Public-key cryptography secures digital information using two mathematically linked keys, a public key that anyone can see and a private key kept secret by the owner. The public key encrypts data or verifies signatures. The private key decrypts data or creates signatures. A message encrypted with someone's public key can only be opened with their private key. This eliminates the need to share a single secret key between parties. When you see "https" in a browser, the server uses public-key cryptography to create an encrypted channel. Email programs supporting OpenPGP or S/MIME use the same math for privacy and sender authentication. Every blockchain transaction relies on public-key signatures to prove ownership. The system works because of mathematical one-way functions. It is easy to compute the public key from the private key, but practically impossible to reverse the process. This asymmetry is what makes secure communication possible between parties who have never met.
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