Signing transactions - Blockchain in Javascript (part 4)

Transactions on a blockchain have to be signed with a private key. This makes sure that people can only spend coins if they have the private key of their wallet.
In this video we will refactor our Javascript blockchain so that it will only accept signed transactions.
We'll use the secp256k1 elliptic curve to generate a keypair. The same algorithm used in Bitcoin. But you can use other algorithms as well.
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[@simplyexplained]

If you were in the live stream and asked some questions -> ask them again here in the comments. KZbin closed the chat :(

[@maximebeaudoin4013]

#1: why did it have to be JS, i'm kinda new to programming but the syntax differs to c# in some areas and i find it less intuitive. #2 why visual studio code and not visual studio? #3 would you consider creating a simple ui to implement the functionalities created here while at the same time addressing the subjet of p2p?

[@andresm9051]

Really good content, keep going! I would like to ask, how to create ,sign and transaction using web3 and ethererum blockchain

[@senteria]

Hello there, great video, however I get result that my chain is not valid and balance is -10

[@nevcheart]

@@senteria I got this as well, my error was in minePendingTransactions()..missing a couple of lines

[@peopleyoumustknow1325]

Very helpful

[@alvinyanson]

For anyone having -10 balance in the first run, see 8:05, he added a rewardTx object in the minePendingTransactions method and push in the pendingTransactions array. I guess he forgot to discuss about it in the video. Anyways thanks Xavier.

[@TamunutonyeHart]

Thanks!

[@daa82]

Yup, couldn’t figure out how he got $90 since the $100 should have been a pending reward that should become part of his balance after a 2nd mining occurs. Should have been -10.

[@gregorystevens5173]

Gr8 catch. Thanks Alvin!

[@shin4ko131]

thank you

[@vsemsimpa4507]

It still incorrect, as he performs the transaction first and only then he receives 100 as a reward for mining the block with the transaction that makes his balance -10. So, ideally, his addTransaction call on line 13 gets rejected, as there are not enough funds. Only after he mines the block and receives the reward, he should be able to transfer some coins.

[@davidwhite4258]

P2P Bro we dying for that to be implemented

[@JamesFrederickstech]

this video is pure gold! thanks for doing this. im going to go back and watch all the previous videos now.

[@asmrtist9058]

Love your Blockchain in Javascript series. Indeed, I learned Angular JS only so I could continue with part 5 of your series.

[@pdhakeph]

I thoroughly enjoyed this learning block chain through implementation. Thank you

[@v85216192]

One of the best tutorials I have seen in CS learnings!

[@rfmemarian8550]

I loved the video. That was the best way to describe block chain to a developer. Thank you for such an effort!

[@AAA-bo1uo]

Been watching youtube for YEARS now, you are literally the *_FIRST_* I *_EVER_* subscribe to! I was able to take everything from first episode in this series to this one in 1 sitting :D Short, precise and on point with an actual clean and clear code, that is scarce! I'm still having problems with signatures but that's because I never dealt with them before.. I never interacted with public and private keys directly before. I'll probably understand it as soon as I code it in myself. Most appreciated mate! Keep up the good work!

[@simplyexplained]

Wow thanks a lot man! I feel honored to be the first creator you subscribed to. Keep coding & keep learning!

[@Boggothefroggo32123]

@@simplyexplained I keep getting the error TypeError: Transaction is not a constructor, how do I fix this?

[@desertfox9613]

By far the best explanation of cryptocurrency technology.

[@alonsourena_]

Excellent video, I really learned a lot, keep going bro. Hope you can keep going with this series

[@Leoninmiami]

You are a stud my friend! thanks for taking the time to put this together!

[@killianpinier5074]

Thank you so much !! I really liked the way you organised your videos. I learned a lot thanks to you ! Keep going 😍

[@GS-xg7sl]

Great tutorials for beginners who want to learn about this new exciting technology. Can you also do a video on Smart Contracts in this series.

[@Plrang]

Simply Fantastic Explained you mean

[@mydentalscaler3462]

Thank you a lot brother! You made it easy and simple to understand! Thanks again

[@mual77]

Another excellent video!! Keep up the good work.

[@EduardsSilins]

You are the best! Thanx for this tuttorial...

