Blockchain tutorial 6: Digital signature

[@TellaTrix]

The way you explain this term is awesome

[@stefanoruns]

Excellent video. At last somebody who goes beyond saying "the sender signs the transaction with his/her private key to generate a digital signature that allows the receiver to verify identity and message", and actually show how this is done!!!!

[@zhenminliu]

Hi, this tutorial on digital signature is getting into the complex part of block chain. Tutorial 6 needs to be view several times for a proper understanding. Not easy, but it's intriguing. Thanks for the tutorial.

[@RahulSaini-wu2rl]

hi mobilefish , you really a greate explainer, i tried many videos and artical but you are awesome

[@deepakguru7791]

Thanks for clearing explaining the confusing topic.

[@mfahad5]

U are amaizng mannn... U are Making crypto easier by your lectures thanks alot man. High respect for u 🌹

[@2030beau]

very nice ... thanks for the demo and very clear.

[@darrenditto9824]

Great explanation!

[@ianbates_]

Thank you! Brilliant! Bravo! This really helped!

[@MastaChafa]

Thank you! I was looking for this kind of technical explanation!

[@prayanshsrivastava1810]

This series is youtube gold

[@fariman-kashani]

best explanation

[@Murugavel-ee123]

Is there will be a validation for this document by other nodes!?

[@_darkerblue]

have watched this multiple times,but couldn't understand one part - Alice first hashes the data then uses pvt key to encrypt the hash but why hash the data in the first place when you can simply encrypt the data?

[@dec41rus]

Thank you!

[@user-rp9iis1en6h]

thank you very much.

[@gloriagain7739]

always grateful~~

[@fakhredin100]

In 2:24, he says the data which is the document is now hashed which gives hash value for comparison. My question is how Bob has the actual data? wasn't he supposed to be the receiver? According to the explanation, so-far he has only decrypted the digital signature which gave him the original hash value which is not the actual data. Can someone please explain. Thank you!

[@salarhussain6189]

bob has the actual data. bob is only trying to verify that the sender of data is alice and the data is not changed in any way. So bob rehashes the actual data and decrypts the digital signature using alice's public key to get the hash that will be compared

[@KurtBogaert]

@@salarhussain6189 which actually means Alice will send 3 pieces of information to Bob : the document unencrypted, her digital signature AND the public key (to decrypt the digital signature to get hash A and to hash the text to get hash B). Right?

[@coronhardman9718]

Bob receives two separate things: 1) the document and 2) the digital signature, separately. Remember, the digital signature is encrypted with both the document and private key together.He puts the 1) document through the hash and creates that hash value. And then he decrypts the 2) signature with her public key), which reveals another hash value for the document. Then he compares both of those values to make sure that they are exactly the same.

[@0xcoder542]

Thank you for the video. Would you mind also explain to use the Web3.eth.sign in this case? Much appreciated.

[@Mobilefish]

I have created some Web3 API examples: www.mobilefish.com/download/ethereum/web3api.html several months ago (I am not sure if the example still works, as web3 API evolve very fast). But to be honest I have not use Web3.eth.sign in a real use case..

[@0xcoder542]

Many Thanks. Yes, Indeed. The version 1.0 is releasing soon.

[@gianlucacucchietti5533]

Thanks!!

[@vvsatyadv7053]

Different different algorithms (MD5 and sha1) give same hash function ? While checking (encryption and decryption) digital signature.? Is it possible if encryption with MD5 and decryption with sha1 algorithms ? Thanks for your tutorial.

[@Mobilefish]

1) MD5 and SHA1 are different hash functions and do not produce the same output. MD5 output size 128 bits SHA1 output size 160 bits 2) MD5 and SHA1 are hash functions, which means for example a document can be hashed to produce a unique "fingerprint". Which means you cannot create the document with this "fingerprint". Hash functions are one-way functions. MD5 and SHA1 are NOT symmetric or asymmetric key algorithms.

[@leeladrttit8802]

What are the requirements for implementation

[@baatar]

Is non-repudiation really enforceable under this scheme? Somebody could have had their private key stolen from them.

[@hachimitsuchai]

How come sometimes I need to import Crypto and sometimes I don't? i.e. sometimes just the "from Crypto.Hash import RSA" works without importing Crypto and sometimes I do have to import Crypto. Also curious why don't you use RSA 2048 instead of 1024? Isn't it more secure?

[@Mobilefish]

It is recommended that you use RSA 2048. Computers are getting stronger, key lengths less than 2048 bits are now considered deprecated by the NIST. Key use prediction: 1024-bit is OK until 2010, then 2048-bit until 2030, then 3072-bit after that. Please keep in mind, the increase in key length corresponds to an exponential increase in CPU usage. 2048 bit key lengths can take upwards of 4 times as much CPU usage compared to 1024 bit key lengths.

[@hachimitsuchai]

ok and when you write "from Crypto.Hash import RSA" why don't you need to import Crypto since Crypto is a python module? Thanks.

[@Mobilefish]

Sorry, do not know the answer.

[@jiaxinl.5097]

Thank you. is it possible we can have the slides?

[@Mobilefish]

All slides can be found at: www.mobilefish.com/developer/blockchain/blockchain_quickguide_tutorial.html

[@RahulSaini-wu2rl]

i am working on web3 and try to use web3.eth.call() but struggling to find a right way to apply this one

[@Mobilefish]

Sorry, but I have never used that api call before. I did not find a use for it...

[@blacksea3677]

Please give me the file SHA256, RSA, Random. thank you

[@web3dopamine]

wher can i get the python files which you have shown in this video and previous video of cryptography ?