Why is it impossible to derive public key from address?


The address is only 160-bits. The public key is 257-bits. So there's no way to go from an address to a public key -- information is missing.

The shortest hash with sufficient security is 160-bits. So Bitcoin uses a 160-bit hash as an address to make the address as short as possible. However, there is no known public key scheme that is sufficiently secure with only 160-bit public keys. So the public key couldn't be used as an account address without making the account longer.

However, the public key is needed to verify a signature. So when you perform a transaction to claim coins sent to an account, you must provide the public key. When validating the transaction, the public key is checked to ensure it has the correct hash (matching the account) and then the signature is checked to ensure it is valid for the transaction and made with the supplied public key. From that point on, the public key corresponding to the address is publicly...

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An "Account" in the Ripple Consensus Ledger represents a holder of XRP and a sender of transactions. The core elements of an account are:

An identifying address, such as rf1BiGeXwwQoi8Z2ueFYTEXSwuJYfV2Jpn An XRP balance. Some of this XRP is set aside for the Reserve. A sequence number, starting at 1 and increasing with each transaction sent from this account. No transaction can be included in a ledger unless the transaction's sequence number matches its sender's next sequence number. A history of transactions that affected this account and its balances. One or more ways to authorize transactions, possibly including:A master key pair intrinsic to the account. (This can be disabled but not changed.) A "regular" key pair that can be rotated. A signer list for multi-signing. (Stored separately from the account's core data.)

In the ledger's data tree, an account's core data is stored in the AccountRoot ledger node type. An account can also be the owner (or partial owner) of...

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Explain Why It Is Impossible to Derive An Analytical Formula For Valuing American Puts.

Explain why it has proved impossible to derive an analytical formula for valuing American Puts, and outline the main techniques that are used to produce approximate valuations for such securities

Investing in stock options is a way used by investors to hedge against risk. It is simply because all the investors could lose if the option is not exercised before the expiration rate is just the option price (that is the premium) that he or she has paid earlier. Call options give the investor the right to buy the underlying stock at the exercise price, X; while the put options give the investor the right to sell the underlying security at X. However only America options can be exercised at any time during the life of the option if the holder sees fit while European options can only be exercised at the expiration rate, and this is the reason why American put options are...

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A very interesting question, I have never been tempted to use static generic classes, but at least it seems possible.

In the context of declaring extension methods, you cannot only declare extension methods for a certain generic type (such as IEnumerable) but also bring the type parameter T into the equation. If we agree to treat IEnumerable and IEnumerable as different types, this makes sense on a conceptual level too.

Being able to declare your extension methods in a static generic class would save you repeating your type parameter constraints over and over again, in effect grouping all extension methods for IEnumerable where T : IComparable together.

According to the specification (citation needed), extension methods can only be declared in static not-nested and not-generic classes. The reason for the first two constraints are fairly obvious:

May not carry any state as it's not a mixin, just syntactic sugar. Must have the same lexical scope as the type...
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As with UE4 4.7, the same problem remains with UE4 4.8: it is impossible to extend from scenecapturecomponent.

Extending from it with a new Blueprint class is not a choice when you create one.

Extending from it with a new C++ Class seems possible, as you can create one, then you can start compiling but compile always fails. And if you try to compile again in Visual Studio, you get the same errors and compiles fails too.

When i say that compiles fails, i mean that even if you add absolutely no code and compile, it fails. So i'd like to know what the problem is and if it is intended to be fixed.

I know that i can write directly in this class and build entirely the editor from source code but on my computer, building UE4 takes 90 minutes. So it would be SO appreciated if it was...

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I can't speak to the implementations out there like Armory and Brainwallet, as I haven't directly used those. But I do understand the protocol and the math well enough to ELI5 this. :3

In order to receive Bitcoin money, you first have to create a private key (which you keep private), and from that a matching address. You can create these offline, even by doing the math on paper if you wish (it's pretty hard math but not impossible for the very patient ;3)

The blockchain doesn't know you've done this. Not yet. But you can't get any money if you never share that public address with people asking for dough. So you emerge from your no electricity concrete bunker with only the public address, and you post that online asking for moneys.

The blockchain still doesn't know yet, all you've done is informally told people about your address. But now they can pay you and that's how the blockchain gets wind of your address.