[@javedahmed1276]

Great stuff man. Please create videos on creating a smart contract

[@zeerobug]

Great video. Now every time you mine, you get a reward, even though there are no txs! Can't wait for chapter 5

[@simplyexplained]

Hmm, this is also the case in Bitcoin I guess. Blocks are added on a steady interval and they don't have to include transactions.

[@tomoya0650]

An interesting blockchain 101. Like it.

[@thenoizy]

Well explained! Thanks

[@miscellaneous9932]

You are the best mate! Cheers!

[@marekczyz3483]

Wow! It is really valuable content!

[@vivekjain010184]

fantastic explanation!

[@christopherequin]

thank you for this new video.

[@ipungdevacademy]

Thanks you are my hero

[@amritkanoi8804]

Dude you are legend !

[@kinahecate9168]

Thanks so much for this

[@IQ88612]

hi, thank you very much for your videos but, what is the peer library in python to that elliptic library in JS?

[@alphansomurray6535]

Good Morning, do you have a tutorial that shows how you would facilitate the block chain code to manage IoT devices like a camera?

[@janhim]

really nice ...

[@Sico10001]

outstanding

[@applicable_simplicity]

One of the important validation is to check if the transaction is send out an amount larger than the current balance. In blockchain, how to check this validation, could you please advise?

[@filipstamcar6553]

You make transaction hash from from address, to address and amount. What is they are same in multiple transactions? Fox example if I send same amount of coins to same address multiple times?

[@simplyexplained]

Aha! You're right, how silly of me! I will include a timestamp to make it unique. Thanks!

[@alvinyanson]

For anyone having 90 balance but chain is false please check your minePendingTransaction method. let block = new Block(Date.now(), this.pendingTransactions, this.getLatestBlock().hash); make sure to add this.getLatestBlock().hash.

[@EliteJLad]

bro thank you sooooo much

[@oguzhany2710]

thank you so much

[@vijayantpawar3137]

When I run it, I got -10 and valid? False . How to fix this please reply.

[@shaheermohammed2865]

Hello Savjee,You are really great.Your way of teaching is excellent.Still i have a doubt.I run your code and even if i don't have any balance in my wallet i am able to make a transaction and sometimes it shows negative values in balance.Can you do something to check the balance in our wallet before making transaction?

[@simplyexplained]

Absolutely! There are still a lot of checks you can implement to make it better as a cryptocurrency

[@jayantkhandelwal7326]

Hi, I have a doubt, as we have removed the reference to previous hash when we removed addblock method, then how are we implementing a blockchain without having previous hash value?

Great video, the signing of transactions was a missing part in the chain. Thanks! By the way, you forgot to re-hash the second block after you changed the amount of the transaction. Hopefully it still wouldn’t be valid due to the incorrect signature at that point.

[@TJ80ify]

yeah mine came out isValid == false

[@GodSavetheWest]

How can that error be fixed??

[@emarciobdirector]

@@GodSavetheWest I also would like to know.

[@TamunutonyeHart]

yeah, i noticed it the same result, invalid

[@alaaradwan7242]

Is this package has a random function that may generate tow pairs of public and private keys with the same values ??!!

[@lukedavitt5357]

at the end of the video, shouldn't the balance be -10, since the reward would still be a pending transaction and not processed yet? ( the same reason why about 5 minutes earlier you had to mine twice to see the reawrd in your balance )

[@elsilossos626]

👏👏👏

[@ailton.duarte]

How to save transation, to not lose it when de program goes down, like when u run de program, how can i save de data from a blockchain? Or the p2p network is the database, if just one is online, we will have all data save!

[@ethernetwink7230]

is there a library like elliptic for python??

[@waqasiqbal3594]

Where do all the transactions are actually saved in the block chain?

[@dinudin7133]

Great explanantion, but at 17:03 i got chain false. though the balance show 90. any idea on this?

[@vlaming6818]

You need to add this.getLatestBlock().hash to the block variable in the minePendingTransaction function.

[@sohaibsoussi9042]

let block = new Block(Date.now(),this.pendingTransactions,this.getLatestBlock().hash)

[@cristiang4774]

What is the difference between a private key and a public key? If only the private key is unique does it mean that you can send coins to multiple wallets that share the same public key at once? And if they are both unique (the private and the public keys) why do we need both and not just the public one (considering it is longer)?

[@simplyexplained]

Private and public key are both unique. The public key is freely shareable with anyone. It's the address of your wallet. The private key on the other hand is used to sign transactions. It proves that the owner of the wallet is taking money out of it. It should be kept secret so only you can spend your coins.

