You must understand the principle of the public and private key system and how it applies to cryptocurrencies. To verify a cryptocurrency transaction there must be a public and a private key and these must be linked together with you as the owner. These keys are heavily encrypted for security and it would take massive computer power to decrypt these keys even if it was possible.
A public key has a tie in with a public address and you need this for cryptocurrency transactions. You use your public key to deposit your cryptocurrencies and let people know that you are available to make transactions (buy and sell cryptocurrencies). Anyone can see your public key.
Your private key must never be shared and acts like a password to protect the cryptocurrencies that you own. All of your private keys must link to public keys for additional security. Private keys determine the balance of your cryptocurrency holdings.