feature/tpm: implement key.HardwareAttestationKey (#17256)

Updates #15830

Signed-off-by: Andrew Lytvynov <awly@tailscale.com>

feature/tpm/attestation_test.go

@@ -0,0 +1,98 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+package tpm
+
+import (
+	"bytes"
+	"crypto"
+	"crypto/ecdsa"
+	"crypto/rand"
+	"crypto/sha256"
+	"encoding/json"
+	"testing"
+)
+
+func TestAttestationKeySign(t *testing.T) {
+	skipWithoutTPM(t)
+	ak, err := newAttestationKey()
+	if err != nil {
+		t.Fatal(err)
+	}
+	t.Cleanup(func() {
+		if err := ak.Close(); err != nil {
+			t.Errorf("ak.Close: %v", err)
+		}
+	})
+
+	data := []byte("secrets")
+	digest := sha256.Sum256(data)
+
+	// Check signature/validation round trip.
+	sig, err := ak.Sign(rand.Reader, digest[:], crypto.SHA256)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !ecdsa.VerifyASN1(ak.Public().(*ecdsa.PublicKey), digest[:], sig) {
+		t.Errorf("ecdsa.VerifyASN1 failed")
+	}
+
+	// Create a different key.
+	ak2, err := newAttestationKey()
+	if err != nil {
+		t.Fatal(err)
+	}
+	t.Cleanup(func() {
+		if err := ak2.Close(); err != nil {
+			t.Errorf("ak2.Close: %v", err)
+		}
+	})
+
+	// Make sure that the keys are distinct via their public keys and the
+	// signatures they produce.
+	if ak.Public().(*ecdsa.PublicKey).Equal(ak2.Public()) {
+		t.Errorf("public keys of distinct attestation keys are the same")
+	}
+	sig2, err := ak2.Sign(rand.Reader, digest[:], crypto.SHA256)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if bytes.Equal(sig, sig2) {
+		t.Errorf("signatures from distinct attestation keys are the same")
+	}
+}
+
+func TestAttestationKeyUnmarshal(t *testing.T) {
+	skipWithoutTPM(t)
+	ak, err := newAttestationKey()
+	if err != nil {
+		t.Fatal(err)
+	}
+	t.Cleanup(func() {
+		if err := ak.Close(); err != nil {
+			t.Errorf("ak.Close: %v", err)
+		}
+	})
+
+	buf, err := ak.MarshalJSON()
+	if err != nil {
+		t.Fatal(err)
+	}
+	var ak2 attestationKey
+	if err := json.Unmarshal(buf, &ak2); err != nil {
+		t.Fatal(err)
+	}
+	t.Cleanup(func() {
+		if err := ak2.Close(); err != nil {
+			t.Errorf("ak2.Close: %v", err)
+		}
+	})
+
+	if !ak2.loaded() {
+		t.Error("unmarshalled key is not loaded")
+	}
+
+	if !ak.Public().(*ecdsa.PublicKey).Equal(ak2.Public()) {
+		t.Error("unmarshalled public key is not the same as the original public key")
+	}
+}