Prepare Circuit Column Extraction & Commitment

[0xVikasRushi]

Current Progress

• prepare: combine SHA256 into ECDSA + JWT circuit; remove age verification, since it will be done during the show phase Prepare circuit ES + SHA256 + JWT Decoding  #7
• prepare: parse the JWT fields into a single column
  • we will commit to this using Hyrax, and share the rerandomised commitment between prepare and show (thus getting proof linking for free)
• show proof: device binding + age verification
  • this will use the parsed JWT column from the prepare proof

Column Commitment from Decoded JWT Claims

In the prepare circuit, we extract the Base64-decoded JWT fields into a 2D array:

signal output jwtClaims[maxMatches][decodedLen];

jwtClaims array holds the decoded claims extracted from the JWT payload using the claim-decoder. Each row is a different claim.

Hyrax Commitments

To prepare this for Hyrax-style vector commitment, i was thinking of doing something like this :

1. Flatten the selected decoded claims into a 1D column vector of field elements.
2. For each claim:
   • Convert the raw byte array directly to a field element (since its fixed size)

Once we have the flattened vector:

witness_column = [roc_birthday, name, exp, iss ...]

We compute the Hyrax-style off-circuit as:

C = w_0 * G_0 + w_1 * G_1 + ... + w_n * G_n + r * H

Where:

• w_i: field elements from the parsed claim vector
• G_i: deterministically derived generator per field (e.g., hash-to-curve of label "gen_i") T256 Curve
• r: blinding scalar
• H: blinding generator

this commitment C, Witness will be passed to show circuit