WEBVTT Kind: captions Language: en 00:00:18.119 --> 00:00:21.480 align:start position:0% one<00:00:19.119> line<00:00:19.420> of<00:00:19.630> code<00:00:19.860> spurred<00:00:20.860> a<00:00:21.039> series<00:00:21.460> of 00:00:21.480 --> 00:00:21.490 align:start position:0% one line of code spurred a series of 00:00:21.490 --> 00:00:28.519 align:start position:0% one line of code spurred a series of momentous<00:00:22.300> events<00:00:22.810> in<00:00:23.020> blockchain<00:00:23.890> history 00:00:28.519 --> 00:00:28.529 align:start position:0% 00:00:28.529 --> 00:00:33.720 align:start position:0% the<00:00:29.529> line<00:00:29.710> of<00:00:29.919> code<00:00:30.189> in<00:00:30.900> red<00:00:32.010> it<00:00:33.010> was<00:00:33.280> moved<00:00:33.519> up 00:00:33.720 --> 00:00:33.730 align:start position:0% the line of code in red it was moved up 00:00:33.730 --> 00:00:37.170 align:start position:0% the line of code in red it was moved up to<00:00:34.480> where<00:00:34.660> the<00:00:34.840> green<00:00:35.019> line<00:00:35.230> is<00:00:35.470> and<00:00:36.030> that<00:00:37.030> was 00:00:37.170 --> 00:00:37.180 align:start position:0% to where the green line is and that was 00:00:37.180 --> 00:00:40.290 align:start position:0% to where the green line is and that was done<00:00:37.420> to<00:00:37.989> neutralize<00:00:38.860> a<00:00:39.250> re-entrant<00:00:40.030> see 00:00:40.290 --> 00:00:40.300 align:start position:0% done to neutralize a re-entrant see 00:00:40.300 --> 00:00:44.040 align:start position:0% done to neutralize a re-entrant see exploit<00:00:40.949> in<00:00:41.949> the<00:00:42.460> following<00:00:42.970> line<00:00:43.210> reward 00:00:44.040 --> 00:00:44.050 align:start position:0% exploit in the following line reward 00:00:44.050 --> 00:00:47.670 align:start position:0% exploit in the following line reward account<00:00:44.379> dot<00:00:44.680> payout<00:00:45.720> which<00:00:46.720> when<00:00:47.199> performed 00:00:47.670 --> 00:00:47.680 align:start position:0% account dot payout which when performed 00:00:47.680 --> 00:00:56.850 align:start position:0% account dot payout which when performed on<00:00:47.799> an<00:00:47.920> attackers<00:00:50.010> account<00:00:52.290> would<00:00:54.420> would<00:00:55.860> lead 00:00:56.850 --> 00:00:56.860 align:start position:0% on an attackers account would would lead 00:00:56.860 --> 00:01:00.570 align:start position:0% on an attackers account would would lead to<00:00:56.890> what<00:00:57.250> happened<00:00:57.610> to<00:00:57.879> the<00:00:58.330> DAO<00:00:59.580> the 00:01:00.570 --> 00:01:00.580 align:start position:0% to what happened to the DAO the 00:01:00.580 --> 00:01:03.359 align:start position:0% to what happened to the DAO the description<00:01:01.030> for<00:01:01.180> this<00:01:01.299> talk<00:01:02.040> was<00:01:03.040> before 00:01:03.359 --> 00:01:03.369 align:start position:0% description for this talk was before 00:01:03.369 --> 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portion of this talk<00:01:12.250> is<00:01:12.280> omitted<00:01:13.560> here's<00:01:14.560> a<00:01:14.680> bonus<00:01:15.130> tip<00:01:15.840> label 00:01:16.830 --> 00:01:16.840 align:start position:0% talk is omitted here's a bonus tip label 00:01:16.840 --> 00:01:21.349 align:start position:0% talk is omitted here's a bonus tip label your<00:01:17.580> untrusted<00:01:18.580> contracts<00:01:19.469> so<00:01:20.469> in<00:01:20.710> the 00:01:21.349 --> 00:01:21.359 align:start position:0% your untrusted contracts so in the 00:01:21.359 --> 00:01:25.069 align:start position:0% your untrusted contracts so in the reward<00:01:22.359> account<00:01:22.659> dot<00:01:22.869> payout<00:01:23.549> account<00:01:24.549> line 00:01:25.069 --> 00:01:25.079 align:start position:0% reward account dot payout account line 00:01:25.079 --> 00:01:27.060 align:start position:0% reward account dot payout account line already<00:01:26.079> you<00:01:26.259> can<00:01:26.409> see<00:01:26.560> that<00:01:26.710> there<00:01:26.829> are<00:01:26.890> two 00:01:27.060 --> 00:01:27.070 align:start position:0% already you can see that there are two 00:01:27.070 --> 00:01:29.819 align:start position:0% already you can see that there are two accounts<00:01:27.520> here<00:01:27.789> and<00:01:28.210> it's<00:01:29.109> not<00:01:29.350> as<00:01:29.500> clear 00:01:29.819 --> 00:01:29.829 align:start position:0% accounts here and it's not as clear 00:01:29.829 --> 00:01:32.599 align:start position:0% accounts here and it's not as clear maybe<00:01:30.340> immediately<00:01:31.119> which<00:01:31.929> account<00:01:32.320> is 00:01:32.599 --> 00:01:32.609 align:start position:0% maybe immediately which account is 00:01:32.609 --> 00:01:36.630 align:start position:0% maybe immediately which account is untrusted<00:01:33.899> so<00:01:34.899> a<00:01:34.929> better<00:01:35.320> way<00:01:35.859> to<00:01:36.340> even 00:01:36.630 --> 00:01:36.640 align:start position:0% untrusted so a better way to even 00:01:36.640 --> 00:01:40.139 align:start position:0% untrusted so a better way to even rewrite<00:01:36.880> this<00:01:37.409> maybe<00:01:38.409> is<00:01:38.799> to<00:01:39.189> reward<00:01:39.700> account 00:01:40.139 --> 00:01:40.149 align:start position:0% rewrite this maybe is to reward account 00:01:40.149 --> 00:01:44.399 align:start position:0% rewrite this maybe is to reward account but<00:01:40.509> payout<00:01:41.490> untrusted<00:01:42.490> account<00:01:42.820> and<00:01:43.409> then 00:01:44.399 --> 00:01:44.409 align:start position:0% but payout untrusted account and then 00:01:44.409 --> 00:01:48.029 align:start position:0% but payout untrusted account and then when<00:01:44.590> people<00:01:44.979> see<00:01:45.189> that<00:01:45.369> it<00:01:46.359> can<00:01:46.659> help<00:01:47.350> help 00:01:48.029 --> 00:01:48.039 align:start position:0% when people see that it can help help 00:01:48.039 --> 00:01:49.980 align:start position:0% when people see that it can help help you<00:01:48.219> be<00:01:48.729> more<00:01:48.759> aware<00:01:49.179> of<00:01:49.210> what<00:01:49.569> might<00:01:49.749> happen 00:01:49.980 --> 00:01:49.990 align:start position:0% you be more aware of what might happen 00:01:49.990 --> 00:01:55.800 align:start position:0% you be more aware of what might happen and<00:01:51.119> as<00:01:52.119> an<00:01:52.299> additional<00:01:52.869> tip<00:01:54.210> message<00:01:55.210> sender 00:01:55.800 --> 00:01:55.810 align:start position:0% and as an additional tip message sender 00:01:55.810 --> 00:02:01.859 align:start position:0% and as an additional tip message sender can<00:01:56.710> also<00:01:56.890> be<00:01:57.719> untrusted<00:01:58.920> so<00:02:00.329> if<00:02:01.329> it's<00:02:01.600> always 00:02:01.859 --> 00:02:01.869 align:start position:0% can also be untrusted so if it's always 00:02:01.869 --> 00:02:04.379 align:start position:0% can also be untrusted so if it's always untrusted<00:02:02.380> then<00:02:02.560> you<00:02:03.310> you<00:02:03.520> definitely<00:02:03.999> need 00:02:04.379 --> 00:02:04.389 align:start position:0% untrusted then you you definitely need 00:02:04.389 --> 00:02:06.809 align:start position:0% untrusted then you you definitely need to<00:02:04.420> put<00:02:04.749> a<00:02:04.780> comment<00:02:04.990> in<00:02:05.170> your<00:02:05.229> code<00:02:05.530> that<00:02:05.859> just 00:02:06.809 --> 00:02:06.819 align:start position:0% to put a comment in your code that just 00:02:06.819 --> 00:02:13.699 align:start position:0% to put a comment in your code that just to<00:02:07.060> make<00:02:07.479> people<00:02:07.509> more<00:02:07.960> aware<00:02:12.120> the<00:02:13.120> MELD<00:02:13.330> allow 00:02:13.699 --> 00:02:13.709 align:start position:0% to make people more aware the MELD allow 00:02:13.709 --> 00:02:16.559 align:start position:0% to make people more aware the MELD allow simon<00:02:14.709> Delarue<00:02:15.160> be<00:02:15.340> a<00:02:15.370> and<00:02:15.730> I<00:02:16.000> start<00:02:16.450> the 00:02:16.559 --> 00:02:16.569 align:start position:0% simon Delarue be a and I start the 00:02:16.569 --> 00:02:19.290 align:start position:0% simon Delarue be a and I start the committee<00:02:16.840> resource<00:02:17.650> for<00:02:18.640> smart<00:02:18.910> contract 