Add plainkey platform

plainkey/export_test.go

@@ -0,0 +1,46 @@
+// -*- 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 "github.com/snapcore/secboot"
+
+const (
+	PlatformName = platformName
+)
+
+type (
+	AdditionalData         = additionalData
+	HashAlg                = hashAlg
+	KeyData                = keyData
+	PlatformKeyDataHandler = platformKeyDataHandler
+	PlatformKeyId          = platformKeyId
+)
+
+var (
+	DeriveAESKey = deriveAESKey
+)
+
+func MockSecbootNewKeyData(fn func(*secboot.KeyParams) (*secboot.KeyData, error)) (restore func()) {
+	orig := secbootNewKeyData
+	secbootNewKeyData = fn
+	return func() {
+		secbootNewKeyData = orig
+	}
+}

plainkey/keydata.go

@@ -0,0 +1,281 @@
+// -*- 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"
+	"encoding/json"
+	"fmt"
+	"hash"
+	"io"
+
+	"golang.org/x/crypto/cryptobyte"
+	cryptobyte_asn1 "golang.org/x/crypto/cryptobyte/asn1"
+	"golang.org/x/crypto/hkdf"
+
+	"github.com/snapcore/secboot"
+)
+
+const (
+	symKeySaltSize = 32
+	nonceSize      = 12
+)
+
+var (
+	nilHash   hashAlg = 0
+	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}
+
+	secbootNewKeyData = secboot.NewKeyData
+)
+
+// 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) Available() bool {
+	return crypto.Hash(a).Available()
+}
+
+func (a hashAlg) New() hash.Hash {
+	return crypto.Hash(a).New()
+}
+
+func (a hashAlg) Size() int {
+	return crypto.Hash(a).Size()
+}
+
+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
+	})
+}
+
+func (a hashAlg) MarshalJSON() ([]byte, error) {
+	var s string
+
+	switch crypto.Hash(a) {
+	case crypto.SHA1:
+		s = "sha1"
+	case crypto.SHA224:
+		s = "sha224"
+	case crypto.SHA256:
+		s = "sha256"
+	case crypto.SHA384:
+		s = "sha384"
+	case crypto.SHA512:
+		s = "sha512"
+	case crypto.Hash(nilHash):
+		s = "null"
+	default:
+		return nil, fmt.Errorf("unknown hash algorithm: %v", crypto.Hash(a))
+	}
+
+	return json.Marshal(s)
+}
+
+func (a *hashAlg) UnmarshalJSON(b []byte) error {
+	var s string
+	if err := json.Unmarshal(b, &s); err != nil {
+		return err
+	}
+
+	switch s {
+	case "sha1":
+		*a = hashAlg(crypto.SHA1)
+	case "sha224":
+		*a = hashAlg(crypto.SHA224)
+	case "sha256":
+		*a = hashAlg(crypto.SHA256)
+	case "sha384":
+		*a = hashAlg(crypto.SHA384)
+	case "sha512":
+		*a = hashAlg(crypto.SHA512)
+	default:
+		// be permissive here and allow everything to be
+		// unmarshalled.
+		*a = nilHash
+	}
+
+	return nil
+}
+
+func deriveAESKey(ikm, salt []byte) []byte {
+	r := hkdf.New(crypto.SHA256.New, ikm, salt, []byte("ENCRYPT"))
+
+	key := make([]byte, 32)
+	if _, err := io.ReadFull(r, key); err != nil {
+		panic(fmt.Sprintf("cannot derive key: %v", err))
+	}
+
+	return key
+}
+
+type additionalData struct {
+	Version    int
+	Generation 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.Generation))
+		d.KDFAlg.MarshalASN1(b)
+		b.AddASN1Enum(int64(d.AuthMode))
+	})
+}
+
+// platformKeyId is a HMAC created by the platform key used to protect
+// a plainkey key blob. It is used to iedntify the loaded platform key
+// to use for key recovery.
+type platformKeyId struct {
+	Alg    hashAlg `json:"alg"`    // the digest algorithm
+	Salt   []byte  `json:"salt"`   // the salt, used as data to the HMAC
+	Digest []byte  `json:"digest"` // the resulting HMAC.
+}
+
+type keyData struct {
+	Version int `json:"version"`
+
+	Salt  []byte `json:"salt"`  // Used to derive the symmetric key from the platform key
+	Nonce []byte `json:"nonce"` // the GCM nonce
+
+	// PlatformKeyID is used to identify the loaded platform key to
+	// use for key recovery.
+	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 typically stored inside of an encrypted container that
+// is unlocked via another mechanism, such as a TPM, and then loaded via [SetPlatformKeys]
+// after unlocking that container.
+//
+// If primaryKey isn't supplied, then one will be generated.
+//
+// This function requires some cryptographically strong randomness, obtained from the rand
+// argument. Whilst this will normally be from [rand.Reader], it can be provided from other
+// secure sources or mocked during tests. Note that the underlying implementation of this
+// platform uses GCM, so rand must be cryptographically secure in order to prevent nonce
+// reuse problems. Calling this function more than once in production with the same platform
+// key and the same sequence of random bytes is a bug.
+func NewProtectedKey(rand io.Reader, platformKey []byte, primaryKey secboot.PrimaryKey) (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)
+		}
+
+	}
+
+	kdfAlg := crypto.SHA256
+	unlockKey, payload, err := secboot.MakeDiskUnlockKey(rand, kdfAlg, primaryKey)
+	if err != nil {
+		return nil, nil, nil, fmt.Errorf("cannot create new unlock key: %w", err)
+	}
+
+	idAlg := crypto.SHA256
+
+	// Obtain a 32-byte salt for deriving the symmetric key, a 12-byte GCM nonce and
+	// a 32-byte salt for the platform key ID.
+	randBytes := make([]byte, symKeySaltSize+nonceSize+idAlg.Size())
+	if _, err := io.ReadFull(rand, randBytes); err != nil {
+		return nil, nil, nil, fmt.Errorf("cannot obtain required random bytes: %w", err)
+	}
+
+	salt := randBytes[:symKeySaltSize]
+	nonce := randBytes[symKeySaltSize : symKeySaltSize+nonceSize]
+	idSalt := randBytes[symKeySaltSize+nonceSize:]
+
+	aad := additionalData{
+		Version:    1,
+		Generation: secboot.KeyDataGeneration,
+		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)
+	}
+
+	id := platformKeyId{
+		Alg:  hashAlg(idAlg),
+		Salt: idSalt,
+	}
+	h := hmac.New(id.Alg.New, platformKey)
+	h.Write(id.Salt)
+	id.Digest = h.Sum(nil)
+
+	b, err := aes.NewCipher(deriveAESKey(platformKey, salt))
+	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 := secbootNewKeyData(&secboot.KeyParams{
+		Handle: &keyData{
+			Version:       1,
+			Salt:          salt,
+			Nonce:         nonce,
+			PlatformKeyID: id,
+		},
+		EncryptedPayload: ciphertext,
+		PlatformName:     platformName,
+		KDFAlg:           kdfAlg,
+	})
+	if err != nil {
+		return nil, nil, nil, fmt.Errorf("cannot create key data: %w", err)
+	}
+
+	return kd, primaryKey, unlockKey, nil
+}