Asymmetric — public-key — cryptography gives you a matched pair: a public key you can broadcast and a private key you guard. Anyone can encrypt to the public key or verify signatures made with the private key; only the holder of the private key decrypts or signs. The math relies on trapdoor problems: easy one direction, hard the other without the secret — integer factorization for RSA, elliptic-curve discrete log for ECDSA.

What problems it solves
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