00:02:19.290 --> 00:02:19.300 align:start position:0% committee resource for smart contract 00:02:19.300 --> 00:02:22.199 align:start position:0% committee resource for smart contract security<00:02:19.780> tips<00:02:20.340> we<00:02:21.340> are<00:02:21.400> grateful<00:02:21.790> to<00:02:21.819> seven 00:02:22.199 --> 00:02:22.209 align:start position:0% security tips we are grateful to seven 00:02:22.209 --> 00:02:26.370 align:start position:0% security tips we are grateful to seven others<00:02:22.420> so<00:02:22.660> far<00:02:22.990> who<00:02:23.380> have<00:02:24.810> our<00:02:25.810> listeners 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developers<00:02:33.280> to<00:02:33.490> write<00:02:33.580> about<00:02:33.880> and<00:02:34.210> the 00:02:34.950 --> 00:02:34.960 align:start position:0% developers to write about and the 00:02:34.960 --> 00:02:37.500 align:start position:0% developers to write about and the content<00:02:35.350> needs<00:02:35.440> to<00:02:35.590> be<00:02:35.710> aggregated<00:02:36.040> and<00:02:36.640> easy 00:02:37.500 --> 00:02:37.510 align:start position:0% content needs to be aggregated and easy 00:02:37.510 --> 00:02:40.140 align:start position:0% content needs to be aggregated and easy for<00:02:37.720> people<00:02:37.750> to<00:02:38.020> find<00:02:38.820> instead<00:02:39.820> of<00:02:39.940> being 00:02:40.140 --> 00:02:40.150 align:start position:0% for people to find instead of being 00:02:40.150 --> 00:02:45.180 align:start position:0% for people to find instead of being fragmented<00:02:40.570> and<00:02:40.990> scattered<00:02:43.740> we<00:02:44.740> start<00:02:45.040> with 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technical the first point is<00:02:53.650> to<00:02:53.770> prepare<00:02:54.070> for<00:02:54.280> failure<00:02:55.980> the<00:02:56.980> firt<00:02:57.370> this 00:02:57.960 --> 00:02:57.970 align:start position:0% is to prepare for failure the firt this 00:02:57.970 --> 00:03:02.010 align:start position:0% is to prepare for failure the firt this is<00:02:58.360> not<00:02:58.720> about<00:02:58.840> defeat<00:02:59.380> or<00:02:59.830> giving<00:03:00.580> up<00:03:00.840> this<00:03:01.840> is 00:03:02.010 --> 00:03:02.020 align:start position:0% is not about defeat or giving up this is 00:03:02.020 --> 00:03:04.560 align:start position:0% is not about defeat or giving up this is to<00:03:02.170> try<00:03:02.380> to<00:03:02.410> be<00:03:02.709> ready<00:03:02.950> for<00:03:03.310> the<00:03:04.150> unknown 00:03:04.560 --> 00:03:04.570 align:start position:0% to try to be ready for the unknown 00:03:04.570 --> 00:03:08.370 align:start position:0% to try to be ready for the unknown unknowns<00:03:06.239> this<00:03:07.239> can<00:03:07.450> be<00:03:07.570> very<00:03:07.780> difficult<00:03:07.959> to 00:03:08.370 --> 00:03:08.380 align:start position:0% unknowns this can be very difficult to 00:03:08.380 --> 00:03:11.540 align:start position:0% unknowns this can be very difficult to do<00:03:08.730> but<00:03:09.730> it<00:03:09.880> is<00:03:10.000> possible<00:03:10.209> in<00:03:10.570> some<00:03:10.780> cases<00:03:11.020> and 00:03:11.540 --> 00:03:11.550 align:start position:0% do but it is possible in some cases and 00:03:11.550 --> 00:03:16.080 align:start position:0% do but it is possible in some cases and the<00:03:12.550> next<00:03:12.790> slide<00:03:12.880> is<00:03:13.150> an<00:03:13.270> example<00:03:13.570> of<00:03:13.750> this<00:03:15.090> the 00:03:16.080 --> 00:03:16.090 align:start position:0% the next slide is an example of this the 00:03:16.090 --> 00:03:18.930 align:start position:0% the next slide is an example of this the second<00:03:16.450> example<00:03:16.870> the<00:03:17.260> second<00:03:18.070> point<00:03:18.220> is<00:03:18.820> to 00:03:18.930 --> 00:03:18.940 align:start position:0% second example the second point is to 00:03:18.940 --> 00:03:22.500 align:start position:0% second example the second point is to roll<00:03:19.360> out<00:03:19.600> carefully<00:03:21.300> production<00:03:22.300> a 00:03:22.500 --> 00:03:22.510 align:start position:0% roll out carefully production a 00:03:22.510 --> 00:03:25.290 align:start position:0% roll out carefully production a production<00:03:23.440> system<00:03:23.620> needs<00:03:24.430> baking<00:03:24.910> time<00:03:25.150> in 00:03:25.290 --> 00:03:25.300 align:start position:0% production system needs baking time in 00:03:25.300 --> 00:03:29.970 align:start position:0% production system needs baking time in production<00:03:27.810> the<00:03:28.810> strongest<00:03:29.230> swords<00:03:29.739> are 00:03:29.970 --> 00:03:29.980 align:start position:0% production the strongest swords are 00:03:29.980 --> 00:03:33.990 align:start position:0% production the strongest swords are forged<00:03:30.370> by<00:03:30.850> repeatedly<00:03:32.040> processing<00:03:33.040> them<00:03:33.250> in 00:03:33.990 --> 00:03:34.000 align:start position:0% forged by repeatedly processing them in 00:03:34.000 --> 00:03:36.410 align:start position:0% forged by repeatedly processing them in a<00:03:34.120> process<00:03:34.900> of<00:03:35.080> putting<00:03:35.290> them<00:03:35.530> in<00:03:35.650> fire<00:03:35.920> and 00:03:36.410 --> 00:03:36.420 align:start position:0% a process of putting them in fire and 00:03:36.420 --> 00:03:40.710 align:start position:0% a process of putting them in fire and hammering<00:03:37.420> them<00:03:37.720> it<00:03:38.500> takes<00:03:38.739> time<00:03:39.510> so<00:03:40.510> for 00:03:40.710 --> 00:03:40.720 align:start position:0% hammering them it takes time so for 00:03:40.720 --> 00:03:42.360 align:start position:0% hammering them it takes time so for contracts<00:03:41.350> they<00:03:41.830> should<00:03:42.040> be<00:03:42.130> put<00:03:42.340> through 00:03:42.360 --> 00:03:42.370 align:start position:0% contracts they should be put through 00:03:42.370 --> 00:03:45.000 align:start position:0% contracts they should be put through test<00:03:42.850> nets<00:03:43.120> and<00:03:43.420> then<00:03:44.140> a<00:03:44.260> beta<00:03:44.470> on<00:03:44.560> maenette 00:03:45.000 --> 00:03:45.010 align:start position:0% test nets and then a beta on maenette 00:03:45.010 --> 00:03:48.259 align:start position:0% test nets and then a beta on maenette before<00:03:45.880> a<00:03:45.910> production<00:03:46.390> launch<00:03:46.600> on<00:03:46.989> main<00:03:47.290> net 00:03:48.259 --> 00:03:48.269 align:start position:0% before a production launch on main net 00:03:48.269 --> 00:03:50.699 align:start position:0% before a production launch on main net keeping<00:03:49.269> contracts<00:03:49.810> simple<00:03:50.140> is<00:03:50.260> an<00:03:50.380> obvious 00:03:50.699 --> 00:03:50.709 align:start position:0% keeping contracts simple is an obvious 00:03:50.709 --> 00:03:53.460 align:start position:0% keeping contracts simple is an obvious tip<00:03:51.330> but<00:03:52.330> the<00:03:52.360> process<00:03:52.840> of<00:03:52.930> simplification 00:03:53.460 --> 00:03:53.470 align:start position:0% tip but the process of simplification 00:03:53.470 --> 00:03:57.630 align:start position:0% tip but the process of simplification can<00:03:54.160> lead<00:03:54.760> to<00:03:54.940> surprising<00:03:55.720> results<00:03:56.560> even<00:03:57.519> in 00:03:57.630 --> 00:03:57.640 align:start position:0% can lead to surprising results even in 00:03:57.640 --> 00:04:01.020 align:start position:0% can lead to surprising results even in the<00:03:57.760> system<00:03:58.150> that<00:03:58.299> already<00:03:58.600> looks<00:03:58.870> simple<00:04:00.030> to 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contribute 00:04:07.900 --> 00:04:11.430 align:start position:0% that everyone is welcome to contribute to<00:04:08.850> be<00:04:09.850> aware<00:04:10.030> of<00:04:10.090> blockchain<00:04:10.630> properties<00:04:11.079> is 00:04:11.430 --> 00:04:11.440 align:start position:0% to be aware of blockchain properties is 00:04:11.440 --> 00:04:16.009 align:start position:0% to be aware of blockchain properties is what<00:04:11.739> the<00:04:11.980> rest<00:04:12.549> of<00:04:12.910> this<00:04:13.150> talk<00:04:13.390> relates<00:04:13.780> to<00:04:14.430> as 00:04:16.009 --> 00:04:16.019 align:start position:0% what