Ciphertext

As explained in Real-World Cryptography

Ciphertext is encrypted data produced from plaintext and intended to be decrypted by an authorized recipient.

When Alice sends a private message through an untrusted messenger, encryption transforms the plaintext into ciphertext: encrypted content that looks random to observers without the secret key. section 1.2 section 4.1

A symmetric-encryption exchange follows these steps:

• Start with plaintext, such as text, an image, or a video represented as bits. section 4.1
• Encrypt the plaintext with a secret key to produce ciphertext. section 1.2 section 4.1
• Transmit the ciphertext; an observer should see random-looking data rather than the message. section 4.1
• Decrypt the ciphertext with the same secret key to recover the original plaintext. section 1.2

Alice sends “hello”

Alice encrypts the plaintext “hello” with a shared key and sends Bob the resulting ciphertext. Bob uses that same key to decrypt it and recover “hello”; the messenger sees only noisy data. section 4.1

Figure 4.2 A cipher with a key can be seen as a permutation: it maps all the possible plaintexts to all the possible ciphertexts.

View ciphertext as one element of a reversible key-dependent mapping between plaintexts and ciphertexts. section 4.2.2

How Real-World Cryptography covers it

How deep it goes

Defines ciphertext, traces symmetric encryption and decryption, and connects AES ciphertext to reversible 128-bit mappings.

Examples

Uses Alice and Bob’s exchanged message, the plaintext “hello,” and AES’s fixed-size 128-bit input and output.

What it assumes

Assumes plaintext and a shared secret key, while treating key agreement as an initial in-person exchange.

What you can do after

Evaluate/understand how encryption produces ciphertext and how authorized decryption recovers plaintext with the shared key.

How it connects

Links ciphertext to plaintext, encryption, decryption, secret keys, symmetric encryption, block ciphers, AES, and confidentiality.

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Also explained in

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  Secure APIsCiphertext is data produced by encrypting plaintext so that it is not readable without the required decryption capability.
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  Software Security for DevelopersCiphertext is data produced by encryption that is intended to be unintelligible without the required cryptographic key.
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  API Design PatternsAn encrypted value is data transformed by encryption so that its original content cannot be read without the required key or decryption process.
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  WordPress Power Toolkit: Harness AI to build next-level websitesAn encrypted message is a message transformed into an encoded representation intended to prevent direct reading without decoding.

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Related concepts

• encryptionproduced by · Encryption is the cryptographic transformation of readable data into ciphertext to conceal its contents, reversible through decryption with appropriate information.
• Kyberproduced by · Kyber is a lattice-based public-key cryptographic scheme based on the learning with errors problem that supports key encapsulation and key exchange.
• initialization vectorconfigures · An initialization vector is a typically nonsecret value supplied to a cryptographic operation to initialize or vary its processing across uses.
• whole-value substitution attackused by · A whole-value substitution attack is an attack in which an attacker replaces one encrypted record value with a ciphertext copied from another record to cause unauthorized plaintext substitution.
• keyboard shift erroraddressed by · A keyboard shift error is a text corruption pattern caused by entering characters adjacent to the intended keys on a keyboard layout.

This explainer was generated by Manning's knowledge graph from the text of Real-World Cryptography. The section links point to the parts of the book it draws on.