]> cvs.zerfleddert.de Git - proxmark3-svn/blobdiff - client/cmdhfmfhard.c
ADD: @marshmellow42 's changes to "hf mfu dump"
[proxmark3-svn] / client / cmdhfmfhard.c
index 6cd5a5b9844a8c3fc94c55ee214af4c6811b221f..9a938d6421aa428ced33e7d6b27e01e32b161758 100644 (file)
 #include "ui.h"
 #include "util.h"
 #include "nonce2key/crapto1.h"
+#include "parity.h"
 
 // uint32_t test_state_odd = 0;
 // uint32_t test_state_even = 0;
 
-#define CONFIDENCE_THRESHOLD   0.99            // Collect nonces until we are certain enough that the following brute force is successfull
-#define GOOD_BYTES_REQUIRED            25
+#define CONFIDENCE_THRESHOLD   0.95            // Collect nonces until we are certain enough that the following brute force is successfull
+#define GOOD_BYTES_REQUIRED            60
 
 
 static const float p_K[257] = {                // the probability that a random nonce has a Sum Property == K 
@@ -90,8 +91,10 @@ static noncelist_t nonces[256];
 static uint16_t first_byte_Sum = 0;
 static uint16_t first_byte_num = 0;
 static uint16_t num_good_first_bytes = 0;
+static uint64_t maximum_states = 0;
+static uint64_t known_target_key;
 
-#define MAX_BEST_BYTES 40
+#define MAX_BEST_BYTES 256
 static uint8_t best_first_bytes[MAX_BEST_BYTES];
 
 
@@ -116,10 +119,10 @@ typedef struct {
 } statelist_t;
 
 
-partial_indexed_statelist_t partial_statelist[17];
-partial_indexed_statelist_t statelist_bitflip;
+static partial_indexed_statelist_t partial_statelist[17];
+static partial_indexed_statelist_t statelist_bitflip;
 
-statelist_t *candidates = NULL;
+static statelist_t *candidates = NULL;
 
 
 static int add_nonce(uint32_t nonce_enc, uint8_t par_enc) 
@@ -130,12 +133,12 @@ static int add_nonce(uint32_t nonce_enc, uint8_t par_enc)
 
        if (p1 == NULL) {                       // first nonce with this 1st byte
                first_byte_num++;
-               first_byte_Sum += parity((nonce_enc & 0xff000000) | (par_enc & 0x08) | 0x01); // 1st byte sum property. Note: added XOR 1
+               first_byte_Sum += evenparity32((nonce_enc & 0xff000000) | (par_enc & 0x08));
                // printf("Adding nonce 0x%08x, par_enc 0x%02x, parity(0x%08x) = %d\n", 
                        // nonce_enc, 
                        // par_enc, 
                        // (nonce_enc & 0xff000000) | (par_enc & 0x08) |0x01, 
-                       // parity((nonce_enc & 0xff000000) | (par_enc & 0x08) | 0x01));
+                       // parity((nonce_enc & 0xff000000) | (par_enc & 0x08));
        }
 
        while (p1 != NULL && (p1->nonce_enc & 0x00ff0000) < (nonce_enc & 0x00ff0000)) {
@@ -165,7 +168,7 @@ static int add_nonce(uint32_t nonce_enc, uint8_t par_enc)
        p2->par_enc = par_enc;
 
        nonces[first_byte].num++;
-       nonces[first_byte].Sum += parity((nonce_enc & 0x00ff0000) | (par_enc & 0x04) | 0x01); // 2nd byte sum property. Note: added XOR 1
+       nonces[first_byte].Sum += evenparity32((nonce_enc & 0x00ff0000) | (par_enc & 0x04));
        nonces[first_byte].updated = true;   // indicates that we need to recalculate the Sum(a8) probability for this first byte
 
        return (1);                             // new nonce added
@@ -183,6 +186,7 @@ static uint16_t PartialSumProperty(uint32_t state, odd_even_t odd_even)
                                part_sum ^= filter(st);
                                st = (st << 1) | ((j >> (3-i)) & 0x01) ;
                        }
+                       part_sum ^= 1;          // XOR 1 cancelled out for the other 8 bits
                } else {
                        for (uint16_t i = 0; i < 4; i++) {
                                st = (st << 1) | ((j >> (3-i)) & 0x01) ;
@@ -273,8 +277,8 @@ static void Tests()
        }
        
