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// Copyright 2025 The Sigstore Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package tink
import (
"crypto"
"crypto/ecdsa"
"crypto/ed25519"
"errors"
"fmt"
"math/big"
"github.com/tink-crypto/tink-go/v2/insecurecleartextkeyset"
"github.com/tink-crypto/tink-go/v2/keyset"
commonpb "github.com/tink-crypto/tink-go/v2/proto/common_go_proto"
ecdsapb "github.com/tink-crypto/tink-go/v2/proto/ecdsa_go_proto"
ed25519pb "github.com/tink-crypto/tink-go/v2/proto/ed25519_go_proto"
tinkpb "github.com/tink-crypto/tink-go/v2/proto/tink_go_proto"
signatureSubtle "github.com/tink-crypto/tink-go/v2/signature/subtle"
"github.com/tink-crypto/tink-go/v2/subtle"
"google.golang.org/protobuf/proto"
)
var (
ecdsaSignerKeyVersion uint32
ed25519SignerKeyVersion uint32
ecdsaSignerTypeURL = "type.googleapis.com/google.crypto.tink.EcdsaPrivateKey"
ed25519SignerTypeURL = "type.googleapis.com/google.crypto.tink.Ed25519PrivateKey"
)
// KeyHandleToSigner converts a key handle to the crypto.Signer interface.
// Heavily pulls from Tink's signature and subtle packages.
func KeyHandleToSigner(kh *keyset.Handle) (crypto.Signer, crypto.Hash, error) {
// extract the key material from the key handle
ks := insecurecleartextkeyset.KeysetMaterial(kh)
k := getPrimaryKey(ks)
if k == nil {
return nil, 0, errors.New("no enabled key found in keyset")
}
switch k.GetTypeUrl() {
case ecdsaSignerTypeURL:
// https://github.com/tink-crypto/tink-go/blob/0aadc94a816408c4bdf95885b3c9860ecfd55fc0/signature/ecdsa/signer_key_manager.go#L48
privKey := new(ecdsapb.EcdsaPrivateKey)
if err := proto.Unmarshal(k.GetValue(), privKey); err != nil {
return nil, 0, fmt.Errorf("error unmarshalling ecdsa private key: %w", err)
}
if err := validateEcdsaPrivKey(privKey); err != nil {
return nil, 0, fmt.Errorf("error validating ecdsa private key: %w", err)
}
// https://github.com/tink-crypto/tink-go/blob/0aadc94a816408c4bdf95885b3c9860ecfd55fc0/signature/subtle/ecdsa_signer.go#L37
hashAlg, curve, _ := getECDSAParamNames(privKey.PublicKey.Params)
p := new(ecdsa.PrivateKey)
c := subtle.GetCurve(curve)
if c == nil {
return nil, 0, errors.New("tink ecdsa signer: invalid curve")
}
p.Curve = c
p.D = new(big.Int).SetBytes(privKey.GetKeyValue())
p.X, p.Y = c.ScalarBaseMult(privKey.GetKeyValue())
hash := getHashFunc(hashAlg)
return p, hash, nil
case ed25519SignerTypeURL:
// https://github.com/tink-crypto/tink-go/blob/0aadc94a816408c4bdf95885b3c9860ecfd55fc0/signature/ed25519/signer_key_manager.go#L47
privKey := new(ed25519pb.Ed25519PrivateKey)
if err := proto.Unmarshal(k.GetValue(), privKey); err != nil {
return nil, 0, fmt.Errorf("error unmarshalling ed25519 private key: %w", err)
}
if err := validateEd25519PrivKey(privKey); err != nil {
return nil, 0, fmt.Errorf("error validating ed25519 private key: %w", err)
}
// https://github.com/tink-crypto/tink-go/blob/0aadc94a816408c4bdf95885b3c9860ecfd55fc0/signature/subtle/ed25519_signer.go#L27
p := ed25519.NewKeyFromSeed(privKey.GetKeyValue())
return p, crypto.SHA512, nil
default:
return nil, 0, fmt.Errorf("unsupported key type: %s", k.GetTypeUrl())
}
}
// getPrimaryKey returns the first enabled key from a keyset.
func getPrimaryKey(ks *tinkpb.Keyset) *tinkpb.KeyData {
for _, k := range ks.GetKey() {
if k.GetKeyId() == ks.GetPrimaryKeyId() && k.GetStatus() == tinkpb.KeyStatusType_ENABLED {
return k.GetKeyData()
}
}
return nil
}
// validateEcdsaPrivKey validates the given ECDSAPrivateKey.
// https://github.com/tink-crypto/tink-go/blob/0aadc94a816408c4bdf95885b3c9860ecfd55fc0/signature/ecdsa/signer_key_manager.go#L151
func validateEcdsaPrivKey(key *ecdsapb.EcdsaPrivateKey) error {
if err := keyset.ValidateKeyVersion(key.Version, ecdsaSignerKeyVersion); err != nil {
return fmt.Errorf("ecdsa: invalid key version in key: %w", err)
}
if err := keyset.ValidateKeyVersion(key.GetPublicKey().GetVersion(), ecdsaSignerKeyVersion); err != nil {
return fmt.Errorf("ecdsa: invalid public version in key: %w", err)
}
hash, curve, encoding := getECDSAParamNames(key.PublicKey.Params)
return signatureSubtle.ValidateECDSAParams(hash, curve, encoding)
}
// getECDSAParamNames returns the string representations of each parameter in
// the given ECDSAParams.
// https://github.com/tink-crypto/tink-go/blob/0aadc94a816408c4bdf95885b3c9860ecfd55fc0/signature/ecdsa/proto.go#L24
func getECDSAParamNames(params *ecdsapb.EcdsaParams) (string, string, string) {
hashName := commonpb.HashType_name[int32(params.GetHashType())]
curveName := commonpb.EllipticCurveType_name[int32(params.GetCurve())]
encodingName := ecdsapb.EcdsaSignatureEncoding_name[int32(params.GetEncoding())]
return hashName, curveName, encodingName
}
// validateEd25519PrivKey validates the given ED25519PrivateKey.
// https://github.com/tink-crypto/tink-go/blob/0aadc94a816408c4bdf95885b3c9860ecfd55fc0/signature/ed25519/signer_key_manager.go#L157
func validateEd25519PrivKey(key *ed25519pb.Ed25519PrivateKey) error {
if err := keyset.ValidateKeyVersion(key.Version, ed25519SignerKeyVersion); err != nil {
return fmt.Errorf("ed25519: invalid key: %w", err)
}
if len(key.KeyValue) != ed25519.SeedSize {
return fmt.Errorf("ed25519: invalid key length, got %d", len(key.KeyValue))
}
return nil
}
// getHashFunc returns the hash function for a given hash name
func getHashFunc(hash string) crypto.Hash {
switch hash {
case "SHA1":
return crypto.SHA1
case "SHA224":
return crypto.SHA224
case "SHA256":
return crypto.SHA256
case "SHA384":
return crypto.SHA384
case "SHA512":
return crypto.SHA512
default:
return crypto.SHA256
}
}
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