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ECDSA verification support #98

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merged 2 commits into from
Aug 13, 2016
Merged

ECDSA verification support #98

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9e8df3c
verify: Don't assume signature method, use key type
titanous Aug 9, 2016
596db52
verify: Add support for ecdsa-sha2-p256 signatures
titanous Aug 9, 2016
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5 changes: 3 additions & 2 deletions data/types.go
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Original file line number Diff line number Diff line change
Expand Up @@ -11,8 +11,9 @@ import (
)

const (
KeyIDLength = sha256.Size * 2
KeyTypeEd25519 = "ed25519"
KeyIDLength = sha256.Size * 2
KeyTypeEd25519 = "ed25519"
KeyTypeECDSA_SHA2_P256 = "ecdsa-sha2-nistp256"
)

type Signed struct {
Expand Down
41 changes: 40 additions & 1 deletion verify/verifiers.go
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Original file line number Diff line number Diff line change
@@ -1,6 +1,12 @@
package verify

import (
"crypto/ecdsa"
"crypto/elliptic"
"crypto/sha256"
"encoding/asn1"
"math/big"

"github.com/flynn/go-tuf/data"
"golang.org/x/crypto/ed25519"
)
Expand All @@ -19,7 +25,8 @@ type Verifier interface {

// Verifiers is used to map key types to Verifier instances.
var Verifiers = map[string]Verifier{
data.KeyTypeEd25519: ed25519Verifier{},
data.KeyTypeEd25519: ed25519Verifier{},
data.KeyTypeECDSA_SHA2_P256: p256Verifier{},
}

type ed25519Verifier struct{}
Expand All @@ -34,3 +41,35 @@ func (ed25519Verifier) Verify(key, msg, sig []byte) error {
func (ed25519Verifier) ValidKey(k []byte) bool {
return len(k) == ed25519.PublicKeySize
}

type ecdsaSignature struct {
R, S *big.Int
}

type p256Verifier struct{}

func (p256Verifier) Verify(key, msg, sigBytes []byte) error {
x, y := elliptic.Unmarshal(elliptic.P256(), key)
k := &ecdsa.PublicKey{
Curve: elliptic.P256(),
X: x,
Y: y,
}

var sig ecdsaSignature
if _, err := asn1.Unmarshal(sigBytes, &sig); err != nil {
return ErrInvalid
}

hash := sha256.Sum256(msg)

if !ecdsa.Verify(k, hash[:], sig.R, sig.S) {
return ErrInvalid
}
return nil
}

func (p256Verifier) ValidKey(k []byte) bool {
x, _ := elliptic.Unmarshal(elliptic.P256(), k)
return x != nil
}
12 changes: 1 addition & 11 deletions verify/verify.go
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Original file line number Diff line number Diff line change
Expand Up @@ -7,7 +7,6 @@ import (

"github.com/flynn/go-tuf/data"
"github.com/tent/canonical-json-go"
"golang.org/x/crypto/ed25519"
)

type signedMeta struct {
Expand Down Expand Up @@ -62,15 +61,7 @@ func (db *DB) VerifySignatures(s *data.Signed, role string) error {
}

valid := make(map[string]struct{})
var sigBytes [ed25519.SignatureSize]byte
for _, sig := range s.Signatures {
if _, ok := Verifiers[sig.Method]; !ok {
return ErrWrongMethod
}
if len(sig.Signature) != len(sigBytes) {
return ErrInvalid
}

if !roleData.ValidKey(sig.KeyID) {
continue
}
Expand All @@ -79,8 +70,7 @@ func (db *DB) VerifySignatures(s *data.Signed, role string) error {
continue
}

copy(sigBytes[:], sig.Signature)
if err := Verifiers[sig.Method].Verify(key.Value.Public, msg, sigBytes[:]); err != nil {
if err := Verifiers[key.Type].Verify(key.Value.Public, msg, sig.Signature); err != nil {
return err
}
valid[sig.KeyID] = struct{}{}
Expand Down
59 changes: 54 additions & 5 deletions verify/verify_test.go
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Original file line number Diff line number Diff line change
@@ -1,6 +1,12 @@
package verify

import (
"crypto"
"crypto/ecdsa"
"crypto/elliptic"
"crypto/rand"
"crypto/sha256"
"io"
"testing"
"time"

Expand All @@ -18,6 +24,31 @@ type VerifySuite struct{}

var _ = Suite(&VerifySuite{})

type ecdsaSigner struct {
*ecdsa.PrivateKey
}

func (s ecdsaSigner) PublicData() *data.Key {
pub := s.Public().(*ecdsa.PublicKey)
return &data.Key{
Type: data.KeyTypeECDSA_SHA2_P256,
Value: data.KeyValue{Public: elliptic.Marshal(pub.Curve, pub.X, pub.Y)},
}
}

func (s ecdsaSigner) Sign(rand io.Reader, msg []byte, opts crypto.SignerOpts) ([]byte, error) {
hash := sha256.Sum256(msg)
return s.PrivateKey.Sign(rand, hash[:], crypto.SHA256)
}

func (s ecdsaSigner) ID() string {
return s.PublicData().ID()
}

func (ecdsaSigner) Type() string {
return data.KeyTypeECDSA_SHA2_P256
}

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Do these definitions belong in the test file?

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Yeah. This patch intentionally implements only verification in the exposed code. This is in preparation for supporting ECDSA signing keys via PKCS11 in external devices like the Yubikey and HSMs. If you can store keys locally, Ed25519 should be used. We're only adding support for ECDSA because the dedicated hardware devices do not support Ed25519.

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Gotcha.

func (VerifySuite) Test(c *C) {
type test struct {
name string
Expand Down Expand Up @@ -45,11 +76,6 @@ func (VerifySuite) Test(c *C) {
role: "foo",
err: ErrUnknownRole,
},
{
name: "wrong signature method",
mut: func(t *test) { t.s.Signatures[0].Method = "foo" },
err: ErrWrongMethod,
},
{
name: "signature wrong length",
mut: func(t *test) { t.s.Signatures[0].Signature = []byte{0} },
Expand Down Expand Up @@ -139,6 +165,29 @@ func (VerifySuite) Test(c *C) {
exp: &expiredTime,
err: ErrExpired{expiredTime},
},
{
name: "valid ecdsa signature",
mut: func(t *test) {
k, _ := ecdsa.GenerateKey(elliptic.P256(), rand.Reader)
s := ecdsaSigner{k}
sign.Sign(t.s, s)
t.s.Signatures = t.s.Signatures[1:]
t.keys = []*data.Key{s.PublicData()}
t.roles["root"].KeyIDs = []string{s.PublicData().ID()}
},
},
{
name: "invalid ecdsa signature",
mut: func(t *test) {
k, _ := ecdsa.GenerateKey(elliptic.P256(), rand.Reader)
s := ecdsaSigner{k}
sign.Sign(t.s, s)
t.s.Signatures[1].Signature[0]++
t.keys = append(t.keys, s.PublicData())
t.roles["root"].KeyIDs = append(t.roles["root"].KeyIDs, s.PublicData().ID())
},
err: ErrInvalid,
},
}
for _, t := range tests {
if t.role == "" {
Expand Down