[Feature] Can bili context encrypt the data files it outputs?

[BsoBird]

Since we may deploy bili context on remote nodes in untrusted environments, encrypting the data files that are written to disk is essential.

[ranxianglei]

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[bot] 🏷 Triage done — this is a real problem, and I'd recommend implementing it with a scoped design. Here's what I verified and what I propose; I'll start coding once you confirm the scope.

What bili actually writes to disk today (per host):

Data	Location	Sensitivity
Session state	~/.local/share/billion-context/sessions/**/*.json	High — the crown jewels
Proxy log	~/.local/state/billion-context/bili.log (+ .old)	Medium
MITM root CA + key	~/.local/share/billion-context/ca/	Medium (regenerable)
Config	~/.config/billion-context/billion-context.json	Low–medium (user-editable)
Cache/state (update throttle, registry cache, proxy-origin)	XDG cache/state dirs	Negligible

The session files are where the real exposure is: each one holds the block summaries, blockContents (the originals of every compressed block — kept so decompress/bili export --full can restore them), and a snapshot of the newest ~16k tokens of the folded conversation. That is effectively the full conversation content — code, pasted secrets, everything — sitting in plaintext JSON on whatever host runs the proxy. On an untrusted remote node, yes, this needs encryption at rest.

Recommended design (v1):

1. Scope: session files only. They're the only disk output containing actual conversation content. Logs are already operator-controllable (ACP_LOG_FILE=off), the CA key is regenerable, and the config must stay human-editable. Logs could be a follow-up if you want them covered too.
2. Mechanism: AES-256-GCM at the persist boundary. File format: 8-byte magic (BILIENC1) + version byte + fresh 12-byte nonce per write + ciphertext + GCM tag. No key material ever touches disk.
3. Key source: env var BILI_ENCRYPTION_KEY (hex or base64, exactly 32 bytes decoded). Opt-in — unset means today's behavior, zero change. Deliberately no key-file option: a key file next to the data on the same untrusted filesystem defeats the threat model; systemd Environment= / container secret injection is the right delivery path.
4. Migration: files without the magic keep loading as plaintext (existing trees don't break); when encryption is enabled, boot rewrites every loaded session once so no plaintext lingers (otherwise already-persisted sessions stay readable until their next dirty write).
5. Failure semantics: GCM auth failure (wrong key / corruption) → treated like today's corrupt-file path (log + skip), plus one prominent boot warning naming how many sessions failed to decrypt. Never silent, never mixed up.
6. Cross-repo dependency (heads-up): the fs I/O itself lives in acp-kernel's StateStore (this repo's src/persist.ts is policy only). So step one is a small kernel change — an optional codec { encode, decode } hook on StateStoreOptions, applied before the temp/spill writes and before JSON.parse — released from acp-kernel first, verified on npm, then bumped here per our cross-repo release rule. The billion-context side is one new module (src/encrypt.ts) + wiring into SessionStore + tests + docs.

Stopgap that already exists: for a fully ephemeral run on a hostile node, BILI_PERSIST=0 + ACP_LOG_FILE=off writes nothing but the regenerable CA/config. That works but throws away restart durability — persistence exists precisely so long sessions survive a restart — which is why encrypt-in-place is the right fix rather than "just disable it."

Question to confirm before I build: OK to proceed with (a) sessions-only scope, (b) env-var key only, (c) off by default? If you want the log file encrypted in v1 as well, say so — it's a modest addition but touches the logger contract.

[BsoBird]

we should process Session state file. also we can use zstd compress or avro file to make file size little.
i think sessions-only scope is good, what do u think?

[ranxianglei]

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[bot] 🏷 Sessions-only it is — agreed on my side too. On your two ideas:

zstd: yes. Conveniently, fzstd is already a build-time dependency of billion-context — it's bundled into dist today and used in the hot path to decode zstd request bodies from Codex Desktop (src/content-encoding.ts). So we get real zstd at zero new-dependency risk, on Node ≥20 including Windows. Order matters: JSON → zstd → AES-256-GCM (encrypting first destroys compressibility). Session JSON is very repetitive (long message texts, repeated structure), so expect roughly 5–10× shrinkage on top of the encryption envelope.

Avro: no — here's why. The persist layer's contract is JSON documents with organic schema evolution: the store stamps an envelope version, and old shapes are adopted through a legacy hook that operates on the parsed JSON — that's exactly how the v1→v3 file migration works. Avro needs fixed, managed schemas per version and would break the kernel's mechanism/policy split (StateStore owns JSON.parse/stringify). And the size win you're after comes from entropy reduction, which zstd already delivers on repetitive text without any schema machinery. Avro would add maintenance cost for ~0 additional shrinkage.