        // #define NUM_STATISTICS 100000
-       // uint64_t statistics[257];
        // uint32_t statistics_odd[17];
+       // uint64_t statistics[257];
        // uint32_t statistics_even[17];
        // struct Crypto1State cs;
        // time_t time1 = clock();
@@ -366,13 +370,25 @@ static void Tests()
        // test_state_odd = pcs->odd & 0x00ffffff;
        // test_state_even = pcs->even & 0x00ffffff;
        crypto1_destroy(pcs);
+       pcs = crypto1_create(0xa6b9aa97b955);
+       printf("Tests: for key = 0xa6b9aa97b955:\nSum(a0) = %d\nodd_state =  0x%06x\neven_state = 0x%06x\n",
+               SumProperty(pcs), pcs->odd & 0x00ffffff, pcs->even & 0x00ffffff);
+       crypto1_byte(pcs, (cuid >> 24) ^ best_first_bytes[0], true);
+       printf("After adding best first byte 0x%02x:\nSum(a8) = %d\nodd_state =  0x%06x\neven_state = 0x%06x\n",
+               best_first_bytes[0],
+               SumProperty(pcs),
+               pcs->odd & 0x00ffffff, pcs->even & 0x00ffffff);
+       //test_state_odd = pcs->odd & 0x00ffffff;
+       //test_state_even = pcs->even & 0x00ffffff;
+       crypto1_destroy(pcs);
+
 
        
        printf("\nTests: number of states with BitFlipProperty: %d, (= %1.3f%% of total states)\n", statelist_bitflip.len[0], 100.0 * statelist_bitflip.len[0] / (1<<20));
 
        printf("\nTests: Actual BitFlipProperties odd/even:\n");
        for (uint16_t i = 0; i < 256; i++) {
-               printf("[%3d]:%c%c ", i, nonces[i].BitFlip[ODD_STATE]?'o':' ', nonces[i].BitFlip[EVEN_STATE]?'e':' ');
+               printf("[%02x]:%c%c ", i, nonces[i].BitFlip[ODD_STATE]?'o':' ', nonces[i].BitFlip[EVEN_STATE]?'e':' ');
                if (i % 8 == 7) {
                        printf("\n");
                }
@@ -385,42 +401,46 @@ static void Tests()
                uint16_t best_sum = nonces[best_byte].Sum;
                uint16_t best_sum8 = nonces[best_byte].Sum8_guess;
                float confidence = nonces[best_byte].Sum8_prob;
-               printf("Byte: %02x, n = %2d, k = %2d, Sum(a8): %3d, Confidence: %2.1f%%\n", best_byte, best_num, best_sum, best_sum8, confidence*100);
+               printf("#%03d Byte: %02x, n = %2d, k = %2d, Sum(a8): %3d, Confidence: %2.1f%%\n", i, best_byte, best_num, best_sum, best_sum8, confidence*100);
        }
+       
+       // printf("\nTests: parity performance\n");
+       // time_t time1p = clock();
+       // uint32_t par_sum = 0;
+       // for (uint32_t i = 0; i < 100000000; i++) {
+               // par_sum += parity(i);
+       // }
+       // printf("parsum oldparity = %d, time = %1.5fsec\n", par_sum, (float)(clock() - time1p)/CLOCKS_PER_SEC);
+
+       // time1p = clock();
+       // par_sum = 0;
+       // for (uint32_t i = 0; i < 100000000; i++) {
+               // par_sum += evenparity32(i);
+       // }
+       // printf("parsum newparity = %d, time = %1.5fsec\n", par_sum, (float)(clock() - time1p)/CLOCKS_PER_SEC);
+
 }
 
