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pgp: support external signer for EdDSA algorithm #318

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83 changes: 83 additions & 0 deletions openpgp/packet/private_key_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -8,19 +8,22 @@ import (
"bytes"
"crypto"
"crypto/dsa"
"crypto/ed25519"
"crypto/elliptic"
"crypto/rand"
"crypto/rsa"
"crypto/x509"
"encoding/hex"
"fmt"
"hash"
"io"
"math/big"
mathrand "math/rand"
"testing"
"time"

"github.com/ProtonMail/go-crypto/openpgp/ecdsa"
pgped25519 "github.com/ProtonMail/go-crypto/openpgp/ed25519"
"github.com/ProtonMail/go-crypto/openpgp/eddsa"
"github.com/ProtonMail/go-crypto/openpgp/elgamal"
"github.com/ProtonMail/go-crypto/openpgp/internal/ecc"
Expand Down Expand Up @@ -449,6 +452,86 @@ func TestEdDSASignerPrivateKeyRandomizeFast(t *testing.T) {
}
}

type externalEd25519Signer struct {
priv ed25519.PrivateKey
err error
}

func (s *externalEd25519Signer) Public() crypto.PublicKey {
return s.priv.Public()
}

func (s *externalEd25519Signer) Sign(rand io.Reader, digest []byte, opts crypto.SignerOpts) ([]byte, error) {
if s.err != nil {
return nil, s.err
}
if opts.HashFunc() != crypto.Hash(0) {
return nil, fmt.Errorf("ed25519 signs the message itself, got hash %v", opts.HashFunc())
}
return s.priv.Sign(rand, digest, opts)
}

func signAndVerifyWithExternalSigner(t *testing.T, priv *PrivateKey, sig *Signature) {
t.Helper()
msg := make([]byte, maxMessageLength)
rand.Read(msg)

h, err := populateHash(sig.Hash, msg)
if err != nil {
t.Fatal(err)
}
if err := sig.Sign(h, priv, nil); err != nil {
t.Fatal(err)
}

if h, err = populateHash(sig.Hash, msg); err != nil {
t.Fatal(err)
}
if err := priv.VerifySignature(h, sig); err != nil {
t.Fatal(err)
}
}

func TestExternalEdDSASignerPrivateKeyRandomizeFast(t *testing.T) {
pub, stdPriv, err := ed25519.GenerateKey(rand.Reader)
if err != nil {
t.Fatal(err)
}
eddsaPub := eddsa.NewPublicKey(ecc.NewEd25519())
eddsaPub.X = pub

priv := &PrivateKey{
PublicKey: *NewEdDSAPublicKey(time.Now(), eddsaPub),
PrivateKey: &externalEd25519Signer{priv: stdPriv},
}
sig := &Signature{
Version: 4,
PubKeyAlgo: PubKeyAlgoEdDSA,
Hash: crypto.SHA256,
}
signAndVerifyWithExternalSigner(t, priv, sig)
}

func TestExternalEd25519SignerPrivateKeyRandomizeFast(t *testing.T) {
pub, stdPriv, err := ed25519.GenerateKey(rand.Reader)
if err != nil {
t.Fatal(err)
}
pgpPub := pgped25519.NewPublicKey()
pgpPub.Point = pub

priv := &PrivateKey{
PublicKey: *NewEd25519PublicKey(time.Now(), pgpPub),
PrivateKey: &externalEd25519Signer{priv: stdPriv},
}
sig := &Signature{
Version: 4,
PubKeyAlgo: PubKeyAlgoEd25519,
Hash: crypto.SHA256,
}
signAndVerifyWithExternalSigner(t, priv, sig)
}

