Public vs Private Keys: What’s the Difference?

HimanshuTamoli — Sat, 26 Sep 2026 13:36:27 +0000

Cryptography uses keys to protect information and verify identities. One of the most important concepts is the difference between public-key cryptography and private-key (symmetric) cryptography.

Public-Key Cryptography

Public-key cryptography uses two mathematically related keys:

Public key — can be shared with anyone.
Private key — must be kept secret.

For example, if someone wants to send you encrypted information, they can use your public key to encrypt it. The corresponding private key can then be used to decrypt it.

Where is it used?

Public-key cryptography is commonly associated with:

Digital signatures — a private key creates a signature, while the public key verifies it.
HTTPS — public-key cryptography is involved in establishing secure web connections.
Secure email and messaging — systems such as PGP and S/MIME use public-key cryptography.
Advantages
The public key can be distributed openly.
It avoids needing to secretly exchange the same key beforehand.
It supports digital signatures and authentication.
Disadvantages

Public-key operations are generally more computationally expensive than symmetric encryption, and managing keys and trust can become complex.

Private-Key / Symmetric Cryptography

Symmetric cryptography uses one shared secret key.

Both the sender and receiver use the same key:

Sender
│
│ Encrypt with secret key
▼
Encrypted Data
│
│ Decrypt with same key
▼
Receiver

The key must be kept secret by everyone who has access to it.

Examples

Common examples include:

AES — widely used for modern data encryption.
DES — an older encryption standard that has largely been replaced by AES.
File encryption — symmetric encryption is commonly used to protect files and stored data.
Advantages
Very fast compared with public-key operations.
Well suited for encrypting large amounts of data.
Efficient for applications that require high-speed encryption.
Disadvantages

The biggest challenge is securely sharing the secret key. If the key is compromised, data protected with that key can also be compromised.

Public Key vs Private Key
Feature Public-Key Cryptography Symmetric Cryptography
Keys Public + private key pair One shared secret key
Key sharing Public key can be shared Secret key must remain private
Speed Generally slower Generally faster
Digital signatures Supported Not the same mechanism
Main challenge Key/trust management Secure key exchange
Common uses HTTPS, digital signatures, secure email AES, file/data encryption

The source distinguishes the two approaches primarily by their key structure, performance, key management, and applications.

The Simple Way to Remember

Think of public-key cryptography as having two different keys:

Public key → share it
Private key → keep it secret

With symmetric cryptography:

One secret key → both sides use it

Understanding this distinction is important when learning technologies such as SSH, HTTPS, TLS, digital signatures, and encryption systems.

DEV Community: HimanshuTamoli

Public vs Private Keys: What’s the Difference?