WEBVTT 1 00:00.440 --> 00:01.130 Welcome back. 2 00:01.430 --> 00:04.820 So far we have traced up to the ninth character. 3 00:04.850 --> 00:08.570 Now we'll continue with the tenth, eleventh, twelfth, and so on. 4 00:09.080 --> 00:10.820 So let's restart this. 5 00:12.440 --> 00:13.610 Go to full screen. 6 00:13.640 --> 00:15.380 Let's restart this. 7 00:18.390 --> 00:28.260 And run to our breakpoint main, and we start over until we come to this call, and then step over this 8 00:28.260 --> 00:28.710 call. 9 00:29.190 --> 00:33.420 And now it's waiting for us to enter our password. 10 00:34.690 --> 00:38.410 And we fished out nine characters from the password. 11 00:39.490 --> 00:41.830 So we type in what we have got so far. 12 00:41.860 --> 00:50.380 L-I-L-2-2-8-1-3-3. 13 00:50.560 --> 00:52.660 L-I-L-2-2-8-1-3-3. 14 00:53.590 --> 00:55.630 But we don't know what's the tenth password. 15 00:55.900 --> 01:00.280 So we're just going to put A, B, C at the back here for 10, 11, 12. 16 01:00.670 --> 01:02.230 A, B, C, hit Enter. 17 01:03.970 --> 01:04.180 Okay. 18 01:04.180 --> 01:05.170 So now we're here. 19 01:05.170 --> 01:08.050 Let's step over until we come to this line. 20 01:08.770 --> 01:10.660 And then we step into this call. 21 01:10.750 --> 01:12.130 Step again. 22 01:12.520 --> 01:15.730 And then now we right-click and graph it, and we trace it. 23 01:17.250 --> 01:18.510 So we trace it. 24 01:20.520 --> 01:22.440 First character, L. 25 01:25.980 --> 01:28.530 Second character, I. 26 01:33.130 --> 01:35.140 Third character, L again. 27 01:39.540 --> 01:41.130 Fourth character, 2. 28 01:44.840 --> 01:46.340 Here is going to loop up. 29 01:50.210 --> 01:51.110 Step over. 30 01:51.680 --> 01:56.420 So now we are here. We are at the fourth and the fifth character again. 31 01:56.420 --> 01:58.010 It is 2, as you can see here. 32 01:58.100 --> 02:02.150 So we are now at the fifth character here, 2. 33 02:03.120 --> 02:04.800 So let's continue. 34 02:06.650 --> 02:07.400 Click on this. 35 02:07.430 --> 02:09.680 We are now the sixth character, which is 8. 36 02:13.750 --> 02:16.600 And this would be the seventh character, which is 1. 37 02:16.600 --> 02:20.050 So we are now here, seventh character, which is 1. 38 02:26.980 --> 02:32.230 Click on this, and this should be the eighth character, which is 3. Eighth character. 39 02:34.010 --> 02:35.540 Continue stepping over. 40 02:37.350 --> 02:39.270 Now we're going to loop up again. 41 02:41.640 --> 02:46.260 Step over, and this should be the ninth character, which is 3. 42 02:46.260 --> 02:49.200 So we are now here at the ninth character. 43 02:50.310 --> 02:53.670 Next one we are going to target is the tenth character. 44 02:53.670 --> 02:55.470 So then continue to step over. 45 02:57.940 --> 03:05.620 Okay, so now we are tenth character, which is 7, but we entered A. We entered A, is it A? 46 03:05.860 --> 03:08.140 So we know that the tenth character is 7. 47 03:08.140 --> 03:11.020 So we can now put 7 over here. 48 03:12.190 --> 03:12.490 All right. 49 03:12.490 --> 03:13.600 Continue to step over. 50 03:13.600 --> 03:20.350 And because we did not put 7, is going to come to this part here and going to set a bad value, which 51 03:20.350 --> 03:21.400 is negative 1. 52 03:21.400 --> 03:26.170 So let's restart again and run to our first breakpoint. 53 03:26.170 --> 03:31.390 And let's step over it until we come to this call. 54 03:31.930 --> 03:37.810 And then we click on this, and we enter the password characters that we have fished out so far, which 55 03:37.810 --> 03:38.620 is L-I-L. 56 03:40.760 --> 03:49.340 L-I-L-2-2-8-1-3-3-7. 57 03:50.630 --> 03:54.500 L-I-L-2-2-8-1-3-3-7. 58 03:55.610 --> 03:59.330 So we don't know what is the eleventh character. 59 03:59.360 --> 04:03.530 B, C, B. So we just put B, C, D at the back. 60 04:03.650 --> 04:04.310 Okay. 61 04:04.430 --> 04:10.040 Just put B, C, D, hit Enter, and we are back. 62 04:10.040 --> 04:12.770 Now we continue to step over until we come to this call. 63 04:13.100 --> 04:15.020 Then we will step into this call. 64 04:15.020 --> 04:21.740 Click again, then right-click and graph this, and continue to trace. 65 04:22.520 --> 04:23.960 So we will trace. 66 04:25.500 --> 04:26.970 First character, L. 67 04:30.620 --> 04:32.750 Second character, I. 68 04:35.870 --> 04:37.730 Third character, L again. 69 04:43.780 --> 04:46.630 Fourth character, 2. 70 04:50.400 --> 04:51.780 Loop, loop back up. 71 04:54.440 --> 04:56.780 This should be the fifth character, which is 2. 72 04:56.960 --> 04:58.400 So we are now here. 73 04:58.400 --> 04:59.420 Fifth character. 74 05:04.360 --> 05:06.340 Click on this. Sixth character is 8. 