Counter mode encryption

As explained in Hacking Cryptography

Counter mode encrypts successive counter values with a block cipher to generate a keystream that is combined with plaintext.

Counter mode (CTR) turns a block cipher into a keystream generator: it encrypts successive counter values, then combines the resulting keystream with plaintext. section 5.3

This approach addresses the problem of encrypting multiple blocks without independently encrypting identical plaintext blocks, as ECB does. section 5.3

Figure 5.4 Stream ciphers generate a keystream, which is subsequently XORed to encrypt. Block ciphers directly output the ciphertext after encryption.

Compare block-cipher output with the keystream-and-XOR structure that counter mode uses. section 5.3

How Hacking Cryptography covers it

How deep it goes

Defines keystream generation and plaintext combination, but does not provide implementation steps or attack analysis.

Examples

Uses a keystream-generation diagram to contrast stream-cipher processing with direct block-cipher ciphertext output.

What you can do after

Evaluate how block-cipher processing can emulate keystream-based encryption across multiple plaintext blocks.

How it connects

Connects block ciphers with stream ciphers, keystreams, XOR, plaintext, ciphertext, and ECB mode.

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Also explained in

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  Real-World CryptographyAES-CTR is a counter-mode construction that applies AES to successive counter values to generate a keystream or pseudorandom-looking output.

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Related concepts

• stream cipherimplements · A stream cipher is an encryption algorithm that combines plaintext sequentially with a generated keystream, typically using XOR.
• Galois/Counter Modeimplemented by · Galois/Counter Mode is an authenticated-encryption mode that combines counter-mode encryption with authentication of ciphertext and associated data.
• CCMPused by · CCMP is an IEEE 802.11 wireless security protocol that combines AES counter-mode encryption with CBC-MAC-based message authentication.
• GCMPused by · GCMP is a wireless data-protection protocol that combines AES counter-mode encryption with GMAC integrity protection.
• encryptionkind of · Encryption is the cryptographic transformation of readable data into ciphertext to conceal its contents, reversible through decryption with appropriate information.
• pseudo-random number generatorproduces · A pseudorandom number generator is a deterministic computational process that uses an initial seed or internal state to produce a sequence with random-like statistical properties.

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