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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"
"crypto/elliptic"
"fmt"
"math/big"
"github.com/tink-crypto/tink-go/v2/insecuresecretdataaccess"
"github.com/tink-crypto/tink-go/v2/keyset"
tinkecdsa "github.com/tink-crypto/tink-go/v2/signature/ecdsa"
tinked25519 "github.com/tink-crypto/tink-go/v2/signature/ed25519"
)
func curveFromTinkECDSACurveType(curveType tinkecdsa.CurveType) (elliptic.Curve, error) {
switch curveType {
case tinkecdsa.NistP256:
return elliptic.P256(), nil
case tinkecdsa.NistP384:
return elliptic.P384(), nil
case tinkecdsa.NistP521:
return elliptic.P521(), nil
default:
// Should never happen.
return nil, fmt.Errorf("unsupported curve: %v", curveType)
}
}
// KeyHandleToSigner constructs a [crypto.Signer] from a Tink [keyset.Handle]'s
// primary key.
//
// NOTE: Tink validates keys on [keyset.Handle] creation.
func KeyHandleToSigner(kh *keyset.Handle) (crypto.Signer, error) {
primary, err := kh.Primary()
if err != nil {
return nil, err
}
switch privateKey := primary.Key().(type) {
case *tinkecdsa.PrivateKey:
publicKey, err := privateKey.PublicKey()
if err != nil {
return nil, err
}
ecdsaPublicKey, ok := publicKey.(*tinkecdsa.PublicKey)
if !ok {
return nil, fmt.Errorf("error asserting ecdsa public key")
}
curveParams, ok := ecdsaPublicKey.Parameters().(*tinkecdsa.Parameters)
if !ok {
return nil, fmt.Errorf("error asserting ecdsa parameters")
}
curve, err := curveFromTinkECDSACurveType(curveParams.CurveType())
if err != nil {
return nil, err
}
// Encoded as: 0x04 || X || Y.
// See https://github.com/tink-crypto/tink-go/blob/v2.3.0/signature/ecdsa/key.go#L335
publicPoint := ecdsaPublicKey.PublicPoint()
xy := publicPoint[1:]
pk := new(ecdsa.PrivateKey)
pk.Curve = curve
pk.X = new(big.Int).SetBytes(xy[:len(xy)/2])
pk.Y = new(big.Int).SetBytes(xy[len(xy)/2:])
pk.D = new(big.Int).SetBytes(privateKey.PrivateKeyValue().Data(insecuresecretdataaccess.Token{}))
return pk, err
case *tinked25519.PrivateKey:
return ed25519.NewKeyFromSeed(privateKey.PrivateKeyBytes().Data(insecuresecretdataaccess.Token{})), err
default:
return nil, fmt.Errorf("unsupported key type: %T", primary.Key())
}
}
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