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Fix CMS CTR-ACPKM decrypt after ASN.1 parameter reinit - #528
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The issue looked like this. It is a file after decryption: bytes after 4096 were incorrect |
Reject negative values in EVP_CTRL_KEY_MESH: Kuznyechik CTR-ACPKM (arg <= 0; -16 previously passed the modulo check and wrapped into the unsigned section_size) and Magma CTR-ACPKM (arg < 0). Rework test_engine_asn1_acpkm_reinit: - run round-trips for lengths around the CMS section boundary (256 KiB for Kuznyechik, 8192 for Magma) and split the decrypt Update right before the boundary; - verify section_size/key_meshing and the *_set flag after param_to_asn1, asn1_to_param and key re-init, not just the round-trip; - check that invalid section sizes are rejected without changing context state and that the context stays usable; - replace T() with ACPKM_CHECK so failures are reported as test results and all resources are freed.
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I ran into an issue with Kuznyechik where, after decrypting files, bytes after offset 4096 were corrupted.
I do not understand the C code or these algorithms well enough, so I asked Codex to investigate it. It produced this pull request.
Codex found that CMS
kuznyechik-ctr-acpkmparameters set the ACPKM section size from ASN.1, but a later cipher reinit overwrote that value with the default section size. As a result, decryption switched keys at the wrong boundary.This PR preserves the ACPKM section size when it was explicitly set from ASN.1 or via ctrl. It also adds a regression test that reproduces the ASN.1 parameter + reinit flow.
Please take a look if this makes sense.