Bernd RodlerandClaude Opus 4.8
d047891ded
Adds roundtrip.mjs, which drives the plugin's own modules directly — no browser, no DOM — and proves the three audit fixes did not break S/MIME. 24 assertions, all passing, against the self-signed spike certificates: PKCS#12 import (both identities, RSA-2048, kdf=600000) key encrypted at rest (32-byte salt, 12-byte IV) unlock yields NON-EXTRACTABLE keys; wrong passphrase rejected sign -> verify: signature valid, signer email matches From encrypt -> decrypt by the intended recipient, plaintext matches sender can read their own Sent copy downgraded message produces no plaintext Two results worth recording. Finding 1 is confirmed against a genuine CMS structure, not just a mock: the spike certs are self-signed, smimeVerify reports signatureValid AND signerEmailMatch true AND selfSigned true, and the gate refuses the auto-import. That is exactly the cert-substitution attack, blocked. The same status with selfSigned:false passes, so the gate is not simply refusing everything. Finding 2 is confirmed end to end: our own encrypt path produces AES-256-GCM, decrypt reports contentAuthenticated:true, so HTML renders without suppression. Only legacy inbound CBC degrades to text. The section-8 assertion is deliberately loose. Swapping the 9-byte AES-GCM OID for the 8-byte 3DES OID also invalidates the enclosing DER lengths, so ASN.1 validation rejects the message before the allowlist is reached — either way no plaintext is produced, and the assertion says which path fired rather than pretending it tested the allowlist. The allowlist itself is asserted precisely in verify-fixes.mjs, which now carries 36 assertions including checks that fail if a legacy CBC OID reappears or the mail path stops using the native engine. Browser-side spike result: the patched plugin installs through the admin channel, resolves to the privileged tier, and activates with "hooks=5, slots=3" and no refusals — so the B-04 gate does not block it. Its S/MIME settings section renders and survives SPA navigation. Key import via the UI could not be automated (native file picker), which is a harness limit rather than a product defect; roundtrip.mjs covers that path directly instead. Findings 4, 5 and 6 remain open. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
S/MIME plugin
End-to-end S/MIME (CMS / PKCS#7) for Bulwark Webmail, implemented as a
privileged (same-origin) plugin. All cryptography runs locally in the
browser using a bundled pkijs / asn1js / webcrypto-liner stack, with no key
material ever leaves the device.
What it does
| Capability | How |
|---|---|
| Sign outgoing mail | onComposeSend builds the MIME, wraps it in opaque CMS SignedData, and submits via api.jmap.sendRaw. |
| Encrypt outgoing mail | onComposeSend builds CMS EnvelopedData to every recipient (AES-256-GCM by default; AES-128 optional) plus the sender, then submits raw. Sign + Encrypt does proper sign-then-encrypt. |
| Verify incoming signatures | onRenderEmailBody fetches the CMS blob (api.jmap.fetchBlob), validates the signature cryptographically, checks validity dates, flags self-signed signers and signer≠From mismatches, and renders the inner body. |
| Decrypt incoming mail | onRenderEmailBody decrypts EnvelopedData with your unlocked key (RSA-OAEP, with an RSAES-PKCS1-v1_5 + 3DES/RC2 legacy fallback for old Outlook/Thunderbird mail). |
| Key management | settings-section slot: import PKCS#12 (.p12/.pfx), unlock/lock, delete, import recipient certificates, set sign/encrypt defaults. |
| Status | email-banner slot shows signature / encryption state; composer-toolbar slot has per-message Sign / Encrypt toggles. |
Security model
- Privileged tier. Declares
tier: "privileged"+crypto:full. PerresolvePluginTier, the same-origin tier is only granted to a signed, admin-approved (managed) bundle after high-risk consent. A self-uploaded copy is refused rather than downgraded; sign and ship it through the admin channel. - Keys at rest. Private keys are imported from PKCS#12 and re-wrapped with AES-256-GCM under a PBKDF2(SHA-256, 600 000) key derived from a passphrase you choose. Stored in IndexedDB; the raw key bytes are never persisted.
- Keys in use. Unlocking imports the key as a non-extractable
CryptoKey. Because the background (hooks) iframe and the visible slot iframes are same-origin, the unlocked handle is shared through a session IndexedDB store. It stays non-extractable and is wiped on app boot and on logout / account switch (configurable), mirroring the former native "in-memory, cleared on reload" behaviour. - Returned HTML still passes through the host sanitizer.
Build
cd repos/plugins/smime
npm install # pulls pkijs / asn1js / pvtsutils / webcrypto-liner + esbuild
npm run build # → dist/index.js (~1.7 MB, under the privileged cap)
npm run package # → smime.zip (manifest.json + index.js) for admin upload
The build aliases the Node crypto builtin (referenced by a dead
typeof process branch in asmcrypto.js) to a browser shim so the bundle is
self-contained.
Layout
src/
index.js entry: activate + hooks + slots (React.createElement UI)
crypto-engine.js pkijs CryptoEngine w/ 3DES/RC2 + legacy PKCS#12 PBE
certificate-utils.js X.509 parse + metadata + capability classification
mime-builder.js deterministic CRLF MIME builder + CMS RFC822 wrapper
mime-parse.js inner-MIME parser for decrypted/verified content
smime-detect.js detect CMS from Content-Type / bodyStructure / attachments
smime-sign.js CMS SignedData (opaque)
smime-encrypt.js CMS EnvelopedData
smime-decrypt.js CMS decrypt + blob normalisation + recipient matching
smime-verify.js CMS signature verification + signer status
pkcs12.js PKCS#12 import + key wrap/unlock
key-storage.js IndexedDB: key records, recipient certs, session keys
util.js uuid / hex / equality helpers
node-crypto-shim.js browser shim for the Node "crypto" builtin
The crypto modules are faithful ports of the host's lib/smime/* (the former
native pipeline), so the plugin produces byte-compatible CMS.
Note on host wiring
The onComposeSend and onRenderEmailBody hook buses and the privileged
api.jmap surface exist in the host (see lib/plugin-hooks.ts,
lib/plugin-sandbox/host-api.ts). The send/render takeover fires once the
host emits those buses from the composer and viewer (the migration that retires
the inline native path). The settings-section, composer-toolbar, and
email-banner slots are active today.