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key.go
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key.go
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package tpm
import (
"context"
"crypto"
"crypto/x509"
"encoding/json"
"errors"
"fmt"
"time"
"github.com/smallstep/go-attestation/attest"
internalkey "go.step.sm/crypto/tpm/internal/key"
"go.step.sm/crypto/tpm/storage"
)
// Key models a TPM 2.0 Key. A Key can be used
// to sign data. When a Key is created, it can be
// attested by an AK, to be able to prove that it
// was created by a specific TPM.
type Key struct {
name string
data []byte
attestedBy string
chain []*x509.Certificate
createdAt time.Time
blobs *Blobs
tpm *TPM
}
// Name returns the Key name. The name uniquely
// identifies the Key if a TPM with persistent
// storage is used.
func (k *Key) Name() string {
return k.name
}
// Data returns the Key data blob. The data blob
// contains all information required for the Key
// to be loaded into the TPM that created it again,
// so that it can be used for signing data.
func (k *Key) Data() []byte {
return k.data
}
// AttestedBy returns the name of the AK the Key was
// attested (certified) by at creation time.
func (k *Key) AttestedBy() string {
return k.attestedBy
}
// WasAttested returns whether or not the Key was
// attested (certified) by an AK at creation time.
func (k *Key) WasAttested() bool {
return k.attestedBy != ""
}
// WasAttestedBy returns whether or not the Key
// was attested (certified) by the provided AK
// at creation time.
func (k *Key) WasAttestedBy(ak *AK) bool {
return k.attestedBy == ak.name
}
// Certificate returns the certificate for the Key, if set.
// Will return nil in case no AK certificate is available.
func (k *Key) Certificate() *x509.Certificate {
if len(k.chain) == 0 {
return nil
}
return k.chain[0]
}
// CertificateChain returns the certificate chain for the Key.
// It can return an empty chain.
func (k *Key) CertificateChain() []*x509.Certificate {
return k.chain
}
// CreatedAt returns the the creation time of the Key.
func (k *Key) CreatedAt() time.Time {
return k.createdAt.Truncate(time.Second)
}
// MarshalJSON marshals the Key to JSON.
func (k *Key) MarshalJSON() ([]byte, error) {
chain := make([][]byte, len(k.chain))
for i, cert := range k.chain {
chain[i] = cert.Raw
}
o := struct {
Name string `json:"name"`
Data []byte `json:"data"`
AttestedBy string `json:"attestedBy,omitempty"`
Chain [][]byte `json:"chain,omitempty"`
CreatedAt time.Time `json:"createdAt"`
}{
Name: k.name,
Data: k.data,
AttestedBy: k.attestedBy,
Chain: chain,
CreatedAt: k.createdAt,
}
return json.Marshal(o)
}
// comparablePublicKey is an interface that allows a crypto.PublicKey to be
// compared to another crypto.PublicKey.
type comparablePublicKey interface {
Equal(crypto.PublicKey) bool
}
// CreateKeyConfig is used to pass configuration
// when creating Keys.
type CreateKeyConfig struct {
// Algorithm to be used, either RSA or ECDSA.
Algorithm string
// Size is used to specify the bit size of the key or elliptic curve. For
// example, '256' is used to specify curve P-256.
Size int
// TODO(hs): move key name to this struct?
}
// AttestKeyConfig is used to pass configuration
// when creating Keys that are to be attested by
// an AK.
type AttestKeyConfig struct {
// Algorithm to be used, either RSA or ECDSA.
Algorithm string
// Size is used to specify the bit size of the key or elliptic curve. For
// example, '256' is used to specify curve P-256.
Size int
// QualifyingData is additional data that is passed to the TPM.
// It can be used as a nonce to ensure freshness of an attestation.
// When used with ACME `device-attest-01`, this contains a hash of
// the key authorization.
QualifyingData []byte
// TODO(hs): add akName and key name to this struct?
}
// CreateKey creates a new Key identified by `name`. If no name is provided,
// a random 10 character name is generated. If a Key with the same name exists,
// `ErrExists` is returned. The Key won't be attested by an AK.
