[WIP]: add plainkey platform

export_test.go

@@ -29,7 +29,6 @@ import (
 var (
 	UnmarshalV1KeyPayload  = unmarshalV1KeyPayload
 	UnmarshalProtectedKeys = unmarshalProtectedKeys
-	KeyDataVersion         = keyDataVersion
 )
 
 type ProtectedKeys = protectedKeys
@@ -129,9 +128,9 @@ func MockStderr(w io.Writer) (restore func()) {
 }
 
 func MockKeyDataVersion(n int) (restore func()) {
-	orig := keyDataVersion
-	keyDataVersion = n
+	orig := KeyDataVersion
+	KeyDataVersion = n
 	return func() {
-		keyDataVersion = orig
+		KeyDataVersion = orig
 	}
 }

keydata.go

@@ -50,7 +50,7 @@ const (
 )
 
 var (
-	keyDataVersion        int = 2
+	KeyDataVersion        int = 2
 	snapModelHMACKDFLabel     = []byte("SNAP-MODEL-HMAC")
 	sha1Oid                   = asn1.ObjectIdentifier{1, 3, 14, 3, 2, 26}
 	sha224Oid                 = asn1.ObjectIdentifier{2, 16, 840, 1, 101, 3, 4, 2, 4}
@@ -926,7 +926,7 @@ func NewKeyData(params *KeyParams) (*KeyData, error) {
 
 	kd := &KeyData{
 		data: keyData{
-			Version:          keyDataVersion,
+			Version:          KeyDataVersion,
 			PlatformName:     params.PlatformName,
 			PlatformHandle:   json.RawMessage(encodedHandle),
 			KDFAlg:           hashAlg(params.KDFAlg),