the rest of this talk relates to as 00:04:16.019 --> 00:04:18.390 align:start position:0% what the rest of this talk relates to as promised<00:04:17.019> here's<00:04:17.290> an<00:04:17.410> example<00:04:17.859> of<00:04:17.950> preparing 00:04:18.390 --> 00:04:18.400 align:start position:0% promised here's an example of preparing 00:04:18.400 --> 00:04:21.960 align:start position:0% promised here's an example of preparing for<00:04:18.579> failure<00:04:20.010> the<00:04:21.010> contract<00:04:21.459> keeps<00:04:21.669> track<00:04:21.940> of 00:04:21.960 --> 00:04:21.970 align:start position:0% for failure the contract keeps track of 00:04:21.970 --> 00:04:26.250 align:start position:0% for failure the contract keeps track of its<00:04:22.180> expected<00:04:22.630> fund<00:04:23.110> balance<00:04:25.260> check 00:04:26.250 --> 00:04:26.260 align:start position:0% its expected fund balance check 00:04:26.260 --> 00:04:28.560 align:start position:0% its expected fund balance check invariants<00:04:26.860> throws<00:04:27.190> if<00:04:27.820> the<00:04:27.940> actual<00:04:28.240> balance 00:04:28.560 --> 00:04:28.570 align:start position:0% invariants throws if the actual balance 00:04:28.570 --> 00:04:30.270 align:start position:0% invariants throws if the actual balance of<00:04:28.750> the<00:04:28.840> contract<00:04:29.350> is<00:04:29.530> smaller<00:04:29.860> than<00:04:30.130> the 00:04:30.270 --> 00:04:30.280 align:start position:0% of the contract is smaller than the 00:04:30.280 --> 00:04:33.990 align:start position:0% of the contract is smaller than the expected<00:04:30.790> balance<00:04:31.680> and 00:04:33.990 --> 00:04:34.000 align:start position:0% expected balance and 00:04:34.000 --> 00:04:35.760 align:start position:0% expected balance and this<00:04:34.090> check<00:04:34.390> invariance<00:04:34.870> is<00:04:35.140> called<00:04:35.470> at<00:04:35.650> the 00:04:35.760 --> 00:04:35.770 align:start position:0% this check invariance is called at the 00:04:35.770 --> 00:04:38.040 align:start position:0% this check invariance is called at the end<00:04:35.800> of<00:04:36.130> some<00:04:36.790> of<00:04:36.940> the<00:04:37.030> key<00:04:37.210> functions<00:04:37.570> in<00:04:37.960> the 00:04:38.040 --> 00:04:38.050 align:start position:0% end of some of the key functions in the 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broken the invariant should<00:04:48.790> not<00:04:48.940> get<00:04:49.150> broken<00:04:49.740> but<00:04:50.740> just<00:04:51.040> in<00:04:51.220> case 00:04:51.480 --> 00:04:51.490 align:start position:0% should not get broken but just in case 00:04:51.490 --> 00:04:55.380 align:start position:0% should not get broken but just in case it<00:04:51.730> does<00:04:52.350> the<00:04:53.350> emergency<00:04:53.860> call<00:04:54.100> will<00:04:54.580> send<00:04:54.910> the 00:04:55.380 --> 00:04:55.390 align:start position:0% it does the emergency call will send the 00:04:55.390 --> 00:04:59.190 align:start position:0% it does the emergency call will send the funds<00:04:55.600> away<00:04:57.300> anyone<00:04:58.300> can<00:04:58.720> invoke<00:04:58.990> the 00:04:59.190 --> 00:04:59.200 align:start position:0% funds away anyone can invoke the 00:04:59.200 --> 00:05:02.160 align:start position:0% funds away anyone can invoke the emergency<00:04:59.860> call<00:05:00.100> and<00:05:00.480> the<00:05:01.480> plan<00:05:01.690> is<00:05:01.840> to<00:05:01.870> have<00:05:02.110> a 00:05:02.160 --> 00:05:02.170 align:start position:0% emergency call and the plan is to have a 00:05:02.170 --> 00:05:06.720 align:start position:0% emergency call and the plan is to have a server<00:05:02.550> call<00:05:03.550> it<00:05:03.730> every<00:05:04.150> second<00:05:05.370> if<00:05:06.370> there<00:05:06.640> is 00:05:06.720 --> 00:05:06.730 align:start position:0% server call it every second if there is 00:05:06.730 --> 00:05:09.060 align:start position:0% server call it every second if there is a<00:05:06.760> breach<00:05:07.030> that<00:05:07.419> the<00:05:07.780> contracts<00:05:08.320> balance<00:05:08.710> is 00:05:09.060 --> 00:05:09.070 align:start position:0% a breach that the contracts balance is 00:05:09.070 --> 00:05:12.600 align:start position:0% a breach that the contracts balance is smaller<00:05:09.550> than<00:05:09.850> what<00:05:10.030> it<00:05:10.120> expects<00:05:10.840> the<00:05:11.310> hope<00:05:12.310> is 00:05:12.600 --> 00:05:12.610 align:start position:0% smaller than what it expects the hope is 00:05:12.610 --> 00:05:14.790 align:start position:0% smaller than what it expects the hope is that<00:05:12.850> most<00:05:13.090> of<00:05:13.300> the<00:05:13.419> funds<00:05:13.660> can<00:05:14.260> be<00:05:14.440> sent<00:05:14.680> to 00:05:14.790 --> 00:05:14.800 align:start position:0% that most of the funds can be sent to 00:05:14.800 --> 00:05:15.630 align:start position:0% that most of the funds can be sent to the<00:05:14.919> workshop 00:05:15.630 --> 00:05:15.640 align:start position:0% the workshop 00:05:15.640 --> 00:05:21.560 align:start position:0% the workshop instead<00:05:16.630> of<00:05:16.750> being<00:05:17.020> drained<00:05:17.290> to<00:05:17.620> an<00:05:17.710> attacker 00:05:21.560 --> 00:05:21.570 align:start position:0% 00:05:21.570 --> 00:05:25.590 align:start position:0% contracts<00:05:22.860> calling<00:05:23.860> each<00:05:23.980> other<00:05:24.190> is<00:05:24.940> powerful 00:05:25.590 --> 00:05:25.600 align:start position:0% contracts calling each other is powerful 00:05:25.600 --> 00:05:29.430 align:start position:0% contracts calling each other is powerful and<00:05:25.840> can<00:05:26.200> lead<00:05:26.440> to<00:05:26.470> emergent<00:05:27.280> use<00:05:27.430> cases<00:05:28.440> but 00:05:29.430 --> 00:05:29.440 align:start position:0% and can lead to emergent use cases but 00:05:29.440 --> 00:05:31.980 align:start position:0% and can lead to emergent use cases but care<00:05:29.710> must<00:05:29.740> be<00:05:30.130> taken<00:05:30.250> for<00:05:30.850> external<00:05:31.750> calls 00:05:31.980 --> 00:05:31.990 align:start position:0% care must be taken for external calls 00:05:31.990 --> 00:05:35.850 align:start position:0% care must be taken for external calls that<00:05:32.620> a<00:05:32.650> contract<00:05:33.100> makes<00:05:34.140> the<00:05:35.140> recommendation 00:05:35.850 --> 00:05:35.860 align:start position:0% that a contract makes the recommendation 00:05:35.860 --> 00:05:38.159 align:start position:0% that a contract makes the recommendation is<00:05:35.950> to<00:05:35.980> avoid<00:05:36.340> calls<00:05:36.700> to<00:05:36.940> untrusted<00:05:37.510> contracts 00:05:38.159 --> 00:05:38.169 align:start position:0% is to avoid calls to untrusted contracts 00:05:38.169 --> 00:05:42.060 align:start position:0% is to avoid calls to untrusted contracts as<00:05:38.710> much<00:05:38.950> as<00:05:39.160> you<00:05:39.250> can<00:05:40.530> untrusted<00:05:41.530> means<00:05:41.710> any 00:05:42.060 --> 00:05:42.070 align:start position:0% as much as you can untrusted means any 00:05:42.070 --> 00:05:45.390 align:start position:0% as much as you can untrusted means any contract<00:05:42.700> that<00:05:43.060> you<00:05:43.240> have<00:05:43.270> not<00:05:43.540> written<00:05:44.400> this 00:05:45.390 --> 00:05:45.400 align:start position:0% contract that you have not written this 00:05:45.400 --> 00:05:47.460 align:start position:0% contract that you have not written this is<00:05:45.610> because<00:05:45.910> if<00:05:46.060> you<00:05:46.150> call<00:05:46.330> someone<00:05:46.720> else's 00:05:47.460 --> 00:05:47.470 align:start position:0% is because if you call someone else's 00:05:47.470 --> 00:05:50.370 align:start position:0% is because if you call someone else's contract<00:05:48.090> they<00:05:49.090> or<00:05:49.419> one<00:05:50.080> of<00:05:50.200> their 00:05:50.370 --> 00:05:50.380 align:start position:0% contract they or one of their 00:05:50.380 --> 00:05:52.800 align:start position:0% contract they or one of their dependencies<00:05:51.130> could<00:05:52.030> accidentally<00:05:52.540> call<00:05:52.780> a 00:05:52.800 --> 00:05:52.810 align:start position:0% dependencies could accidentally call a 00:05:52.810 --> 00:05:55.920 align:start position:0% dependencies