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.
70 lines
1.6 KiB
Go
70 lines
1.6 KiB
Go
// Copyright 2018 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// Package detrand provides deterministically random functionality.
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//
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// The pseudo-randomness of these functions is seeded by the program binary
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// itself and guarantees that the output does not change within a program,
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// while ensuring that the output is unstable across different builds.
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package detrand
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import (
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"encoding/binary"
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"hash/fnv"
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"os"
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)
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// Disable disables detrand such that all functions returns the zero value.
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// This function is not concurrent-safe and must be called during program init.
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func Disable() {
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randSeed = 0
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}
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// Bool returns a deterministically random boolean.
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func Bool() bool {
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return randSeed%2 == 1
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}
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// Intn returns a deterministically random integer between 0 and n-1, inclusive.
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func Intn(n int) int {
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if n <= 0 {
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panic("must be positive")
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}
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return int(randSeed % uint64(n))
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}
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// randSeed is a best-effort at an approximate hash of the Go binary.
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var randSeed = binaryHash()
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func binaryHash() uint64 {
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// Open the Go binary.
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s, err := os.Executable()
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if err != nil {
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return 0
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}
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f, err := os.Open(s)
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if err != nil {
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return 0
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}
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defer f.Close()
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// Hash the size and several samples of the Go binary.
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const numSamples = 8
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var buf [64]byte
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h := fnv.New64()
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fi, err := f.Stat()
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if err != nil {
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return 0
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}
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binary.LittleEndian.PutUint64(buf[:8], uint64(fi.Size()))
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h.Write(buf[:8])
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for i := int64(0); i < numSamples; i++ {
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if _, err := f.ReadAt(buf[:], i*fi.Size()/numSamples); err != nil {
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return 0
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}
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h.Write(buf[:])
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}
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return h.Sum64()
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}
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