Now the blockchain records that all kind of...

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Ever try putting toothpaste back into the tube?

1. welcome to LinuxQuestions.org. i am a newbie to linux and have learned more about linux in this forum then i have in all the books and web pages i have read over the time ive played with linux. ppl here may give you something that is over your head, but if you ask them to back up and give you some more basic instructions they have always done so for me. very helpful IMHO, and i look forward to coming to these forums so i can learn more.

2. if you are using basic DSL connection that is either PPPoA or bridged ATM, as those are the only other 2 opptions for DSL other then the one flavor you stated is not part of it, then you can connect directly to the net with linux.

were i am now is on a PPPoA ADSL connection behind a Zyxel 642R router. my RH9 box connected from before the first boot with zero problems. at...

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There is more to a bitcoin wallet than just the address itself. It also contains the public and private key for each of your bitcoin addresses. Your bitcoin private key is a randomly generated string (numbers and letters), allowing bitcoins to be spent. A private key is always mathematically related to the bitcoin wallet address, but is impossible to reverse engineer thanks to a strong encryption code base.

If you don’t back up your private key and you lose it, you can no longer access your bitcoin wallet to spend funds.

As mentioned, there is also a public key. This causes some confusion, as some people assume that a bitcoin wallet address and the public key are the same. That is not the case, but they are mathematically related. A bitcoin wallet address is a hashed version of your public key.

Every public key is 256 bits long — sorry, this is mathematical stuff — and the final hash (your wallet address) is 160 bits long. The public key is used to ensure you...

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This is a follow-up to

my 2005 post on the same subject

which I believe sets a personal record for the longest time between parts of a series. (Of course, I didn't know it was a series when I started it.) Please read the previous article in this series, as this post assumes knowledge of part one.


OK, now that you've read that, it's clear why you can only access a protected member from an instance of an object known to be of a type at least as derived as the current context. You can therefore deduce the answer to the question asked to me by a (very polite) reader this morning: Why did this code compile in C# 2.0 but give an error in C# 3.0?

public abstract class Item{
private Item _parent;
public Item Parent {
get { return _parent; }
protected set { _parent = value; }
public class Bag:Item{
private List list = new List();
public void Add(Item item)
item.Parent = this; //...

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Question 7 from the Impossible Quiz 2 contains a task that says "Use the right key!". Below it there are 4 keys: a small dark-grey one, a slightly bigger silver one, a strange-looking light blue and green key, and lastly a smaller gold key. Next to them is a door handle with eyes and a keyhole that serves as its mouth, complete with a tongue and some teeth.

Seems like a complicated question, but the truth is that none of them are the correct key. In fact, you're not actually looking for a key to insert in that keyhole. Rather, what the question wants you to do is to use the right arrow key of your keyboard. Press it in order to proceed to the next question.

Mobile version

Due to a lack of an in-game keyboard, this question was replaced on the iOS version of The Impossible Quiz 2. The new question says "What is the principal part of a horse?". The option boxes say "Legs", "Mane", "Body" and "Head". The correct answer is "Mane", because it's homophone of the...

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Wallets are containers for private keys, usually implemented as structured files or simple databases. Another method for making keys is deterministic key generation. Here you derive each new private key, using a one-way hash function from a previous private key, linking them in a sequence. As long as you can re-create that sequence, you only need the first key (known as a seed or master key) to generate them all. In this section we will examine the different methods of key generation and the wallet structures that are built around them.

Nondeterministic (Random) Wallets

In the first bitcoin clients, wallets were simply collections of randomly generated private keys. This type of wallet is called a Type-0 nondeterministic wallet. For example, the Bitcoin Core client pregenerates 100 random private keys when first started and generates more keys as needed, using each key only once. This type of wallet is nicknamed "Just a Bunch Of Keys," or JBOK, and such wallets are...

