Public key and private key example

Public-key cryptography (PKC) is a technology often used to validate the authenticity of data using asymmetric encryption. PKC was first used primarily to encrypt and decrypt messages in traditional computing. Cryptocurrencies now use this technology to encrypt and decrypt transactions. Without PKC, the technology underpinning cryptocurrencies would be practically impossible.

The key to PKC is “trapdoor functions,” one-way mathematical functions that are easy to solve in one way, but nearly impossible to crack in the reverse. While it might be possible, it would likely take a supercomputer — and thousands of years — to reverse engineer these functions.

A public key allows you to receive cryptocurrency transactions. It’s a cryptographic code that’s paired to a private key. While anyone can send transactions to the public key, you need the private key to “unlock” them and prove that you are the owner of the cryptocurrency received in the transaction. The public key that can receive transactions is usually an address, which is simply a shortened form of your public key.

Therefore, you can freely share your public key without worry. You may have seen donation pages for content-creators or charities with the public keys for their crypto addresses online. While anyone can donate, you’d need the private key to unlock and access the donated funds.

Here is one crucial piece of advice to remember: Never share your private key with anyone. A private key gives you the ability to prove ownership or spend the funds associated with your public address. A private key can take many forms:

• 256 character long binary code

• 64 digit hexadecimal code

• QR code

• Mnemonic phrase

Regardless of its form, a private key is an astronomically large number, and it’s large for a good reason. While you can generate a public key with a private key, doing the opposite is practically impossible because of the one-way “trapdoor” function. You can have any number of public keys connected to a private key.

For a transaction on the blockchain to be complete, it needs to be signed. The steps for someone to send you a transaction are:

1. A transaction is encrypted using a public key. The transaction can only be decrypted by the accompanying private key.  

2. Next, the transaction is signed using the private key, which proves that the transaction hasn’t been modified. The digital signature is generated through combining the private key with the data being sent in the transaction. 

3. Finally, the transaction can be verified as authentic using the accompanying public key.

You digitally sign a transaction to prove you’re the owner of the funds. Nodes check and authenticate transactions automatically. Any unauthenticated transactions get rejected by the network. An authentic, mined transaction on the blockchain is irreversible.

Your private keys are in a cryptocurrency wallet, which is typically mobile or desktop software or a specialized hardware device. Your private keys are not on the cryptocurrency blockchain network. If you keep cryptocurrency on an exchange, then the exchange is the custodian of your private keys; you’re trusting it with your keys in the same way you’d trust a bank’s vault to hold your gold.

If you transfer your cryptocurrency from an exchange to a non-custodial wallet, then you are in control of your keys. Because of the configuration and functionality of cryptocurrency wallets, you’ll likely never handle the private keys directly as wallets generally manage them for you automatically. Typically, you’re given a seed phrase that encodes your private keys as a back-up.

How public and private keys work together is fundamental to understanding how cryptocurrency transactions function. When you say you have cryptocurrency, what you’re really saying is you have a private key that proves ownership of that cryptocurrency. Since it’s stored on the blockchain, anyone can verify you as the owner with your public key.

The choice of “holding your own keys” or trusting a custodian depends on your philosophy, risk-tolerance, and a host of other factors. If you hold your own private keys, consider modern HD wallets, which can do a great job of managing your private keys, and remember to never share them. If you choose a custodial solution like an exchange, make sure you choose a trusted, reputable company that places a high emphasis on security and regulation.

A public key and a private key constitute a key pair, which is generated by using an encryption algorithm. A key pair is used for asymmetric encryption. A public key is used to encrypt sessions and verify digital signatures, and its paired private key is used to decrypt the session data. This ensures the security of data transmission. A public key is disclosed to the public, and its paired private key is private to the user that creates the key pair.

A key pair that is generated by using an encryption algorithm is unique around the world. If you use a key in a key pair to encrypt a piece of data, the data can be decrypted only by using the other key in the key pair. For example, data that is encrypted by using a public key can be decrypted only by using its paired private key. Data that is encrypted by using a private key can be decrypted only by using its paired public key.