CYPHERPUNK

What is the difference between symmetric and asymmetric cryptography?
With symmetric cryptography, the same key is used for both encryption and decryption. A sender and a recipient must already have a shared key that is known to both. Key distribution is a tricky problem and was the impetus for developing asymmetric cryptography.

With asymmetric crypto, two different keys are used for encryption and decryption. Every user in an asymmetric cryptosystem has both a public key and a private key. The private key is kept secret at all times, but the public key may be freely distributed.

Data encrypted with a public key may only be decrypted with the corresponding private key. So, sending a message to John requires encrypting that message with John’s public key. Only John can decrypt the message, as only John has his private key. Any data encrypted with a private key can only be decrypted with the corresponding public key. 
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Это очень хороший и понятный обзор различий между симметричным и асимметричным шифрованием. Этот пост помогает понять, почему важно правильно использовать оба типа ключей в асимметричном криптосистеме.