Types of Encryption Explained: Symmetric vs Asymmetric

1What Is Encryption?

Encryption is the process of converting readable data, called plaintext, into an unreadable form called ciphertext, using an algorithm and a key. Only someone holding the correct key can convert the ciphertext back into plaintext.

It protects data both at rest, such as files on a disk, and in transit, such as information moving across a network. The strength of an encryption scheme depends on the algorithm used and the length and secrecy of the key.

2Symmetric Encryption

Symmetric encryption uses the same key to both encrypt and decrypt data. It is computationally efficient, which is why it is used for encrypting large amounts of data, such as files or a live network connection.

The tradeoff is key distribution: both parties need the same secret key before communication starts, and if that key is intercepted in transit, the encryption is compromised.

• AES (Advanced Encryption Standard): the current standard for symmetric encryption, used in disk encryption, VPNs, and TLS sessions.
• ChaCha20: a modern stream cipher often used on mobile devices where AES hardware acceleration is unavailable.
• DES and 3DES: older standards now considered insecure or deprecated for new systems.

3Asymmetric Encryption

Asymmetric encryption, also called public-key cryptography, uses a mathematically linked pair of keys: a public key that can be shared openly, and a private key that must be kept secret. Data encrypted with the public key can only be decrypted with the matching private key.

This solves the key distribution problem central to symmetric encryption, since the public key never needs to be kept secret. The cost is speed: asymmetric algorithms are far slower than symmetric ones for large amounts of data.

• RSA: widely used for key exchange and digital signatures, based on the difficulty of factoring large numbers.
• Elliptic Curve Cryptography (ECC): achieves similar security to RSA with much shorter keys, common in modern TLS and mobile systems.
• Diffie-Hellman: a key exchange method that lets two parties agree on a shared secret over an insecure channel.

4Hashing vs Encryption

Hashing is often confused with encryption, but it serves a different purpose. A hash function takes input of any size and produces a fixed-size output, and this process is one-way: there is no key that reverses a hash back to its original input.

Hashing is used to verify integrity, such as confirming a downloaded file was not altered, and to store passwords, where the system only ever compares hashes rather than storing the original password.

5How TLS Uses Both Types

TLS, the protocol that secures HTTPS connections, is a practical example of symmetric and asymmetric encryption working together. During the handshake, the browser and server use asymmetric encryption to safely agree on a shared secret, without ever transmitting that secret directly.

Once the handshake completes, the connection switches to symmetric encryption using that shared secret, because it is fast enough to encrypt the full flow of web traffic in real time.

6End-to-End Encryption

End-to-end encryption means that only the sender and the intended recipient can read a message, not any server or service that carries it along the way. Messaging apps that support this use asymmetric keys generated on each user's device, so even the app provider cannot read message content.

This differs from encryption in transit alone, where data might be encrypted between the user and the server, but the server itself can still read it before forwarding it on.

7Choosing the Right Approach

In practice, most engineers do not choose an encryption scheme from scratch; they select well-tested protocols and libraries that already combine the right algorithms correctly, such as TLS for network traffic or established libraries for at-rest encryption.

The important skill is recognizing which category a problem falls into: securing data in transit, securing data at rest, or verifying integrity, since each maps to a different tool.

8Learning More About Security

Understanding encryption is foundational for anyone working toward a security-focused role, since it underpins topics like secure network design, key management, and threat modeling.

A structured security engineering path builds from these fundamentals toward practical skills in defending real systems.