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.
54 lines
1.3 KiB
Go
54 lines
1.3 KiB
Go
package logging
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import "encoding/json"
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// Forbidden reports whether key is a secrets/PII field name that must never be
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// persisted in cleartext (logs, audit snapshots, alert payloads).
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func Forbidden(key string) bool { return forbiddenKeys[key] }
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// Redact returns "[REDACTED]" when key is forbidden, otherwise val. Use it when
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// projecting attributes into a non-log sink (e.g. alert events).
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func Redact(key, val string) string {
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if forbiddenKeys[key] {
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return "[REDACTED]"
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}
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return val
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}
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// RedactJSON returns a copy of a JSON document with every forbidden key's value
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// (at any depth) replaced by "[REDACTED]". This is the defense-in-depth scrubber
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// the audit sink applies to before/after snapshots so PII cannot land in the
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// immutable audit log. Non-JSON or unparseable input is returned unchanged.
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func RedactJSON(b []byte) []byte {
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if len(b) == 0 {
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return b
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}
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var v any
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if err := json.Unmarshal(b, &v); err != nil {
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return b
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}
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redactValue(v)
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out, err := json.Marshal(v)
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if err != nil {
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return b
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}
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return out
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}
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func redactValue(v any) {
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switch t := v.(type) {
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case map[string]any:
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for k, val := range t {
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if forbiddenKeys[k] {
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t[k] = "[REDACTED]"
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continue
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}
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redactValue(val)
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}
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case []any:
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for _, e := range t {
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redactValue(e)
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}
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}
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}
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