mesh-host/cmd/mesh-host/movesecret.go

package main

import (
	"context"
	"crypto/rand"
	"crypto/subtle"
	"encoding/base64"
	"encoding/json"
	"errors"
	"fmt"
	"os"
	"time"

	"golang.org/x/crypto/nacl/box"

	"github.com/novox/mesh-host/internal/identity"
	"github.com/novox/mesh-host/internal/link"
)

// The move of a value sealed to this machine into the vault (design 57's V3, issue 676; internal/link
// movesecret.go). The controller cannot open what it holds; this machine can open what was sealed to it, and so
// hands it to the vault, sealed to a key the vault made for the call. The value is in this process for that one
// call and written nowhere.

// vaultAsk asks one of the vault's verbs in this engine's own name and answers its result.
type vaultAsk func(verb string, args any) (json.RawMessage, error)

// moveSecretFrom is the engine's move: this machine's sealing key, read for each ask, and the vault asked over
// the link open now.
func moveSecretFrom(statePath string, queue *link.Session) link.MoveSecretFunc {
	return func(m link.MoveSecret) (link.MovedSecret, error) {
		key, err := identity.LoadSealingKey(identity.SealingKeyPath(statePath))
		if err != nil {
			return link.MovedSecret{}, err
		}
		ask := func(verb string, args any) (json.RawMessage, error) {
			return queue.AskVault(context.Background(), verb, args)
		}
		moved, err := moveIntoTheVault(ask, key, m)
		if err != nil {
			fmt.Fprintf(os.Stderr, "mesh-host: a value was not moved into the vault: %v\n", err)
		}
		return moved, err
	}
}

// moveIntoTheVault opens the row's value with this machine's sealing key, hands it to the vault's move-in in its two
// steps, and answers what the vault kept once its read-back — sealed to a key made here for this one call — opens
// to the same value.
func moveIntoTheVault(ask vaultAsk, key identity.SealingKey, m link.MoveSecret) (link.MovedSecret, error) {
	if m.SealedTo != "" && m.SealedTo != key.Public {
		return link.MovedSecret{}, errors.New("the controller's store says this value was sealed to a sealing key this " +
			"machine no longer has, so it cannot be opened here")
	}
	value, err := key.Unseal(m.Sealed)
	if err != nil {
		return link.MovedSecret{}, fmt.Errorf("the value does not open with this machine's sealing key: %w", err)
	}
	defer wipe(value)

	// This machine's sealing key, stated in its own name: the key the vault seals the core's credentials to for the
	// controller to carry here (novox/hq ADR 0349 §16, issue 763), never a key the controller names.
	first := map[string]any{"origin": m.Origin, "generation": m.Generation, "sealing_key": key.Public}
	if !m.MadeAt.IsZero() {
		first["made_at"] = m.MadeAt.UTC().Format(time.RFC3339Nano)
	}
	if m.Own() {
		first["node"], first["module"], first["name"] = m.Node, m.Module, m.Name
	} else {
		first["provider"], first["provision"] = m.Provider, m.Provision
		first["consumer"], first["consumer_module"] = m.Consumer, m.ConsumerModule
		if m.Local != "" {
			first["local"] = m.Local
		}
	}
	raw, err := ask("move-in", first)
	if err != nil {
		return link.MovedSecret{}, fmt.Errorf("the vault did not open the move: %w", err)
	}
	var opened struct {
		Call   string `json:"call"`
		SealTo string `json:"seal_to"`
		Secret string `json:"secret"`
	}
	if err := json.Unmarshal(raw, &opened); err != nil || opened.Call == "" || opened.SealTo == "" {
		return link.MovedSecret{}, errors.New("the vault answered no call and no key to seal to")
	}
	sealed, err := identity.Seal(opened.SealTo, value)
	if err != nil {
		return link.MovedSecret{}, fmt.Errorf("the vault's key for the call is not a sealing key: %w", err)
	}
	backPub, backPriv, err := box.GenerateKey(rand.Reader)
	if err != nil {
		return link.MovedSecret{}, err
	}
	defer wipe(backPriv[:])
	raw, err = ask("move-in", map[string]any{"call": opened.Call, "sealed": sealed,
		"read_back_to": base64.StdEncoding.EncodeToString(backPub[:])})
	if err != nil {
		return link.MovedSecret{}, fmt.Errorf("the vault did not take %s: %w", opened.Secret, err)
	}
	var kept struct {
		Name       string `json:"name"`
		Generation int    `json:"generation"`
		Unchanged  bool   `json:"unchanged"`
		ReadBack   string `json:"read_back"`
	}
	if err := json.Unmarshal(raw, &kept); err != nil || kept.Name == "" || kept.ReadBack == "" {
		return link.MovedSecret{}, fmt.Errorf("the vault answered %s with no read-back", opened.Secret)
	}
	blob, err := base64.StdEncoding.DecodeString(kept.ReadBack)
	if err != nil {
		return link.MovedSecret{}, fmt.Errorf("the vault's read-back of %s is not sealed", kept.Name)
	}
	back, ok := box.OpenAnonymous(nil, blob, backPub, backPriv)
	if !ok {
		return link.MovedSecret{}, fmt.Errorf("the vault's read-back of %s does not open with the key made for it", kept.Name)
	}
	defer wipe(back)
	if subtle.ConstantTimeCompare(back, value) != 1 {
		return link.MovedSecret{}, fmt.Errorf("the vault keeps %s, but it read back another value than the one handed "+
			"in: the move of it did not hold", kept.Name)
	}
	return link.MovedSecret{Secret: kept.Name, Generation: kept.Generation, Unchanged: kept.Unchanged}, nil
}

func wipe(b []byte) {
	for i := range b {
		b[i] = 0
	}
}