 
-static void sort_best_first_bytes(void)
+static int common_bits(uint8_t byte1, uint8_t byte2) 
 {
-       // find the best choice for the very first byte (b)
-       float min_p_K = 1.0;
-       float max_prob_min_p_K = 0.0;
-       uint8_t best_byte = 0;
-       for (uint16_t i = 0; i < 256; i++ ) {
-               float prob1 = nonces[i].Sum8_prob;
-               uint16_t sum8 = nonces[i].Sum8_guess;
-               if (p_K[sum8] <= min_p_K && prob1 > CONFIDENCE_THRESHOLD) {
-                       if (p_K[sum8] < min_p_K) {
-                               min_p_K = p_K[sum8];
-                               best_byte = i;
-                               max_prob_min_p_K = prob1;
-                       } else if (prob1 > max_prob_min_p_K) {
-                               max_prob_min_p_K = prob1;
-                               best_byte = i;
-                       }
-               }
+       uint8_t common_bits = byte1 ^ byte2;
+       uint8_t j = 0;
+       while ((common_bits & 0x01) == 0 && j < 8) {
+               j++;
+               common_bits >>= 1;
        }
-       best_first_bytes[0] = best_byte;
-       // printf("Best Byte = 0x%02x, Sum8=%d, prob=%1.3f\n", best_byte, nonces[best_byte].Sum8_guess, nonces[best_byte].Sum8_prob);
-               
-       // sort the most probable guesses as following bytes (b')       
+       return j;
+}
+
+
+static void sort_best_first_bytes(void)
+{
+       // first, sort based on probability for correct guess   
        for (uint16_t i = 0; i < 256; i++ ) {
-               if (i == best_first_bytes[0]) {
-                       continue;
-               }
-               uint16_t j = 1;
+               uint16_t j = 0;
                float prob1 = nonces[i].Sum8_prob;
-               float prob2 = nonces[best_first_bytes[1]].Sum8_prob;
+               float prob2 = nonces[best_first_bytes[0]].Sum8_prob;
                while (prob1 < prob2 && j < MAX_BEST_BYTES-1) {
                        prob2 = nonces[best_first_bytes[++j]].Sum8_prob;
                }
@@ -431,6 +451,70 @@ static void sort_best_first_bytes(void)
                        best_first_bytes[j] = i;
                }
        }
+
+       // determine, how many are above the CONFIDENCE_THRESHOLD
+       uint16_t num_good_nonces = 0;
+       for (uint16_t i = 0; i < MAX_BEST_BYTES; i++) {
+               if (nonces[best_first_bytes[i]].Sum8_prob > CONFIDENCE_THRESHOLD) {
+                       ++num_good_nonces;
+               }
+       }
+       
+       uint16_t best_first_byte = 0;
+
+       // select the best possible first byte based on number of common bits with all {b'}
+       // uint16_t max_common_bits = 0;
+       // for (uint16_t i = 0; i < num_good_nonces; i++) {
+               // uint16_t sum_common_bits = 0;
+               // for (uint16_t j = 0; j < num_good_nonces; j++) {
+                       // if (i != j) {
+                               // sum_common_bits += common_bits(best_first_bytes[i],best_first_bytes[j]);
+                       // }
+               // }
+               // if (sum_common_bits > max_common_bits) {
+                       // max_common_bits = sum_common_bits;
+                       // best_first_byte = i;
+               // }
+       // }
+
+       // select best possible first byte {b} based on least likely sum/bitflip property
+       float min_p_K = 1.0;
+       for (uint16_t i = 0; i < num_good_nonces; i++ ) {
+               uint16_t sum8 = nonces[best_first_bytes[i]].Sum8_guess;
+               float bitflip_prob = 1.0;
+               if (nonces[best_first_bytes[i]].BitFlip[ODD_STATE] || nonces[best_first_bytes[i]].BitFlip[EVEN_STATE]) {
+                       bitflip_prob = 0.09375;
+               }
+               if (p_K[sum8] * bitflip_prob <= min_p_K) {
+                       min_p_K = p_K[sum8] * bitflip_prob;
+                       best_first_byte = i;
+               }
+       }
+
+       // use number of commmon bits as a tie breaker
+       uint16_t max_common_bits = 0;
+       for (uint16_t i = 0; i < num_good_nonces; i++) {
+               float bitflip_prob = 1.0;
+               if (nonces[best_first_bytes[i]].BitFlip[ODD_STATE] || nonces[best_first_bytes[i]].BitFlip[EVEN_STATE]) {
+                       bitflip_prob = 0.09375;
+               }
+               if (p_K[nonces[best_first_bytes[i]].Sum8_guess] * bitflip_prob == min_p_K) {
+                       uint16_t sum_common_bits = 0;
+                       for (uint16_t j = 0; j < num_good_nonces; j++) {
+                               sum_common_bits += common_bits(best_first_bytes[i],best_first_bytes[j]);
+                       }
+                       if (sum_common_bits > max_common_bits) {
+                               max_common_bits = sum_common_bits;
+                               best_first_byte = i;
+                       }
+               }
+       }       
+
+       // swap best possible first bytes to the pole position
+       uint16_t temp = best_first_bytes[0];
+       best_first_bytes[0] = best_first_bytes[best_first_byte];
+       best_first_bytes[best_first_byte] = temp;
+       
 }
 
