Decryption

Intermediate
Updated Jul 21, 2026

What Is Decryption?

Decryption is the process of reverting an encryption process so that previously encrypted information can be read or accessed again. In simple terms, it converts unreadable data, known as ciphertext, back into its original readable form, known as plaintext.

While encryption makes data unreadable to anyone without authorization, decryption does the opposite: it restores the information to its original and understandable form. Both processes rely on a specific type of cryptographic key.

How Decryption Works

Decryption keys are generated by cryptographic algorithms and are usually represented as a string of numbers and letters. A piece of encrypted information can be converted back to its original form by applying the corresponding decryption key.

Without the correct key, decryption becomes far more difficult and could, in theory, only be achieved through brute-force attacks that try many possible keys. Robust encryption algorithms are designed to generate keys that are practically impossible to break, because the number of possible combinations would require an impractical amount of time and computing power to test.

Symmetric vs. Asymmetric Decryption

Cryptographic keys are used in both symmetric and asymmetric encryption. Depending on how the keys are generated and used, the techniques can be divided into two broad groups: symmetric key cryptography and public key cryptography.

In symmetric key cryptography, the same key is used to both encrypt and decrypt a piece of information. Until 1976, this was the only widely known type of encryption technique. The main consideration is that both parties must share the same secret key, and that key needs to be kept private.

On the other hand, public key cryptography, also called asymmetric encryption, uses a pair of mathematically related keys: a public key and a private key. Data encrypted with the public key can only be decrypted with the matching private key. This means the public key can be shared openly, while the private key stays secret and performs the decryption.