Cryptographic Encryption Methods

Symmetric encryption

One secret key encrypts and decrypts. It’s fast and suited for bulk data, but both parties need the same key first, and getting it to the other side securely is the hard part.

flowchart LR
  plain1[Plaintext] -->|"🔑 shared key"| cipher[Ciphertext]
  cipher -->|"🔑 shared key"| plain2[Plaintext]

Examples: AES, ChaCha20.

Asymmetric encryption

Each party has a key pair. The public key can be shared with anyone and only encrypts; the matching private key never leaves its owner and decrypts. Reversed, the private key creates signatures that anyone can check with the public key.

flowchart LR
  plain1[Plaintext] -->|"🔓 public key"| cipher[Ciphertext]
  cipher -->|"🔑 private key"| plain2[Plaintext]

Examples: RSA, elliptic curves (ECDSA, Ed25519 for signatures).

Hybrid encryption

Asymmetric encryption is roughly a thousand times slower and limited in message size, so real protocols combine both: the asymmetric part (or a Diffie-Hellman exchange) agrees on a random symmetric session key, and the data itself is encrypted symmetrically. TLS, SSH, PGP and age all work this way.

sequenceDiagram
  participant A as Alice
  participant B as Bob
  B->>A: public key
  Note left of A: random session key K
  A->>B: K encrypted with Bob's public key
  Note right of B: decrypts K with private key
  A->>B: data encrypted with K (AES)
  B->>A: data encrypted with K (AES)

Property	Symmetric	Asymmetric
Keys	one shared secret	public and private key pair
Speed	fast, hardware-accelerated	slow
Typical key size	128–256 bit	2048–4096 bit RSA, 256 bit elliptic curve
Used for	bulk data	key exchange, signatures