Derive BastionID (#302)

go.mod

@@ -11,7 +11,7 @@ require (
 	github.com/prometheus/client_golang v1.19.1
 	github.com/transparency-dev/armored-witness-boot v0.1.0
 	github.com/transparency-dev/armored-witness-common v0.0.0-20240313170947-0b19d0fb8b95
-	github.com/transparency-dev/armored-witness-os v0.1.2
+	github.com/transparency-dev/armored-witness-os v0.1.3-0.20240524123036-bdd4b0b96386
 	github.com/transparency-dev/formats v0.0.0-20231205184308-949529efd6b3
 	github.com/transparency-dev/serverless-log v0.0.0-20231215122707-66f68a7705f5
 	github.com/transparency-dev/witness v0.0.0-20240311170858-5de1177dc362

go.sum

@@ -57,8 +57,8 @@ github.com/transparency-dev/armored-witness-boot v0.1.0 h1:OBlz71PCmPju9cDI1VEmy
 github.com/transparency-dev/armored-witness-boot v0.1.0/go.mod h1:XpiSLWNiDplWVYjtR1FY/wyFqiWK++5pLCiYe3PZZC8=
 github.com/transparency-dev/armored-witness-common v0.0.0-20240313170947-0b19d0fb8b95 h1:qOh9vp/TLfJ1X46bk756se0wdlKHSV2TrGUMa3kz91w=
 github.com/transparency-dev/armored-witness-common v0.0.0-20240313170947-0b19d0fb8b95/go.mod h1:cb6aKsLVU2OUk8+UjD8xvzxU84miHXLMHJaxO2gHDus=
-github.com/transparency-dev/armored-witness-os v0.1.2 h1:t8IrQQ9n0+lqvhASGfc9NOuEH3bykPSjtcMbWnARMZE=
-github.com/transparency-dev/armored-witness-os v0.1.2/go.mod h1:Yt2PelPhnZ5Vc+/XJRPHoFaV5gTBw9xBXcMQJZTwSVM=
+github.com/transparency-dev/armored-witness-os v0.1.3-0.20240524123036-bdd4b0b96386 h1:WHmJqV1L7dqAR5WXhOpFDL5jo4Rp2gCzvtmDh5FcX7E=
+github.com/transparency-dev/armored-witness-os v0.1.3-0.20240524123036-bdd4b0b96386/go.mod h1:N+hTvqWTb08EeJC+DLEIPvnG4uI9ibnJVIA+oZaOBn4=
 github.com/transparency-dev/formats v0.0.0-20231205184308-949529efd6b3 h1:Mpx9pqc7bKrx2QQxKL3SPbLIGH4gTBR1ZFrNuKq3CcY=
 github.com/transparency-dev/formats v0.0.0-20231205184308-949529efd6b3/go.mod h1:tY9Z9oBaYdQt4NWIhsFAtv0altwLk+K9Gg/2tbS0eBQ=
 github.com/transparency-dev/merkle v0.0.2 h1:Q9nBoQcZcgPamMkGn7ghV8XiTZ/kRxn1yCG81+twTK4=

trusted_applet/key.go

@@ -16,6 +16,7 @@ package main
 
 import (
 	"crypto/aes"
+	"crypto/ed25519"
 	"crypto/sha256"
 	"encoding/binary"
 	"fmt"
@@ -37,6 +38,8 @@ var (
 	witnessPublicKey            string
 	witnessSigningKey           string
 	witnessPublicKeyAttestation string
+	bastionSigningKey           ed25519.PrivateKey
+	bastionIDAttestation        string
 )
 
 // deriveIdentityKeys creates this witness' signing and attestation identities.
@@ -68,6 +71,8 @@ func deriveIdentityKeys() {
 		prefix = "DEV:"
 	}
 
+	// Other than via the identity counter, the diversifier and key name in here
+	// MUST NOT be changed, or we'll break the invariant that this key is static.
 	witnessSigningKey, witnessPublicKey = deriveNoteSigner(
 		fmt.Sprintf("%sWitnessKey-id:%d", prefix, status.IdentityCounter),
 		status.Serial,
@@ -89,6 +94,18 @@ func deriveIdentityKeys() {
 	// were derived on a known armored witness unit.
 	witnessPublicKeyAttestation = attestID(&status, witnessPublicKey)
 
+	// Other than via the counter, the diversifier and key name in here
+	// MUST NOT be changed, or we'll break the invariant that this key is static.
+	bastionSec, bastionPub := deriveEd25519(
+		fmt.Sprintf("%sBastionKey-id:0", prefix),
+		status.Serial)
+	bastionSigningKey = bastionSec
+	bastionID := fmt.Sprintf("%064x", sha256.Sum256(bastionPub))
+
+	// Attest to the bastion ID so we can convince others that this ID
+	// was derived on a known armored witness unit
+	bastionIDAttestation = attestBastion(&status, bastionID)
+
 }
 
 // attestID uses attestSigningKey to sign a note which binds the passed in witness ID to this device's
@@ -109,6 +126,24 @@ func attestID(status *api.Status, pubkey string) string {
 	return attestNote(status, aN)
 }
 
+// attestBastion uses attestSigningKey to sign a note which binds the passed in witness ID to this device's
+// serial number and current identity counter.
+//
+// The witness ID attestation note contents is formatted like so:
+//
+//	"ArmoredWitness BastionID attestation v1"
+//	<Device serial string>
+//	<Witness BastionID counter in decimal>
+//	<Witness BastionID ASCII hex string>
+//
+// Returns the note verifier string which can be used to open the note, and the note containing the witness ID attestation.
+func attestBastion(status *api.Status, bastionID string) string {
+	aN := &note.Note{
+		Text: fmt.Sprintf("ArmoredWitness BastionID attestation v1\n%s\n%d\n%s\n", status.Serial, 0, bastionID),
+	}
+	return attestNote(status, aN)
+}
+
 func attestNote(status *api.Status, aN *note.Note) string {
 	aSigner, err := note.NewSigner(attestSigningKey)
 	if err != nil {
@@ -137,6 +172,19 @@ func deriveNoteSigner(diversifier string, uniqueID string, keyName func(io.Reade
 	return sec, pub
 }
 
+// deriveEd25519 uses the hardware secret to device a new ed25519 keypair.
+//
+// diversifier should uniquely specify the key's intended usage, uniqueID should be the
+// device's h/w unique identifier.
+func deriveEd25519(diversifier string, uniqueID string) (ed25519.PrivateKey, ed25519.PublicKey) {
+	r := deriveHKDF(diversifier, uniqueID)
+	pub, priv, err := ed25519.GenerateKey(r)
+	if err != nil {
+		log.Fatalf("Failed to generate derived ed25519 key: %v", err)
+	}
+	return priv, pub
+}
+
 // randomName generates a random human-friendly name.
 func randomName(rnd io.Reader) string {
 	// Figure out our name

trusted_applet/main.go

@@ -184,6 +184,7 @@ func main() {
 		Identity:          witnessPublicKey,
 		IDAttestPublicKey: attestPublicKey,
 		AttestedID:        witnessPublicKeyAttestation,
+		AttestedBastionID: bastionIDAttestation,
 	}, nil)
 
 	klog.Infof("Attestation key:\n%s", attestPublicKey)
@@ -281,6 +282,7 @@ func runWithNetworking(ctx context.Context) error {
 		Identity:          witnessPublicKey,
 		IDAttestPublicKey: attestPublicKey,
 		AttestedID:        witnessPublicKeyAttestation,
+		AttestedBastionID: bastionIDAttestation,
 		IP:                addr.Address.String(),
 	}, nil)