# What is the difference between symmetric and asymmetric encryption? URL: https://webvpn.org/encryption/symmetric-vs-asymmetric-encryption/ Updated: 2026-09-10 Symmetric vs asymmetric encryption explained: how public and private key encryption works, where each is used, and how password-based encryption fits in. The difference between symmetric and asymmetric encryption is the number of keys. Symmetric encryption uses a single secret key to both encrypt and decrypt, which makes it fast but requires both parties to already share the key. Asymmetric encryption uses a pair of keys, a public key that anyone may have and a private key that only the owner holds, so that anyone can encrypt a message that only the owner can read, which solves key sharing at the cost of speed. Nearly every real system uses both together. Understanding this difference is the key to understanding how HTTPS, encrypted messaging, PGP, VPNs and passkeys work, because they all combine the two types in the same pattern. This guide explains each type, how public and private key encryption works, why the two are combined, where you meet each, and how password-based encryption fits in. ## Symmetric encryption: one shared key In symmetric encryption, the sender and receiver hold the same secret key. The sender encrypts with it; the receiver decrypts with it. The algorithms are efficient enough to encrypt gigabytes per second on ordinary hardware, which is why symmetric encryption protects the bulk of data everywhere: files, disks, database records, and the contents of every HTTPS connection and VPN tunnel. AES, the Advanced Encryption Standard, is the dominant symmetric algorithm, used with 128-bit or 256-bit keys; ChaCha20 is a widely used alternative, especially on devices without hardware AES acceleration. The AES guides on this site cover them in detail. The difficulty is key distribution. If two people who have never met want to communicate, how does the first get the key to the second without an eavesdropper seeing it? Sending it over the same channel defeats the purpose. Meeting in person does not scale to a web browser talking to a server on another continent. Symmetric encryption alone cannot solve this. ## Asymmetric encryption: a public key and a private key Asymmetric encryption, or public-key cryptography, solves key distribution with mathematics that makes two keys related but not interchangeable. You generate a key pair. The public key can be published anywhere. The private key never leaves you. Anything encrypted with the public key can be decrypted only with the private key, and there is no practical way to compute the private key from the public one. Now a stranger can send you a secret: they take your public key, encrypt their message, and send the ciphertext. Only you can read it. No secret needed to be shared in advance. The same key pair works in reverse for digital signatures. You produce a signature over a message with your private key; anyone with your public key can verify that the signature is valid, which proves the message came from someone holding your private key and has not been changed. Signatures are how software updates, website certificates and PGP-signed emails prove their origin. RSA, based on the difficulty of factoring large numbers, and elliptic-curve cryptography, based on a different hard problem with much smaller keys, are the two families in use. The RSA and ECC guide on this site explains them. ## Why asymmetric encryption is not used for everything Asymmetric operations are thousands of times slower than symmetric ones and can only encrypt small amounts of data at a time, roughly the size of the key. Encrypting a video or a disk with RSA would be impractically slow. Asymmetric encryption is therefore used for exactly the tasks symmetric encryption cannot do: agreeing on a key between strangers and proving identity. ## How the two are combined The pattern is called hybrid encryption and appears everywhere. - The parties use asymmetric cryptography to establish a shared secret: either one side encrypts a fresh random key to the other's public key, or both sides run a key agreement protocol such as Diffie-Hellman over elliptic curves. - Both sides now hold the same symmetric key, which no eavesdropper could derive. - They encrypt the actual data with fast symmetric encryption using that key. - Signatures or certificates, built on asymmetric keys, prove that each side is who it claims to be, preventing an attacker from impersonating one party during the key exchange. When your browser connects to a website over HTTPS, this happens in milliseconds: the site proves its identity with a certificate, the two sides agree a session key, and AES protects everything after. The HTTPS guide on this site follows it step by step. End-to-end encrypted messengers, PGP email and VPN tunnels do the same in their own ways. ## Where you meet each type - Symmetric only: encrypting a file with a password, full-disk encryption, an encrypted USB drive, a password manager vault, a Wi-Fi network. One party, one key, no distribution problem. - Asymmetric plus symmetric: HTTPS, VPN handshakes, PGP and encrypted email, end-to-end messaging, encrypted cloud storage sharing, SSH. - Asymmetric for identity: code signing, website certificates, passkeys and hardware security keys, which prove who you are by signing a challenge with a private key that never leaves the device. ## Password-based encryption Many symmetric uses involve a human, and humans cannot remember a 256-bit random key. Password-based encryption bridges the gap with a key derivation function: a deliberately slow algorithm that takes your password and a random salt and produces a key of the right length. The slowness matters, because it makes each password guess expensive for an attacker. Modern functions such as Argon2, scrypt and PBKDF2 with a high iteration count are designed for this. The resulting encryption is exactly as strong as the password. A 256-bit AES key derived from a six-character password has about as many effective possibilities as the password does, and an attacker guesses passwords rather than keys. Long, unique passphrases are what make password-based encryption live up to the algorithm behind it. ## A quick reference Property Symmetric Asymmetric Keys One shared secret Public and private pair Speed Very fast Slow Data size Unlimited Small, about key size Key sharing Must be pre-shared or agreed Public key can be published Main uses Bulk data, disks, files, connection contents Key exchange, signatures, identity Examples AES, ChaCha20 RSA, ECC, Diffie-Hellman ## What cryptographers and standards bodies say The framing here follows the standard treatment of the subject. Standards bodies specify approved symmetric algorithms for data protection and approved asymmetric algorithms for key establishment and signatures, and describe hybrid schemes as the normal way to combine them. Cryptography educators consistently present public-key cryptography as the solution to the key distribution problem that limited symmetric cryptography for centuries, while emphasising that symmetric encryption remains the workhorse for data. Protocol designers document that modern secure protocols, from TLS to messaging, use asymmetric operations only for the handshake and identity, then hand off to symmetric encryption for performance. ## Recognise the pattern Once you see the pattern, every encrypted system on this site reads the same way: asymmetric keys to meet and prove identity, symmetric keys to carry the data, and a password or hardware to protect the keys themselves. That is what the difference between symmetric and asymmetric encryption is for, and knowing it lets you judge any product's claims by asking which part is doing what. ## FAQ Q: What is symmetric encryption? A: Encryption where the same secret key is used to encrypt and decrypt. It is fast and efficient and is used for protecting files, disks and the contents of network connections. AES is the standard symmetric algorithm. Its drawback is that both parties must already share the key. Q: What is asymmetric encryption? A: Encryption using a mathematically linked key pair: a public key that can be shared freely and a private key kept secret. Anything encrypted with the public key can only be decrypted with the private key. It solves key distribution and enables digital signatures, at the cost of being much slower than symmetric encryption. Q: How does public and private key encryption work? A: You generate a key pair and publish the public key. Someone who wants to send you a secret encrypts it with your public key; only your private key can decrypt it. For signatures the roles reverse: you sign with your private key and anyone verifies with your public key, proving the message came from you and was not altered. Q: Which is more secure, symmetric or asymmetric encryption? A: Neither is more secure in general; both are secure at appropriate key sizes. They differ in purpose. Symmetric encryption protects data efficiently; asymmetric encryption lets strangers establish a shared secret and verify identities. Real systems use asymmetric encryption to agree on a symmetric key, then symmetric encryption for the data. Q: What is password-based encryption? A: Symmetric encryption where the key is derived from a password using a deliberately slow function, so that a password you can remember becomes a key a computer can use. It is only as strong as the password, which is why long, unique passphrases matter for encrypted files and disks.