Ciphertext Definition

KZero Staff
Jul 27, 2023

What is a Ciphertext?

Encryption algorithms are designed to protect data confidentiality. They transform data into a format that is readable only with knowledge of the associated encryption key.

A ciphertext is the end result of this transformation. If a secure encryption algorithm was used, this value will be indistinguishable from a random value, leaking no information about the original message.

How Encryption Works

Ciphertexts are the result of applying an encryption algorithm to data. Encryption algorithms are mathematical functions that scramble data in a way that makes it unrecoverable without the correct decryption key.

Encryption algorithms come in two main types. Symmetric algorithms use the same key for encryption and decryption, while asymmetric encryption algorithms use a pair of related keys (public key for encryption, private key for decryption).

When working with encryption, the algorithm used can be public and should be a well-reviewed one – like the Advanced Encryption Standard (AES). The only secret should be the secret key. This rule is known as Kerckhoff’s Principle.

When to Use a Ciphertext

Ciphertexts are designed to be secure against potential eavesdroppers. If an attacker doesn’t know the proper decryption key, there is no way for them to restore the original message.

There are a few different states that data can be in, including:

  • Data at Rest: Data at rest should be encrypted, replacing plaintexts with the corresponding ciphertext. This makes it more difficult for unauthorized users to access potentially sensitive data.
  • Data in Transit: Secure web protocols, like HTTPS, use Transport Layer Security (TLS) for confidentiality, integrity, and authentication protection. These protocols use encryption to ensure that an eavesdropper can’t read data as it flows over untrusted and potentially public networks. While HTTPS should always be used for payment pages and other sensitive data, many websites are switching over to using HTTPS by default for all web content to enhance privacy and security.
  • Data in Use: Encrypting data in use is a difficult challenge because, with most cryptographic algorithms, mathematical operations on ciphertexts don’t work properly. For example, the sum of two ciphertexts doesn’t produce the same result as encrypting the sum of their plaintexts. For this reason, data is usually decrypted for use; however, homomorphic encryption – which allows mathematical operations on encrypted data – is an area of active research.

In general, if data is in an unchanging state (i.e. not in use), it should be encrypted. However, there are a few cases where encryption is the wrong choice for storing data. For example, passwords should be stored as hashes, not encrypted. The reason for this is that an attacker who gains access to the encryption key could decrypt and steal everyone’s passwords.


Ciphertexts are the result of encrypting data to protect confidentiality. Unless someone has the right encryption key, they can’t read the data. This makes encryption a great tool for access control and ensuring data security. However, this security is only as good as the encryption algorithm used and how well the private key is protected against exposure.

KZero Staff

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