could accidentally call a malicious<00:05:53.350> contract<00:05:53.890> in<00:05:54.660> the<00:05:55.660> chain<00:05:55.900> of 00:05:55.920 --> 00:05:55.930 align:start position:0% malicious contract in the chain of 00:05:55.930 --> 00:05:59.550 align:start position:0% malicious contract in the chain of contract<00:05:56.530> calls<00:05:57.030> all<00:05:58.030> it<00:05:58.300> takes<00:05:58.540> is<00:05:58.930> for<00:05:59.500> one 00:05:59.550 --> 00:05:59.560 align:start position:0% contract calls all it takes is for one 00:05:59.560 --> 00:06:02.030 align:start position:0% contract calls all it takes is for one contract<00:06:00.250> to<00:06:00.820> make<00:06:01.000> a<00:06:01.030> mistake 00:06:02.030 --> 00:06:02.040 align:start position:0% contract to make a mistake 00:06:02.040 --> 00:06:06.120 align:start position:0% contract to make a mistake thus<00:06:03.450> assume<00:06:04.450> that<00:06:04.690> untrusted<00:06:05.229> contracts<00:06:05.890> are 00:06:06.120 --> 00:06:06.130 align:start position:0% thus assume that untrusted contracts are 00:06:06.130 --> 00:06:10.020 align:start position:0% thus assume that untrusted contracts are malicious<00:06:07.560> avoid<00:06:08.560> calling<00:06:09.040> do<00:06:09.250> something<00:06:09.760> or 00:06:10.020 --> 00:06:10.030 align:start position:0% malicious avoid calling do something or 00:06:10.030 --> 00:06:14.600 align:start position:0% malicious avoid calling do something or address<00:06:10.900> call<00:06:11.440> on<00:06:12.040> an<00:06:12.490> untrusted<00:06:13.240> contract 00:06:14.600 --> 00:06:14.610 align:start position:0% address call on an untrusted contract 00:06:14.610 --> 00:06:17.270 align:start position:0% address call on an untrusted contract the<00:06:15.610> key<00:06:15.790> point<00:06:16.060> is<00:06:16.240> that<00:06:16.270> after<00:06:16.630> any 00:06:17.270 --> 00:06:17.280 align:start position:0% the key point is that after any 00:06:17.280 --> 00:06:20.880 align:start position:0% the key point is that after any untrusted<00:06:18.280> call<00:06:19.110> assume<00:06:20.110> that<00:06:20.380> the<00:06:20.500> state<00:06:20.740> of 00:06:20.880 --> 00:06:20.890 align:start position:0% untrusted call assume that the state of 00:06:20.890 --> 00:06:23.540 align:start position:0% untrusted call assume that the state of your<00:06:21.010> contract<00:06:21.520> has<00:06:21.760> been<00:06:21.790> manipulated 00:06:23.540 --> 00:06:23.550 align:start position:0% your contract has been manipulated 00:06:23.550 --> 00:06:29.820 align:start position:0% your contract has been manipulated here's<00:06:24.550> a<00:06:24.669> diagram<00:06:25.180> to<00:06:25.240> help<00:06:28.500> there's<00:06:29.500> a<00:06:29.590> few 00:06:29.820 --> 00:06:29.830 align:start position:0% here's a diagram to help there's a few 00:06:29.830 --> 00:06:32.460 align:start position:0% here's a diagram to help there's a few things<00:06:30.070> here<00:06:30.340> but<00:06:30.520> let's<00:06:30.760> start<00:06:31.360> at<00:06:31.540> the<00:06:31.810> foo 00:06:32.460 --> 00:06:32.470 align:start position:0% things here but let's start at the foo 00:06:32.470 --> 00:06:36.330 align:start position:0% things here but let's start at the foo function<00:06:33.540> it<00:06:34.540> decrements<00:06:34.780> X<00:06:35.350> and<00:06:36.040> then<00:06:36.190> it 00:06:36.330 --> 00:06:36.340 align:start position:0% function it decrements X and then it 00:06:36.340 --> 00:06:40.110 align:start position:0% function it decrements X and then it calls<00:06:36.550> a<00:06:37.000> an<00:06:37.540> untrusted<00:06:38.200> contract<00:06:39.120> the 00:06:40.110 --> 00:06:40.120 align:start position:0% calls a an untrusted contract the 00:06:40.120 --> 00:06:42.630 align:start position:0% calls a an untrusted contract the fallback<00:06:40.390> function<00:06:41.140> of<00:06:41.380> the<00:06:42.160> untrusted 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realize<00:06:52.910> that<00:06:53.360> reentrant<00:06:54.200> si 00:06:54.430 --> 00:06:54.440 align:start position:0% important to realize that reentrant si 00:06:54.440 --> 00:06:57.970 align:start position:0% important to realize that reentrant si can<00:06:55.040> use<00:06:55.570> any<00:06:56.570> of<00:06:56.810> the<00:06:56.930> contracts<00:06:57.530> public 00:06:57.970 --> 00:06:57.980 align:start position:0% can use any of the contracts public 00:06:57.980 --> 00:07:01.630 align:start position:0% can use any of the contracts public functions<00:06:59.200> meaning<00:07:00.200> an<00:07:00.440> attacker<00:07:00.830> can 00:07:01.630 --> 00:07:01.640 align:start position:0% functions meaning an attacker can 00:07:01.640 --> 00:07:06.810 align:start position:0% functions meaning an attacker can re-enter<00:07:02.380> using<00:07:03.380> the<00:07:04.280> function<00:07:04.730> G<00:07:05.000> or<00:07:05.210> bar 00:07:06.810 --> 00:07:06.820 align:start position:0% re-enter using the function G or bar 00:07:06.820 --> 00:07:11.350 align:start position:0% re-enter using the function G or bar this<00:07:07.820> is<00:07:08.000> why<00:07:08.150> after<00:07:08.650> the<00:07:09.650> untrusted<00:07:10.220> call<00:07:10.430> the 00:07:11.350 --> 00:07:11.360 align:start position:0% this is why after the untrusted call the 00:07:11.360 --> 00:07:14.080 align:start position:0% this is why after the untrusted call the contract<00:07:11.870> can't<00:07:12.350> assume<00:07:12.680> anything<00:07:13.010> at<00:07:13.640> all 00:07:14.080 --> 00:07:14.090 align:start position:0% contract can't assume anything at all 00:07:14.090 --> 00:07:21.310 align:start position:0% contract can't assume anything at all about<00:07:14.330> the<00:07:14.480> values<00:07:15.020> of<00:07:15.230> X<00:07:15.800> or<00:07:16.100> Y<00:07:16.400> a<00:07:19.990> second<00:07:20.990> tip 00:07:21.310 --> 00:07:21.320 align:start position:0% about the values of X or Y a second tip 00:07:21.320 --> 00:07:25.800 align:start position:0% about the values of X or Y a second tip is<00:07:21.560> to<00:07:22.490> use<00:07:22.520> sand<00:07:23.390> and<00:07:23.750> avoid<00:07:24.620> call<00:07:25.010> dot<00:07:25.250> value 00:07:25.800 --> 00:07:25.810 align:start position:0% is to use sand and avoid call dot value 00:07:25.810 --> 00:07:29.110 align:start position:0% is to use sand and avoid call dot value if<00:07:26.810> you've<00:07:27.740> seen<00:07:27.980> examples<00:07:28.160> of<00:07:28.640> vulnerable 00:07:29.110 --> 00:07:29.120 align:start position:0% if you've seen examples of vulnerable 00:07:29.120 --> 00:07:32.190 align:start position:0% if you've seen examples of vulnerable code<00:07:29.530> especially<00:07:30.530> regarding<00:07:31.370> re-entrance<00:07:31.910> e 00:07:32.190 --> 00:07:32.200 align:start position:0% code especially regarding re-entrance e 00:07:32.200 --> 00:07:36.940 align:start position:0% code especially regarding re-entrance e they<00:07:33.200> all<00:07:33.380> involve<00:07:33.860> call<00:07:34.580> dot<00:07:34.820> value<00:07:35.950> because 00:07:36.940 --> 00:07:36.950 align:start position:0% they all involve call dot value because 00:07:36.950 --> 00:07:40.440 align:start position:0% they all involve call dot value because using<00:07:37.490> sand<00:07:38.020> instead<00:07:39.020> of<00:07:39.320> call<00:07:39.530> dot<00:07:39.740> value 00:07:40.440 --> 00:07:40.450 align:start position:0% using sand instead of call dot value 00:07:40.450 --> 00:07:43.930 align:start position:0% using sand instead of call dot value does<00:07:41.450> not<00:07:41.480> give<00:07:41.870> the<00:07:42.080> attacker<00:07:42.380> enough<00:07:43.190> gas<00:07:43.520> to 00:07:43.930 --> 00:07:43.940 align:start position:0% does not give the attacker enough gas to 00:07:43.940 --> 00:07:47.800 align:start position:0% does not give the attacker enough gas to do<00:07:44.840> damage<00:07:45.110> with<00:07:45.290> reentrant<00:07:46.130> see<00:07:46.810> the 00:07:47.800 --> 00:07:47.810 align:start position:0% do damage with reentrant see the 00:07:47.810 --> 00:07:52.720 align:start position:0% do damage with reentrant see the attacker<00:07:48.080> only<00:07:48.500> gets<00:07:49.480> 2300<00:07:50.480> gas<00:07:51.669> with<00:07:52.669> the 00:07:52.720 --> 00:07:52.730 