[@subhambanerjee6334]

hey when i am running the code it shows an error that it should have from and to adrees

[@iBaldie]

How do you release your code so it’s decentralised and can be used? How is this done? Great tutorials!

[@simplyexplained]

Not sure I understand your question. You usually just put your code up on a website so everyone can download it. That's how all cryptocurrencies do it. They let anyone download their client from their site.

[@mauriciowkjhef]

Should 'fromWallet' balance be checked before pushing into pending transaction?

[@simplyexplained]

Yes it should be!

[@abigaildien3252]

I finally got the terminal working now my testing is way off....lol

[@gizemcelik6240]

Hey there Savjee! i have a quick question. I am trying to understand the whole Bitcoin topic and your videos are super great. But when i am coding along i am getting an error msg that says that my block.transaction in the getBalanceOfAddress method is not iterable. i have double checked everything and its not different from your code. any ideas on where the issue is?

[@simplyexplained]

Is your version of nodejs up-to-date?

[@gizemcelik6240]

@@simplyexplained it actually wasnt, now everything is working. thank you!

[@aliharmanansari7148]

Great Video, but I didn't understand that how can some Wallet send 10 coins when it has 0 balance. From where is the initial balance is coming form, and can a wallet have negative balance?

[@anonymousnearseattle2788]

Maybe all of Bitcoin's starting coins were purchased by the Federal Reserve! 😁

[@asmrtist9058]

9:39 "We want to verify that the hash of this block" - shouldn't it be "hash of this transaction"?

[@newsquest1169]

You can build a blockchain on dpow block chain

[@asdeq2006]

why don't we need to take account of the nonce in checking the validity of the blockchain in this example? Otherwise, someone may easily tamper the data in the blockchain and re-calculate the hash of every block in the blockchain rapidly.

[@Boggothefroggo32123]

I get an error that says TypeError: Transaction is not a constructor how do I fix this?

[@rockey9045]

Can anybody tell me where the source to this presentation are?

[@auroraiiit5765]

Kind request. i am unable to figure out why there is an error ( No signature in this transaction) even when my code is the same as here and even matches source code. have checked it several times .... pls help

[@ElChe-Ko]

Aren't you checking anywhere if the account has enough money to allow the transaction?

[@asmrtist9058]

16:42 How does the balance of 90 make sense? Doesn't the subsequent block have to be mined for the reward to be accounted for? At least that's how my blockchain works now and I have pretty much copied your code.

[@brianjianzhao3238]

Hey, I am having the same issue here. I followed his implementation. Rewards transaction is not chained at the moment when it is created. It will only be push into the block and chained when next time the mining process completes. I think there is something wrong with here.

[@pisanvs]

You can push the transaction to the pendingTransactions array before mining it.

[@zephirusvideos]

Someone knows how can I implement the "signTransaction" method in java?

[@florencebeukes287]

So “From wallet” can be anybody’s wallet?

[@technologybanglavideo6696]

Which IDE have you used for coding ?Please details

[@kshitijvengurlekar1192]

vscode

[@technologybanglavideo6696]

@@kshitijvengurlekar1192 if you create a video which is how to install.. Which IDE and basic running mechanism.. It will be very helpful...for windows operating system..

[@kshitijvengurlekar1192]

@@technologybanglavideo6696 1. I would highly recommend you to use Linux 2. There are already many videos about how to install VSCode on Windows/Linux.

[@x0r1k]

You've left a big issue: anyone can pretend that he get a transaction from null address. That's why reward transaction should go to the current block, no to the pending list

[@simplyexplained]

Yes, this was fixed on GitHub. Can't update the video though.

[@florencebeukes287]

Can I run this code on BlockChain ?

[@JaneDoe-od4ep]

I cant get the trick with the public key and the wallet address. You say the transaction isnt valid if my wallet address != public key ... ??? Like I install electrum and create a wallet with address like 'ab1d'. Then I generate a pair of keys like public: '123f' and private: 'r45t'. So 'ab1d' != '123f'. No my transactions are ever valid? Dafak?

[@algrinotop7340]

But how do we sign it on a website

[@incog4600]

Hey when I check if the chain is valid normally it returns false. How can I fix this?

