, uint32_t in)\r
 {\r
        in <<= 24;\r
        for(*tbl <<= 1; tbl <= *end; *++tbl <<= 1)\r
@@ -183,6 +184,7 @@ struct Crypto1State* lfsr_recovery32(uint32_t ks2, uint32_t in)
        uint32_t *even_head = 0, *even_tail = 0, eks = 0;\r
        int i;\r
 \r
+       // split the keystream into an odd and even part\r
        for(i = 31; i >= 0; i -= 2)\r
                oks = oks << 1 | BEBIT(ks2, i);\r
        for(i = 30; i >= 0; i -= 2)\r
@@ -199,6 +201,7 @@ struct Crypto1State* lfsr_recovery32(uint32_t ks2, uint32_t in)
 \r
        statelist->odd = statelist->even = 0;\r
 \r
+       // initialize statelists: add all possible states which would result into the rightmost 2 bits of the keystream\r
        for(i = 1 << 20; i >= 0; --i) {\r
                if(filter(i) == (oks & 1))\r
                        *++odd_tail = i;\r
@@ -206,11 +209,15 @@ struct Crypto1State* lfsr_recovery32(uint32_t ks2, uint32_t in)
                        *++even_tail = i;\r
        }\r
 \r
+       // extend the statelists. Look at the next 8 Bits of the keystream (4 Bit each odd and even):\r
        for(i = 0; i < 4; i++) {\r
                extend_table_simple(odd_head,  &odd_tail, (oks >>= 1) & 1);\r
                extend_table_simple(even_head, &even_tail, (eks >>= 1) & 1);\r
        }\r
 \r
+       // the statelists now contain all states which could have generated the last 10 Bits of the keystream.\r
+       // 22 bits to go to recover 32 bits in total. From now on, we need to take the "in"\r
+       // parameter into account.\r
        in = (in >> 16 & 0xff) | (in << 16) | (in & 0xff00);\r
        recover(odd_head, odd_tail, oks,\r
                even_head, even_tail, eks, 11, statelist, in << 1);\r
@@ -439,16 +446,14 @@ static uint32_t fastfwd[2][8] = {
  * encrypt the NACK which is observed when varying only the 3 last bits of Nr\r
  * only correct iff [NR_3] ^ NR_3 does not depend on Nr_3\r
  */\r
- // TO VERIFY \r
 uint32_t *lfsr_prefix_ks(uint8_t ks[8], int isodd)\r
 {\r
        uint32_t *candidates = malloc(4 << 10);\r
+       if(!candidates) return 0;\r
+       \r
        uint32_t c,  entry;\r
        int size = 0, i, good;\r
 \r
-       if(!candidates)\r
-               return 0;\r
-\r
        for(i = 0; i < 1 << 21; ++i) {\r
                for(c = 0, good = 1; good && c < 8; ++c) {\r
                        entry = i ^ fastfwd[isodd][c];\r
@@ -467,9 +472,7 @@ uint32_t *lfsr_prefix_ks(uint8_t ks[8], int isodd)
 /** check_pfx_parity\r
  * helper function which eliminates possible secret states using parity bits\r
  */\r
-static struct Crypto1State*\r
-check_pfx_parity(uint32_t prefix, uint32_t rresp, uint8_t parities[8][8],\r
-               uint32_t odd, uint32_t even, struct Crypto1State* sl)\r
+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)\r
 {\r
        uint32_t ks1, nr, ks2, rr, ks3, c, good = 1;\r
 \r
@@ -497,7 +500,6 @@ check_pfx_parity(uint32_t prefix, uint32_t rresp, uint8_t parities[8][8],
        return sl + good;\r
 }\r
 \r
-\r
 /** lfsr_common_prefix\r
  * Implentation of the common prefix attack.\r
  * Requires the 28 bit constant prefix used as reader nonce (pfx)\r
@@ -507,8 +509,7 @@ check_pfx_parity(uint32_t prefix, uint32_t rresp, uint8_t parities[8][8],
  * It returns a zero terminated list of possible cipher states after the\r
  * tag nonce was fed in\r
  */\r
-struct Crypto1State*\r
-lfsr_common_prefix(uint32_t pfx, uint32_t rr, uint8_t ks[8], uint8_t par[8][8])\r
+struct Crypto1State* lfsr_common_prefix(uint32_t pfx, uint32_t rr, uint8_t ks[8], uint8_t par[8][8])\r
 {\r
        struct Crypto1State *statelist, *s;\r
        uint32_t *odd, *even, *o, *e, top;\r
@@ -516,12 +517,11 @@ lfsr_common_prefix(uint32_t pfx, uint32_t rr, uint8_t ks[8], uint8_t par[8][8])
        odd = lfsr_prefix_ks(ks, 1);\r
        even = lfsr_prefix_ks(ks, 0);\r
        \r
-       s = statelist = malloc((sizeof *statelist) << 20);\r
+       s = statelist = malloc((sizeof *statelist) << 21);\r
        if(!s || !odd || !even) {\r
                free(statelist);\r
-               free(odd);\r
-               free(even);\r
-               return 0;\r
+               statelist = 0;\r
+               goto out;\r
        }\r
 \r
        for(o = odd; *o + 1; ++o)\r
@@ -533,9 +533,8 @@ lfsr_common_prefix(uint32_t pfx, uint32_t rr, uint8_t ks[8], uint8_t par[8][8])
                        }\r
 \r
        s->odd = s->even = 0;\r
-\r
+out:\r
        free(odd);\r
        free(even);\r
-\r
        return statelist;\r
-}\r
+}
\ No newline at end of file