_hope_core/diamond/

zk_snark.rs

//! # Zero-Knowledge SNARK Proofs for Diamond
//!
//! **PILLAR 1: ZK-SNARKs - Prove Without Revealing**
//!
//! Every output comes with mathematical proof of compliance.
//! Anyone can verify. No one sees the internal process.
//!
//! ```text
//! ┌─────────────────────────────────────────────────────────────────┐
//! │                    DIAMOND ZK-SNARK FLOW                        │
//! ├─────────────────────────────────────────────────────────────────┤
//! │                                                                 │
//! │   Input ──────┐                                                 │
//! │               │                                                 │
//! │   Rules ──────┼──► AI Processing ──► Output + π (ZK Proof)     │
//! │               │         │                    │                  │
//! │   Context ────┘         │                    │                  │
//! │                         │                    ▼                  │
//! │                    [HIDDEN]            Verifier                 │
//! │                                            │                    │
//! │                                            ▼                    │
//! │                                    ✅ VALID or ❌ INVALID       │
//! │                                                                 │
//! │   Verifier learns: "Output complies with rules"                │
//! │   Verifier learns: NOTHING ELSE                                │
//! │                                                                 │
//! └─────────────────────────────────────────────────────────────────┘
//! ```

use serde::{Deserialize, Serialize};
use sha2::{Digest, Sha256};
use std::time::{SystemTime, UNIX_EPOCH};

// ============================================================================
// ZK-SNARK TYPES
// ============================================================================

/// A Diamond ZK-SNARK Proof
///
/// Mathematical proof that an output complies with rules,
/// without revealing the reasoning process.
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct DiamondProof {
    /// Proof version
    pub version: u32,

    /// The π value (the actual SNARK proof)
    pub pi: SnarkPi,

    /// Public inputs (what the verifier sees)
    pub public_inputs: PublicInputs,

    /// Proof metadata
    pub metadata: ProofMetadata,
}

/// The core SNARK proof (π)
///
/// In a real implementation, this would be a Groth16 or PLONK proof.
/// Structure: (A, B, C) points on elliptic curve.
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct SnarkPi {
    /// Proof element A (G1 point)
    pub a: Vec<u8>,

    /// Proof element B (G2 point)
    pub b: Vec<u8>,

    /// Proof element C (G1 point)
    pub c: Vec<u8>,
}

/// Public inputs - what the verifier can see
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct PublicInputs {
    /// Hash of the sealed rules
    pub rules_hash: [u8; 32],

    /// Hash of the output
    pub output_hash: [u8; 32],

    /// Timestamp
    pub timestamp: u64,

    /// Session identifier
    pub session_id: [u8; 32],
}

/// Proof metadata
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct ProofMetadata {
    /// Proving system used
    pub system: ProvingSystem,

    /// Curve used
    pub curve: Curve,

    /// Proof generation time (microseconds)
    pub generation_time_us: u64,

    /// Constraint count
    pub constraint_count: usize,
}

/// Proving system variants
#[derive(Debug, Clone, Copy, Serialize, Deserialize)]
pub enum ProvingSystem {
    /// Groth16 - most compact proofs
    Groth16,
    /// PLONK - universal setup
    Plonk,
    /// Bulletproofs - no trusted setup
    Bulletproofs,
    /// STARK - post-quantum secure
    Stark,
}

/// Elliptic curve variants
#[derive(Debug, Clone, Copy, Serialize, Deserialize)]
pub enum Curve {
    /// BN254 (fast, 128-bit security)
    Bn254,
    /// BLS12-381 (higher security)
    Bls12_381,
    /// Pasta curves (for Halo2)
    Pasta,
}

// ============================================================================
// SNARK CIRCUIT
// ============================================================================

/// A SNARK circuit representing the compliance check
///
/// The circuit encodes: "I know a valid reasoning path from
/// input + rules to output, without revealing the path."
#[derive(Debug, Clone)]
pub struct SnarkCircuit {
    /// Rules encoded as constraints
    rule_constraints: Vec<CircuitConstraint>,

    /// Number of public inputs
    num_public: usize,

    /// Number of private inputs (witness)
    num_private: usize,

    /// Total constraints
    num_constraints: usize,
}

/// A constraint in the circuit
#[derive(Debug, Clone)]
pub struct CircuitConstraint {
    /// Constraint type
    pub constraint_type: ConstraintType,

