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NTE_BUFFER_TOO_SMALL
NTE_BUFFER_TOO_SMALL identifies a failure in output sizing. The destination cannot hold the result or property value, commonly because the caller skipped the size-query pass or reused a stale length after parameters changed. Diagnose output sizing at the first component that returned the value, not the last user-interface layer that displayed it; later cleanup and fallback attempts can produce different secondary errors.
Read the failure at the correct layer
Many Windows cryptographic APIs use caller-owned byte buffers with exact sizing and aliasing rules. Capacity, byte-versus-character units, two-pass size queries, padding expansion, and permitted in-place layouts all belong to the call contract., inspect address ranges and lengths, not just pointer equality or a nominal array size.
Build an incident record
- Input and output base addresses, byte lengths, and the range each one occupies
Call the API in its documented size-query mode and retain the returned byte count.
Distinguishes byte capacity from address-range overlap. - The size returned by a query pass and every parameter that changed before the data pass
Distinguish character counts from byte counts and include terminators only where the API specifies them.
Detects stale lengths after parameters or key state changed. - Algorithm, mode, padding, tag, property, and provider-specific in-place rules
Do not assume a previous ciphertext, signature, key blob, or property size remains valid for a new algorithm or key.
Shows whether the provider supports the proposed in-place layout.
Preserve the evidence chain
Correlate the last successful operation with provider installation or update, key creation or renewal, profile or session changes, device insertion and removal, policy refresh, and the first failing call. The order matters: a provider error that starts immediately after a key migration suggests a different boundary from one that appears only after a service account changes.
- a minimal reproducer that names the API, provider, key or container, flags, and nonsecret input sizes.
- In the path, provider, device, profile, and operating-system event records covering the last success and first failure.
- In the path, a known-good control result produced under the same identity, architecture, and provider selection.
Use two comparison axes
Allocate distinct input and output buffers from the latest size returned by the same key and parameter set., preserve the original input, call the operation once, and compare reported lengths. Then test in-place behavior only when the API explicitly documents it in an output sizing investigation.
| Test | Interpretation |
|---|---|
| Same input, known-good path | For output sizing, success moves attention toward the selected provider, policy, device, context, or transaction state. |
| Known-good input, failing path | For output sizing, failure suggests that the environment or selected object is independently unable to perform the operation. |
| Original path after one isolated change | For output sizing, this comparison demonstrates whether the proposed correction addresses the original condition. |
Do not collapse it into a neighboring code
Unlike NTE_BUFFERS_OVERLAP, this result concerns capacity rather than aliasing between source and destination ranges. A larger buffer does not cure forbidden overlap, and separate buffers do not cure insufficient capacity. Keep those hypotheses separate so a test does not accidentally change both conditions.
For output sizing, also retain the original numeric value; neighboring constants can encode materially different remediation paths even when an application presents all of them as an authentication, certificate, or security failure.
Verification after the change
In the path, resolution requires correct byte ranges and sizes for the exact algorithm and provider, including repeated calls where output length varies with padding or encoded content. Keep a regression case that uses nonsecret identifiers and expected outcomes, including one negative control that must continue to fail.
Technical references
These sources define the HRESULT and the relevant output sizing interface, protocol, or data format.
- Microsoft Open Specifications: HRESULT values.
- Microsoft: CNG key storage functions.
- Microsoft: CNG primitive cryptography functions.
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