Getting started tutorial doesn't seem to work anymore

[michal-wrzosek]

Hi,
I tried to follow the "Getting started" tutorial but no matter what I do to my circuit when proving I end up with [ERROR] snarkJS: Error: Scalar size does not match.

Do I miss something here?

Here's a Dockerfile to be able to reproduce the issue and all the steps:

FROM node:20

RUN curl --proto '=https' --tlsv1.2 https://sh.rustup.rs -sSf | sh -s -- -y

ENV PATH="/root/.cargo/bin:${PATH}"

RUN git clone https://github.com/iden3/circom.git

WORKDIR /circom

RUN git checkout v2.1.9

RUN cargo build --release

RUN cargo install --path circom

RUN npm install -g [email protected]

WORKDIR /circuits

RUN cat <<EOF > ./multiplier.circom
pragma circom 2.0.0;

template Multiplier2() {
  signal input a;
  signal input b;
  signal output c;
  c <== a*b;
}

component main = Multiplier2();
EOF

RUN cat <<EOF > ./multiplier-input.json
{ "a": "2", "b": "3" }
EOF

# This is super slow to build in docker so I'm going to use the prebuilt one
# RUN snarkjs powersoftau new bn128 12 ./pot12_0000.ptau
# RUN snarkjs powersoftau contribute ./pot12_0000.ptau ./pot12_0001.ptau --name="First contribution"

RUN curl -O https://hermez.s3-eu-west-1.amazonaws.com/powersOfTau28_hez_final_08.ptau

RUN mkdir ./multiplier

RUN circom ./multiplier.circom \
  --wasm \
  --r1cs \
  --O0 \
  --sym \
  --inspect \
  -o ./multiplier

RUN snarkjs r1cs info \
  ./multiplier/multiplier.r1cs

RUN node ./multiplier/multiplier_js/generate_witness.js \
  ./multiplier/multiplier_js/multiplier.wasm \
  ./multiplier-input.json \
  ./multiplier/multiplier.wtns

RUN snarkjs powersoftau prepare phase2 \
  ./powersOfTau28_hez_final_08.ptau \
  ./multiplier/multiplier.ptau

RUN snarkjs groth16 setup \
  ./multiplier/multiplier.r1cs \
  ./multiplier/multiplier.ptau \
  ./multiplier/multiplier-0000.zkey

RUN snarkjs zkey contribute \
  ./multiplier/multiplier-0000.zkey \
  ./multiplier/multiplier.zkey \
  --name="John Doe" \
  -e="Random entropy"

RUN snarkjs zkey export verificationkey \
  ./multiplier/multiplier.zkey \
  ./multiplier/multiplier-verification-key.json

RUN snarkjs groth16 prove \
  ./multiplier/multiplier.zkey \
  ./multiplier/multiplier.wtns \
  ./multiplier/multiplier-proof.json \
  ./multiplier/multiplier-public.json

CMD snarkjs groth16 verify \
  ./multiplier/multiplier-verification-key.json \
  ./multiplier/multiplier-proof.json \
  ./multiplier/multiplier-public.json

Save this as "Dockerfile" file then build and run like this:

docker build -t zk-proofs .
docker run zk-proofs

Interestingly, running the prove/verify part from within the node script (not through CLI) works just fine.