 
@@ -512,7 +596,7 @@ static int read_nonce_file(void)
 }
 
 
-int static acquire_nonces(uint8_t blockNo, uint8_t keyType, uint8_t *key, uint8_t trgBlockNo, uint8_t trgKeyType, bool nonce_file_write, bool slow)
+static int acquire_nonces(uint8_t blockNo, uint8_t keyType, uint8_t *key, uint8_t trgBlockNo, uint8_t trgKeyType, bool nonce_file_write, bool slow)
 {
        clock_t time1 = clock();
        bool initialize = true;
@@ -617,10 +701,10 @@ int static acquire_nonces(uint8_t blockNo, uint8_t keyType, uint8_t *key, uint8_
                fclose(fnonces);
        }
        
-       PrintAndLog("Acquired a total of %d nonces in %1.1f seconds (%d nonces/minute)", 
+       PrintAndLog("Acquired a total of %d nonces in %1.1f seconds (%0.0f nonces/minute)", 
                total_num_nonces, 
                ((float)clock()-time1)/CLOCKS_PER_SEC, 
-               total_num_nonces*60*CLOCKS_PER_SEC/(clock()-time1));
+               total_num_nonces*60.0*CLOCKS_PER_SEC/((float)clock()-time1));
        
        return 0;
 }
@@ -628,7 +712,7 @@ int static acquire_nonces(uint8_t blockNo, uint8_t keyType, uint8_t *key, uint8_
 
 static int init_partial_statelists(void)
 {
-       const uint32_t sizes_odd[17] = { 125601, 0, 17607, 0, 73421, 0, 182033, 0, 248801, 0, 181737, 0, 74241, 0, 18387, 0, 126757 };
+       const uint32_t sizes_odd[17] = { 126757, 0, 18387, 0, 74241, 0, 181737, 0, 248801, 0, 182033, 0, 73421, 0, 17607, 0, 125601 };
        const uint32_t sizes_even[17] = { 125723, 0, 17867, 0, 74305, 0, 178707, 0, 248801, 0, 185063, 0, 73356, 0, 18127, 0, 126634 };
        
        printf("Allocating memory for partial statelists...\n");
@@ -712,7 +796,7 @@ static void add_state(statelist_t *sl, uint32_t state, odd_even_t odd_even)
 }
 
 
-uint32_t *find_first_state(uint32_t state, uint32_t mask, partial_indexed_statelist_t *sl, odd_even_t odd_even)
+static uint32_t *find_first_state(uint32_t state, uint32_t mask, partial_indexed_statelist_t *sl, odd_even_t odd_even)
 {
        uint32_t *p = sl->index[odd_even][(state & mask) >> (20-STATELIST_INDEX_WIDTH)];                // first Bits as index
 
