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aes: add dupctx for AES-GCM and AES-CCM - #518
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ColtonWilley wants to merge 2 commits into
Open
ColtonWilley wants to merge 2 commits into
ColtonWilley wants to merge 2 commits into
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EVP_CIPHER_CTX_copy failed for GCM/CCM, breaking pyca/cryptography's AESGCM, which copies a keyed context per operation. The copy re-keys its own Aes from the saved key; streaming GCM refuses a copy mid-operation, and final starts the stream if no update followed the IV.
Copy keyed base contexts as pyca/cryptography does: the copies must match the default provider, decrypt, and leave the base reusable. GCM also finalises an empty message straight after the IV.
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🔵 Needs a closer look
Cryptographic buffer ownership and active-stream copy boundaries remain untested and require human review.
1 open issue
What changed in this PR
Adds AES-GCM/CCM context duplication to support EVP_CIPHER_CTX_copy, including pyca/cryptography’s per-operation copies of keyed contexts.
Changes:
- Re-keys duplicated contexts and deep-copies cached buffers, while rejecting active streaming GCM copies.
- Initializes streaming GCM during finalization when no update follows the IV, and clears sensitive context memory on release.
- Adds copy regression tests across AES key sizes, including empty-message GCM operations.
| File | Description |
|---|---|
| test/unit.h | Declares the AEAD context-copy test. |
| test/unit.c | Registers the new regression test. |
| test/test_aestag.c | Tests keyed-context copies against OpenSSL results. |
| src/wp_aes_aead.c | Implements duplication, key retention, cleanup, and GCM finalization changes. |
Review effort: Balanced
Comment on lines
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| base[0] = aead_base(cipher[1], 1, ccm, key); | ||
| base[1] = aead_base(cipher[1], 0, ccm, key); |
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AES-GCM/CCM had no dupctx, so
EVP_CIPHER_CTX_copyfailed and pyca/cryptography's AESGCM, which copies a keyed context per operation, failed on every call. The copy re-keys its own Aes from a saved key and deep-copies cached AAD/input; streaming GCM refuses a copy once data has been processed. GCM final now starts the stream when no update followed the IV.