implementing-zero-knowledge-proof-for-authentication

name	implementing-zero-knowledge-proof-for-authentication
description	Zero-Knowledge Proofs (ZKPs) allow a prover to demonstrate knowledge of a secret (such as a password or private key) without revealing the secret itself. This skill implements the Schnorr identificati
domain	cybersecurity
subdomain	cryptography
tags	["cryptography","zero-knowledge-proof","authentication","privacy","zkp"]
version	1.0
author	mahipal
license	Apache-2.0
nist_csf	["PR.DS-01","PR.DS-02","PR.DS-10"]

Implementing Zero-Knowledge Proof for Authentication

Overview

Zero-Knowledge Proofs (ZKPs) allow a prover to demonstrate knowledge of a secret (such as a password or private key) without revealing the secret itself. This skill implements the Schnorr identification protocol and a simplified ZKPP (Zero-Knowledge Password Proof) using the discrete logarithm problem, enabling authentication where the server never learns the user's password.

When to Use

• When deploying or configuring implementing zero knowledge proof for authentication capabilities in your environment
• When establishing security controls aligned to compliance requirements
• When building or improving security architecture for this domain
• When conducting security assessments that require this implementation

Common Misconfigurations & Verification

• Predictable challenge / nonce reuse: in Schnorr, reusing the commitment randomness r across two challenges leaks the secret x via x = (s1 - s2)/(c1 - c2). Generate r from a CSPRNG per proof and never reuse it. Verify two runs produce different t values.
• Weak Fiat-Shamir transcript: the non-interactive challenge must hash the full transcript including the public key and commitment (c = H(g, y, t, msg)), not just t — otherwise proofs are forgeable or transferable. Use a collision-resistant hash.
• Verifier-chosen challenge skipped / replay: without binding to a fresh server nonce or message, a captured transcript can be replayed. Include a server-supplied challenge or message and reject duplicates.
• Insecure group parameters: use a safe prime p and prime-order subgroup q; validate that y lies in the correct subgroup to avoid small-subgroup attacks.
• Secret transmitted or logged: confirm the server never receives or stores x.
• Mandatory tests: (1) honest prover always verifies (completeness); (2) a random/forged response without x fails verification (soundness); (3) the server transcript never contains the secret (zero-knowledge); (4) repeated authentications yield distinct transcripts; (5) a replayed transcript is rejected.

Prerequisites

• Familiarity with cryptography concepts and tools