    /// Left input wires
    pub left: Vec<(usize, i64)>,

    /// Right input wires
    pub right: Vec<(usize, i64)>,

    /// Output wire
    pub output: Vec<(usize, i64)>,
}

/// Types of constraints
#[derive(Debug, Clone)]
pub enum ConstraintType {
    /// Multiplication gate: L * R = O
    Multiplication,
    /// Addition gate: L + R = O
    Addition,
    /// Boolean constraint: x * (1-x) = 0
    Boolean,
    /// Range constraint: 0 <= x < 2^n
    Range(u32),
    /// Custom constraint
    Custom(String),
}

impl SnarkCircuit {
    /// Create a new circuit from sealed rules
    pub fn from_rules(rules: &[String]) -> Self {
        let mut constraints = Vec::new();

        for (i, rule) in rules.iter().enumerate() {
            // Each rule becomes a set of constraints
            let rule_constraints = Self::rule_to_constraints(rule, i);
            constraints.extend(rule_constraints);
        }

        let num_constraints = constraints.len();

        SnarkCircuit {
            rule_constraints: constraints,
            num_public: 3,                    // rules_hash, output_hash, timestamp
            num_private: num_constraints * 2, // witness values
            num_constraints,
        }
    }

    /// Convert a rule to circuit constraints
    fn rule_to_constraints(rule: &str, index: usize) -> Vec<CircuitConstraint> {
        // Additional constraints based on rule content
        // This is simplified - real implementation would parse the rule
        let _rule_hash = Sha256::digest(rule.as_bytes());

        // Base constraint: rule compliance boolean
        // compliance[i] * (1 - compliance[i]) = 0 (ensures boolean)
        vec![CircuitConstraint {
            constraint_type: ConstraintType::Boolean,
            left: vec![(index, 1)],
            right: vec![(index, -1), (0, 1)], // 1 - x
            output: vec![],
        }]
    }

    /// Get circuit statistics
    pub fn stats(&self) -> CircuitStats {
        CircuitStats {
            num_constraints: self.num_constraints,
            num_public_inputs: self.num_public,
            num_private_inputs: self.num_private,
            num_rules: self.rule_constraints.len(),
        }
    }
}

/// Circuit statistics
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct CircuitStats {
    pub num_constraints: usize,
    pub num_public_inputs: usize,
    pub num_private_inputs: usize,
    pub num_rules: usize,
}

// ============================================================================
// PROVING AND VERIFYING KEYS
// ============================================================================

/// Proving key (used to generate proofs)
///
/// This is generated during trusted setup.
/// MUST be kept secure - leaking allows fake proofs!
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct ProvingKey {
    /// Key identifier
    pub id: [u8; 32],

    /// The actual key material (in practice, much larger)
    pub key_material: Vec<u8>,

    /// Circuit this key is for
    pub circuit_hash: [u8; 32],

    /// Creation timestamp
    pub created_at: u64,
}

/// Verifying key (used to verify proofs)
///
/// This can be public - anyone can verify.
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct VerifyingKey {
    /// Key identifier (matches ProvingKey.id)
    pub id: [u8; 32],

    /// The actual key material
    pub key_material: Vec<u8>,

    /// Circuit this key is for
    pub circuit_hash: [u8; 32],

    /// Alpha (G1 point)
    pub alpha: Vec<u8>,

    /// Beta (G2 point)
    pub beta: Vec<u8>,

    /// Gamma (G2 point)
    pub gamma: Vec<u8>,

    /// Delta (G2 point)
    pub delta: Vec<u8>,
}

// ============================================================================
// PROOF VERIFIER
// ============================================================================

/// The Diamond Proof Verifier
///
/// Verifies ZK proofs in O(1) time.
/// Anyone can verify. No secrets needed.
pub struct ProofVerifier {
    /// Verifying key (used for pairing verification in production)
    #[allow(dead_code)]
    vk: VerifyingKey,

    /// Expected rules hash
    expected_rules_hash: [u8; 32],

    /// Maximum proof age (seconds)
    max_age: u64,
}

impl ProofVerifier {
    /// Create a new verifier
    pub fn new(vk: VerifyingKey, rules: &[String], max_age: u64) -> Self {
        let expected_rules_hash = Self::hash_rules(rules);

        ProofVerifier {
            vk,
            expected_rules_hash,
            max_age,
        }
    }

    /// Hash rules for comparison
    fn hash_rules(rules: &[String]) -> [u8; 32] {
        let mut hasher = Sha256::new();
        hasher.update(b"DIAMOND_RULES:");
        for rule in rules {
            hasher.update(rule.as_bytes());
            hasher.update(b"\x00");
        }
        hasher.finalize().into()
    }

    /// Verify a Diamond proof
    ///
    /// Returns Ok(true) if valid, Err if invalid.
    ///
    /// Verification is O(1) - constant time regardless of computation size!
    pub fn verify(&self, proof: &DiamondProof) -> Result<bool, VerificationError> {
        // Step 1: Check version
        if proof.version != 1 {
            return Err(VerificationError::UnsupportedVersion(proof.version));
        }

        // Step 2: Check rules hash
        if proof.public_inputs.rules_hash != self.expected_rules_hash {
            return Err(VerificationError::RulesMismatch);
        }

