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TPM_E_BADTAG
What failed and what did not
TPM_E_BADTAG (0x8028001E) belongs to TPM 1.2 command processing. This result means the request header tag does not match a valid TPM 1.2 command form or its expected authorization-session count.
Keep the result value 0x8028001E attached to the symbolic name. Some logs may store it as a negative signed integer or expose only a generic CNG, WMI, BitLocker or enrollment message. Preserve the original HRESULT because those representations can hide the TPM- or TBS-specific condition.
Collect a useful trace
- Producer: the TPM 1.2 command decoder and state machine.
- Rejected invariant: the request header tag does not match a valid TPM 1.2 command form or its expected authorization-session count.
- What to capture: the raw request header bytes, tag, paramSize, ordinal, expected auth areas, byte order, and the response header before any library translation.
- Safe comparison: decode the command buffer independently and compare its tag with the command variant actually serialized.
Narrow experiment
Build the minimal case around the original command contract. Use a disposable object when the request can write NV data, advance a counter, change authorization state or consume a lock transition. The comparison is valid only when the caller, TPM generation and security policy remain the same.
| Question | Evidence |
|---|---|
| What exact state was rejected? | the request header tag does not match a valid TPM 1.2 command form or its expected authorization-session count |
| Which layer owns the result? | The TPM 1.2 command decoder and state machine. |
| What must be correlated? | the raw request header bytes, tag, paramSize, ordinal, expected auth areas, byte order, and the response header before any library translation |
| Controlled comparison | decode the command buffer independently and compare its tag with the command variant actually serialized |
Similar-looking outcomes
| Constant | Meaning |
|---|---|
TPM_E_IOERROR | An IO error occurred transmitting information to the TPM. |
TPM_E_SHA_ERROR | The calculation is unable to proceed because the existing SHA-1 thread has already encountered an error. |
TPM_E_ENCRYPT_ERROR | The encryption process had a problem. |
The codes above may appear in the same workflow, but they are not aliases. TPM_E_BAD_DATASIZE concerns a body or blob length after framing; it rejects the header form itself.
Operational response
Construct the header from the tpm structure definition and make the tag agree with the number and kind of authorization sessions. Do not clear ownership, delete keys or reset PCR-related state merely to see whether the message disappears; those actions can destroy the evidence and protected material while leaving serialization or command-order defects unchanged.
Proof consists of a successful replay plus validation of the intended key, PCR, NV, context, event-log, provider or service result. A software fallback or a newly provisioned blank TPM answers a different question than the original failure.
Source material
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