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Encryption

Encryption makes data unreadable to anyone without the key. Symmetric encryption uses the same key to lock and unlock, and is fast. Asymmetric encryption has a key pair: a public key anyone can use, and a private key only the owner has.

C = E_k(M),\ M = D_k(C)

symmetric: the same key k

C = E_{pub}(M),\ M = D_{priv}(C)

asymmetric: public and private key

Symbols

$M$	plaintext
$C$	ciphertext
$k$	key

Example

HTTPS uses asymmetric encryption to agree on a shared key, and then fast symmetric encryption for the rest of the conversation.

The private key must never be shared or put in the code.

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