Blockchain - Sicherheit auch ohne Trust Center

1. 00:00Let's take a look at ourselves, how the data exchange takes place in the Bitcoin system.
2. 00:06This is a network, our peer-to-peer network, where the participants in the Bitcoin system are then distributed.
3. 00:14And this data exchange was essential, the data exchange was yes, the transactions,
4. 00:21not only between the two participants concerned, but the transactions were collected from all participants in the network.
5. 00:30All participants had the chance to were also in competition to form there blocks, and these blocks must also be propagated over the network,
6. 00:39so that each participant is able to verify, if what the other participants did was all right.
7. 00:48That's the Nakamoto consensus.
8. 00:51So, so the question, if now a participant wants to join such a net - It is spread all over the world, the circle of participants is not predetermined, as we do in such a typical peer-to-peer network -
9. 01:04then questions arise, two questions namely:
10. 01:06First question, how can I join the system? how can I start acquiring Bitcoins and pay with Bitcoins?
11. 01:16And the second question to answer, how about exchanging data over such a large network? what must be taken into account, for example with regard to temporal sequences?
12. 01:28Let us start with the first question, namely accession:
13. 01:32The DNS seed is the starting point for joining the Bitcoin blockchain. DNS is the Domain Name System that is established on the Internet.
14. 01:48and there ensures that the names that we humans can read and speakable names can be converted into Internet addresses.
15. 01:55These are combinations of numbers in a completely fixed scheme, with the usual Internet protocol 4, these are 4 groups of numbers, which in the Internet Protocol form the exact address of the computer,
16. 02:11So the DNS makes sure that if you have on your browser HPI.de or openHPI.de, then the packages
17. 02:22should be sent to the computer with the command to HPI.de respectively to openHPI.de. belonging internet address in this scheme.
18. 02:31And Seed, that's like seed from which this network grows.
19. 02:39The DNS seed are Internet addresses of servers, which enable new participants to join the Bitcoin network.
20. 02:55This server, if it was then addressed via the Internet address, if the participant is there now to the wants to become a member of this Bitcoin network,
21. 03:06then the server sends it a random List of selected participants who are already in the network.
22. 03:18And via these participants he can now connect to the network, can therefore begin to initiate transactions itself, can be the target of transactions,
23. 03:31can also receive the other transactions, which are distributed over the whole network and which each participant collects.
24. 03:42The blocks he can form, he can compete with others, to form such blocks.
25. 03:48The blocks that are then attached to the chain, must be distributed over the network.
26. 03:53This is done via these randomly selected participants in the network, that's what DNA Seed looks like.
27. 04:03What about the neighbourhood relations now?
28. 04:08So every knot has neighbors, for the newbie it's the neighbors, that are selected at random from the list he has there from a server in the DNS Seed.
29. 04:22That's the one he's actively connected to, and then, of course, there are neighborhood nodes that have connected to him.
30. 04:31So these are the neighbors of a node, a participant in the Bitcoin network, typically there are so 7 neighbors that a participant has.
31. 04:41So most of the knots here, they have these seven neighbors, but there are a few knots that have a lot of neighbors.
32. 04:50What situation the reason for this?
33. 04:53Well, the ones who build the blocks, the miners, who, of course, want to get their blocks very fast. - this is a competition, this block production -
34. 05:02who of course want their blocks very fast across the Bitcoin network.
35. 05:08And the more neighbors they have. the block into the network, it has to be distributed, so append it to the blockchain.
36. 05:19And accordingly also, many neighbors help that this survey about the transactions, the individual transactions end up very quickly with him.
37. 05:28The large amount but the end users in the network, who only has the idea of being redundantly connected to the network, so typically they get along fine with the 7 knots.
38. 05:44Now the question is, so if most knots have few neighbors, how can the data now, the transactions, the blocks,
39. 05:55distributed efficiently in the network, that they get to each participant as quickly as possible.
40. 06:02Because this phase of data distribution, this is the phase where mistakes can occur,
41. 06:07where it's not yet certain, it's now an accepted transaction, already welded in a block that was considered valid, or is that another message that's still on the move.
42. 06:24I may catch it again - hopefully you'll see this through the color - how that's spreading all the time.
43. 06:31And this time as an example of a data distribution - and this is interesting - you just saw it in the logs,
44. 06:41How's that? Infections spread very quickly, or even uncontrolled, rumors spread very quickly.
45. 06:50Maybe if you were to follow that in this picture, so the messages, the transaction information, the blocks are distributed over the Bitcoin network.
46. 07:04And there are protocols, communication protocols, that can be used there, the so-called Gossip protocols. - Gossip means rumor -
47. 07:15and there is simply the communication in each case with a selection of random neighbors,
48. 07:22and then you can prove in probability theory, that the data, that is, the transactions, the blocks, whatever's being sent in the Bitcoin network.
49. 07:32will most likely arrive in logarithmically many steps, to every node in the network.
50. 07:40So that this distribution over these n nodes in the network, is achieved through a logarithmic process.
51. 07:49It's gradual, it takes time, compared to n, logarithm n is very small, but it's the same, it's not zero,
52. 07:58so this data transfer is an important point.
53. 08:01If we take a look at this now, a message is generated, a transaction has been executed, or a block has been created,
54. 08:11that's then sent to the randomly selected neighbors, and in this way the whole network is reached.
55. 08:20So here's this messaging, joining the Bitcoin network, in the Bitcoin blockchain network.
56. 08:30In other blockchains this is usually very similarly organized, although there may well be differences.
57. 08:39But we are talking about the very first blockchain here this second week,
58. 08:43that in the context of the Bitcoin system. has been established and developed.

To enable the transcript, please select a language in the video player settings menu.