While RSA encryption works as you describe, with public and private keys, many other forms of encryption use a single key and a reversible operation for encrypting/decrypting.

In general symmetric ciphers are considered harder to break than asymmetric ones of similar length. They are also often simpler to compute.

In reply to Re (tilly) 2: Difference between encoding and encryption? by tilly
in thread Difference between encoding and encryption? by r.joseph

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