@@ -738,7 +822,7 @@ static bool remaining_bits_match(uint8_t num_common_bits, uint8_t byte1, uint8_t
                        uint32_t bit_diff = ((byte1 ^ byte2) << (17-j)) & 0x00010000;                                   // difference of (j-1)th bit -> bit 16
                        uint32_t filter_diff = filter(state1 >> (4-j/2)) ^ filter(state2 >> (4-j/2));   // difference in filter function -> bit 0
                        uint32_t mask_y12_y13 = 0x000000c0 >> (j/2);
-                       uint32_t state_diff = (state1 ^ state2) & mask_y12_y13;                                                 // difference in state bits 12 and 13 -> bits 6/7 ... 4/5
+                       uint32_t state_diff = (state1 ^ state2) & mask_y12_y13;                                                 // difference in state bits 12 and 13 -> bits 6/7 ... 3/4
                        uint32_t all_diff = parity(bit_diff | state_diff | filter_diff);                                // use parity function to XOR all 4 bits
                        if (all_diff) {                 // invariant doesn't hold any more. Accept this state.
                                // if ((odd_even == ODD_STATE && state1 == test_state_odd)
@@ -848,6 +932,79 @@ static bool all_other_first_bytes_match(uint32_t state, odd_even_t odd_even)
 }
 
