I am trying to understand what is the private key in Ethereum. Help please.

  1. Private key = the address?
  2. Private key = the password/passphrase?
  3. Private key = the text seen when we open the file in the keystore folder?
  4. Private key = something other than the above?
  • Besides the answers below, here is an answer that will help you understand how the private key is stored in the file in the keystore folder. ethereum.stackexchange.com/questions/15494/… – Ajoy Bhatia Jul 4 '17 at 18:43
  • Note: I've edited the title from "Where...?" to "What...?". The question itself is asking what the private key is, not where it's kept. – Richard Horrocks Jul 4 '17 at 21:28
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    @RichardHorrocks: See scam attempt in the answer that was posted here yesterday. – goodvibration Dec 17 '20 at 8:40

in short :

the private key(secret big number) is created by your wallet randomly, then encrypted(with you password) and stored in the UTC file in the keystore folder. the address is calculated from the public key which is derived from the private key.

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    When you say " ... public key which is deactivated from the private key ... ", I think that you mean "derived from the private key". – Ajoy Bhatia Jul 4 '17 at 18:39
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    exactly sorry for the awfull typo – Badr Bellaj Jul 4 '17 at 18:44
  • And when I am asked to type in my private key — what exactly do I need to type in? – Martin May 17 '18 at 10:46
  • Why does that matter? I just want my private key decrypted in clear text. Is that to much to ask? But to put your mind at rest: Minds.com which currently runs on the Rinkeby test net. So no real money is at risk. – Martin May 17 '18 at 10:52

To get a better understanding of what a private key in Ethereum is, you need to understand what Asymmetric cryptography is. https://en.wikipedia.org/wiki/Public-key_cryptography

There are two popular asymmetric cryptography algorithms. RSA and ECDSA. Ethereum uses ECDSA (Elliptic Curve Digital Signature Algorithm). You can see how ECDSA functions here. https://blog.cloudflare.com/a-relatively-easy-to-understand-primer-on-elliptic-curve-cryptography/

To put the above in perspective in simple terms - A private key is a very large random number that is used to generate a public key. This public key is used to create your address on the Ethereum blockchain. The private key allows you to sign transactions. These transactions can be verified by other participants on the chain against your Public key.

To better educate yourselves, use the link below to generate your private key on your own machine and derive your address on the Ethereum network. https://kobl.one/blog/create-full-ethereum-keypair-and-address/

Now a private key is very hard to remember, so wallets allow you to store your private key in them secured with a password (using symmetric cryptography). What this means is, you can sign your transaction on that same wallet instance using an easy to remember the password. It is very important to understand that this password is not your private key, and if you lose access to this wallet, your password will not allow you to retrieve the private key from other wallets.

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    And how do I decrypt the private key from my wallet? Why is everybody dancing around answering that question. – Martin May 17 '18 at 10:55
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    You can decrypt your encrypted private key with your wallet password. – Omkar Khair May 18 '18 at 4:08

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