[@aaryamangupta]

Yes

[@sohaibsoussi9042]

let block = new Block(Date.now(),this.pendingTransactions,this.getLatestBlock().hash)

[@miQize]

If a null sender address is valid for a transaction, what stops users from just sending new transactions to themselves from a null address?

[@fsra16]

I have the same question

[@ravard4336]

the solution could be to add a verification that allows ONLY-ONE transaction from a null address per block so the miner will take it for himself 🤔 (I don't know if it is implemented that way in real blockchains it's just an idea)

[@TT-jq3kj]

sir say ec is not const help me

[@ArnoneWilliam]

What if someone sends 1 coin to me, and i duplicate the message of that transaction? They have already signed that transaction, so i can steal all of their coins by duplicating that transaction over and over.

[@ravard4336]

Like the balance of the sender some verifications seem to not be implemented to facilitate the understanding of the whole concept. a transaction is unique on the blockchain and it's defined by its hash, before adding a new transaction, miners have to go through the all ledger to ensure another transaction with the same hash does not already exist I presume

[@fungchan9216]

It shows node:internal/modules/cjs/loader:936 throw err; ^ when I run in terminal, anyone know why?

[@SirJul]

Did you cd src?

[@whoamiwhoami1300]

Min 4:42

[@bspanda98]

Do you make a video how to fork neo.

[@simplyexplained]

Probably not

[@bspanda98]

Simply Explained - Savjee why not it is legal and easy to held

[@simplyexplained]

I don't think people should randomly fork cryptocurrencies to start their own. There is a lot of knowledge needed to maintain your own cryptocurrency. I know it's legal, but I don't think a video would be a good idea.

[@bspanda98]

but you need to make it one for knowledge purpose am I right

[@as269]

still get balance is 0 ?!

[@jessedampare1379]

I keep getting -10 when i run the code🤔

[@SarthakGupta]

17:09 Balance: -10 Is Chain Valid: true Why???

[@dillonstreator4159]

I have this as well. It should be -10 because the 100 reward for mining is still in the pending transactions and will not be rewarded until the next block is successfully mined.

[@victorgeorgiev4079]

most likely you have an error with minePendingTransactions() and for the validation most likely you are not checking the correct lenght in isChainValid()

[@stocksandblocks9661]

bitcoin is gonna change our lives. We help people to know it

[@winniepooh2533]

@Simply Explained I created my own crypto from this video series, I did it for getting more into js, can I show and share it to my friends just to make them understand the working of crypto? I need your permission because I used your code to make my crypto, and I will offcourse give your channel a huge credit.

[@snaplu4683]

forgot to add this.signature in Transaction class

[@mental_block]

I had a doubt, if we can see public key of others, can we not create key object using ec.keyfrompublic and then extract the private key of that person?plz reply

[@simplyexplained]

No, the keyfrompublic method wont be able to extract the private key. It will just allow you to encrypt a message for the person who has the private key.

[@mental_block]

@@simplyexplained thanks for clearing my doubt

[@primerib7377]

Does this really work?

[@simplyexplained]

It's a very basic implementation, but yes ;)

[@lyferp]

bro you made the same code in the start as in the 3 vid

[@mmm-cake]

So the more pertinent danger at least with BTC are the thousands of “dormant” wallets which randomly become active when the price spikes …. lol you all know good damn well a rug pull is always ahead no matter what the asset is

[@cliffbartle3772]

The same people that wrote these programs are the same or similar characters that wrote the MCAS program for the Boeing 737 Max, get my drift?? And the tax programs and all yje government programs, and we just swallow it.

[@pisanvs]

And??

[@alendhassan6301]

amazing, but why you are ignoring (nonce)? in all your videos?

[@simplyexplained]

Nonce has been implemented in the first video.

[@alendhassan6301]

@@simplyexplained actually in the second video you did by incrementing it in mining, thank you for that, but I mean, nonce is used so the other blocks in the chain can confirm the new mined block to be able to join them in the chain, right?, I don't see this part, hopefully you understand my saying ? thanks

[@simplyexplained]

Hmm I don't follow. Nonce is just used for mining and to calculate the hash of the block (AFAIK).

[@michaelthedriver242]

Command Prompt: "cannot find module 'elliptic'.

[@youssrakhattab5332]

me too, did you find any solution for that?????

[@aofeizhang8735]

Am I too stupid to understand this? Learned entry level java before...