CEP XML parsing, signature checks and transaction binding

Parsing checks the document shape

An XML parser extracts fields; it cannot establish that a bank signed the document. GridZen bounds document size and structure and rejects external entities. A PDF or screenshot alone does not enter this XML verification route. Never treat a file name, a displayed seal or the phrase “valid payment” as authenticity evidence.

Check the signature against the exact original

The signature check is a separate server-side step against the official validation service. Its response must refer to the exact original XML and signed material. Callers cannot upload their own successful validation HTML. Preserve the original bytes and SHA-256; changing whitespace in signed material may change what was signed.

An unavailable validator produces a pending or review result, not a fabricated success. A signature result also does not establish that the supplied document belongs to the merchant’s expected order.

Bind the evidence to the expected operation

Compare all six operation fields independently. Institution labels are interpreted using institution codes and explicit aliases, not unrestricted fuzzy matching. The observed signed-chain structure is checked before a verified result is returned. Keep the signature outcome, binding checks and beneficiary-name comparison as separate fields in your audit record.