Authenticity

As explained in Hacking Cryptography

Authenticity is the security property of establishing that a message is genuine and originated as claimed.

Authenticity establishes that a message or digital entity is genuine and originated as claimed. It extends integrity: integrity detects modification, while authenticity links the data to an entity that controlled it. section 1.1 section 1.2.3

Signed login token

After a successful login, a website signs a token containing the username. On later visits, it verifies the signature and trusts that it issued the token, allowing the token to authenticate the user without another password. section 1.2.3

Cryptographic mechanisms implement authenticity in different ways. A MAC uses a shared secret to authenticate messages, but poorly designed secret-prefix or secret-suffix constructions can enable attacks such as length extension. HMAC is designed to resist length-extension and collision attacks. Digital signatures provide asymmetric authenticity: anyone with the public key can verify a message, but only the private-key holder should create signatures. section 7.0 section 9.2

A valid authenticity check supports trust only when the cryptographic scheme and implementation remain secure. Signature forgery attacks, reused ECDSA nonces, and vulnerable padding can defeat that assumption; verification alone does not let verifiers create signatures. section 9.2 section 9.0

Figure 1.1 Security goals of cryptography

Use the security-goals diagram to distinguish authenticity from confidentiality and integrity. section 1.1

How Hacking Cryptography covers it

How deep it goes

Explains integrity’s relationship to authenticity, then examines MAC constructions, HMAC defenses, signatures, and concrete forgery attacks.

Examples

Uses messaging identity, payment transactions, signed login tokens, envelopes, MAC attacks, and digital-signature forgery scenarios.

What it assumes

Teaches confidentiality, integrity, and authenticity from basic security goals before assuming familiarity with MACs, hashes, and signatures.

What you can do after

Evaluate/understand when integrity evidence identifies a sender, and distinguish shared-secret MACs from asymmetric signature verification.

How it connects

Connects authenticity with integrity, message authentication codes, HMAC, digital signatures, confidentiality, and nonrepudiation.

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Also explained in

• 

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  Authorization in ActionAuthenticity is the property of being able to establish with confidence who the parties to a communication are and prove that identity to others.
• 

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  Introduction to Generative AI, Second EditionAuthenticity is the perceived genuineness or fidelity of a person, identity, expression, or creative work.
• 

  liveBookmanning.com
  Lead Developer Career GuideThe quality of behaving and communicating in a genuine manner consistent with one's actual experiences and values.

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Related concepts

• data integritykind of · Data integrity is the property that data remains accurate, complete, consistent, and valid, with changes made only through authorized actions.
• authenticated encryption with associated dataproduced by · Authenticated encryption with associated data is a cryptographic construction that encrypts plaintext while authenticating the ciphertext and optional unencrypted associated data.
• digital signatureaddressed by · A digital signature is cryptographic data generated with a private key and verified with corresponding public information to authenticate data or its signer and detect alteration.
• privacycontrasts with · Privacy is the protection and controlled handling of information or activities to prevent inappropriate access, collection, use, or disclosure.
• security objectivekind of · A security objective is a desired outcome concerning the protection of information, systems, assets, or organizational interests.
• Galois/Counter Modeproduced by · Galois/Counter Mode is an authenticated-encryption mode that combines counter-mode encryption with authentication of ciphertext and associated data.

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.