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fwtpm: size RSASSA DigestInfo buffers for SHA-512, check Sign digest … - #655

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wolfSSL:masterfrom
embhorn:zd22700
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fwtpm: size RSASSA DigestInfo buffers for SHA-512, check Sign digest …#655
embhorn wants to merge 2 commits into
wolfSSL:masterfrom
embhorn:zd22700

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@embhorn embhorn commented Oct 27, 2026 •
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Size checking in FwSignDigestAndAppend, FwVerifySignatureCore, and TPM2_Sign

  • Size both buffers with MAX_DER_DIGEST_SZ, the constant wolfCrypt uses for this encoding.
  • Reject TPM2_Sign with TPM_RC_SIZE when the digest size does not match the resolved scheme hashAlg, matching FwCmd_SignDigest.
  • examples/pcr/policy_sign: the local buffer was 73 bytes; size it with WOLFTPM_MAX_DER_DIGEST_SZ (100)
  • tests: add RSASSA-SHA512 Sign/VerifySignature and Sign digest-size mismatch tests, run the SignDigest RSA roundtrip with SHA-512 too, and move BuildRsa2048SignPrimary out of the WOLFTPM_V185 block so builds without v1.85 can use it.

Fixes ZD22700

Thanks to Alexandre Laroche for submitting this issue and confirming the fix.

@embhorn
fwtpm: size RSASSA DigestInfo buffers for SHA-512, check Sign digest …
c5a6553 
…size

FwSignDigestAndAppend and FwVerifySignatureCore sized their PKCS#1
v1.5 DigestInfo buffers as WC_MAX_DIGEST_SIZE + MAX_ENCODED_DIG_ASN_SZ,
which leaves out the outer SEQUENCE and the AlgorithmIdentifier. A
SHA-512 DigestInfo is 83 bytes. Size both buffers with
MAX_DER_DIGEST_SZ, the constant wolfCrypt uses for this encoding.

- Reject TPM2_Sign with TPM_RC_SIZE when the digest size does not
  match the resolved scheme hashAlg (Part 3 Sec.20.2.1), matching
  FwCmd_SignDigest.
- examples/pcr/policy_sign: size the DigestInfo buffer with
  WOLFTPM_MAX_DER_DIGEST_SZ, since older wolfSSL does not export
  MAX_DER_DIGEST_SZ.
- tests: add RSASSA-SHA512 Sign/VerifySignature and Sign digest-size
  mismatch tests, run the SignDigest RSA roundtrip with SHA-512 too,
  and move BuildRsa2048SignPrimary out of the WOLFTPM_V185 block so
  builds without v1.85 can use it.
@embhorn embhorn self-assigned this Oct 27, 2026
Copilot AI balanced review requested due to automatic review settings October 27, 2026 16:06
Copilot AI reviewed Oct 27, 2026

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@embhorn
embhorn requested a review from dgarske October 27, 2026 16:18
dgarske
dgarske requested changes Oct 27, 2026
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Comment thread examples/pcr/policy_sign.c Outdated
Comment thread src/fwtpm/fwtpm_crypto.c Outdated
@embhorn
embhorn requested a review from dgarske October 27, 2026 18:30
@dgarske dgarske self-assigned this Oct 27, 2026
@embhorn

embhorn commented Oct 28, 2026

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Customer has confirmed this fix

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