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STATUS_AUTH_TAG_MISMATCH
Authenticated encryption rejected the ciphertext or associated data
Authenticated-encryption modes validate an authentication tag over the ciphertext and, where applicable, additional authenticated data. This status means the recomputed tag did not match. The ciphertext must be treated as unauthenticated, and plaintext output from the failed operation must not be consumed even when some bytes were produced before the failure was reported.
A mismatch can result from corruption or tampering, but it also occurs when the key, nonce or IV, tag length, algorithm parameters, ciphertext boundaries, or associated data differ between encryption and decryption. Reusing a nonce can create a separate security failure and should not be used as a troubleshooting shortcut.
What to inspect
- Compare key identifier, nonce or IV, tag bytes and length, ciphertext length, and associated data on both sides.
- Verify that framing does not include or omit headers, padding, or trailer bytes differently.
- Preserve the failing record for analysis, but do not log secret keys or decrypted plaintext.
- Reject the record atomically; retry only after correcting inputs or retrieving an intact copy.
References
- Microsoft Open Specifications: NTSTATUS values
- NIST SP 800-38D: GCM and authentication tags
- Microsoft Windows SDK metadata: ntstatus.h
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