WEBVTT 0 00:00.810 --> 00:01.750 Hello guys! 1 00:01.860 --> 00:05.220 In this lecture we'll talk about hashes! 2 00:05.220 --> 00:14.130 You'll find them in many areas of computer science. Hashes are a critical part of best art systems digital, 3 00:14.130 --> 00:22.220 signatures, security certificates, blockchain technology cryptocurrencies like Bitcoint and Ethereum 4 00:22.590 --> 00:29.730 or even how the supermarket POS verifies the PIN of your credit card when you want to pay for 5 00:29.730 --> 00:30.440 something. 6 00:30.970 --> 00:40.240 Let's dive deeper into hashes! A hashing algorithm is a cryptographic function that takes an input, runs it 7 00:40.320 --> 00:49.310 through some magical mathematical processes and then creates a unique output called hash.The output 8 00:49.310 --> 00:58.760 hash is sometimes called message digest checksum or cryptographic fingerprint. The input of the hash 9 00:58.760 --> 01:06.620 function can be literally anything from binary information like a file a packet a single character to 10 01:06.620 --> 01:15.100 a word or a phrase. I'd like to show you a practical example using a Linux machine (since it already has 11 01:15.190 --> 01:20.680 all applications needed to calculate hashes). If you are using Windows 12 01:20.680 --> 01:23.710 you need to install the required tools. 13 01:24.130 --> 01:32.410 So I'm executing sha256sum /etc/passwd 14 01:32.460 --> 01:41.630 Let's take a deeper look at the command, its argument and its output. The hash function or the hash algorithm 15 01:41.630 --> 01:54.110 used is sha256; sha stands for Secure Hash Algorithm, is pronounced sha, and is in fact a family of more 16 01:54.110 --> 01:59.020 more hash protocols. Sha256sum 17 01:59.050 --> 02:07.920 is the Linux application, the tool that implements the hash protocol which as I said is sha256. 18 02:10.150 --> 02:19.120 /etc/passwd is the input of the hash function and this string written in hexadecimal or base 16 19 02:19.420 --> 02:29.490 is the hash of the input. We can simply say that sha256 hash of password file is this value, 20 02:30.650 --> 02:38.490 the value you are seeing right now. You should know that all hash algorithms are public. They are like a public 21 02:38.490 --> 02:49.370 math formula that anyone can see and use; for example sha256 is part of a bigger family of hash algorithms 22 02:49.640 --> 02:55.280 called sha-2. You can read more about them even on Wikipedia. 23 02:58.530 --> 03:06.330 Look, this is the pseudo code for a sha256 algorithm; you can implement it in any programming language. 24 03:07.980 --> 03:08.880 It's public! 25 03:11.350 --> 03:20.290 Other well known hash algorithms besides sha-2 are md5 and sha1 which are considered insecure 26 03:20.560 --> 03:21.760 and obsolete. 27 03:21.760 --> 03:23.820 Let’s see the hash of Linux 28 03:23.840 --> 03:27.050 word calculated with md5 and sha1: 29 03:27.090 --> 03:32.210 echo -n the word "linux" 30 03:32.320 --> 03:34.830 You can write anything you want. 31 03:34.900 --> 03:37.260 | md5sum 32 03:37.270 --> 03:48.880 -n is used not to add a new line; by default the echo command ends a new line at the end. 33 03:49.010 --> 03:52.790 I want to calculated the hash only of this word. 34 03:55.570 --> 03:59.230 And the hash calculated using sha1 35 04:02.340 --> 04:03.520 That's the hash. 36 04:03.700 --> 04:04.490 They are written 37 04:04.500 --> 04:12.610 always in hexadecimal numbers; Other very secure and new hash 38 04:12.660 --> 04:25.260 algorithms are sha-3 or Keccak, Blake2b and RIPEMD-160. Blake2b is used by Ethereum 2.0 and RIPEMD-160 39 04:25.270 --> 04:34.710 is one of the two hash functions used by Bitcoin. And they were never 40 04:34.710 --> 04:46.920 hacked! Another way to calculate a hash is using the openssl command like this: 41 04:46.920 --> 04:53.930 openssl dgst -sha3-256 42 04:53.960 --> 05:00.070 This is the hash algorithm and the file for example /etc/passwd 43 05:00.280 --> 05:00.880 Okay. 44 05:00.990 --> 05:02.400 This is the hash. 45 05:02.640 --> 05:08.780 This is different than this one because it's another hash algorithm used. 46 05:09.030 --> 05:12.000 Or you can calculate the hash of a string 47 05:12.000 --> 05:12.690 this way: 48 05:13.200 --> 05:25.040 echo -n "linux" | openssl dgst -rmd160 49 05:25.100 --> 05:36.030 That's the hash; you can see a list of all hash algorithms implemented in openssl 50 05:36.190 --> 05:39.670 by executing openssl and then help. 51 05:47.330 --> 05:52.450 These are all hash algorithms implemented in openssl. 52 05:57.020 --> 05:58.660 Let's try another example! 53 05:58.750 --> 06:07.310 Let’s calculate the hash of word “linux” using this time the sha512 algorithm, in different ways: 54 06:07.580 --> 06:08.940 In the first example 55 06:08.990 --> 06:20.320 I'll be using the sha512sum command like this: echo -n "linux" | sha512sum 56 06:20.520 --> 06:25.260 This is the hash; Or using the openssl command. 57 06:32.850 --> 06:44.790 This is the hash! I can also use an online tool to calculate the hash; I am selecting sha512 and the 58 06:44.790 --> 06:46.060 input Linux. 59 06:46.060 --> 06:55.600 And this is the hash and we notice something very important: no matter how we calculate the hash if we 60 06:55.600 --> 07:00.610 use the same algorithm we get the same hash, the same output. 61 07:00.610 --> 07:01.990 Look at this output 62 07:04.640 --> 07:08.210 and look at the same output here. 63 07:08.390 --> 07:16.010 This is one of the properties of hashes which is called determinism and it means that the output of 64 07:16.010 --> 07:19.610 a hash function doesn't change between runs. 65 07:19.610 --> 07:23.400 It's in fact the same mathematical process applied. 66 07:24.300 --> 07:32.220 These hash functions are also called one way functions. Another important property of a hash function 67 07:32.550 --> 07:39.690 is that it's very easy to compute the hash from the given input but infeasible to find out the original 68 07:39.690 --> 07:47.840 input from the resulting hash; or if you have the hash you are seeing right now there is no way to find 69 07:47.840 --> 07:55.790 out what information, what word, file or packet, has given that hash. 70 07:55.790 --> 07:58.660 Note that hashing is not encryption. 71 07:58.700 --> 08:01.540 There is no secret, no key in hashing.