align:start position:0% attacker only gets 2300 gas with the 00:07:52.730 --> 00:07:53.890 align:start position:0% attacker only gets 2300 gas with the great<00:07:52.910> power<00:07:53.090> comes<00:07:53.270> great<00:07:53.690> responsibility 00:07:53.890 --> 00:07:53.900 align:start position:0% great power comes great responsibility 00:07:53.900 --> 00:07:57.990 align:start position:0% great power comes great responsibility and<00:07:55.150> that<00:07:56.150> applies<00:07:56.480> to<00:07:56.510> call<00:07:56.930> dot<00:07:57.169> value<00:07:57.590> and 00:07:57.990 --> 00:07:58.000 align:start position:0% and that applies to call dot value and 00:07:58.000 --> 00:08:01.630 align:start position:0% and that applies to call dot value and so<00:07:59.000> the<00:07:59.210> tip<00:07:59.390> is<00:07:59.600> to<00:07:59.690> use<00:07:59.900> scent<00:08:00.320> and<00:08:00.640> avoid 00:08:01.630 --> 00:08:01.640 align:start position:0% so the tip is to use scent and avoid 00:08:01.640 --> 00:08:07.510 align:start position:0% so the tip is to use scent and avoid call<00:08:02.030> dot<00:08:02.240> value<00:08:04.960> perhaps<00:08:05.960> the<00:08:06.169> most<00:08:06.520> mature 00:08:07.510 --> 00:08:07.520 align:start position:0% call dot value perhaps the most mature 00:08:07.520 --> 00:08:11.020 align:start position:0% call dot value perhaps the most mature best<00:08:07.910> practice<00:08:08.390> is<00:08:08.540> to<00:08:08.570> handle<00:08:09.229> errors<00:08:09.890> in<00:08:10.280> raw 00:08:11.020 --> 00:08:11.030 align:start position:0% best practice is to handle errors in raw 00:08:11.030 --> 00:08:14.350 align:start position:0% best practice is to handle errors in raw calls<00:08:11.979> Rock<00:08:12.979> holes<00:08:13.250> such<00:08:13.940> as<00:08:14.120> address 00:08:14.350 --> 00:08:14.360 align:start position:0% calls Rock holes such as address 00:08:14.360 --> 00:08:18.790 align:start position:0% calls Rock holes such as address thoughts<00:08:14.900> and<00:08:15.260> and<00:08:15.560> address<00:08:16.460> dot<00:08:16.760> call<00:08:17.800> return 00:08:18.790 --> 00:08:18.800 align:start position:0% thoughts and and address dot call return 00:08:18.800 --> 00:08:22.420 align:start position:0% thoughts and and address dot call return false<00:08:19.130> if<00:08:19.580> they<00:08:20.030> fail<00:08:20.919> this<00:08:21.919> is<00:08:22.130> unlike 00:08:22.420 --> 00:08:22.430 align:start position:0% false if they fail this is unlike 00:08:22.430 --> 00:08:25.120 align:start position:0% false if they fail this is unlike invoking<00:08:22.760> a<00:08:22.940> do<00:08:23.120> something<00:08:23.570> method<00:08:24.130> which 00:08:25.120 --> 00:08:25.130 align:start position:0% invoking a do something method which 00:08:25.130 --> 00:08:28.300 align:start position:0% invoking a do something method which propagates<00:08:25.790> an<00:08:25.940> exception<00:08:26.650> if<00:08:27.650> it<00:08:27.979> encounters 00:08:28.300 --> 00:08:28.310 align:start position:0% propagates an exception if it encounters 00:08:28.310 --> 00:08:34.360 align:start position:0% propagates an exception if it encounters one<00:08:30.010> so<00:08:31.010> the<00:08:31.250> good<00:08:31.400> example<00:08:32.030> is<00:08:32.240> to<00:08:33.370> check 00:08:34.360 --> 00:08:34.370 align:start position:0% one so the good example is to check 00:08:34.370 --> 00:08:36.790 align:start position:0% one so the good example is to check check<00:08:34.969> the<00:08:35.120> result<00:08:35.450> and<00:08:35.630> the<00:08:35.960> bad<00:08:36.110> example<00:08:36.650> is 00:08:36.790 --> 00:08:36.800 align:start position:0% check the result and the bad example is 00:08:36.800 --> 00:08:43.270 align:start position:0% check the result and the bad example is an<00:08:37.339> unchecked<00:08:37.820> send<00:08:38.240> a<00:08:41.860> tip<00:08:42.860> that<00:08:43.099> goes 00:08:43.270 --> 00:08:43.280 align:start position:0% an unchecked send a tip that goes 00:08:43.280 --> 00:08:46.600 align:start position:0% an unchecked send a tip that goes together<00:08:43.550> with<00:08:44.480> using<00:08:44.930> send<00:08:45.230> is<00:08:45.740> to<00:08:46.460> keep 00:08:46.600 --> 00:08:46.610 align:start position:0% together with using send is to keep 00:08:46.610 --> 00:08:50.950 align:start position:0% together with using send is to keep fallback<00:08:47.060> functions<00:08:47.510> simple<00:08:49.720> the<00:08:50.720> last 00:08:50.950 --> 00:08:50.960 align:start position:0% fallback functions simple the last 00:08:50.960 --> 00:08:53.829 align:start position:0% fallback functions simple the last fallback<00:08:51.410> function<00:08:52.010> is<00:08:52.250> advised<00:08:53.240> against 00:08:53.829 --> 00:08:53.839 align:start position:0% fallback function is advised against 00:08:53.839 --> 00:08:58.540 align:start position:0% fallback function is advised against because<00:08:54.200> one<00:08:54.770> it<00:08:55.700> uses<00:08:56.000> more<00:08:56.390> than<00:08:57.400> 23-hundred 00:08:58.540 --> 00:08:58.550 align:start position:0% because one it uses more than 23-hundred 00:08:58.550 --> 00:09:03.730 align:start position:0% because one it uses more than 23-hundred ass<00:09:00.100> second<00:09:01.100> it<00:09:01.370> asks<00:09:01.820> callers<00:09:02.320> to<00:09:03.320> break<00:09:03.560> the 00:09:03.730 --> 00:09:03.740 align:start position:0% ass second it asks callers to break the 00:09:03.740 --> 00:09:07.300 align:start position:0% ass second it asks callers to break the tip<00:09:03.920> of<00:09:04.160> using<00:09:04.519> sand<00:09:04.850> and<00:09:05.380> asks<00:09:06.380> them<00:09:06.620> to<00:09:07.130> use 00:09:07.300 --> 00:09:07.310 align:start position:0% tip of using sand and asks them to use 00:09:07.310 --> 00:09:15.370 align:start position:0% tip of using sand and asks them to use the<00:09:07.519> riskier<00:09:08.089> call<00:09:08.750> dot<00:09:08.990> value<00:09:09.410> a<00:09:14.079> call<00:09:15.079> depth 00:09:15.370 --> 00:09:15.380 align:start position:0% the riskier call dot value a call depth 00:09:15.380 --> 00:09:18.579 align:start position:0% the riskier call dot value a call depth attack<00:09:15.880> can<00:09:16.880> be<00:09:16.910> used<00:09:17.300> by<00:09:17.720> an<00:09:17.839> attacker<00:09:18.200> to 00:09:18.579 --> 00:09:18.589 align:start position:0% attack can be used by an attacker to 00:09:18.589 --> 00:09:22.740 align:start position:0% attack can be used by an attacker to make<00:09:19.430> all<00:09:19.670> of<00:09:19.700> your<00:09:20.149> contracts<00:09:20.660> calls<00:09:21.350> to<00:09:21.709> fail 00:09:22.740 --> 00:09:22.750 align:start position:0% make all of your contracts calls to fail 00:09:22.750 --> 00:09:25.660 align:start position:0% make all of your contracts calls to fail the<00:09:23.750> theme<00:09:23.930> the<00:09:24.620> etherium<00:09:24.980> virtual<00:09:25.370> machine 00:09:25.660 --> 00:09:25.670 align:start position:0% the theme the etherium virtual machine 00:09:25.670 --> 00:09:27.480 align:start position:0% the theme the etherium virtual machine has<00:09:25.820> what<00:09:26.029> the<00:09:26.149> yellow<00:09:26.390> paper<00:09:26.630> calls<00:09:26.959> a 00:09:27.480 --> 00:09:27.490 align:start position:0% has what the yellow paper calls a 00:09:27.490 --> 00:09:31.690 align:start position:0% has what the yellow paper calls a contract<00:09:28.490> a<00:09:28.910> message<00:09:29.660> called<00:09:30.290> slash<00:09:30.920> contract 00:09:31.690 --> 00:09:31.700 align:start position:0% contract a message called slash contract 00:09:31.700 --> 00:09:34.690 align:start position:0% contract a message called slash contract creation<00:09:32.329> stack<00:09:32.930> and<00:09:33.320> it<00:09:34.100> has<00:09:34.220> a<00:09:34.250> maximum 00:09:34.690 --> 00:09:34.700 align:start position:0% creation stack and it has a maximum 00:09:34.700 --> 00:09:38.980 align:start position:0% creation stack and it has a maximum depth<00:09:35.089> of<00:09:35.740> 1,024<00:09:37.120> an<00:09:38.120> attacker<00:09:38.510> can<00:09:38.810> make 00:09:38.980 --> 00:09:38.990 align:start position:0% depth of 1,024 an attacker can make 00:09:38.990 --> 00:09:41.290 align:start position:0% depth of 1,024 an