Homework on Public and Private Keys - Questions

[emurzello]

So the private keys are essentially your Digital signature on the blockchain, by that I mean as your private key is used as an identifier. so people know who is sending / making a transaction?

[Cestrada]

1. A public key which is seen by all is derived from a private key which is a random string of numbers seen only by its owner. The private key is statistically almost impossible to duplicate.
2. The 2 use cases for public key cryptography are encryption which means sending private messages on the unsecured network and digital signatures which verifies the sender.

[Gabiwan68]

Public & Private Key - Homework
1- All begins with the generation of your private key which is a random and very large number stored in your computer. Then from your private key, your public key is generated. This an be accessed by anyone to use it to send encrypted messages to you. ANd only you can read thjose messages by using your private key
2- Public and Private key are used in two manners:

• To encrypt information
• to Sign digitally and verify identities

[Francine]

1. Describe the concept of public and private key with your own words.
Any person can encrypt a message using the someone’s public key , but that encrypted message can only be decrypted with the receiver’s private key. Anyone can encrypt messages using a public key, but only the holder of the paired private key can decrypt such a message. The security of the system depends on the secrecy of the private key, which must not become known to any other.

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

Public key cryptography - 2 major use cases:

1. Encryption
2. Digital signatures – identification, integrity of a particular message, (used in crypto)

This is essential in Blockchain because we don’t have a central authority that keeps track of all accounts. Instead each wallet is based on the Public and Private key.
Each wallet is built on this technology.

1) Simpler scenario
“In the Diffie–Hellman key exchange scheme, each party generates a public/private key pair and distributes the public key of the pair. After obtaining an authentic (NB, this is critical) copy of each other’s public keys, Alice and Bob can compute a shared secret offline. The shared secret can be used, for instance, as the key for a symmetric cipher which will be, in essentially all cases, much faster.”

(opposite names in this case)
Alice communicates with Bob through an open network, everyone can see and listen. Therefore, we need to do an encryption. So, in order to receive secret messages, Bob generates a number (his computer comes up with a random number) and Bob calls that number the private key, he keeps it secret to himself. Then he takes this private key and generates a public key thought a special formula. The public key is derived from the private key. The public key can be shared everywhere, (Twitter, ect…) it is for the world to see. This public key has a special property, there’s no way for anyone to take Bob’s public key and go to his private key. It is impossible.
In order to send a private message to Bob through an open communication channel, Alice takes this message and encrypts it with Bob’s public key. She takes his public key and encrypts the message, so now this message becomes unreadable. No one can read, only Alice. And the only way to decrypt this message is to use the private key, and the only key that will open up this message is Bob’s private key.
When the public key is generated from the private key, the mathematical relationship between this two numbers (the keys are random numbers) is that anyone can use the public keys and only the private key will decrypt the message.
If for some reason Bob loses the private key, he will not be able to decrypt. And if someone steals Bob’s private key, then they will be able to read all the messages that people are sending through thr public key. That’s why is so important to keep the private key secret.
This is not used in blockchain.

2) Digital Signatures. - Used in Blockchain - Digital signatures, in which a message is signed with the sender’s private key and can be verified by anyone who has access to the sender’s public key. This verification proves that the sender had access to the private key, and therefore is very likely to be the person associated with the public key. This also ensures that the message has not been tampered with, as a signature is mathematically bound to the message it originally was made from, and verification will fail for practically any other message, no matter how similar to the original message.

“In the Diffie–Hellman key exchange scheme, each party generates a public/private key pair and distributes the public key of the pair. After obtaining an authentic (NB, this is critical) copy of each other’s public keys, Alice and Bob can compute a shared secret offline. The shared secret can be used, for instance, as the key for a symmetric cipher which will be, in essentially all cases, much faster. Diffie–Hellman key exchange[nb 1] is a method of securely exchanging cryptographic keys over a public channel and was one of the first public-key protocols as conceived by Ralph Merkle and named after Whitfield Diffie and Martin Hellman.[1][2] DH is one of the earliest practical examples of public key exchange implemented within the field of cryptography.
In this example the message is digitally signed, but not encrypted. 1) Alice signs a message with her private key. 2) Bob can verify that Alice sent the message and that the message has not been modified.”

This is what we use the most. In digital signatures, it is all about verifying who sent a particular message.

Let’s say Alice sends a message to Bob. This message doen’t even have to be encrypted, it’s just a message. But Bob wants to verify that it was really Alice who sent the message. So what Alice does, is she generates a private key, then she derives a public key from that private key.
Next, she uses the private key to send this message. She uses the private key to sign. She does a mathematical equation which takes this random number which is the private key and signs the message. It doesn’t necessarily encrypt. She could if she wanted, she could take his public key. (Remember that to encrypt a message for Bob she would need to have his public key). Anyways, so she signs the message and this message now has a signature. So, when Bob receives it, he will be able to mathematically see that this signature actually comes from the private key that generated Alice’s public key. So he can verify that that signature was actually from Alice’s private key. Basically, I have the message, I check the signature, and I check the public key of whoever sent it and then mathematically I can compare those two numbers, the signature and the public key and see if they correspond.
And this is how Bitcoin transactions are sent. Because when I send a bitcoin transaction, my private key signs that transaction, so that everyone else can see that I actually did spend my bitcoin and not anyone else, because I am the only one who has my private key.
In Bitcoin I have the following situation: When I start my Bitcoin wallet, my computer will generate a private key, and this is a random number. If my computer generates a private key that has already been generated by someone else’s computer and they have a lot of money in their wallet, I will get access to that money. But the practical chances of that are zero. Because we are talking about such astronomically large numbers, so for me to guess a number that someone has guessed is practically impossible.
So, in bitcoin we generate a private key, from this private key I create a public key. From the public key I create a Bitcoin address (kind of like the public key but with an extra layer of security).
When I want to send Bitcoin, I need to use my private key to sign that transaction. So other members of the network will know that I actually signed it. If I lose my private key and have not signed the transaction, I will have lost my coins. Or if someone else gets my key and is able to sign then they have stolen my funds. That’s why it’s important to have my private keys safe and secret.
And when I receive funds, people send them to my Bitcoin address, which is linked to my private key, because it is generated from my private key, and I can send the money they send to me with my private key. But there’s no way for them to take my public address and figure out my public key and then my private key. That is impossible.
WALLET
PRIVATE KEY  PUBLIC KEY  Bitcoin Address