func (t *TPM) CreateKey(ctx context.Context, name string, config CreateKeyConfig) (key *Key, err error) {
if err = t.open(goTPMCall(ctx)); err != nil {
return nil, fmt.Errorf("failed opening TPM: %w", err)
}
defer closeTPM(ctx, t, &err)
now := time.Now()
if name, err = processName(name); err != nil {
return nil, err
}
if _, err := t.store.GetKey(name); err == nil {
return nil, fmt.Errorf("failed creating key %q: %w", name, ErrExists)
}
createConfig := internalkey.CreateConfig{
Algorithm: config.Algorithm,
Size: config.Size,
}
if err := t.validate(&createConfig); err != nil {
return nil, fmt.Errorf("invalid key creation parameters: %w", err)
}
data, err := internalkey.Create(t.rwc, prefixKey(name), createConfig)
if err != nil {
return nil, fmt.Errorf("failed creating key %q: %w", name, err)
}
key = &Key{
name: name,
data: data,
createdAt: now,
tpm: t,
}
if err := t.store.AddKey(key.toStorage()); err != nil {
return nil, fmt.Errorf("failed adding key %q to storage: %w", name, err)
}
if err := t.store.Persist(); err != nil {
return nil, fmt.Errorf("failed persisting key %q to storage: %w", name, err)
}
return
}
type attestValidationWrapper attest.KeyConfig
func (w attestValidationWrapper) Validate() error {
switch w.Algorithm {
case "RSA":
if w.Size > 2048 {
return fmt.Errorf("%d bits RSA keys are (currently) not supported in go.step.sm/crypto; maximum is 2048", w.Size)
}
case "ECDSA":
break
default:
return fmt.Errorf("unsupported algorithm %q", w.Algorithm)
}
return nil
}
// AttestKey creates a new Key identified by `name` and attested by the AK
// identified by `akName`. If no name is provided, a random 10 character
// name is generated. If a Key with the same name exists, `ErrExists` is
// returned.
func (t *TPM) AttestKey(ctx context.Context, akName, name string, config AttestKeyConfig) (key *Key, err error) {
if err = t.open(ctx); err != nil {
return nil, fmt.Errorf("failed opening TPM: %w", err)
}
defer closeTPM(ctx, t, &err)
now := time.Now()
if name, err = processName(name); err != nil {
return nil, err
}
if _, err := t.store.GetKey(name); err == nil {
return nil, fmt.Errorf("failed creating key %q: %w", name, ErrExists)
}
ak, err := t.store.GetAK(akName)
if err != nil {
return nil, fmt.Errorf("failed getting AK %q: %w", akName, err)
}
loadedAK, err := t.attestTPM.LoadAK(ak.Data)
if err != nil {
return nil, fmt.Errorf("failed loading AK %q: %w", akName, err)
}
defer loadedAK.Close(t.attestTPM)
keyConfig := attest.KeyConfig{
Algorithm: attest.Algorithm(config.Algorithm),
Size: config.Size,
QualifyingData: config.QualifyingData,
Name: prefixKey(name),
}
if err := t.validate(attestValidationWrapper(keyConfig)); err != nil {
return nil, fmt.Errorf("invalid key attestation parameters: %w", err)
}
akey, err := t.attestTPM.NewKey(loadedAK, &keyConfig)
if err != nil {
return nil, fmt.Errorf("failed creating key %q: %w", name, err)
}
defer akey.Close()
data, err := akey.Marshal()
if err != nil {
return nil, fmt.Errorf("failed marshaling key %q: %w", name, err)
}
key = &Key{
name: name,
data: data,
attestedBy: akName,
createdAt: now,
tpm: t,
}
if err := t.store.AddKey(key.toStorage()); err != nil {
return nil, fmt.Errorf("failed adding key %q to storage: %w", name, err)
}
if err := t.store.Persist(); err != nil {
return nil, fmt.Errorf("failed persisting key %q: %w", name, err)
}
return
}
// GetKey returns the Key identified by `name`. It returns `ErrNotfound`
// if it doesn't exist.
func (t *TPM) GetKey(ctx context.Context, name string) (key *Key, err error) {
if err = t.open(ctx); err != nil {
return nil, fmt.Errorf("failed opening TPM: %w", err)
}
defer closeTPM(ctx, t, &err)
skey, err := t.store.GetKey(name)
if err != nil {
if errors.Is(err, storage.ErrNotFound) {
return nil, fmt.Errorf("failed getting key %q: %w", name, ErrNotFound)
}
return nil, fmt.Errorf("failed getting key %q: %w", name, err)
}
return keyFromStorage(skey, t), nil
}
// ListKeys returns a slice of Keys. The result is (currently)
// not ordered.
func (t *TPM) ListKeys(ctx context.Context) (keys []*Key, err error) {
if err = t.open(ctx); err != nil {
return nil, fmt.Errorf("failed opening TPM: %w", err)
}
defer closeTPM(ctx, t, &err)
skeys, err := t.store.ListKeys()
if err != nil {
return nil, fmt.Errorf("failed listing keys: %w", err)
}
keys = make([]*Key, 0, len(skeys))
for _, skey := range skeys {
keys = append(keys, keyFromStorage(skey, t))
}
return
}
// GetKeysAttestedBy returns a slice of Keys attested by the AK
// identified by `akName`. The result is (currently) not ordered.
func (t *TPM) GetKeysAttestedBy(ctx context.Context, akName string) (keys []*Key, err error) {
if err = t.open(ctx); err != nil {
return nil, fmt.Errorf("failed opening TPM: %w", err)
}
defer closeTPM(ctx, t, &err)
skeys, err := t.store.ListKeys()
if err != nil {
return nil, fmt.Errorf("failed listing keys: %w", err)
}
keys = make([]*Key, 0, len(skeys))
for _, skey := range skeys {
if skey.AttestedBy == akName {
keys = append(keys, keyFromStorage(skey, t))
}
}
return
}
// DeleteKey removes the Key identified by `name`. It returns `ErrNotfound`
// if it doesn't exist.