plainkey/keydata.go

@@ -0,0 +1,182 @@
+// -*- Mode: Go; indent-tabs-mode: t -*-
+
+/*
+ * Copyright (C) 2023 Canonical Ltd
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 3 as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ */
+
+package plainkey
+
+import (
+	"crypto"
+	"crypto/aes"
+	"crypto/cipher"
+	"crypto/hmac"
+	"encoding/asn1"
+	"fmt"
+	"io"
+
+	"golang.org/x/crypto/cryptobyte"
+	cryptobyte_asn1 "golang.org/x/crypto/cryptobyte/asn1"
+
+	"github.com/snapcore/secboot"
+)
+
+var (
+	sha1Oid   = asn1.ObjectIdentifier{1, 3, 14, 3, 2, 26}
+	sha224Oid = asn1.ObjectIdentifier{2, 16, 840, 1, 101, 3, 4, 2, 4}
+	sha256Oid = asn1.ObjectIdentifier{2, 16, 840, 1, 101, 3, 4, 2, 1}
+	sha384Oid = asn1.ObjectIdentifier{2, 16, 840, 1, 101, 3, 4, 2, 2}
+	sha512Oid = asn1.ObjectIdentifier{2, 16, 840, 1, 101, 3, 4, 2, 3}
+)
+
+// hashAlg corresponds to a digest algorithm.
+// XXX: This is the third place this appears now - we almost certainly want to put this
+// in one place. Maybe for another PR.
+type hashAlg crypto.Hash
+
+func (a hashAlg) marshalASN1(b *cryptobyte.Builder) {
+	b.AddASN1(cryptobyte_asn1.SEQUENCE, func(b *cryptobyte.Builder) { // AlgorithmIdentifier ::= SEQUENCE {
+		var oid asn1.ObjectIdentifier
+
+		switch crypto.Hash(a) {
+		case crypto.SHA1:
+			oid = sha1Oid
+		case crypto.SHA224:
+			oid = sha224Oid
+		case crypto.SHA256:
+			oid = sha256Oid
+		case crypto.SHA384:
+			oid = sha384Oid
+		case crypto.SHA512:
+			oid = sha512Oid
+		default:
+			b.SetError(fmt.Errorf("unknown hash algorithm: %v", crypto.Hash(a)))
+			return
+		}
+		b.AddASN1ObjectIdentifier(oid) // algorithm OBJECT IDENTIFIER
+		b.AddASN1NULL()                // parameters ANY DEFINED BY algorithm OPTIONAL
+	})
+}
+
+type additionalData struct {
+	version     int
+	baseVersion int
+	kdfAlg      hashAlg
+	authMode    secboot.AuthMode
+}
+
+func (d additionalData) marshalASN1(b *cryptobyte.Builder) {
+	b.AddASN1(cryptobyte_asn1.SEQUENCE, func(b *cryptobyte.Builder) {
+		b.AddASN1Int64(int64(d.version))
+		b.AddASN1Int64(int64(d.baseVersion))
+		d.kdfAlg.marshalASN1(b)
+		b.AddASN1Enum(int64(d.authMode))
+	})
+}
+
+type platformKeyId struct {
+	Alg    hashAlg `json:"alg"`
+	Salt   []byte  `json:"salt"`
+	Digest []byte  `json:"digest"`
+}
+
+type keyData struct {
+	Version int    `json:"version"`
+	Nonce   []byte `json:"nonce"`
+
+	PlatformKeyID platformKeyId `json:"platform-key-id"`
+}
+
+// NewProtectedKey creates a new key that is protected by this platform with the supplied
+// platform key. The platform key is stored inside of an encrypted container that is unlocked
+// via another mechanism, such as a TPM, and then loaded via [InitPlatform] after unlocking
+// that container.
+//
+// If primaryKey isn't supplied, then one will be generated. The kdfAlg specifies the algorithm
+// used to derive the unlock key from the primary key and internally generated unique key.
+func NewProtectedKey(rand io.Reader, platformKey []byte, primaryKey secboot.PrimaryKey, kdfAlg crypto.Hash) (protectedKey *secboot.KeyData, primaryKeyOut secboot.PrimaryKey, unlockKey secboot.DiskUnlockKey, err error) {
+	if len(primaryKey) == 0 {
+		primaryKey = make(secboot.PrimaryKey, 32)
+		if _, err := io.ReadFull(rand, primaryKey); err != nil {
+			return nil, nil, nil, fmt.Errorf("cannot obtain primary key: %w", err)
+		}
+
+	}
+
+	unlockKey, payload, err := secboot.MakeDiskUnlockKey(rand, crypto.SHA256, primaryKey)
+	if err != nil {
+		return nil, nil, nil, fmt.Errorf("cannot create new unlock key: %w", err)
+	}
+
+	nonce := make([]byte, 12)
+	if _, err := io.ReadFull(rand, nonce); err != nil {
+		return nil, nil, nil, fmt.Errorf("cannot obtain nonce: %w", err)
+	}
+
+	aad := additionalData{
+		version:     1,
+		baseVersion: secboot.KeyDataVersion,
+		kdfAlg:      hashAlg(kdfAlg),
+		authMode:    secboot.AuthModeNone,
+	}
+	builder := cryptobyte.NewBuilder(nil)
+	aad.marshalASN1(builder)
+	aadBytes, err := builder.Bytes()
+	if err != nil {
+		return nil, nil, nil, fmt.Errorf("cannot serialize AAD: %w", err)
+	}
+
+	idAlg := crypto.SHA256
+	salt := make([]byte, idAlg.Size())
+	if _, err := io.ReadFull(rand, salt); err != nil {
+		return nil, nil, nil, fmt.Errorf("cannot obtain salt for platform key ID: %w", err)
+	}
+	id := platformKeyId{
+		Alg:  hashAlg(idAlg),
+		Salt: salt,
+	}
+	h := hmac.New(idAlg.New, salt)
+	h.Write(platformKey)
+	id.Digest = h.Sum(nil)
+
+	b, err := aes.NewCipher(platformKey)
+	if err != nil {
+		return nil, nil, nil, fmt.Errorf("cannot create cipher: %w", err)
+	}
+	aead, err := cipher.NewGCM(b)
+	if err != nil {
+		return nil, nil, nil, fmt.Errorf("cannot create AEAD: %w", err)
+	}
+	ciphertext := aead.Seal(nil, nonce, payload, aadBytes)
+
+	kd, err := secboot.NewKeyData(&secboot.KeyParams{
+		Handle: &keyData{
+			Version:       1,
+			Nonce:         nonce,
+			PlatformKeyID: id,
+		},
+		EncryptedPayload:  ciphertext,
+		PrimaryKey:        primaryKey,    // XXX: will be removed in a pending PR
+		SnapModelAuthHash: crypto.SHA256, // XXX: will be removed in a pending PR
+		PlatformName:      platformName,
+		KDFAlg:            kdfAlg,
+	})
+	if err != nil {
+		return nil, nil, nil, fmt.Errorf("cannot create key data: %w", err)
+	}
+
+	return kd, primaryKey, unlockKey, nil
+}

