Asymmetric cryptography requires a pair of keys - public (shared) and private Archived Message
Posted by sashimi on May 30, 2019, 10:34 pm, in reply to "Can I be dense please : ). Which private keys? nm"
Some mathematical operations are much harder to do in one direction than another e.g. factoring primes. Public and private keys are analogous to the difference in difficulty of such operations. The public keys used for encryption can be publicly listed on keyservers or swapped in person. You encrypt a message to me using my public key and I decrypt using my private key. I respond by encrypting my reply using your public key and you decrypt using your private key. And so it goes. One caveat is that the subject line is not encrypted (it'd become unwieldy as you'd need a massive block of text to maintain security), so one can refer to the actual subject in the message body, and encrypt that as per standard. https://gnupg.org/faq/gnupg-faq.html#define_asymc
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