// Tests correctness when encrypting an EdDSA private key with a password.
func TestEncryptDecryptEdDSAPrivateKeyRandomizeFast(t *testing.T) {
password := make([]byte, 20)
Expand Down
78 changes: 61 additions & 17 deletions openpgp/packet/signature.go
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Original file line number Diff line number Diff line change
Expand Up @@ -994,7 +994,8 @@ func (sig *Signature) Sign(h hash.Hash, priv *PrivateKey, config *Config) (err e
switch priv.PubKeyAlgo {
case PubKeyAlgoRSA, PubKeyAlgoRSASignOnly:
// supports both *rsa.PrivateKey and crypto.Signer
sigdata, err := priv.PrivateKey.(crypto.Signer).Sign(config.Random(), digest, sig.Hash)
var sigdata []byte
sigdata, err = priv.PrivateKey.(crypto.Signer).Sign(config.Random(), digest, sig.Hash)
if err == nil {
sig.RSASignature = encoding.NewMPI(sigdata)
}
Expand All @@ -1006,7 +1007,8 @@ func (sig *Signature) Sign(h hash.Hash, priv *PrivateKey, config *Config) (err e
if len(digest) > subgroupSize {
digest = digest[:subgroupSize]
}
r, s, err := dsa.Sign(config.Random(), dsaPriv, digest)
var r, s *big.Int
r, s, err = dsa.Sign(config.Random(), dsaPriv, digest)
if err == nil {
sig.DSASigR = new(encoding.MPI).SetBig(r)
sig.DSASigS = new(encoding.MPI).SetBig(s)
Expand All @@ -1028,30 +1030,71 @@ func (sig *Signature) Sign(h hash.Hash, priv *PrivateKey, config *Config) (err e
sig.ECDSASigS = new(encoding.MPI).SetBig(s)
}
case PubKeyAlgoEdDSA:
sk := priv.PrivateKey.(*eddsa.PrivateKey)
r, s, err := eddsa.Sign(sk, digest)
if err == nil {
sig.EdDSASigR = encoding.NewMPI(r)
sig.EdDSASigS = encoding.NewMPI(s)
if sk, ok := priv.PrivateKey.(*eddsa.PrivateKey); ok {
var r, s []byte
r, s, err = eddsa.Sign(sk, digest)
if err == nil {
sig.EdDSASigR = encoding.NewMPI(r)
sig.EdDSASigS = encoding.NewMPI(s)
}
} else {
// Pure EdDSA, digest is message to sign
pub := priv.PublicKey.PublicKey.(*eddsa.PublicKey)
var b []byte
b, err = priv.PrivateKey.(crypto.Signer).Sign(config.Random(), digest, crypto.Hash(0))
if err == nil {
if len(b) != 2*len(pub.X) {
err = errors.InvalidArgumentError("signer returned an eddsa signature of unexpected length")
} else {
r, s := pub.GetCurve().MarshalSignature(b)
sig.EdDSASigR = encoding.NewMPI(r)
sig.EdDSASigS = encoding.NewMPI(s)
}
}
}
case PubKeyAlgoEd25519:
sk := priv.PrivateKey.(*ed25519.PrivateKey)
signature, err := ed25519.Sign(sk, digest)
if err == nil {
sig.EdSig = signature
if sk, ok := priv.PrivateKey.(*ed25519.PrivateKey); ok {
var signature []byte
signature, err = ed25519.Sign(sk, digest)
if err == nil {
sig.EdSig = signature
}
} else {
var b []byte
b, err = priv.PrivateKey.(crypto.Signer).Sign(config.Random(), digest, crypto.Hash(0))
if err == nil {
if len(b) != ed25519.SignatureSize {
err = errors.InvalidArgumentError("signer returned an ed25519 signature of unexpected length")
} else {
sig.EdSig = b
}
}
}
case PubKeyAlgoEd448:
sk := priv.PrivateKey.(*ed448.PrivateKey)
signature, err := ed448.Sign(sk, digest)
if err == nil {
sig.EdSig = signature
if sk, ok := priv.PrivateKey.(*ed448.PrivateKey); ok {
var signature []byte
signature, err = ed448.Sign(sk, digest)
if err == nil {
sig.EdSig = signature
}
} else {
var b []byte
b, err = priv.PrivateKey.(crypto.Signer).Sign(config.Random(), digest, crypto.Hash(0))
if err == nil {
if len(b) != ed448.SignatureSize {
err = errors.InvalidArgumentError("signer returned an ed448 signature of unexpected length")
} else {
sig.EdSig = b
}
}
}
case PubKeyAlgoMldsa65Ed25519, PubKeyAlgoMldsa87Ed448:
if sig.Version != 6 {
return errors.StructuralError("cannot use MldsaEdDsa on a non-v6 signature")
}
sk := priv.PrivateKey.(*mldsa_eddsa.PrivateKey)
dSig, ecSig, err := mldsa_eddsa.Sign(sk, digest)
var dSig, ecSig []byte
dSig, ecSig, err = mldsa_eddsa.Sign(sk, digest)

if err == nil {
sig.MldsaSig = dSig
Expand All @@ -1062,7 +1105,8 @@ func (sig *Signature) Sign(h hash.Hash, priv *PrivateKey, config *Config) (err e
return errors.StructuralError("cannot use SLH-DSA on a non-v6 signature")
}
sk := priv.PrivateKey.(*slhdsa.PrivateKey)
dSig, err := slhdsa.Sign(sk, digest)
var dSig []byte
dSig, err = slhdsa.Sign(sk, digest)

if err == nil {
sig.SlhdsaSig = dSig
Expand Down