[Bell]

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

The computer generates a private key, this private key generates a public key. The public key can be used by a sender to send an encrypted message. The receiver uses the private key to decode the message once it recognizes the public key.

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

Encryption and digital signature

[GiuZuk]

1 A secure way to establish a communication / exchange between a sender and a recipient, whatever the subject is, a message, a value, or a Bitcoin!

2 1, Encryption
2, Digital signature
for sending, receiving

[Alex_Cheung]

1. A key is a number that is used to refer back to an address. A private key would be a key that only the owner knows, and the public key is a key that can be known by everyone.

2. A public key can be used to allow others to send messages to your specific address. The cryptography itself can be used more generally for signatures and encryption.

[JJBD]

A private key is large random number generated by a computer where only you can see. A public key is generated from your private key and can be seen/used by others.
The first use would be to encrypt a private message. The second use would be to ensure integrity via a digital signature, as used in Bitcoin.

[MarcelJ]

Answers to the “public and private keys” questions:

1. Public key is something that can be shared with everyone. It is derived from the private key. The private key should be kept in a safe place.

2. Encryption and digital signatures

[shonesto]

1. Private key is used to is the only mine and kept private mostly for the purpose of sending or verifying who I am and a public key is derived from the private key and is therefore paired with the private key. Others can send and use this key to encrypt and send an encrypted message to me where my private key can then read the message
2. Digital signature is one use and encryption is another

[Philipp]

They are a combination of unique digits that ensure the privacy of a message between 2 individuals. from the private key you can generate a public key. people can see your public key and encrypt a message with it that only the person who ownes the private key to that public key can open.

the encryption of messages and as a signature to make sure its really you.

[Alko89]

@emurzello

by that I mean as your private key is used as an identifier. so people know who is sending / making a transaction?

The signature is used as an identifier, that was signed with the private key, not the private key itself.

[Blaize]

1.        Public key – Address that everyone knows, can be shared with everyone. 
          Private key- meant only for yourself and to decrypt information made by the public key               
   

2. Can be used for digital fingerprint and verify that you as a sender.

[Cosmin_Fechet]

1. The private key is generated by a computer and is composed by random words and numbers, then the private hey is introduced in a hash function that generates a private key.

2. The two used cases are encryption and digital signatures.

[Picepil]

Private keys are huge alphanumeric phrases generated randomly by a computer, used for encryption and to digitally sign secure messages. A public key is generated by a private key in a unidirectional fashion that is secure and encrypted via SHA-256 function. Your private key is your ID for your signature. Sending messages is done with the public key which is verified by a private key.

[Ustinovk]

1- Public Key is the child of Private key so Public key is the output and the Ptivate Key the input.
Then Private key as the mother is the core of the owner digital signature which can be use to access its output. Then on the other side Public Key will be the front end for any interaction with an specific group or community.

2-

• Deposit to and BTC address
• Access or communication to an open channel or group.

[dsutter]

1. The private key is generated as a very large random number. The public key is derived from the private key. It is not possible to regenerate the private key from the public key.

2. Public-key cryptography can be used for encryption and digital signatures.

[Zidea]

1. Private key is a cryptographic form os numbers and letters generated by a computer. A public key is another form of letters and numbers created by a math function using the private key.
2. A) cryptographic message encryption
   B) digital signatures.

[crypto82]

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

Encryption is a process where a computer randomly generates a private key and then also generates a public key. The public key is viewable to anyone, and the private key is only known to the individual, unless they lose it and somebody else finds it. If a person 1 wants to send a message to person 2, they will send it using the public key of that person, which will encrypt it so that it will appear as gibberish to anyone but person 2. In order to decrypt the message, person 2 can only do so with their private key. If they lose it and someone else find it, that person can then use the same process to decrypt a message sent via the public key.

2. What 2 use-cases can public key cryptography be used for?
   Encryption is one, Private Signature to confirm sent by expected person, by being representative of private key is another.

[shawnf8992]

Homework on Public and Private Keys - Questions

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

2. Public key and private key are used in cryptography to encrypt and decrypt messages. Private key is a random number using which a public key is derived. If a person wants to send a message over unsecured network he can encrypt message using a public key published by recipient which is actually derived from the private key. The encrypted message can only be decrypted by the recipient who has the private key. Also it can be used to digitally sign a message.

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

Encryption and Digital signature