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I've got a very simple but for me a difficult question. I analyzed the public key cryptography and understand the process. But I didn't understand why is only the receiver able to decrypt to message.
Please give an advice. when the sender encrypts the message with the public key why isn't any man in the middle not able to decrypt when he knows the public key.
Thanks a lot before
The whole point of public key cryptography is that there is a secret key, which, if the system is to be any good, cannot be easily computed from the public key, but is known to the legitimate owner of the public (i.e. the one who generated and published it). And decryption uses the secret key, not the public one. Encryption only uses the public key.
But the point is that in order to know (or believe) the public key you are using is actually the one that the intended recipient has the private key for, some extra mechanisms (like signed certificates and certificate authorities, or some trusted third party, etc.) are needed. This is what is called PKI for short, in essence.
