Commit Graph
2 Commits
Author SHA1 Message Date
jaap-jan e3fd3e1728 Sync and authenticate with SSH keys on the client
Completes the client half of SSH keys: they sync alongside hosts, appear in
their own list, and can be selected to authenticate a connection instead of
typing a password.

The reconciler and the repository were Host-typed throughout, so the choice was
to generalise them or to keep a second copy per item type. Generalised, because
ItemReconciler's whole premise is that the pull and the push paths must answer
the same collision the same way — two copies would drift the first time one of
them was fixed. What is genuinely per-type now arrives through
IItemKind<TSecret>: the cipher, the merge, the plaintext columns, and the noun
to use when telling a person what happened to their item. Generic where the
server's IItemKind is not, and for the reason that reverses there — the client
needs the concrete type, because it merges field by field.

The pull filter is derived from the same registry that builds the reconcilers.
That is the specific failure being designed out: an item type that encrypts,
merges and lists perfectly and is never once requested from the server, so it
works on the machine that made it and exists nowhere else.

No client cache migration. The item table's primary key and the outbox's unique
index already carry the entity type, and AadResourceTypes already mapped SshKey
— so a host and a key may share an id and never see each other's rows, which
SshKeySyncTests now arranges deliberately.

A key hands the server nothing in plaintext. There is a public_key_fingerprint
column and it would be accepted; leaving it null is deliberate. A fingerprint is
not secret but it is a stable identifier for a key pair, so filling it would let
an operator tell which of their users hold the same key and correlate one across
vaults, for a column nothing reads. The design allows itself one plaintext
concession — the relay address, which the relay cannot work without — and this
is not that.

A key is chosen per connection rather than bound to a host, which works the way
ssh -i does. Binding one needs a field on HostSecret and therefore a payload
schema bump, which makes every host written afterwards read-only on an older
build; worth doing deliberately rather than as a side effect of adding keys.

Three things this found, all of them by being falsified rather than by review:

- Making the reconciler generic silently turned a record comparison into
  reference equality, because == on a type parameter is not value equality. The
  effect would have been a conflict recorded on every pass for an unacknowledged
  create that had in fact landed. Sabotaging the fix left all 73 tests passing —
  nothing covered that branch — so ConflictMatrixTests now has
  AnUnacknowledgedCreateThatDidLand_IsDroppedQuietly, which fails without it.

- A test asserting that a blank passphrase reaches SSH.NET as null was vacuous:
  it exercised the editor, not the credential path, and passed with the guard
  deleted. Resolved by making SshKeySecret.Passphrase normalise an empty string
  to null, so there is one spelling of one state — which also keeps two clients
  from producing different payload bytes for an identical key. That exposed a
  wider gap: SshKeySecret, its codec and its merge had no direct unit tests at
  all. They have 25 now.

- The reason first given for that normalisation was false. It claimed SSH.NET
  rejects a passphrase supplied for an unprotected key; measured against a real
  sshd it ignores it and authenticates anyway. Corrected everywhere it was
  stated and recorded in docs/platform-flags.md. The same test file also closes
  a real hole: SshPrivateKeyCredential had never been exercised against a
  server, because the existing key test builds SSH.NET's auth method directly
  and bypasses the path a vault-held key actually takes.

Only one editor may be open at a time. Both sit in the same 340-pixel column as
Auto rows and their heights together exceed it at the window's minimum size, so
two open editors put the lower one's Save and Cancel past the bottom edge — the
same failure this window already shipped once with the setup screens. Expressed
as a state rule because that is the only form of it this repository can check:
nothing here loads a .axaml. The refusal keeps what was typed, since in the key
editor that is a pasted private key the user may have nowhere else.

The end-to-end slice now carries a key as well as a host, so both item types go
through the real API, the real PostgreSQL and the real crypto in one pass — the
three hand-kept mappings between enums that do not line up are the reason that
is worth doing rather than trusting the unit suites.

735 tests green, including the container-backed SSH and end-to-end suites. Zero
warnings, dotnet format clean.
2026-07-29 20:27:23 +02:00
jaap-jan c4dbd85da0 Add the client's SSH key model, codec, merge and cipher
The client can now seal and open an SSH key item. Nothing consumes it yet —
the repository, the sync engine's per-type handling and the UI come next — but
this is the layer everything above it depends on, and it is the layer where
the crypto has to be right.

SshKeySecret holds the private key as an ordinary string, deliberately, and
says so: a .NET string cannot be wiped, so the material lives until the GC
reuses the memory. libsodium's guarded memory was considered and rejected
because the passphrase protecting the key, the password on the next item and
the JSON the codec just parsed are all strings on the same heap — protecting
one field among them reads as security and buys nothing. What the design does
give is that the key never reaches the disk in plaintext, never reaches the
server at all, and is handed to SSH.NET through a MemoryStream so there is no
temporary key file to leak.

Validation refuses a public key by name. ssh-keygen writes two files whose
names differ by four characters, and pasting the wrong one otherwise produces
a vault item that looks fine and fails at connection time with an
authentication error that says nothing about which file you chose.

The merge redacts the private key and its passphrase from the conflict log.
A host conflict shows both values so the loser can be put back; doing that for
a private key would write the discarded key into a log that is designed to be
read rather than used and is deliberately retained after acknowledgement. Two
different private keys are not something anyone reconciles by reading them
side by side.

And the lesson worth recording, because it nearly shipped: the first version
of AadResourceTypeTests proved nothing. It checked that a key payload does not
open as a host and vice versa — true however both ciphers are misconfigured,
because Seal and TryOpen share one constant, so changing it changes both and
the round trip still works. Sealing every private key as if it were a vault
passed all twelve tests. The tests now open a sealed payload independently
through ItemKeys with the resource type named out of band, and that does fail
under the same sabotage. A test that only compares an implementation against
itself cannot catch a self-consistent mistake.

The trap it defends: SyncEntityType.SshKey is 3, AadResourceType.SshKey is 6,
because the crypto enum also carries None, User, Device and Vault ahead of the
item types. A cast between them is a specification violation that encrypts
cleanly and would only surface when another implementation refused the item.
2026-07-29 15:33:28 +02:00