Cryptography i courserahttps www.coursera.org learn crypto
Various fields, industries, and sectors are looking for specialists in cryptocurrency—including banking, accounting, oil and gas, insurance, and retailers, with particular growth in media, logistics, and legal compliance. As for specific titles related to cryptocurrency, learners can look forward to becoming Blockchain Developers, Splunk Developer, Crypto Community Manager, Cryptocurrency Researcher, and others.
Learners can enjoy exploring cryptocurrency with instructors specializing in Computer Science, Financial Management, Business, and other disciplines. Course content on cryptocurrency is delivered via video lectures, readings, quizzes, and other types of assignments. Cryptocurrency in its basic form is a form of digital currency, a type of payment that is increasingly used online and exchanged for goods and services. Because of this, you might want to have experience in using digital payments over the internet.
You might also want to have experience in knowing how businesses pay for goods and services from another company. More often, online payments are used. Soon, paying in cryptocurrency rather than a national country-backed currency will be how digital payments will be made.
Cryptocurrency is also seen as an investment in a future type of business model, in which retail and institutional investors invest in the future of cryptocurrency. This course was suggested by my mentor to allow me to get in depth knowledge in cryptography. The course conveys all the latest protocols and mechanisms. Frequently Asked Questions When will I have access to the lectures and assignments?
Access to lectures and assignments depends on your type of enrollment. If you take a course in audit mode, you will be able to see most course materials for free. To access graded assignments and to earn a Certificate, you will need to purchase the Certificate experience, during or after your audit.
If you don't see the audit option: The course may not offer an audit option. You can try a Free Trial instead, or apply for Financial Aid. The course may offer 'Full Course, No Certificate' instead.
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But, if there are zero data at the end of the block of data, we can use this PKS 7 to encode a padding character with pattern as follows. If there's only one byte to be pad, we'll put 01 there, hexadecimal 01 there. If there are two character to be pad, we will put 02 02 hexadecimal for it and so on.
If you have a nine byte, then 09 09 09 and so on. And here, we show how small code, the two-line code, that actually measure how many padding character need to be, and then the next very small code actually repeat the pattern with a single statement. What happen to the 16 byte last plaintext block, happen to be having 01 as the last byte? Now, we will be confused, right? At the end, when we decrypt, is that a 16 byte data with 01 as the data byte, or is that a 16 byte with 01 as a data byte?
Solution here is to add one block 16 byte all zero at the end. Just try to figure out the reason behind it. AES has three different key size, , , How can we generate such bit patterns for the key with precise bit lines? Kind of tricky here. One easy solutions, actually kind of amazing, we can actually use md5 functions, sha message digest function. How about bit key? I will let you figure out as an exercise what kind of function you should use or taking some of the message function and then do some sort of bit mask, remove the remaining bit, that's the hint.
PHP's solution is using the hash functions. The hash function provided in PHP allow you to tag three parameter. The first parameter actually indicate the hashing function. In this case, we put in the first parameter as a string, sha The hashing function, understand we are using message digest function with sha hashing. The second parameter is the mnemonic, the key, or we can call it just the parent tag we try to do hashing.
Same thing for md5. So just md5 taking two parameter, the first parameter is that mnemonic content or the mnemonic key in our case. It will produce bit. Similar to other language also, we'll provide this set of function. In Java, for example, they provide a class called KeyGenerator. Typically, we declare variable such as kg and we assign with KeyGenerator that instance.
The parameter we provide there is talking about the kind of key we are going to generate. For example, in this case, we are generate key for AES. And then, with this return handle kg, we can call the method, is method init and provide the parameter which is the key length. It can be , it can be In this case, we use and that also provide a solution to the question I just posed to you. And after we set up the kg, we then using kg. In this case, bit. And what is IV size actually return?
The hint here is, see the figure below. And it turns out, it's completely doable. And we'll talk about anonymous digital cash later on. Just to give you a hint, I'll say that the way we do it is basically by making sure that if Alice spends the coin once then no one knows who she is, but if she spends the coin more than once, all of a sudden, her identity is completely exposed and then she could be subject to all sorts of legal problems.
And so that's how anonymous digital cash would work at a high level and we'll see how to implement it later on in the course. Another application of cryptography has to do with more abstract protocols, but before I speak the general result, I want to give you two examples.
So the first example has to do with election systems. So here's the election problem. And voters vote for these parties. So for example, this voter could have voted for party zero, this voter voted for party one. And so on. So in this election, party zero got three votes and party two got two votes.
So the winner of the election, of course, is party zero. But more generally, the winner of the election is the party who receives the majority of the votes. Now, the voting problem is the following. The voters would somehow like to compute the majority of the votes, but do it in such a way such that nothing else is revealed about their individual votes. So the question is how to do that? And to do so, we're gonna introduce an election center who's gonna help us compute the majority, but keep the votes otherwise secret.