attacker can make recursive<00:09:39.529> calls<00:09:39.769> to<00:09:40.339> bring<00:09:40.579> the<00:09:40.850> depth<00:09:41.029> to 00:09:41.290 --> 00:09:41.300 align:start position:0% recursive calls to bring the depth to 00:09:41.300 --> 00:09:45.910 align:start position:0% recursive calls to bring the depth to 1023<00:09:42.610> call<00:09:43.610> your<00:09:43.940> function<00:09:44.410> which<00:09:45.410> brings<00:09:45.740> the 00:09:45.910 --> 00:09:45.920 align:start position:0% 1023 call your function which brings the 00:09:45.920 --> 00:09:49.840 align:start position:0% 1023 call your function which brings the depth<00:09:46.100> to<00:09:46.480> 1024<00:09:47.480> and<00:09:48.279> now<00:09:49.279> all<00:09:49.550> of<00:09:49.579> your 00:09:49.840 --> 00:09:49.850 align:start position:0% depth to 1024 and now all of your 00:09:49.850 --> 00:09:53.889 align:start position:0% depth to 1024 and now all of your contracts<00:09:50.360> calls<00:09:50.750> will<00:09:51.500> fail<00:09:51.769> in<00:09:52.899> this 00:09:53.889 --> 00:09:53.899 align:start position:0% contracts calls will fail in this 00:09:53.899 --> 00:09:57.519 align:start position:0% contracts calls will fail in this example<00:09:54.760> simple<00:09:55.760> example<00:09:56.300> an<00:09:56.510> attacker<00:09:57.260> can 00:09:57.519 --> 00:09:57.529 align:start position:0% example simple example an attacker can 00:09:57.529 --> 00:10:01.380 align:start position:0% example simple example an attacker can force<00:09:57.800> a<00:09:58.010> recipient<00:09:58.660> to<00:09:59.660> lose<00:09:59.839> their<00:10:00.079> refund 00:10:01.380 --> 00:10:01.390 align:start position:0% force a recipient to lose their refund 00:10:01.390 --> 00:10:03.730 align:start position:0% force a recipient to lose their refund so<00:10:02.390> the<00:10:02.540> attacker<00:10:02.839> recurse<00:10:03.170> is<00:10:03.350> to<00:10:03.470> bring<00:10:03.620> the 00:10:03.730 --> 00:10:03.740 align:start position:0% so the attacker recurse is to bring the 00:10:03.740 --> 00:10:07.170 align:start position:0% so the attacker recurse is to bring the depth<00:10:03.920> to<00:10:04.160> 1023<00:10:05.060> then<00:10:05.839> calls<00:10:06.140> withdraw<00:10:06.620> refund 00:10:07.170 --> 00:10:07.180 align:start position:0% depth to 1023 then calls withdraw refund 00:10:07.180 --> 00:10:10.060 align:start position:0% depth to 1023 then calls withdraw refund using<00:10:08.180> the<00:10:08.300> address<00:10:08.630> of<00:10:08.870> a<00:10:09.050> victim<00:10:09.440> recipient 00:10:10.060 --> 00:10:10.070 align:start position:0% using the address of a victim recipient 00:10:10.070 --> 00:10:17.170 align:start position:0% using the address of a victim recipient and<00:10:10.450> the<00:10:11.450> depth<00:10:11.660> is<00:10:11.839> now<00:10:12.050> at<00:10:13.089> 1024<00:10:15.550> the<00:10:16.550> refunds 00:10:17.170 --> 00:10:17.180 align:start position:0% and the depth is now at 1024 the refunds 00:10:17.180 --> 00:10:19.030 align:start position:0% and the depth is now at 1024 the refunds for<00:10:17.390> the<00:10:17.510> recipient<00:10:18.020> will<00:10:18.200> be<00:10:18.350> set<00:10:18.589> to<00:10:18.740> zero 00:10:19.030 --> 00:10:19.040 align:start position:0% for the recipient will be set to zero 00:10:19.040 --> 00:10:21.639 align:start position:0% for the recipient will be set to zero this<00:10:20.000> pointer<00:10:20.360> doesn't<00:10:20.630> work<00:10:20.810> well<00:10:21.200> to<00:10:21.470> show 00:10:21.639 --> 00:10:21.649 align:start position:0% this pointer doesn't work well to show 00:10:21.649 --> 00:10:28.180 align:start position:0% this pointer doesn't work well to show that<00:10:22.149> and<00:10:26.110> when<00:10:27.110> the<00:10:27.260> victim<00:10:27.529> calls<00:10:27.770> withdraw 00:10:28.180 --> 00:10:28.190 align:start position:0% that and when the victim calls withdraw 00:10:28.190 --> 00:10:30.579 align:start position:0% that and when the victim calls withdraw a<00:10:28.220> refund<00:10:28.730> that<00:10:29.570> the<00:10:29.720> send<00:10:29.930> will<00:10:30.079> fail<00:10:30.320> and 00:10:30.579 --> 00:10:30.589 align:start position:0% a refund that the send will fail and 00:10:30.589 --> 00:10:33.069 align:start position:0% a refund that the send will fail and then<00:10:31.010> when<00:10:31.279> the<00:10:31.399> victim<00:10:31.700> calls<00:10:31.940> tries<00:10:32.930> to 00:10:33.069 --> 00:10:33.079 align:start position:0% then when the victim calls tries to 00:10:33.079 --> 00:10:34.780 align:start position:0% then when the victim calls tries to withdraw<00:10:33.320> their<00:10:33.500> own<00:10:33.620> refund<00:10:34.070> the<00:10:34.430> refund 00:10:34.780 --> 00:10:34.790 align:start position:0% withdraw their own refund the refund 00:10:34.790 --> 00:10:37.120 align:start position:0% withdraw their own refund the refund will<00:10:34.940> already<00:10:35.180> be<00:10:35.300> set<00:10:35.570> to<00:10:35.690> zero<00:10:35.990> so<00:10:36.350> they 00:10:37.120 --> 00:10:37.130 align:start position:0% will already be set to zero so they 00:10:37.130 --> 00:10:41.170 align:start position:0% will already be set to zero so they can't<00:10:37.339> get<00:10:37.520> it<00:10:37.610> back<00:10:39.220> as<00:10:40.220> an<00:10:40.430> improvement<00:10:40.790> the 00:10:41.170 --> 00:10:41.180 align:start position:0% can't get it back as an improvement the 00:10:41.180 --> 00:10:43.800 align:start position:0% can't get it back as an improvement the return<00:10:41.449> value<00:10:41.810> of<00:10:41.990> send<00:10:42.500> could<00:10:42.800> be<00:10:42.920> checked 00:10:43.800 --> 00:10:43.810 align:start position:0% return value of send could be checked 00:10:43.810 --> 00:10:47.350 align:start position:0% return value of send could be checked however<00:10:44.810> a<00:10:45.199> preferred<00:10:45.829> solution<00:10:46.820> is<00:10:47.089> to<00:10:47.240> write 00:10:47.350 --> 00:10:47.360 align:start position:0% however a preferred solution is to write 00:10:47.360 --> 00:10:49.420 align:start position:0% however a preferred solution is to write this<00:10:47.510> contract<00:10:48.050> so<00:10:48.500> that<00:10:48.709> message<00:10:48.890> sender 00:10:49.420 --> 00:10:49.430 align:start position:0% this contract so that message sender 00:10:49.430 --> 00:10:52.689 align:start position:0% this contract so that message sender will<00:10:49.610> pull<00:10:49.850> their<00:10:50.120> refund<00:10:50.540> as<00:10:51.370> opposed<00:10:52.370> to<00:10:52.490> the 00:10:52.689 --> 00:10:52.699 align:start position:0% will pull their refund as opposed to the 00:10:52.699 --> 00:10:56.259 align:start position:0% will pull their refund as opposed to the insecure<00:10:53.240> contracts<00:10:53.779> approach<00:10:54.110> of<00:10:55.269> pushing 00:10:56.259 --> 00:10:56.269 align:start position:0% insecure contracts approach of pushing 00:10:56.269 --> 00:11:01.000 align:start position:0% insecure contracts approach of pushing the<00:10:56.360> refund<00:10:56.720> to<00:10:56.930> recipient<00:10:59.529> this<00:11:00.529> has<00:11:00.740> had 00:11:01.000 --> 00:11:01.010 align:start position:0% the refund to recipient this has had 00:11:01.010 --> 00:11:02.680 align:start position:0% the refund to recipient this has had to<00:11:01.040> be<00:11:01.190> a<00:11:01.220> quick<00:11:01.460> presentation<00:11:01.640> and<00:11:02.270> there's 00:11:02.680 --> 00:11:02.690 align:start position:0% to be a quick presentation and there's 00:11:02.690 --> 00:11:05.050 align:start position:0% to be a quick presentation and there's plenty<00:11:03.170> more<00:11:03.320> information<00:11:04.100> and<00:11:04.370> examples 00:11:05.050 --> 00:11:05.060 align:start position:0% plenty more information and examples 00:11:05.060 --> 00:11:06.280 align:start position:0% plenty more information and examples such<00:11:05.450> as<00:11:05.480> pull<00:11:05.900> over 00:11:06.280 --> 00:11:06.290 align:start position:0% such as pull over 00:11:06.290 --> 00:11:09.880 align:start position:0% such as pull over push<00:11:07.390> denial<00:11:08.390> of<00:11:08.540> service<00:11:08.900> against<00:11:09.260> contracts 00:11:09.880 --> 00:11:09.890 align:start position:0% push denial