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Circom Workshop 2


The second circom workshop: we dig deeper into a few key circuits such as zk-group-sig, isZero, and Num2Bits.

Pre-Session Reading/Setup

Circom workshop #1 would be helpful as they build on each other.

To check your understanding, we'd recommend trying to implement any of IsZero, IsEqual, Num2Bits, GreaterThan, QuinSelector, RangeProof, IsNegative, or Modulo by hand without just copy-pasting code from circomlib or references.

  • IsZero, IsEqual, Num2Bits, GreaterThan can be found in circomlib (comparators and bitify), and do what you'd expect them to do.
  • QuinSelector is a circuit that takes as input an array in[nElements], an index index, and outputs the value of in[index].
  • RangeProof is a circuit that takes in upper lower and test, outputs 1 if test is in the range and 0 otherwise.
  • IsNegative is a circuit that takes in an input, outputs 1 if input is negative and 0 otherwise. We define a convention: "Negative" is by convention considered to be any residue in (p/2, p-1], and Positive is anything in [1, p/2)
  • Modulo (hard) takes in a dividend and divisor, and outputs a quotient and remainder. it is acceptable to first range proof your dividend and divisor to be at most some large number (say 1e12), and assume that everything is positive.
  • QuinSelector, RangeProof, IsNegative, and Modulo can be found in the dark forest circuits repo