 
+static bool all_bit_flips_match(uint32_t state, odd_even_t odd_even) 
+{
+       for (uint16_t i = 0; i < 256; i++) {
+               if (nonces[i].BitFlip[odd_even] && i != best_first_bytes[0]) {
+                       uint8_t j = 0; // number of common bits
+                       uint8_t common_bits = best_first_bytes[0] ^ i;
+                       uint32_t mask = 0xfffffff0;
+                       if (odd_even == ODD_STATE) {
+                               while ((common_bits & 0x01) == 0 && j < 8) {
+                                       j++;
+                                       common_bits >>= 1;
+                                       if (j % 2 == 0) {               // the odd bits
+                                               mask >>= 1;
+                                       }
+                               }
+                       } else {
+                               while ((common_bits & 0x01) == 0 && j < 8) {
+                                       j++;
+                                       common_bits >>= 1;
+                                       if (j % 2 == 1) {               // the even bits
+                                               mask >>= 1;
+                                       }
+                               }
+                       }
+                       mask &= 0x000fffff;
+                       //printf("bytes 0x%02x and 0x%02x: %d common bits, mask = 0x%08x, state = 0x%08x, sum_a8 = %d", best_first_bytes[0], best_first_bytes[i], j, mask, state, sum_a8);
+                       bool found_match = false;
+                       uint32_t *p = find_first_state(state, mask, &statelist_bitflip, 0);
+                       if (p != NULL) {
+                               while ((state & mask) == (*p & mask) && (*p != 0xffffffff)) {
+                                       if (remaining_bits_match(j, best_first_bytes[0], i, state, (state&0x00fffff0) | *p, odd_even)) {
+                                               found_match = true;
+                                               // if ((odd_even == ODD_STATE && state == test_state_odd)
+                                                       // || (odd_even == EVEN_STATE && state == test_state_even)) {
+                                                       // printf("all_other_first_bytes_match(): %s test state: remaining bits matched. Bytes = %02x, %02x, Common Bits=%d, mask=0x%08x, PartSum(a8)=%d\n", 
+                                                               // odd_even==ODD_STATE?"odd":"even", best_first_bytes[0], best_first_bytes[i], j, mask, part_sum_a8);
+                                               // }
+                                               break;
+                                       } else {
+                                               // if ((odd_even == ODD_STATE && state == test_state_odd)
+                                                       // || (odd_even == EVEN_STATE && state == test_state_even)) {
+                                                       // printf("all_other_first_bytes_match(): %s test state: remaining bits didn't match. Bytes = %02x, %02x, Common Bits=%d, mask=0x%08x, PartSum(a8)=%d\n", 
+                                                               // odd_even==ODD_STATE?"odd":"even", best_first_bytes[0], best_first_bytes[i], j, mask, part_sum_a8);
+                                               // }
+                                       }
+                                       p++;
+                               }       
+                       } else {
+                               // if ((odd_even == ODD_STATE && state == test_state_odd)
+                                       // || (odd_even == EVEN_STATE && state == test_state_even)) {
+                                       // printf("all_other_first_bytes_match(): %s test state: couldn't find a matching state. Bytes = %02x, %02x, Common Bits=%d, mask=0x%08x, PartSum(a8)=%d\n", 
+                                               // odd_even==ODD_STATE?"odd":"even", best_first_bytes[0], best_first_bytes[i], j, mask, part_sum_a8);
+                               // }
+                       }               
+                       if (!found_match) {
+                               // if ((odd_even == ODD_STATE && state == test_state_odd)
+                                       // || (odd_even == EVEN_STATE && state == test_state_even)) {
+                                       // printf("all_other_first_bytes_match(): %s test state: Eliminated. Bytes = %02x, %02x, Common Bits = %d\n", odd_even==ODD_STATE?"odd":"even", best_first_bytes[0], best_first_bytes[i], j);
+                               // }
+                               return false;
+                       }
+               }
+
+       }
+       
+       return true;
+}
+
+
+#define INVALID_BIT (1<<30)
+#define SET_INVALID(pstate) (*(pstate) |= INVALID_BIT)
+#define IS_INVALID(state) (state & INVALID_BIT)
+
 static int add_matching_states(statelist_t *candidates, uint16_t part_sum_a0, uint16_t part_sum_a8, odd_even_t odd_even)
 {
        uint32_t worstcase_size = 1<<20;
@@ -863,15 +1020,20 @@ static int add_matching_states(statelist_t *candidates, uint16_t part_sum_a0, ui
                if (p2 != NULL) {
                        while (((*p1 << 4) & search_mask) == (*p2 & search_mask) && *p2 != 0xffffffff) {
                                if (all_other_first_bytes_match((*p1 << 4) | *p2, odd_even)) {
+                                       if (all_bit_flips_match((*p1 << 4) | *p2, odd_even)) { 
                                        add_state(candidates, (*p1 << 4) | *p2, odd_even);
                                }
+                               }
                                p2++;
                        }
                }
-               p2 = candidates->states[odd_even];
-               p2 += candidates->len[odd_even];
-               *p2 = 0xffffffff;
        }
+
+       // set end of list marker
+       uint32_t *p = candidates->states[odd_even];
+       p += candidates->len[odd_even];
+       *p = 0xffffffff;
+
        candidates->states[odd_even] = realloc(candidates->states[odd_even], sizeof(uint32_t) * (candidates->len[odd_even] + 1));
 
        return 0;
@@ -906,22 +1068,39 @@ static void TestIfKeyExists(uint64_t key)
 
        uint32_t state_odd = pcs->odd & 0x00ffffff;
        uint32_t state_even = pcs->even & 0x00ffffff;
-       printf("Tests: searching for key %llx after first byte 0x%02x (state_odd = 0x%06x, state_even = 0x%06x) ...\n", key, best_first_bytes[0], state_odd, state_even);
+       //printf("Tests: searching for key %llx after first byte 0x%02x (state_odd = 0x%06x, state_even = 0x%06x) ...\n", key, best_first_bytes[0], state_odd, state_even);
        