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Why is it impossible to stop thinking, to render the mind a complete blank?
—John Hendrickson, via email

Barry Gordon, professor of neurology and cognitive science at the Johns Hopkins University School of Medicine, replies:

Forgive your mind this minor annoyance because it has worked to save your life—or more accurately, the lives of your ancestors. Most likely you have not needed to worry whether the rustling in the underbrush is a rabbit or a leopard, or had to identify the best escape route on a walk by the lake, or to wonder whether the funny pattern in the grass is a snake or dead branch. Yet these were life-or-death decisions to our ancestors. Optimal moment-to-moment readiness requires a brain that is working constantly, an effort that takes a great deal of energy. (To put this in context, the modern human brain is only 2 percent of our body weight, but it uses 20 percent of our resting energy.) Such an energy-hungry brain, one that is constantly...

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Doing our part and trusting in God is the key to opening the “windows” of heaven

The book of Hebrews contains a verse that each Christian should pay close attention to.

Hebrews 11:6
And without faith it is impossible to please God, because anyone who comes to him must believe that he exists and that he rewards those who earnestly seek him.

To understand this verse we first have to understand that faith is “trust.” Once we understand that, we can understand why it is impossible to please God without faith. If we could please God without faith, we could please God without trusting Him. Have you ever had someone distrust you? Have you ever had someone you had helped again and again distrust you? That is a very painful experience.

No one has given more, loved more, or done more for people than God. He is constantly loving and helping people, and even sent His only begotten Son to be tortured and killed for us. If after all He has done, someone still...

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I've found the answer on Serverfault: Create a public SSH key from the private key?

The option -y outputs the public key:

ssh-keygen -y -f ~/.ssh/id_rsa > ~/.ssh/id_rsa.pub

As a side note, the comment of the public key is lost. I've had a site which required the comment (Launchpad?), so you need to edit ~/.ssh/id_rsa.pub and append a comment to the first line with a space between the comment and key data. An example public key is shown truncated below.

ssh-rsa AAAA..../VqDjtS5 ubuntu@ubuntu

For keys that were added to the SSH Agent (a program that runs in the background and avoids the need for re-entering the keyfile passphrase over and over again), you can use the ssh-add -L command to list the public keys for keys that were added to the agent (via ssh-add -l). This is useful when the SSH key is stored on a smartcard (and access to the private key file is not...

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Have you ever seen this error:

The site's security certificate is not trusted! You attempted to reach https://www.site.com, but the server presented a certificate issued by an entity that is not trusted by your computer's operating system. This may mean that the server has generated its own security credentials, which Chrome cannot rely on for identity information, or an attacker may be trying to intercept your communications.You should not proceed, especially if you have never seen this warning before for this site.

This abstruse error means that Windows has not been configured to trust certificates from the website you’re trying to access.

This can happen when you start using a new computer because the OS doesn’t have the root certificates from any (or some) trusted authorities; therefore, it fails to automatically accept those certificates.

I’ll explain what all this means in a moment but the bottom line is that if you’re missing certain trusted...

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A man is as old as his arteries (Dr. Thomas Sydenham, 1680)
Just because (almost) every medical doctor thinks that atherosclerosis is incurable and it is not unanimously proven that it might regress, doesn't necessarily mean it's true.

In 1998, I began recommending to my friends and acquaintances the micronutritional artery cleansing. My recommendation was based on the belief that it could help save their lives. For me, "artery self-cleansing" represented everything that natural, targeted cardiovascular support should be to stop and reverse the catastrophic effects of atherosclerosis.

Today, that belief soundly confirmed by years of experience is stronger than ever. That's why I'm sharing this concept with you. Once you know what to do and how to do it you will be in better control of the quality of your cardiovascular health, provided you wish so. As someone once said, don't be afraid to go out on a limb; that's where the fruit is.

- Andrew Mierzejewski,...
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Friends and Citizens:

The period for a new election of a citizen to administer the executive government of the United States being not far distant, and the time actually arrived when your thoughts must be employed in designating the person who is to be clothed with that important trust, it appears to me proper, especially as it may conduce to a more distinct expression of the public voice, that I should now apprise you of the resolution I have formed, to decline being considered among the number of those out of whom a choice is to be made.

I beg you, at the same time, to do me the justice to be assured that this resolution has not been taken without a strict regard to all the considerations appertaining to the relation which binds a dutiful citizen to his country; and that in withdrawing the tender of service, which silence in my situation might imply, I am influenced by no diminution of zeal for your future interest, no deficiency of grateful respect for...

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