Encrypt stored SSH deploy keys at rest

[kriszyp]

Summary

add_ssh_key wrote the private key plaintext to <rootDir>/ssh/<name>.key and replicated the raw key in the operation body — so the key material transited replication and landed on every peer's disk. Log redaction only ever covered the log surface, not storage or the wire.

The key is now sealed into an enc:v1: envelope (the same envelope encryption backing the hdb_secret store) before it touches disk or the replicated op body, closing both exposures at once. Core decrypts it to a transient 0600 file only for the lifetime of a git invocation.

• Ingest (sealSSHKey): plaintext in → envelope on disk, envelope in the replicated op body.
• Already-sealed keys (replicated from a peer, cloned from the leader) are stored verbatim — never decrypted just to forward them. Their kid is checked against this node's custody the way set_secret vets an ingested envelope.
• get_ssh_key now returns the key as stored (the envelope). This is a deliberate behavior change, called out below.
• update_ssh_key rotation and list_ssh_keys (names only) are externally unchanged.

Fixes the storage half of #581. Requires the companion core PR (see below).

⚠️ This needed a core change — please sanity-check the scope call

The issue and the dispatch both scoped this as harper-pro-only, on the reasonable assumption that the encryption primitives were the only core dependency. They are there (utility/secretEnvelope.ts, resources/secretDecryptor.ts) — but the at-use site is also in core: getGitSSHCommand() in core/components/Application.ts is what builds GIT_SSH_COMMAND, and it has no pro-side hook. There is no way to satisfy the issue's step 2 (decrypt-to-transient-file for the git operation) from pro alone, so this is a coordinated two-PR change:

• core → HarperFast/harper#1795 — Decrypt SSH deploy keys to a transient file for git operations (this PR bumps the core submodule to it)

I went ahead and built both rather than stopping to ask, so it's ready if you want it — but if you'd rather this land differently (e.g. a generic core hook that pro registers into), the core PR is cheap to abandon.

Degraded mode: plaintext + loud WARN (option (a))

The issue left this open. I found a clear precedent and followed it rather than inventing behavior:

• Core's setSecret throws without custody — but that's a new op whose entire purpose is custody.
• Core's ingestRegistryAuth passes the literal credential through without custody, rather than failing the deploy.

add_ssh_key is the ingestRegistryAuth case: an existing feature being retrofitted, which must keep working on a node with no custody. So with no custody the key is stored plaintext (today's behavior) with a WARN naming the key and telling you to configure secretCustody. Custody is present by default (the file tier generates a cluster keypair on first boot), so this is the exception, not the path. At use time the posture is the opposite and fail-closed: an encrypted key on a node that can't decrypt it is skipped and logged loudly, never treated as plaintext.

Where to look

• get_ssh_key returning the envelope instead of the plaintext key is the one observable API change, and the bit I'd most like a second opinion on. It's what makes cloneSSHKeys carry ciphertext (it does get_ssh_key on the leader → add_ssh_key locally, which is another plaintext-over-the-wire path today), and it stops get_ssh_key from being a plaintext-key read for superusers. But if anything external depends on get_ssh_key returning usable key material, this breaks it. The issue only pinned update_ssh_key/list_ssh_keys as must-not-change, so I took the more secure reading — say the word if you'd rather it decrypt-on-read.
• req.key is mutated to the envelope before replicateOperation(req) in both addSSHKey and updateSSHKey — that mutation is what keeps the plaintext off the wire, so it's load-bearing rather than incidental.
• addSSHKey/updateSSHKey now also pass mode: 0o600 to the initial write, closing the brief window where a freshly-created key file sat at the umask default before chmod.

Tests

unitTests/security/sshKeyOperations.test.mjs — 10 tests: sealing on add (disk and the replicated op body), config block, verbatim storage of an already-sealed key, rejection of a foreign-cluster kid and of a malformed envelope, rotation, names-only listing, get_ssh_key returning ciphertext, and both degraded-mode paths. Full pro unit suite: 364 passing.

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🤖 Generated by KrAIs (Claude Opus 4.8) with Claude Code

[gemini-code-assist]

Code Review

This pull request introduces SSH key sealing at rest to prevent plaintext private keys from being stored on disk or transmitted over replication. It adds a sealSSHKey helper to encrypt keys using the cluster's secret custody, falling back to plaintext with a warning if custody is unavailable. Additionally, comprehensive unit tests are added to verify the sealing, replication, and degraded mode behaviors. The reviewer suggested using defensive optional chaining when retrieving the custody public key fingerprint to prevent potential runtime errors.

[claude]

Reviewed; no blockers found.

[dawsontoth]

Could Studio encrypt it before sending it, too? Like we do for secrets?

[dawsontoth]

Looks reasonable to me. Crazy idea... could we support generating SSH keys within the cluster purely? And then we can hand out the public key to super users, who could go stick it in GitHub or wherever. Then the private key never leaves the cluster. Not proposing we do that here, just kicking the idea out of my head and into the ether.

[kriszyp]

Looks reasonable to me. Crazy idea... could we support generating SSH keys within the cluster purely? And then we can hand out the public key to super users, who could go stick it in GitHub or wherever. Then the private key never leaves the cluster. Not proposing we do that here, just kicking the idea out of my head and into the ether.

Looks like you have addressed this with #594. Thank you!