And what the parties will do is they will each send the funny encryption of their votes to the election center in such a way that at the end of the election, the election center is able to compute and output the winner of the election. However, other than the winner of the election, nothing else is revealed about the individual votes. The individual votes otherwise remain completely private. Of course the election center is also gonna verify that this voter for example is allowed to vote and that the voter has only voted once.
But other than that information the election center and the rest of the world learned nothing else about that voter's vote other than the result of the election. So this is an example of a protocol that involves six parties.
In this case, there are five voters in one election center. These parties compute amongst themselves. And at the end of the computation, the result of the election is known but nothing else is revealed about the individual inputs. Now a similar problem comes up in the context of private auctions. So in a private auction every bidder has his own bid that he wants to bid. And now suppose the auction mechanism that's being used is what's called a Vickrey auction where the definition of a Vickrey auction is that the winner is the highest bidder.
But the amounts that the winner pays is actually the second highest bid. So he pays the second highest bid. Okay, so this is a standard auction mechanism called the Vickrey auction. And now what we'd like to do is basically enable the participants to compute, to figure out who the highest bidder is and how much he's supposed to pay, but other than that, all other information about the individual bids should remain secret.
So for example, the actual amount that the highest bidder bid should remain secret. The only thing that should become public is the second highest bid and the identity of the highest bidder. So again now, the way we will do that is we'll introduce an auction center, and in a similar way, essentially, everybody will send their encrypted bids to the auction center. The auction center will compute the identity of the winner and in fact he will also compute the second highest bid but other than these two values, nothing else is revealed about the individual bids.
Now, this is actually an example of a much more general problem called secure multi-party computation. Let me explain what secure multi-party computation is about. So here, basically abstractly, the participants have a secret inputs to themselves. So, in the case of an election, the inputs would be the votes. In the case of an auction, the inputs would be the secret bids. And then what they would like to do is compute some sort of a function of their inputs.
Again, in the case of an election, the function's a majority. In the case of auction, the function happens to be the second highest, largest number among x one to x four. And the question is, how can they do that, such that the value of the function is revealed, but nothing else is revealed about the individual votes? So let me show you kind of a dumb, insecure way of doing it. What we do is introduce a trusted party. And then, this trusted authority basically collects individual inputs.
And it kinda promises to keep the individual inputs secret, so that only it would know what they are. And then, it publishes the value of the function, to the world. So, the idea is now that the value of the function became public, but nothing else is revealed about the individual inputs.
But, of course, you got this trusted authority that you got to trust, and if for some reason it's not trustworthy, then you have a problem. And so, there's a very central theorem in crypto and it really is quite a surprising fact. That says that any computation you'd like to do, any function F you'd like to compute, that you can compute with a trusted authority, you can also do without a trusted authority.
Let me at a high level explain what this means. Basically, what we're gonna do, is we're gonna get rid of the authority. So the parties are actually not gonna send their inputs to the authority. And, in fact, there's no longer going to be an authority in the system. Instead, what the parties are gonna do, is they're gonna talk to one another using some protocol.
Such that at the end of the protocol all of a sudden the value of the function becomes known to everybody. And yet nothing other than the value of the function is revealed. In other words, the individual inputs is still kept secret. But again there's no authority, there's just a way for them to talk to one another such that the final output is revealed.
So this is a fairly general result, it's kind of a surprising fact that is at all doable. And in fact it is and towards the end of the class we'll actually see how to make this happen. Now, there are some applications of cryptography that I can't classify any other way other than to say that they are purely magical. Let me give you two examples of that. So the first is what's called privately outsourcing computation. So I'll give you an example of a Google search just to illustrate the point.
So imagine Alice has a search query that she wants to issue. It turns out that there are very special encryption schemes such that Alice can send an encryption of her query to Google. And then because of the property of the encryption scheme Google can actually compute on the encrypted values without knowing what the plain texts are.
So Google can actually run its massive search algorithm on the encrypted query and recover in encrypted results. Google will send the encrypted results back to Alice. Alice will decrypt and then she will receive the results. But the magic here is all Google saw was just encryptions of her queries and nothing else. And so, Google as a result has no idea what Alice just searched for and nevertheless Alice actually learned exactly what she wanted to learn.
Okay so, these are magical kind of encryption schemes. They're fairly recent, this is only a new development from about two or three years ago, that allows us to compute on encrypted data, even though we don't really know what's inside the encryption. Now, before you rush off and think about implementing this, I should warn you that this is really at this point just theoretical, in the sense that running a Google search on encryption data probably would take a billion years.
But nevertheless, just the fact that this is doable is already really surprising, and is already quite useful for relatively simple computations.
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