        // Step 3: Check timestamp (freshness)
        let now = SystemTime::now()
            .duration_since(UNIX_EPOCH)
            .unwrap()
            .as_secs();

        if now - proof.public_inputs.timestamp > self.max_age {
            return Err(VerificationError::ProofExpired {
                age: now - proof.public_inputs.timestamp,
                max: self.max_age,
            });
        }

        // Step 4: Verify the SNARK proof mathematically
        // This is where the magic happens - pairing check
        self.verify_pairing(&proof.pi, &proof.public_inputs)?;

        Ok(true)
    }

    /// Verify the pairing equation
    ///
    /// For Groth16: e(A, B) = e(α, β) · e(L, γ) · e(C, δ)
    ///
    /// This is a simplified simulation - real implementation would use
    /// actual elliptic curve pairings (bn254, bls12-381).
    fn verify_pairing(
        &self,
        pi: &SnarkPi,
        public_inputs: &PublicInputs,
    ) -> Result<(), VerificationError> {
        // In a real implementation:
        // 1. Compute L = Σ public_inputs[i] * vk.ic[i]
        // 2. Verify: e(A, B) = e(vk.alpha, vk.beta) · e(L, vk.gamma) · e(C, vk.delta)

        // Simulate verification by checking proof structure
        if pi.a.is_empty() || pi.a.iter().all(|&b| b == 0) {
            return Err(VerificationError::InvalidProofStructure(
                "A element is zero or empty".into(),
            ));
        }

        if pi.b.is_empty() || pi.b.iter().all(|&b| b == 0) {
            return Err(VerificationError::InvalidProofStructure(
                "B element is zero or empty".into(),
            ));
        }

        if pi.c.is_empty() || pi.c.iter().all(|&b| b == 0) {
            return Err(VerificationError::InvalidProofStructure(
                "C element is zero or empty".into(),
            ));
        }

        // Verify public inputs are properly formed
        if public_inputs.output_hash.iter().all(|&b| b == 0) {
            return Err(VerificationError::InvalidPublicInput(
                "Output hash is zero".into(),
            ));
        }

        // In reality, the pairing check would happen here
        // For simulation, we accept if structure is valid

        Ok(())
    }

    /// Batch verify multiple proofs (more efficient)
    pub fn batch_verify(&self, proofs: &[DiamondProof]) -> Result<bool, VerificationError> {
        // In real implementation, batch verification is faster than
        // verifying proofs individually due to pairing optimizations

        for proof in proofs {
            self.verify(proof)?;
        }

        Ok(true)
    }
}

/// Verification errors
#[derive(Debug, Clone, Serialize, Deserialize)]
pub enum VerificationError {
    UnsupportedVersion(u32),
    RulesMismatch,
    ProofExpired { age: u64, max: u64 },
    InvalidProofStructure(String),
    InvalidPublicInput(String),
    PairingCheckFailed,
}

impl std::fmt::Display for VerificationError {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        match self {
            Self::UnsupportedVersion(v) => write!(f, "Unsupported proof version: {}", v),
            Self::RulesMismatch => write!(f, "Rules hash mismatch"),
            Self::ProofExpired { age, max } => {
                write!(f, "Proof expired: age {} > max {}", age, max)
            }
            Self::InvalidProofStructure(s) => write!(f, "Invalid proof structure: {}", s),
            Self::InvalidPublicInput(s) => write!(f, "Invalid public input: {}", s),
            Self::PairingCheckFailed => write!(f, "Pairing check failed"),
        }
    }
}

impl std::error::Error for VerificationError {}

// ============================================================================
// PROOF GENERATOR (for Diamond-enabled AI)
// ============================================================================

/// Diamond Proof Generator
///
/// Generates ZK proofs for AI outputs.
pub struct ProofGenerator {
    /// Proving key
    pk: ProvingKey,

    /// Circuit
    circuit: SnarkCircuit,

    /// Session ID
    session_id: [u8; 32],
}

impl ProofGenerator {
    /// Create a new proof generator
    pub fn new(pk: ProvingKey, rules: &[String]) -> Self {
        let circuit = SnarkCircuit::from_rules(rules);

        let mut session_id = [0u8; 32];
        rand::RngCore::fill_bytes(&mut rand::rngs::OsRng, &mut session_id);

        ProofGenerator {
            pk,
            circuit,
            session_id,
        }
    }

    /// Generate a proof for an output
    pub fn prove(&self, output: &str, rules_hash: [u8; 32]) -> DiamondProof {
        let start = std::time::Instant::now();

        // Compute output hash
        let output_hash: [u8; 32] = Sha256::digest(output.as_bytes()).into();

        // Generate timestamp
        let timestamp = SystemTime::now()
            .duration_since(UNIX_EPOCH)
            .unwrap()
            .as_secs();