plainkey/platform.go

@@ -0,0 +1,155 @@
+// -*- Mode: Go; indent-tabs-mode: t -*-
+
+/*
+ * Copyright (C) 2023 Canonical Ltd
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 3 as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ */
+
+package plainkey
+
+import (
+	"bytes"
+	"crypto"
+	"crypto/aes"
+	"crypto/cipher"
+	"crypto/hmac"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"runtime"
+	"sync/atomic"
+
+	"golang.org/x/crypto/cryptobyte"
+
+	"github.com/snapcore/secboot"
+)
+
+const (
+	platformName = "plainkey"
+)
+
+var (
+	platformStatus uint32
+	platformKeys   [][]byte
+)
+
+const (
+	statusUninitialized uint32 = 0
+	statusInitializing  uint32 = 1
+	statusInitialized   uint32 = 2
+)
+
+// InitPlatform sets the key used to protect and recover objects with this platform.
+func InitPlatform(keys ...[]byte) {
+	if !atomic.CompareAndSwapUint32(&platformStatus, statusUninitialized, statusInitializing) {
+		panic("cannot call InitPlatform more than once")
+	}
+	platformKeys = keys
+	secboot.RegisterPlatformKeyDataHandler(platformName, &platformKeyDataHandler{})
+	atomic.StoreUint32(&platformStatus, statusInitialized)
+}
+
+func getPlatformKey(id *platformKeyId) ([]byte, error) {
+	alg := crypto.Hash(id.Alg)
+	if !alg.Available() {
+		return nil, errors.New("digest algorithm unavailable")
+	}
+
+	for {
+		switch atomic.LoadUint32(&platformStatus) {
+		case statusUninitialized:
+			// Nothing has called InitPlatform yet
+			panic("must call InitPlatform")
+		case statusInitializing:
+			// InitPlatform is currently executing, so it's ok to busy loop here
+			runtime.Gosched()
+		case statusInitialized:
+			// InitPlatform was called
+			for _, key := range platformKeys {
+				h := hmac.New(alg.New, id.Salt)
+				h.Write(key)
+				if bytes.Equal(h.Sum(nil), id.Digest) {
+					return key, nil
+				}
+			}
+			return nil, errors.New("no key available")
+		default:
+			panic("unexpected status value")
+		}
+	}
+}
+
+type platformKeyDataHandler struct{}
+
+func (*platformKeyDataHandler) RecoverKeys(data *secboot.PlatformKeyData, encryptedPayload []byte) ([]byte, error) {
+	var kd keyData
+	if err := json.Unmarshal(data.EncodedHandle, &kd); err != nil {
+		return nil, &secboot.PlatformHandlerError{
+			Type: secboot.PlatformHandlerErrorInvalidData,
+			Err:  err,
+		}
+	}
+
+	aad := additionalData{
+		version:     kd.Version,
+		baseVersion: data.Version,
+		kdfAlg:      hashAlg(data.KDFAlg),
+		authMode:    data.AuthMode,
+	}
+	builder := cryptobyte.NewBuilder(nil)
+	aad.marshalASN1(builder)
+	aadBytes, err := builder.Bytes()
+	if err != nil {
+		return nil, &secboot.PlatformHandlerError{
+			Type: secboot.PlatformHandlerErrorInvalidData,
+			Err:  fmt.Errorf("cannot serialize AAD: %w", err),
+		}
+	}
+
+	key, err := getPlatformKey(&kd.PlatformKeyID)
+	if err != nil {
+		return nil, &secboot.PlatformHandlerError{
+			Type: secboot.PlatformHandlerErrorInvalidData,
+			Err:  fmt.Errorf("cannot select platform key: %w", err),
+		}
+	}
+
+	b, err := aes.NewCipher(key)
+	if err != nil {
+		return nil, fmt.Errorf("cannot create cipher: %w", err)
+	}
+	aead, err := cipher.NewGCM(b)
+	if err != nil {
+		return nil, fmt.Errorf("cannot create AEAD: %w", err)
+	}
+
+	payload, err := aead.Open(nil, kd.Nonce, encryptedPayload, aadBytes)
+	if err != nil {
+		return nil, &secboot.PlatformHandlerError{
+			Type: secboot.PlatformHandlerErrorInvalidData,
+			Err:  fmt.Errorf("cannot open payload: %w", err),
+		}
+	}
+
+	return payload, nil
+}
+
+func (*platformKeyDataHandler) RecoverKeysWithAuthKey(data *secboot.PlatformKeyData, encryptedPayload, key []byte) ([]byte, error) {
+	return nil, errors.New("unsupported action")
+}
+
+func (*platformKeyDataHandler) ChangeAuthKey(data *secboot.PlatformKeyData, old, new []byte) ([]byte, error) {
+	return nil, errors.New("unsupported action")
+}