What problem does it solve? Signing fiscal documents (receipts, Z-reports) for the Ukrainian tax authority's fiscal server (ЄВПЕЗ/ФСКО) fails with cryptic rejections when the CAdES signature does not meet strict normative rules. This Skill consolidates the verified signature requirements, error codes, and rejection causes so you can produce accepted signatures and diagnose failures. ## Core Features & Use Cases - Signature format rules: Documents the mandatory DSTU 4145-2002 algorithm, CAdES-E-T/enveloping structure, embedded signer certificate, and the forbidden elements (CRL, OCSP responses, issuer certificates, content-time-stamp) that cause rejections. - Error diagnosis: Maps fiscal server error codes (9 DocumentValidationError, 12 CryptographyError, 3 InvalidTin) to their typical root causes, including OCSP outages at certificate authorities. - Kupina hash migration: Explains the DSTU 7564 (Kupina) transition, the new signature OID 1.2.804.2.1.1.1.1.3.6.1.1, and the September 2026 enforcement timeline. - Use Case: Your PRRO integration returns "DocumentValidationError" for every signed receipt. Use this Skill to identify that a forbidden content-time-stamp was added to the CMS SignedData and correct the UAPKI SIGN parameters. ## Quick Start Ask the assistant to check why the fiscal server rejects your signed PRRO receipt and which UAPKI signParams to use.