func (t *TPM) DeleteKey(ctx context.Context, name string) (err error) {
if err := t.open(ctx); err != nil {
return fmt.Errorf("failed opening TPM: %w", err)
}
defer closeTPM(ctx, t, &err)
key, err := t.store.GetKey(name)
if err != nil {
if errors.Is(err, storage.ErrNotFound) {
return fmt.Errorf("failed getting key %q: %w", name, ErrNotFound)
}
return fmt.Errorf("failed getting key %q: %w", name, err)
}
if err := t.attestTPM.DeleteKey(key.Data); err != nil {
return fmt.Errorf("failed deleting key %q: %w", name, err)
}
if err := t.store.DeleteKey(name); err != nil {
return fmt.Errorf("failed deleting key %q from storage: %w", name, err)
}
if err := t.store.Persist(); err != nil {
return fmt.Errorf("failed persisting storage: %w", err)
}
return
}
// Signer returns a crypto.Signer backed by the Key.
func (k *Key) Signer(ctx context.Context) (crypto.Signer, error) {
return k.tpm.GetSigner(ctx, k.name)
}
// CertificationParameters returns information about the key that can be used to
// verify key certification.
func (k *Key) CertificationParameters(ctx context.Context) (params attest.CertificationParameters, err error) {
if err = k.tpm.open(ctx); err != nil {
return params, fmt.Errorf("failed opening TPM: %w", err)
}
defer closeTPM(ctx, k.tpm, &err)
loadedKey, err := k.tpm.attestTPM.LoadKey(k.data)
if err != nil {
return attest.CertificationParameters{}, fmt.Errorf("failed loading key %q: %w", k.name, err)
}
defer loadedKey.Close()
params = loadedKey.CertificationParameters()
return
}
// Blobs returns a container for the private and public key blobs.
// The resulting blobs are compatible with tpm2-tools, so can be used
// like this (after having been written to key.priv and key.pub):
//
// tpm2_load -C 0x81000001 -u key.pub -r key.priv -c key.ctx
func (k *Key) Blobs(ctx context.Context) (blobs *Blobs, err error) {
if k.blobs != nil {
return k.blobs, nil
}
if err = k.tpm.open(ctx); err != nil {
return nil, fmt.Errorf("failed opening TPM: %w", err)
}
defer closeTPM(ctx, k.tpm, &err)
key, err := k.tpm.attestTPM.LoadKey(k.data)
if err != nil {
return nil, fmt.Errorf("failed loading key: %w", err)
}
defer key.Close()
public, private, err := key.Blobs()
if err != nil {
return nil, fmt.Errorf("failed getting key blobs: %w", err)
}
k.setBlobs(private, public)
return k.blobs, nil
}
// SetCertificateChain associates an X.509 certificate chain with the Key.
// If the public key doesn't match the public key in the first certificate
// in the chain (the leaf), an error is returned.
func (k *Key) SetCertificateChain(ctx context.Context, chain []*x509.Certificate) (err error) {
if err = k.tpm.open(ctx); err != nil {
return fmt.Errorf("failed opening TPM: %w", err)
}
defer closeTPM(ctx, k.tpm, &err)
signer, err := k.Signer(internalCall(ctx)) // TODO: cache the crypto.PublicKey after its first load instead?
if err != nil {
return fmt.Errorf("failed getting signer for key: %w", err)
}
leaf := chain[0]
leafPK, ok := leaf.PublicKey.(crypto.PublicKey)
if !ok {
return fmt.Errorf("unexpected type for certificate public key: %T", leaf.PublicKey)
}
publicKey, ok := leafPK.(comparablePublicKey)
if !ok {
return errors.New("certificate public key can't be compared to a crypto.PublicKey")
}
if !publicKey.Equal(signer.Public()) {
return errors.New("public key does not match the leaf certificate public key")
}
k.chain = chain // TODO(hs): deep copy, so that certs can't be changed by pointer?
if err := k.tpm.store.UpdateKey(k.toStorage()); err != nil {
return fmt.Errorf("failed updating key %q: %w", k.name, err)
}
return
}
// toStorage transforms the Key to the struct used for
// persisting Keys.
func (k *Key) toStorage() *storage.Key {
return &storage.Key{
Name: k.name,
Data: k.data,
AttestedBy: k.attestedBy,
Chain: k.chain,
CreatedAt: k.createdAt.UTC(),
}
}
// keyFromStorage recreates a Key from the struct used for
// persisting Keys.
func keyFromStorage(sk *storage.Key, t *TPM) *Key {
return &Key{
name: sk.Name,
data: sk.Data,
attestedBy: sk.AttestedBy,
chain: sk.Chain,
createdAt: sk.CreatedAt.Local(),
tpm: t,
}
}