Symmetric vs Asymmetric Encryption and Hashing Explained

Symmetric

Same key encrypts and decrypts.

Keys

One shared secret

Speed

Fast

Use case

Bulk data (TLS session, disks, VPN payload)

Key size

128, 192, 256 bits

Catch

How do you share the key?

Examples

AES3DESDESRC4

Asymmetric

Public key encrypts, private key decrypts.

Keys

Public + private pair

Speed

Slow (math heavy)

Use case

Key exchange, signatures, certificates

Key size

2048-bit and up

Catch

Too slow for bulk data

Examples

RSAECC

Hashing

One-way fingerprint. No key.

Keys

None

Speed

Very fast

Use case

Integrity checks, fingerprints, password storage (with salt)

Output size

160, 256, 512 bits (fixed)

Catch

Not reversible; not for confidentiality

Examples

SHA-256SHA-512SHA-1MD5

MAC / HMAC

Hash + secret key. Proves who.

Keys

One shared secret

Speed

Fast (hash speed)

Use case

Authenticate AND integrity-check messages

Output size

Same as underlying hash

Catch

Both sides must share the key (symmetric trust)

Examples

HMAC-SHA256HMAC-SHA1

Digital signatures

Combine a hash with asymmetric encryption to prove a message came from a specific signer AND was not modified.

signature = encrypt_with_private_key( hash(message) )

How TLS actually works

Asymmetric is too slow to encrypt every byte, and symmetric needs a shared key first. TLS uses asymmetric to exchange a fresh symmetric session key, then encrypts the conversation symmetrically. Best of both.

Words that show up everywhere

Salt

Random per-password value stored next to the hash. Stops rainbow-table attacks and makes identical passwords hash differently.

Initialization Vector. A random starter value mixed in before encryption so the same plaintext does not produce the same ciphertext every time.

Nonce

Number used ONCE. Similar to an IV but with the rule that it must never be repeated with the same key.

Collision

Two different inputs that produce the same hash. MD5 and SHA-1 have known collisions and are no longer considered safe for signatures.