+       uint64_t count = 0;
        for (statelist_t *p = candidates; p != NULL; p = p->next) {
+               bool found_odd = false;
+               bool found_even = false;
                uint32_t *p_odd = p->states[ODD_STATE];
                uint32_t *p_even = p->states[EVEN_STATE];
                while (*p_odd != 0xffffffff) {
-                       if (*p_odd == state_odd) printf("o");
+                       if ((*p_odd & 0x00ffffff) == state_odd) {
+                               found_odd = true;
+                               break;
+                       }
                        p_odd++;
                }
                while (*p_even != 0xffffffff) {
-                       if (*p_even == state_even) printf("e");
+                       if ((*p_even & 0x00ffffff) == state_even) {
+                               found_even = true;
+                       }
                        p_even++;
                }
-               printf("|");
+               count += (p_odd - p->states[ODD_STATE]) * (p_even - p->states[EVEN_STATE]);
+               if (found_odd && found_even) {
+                       PrintAndLog("Key Found after testing %lld (2^%1.1f) out of %lld (2^%1.1f) keys. A brute force would have taken approx %lld minutes.", 
+                               count, log(count)/log(2), 
+                               maximum_states, log(maximum_states)/log(2),
+                               (count>>22)/60);
+                       crypto1_destroy(pcs);
+                       return;
+               }
        }
-       printf("\n");
+
+       printf("Key NOT found!\n");
        crypto1_destroy(pcs);
 }
 
@@ -932,7 +1111,7 @@ static void generate_candidates(uint16_t sum_a0, uint16_t sum_a8)
        
        statelist_t *current_candidates = NULL;
        // estimate maximum candidate states
-       uint64_t maximum_states = 0;
+       maximum_states = 0;
        for (uint16_t sum_odd = 0; sum_odd <= 16; sum_odd += 2) {
                for (uint16_t sum_even = 0; sum_even <= 16; sum_even += 2) {
                        if (sum_odd*(16-sum_even) + (16-sum_odd)*sum_even == sum_a0) {
@@ -969,9 +1148,6 @@ static void generate_candidates(uint16_t sum_a0, uint16_t sum_a8)
        }
        printf("Number of remaining possible keys: %lld (2^%1.1f)\n", maximum_states, log(maximum_states)/log(2.0));
 
-       TestIfKeyExists(0xffffffffffff);
-       TestIfKeyExists(0xa0a1a2a3a4a5);
-       
 }
 
 
@@ -998,8 +1174,28 @@ static void Check_for_FilterFlipProperties(void)
 }
 
 
-int mfnestedhard(uint8_t blockNo, uint8_t keyType, uint8_t *key, uint8_t trgBlockNo, uint8_t trgKeyType, bool nonce_file_read, bool nonce_file_write, bool slow) 
+static void brute_force(void)
 {
+       if (known_target_key != -1) {
+               PrintAndLog("Looking for known target key in remaining key space...");
+               TestIfKeyExists(known_target_key);
+               return;
+       } else {
+               PrintAndLog("Brute Force phase is not implemented.");
+               return;
+       }
+       
+
+}
+
+
+int mfnestedhard(uint8_t blockNo, uint8_t keyType, uint8_t *key, uint8_t trgBlockNo, uint8_t trgKeyType, uint8_t *trgkey, bool nonce_file_read, bool nonce_file_write, bool slow) 
+{
+       if (trgkey != NULL) {
+               known_target_key = bytes_to_num(trgkey, 6);
+       } else {
+               known_target_key = -1;
+       }
        
        // initialize the list of nonces
        for (uint16_t i = 0; i < 256; i++) {
@@ -1021,7 +1217,7 @@ int mfnestedhard(uint8_t blockNo, uint8_t keyType, uint8_t *key, uint8_t trgBloc
                if (read_nonce_file() != 0) {
                        return 3;
                }
-               num_good_first_bytes = estimate_second_byte_sum();
+               num_good_first_bytes = MIN(estimate_second_byte_sum(), GOOD_BYTES_REQUIRED);
        } else {                                        // acquire nonces.
                uint16_t is_OK = acquire_nonces(blockNo, keyType, key, trgBlockNo, trgKeyType, nonce_file_write, slow);
                if (is_OK != 0) {
@@ -1050,7 +1246,7 @@ int mfnestedhard(uint8_t blockNo, uint8_t keyType, uint8_t *key, uint8_t trgBloc
 
        generate_candidates(first_byte_Sum, nonces[best_first_bytes[0]].Sum8_guess);
        
-       PrintAndLog("Brute force phase not yet implemented");
+       brute_force();
        
        return 0;
 }
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