of service against contracts 00:11:09.890 --> 00:11:13.180 align:start position:0% push denial of service against contracts and<00:11:10.360> re-entrance<00:11:11.360> e<00:11:11.540> that<00:11:12.350> can<00:11:12.530> be<00:11:12.620> found<00:11:12.800> in 00:11:13.180 --> 00:11:13.190 align:start position:0% and re-entrance e that can be found in 00:11:13.190 --> 00:11:20.560 align:start position:0% and re-entrance e that can be found in the<00:11:13.400> repo<00:11:13.700> and<00:11:13.970> wiki<00:11:14.600> page<00:11:18.130> to<00:11:19.130> recap<00:11:19.550> some<00:11:19.910> of 00:11:20.560 --> 00:11:20.570 align:start position:0% the repo and wiki page to recap some of 00:11:20.570 --> 00:11:23.560 align:start position:0% the repo and wiki page to recap some of the<00:11:20.780> main<00:11:20.990> points<00:11:21.790> for<00:11:22.790> smart<00:11:23.150> contract 00:11:23.560 --> 00:11:23.570 align:start position:0% the main points for smart contract 00:11:23.570 --> 00:11:28.090 align:start position:0% the main points for smart contract security<00:11:24.080> are<00:11:24.790> prepare<00:11:25.790> for<00:11:26.000> failure<00:11:27.100> rollout 00:11:28.090 --> 00:11:28.100 align:start position:0% security are prepare for failure rollout 00:11:28.100 --> 00:11:33.060 align:start position:0% security are prepare for failure rollout carefully<00:11:29.470> keep<00:11:30.470> contracts<00:11:31.100> simple<00:11:31.550> and 00:11:33.060 --> 00:11:33.070 align:start position:0% carefully keep contracts simple and 00:11:33.070 --> 00:11:36.250 align:start position:0% carefully keep contracts simple and calling<00:11:34.070> untrusted<00:11:34.760> contracts<00:11:35.420> is<00:11:35.810> always 00:11:36.250 --> 00:11:36.260 align:start position:0% calling untrusted contracts is always 00:11:36.260 --> 00:11:40.270 align:start position:0% calling untrusted contracts is always dangerous<00:11:37.780> the<00:11:38.780> danger<00:11:39.110> may<00:11:39.290> seem<00:11:39.530> small<00:11:39.770> but 00:11:40.270 --> 00:11:40.280 align:start position:0% dangerous the danger may seem small but 00:11:40.280 --> 00:11:43.630 align:start position:0% dangerous the danger may seem small but if<00:11:41.150> an<00:11:41.270> attacker<00:11:41.570> finds<00:11:42.230> and<00:11:42.440> exploits<00:11:43.280> a<00:11:43.430> bug 00:11:43.630 --> 00:11:43.640 align:start position:0% if an attacker finds and exploits a bug 00:11:43.640 --> 00:11:47.430 align:start position:0% if an attacker finds and exploits a bug in<00:11:43.880> a<00:11:43.970> compiler<00:11:44.540> that<00:11:45.040> is<00:11:46.040> targeting<00:11:46.490> the<00:11:46.610> EVM 00:11:47.430 --> 00:11:47.440 align:start position:0% in a compiler that is targeting the EVM 00:11:47.440 --> 00:11:50.220 align:start position:0% in a compiler that is targeting the EVM they<00:11:48.440> are<00:11:48.560> likely<00:11:48.830> to<00:11:49.190> do<00:11:49.280> much<00:11:49.490> more<00:11:49.850> damage 00:11:50.220 --> 00:11:50.230 align:start position:0% they are likely to do much more damage 00:11:50.230 --> 00:11:55.120 align:start position:0% they are likely to do much more damage if<00:11:51.230> their<00:11:51.500> untrusted<00:11:52.040> code<00:11:52.120> is<00:11:53.120> executed<00:11:54.130> then 00:11:55.120 --> 00:11:55.130 align:start position:0% if their untrusted code is executed then 00:11:55.130 --> 00:11:58.690 align:start position:0% if their untrusted code is executed then one<00:11:55.540> where<00:11:56.540> they<00:11:57.050> only<00:11:57.230> have<00:11:57.590> a<00:11:57.830> compiler<00:11:58.280> bug 00:11:58.690 --> 00:11:58.700 align:start position:0% one where they only have a compiler bug 00:11:58.700 --> 00:12:03.670 align:start position:0% one where they only have a compiler bug to<00:11:59.360> work<00:11:59.570> with<00:12:01.330> here<00:12:02.330> are<00:12:02.450> the<00:12:02.480> links<00:12:02.930> to<00:12:03.650> a 00:12:03.670 --> 00:12:03.680 align:start position:0% to work with here are the links to a 00:12:03.680 --> 00:12:06.850 align:start position:0% to work with here are the links to a security<00:12:04.070> resource<00:12:04.610> of<00:12:04.940> the<00:12:05.540> community<00:12:05.960> by 00:12:06.850 --> 00:12:06.860 align:start position:0% security resource of the community by 00:12:06.860 --> 00:12:10.930 align:start position:0% security resource of the community by the<00:12:06.890> committee<00:12:07.310> for<00:12:07.730> the<00:12:08.210> community<00:12:08.660> I<00:12:09.940> also 00:12:10.930 --> 00:12:10.940 align:start position:0% the committee for the community I also 00:12:10.940 --> 00:12:12.640 align:start position:0% the committee for the community I also have<00:12:11.120> slides<00:12:11.390> regarding<00:12:11.810> denial<00:12:12.110> of<00:12:12.230> service 00:12:12.640 --> 00:12:12.650 align:start position:0% have slides regarding denial of service 00:12:12.650 --> 00:12:16.720 align:start position:0% have slides regarding denial of service and<00:12:12.920> pull<00:12:13.520> over<00:12:13.820> push<00:12:14.120> or<00:12:14.840> can<00:12:15.530> take<00:12:15.830> two 00:12:16.720 --> 00:12:16.730 align:start position:0% and pull over push or can take two 00:12:16.730 --> 00:12:20.530 align:start position:0% and pull over push or can take two questions<00:12:17.210> in<00:12:17.420> the<00:12:17.540> remaining<00:12:18.670> three<00:12:19.670> minutes 00:12:20.530 --> 00:12:20.540 align:start position:0% questions in the remaining three minutes 00:12:20.540 --> 00:12:27.280 align:start position:0% questions in the remaining three minutes any<00:12:21.440> questions<00:12:25.990> ok 00:12:27.280 --> 00:12:27.290 align:start position:0% any questions ok 00:12:27.290 --> 00:12:30.300 align:start position:0% any questions ok I<00:12:28.190> can<00:12:28.520> quickly<00:12:28.700> go<00:12:28.970> through<00:12:29.000> a<00:12:29.270> couple<00:12:29.810> more 00:12:30.300 --> 00:12:30.310 align:start position:0% I can quickly go through a couple more 00:12:30.310 --> 00:12:37.120 align:start position:0% I can quickly go through a couple more so<00:12:33.370> so<00:12:34.370> quickly<00:12:34.670> in<00:12:34.940> this<00:12:35.120> a<00:12:36.040> denial<00:12:37.040> of 00:12:37.120 --> 00:12:37.130 align:start position:0% so so quickly in this a denial of 00:12:37.130 --> 00:12:38.950 align:start position:0% so so quickly in this a denial of service<00:12:37.190> against<00:12:37.820> the<00:12:37.910> contract<00:12:38.420> there<00:12:38.870> are 00:12:38.950 --> 00:12:38.960 align:start position:0% service against the contract there are 00:12:38.960 --> 00:12:41.410 align:start position:0% service against the contract there are many<00:12:39.110> ways<00:12:40.010> that<00:12:40.070> pitfalls<00:12:41.030> that<00:12:41.090> you<00:12:41.210> can 00:12:41.410 --> 00:12:41.420 align:start position:0% many ways that pitfalls that you can 00:12:41.420 --> 00:12:44.770 align:start position:0% many ways that pitfalls that you can encounter<00:12:41.720> them<00:12:42.370> one<00:12:43.370> is<00:12:43.580> an<00:12:44.000> unexpected 00:12:44.770 --> 00:12:44.780 align:start position:0% encounter them one is an unexpected 00:12:44.780 --> 00:12:46.660 align:start position:0% encounter them one is an unexpected throw<00:12:45.020> which<00:12:45.290> is<00:12:45.320> what<00:12:45.620> this<00:12:45.740> code<00:12:46.490> example 00:12:46.660 --> 00:12:46.670 align:start position:0% throw which is what this code example 00:12:46.670 --> 00:12:50.110 align:start position:0% throw which is what this code example here<00:12:47.180> is<00:12:47.240> about<00:12:47.560> but<00:12:48.560> hitting<00:12:49.520> the<00:12:49.730> block<00:12:49.910> s 00:12:50.110 --> 00:12:50.120 align:start position:0% here is about but hitting the block s 00:12:50.120 --> 00:12:52.390 align:start position:0% here is about but hitting the block s limit<00:12:50.450> is<00:12:50.570> another<00:12:50.840> example<00:12:51.400> iterating 00:12:52.390 --> 00:12:52.400 align:start position:0% limit is another example iterating 00:12:52.400 --> 00:12:53.800 align:start position:0% limit is another example iterating through<00:12:52.430> an<00:12:52.700> unbounded<00:12:53.180> to<00:12:53.330> raise<00:12:53.480> another 