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3DS message flow & JWS signing
Build a real EMV 3DS 2.x AReq, watch the ACS decide frictionless vs. challenge, sign a real ARes as a JWS with ECDSA, then verify it — or tamper with it and watch the signature catch it.
What's happening under the hood →·Read the Elliptic Curve Cryptography (ECC / ECDSA) module for the full explanation →·See the 3-D Secure and tokenization: protecting a transaction that never touches a chip use case →
1. The ACS generates its signing key
A real P-256 ECDSA key pair — the ACS's identity for every ARes it signs.