solana_zk_token_sdk/instruction/
ciphertext_commitment_equality.rs

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//! The ciphertext-commitment equality proof instruction.
//!
//! A ciphertext-commitment equality proof is defined with respect to a twisted ElGamal ciphertext
//! and a Pedersen commitment. The proof certifies that a given ciphertext and a commitment pair
//! encrypts/encodes the same message. To generate the proof, a prover must provide the decryption
//! key for the first ciphertext and the Pedersen opening for the commitment.

#[cfg(not(target_os = "solana"))]
use {
    crate::{
        encryption::{
            elgamal::{ElGamalCiphertext, ElGamalKeypair},
            pedersen::{PedersenCommitment, PedersenOpening},
        },
        errors::{ProofGenerationError, ProofVerificationError},
        sigma_proofs::ciphertext_commitment_equality_proof::CiphertextCommitmentEqualityProof,
        transcript::TranscriptProtocol,
    },
    merlin::Transcript,
    std::convert::TryInto,
};
use {
    crate::{
        instruction::{ProofType, ZkProofData},
        zk_token_elgamal::pod,
    },
    bytemuck_derive::{Pod, Zeroable},
};
/// The instruction data that is needed for the
/// `ProofInstruction::VerifyCiphertextCommitmentEquality` instruction.
///
/// It includes the cryptographic proof as well as the context data information needed to verify
/// the proof.
#[derive(Clone, Copy, Pod, Zeroable)]
#[repr(C)]
pub struct CiphertextCommitmentEqualityProofData {
    pub context: CiphertextCommitmentEqualityProofContext,
    pub proof: pod::CiphertextCommitmentEqualityProof,
}

/// The context data needed to verify a ciphertext-commitment equality proof.
#[derive(Clone, Copy, Pod, Zeroable)]
#[repr(C)]
pub struct CiphertextCommitmentEqualityProofContext {
    /// The ElGamal pubkey
    pub pubkey: pod::ElGamalPubkey, // 32 bytes

    /// The ciphertext encrypted under the ElGamal pubkey
    pub ciphertext: pod::ElGamalCiphertext, // 64 bytes

    /// The Pedersen commitment
    pub commitment: pod::PedersenCommitment, // 32 bytes
}

#[cfg(not(target_os = "solana"))]
impl CiphertextCommitmentEqualityProofData {
    pub fn new(
        keypair: &ElGamalKeypair,
        ciphertext: &ElGamalCiphertext,
        commitment: &PedersenCommitment,
        opening: &PedersenOpening,
        amount: u64,
    ) -> Result<Self, ProofGenerationError> {
        let context = CiphertextCommitmentEqualityProofContext {
            pubkey: pod::ElGamalPubkey(keypair.pubkey().into()),
            ciphertext: pod::ElGamalCiphertext(ciphertext.to_bytes()),
            commitment: pod::PedersenCommitment(commitment.to_bytes()),
        };
        let mut transcript = context.new_transcript();
        let proof = CiphertextCommitmentEqualityProof::new(
            keypair,
            ciphertext,
            opening,
            amount,
            &mut transcript,
        );
        Ok(CiphertextCommitmentEqualityProofData {
            context,
            proof: proof.into(),
        })
    }
}

impl ZkProofData<CiphertextCommitmentEqualityProofContext>
    for CiphertextCommitmentEqualityProofData
{
    const PROOF_TYPE: ProofType = ProofType::CiphertextCommitmentEquality;

    fn context_data(&self) -> &CiphertextCommitmentEqualityProofContext {
        &self.context
    }

    #[cfg(not(target_os = "solana"))]
    fn verify_proof(&self) -> Result<(), ProofVerificationError> {
        let mut transcript = self.context.new_transcript();

        let pubkey = self.context.pubkey.try_into()?;
        let ciphertext = self.context.ciphertext.try_into()?;
        let commitment = self.context.commitment.try_into()?;
        let proof: CiphertextCommitmentEqualityProof = self.proof.try_into()?;

        proof
            .verify(&pubkey, &ciphertext, &commitment, &mut transcript)
            .map_err(|e| e.into())
    }
}

#[allow(non_snake_case)]
#[cfg(not(target_os = "solana"))]
impl CiphertextCommitmentEqualityProofContext {
    fn new_transcript(&self) -> Transcript {
        let mut transcript = Transcript::new(b"CtxtCommEqualityProof");
        transcript.append_pubkey(b"pubkey", &self.pubkey);
        transcript.append_ciphertext(b"ciphertext", &self.ciphertext);
        transcript.append_commitment(b"commitment", &self.commitment);
        transcript
    }
}

#[cfg(test)]
mod test {
    use {
        super::*,
        crate::encryption::{elgamal::ElGamalKeypair, pedersen::Pedersen},
    };

    #[test]
    fn test_ctxt_comm_equality_proof_correctness() {
        let keypair = ElGamalKeypair::new_rand();
        let amount: u64 = 55;
        let ciphertext = keypair.pubkey().encrypt(amount);
        let (commitment, opening) = Pedersen::new(amount);

        let proof_data = CiphertextCommitmentEqualityProofData::new(
            &keypair,
            &ciphertext,
            &commitment,
            &opening,
            amount,
        )
        .unwrap();

        assert!(proof_data.verify_proof().is_ok());
    }
}