00:12:53.800 --> 00:12:53.810 align:start position:0% through an unbounded to raise another 00:12:53.810 --> 00:12:56.470 align:start position:0% through an unbounded to raise another example<00:12:54.820> misunderstanding<00:12:55.820> gas<00:12:55.970> refunds 00:12:56.470 --> 00:12:56.480 align:start position:0% example misunderstanding gas refunds 00:12:56.480 --> 00:13:01.300 align:start position:0% example misunderstanding gas refunds will<00:12:57.050> also<00:12:57.380> cause<00:12:58.370> the<00:12:58.520> same<00:12:58.730> issue<00:13:00.010> so<00:13:01.010> in 00:13:01.300 --> 00:13:01.310 align:start position:0% will also cause the same issue so in 00:13:01.310 --> 00:13:06.310 align:start position:0% will also cause the same issue so in this<00:13:01.490> example<00:13:02.060> contract<00:13:03.460> the<00:13:04.460> the<00:13:05.240> line<00:13:06.110> with 00:13:06.310 --> 00:13:06.320 align:start position:0% this example contract the the line with 00:13:06.320 --> 00:13:08.800 align:start position:0% this example contract the the line with the<00:13:06.410> throw<00:13:06.680> means<00:13:07.490> that<00:13:07.820> a<00:13:08.060> current<00:13:08.450> leader 00:13:08.800 --> 00:13:08.810 align:start position:0% the throw means that a current leader 00:13:08.810 --> 00:13:12.310 align:start position:0% the throw means that a current leader that<00:13:09.440> refuses<00:13:09.980> payment<00:13:10.430> will<00:13:11.420> permanently<00:13:11.930> be 00:13:12.310 --> 00:13:12.320 align:start position:0% that refuses payment will permanently be 00:13:12.320 --> 00:13:13.429 align:start position:0% that refuses payment will permanently be the<00:13:12.470> leader 00:13:13.429 --> 00:13:13.439 align:start position:0% the leader 00:13:13.439 --> 00:13:16.460 align:start position:0% the leader and<00:13:14.179> the<00:13:15.179> throw<00:13:15.419> cannot<00:13:15.749> be<00:13:15.899> removed<00:13:16.199> in<00:13:16.349> this 00:13:16.460 --> 00:13:16.470 align:start position:0% and the throw cannot be removed in this 00:13:16.470 --> 00:13:20.509 align:start position:0% and the throw cannot be removed in this case<00:13:16.829> because<00:13:17.579> otherwise<00:13:18.109> some<00:13:19.109> other<00:13:19.519> person 00:13:20.509 --> 00:13:20.519 align:start position:0% case because otherwise some other person 00:13:20.519 --> 00:13:24.229 align:start position:0% case because otherwise some other person can<00:13:20.939> do<00:13:21.869> a<00:13:21.899> call<00:13:22.679> depth<00:13:23.039> attack<00:13:23.429> against<00:13:23.939> bid 00:13:24.229 --> 00:13:24.239 align:start position:0% can do a call depth attack against bid 00:13:24.239 --> 00:13:27.349 align:start position:0% can do a call depth attack against bid and<00:13:24.799> what<00:13:25.799> that<00:13:25.979> means<00:13:26.279> is<00:13:26.609> that<00:13:26.669> they<00:13:27.149> will 00:13:27.349 --> 00:13:27.359 align:start position:0% and what that means is that they will 00:13:27.359 --> 00:13:29.539 align:start position:0% and what that means is that they will get<00:13:27.569> to<00:13:27.629> be<00:13:27.899> the<00:13:28.019> current<00:13:28.379> leader<00:13:28.619> without 00:13:29.539 --> 00:13:29.549 align:start position:0% get to be the current leader without 00:13:29.549 --> 00:13:32.899 align:start position:0% get to be the current leader without having<00:13:29.939> had<00:13:30.089> to<00:13:30.269> pay<00:13:30.449> the<00:13:30.779> previous<00:13:31.289> leader<00:13:31.909> so 00:13:32.899 --> 00:13:32.909 align:start position:0% having had to pay the previous leader so 00:13:32.909 --> 00:13:34.279 align:start position:0% having had to pay the previous leader so in<00:13:33.029> this<00:13:33.119> example<00:13:33.299> you<00:13:33.629> can<00:13:33.869> just<00:13:34.049> remove 00:13:34.279 --> 00:13:34.289 align:start position:0% in this example you can just remove 00:13:34.289 --> 00:13:39.079 align:start position:0% in this example you can just remove throw<00:13:34.619> and<00:13:35.659> for<00:13:36.659> the<00:13:36.749> final<00:13:37.609> tip<00:13:38.609> that<00:13:38.849> we<00:13:38.970> only 00:13:39.079 --> 00:13:39.089 align:start position:0% throw and for the final tip that we only 00:13:39.089 --> 00:13:42.319 align:start position:0% throw and for the final tip that we only have<00:13:39.269> time<00:13:39.419> for<00:13:39.479> here<00:13:39.959> is<00:13:40.309> to<00:13:41.309> change<00:13:42.059> this 00:13:42.319 --> 00:13:42.329 align:start position:0% have time for here is to change this 00:13:42.329 --> 00:13:47.989 align:start position:0% have time for here is to change this into<00:13:42.689> a<00:13:42.839> pull<00:13:43.109> over<00:13:43.259> push<00:13:44.629> system<00:13:45.629> and<00:13:46.369> so<00:13:47.369> the 00:13:47.989 --> 00:13:47.999 align:start position:0% into a pull over push system and so the 00:13:47.999 --> 00:13:51.589 align:start position:0% into a pull over push system and so the left<00:13:48.179> side<00:13:48.299> is<00:13:48.749> the<00:13:49.549> auction<00:13:50.549> contract<00:13:51.329> that 00:13:51.589 --> 00:13:51.599 align:start position:0% left side is the auction contract that 00:13:51.599 --> 00:13:54.739 align:start position:0% left side is the auction contract that was<00:13:51.749> shown<00:13:51.989> this<00:13:52.439> couple<00:13:53.069> of<00:13:53.099> slides<00:13:53.369> ago<00:13:53.749> this 00:13:54.739 --> 00:13:54.749 align:start position:0% was shown this couple of slides ago this 00:13:54.749 --> 00:13:57.739 align:start position:0% was shown this couple of slides ago this time<00:13:55.019> instead<00:13:55.379> of<00:13:55.499> doing<00:13:55.589> a<00:13:56.069> sent<00:13:56.459> to<00:13:56.879> the 00:13:57.739 --> 00:13:57.749 align:start position:0% time instead of doing a sent to the 00:13:57.749 --> 00:14:00.079 align:start position:0% time instead of doing a sent to the recipient<00:13:58.079> it<00:13:58.859> just<00:13:59.189> the<00:13:59.459> contract<00:13:59.879> just 00:14:00.079 --> 00:14:00.089 align:start position:0% recipient it just the contract just 00:14:00.089 --> 00:14:03.889 align:start position:0% recipient it just the contract just keeps<00:14:00.299> track<00:14:00.569> of<00:14:00.629> the<00:14:00.929> refunds<00:14:01.319> that<00:14:02.749> that<00:14:03.749> are 00:14:03.889 --> 00:14:03.899 align:start position:0% keeps track of the refunds that that are 00:14:03.899 --> 00:14:06.319 align:start position:0% keeps track of the refunds that that are owed<00:14:04.079> to<00:14:04.619> whoever<00:14:04.919> the<00:14:05.189> highest<00:14:05.489> bidder<00:14:06.119> is 00:14:06.319 --> 00:14:06.329 align:start position:0% owed to whoever the highest bidder is 00:14:06.329 --> 00:14:10.389 align:start position:0% owed to whoever the highest bidder is and<00:14:07.099> then<00:14:08.099> on<00:14:08.249> the<00:14:08.339> right<00:14:08.519> side<00:14:08.789> is<00:14:09.149> the<00:14:09.349> pull 00:14:10.389 --> 00:14:10.399 align:start position:0% and then on the right side is the pull 00:14:10.399 --> 00:14:13.849 align:start position:0% and then on the right side is the pull method<00:14:11.399> where<00:14:12.149> everything<00:14:13.019> works<00:14:13.229> based<00:14:13.619> off 00:14:13.849 --> 00:14:13.859 align:start position:0% method where everything works based off 00:14:13.859 --> 00:14:18.199 align:start position:0% method where everything works based off message<00:14:14.369> sender<00:14:14.819> and<00:14:15.949> by<00:14:16.949> doing<00:14:17.159> this<00:14:17.399> an 00:14:18.199 --> 00:14:18.209 align:start position:0% message sender and by doing this an 00:14:18.209 --> 00:14:19.849 align:start position:0% message sender and by doing this an attacker<00:14:18.539> can<00:14:18.779> basically<00:14:19.169> only<00:14:19.589> attack 00:14:19.849 --> 00:14:19.859 align:start position:0% attacker can basically only attack 00:14:19.859 --> 00:14:35.380 align:start position:0% attacker can basically only attack themselves<00:14:22.399> so<00:14:24.919> that's<00:14:25.919> it 00:14:35.380 --> 00:14:35.390 align:start position:0% 00:14:35.390 --> 00:14:44.830 align:start position:0% you 00:14:44.830 --> 00:14:44.840 align:start position:0% 00:14:44.840 --> 00:14:46.900 align:start position:0% you