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andodeki d4e3e9a443 feat(pdf): encryption on save — AES-128 and AES-256 (Phase 6, part one) ... ADR 0024. This reverses ADR 0005's "never write encryption", and the reason it is safe to reverse is that the facts changed underneath it. A crate that only reads cannot produce weak ciphertext, so refusing to write any was free. Now that Phase 4 creates documents and Phase 5 edits them, the refusal does something worse than protect nobody: open a password-protected file, change one annotation, save, and the output is plaintext. No error, no warning — the protection is silently dropped. That is this project's recurring failure mode in the one place where the consequence is a breach. The principle survives in a narrower form: no hand-rolled crypto, and no weak cipher offered as an option. RC4 stays readable because files use it and is not writable — EncryptionAlgorithm has no RC4 variant, so the refusal is a type, not a runtime check someone can route around. The encryptor is the literal inverse of the decryptor and imports its primitives rather than restating them; two implementations of one algorithm drift, and here they drift towards "decrypts to garbage". Every unit test round-trips through the existing Decryptor. Encryption sits at one choke point: PdfWriter holds the Encryptor and write_object_at encrypts everything passing through. Not per call site — there are twenty-two of those in PdfDocBuilder, and one stream written in the clear inside an encrypted document is not a partial failure, it is a leak that no reader will report because the file is otherwise valid. The /Encrypt dictionary is the single deliberate exemption: it holds the salts a reader needs before it has a key, so encrypting it bricks the file. Verified against implementations we share no code with, now gated in CI: ok qpdf opens it with the password ok it really is AES-256 ok the wrong password is refused ok poppler decrypts the content ok no plaintext in the encrypted file Four mutations, all killed — two only after the tests were strengthened, and both misses are the interesting part: A fixed IV survived two_saves_of_one_document_are_not_byte_identical, because the AES-256 file key is fresh per save and that alone makes the output differ. The property actually needed is narrower: one encryptor, identical plaintext, different bytes. In CBC a repeated IV under one key leaks that two plaintexts are equal. A wrong /Length survived because our own reader recovers by scanning for endstream — a robustness fix from ADR 0023. An independent reader that trusts /Length reads a truncated stream and decrypts garbage. A lenient reader hides a broken writer, which is why the external gate exists. The /Length test itself had a bug first: it searched a from_utf8_lossy view and reported a stream declaring 80 bytes holding 156. Ciphertext is not UTF-8; the replacement characters shifted every offset. Unencrypted output stays byte-reproducible; encrypted output cannot be, and a test asserts that loss rather than leaving it implicit. pdf: 1220 passed (was 1187). pdf-ui: green. Coverage 88.21%, encrypt_write.rs at 96.5%. Signing is NOT started. It needs the trust-anchor decision ADR 0010 deferred: VerificationStatus::Valid is unreachable by construction, and making sign -> verify pass is a policy change, not an implementation detail. The plan's Phase 6 status now says so.		2026-08-18 07:27:45 +00:00
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generate_sample.rs	feat(pdf): encryption on save — AES-128 and AES-256 (Phase 6, part one)	2026-08-18 07:27:45 +00:00