4d9a26498e
Paste a secret, get a link, send it. The first person to open it and press
Reveal sees the secret; the link dies at that moment. The recipient needs a
browser and nothing else — no account, no client, no installed tooling.
The server cannot read what it stores. AES-256-GCM happens in the browser and
the key lives in the URL fragment, which browsers never transmit, so hushd
holds ciphertext and no key material. That is a property of where the key sits
rather than a promise about our conduct, which is why there is deliberately no
endpoint accepting a plaintext secret and no server-side-encryption fallback:
two guarantees behind one URL would be worse than one honest guarantee.
Three decisions carry the design:
* GET /s/{id} touches NO storage, not even to check existence. Slack, Teams,
WhatsApp, iMessage and Outlook Safe Links all fetch a URL before a human
sees it, so destroying on GET would destroy most secrets in transit and the
recipient's "already used" would be indistinguishable from interception.
Only POST /reveal consumes. Bot user-agent detection is an arms race;
removing the side effect from GET is not. Pinned by
TestGettingTheRevealPageNeverConsumesTheSecret.
* Destruction is one Redis GETDEL, which is atomic. GET-then-DEL has a window
where two simultaneous readers both win, and for a one-time secret that
window is the product. The store contract demands atomicity and the same
concurrency test runs against both implementations.
* Missing, already-revealed, expired and evicted are ONE indistinguishable
410. Separating them would confirm to a prober that a given link was real.
The secret id IS the capability, so secret.ID is a struct whose every
accidental path — %v, %s, String(), slog, json.Marshal — emits a redacted
handle or refuses, and the raw value needs an explicit Value(). The first
version tried to prevent leaks by implementing no String() at all; its own test
caught that Go's fmt prints unexported fields anyway, so forbidding the method
had removed the control rather than the leak.
Operationally: structured JSON on stdout in the fleet's wire format, which
Vector already collects with no annotation; six hush_* metrics on the chassis
registry with no id, IP or path in any label; five alert rules wired into
vmalert. The public Ingress enumerates /, /s/ and /api/ so /metrics, /healthz
and /readyz share the port but are unreachable from the internet — no
basic-auth middleware to maintain and get wrong.
Dependencies are vendored because go-chassis is private: the Woodpecker test
step and the in-cluster Kaniko build both run -mod=vendor with GOPROXY=off and
hold no git credential.
cmd/hush-mcp is a stdio MCP server doing the same client-side crypto locally,
so using hush from an agent preserves the same guarantee as using it from a
browser.
85 lines
3.4 KiB
Go
85 lines
3.4 KiB
Go
package main
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import "github.com/prometheus/client_golang/prometheus"
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// Metrics are hush's own series, registered on the chassis's private registry
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// via chassis.Config.Collectors so /metrics is one scrape.
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//
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// Cardinality rule applied throughout: NO label ever carries a secret id, a
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// client IP, or a URL path. A metric label lands in the time series index and
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// stays there, so a per-secret label would be both a capability leak and an
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// unbounded index. Every label below is a closed enum.
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type Metrics struct {
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Created prometheus.Counter
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Revealed *prometheus.CounterVec // result: ok | gone
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Rejected *prometheus.CounterVec // reason: closed enum, see rejection reasons
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Bytes prometheus.Histogram
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StoreUp prometheus.Gauge
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Limited prometheus.Counter
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}
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// Rejection reasons. A closed set, mirrored by the API error codes, so
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// `hush_secrets_rejected_total{reason="ciphertext_too_large"}` and the 422 a
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// caller saw are the same vocabulary.
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const (
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reasonTooLarge = "ciphertext_too_large"
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reasonInvalid = "ciphertext_invalid"
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reasonEmpty = "ciphertext_empty"
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reasonTTL = "ttl_out_of_range"
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reasonMalformed = "malformed_request"
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)
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func newMetrics() *Metrics {
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return &Metrics{
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Created: prometheus.NewCounter(prometheus.CounterOpts{
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Name: "hush_secrets_created_total",
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Help: "Secrets accepted and stored.",
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}),
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Revealed: prometheus.NewCounterVec(prometheus.CounterOpts{
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Name: "hush_secrets_revealed_total",
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Help: "Reveal attempts by outcome. `gone` covers already-revealed, expired, never-existed and evicted, which the service does not distinguish.",
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}, []string{"result"}),
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Rejected: prometheus.NewCounterVec(prometheus.CounterOpts{
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Name: "hush_secrets_rejected_total",
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Help: "Create attempts refused by validation, by reason.",
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}, []string{"reason"}),
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Bytes: prometheus.NewHistogram(prometheus.HistogramOpts{
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Name: "hush_secret_ciphertext_bytes",
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Help: "Size of stored ciphertext.",
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// Hand-picked rather than DefBuckets (which tops out at 10): this
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// measures bytes up to a 64 KiB cap, so the buckets straddle
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// credential-sized (hundreds of bytes) through the limit.
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Buckets: []float64{256, 1024, 4096, 16384, 65536},
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}),
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StoreUp: prometheus.NewGauge(prometheus.GaugeOpts{
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Name: "hush_store_up",
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Help: "1 when the last readiness probe reached Redis, 0 otherwise.",
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}),
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Limited: prometheus.NewCounter(prometheus.CounterOpts{
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Name: "hush_rate_limited_total",
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Help: "Requests refused by the create rate limit. A sustained rise is the abuse signal.",
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}),
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}
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}
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// Collectors is what gets handed to chassis.Config.Collectors. The chassis owns
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// a private registry and exposes no accessor, so this slice is the only way
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// hush's series reach /metrics.
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func (m *Metrics) Collectors() []prometheus.Collector {
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return []prometheus.Collector{m.Created, m.Revealed, m.Rejected, m.Bytes, m.StoreUp, m.Limited}
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}
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// Prime initialises the label combinations that alerting queries reference.
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//
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// Without this, `rate(hush_secrets_revealed_total{result="gone"}[15m])` returns
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// no data until the first `gone` ever happens, and an alert written against a
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// missing series is an alert that cannot fire. Priming makes the series exist
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// at zero from boot.
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func (m *Metrics) Prime() {
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m.Revealed.WithLabelValues("ok")
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m.Revealed.WithLabelValues("gone")
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for _, r := range []string{reasonTooLarge, reasonInvalid, reasonEmpty, reasonTTL, reasonMalformed} {
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m.Rejected.WithLabelValues(r)
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}
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}
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