pepper_solidity_export

Script to export zkSnark proofs generated with pepper into solidity smart contracts.

Pepper Installation

Install pepper to ~/pequin (or chose another path and replace all occurrences in this tutorial).

To create a proof that is verifiable on the EVM, you need to replace the default curve -DCURVE_BN128 with the EVM curve -DCURVE_ALT_BN128 in ~/pequin/pepper/Makefile.

Next, export pepper's libsnark installation folder into $LIBSNARK (our script shares the pepper's dependency instead of reinstalling it).

export LIBSNARK=~/pequin/thirdparty/libsnark/

Exporting verification key into a smart contract

Assuming you have written a snark myapp.c. Inside ~/pequin/pepper run:

./pepper_compile_and_setup_P.sh myapp
./pepper_compile_and_setup_V.sh myapp myapp.vkey myapp.pkey myapp.raw_vkey

The last argument pepper_compile_and_setup_V is important. This will export the unprocessed verification key, which is needed to create the smart contract.

Then inside the pepper_solidity_export repository run:

make export
bin/export contract ~/pequin/pepper/verification_material/myapp.raw_vkey

Deploy the generated smart contract e.g. using Remix

Verifying a pepper proof on the EVM

Inside ~/pequin/pepper create a proof and also copy the inputs and outputs:

bin/pepper_prover_myapp prove myapp.pkey myapp.inputs myapp.outputs myapp.proof
cat prover_verifier_shared/myapp.inputs
cat prover_verifier_shared/myapp.outputs

Then inside the pepper_solidity_export repository run:

bin/export proof ~/pequin/pepper/prover_verifier_shared/myapp.proof

Amend the output of this script with another array containing all inputs and outputs you printed in the step above:

<exported proof>, [i_1, ..., i_n, o_1, ..., o_n]

Very large inputs/outputs might have to be converted into hex-strings. This can be easily done using python's hex() method.

Call verifyTx on your deployed smart contract with this list. You should see a transaction emitting a Verified event.