How to send strings as signals to circom?

Question

I want to create a circuit to measure the length of a string in Circom. There are only numeric data types, how can I do that?

Answer 1

You can supply string as a series of bytes. You can:

• Make your circuit take in an array of signals of length 256
• Iterate over the array
• Look for first 0 byte
• Save the index as string length

This will allow you to measure string lengths of up to 256 bytes.

Answer 2

You can convert your string to an array of numbers (bytes) using an encoding appropriate to your use case, e.g. Unicode or ASCII.