fix(sdk): reject GMAC root signatures (DSPX-4703) - #4030
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Included review availability: Your plan provides up to 1 included review per hour; 0 remain after this review. 📝 WalkthroughWalkthroughThe SDK now separates segment and root integrity calculations. Root signatures accept only HS256, while segment signatures support HS256 and GMAC. The server places pprof endpoints behind authentication and limits profiling duration and request body size. ChangesIntegrity enforcement
Profiling endpoint controls
Priority: ➖ Normal Estimated code review effort: 4 (Complex) | ~45 minutes Change: Bug fix Sequence Diagram(s)sequenceDiagram
participant Client
participant AuthN
participant pprofHandler
participant ProfilingEndpoint
Client->>AuthN: Send profiling request
AuthN->>pprofHandler: Forward authenticated request
pprofHandler->>pprofHandler: Validate duration and body size
pprofHandler->>ProfilingEndpoint: Serve valid request
Suggested reviewers: Merge Risk: ⚪ Minimal · up to No unresolved merge-blocking issue remains. 🚥 Pre-merge checks | ✅ 4 | ❌ 1❌ Failed checks (1 warning)
✅ Passed checks (4 passed)
Full details: Docstring CoverageExplanation Docstring coverage is 52.38% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 42 functions across 6 files. (1 skipped: 1 unsupported.)
✨ Finishing Touches 💡 2📝 Generate docstrings 💡
🛠️ Fix failing CI checks 💡
🧪 Generate unit tests (beta)
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dmihalcik-virtru
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Inline comments:
In `@sdk/schema/manifest.schema.json`:
- Around line 132-134: Update the root-signature algorithm schema constraint
near the algorithm description to accept any case variant of HS256 while
rejecting all other values, keeping it consistent with validateRootSignature’s
case-insensitive validation.
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📒 Files selected for processing (6)
sdk/schema/manifest-lax.schema.jsonsdk/schema/manifest.schema.jsonsdk/tdf.gosdk/tdf_helpers_test.gosdk/tdf_readat_test.gosdk/tdf_root_signature_test.go
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Code reviewFound 1 issue:
platform/sdk/schema/manifest.schema.json Lines 131 to 135 in b1b8af9 Lines 1646 to 1648 in b1b8af9 🤖 Generated with Claude Code - If this code review was useful, please react with 👍. Otherwise, react with 👎. |
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A ZTDF's root signature is the only thing that authenticates the manifest's
ordered list of segment hashes. AES-GCM tags bind a segment's own bytes and
nothing about its index, its neighbours, or how many segments there are, so
segment-level integrity cannot notice a truncated, reordered, or duplicated
segment list.
`calculateSignature` applied one dispatch to both jobs. For a segment that is
correct: "GMAC" means read back the AES-GCM tag the cipher just computed over
that segment's ciphertext. For the root it is not, because the aggregate hash
never passes through AES-GCM -- there is no tag to read out, so the function
returned a copy of the trailing bytes of its own input, i.e. the last segment
hash. Manifest data compared against manifest data, with the payload key never
used.
`validateRootSignature` took the algorithm from `manifest.rootSignature.alg`,
which is unauthenticated, and coerced anything unrecognised to HS256 while
honouring "GMAC" in any casing. An attacker with no key could therefore take an
HS256-rooted TDF, rewrite the root to `alg: "GMAC"` with a signature copied
from the last segment hash, and then truncate, reorder, or duplicate segments
with the whole thing still verifying.
Read path (sdk):
- Retire `calculateSignature` in favour of four functions that cannot be
misapplied: `hmacIntegrity`, `readAEADTag` (unexported, reachable only
through `segmentIntegrity`), `segmentIntegrity` (HS256 or GMAC), and
`rootIntegrity` (HS256 only).
- `validateRootSignature` now fails closed on a case-insensitive allowlist:
anything other than HS256 returns ErrUnsupportedRootIntegrityAlgorithm,
surfaced to callers as ErrRootSignatureFailure (which wraps ErrTampered).
An absent `alg` still means HS256, as before; the HMAC must verify either
way.
- `manifestSegmentIntegrityAlg` keeps the segment path permissive, since both
algorithms are meaningful over ciphertext.
- manifest.schema.json constrains `rootSignature.alg` to HS256.
manifest-lax.schema.json deliberately stays permissive so it can still
parse hostile input for testing.
Write path, both `sdk` and `sdk/experimental/tdf`:
- Split `IntegrityAlgorithm` into `RootIntegrityAlg` (RootHS256 only) and
`SegmentIntegrityAlg` (SegmentHS256, SegmentGMAC). One type could not
express that the two positions accept different sets, which is what let a
GMAC root be configured in the first place. Each type's String() returns
the manifest spelling, and a non-spelling fallback out of range, so a value
with no legal name cannot reach a manifest.
- `IntegrityAlgorithm`, `HS256` and `GMAC` remain as deprecated untyped
constants with their original numeric values, so existing callers still
compile and convert to the matching new constant.
- The experimental writer previously accepted `WithIntegrityAlgorithm(GMAC)`
and emitted the forged-by-construction root described above; Finalize now
returns ErrUnsupportedRootIntegrityAlgorithm. `Option` cannot return an
error, so Finalize is the only place to catch it.