So the final format when enabled: BILIENC1 magic + version byte + 12-byte nonce + AES-256-GCM(zstd(JSON)). Everything else as proposed: key via BILI_ENCRYPTION_KEY env only (hex or base64, exactly 32 bytes decoded), off by default, legacy plaintext files keep loading and are re-encrypted once at boot, GCM auth failure = corrupt-file handling + one prominent boot warning.

One process note: the file I/O itself lives in acp-kernel's StateStore, so step 1 is a small kernel PR adding an optional codec { encode, decode } hook (applied around the temp/spill writes and the read path), released first per our cross-repo rule; then the billion-context side lands on top. Starting now — I'll link both PRs here as they open.

[BsoBird]

We need to support gracefully taking over existing unencoded data files after a new version is released. Ideally, if we have encryption enabled in the configuration, we should process the old data files once, generate new encrypted files, and then delete the old data files.

[ranxianglei]

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[bot] 🏷 Agreed — eager one-shot takeover at boot, no lazy re-encryption. Design:

When BILI_ENCRYPTION_KEY is set, SessionStore.boot() runs a migration pass before loading:

1. Walk the sessions tree (incl. .fb.json spills), peek the first 8 bytes of each .json — O(1) per file, no marker file needed.
2. Files with the BILIENC1 magic: skip (already migrated).
3. Files without (legacy plaintext): parse the envelope, re-serialize it byte-for-byte (version/savedAt/id/payload untouched), encode with AES-256-GCM(zstd(...)), and write it back to the same path via temp-file + rename.

The atomic rename makes "delete the old file" inherent: the plaintext is replaced in place, so there is never a moment where both copies exist (or neither does). A crash mid-migration leaves each file either old or new — the next boot simply finishes the remaining files. Files that fail to parse are left as-is with a warning (same tolerance as today's corrupt-file handling). Boot logs how many files were migrated.

Status: the mechanism half is ready for review — ranxianglei/acp-kernel#249 adds an optional codec hook to the kernel StateStore (encode around every write, decode around every read; decode failure = corrupt-file skip; default off = zero behavior change). It needs your merge so CI can publish 0.0.64; the billion-context side (key handling, BILIENC1 format, eager migration, docs, tests) lands as a follow-up PR pinned to 0.0.64 — I'm building it now and will link it here.

中文摘要：按你的要求采用启动时一次性迁移——加密开启时扫描旧明文会话文件，逐个原子替换为加密文件（同名 temp+rename，旧文件天然被覆盖删除，崩溃可自愈），内核侧 codec 钩子 PR 已提交待合并。

[ranxianglei]

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[bot] 🏷 Implementation is done on both sides — both PRs are open:

1. Mechanism (kernel): ranxianglei/acp-kernel#249 — optional codec hook on StateStore (encode around every write incl. spills, decode around every read; decode failure = corrupt-file skip; default off = zero behavior change). Needs your merge so CI publishes acp-kernel 0.0.64.
2. Feature (this repo): ranxianglei/billion-context#711 — everything else:
   • BILI_ENCRYPTION_KEY (env-only, hex/base64, exactly 32 bytes; invalid value aborts startup); unset = today's plaintext behavior.
   • BILIENC1 format: AES-256-GCM over zstd-compressed JSON (compress-then-encrypt, per your size point — expect ~5–10× smaller files; zstd via built-in node:zlib on Node ≥ 22.15, raw mode byte on older runtimes). Avru… avro was not needed: zstd alone covers the size goal without breaking the JSON envelope-versioning contract.
   • Your migration requirement as specified: when encryption is enabled, boot processes every existing unencoded file once, writes the encrypted version, and the old plaintext is gone — done as an atomic in-place rename per file (crash mid-migration self-heals on next boot; unreadable files are left alone with a warning; .fb.json spills covered).
   • Wrong key at boot → GCM auth failure → affected sessions skip as corrupt (logged, no crash).
   • 9 new tests (roundtrip, tamper/wrong-key rejection, legacy passthrough, eager migration + idempotency, spill coverage, fail-fast key validation, no-key zero-change); full suite 1376/1376 green locally; docs in CONFIGURATION.md + zh-CN.

One sequencing note: PR #711 currently pins acp-kernel 0.0.63 and will show red CI until 0.0.64 exists on npm — the moment #249 merges and CI publishes it, I add the pin+lockfile commit, re-run the full pre-flight, and #711 goes green. No other open items.