75 05:06.370 --> 05:07.450 We are now here. 76 05:07.450 --> 05:07.870 8. 77 05:12.330 --> 05:13.530 And over here. 78 05:14.580 --> 05:19.680 Uh, this will be, uh, seventh character, which is 1, over here. 79 05:19.950 --> 05:21.510 This 1 over here. 80 05:26.100 --> 05:29.520 And now this will be eighth character, which is 3. 81 05:29.760 --> 05:31.290 So this is eighth character. 82 05:31.290 --> 05:31.920 3. 83 05:35.200 --> 05:41.290 Okay, now it's going to go back up, loop again. Step over, and we are back on the loop on top. 84 05:41.470 --> 05:42.580 Continue stepping. 85 05:42.580 --> 05:43.570 Come over here. 86 05:43.570 --> 05:48.970 And this should be your ninth character, which is 3 again, this one. 87 05:50.770 --> 05:56.440 Now notice that when comparing characters, you will have a single quote over here and a single quote 88 05:56.440 --> 05:57.160 over here. 89 05:57.190 --> 05:57.940 Remember that. 90 06:01.670 --> 06:02.090 Okay. 91 06:02.090 --> 06:03.620 So let's continue. 92 06:04.580 --> 06:08.510 Now here is comparing -, which is whether is zero or not. 93 06:09.290 --> 06:11.720 In our case, it's not zero, not end of the string. 94 06:11.720 --> 06:13.550 So it's going to go to compare. 95 06:13.550 --> 06:19.940 Now the eleventh, the tenth character. Tenth character is 7. 96 06:19.940 --> 06:20.990 So we got it right. 97 06:21.080 --> 06:22.880 Step over. 98 06:25.440 --> 06:27.720 Now it's checking whether you're end of the string or not. 99 06:27.810 --> 06:30.450 If you're end of the string, it will be a null terminator. 100 06:30.450 --> 06:33.900 That means - should be zero, zero, but it is -. 101 06:34.320 --> 06:35.970 Is this two bytes here, 3, 7? 102 06:35.970 --> 06:37.350 But it is not zero, zero. 103 06:37.740 --> 06:39.990 - is 3, 3, - is 3, 7. 104 06:40.650 --> 06:45.030 - is the first byte, first-level byte of the register. 105 06:45.330 --> 06:47.730 - is the second byte of the register. 106 06:48.780 --> 06:51.150 So in this case, it is not zero. 107 06:51.720 --> 06:53.220 So it's going to go straight. 108 06:54.600 --> 06:55.230 Step over. 109 06:55.230 --> 07:01.650 And now it's comparing the eleventh character. Eleventh character is not a character. It is a null terminator. 110 07:01.650 --> 07:01.980 See that? 111 07:03.240 --> 07:07.800 Remember I told you just now a character will have single quote like this, but in this case it is not 112 07:07.800 --> 07:10.320 single quote, it is just the value zero. 113 07:10.320 --> 07:13.020 So this is called a null terminator. 114 07:13.020 --> 07:19.890 That means it is expecting your eleventh character, which is B here. Eleventh character should be a null terminator. 115 07:20.400 --> 07:26.130 And in programming, when you input something to insert a null terminator, you press the Enter key. 116 07:26.400 --> 07:29.070 But our Enter key was at the back here, after the D. 117 07:29.790 --> 07:32.430 So our null terminator is at the back here, not here. 118 07:32.430 --> 07:35.670 So it is expecting your null terminator to be in this position. 119 07:35.700 --> 07:39.690 B. That means the password is only up to 7. 120 07:39.990 --> 07:42.090 Then after that will be an Enter key. 121 07:42.090 --> 07:44.550 When you press Enter, it sets the null terminator. 122 07:44.550 --> 07:50.670 So that suggests that the password is simply L-I-L-2-2-8-1-3-3-7. 123 07:50.670 --> 07:51.300 That's it. 124 07:51.810 --> 07:57.960 Okay, so to test our hypothesis, we can just directly now double-click on this and enter 125 07:58.230 --> 08:06.030 L-I-L, L-I-L-2-2-8-1-3-3-7. 126 08:06.030 --> 08:09.450 And press the Enter key to insert the null terminator. 127 08:09.990 --> 08:10.770 Nice job. 128 08:10.770 --> 08:11.730 Password found. 129 08:11.790 --> 08:17.970 So this is how we can fish the long passwords using deep loop tracing. 130 08:17.970 --> 08:19.170 Why is it deep loop tracing? 131 08:19.170 --> 08:25.530 Because we have to loop multiple times, I think at least three times before we fish out the entire 132 08:25.530 --> 08:26.250 password. 133 08:26.550 --> 08:30.060 Each time it loops, it adds 4 to the counter. 134 08:30.300 --> 08:32.040 - is your counter. 135 08:32.040 --> 08:34.020 As you can see, this is - counter. 136 08:34.800 --> 08:39.930 Okay, so that's how you can perform deep loop tracing. 137 08:40.230 --> 08:41.940 That's all for this video. 138 08:42.540 --> 08:46.620 In the next one, we are going to look at how to patch this to show the correct password. 139 08:46.620 --> 08:52.470 No matter what the password is revealed, try that on your own first, and then watch the next video. 140 08:52.980 --> 08:54.240 Thank you for watching.