Homework on Public and Private Keys - Questions

Blockchain and Bitcoin 101
#1411

Elliptic curve is a mathematical function used in modern encryption :slight_smile: explaining how exactly it works would be a bit out of the scope of this topic :slight_smile: you can get more info about it in the Cryptography and Privacy coins course or read about it online :slight_smile:

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#1412
  1. Describe the concept of public and private key with your own words.

a public key is derived from the private key. Each public key can be used to derive a bitcoin address. A private key is required to sign a message or to decrypt a message that has been encrypted with the associated public key.

  1. What 2 use-cases can public key cryptography be used for?

Send value, sign message

#1413

Email services don’t use encryption (at least not by default). Some email providers use end to end encryption, but only if you sent the email to the user with the same provider.
For example sending email from protonmail to protonmail will encrypt the email, sending from protonmail to gmail will not.

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#1414

I’m not really a mathematician. But private keys are used to create signatures (so P to S). You can then verify it using the public key :slight_smile:

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#1415

You can’t really send value using cryptography, we use TCP for that :stuck_out_tongue: but you can encrypt the value before sending it :slight_smile:

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#1416

  • Describe the concept of public and private key with your own words.
    A public key can be generated by anyone and shared openly accross public networks. The public key is used to encrypt information. *edited
    A private key is used to generate the public key which is a one way function and does not allow for reproduction of the private key. It can then decrypt the information generated with the public key. *edited

  • What 2 use-cases can public key cryptography be used for?
    Sending and receiving messages.
    Creating secure digital signatures.

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#1417

You are correct :slight_smile: there are a few issues with the terminology I would fix if you don’t mint :slight_smile: Keys don’t store any value, they just encrypt it. The data can then be stored anywhere be it on a website or on the blockchain :slight_smile:

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#1418

Ahh yes, excellent point. That is indeed how I imagined it but chose the wrong word. Thanks! :slight_smile:

#1419
  1. In encryption, the computer first generates a random number. This is the private key. The private key is then used to generate a new number, that is the public key. It is possible to go from private key to public key, but it is impossible to go from public key to private key. The private key is meant to keep private, and is used to decrypt information or digital signatures.
  2. Public key cryptography has two use cases. The first one is encryption. This can for example be used to keep messages private from the public so that only the intended recipient can read the information. The other use case is digital signatures, as in cryptocurrencies.
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#1420
  1. A public key is derived from a private key, that is simply a random number. The public key is used as public information that one can shared without thinking twice with everyone. As said the public key is strictly linked to its private key such that its owner can easily rely on the fact that only him/her can effectively redeem the property of that public key (unless one lost the private key)
  2. First use is to encrypt data/message. Take two persons Alice and Bob. Alice want to communicate with Bob some personal things, but the only way to do that is through a unsafe public network, thus, B generate a random number “private key” from which derived a second number “public key”. B holds for himself the private key, but share to Alice (through the unsafe network) the public key. At this point Alice use Bob’s public key to encrypt her message, and send it to Bob. Since no one can decrypt the message only with the public key, the encrypted message arrive safely to Bob, that finally will use his private key to redeem the property of used public key and decrypt the message.
    Second use cases is as “digital signature”. Digital signature is used in order to know the owner of a message or transaction. Is like a digital identification number that can be used as follow:
    Alice generate a private key and use that to sign a message. Bob then use the shared public key of Alice to verify if that message/transaction signed really comes from Alice. Of course this is possible only because the two keys are mathematically linked between each other and no one can derived the private key starting from a public key, as said already seen is unfeasible.
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#1421

#1. you have a random number that you can use to sign messages but its a super long number. that’s called a private key. you take that private key and do something with it and make a public key. you put the public key on the web for everyone to see. they can send stuff to you through the public key but only you can open it will your private key. its like a weird mail box. the mailman has a key to open the drop box. anyone can use the key. but only you have the key to open the mail box itself and open and get the mail.

#2. being able for someone to give you messeges that are encrypted and only you can decript them with your private key, to prove if you wrote something.

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#1422

You can also use the key for digital signatures, where you can sign a message with the private key and others can use the public key to prove you were the one that wrote the message :slight_smile:

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#1423
  1. Your private key is a random number and from this the public is derived. You can use these to encrypt and decrypt information sent.
  2. Encryption - to safely send information on a public network.
    Digital signatures - used in Bitcoin for sending and receiving transactions
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#1424

1. Public key cryptography allows someone to send their public key in an open, insecure channel.
Having a friend’s public key allows you to encrypt messages to them. Your private key is used to decrypt messages encrypted to you

2. What 2 use-cases can public-key cryptography be used for?

The most obvious application of a public key encryption system is in encrypting communication to provide confidentiality – a message that a sender encrypts using the recipient’s public key can be decrypted only by the recipient’s paired private key.

Another application in public-key cryptography is the digital signature. Digital signature schemes can be used for sender authentication.

Further applications built on this foundation include: digital cash, password-authenticated key agreement, time-stamping services, non-compete protocols, etc

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#1425

  1. Private keys are, used for spending the sending bitcoins, they are used for sending bitcoin transactions, Public keys are generated from private keys. User A will send a btc transactions to user B by signing it with there private key. Everyone in the network will be able to prove that this transaction is legitimate, by using the signature and the public key from User A.
    Also for sending encrypted messages the sender uses the receivers public key to encrypt the message and then the receiver can decrypt the message with there private key.

  2. Encrypting messages and digital signatures.

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#1426

A private key is generated by your computer which creates a random large number
A public key is generated from this number which will be shared in order to receive message that can only be read by the owner of the private key.
The 2 cases for public keys are encryption and digital signatures

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#1427

  1. The private key is generated by the author, who then creates a public key to give them the option of sharing securley with others should they wish. Once shared with others, they can see the public key only and not the private key, that is kept safe by the author, therefore a secure way of sending information over a network.

  2. Sending documents and information and sending funds securely without the need for a 3rd party.

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#1428

Homework on Public and Private Keys - Questions

  1. Describe the concept of public and private key with your own words.
    A. Private & Public keys are used in cryptography to encrypt and decrypt data. data can be signed using private keys and public keys can be used ti verify that signature
  2. What 2 use-cases can public key cryptography be used for?
    A. Encryption and Digital Signatures
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#1429
  1. Public keys can be seen by anyone and this is derived from the private key, you cannot derive a private key from a public key, hence it’s only a one-way function.
  2. The 2 use cases are for encryption of data and digital signatures.
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#1430

  1. Describe the concept of public and private key with your own words.
    Private Key is a random number and should be secretly kept - in no case show or give this to other
    people. The Public Key derives from the private key and can be distributed everywhere.
    A legitimate pair of public and private Key make the Bitcoin address.

  2. What 2 use-cases can public key cryptography be used for?
    The use cases are:

  3. Encryption - You can encrypt a message with the public key of a person and the recipient can decrypt it with his/her private key - encryption is not really used in Crypto

  4. Digital signature

You use your Public Key as an address that people can send funds to. The private key basically grants you access to those funds.

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