中文摘要：两侧 PR 均已提交——内核 codec 钩子（acp-kernel#249，待你合并发布 0.0.64）与本仓库加密功能（#711：BILI_ENCRYPTION_KEY、BILIENC1 = AES-256-GCM(zstd(JSON))、启动时一次性原子迁移旧明文文件、9 个新测试全绿）；待 0.0.64 发布后补 pin 提交即可转绿。

[ranxianglei]

这里有一个问题,现在加密是对称加密还是非对称加密.如果是对称加密,是不是密码本会被泄露?使得加密徒劳?

[ranxianglei]

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[bot] 🏷 好问题，直接回答：

是的，对称加密（AES-256-GCM，一个 32 字节密钥同时用于加解密）。这是刻意选择，不是疏忽：

1. 威胁模型决定算法。 [Feature] Can bili context encrypt the data files it outputs? #708 防的是「数据文件的离线访问」：被拷走的磁盘镜像、泄露的备份、被同步到云盘的状态目录、回收后转手的节点——即攻击者能读文件但没有密钥。这个模型里加密方和解密方是同一个进程（bili 每次请求都要读写这些文件），非对称加密只在「不能看到明文的一方 ≠ 加密方」时才有价值（比如把密文交给持私钥的第三方），此处两个角色重合，用非对称只会增加复杂度而不增加任何保护。所有成熟的静态文件加密方案（LUKS/dm-crypt、age、sops、KMS 信封加密）都是同一形态：对称数据密钥 + 密钥从文件系统之外注入。

2. 密钥在哪、会不会泄露？ 密钥只经 BILI_ENCRYPTION_KEY 环境变量注入，设计上不落盘、不进日志、不进配置文件——这也是我们明确不支持「密钥文件」的原因：把密钥放在数据旁边，正是你担心的「密码本一起泄露、加密徒劳」的场景，我们在设计层面直接封死了这条路。密钥的暴露面（进程环境/内存）严格小于数据的暴露面（长期驻留磁盘的文件）。

3. 诚实的边界——它防不了什么： 如果攻击者已经拿到运行中节点的 root，他可以从进程环境或内存里直接读到密钥。但注意：那个场景下他同样能直接从 bili 进程内存里读出全部会话内容（进程本来就在内存里持有完整上下文），文件加密在那里也救不了。要防「活的实时全权攻击」，答案是 TEE/机密虚拟机，或者干脆不持久化（BILI_PERSIST=0），而不是非对称加密。

一句话：对称 + 外部注入密钥是「不可信存储上的文件」的行业标准答案；它防的是文件离开你的控制，不是坐在进程里面的攻击者。

(English: Yes — symmetric AES-256-GCM, deliberately. The threat model is offline file access (stolen volumes/backups/synced dirs): the attacker can read the file but not the key, which is injected only via the BILI_ENCRYPTION_KEY env var and never written to disk/logs/config — key-file support was explicitly rejected because a key beside the data is exactly the "key leaks too" failure. Asymmetric crypto adds nothing here because the same process both encrypts and decrypts. It does NOT protect against a live full-root attacker on the running node — that attacker reads the key from the process environment and the conversation from process memory alike; for that threat use a TEE or BILI_PERSIST=0.)

[ranxianglei]

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[bot] 🏷 跟进：上面「防离线、不防活的 root」的边界说明已写进 PR #711 的 CONFIGURATION.md（含中文版），避免后续部署的人产生同样疑问。分支上另有一处小加固已合入：迁移中途崩溃遗留的 .tmp-enc-* 临时文件现在会在下次启动时被清扫（此前会永久残留）。全量 pre-flight 重新跑过：typecheck ✓ / 1377 tests ✓ / build ✓。

唯一待办不变：等 acp-kernel#249 合并发布 0.0.64，我补 pin+lockfile 提交后 #711 即转绿。

(Follow-up: the "defends offline file access, not live full-root" boundary from the answer above is now documented in PR #711's CONFIGURATION docs (EN + ZH). The branch also picked up a small hardening — orphaned .tmp-enc-* temps from a crashed migration are now swept at next boot. Full pre-flight re-run green.)

[ranxianglei]

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[bot] 🏷 更正上一条的链接笔误：PR 地址是 #711 （上一条里 github.com 后漏了斜杠）。其余内容不变。

[ranxianglei]

所以我在想 如果攻击者能拿到bili的内存,加密意义何在?
如果是对称的加密,明文密钥岂不是直接传输?最后防止偷窥的目标是否能达到