        // Generate the SNARK proof
        // In real implementation, this would be the expensive part
        let pi = self.generate_snark(output, &rules_hash);

        let generation_time = start.elapsed().as_micros() as u64;

        DiamondProof {
            version: 1,
            pi,
            public_inputs: PublicInputs {
                rules_hash,
                output_hash,
                timestamp,
                session_id: self.session_id,
            },
            metadata: ProofMetadata {
                system: ProvingSystem::Groth16,
                curve: Curve::Bn254,
                generation_time_us: generation_time,
                constraint_count: self.circuit.num_constraints,
            },
        }
    }

    /// Generate SNARK proof elements
    fn generate_snark(&self, output: &str, rules_hash: &[u8; 32]) -> SnarkPi {
        // In real implementation, this would:
        // 1. Build witness from output and private computation
        // 2. Compute A, B, C points using proving key
        // 3. Return the proof

        // Simulation: generate deterministic "proof" from inputs
        let mut hasher = Sha256::new();
        hasher.update(b"SNARK_A:");
        hasher.update(output.as_bytes());
        hasher.update(rules_hash);
        hasher.update(&self.pk.key_material);
        let a_hash = hasher.finalize();

        let mut a = vec![0u8; 64];
        a[..32].copy_from_slice(&a_hash);
        a[32..].copy_from_slice(&a_hash);

        let mut hasher = Sha256::new();
        hasher.update(b"SNARK_B:");
        hasher.update(&a);
        let b_hash = hasher.finalize();

        let mut b = vec![0u8; 128];
        for i in 0..4 {
            b[i * 32..(i + 1) * 32].copy_from_slice(&b_hash);
        }

        let mut hasher = Sha256::new();
        hasher.update(b"SNARK_C:");
        hasher.update(&b);
        let c_hash = hasher.finalize();

        let mut c = vec![0u8; 64];
        c[..32].copy_from_slice(&c_hash);
        c[32..].copy_from_slice(&c_hash);

        SnarkPi { a, b, c }
    }
}

// ============================================================================
// TESTS
// ============================================================================

#[cfg(test)]
mod tests {
    use super::*;

    fn create_test_keys() -> (ProvingKey, VerifyingKey) {
        let mut key_material = vec![0u8; 256];
        rand::RngCore::fill_bytes(&mut rand::rngs::OsRng, &mut key_material);

        let circuit_hash: [u8; 32] = Sha256::digest(b"test_circuit").into();

        let pk = ProvingKey {
            id: [1u8; 32],
            key_material: key_material.clone(),
            circuit_hash,
            created_at: 0,
        };

        let vk = VerifyingKey {
            id: [1u8; 32],
            key_material,
            circuit_hash,
            alpha: vec![1u8; 64],
            beta: vec![2u8; 128],
            gamma: vec![3u8; 128],
            delta: vec![4u8; 128],
        };

        (pk, vk)
    }

    #[test]
    fn test_circuit_from_rules() {
        let rules = vec!["Do no harm".to_string(), "Respect privacy".to_string()];

        let circuit = SnarkCircuit::from_rules(&rules);
        let stats = circuit.stats();

        assert!(stats.num_constraints > 0);
        assert_eq!(stats.num_public_inputs, 3);
    }

    #[test]
    fn test_proof_generation() {
        let rules = vec!["Do no harm".to_string()];
        let (pk, _vk) = create_test_keys();

        let generator = ProofGenerator::new(pk, &rules);

        let rules_hash = ProofVerifier::hash_rules(&rules);
        let proof = generator.prove("Hello, world!", rules_hash);

        assert_eq!(proof.version, 1);
        assert!(!proof.pi.a.iter().all(|&b| b == 0));
    }

    #[test]
    fn test_proof_verification() {
        let rules = vec!["Do no harm".to_string()];
        let (pk, vk) = create_test_keys();

        let generator = ProofGenerator::new(pk, &rules);
        let verifier = ProofVerifier::new(vk, &rules, 300);

        let rules_hash = ProofVerifier::hash_rules(&rules);
        let proof = generator.prove("Test output", rules_hash);

        let result = verifier.verify(&proof);
        assert!(result.is_ok());
        assert!(result.unwrap());
    }

    #[test]
    fn test_wrong_rules_fails() {
        let rules1 = vec!["Rule A".to_string()];
        let rules2 = vec!["Rule B".to_string()];
        let (pk, vk) = create_test_keys();

        let generator = ProofGenerator::new(pk, &rules1);
        let verifier = ProofVerifier::new(vk, &rules2, 300);

        let rules_hash = ProofVerifier::hash_rules(&rules1);
        let proof = generator.prove("Test", rules_hash);

        let result = verifier.verify(&proof);
        assert!(matches!(result, Err(VerificationError::RulesMismatch)));
    }
}