Unit tests in both packages pin the boundary each helper enforces, and the
experimental writer's Finalize tests pin the write-side refusal. End-to-end
coverage of the attack itself -- truncation, reordering, GMAC in four casings,
and an unknown algorithm that must not be coerced -- lives in the cross-SDK
corpus, so every SDK is held to the same behaviour rather than Go alone.
Every golden TDF in the cross-SDK corpus is already `alg: HS256`, so no
existing well-formed file is affected.
Refs: DSPX-4703, and the write-side controls in DSPX-4736.
Signed-off-by: Dave Mihalcik <dmihalcik@virtru.com>
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Proposed Changes
The bug
A ZTDF's root signature is the only thing that authenticates the manifest's ordered list of segment hashes. AES-GCM tags bind a segment's own bytes and say nothing about its index, its neighbours, or how many segments exist — so segment-level integrity structurally cannot notice a truncated, reordered, or duplicated segment list.
calculateSignatureapplied one dispatch to both jobs:For a segment that is correct —
datais ciphertext, and its last 16 bytes really are the AES-GCM tag the cipher just computed. For the root it is not: the aggregate hash never passes through AES-GCM, so there is no tag to read out. The function returned a copy of the trailing bytes of its own input — that is, the last segment hash. Manifest data compared against manifest data, with the payload key never used.And the algorithm was taken from the manifest, which is unauthenticated:
Note it also coerced anything unrecognised to HS256 rather than rejecting it.
Why this is not opt-in
The producer never has to choose GMAC. Because
rootSignature.algis read from the manifest, an attacker with no key can take any HS256-rooted TDF, rewrite the root toalg: "GMAC"with a signature copied from the last segment hash, and then truncate, reorder, or duplicate segments — and the whole thing still verifies.The fix — read path
calculateSignaturefor four functions that cannot be misapplied:hmacIntegrity— the HMAC primitivereadAEADTag— unexported, reachable only throughsegmentIntegrity, so tag-extraction can no longer be pointed at a non-AEAD inputsegmentIntegrity— HS256 or GMACrootIntegrity— HS256 onlyvalidateRootSignaturefails closed on a case-insensitive allowlist. Anything other than HS256 returnsErrUnsupportedRootIntegrityAlgorithm, surfaced asErrRootSignatureFailure(which wrapsErrTampered). An absentalgstill means HS256, as before — the HMAC must verify either way.manifestSegmentIntegrityAlgkeeps the segment path permissive; both algorithms are meaningful there.manifest.schema.jsonconstrainsrootSignature.algto["HS256"].manifest-lax.schema.jsondeliberately stays permissive so it can still parse hostile input for testing.The fix — write path, and the type split
One
IntegrityAlgorithmtype could not express that the two positions accept different sets of values, which is what let a GMAC root be configured in the first place. Bothsdkandsdk/experimental/tdfnow have:Each type's
String()returns the manifest spelling, and a deliberately non-spelling fallback out of range, so a value with no legal name cannot reach a manifest.rootIntegrity/segmentIntegritystill validate, because both types are int-backed.IntegrityAlgorithm,HS256andGMACremain, marked Deprecated, as untyped constants with their original numeric values — existing callers keep compiling and convert to the matching new constant.This also closes a live hole in the experimental writer:
WithIntegrityAlgorithm(GMAC)previously emitted the forged-by-construction root described above.Optioncannot return an error, soFinalizeis where it is caught, and it now returnsErrUnsupportedRootIntegrityAlgorithm. (One example inexample_test.gowas passingGMACand had to be corrected — that example was producing a file no conforming reader should accept.)New exported API
sdkandsdk/experimental/tdf:RootIntegrityAlg,RootHS256,SegmentIntegrityAlg,SegmentHS256,SegmentGMAC,ErrUnsupportedSegmentIntegrityAlgorithm,ErrUnsupportedRootIntegrityAlgorithm. Insdk/experimental/tdf,WithIntegrityAlgorithmandWithSegmentIntegrityAlgorithmkeep their names but now take the corresponding new type. The stablesdkstill exposes no public option for either algorithm; those are #4029 (DSPX-4736), a sibling PR offmain, not a dependency.Compatibility
Every golden TDF in the cross-SDK corpus is already
rootSignature.alg = "HS256"withsegmentHashAlg = "GMAC"— verified by dumping all 8 manifests. No existing well-formed file is affected. A file that this rejects is one no honest writer produces.Checklist
Testing Instructions
Unit coverage in both packages: each algorithm's manifest spelling and the deliberately unusable fallback out of range, GMAC over a too-short ciphertext, every non-HS256 root value refused, the deprecated constants still landing on the matching new ones, GMAC refused as a root through
Finalize, and both segment algorithms round-tripping throughFinalizewith the root still HS256.End-to-end coverage of the attack lives in the cross-SDK corpus (opentdf/tests#594,
spec/DSPX-4703.md): keyless truncation and reordering under a forged GMAC root, GMAC in four casings (GMAC/gmac/GMac/gMaC) both forged and declared-only, an unknown algorithm that must not be coerced to HS256, and the positive controls (untouched round-trip, HS256 in any casing, absentalg). Holding every SDK to that behaviour is worth more than a Go-only copy of it, and the corpus was where the exploit was demonstrated in the first place.Related
spec/DSPX-4703.mdinopentdf/testsmain, not a dependencyCross-SDK coverage lives in opentdf/tests#594.
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