Before you invest in any cryptocurrency, you'll be issued what are called public and private keys. These are long, unique blocks of encryption that identify specific currency holders, and are just one layer of security to ensure the privacy of all transactions. Even though both your keys are linked specifically to you, none of your personal information is encrypted into them; that is to say, no one who trades with you will know your name, address or account number unless you add that information yourself.
Your public key is exactly that; it's a code that's available to anyone who trades with you. Potentially, it could be available to even more people; many exchanges maintain a database of all their investors that are publicly accessible, and these directories include the investors' public keys to make transactions easier. Here's how the public key works: let's say an investor wants to make a trade with you. They attach the information pertinent to the trade to your public key and send it to you. Your public key assures the details of this particular transaction will be known only to you and the investor instigating the trade.
By contrast, your private key is known only to you, and it should remain that way. It's a good idea to protect your private key as you would your bank account or Social Security number, for anyone with access to it also has access to your entire digital currency account. In the trade scenario above, you would use your private key to accept the details of the trade. It serves as your digital signature, and finalizes the transaction. If you feel either of your keys have been compromised, or are being used by someone not authorized to use them, contact the entity that issued them to you immediately, and get new ones.
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