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/*
*
* Copyright 2022 Google LLC
*
* 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
*
* https://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 remotesigner offloads private key operations to S2Av2.
package remotesigner
import (
"crypto"
"crypto/rsa"
"crypto/x509"
"fmt"
"io"
"github.com/google/s2a-go/stream"
"google.golang.org/grpc/codes"
"google.golang.org/grpc/grpclog"
s2av2pb "github.com/google/s2a-go/internal/proto/v2/s2a_go_proto"
)
// remoteSigner implementes the crypto.Signer interface.
type remoteSigner struct {
leafCert *x509.Certificate
s2AStream stream.S2AStream
}
// New returns an instance of RemoteSigner, an implementation of the
// crypto.Signer interface.
func New(leafCert *x509.Certificate, s2AStream stream.S2AStream) crypto.Signer {
return &remoteSigner{leafCert, s2AStream}
}
func (s *remoteSigner) Public() crypto.PublicKey {
return s.leafCert.PublicKey
}
func (s *remoteSigner) Sign(rand io.Reader, digest []byte, opts crypto.SignerOpts) (signature []byte, err error) {
signatureAlgorithm, err := getSignatureAlgorithm(opts, s.leafCert)
if err != nil {
return nil, err
}
req, err := getSignReq(signatureAlgorithm, digest)
if err != nil {
return nil, err
}
if grpclog.V(1) {
grpclog.Infof("Sending request to S2Av2 for signing operation.")
}
if err := s.s2AStream.Send(&s2av2pb.SessionReq{
ReqOneof: &s2av2pb.SessionReq_OffloadPrivateKeyOperationReq{
OffloadPrivateKeyOperationReq: req,
},
}); err != nil {
grpclog.Infof("Failed to send request to S2Av2 for signing operation.")
return nil, err
}
resp, err := s.s2AStream.Recv()
if err != nil {
grpclog.Infof("Failed to receive signing operation response from S2Av2.")
return nil, err
}
if (resp.GetStatus() != nil) && (resp.GetStatus().Code != uint32(codes.OK)) {
return nil, fmt.Errorf("failed to offload signing with private key to S2A: %d, %v", resp.GetStatus().Code, resp.GetStatus().Details)
}
return resp.GetOffloadPrivateKeyOperationResp().GetOutBytes(), nil
}
// getCert returns the leafCert field in s.
func (s *remoteSigner) getCert() *x509.Certificate {
return s.leafCert
}
// getStream returns the s2AStream field in s.
func (s *remoteSigner) getStream() stream.S2AStream {
return s.s2AStream
}
func getSignReq(signatureAlgorithm s2av2pb.SignatureAlgorithm, digest []byte) (*s2av2pb.OffloadPrivateKeyOperationReq, error) {
if (signatureAlgorithm == s2av2pb.SignatureAlgorithm_S2A_SSL_SIGN_RSA_PKCS1_SHA256) || (signatureAlgorithm == s2av2pb.SignatureAlgorithm_S2A_SSL_SIGN_ECDSA_SECP256R1_SHA256) || (signatureAlgorithm == s2av2pb.SignatureAlgorithm_S2A_SSL_SIGN_RSA_PSS_RSAE_SHA256) {
return &s2av2pb.OffloadPrivateKeyOperationReq{
Operation: s2av2pb.OffloadPrivateKeyOperationReq_SIGN,
SignatureAlgorithm: signatureAlgorithm,
InBytes: &s2av2pb.OffloadPrivateKeyOperationReq_Sha256Digest{
Sha256Digest: digest,
},
}, nil
} else if (signatureAlgorithm == s2av2pb.SignatureAlgorithm_S2A_SSL_SIGN_RSA_PKCS1_SHA384) || (signatureAlgorithm == s2av2pb.SignatureAlgorithm_S2A_SSL_SIGN_ECDSA_SECP384R1_SHA384) || (signatureAlgorithm == s2av2pb.SignatureAlgorithm_S2A_SSL_SIGN_RSA_PSS_RSAE_SHA384) {
return &s2av2pb.OffloadPrivateKeyOperationReq{
Operation: s2av2pb.OffloadPrivateKeyOperationReq_SIGN,
SignatureAlgorithm: signatureAlgorithm,
InBytes: &s2av2pb.OffloadPrivateKeyOperationReq_Sha384Digest{
Sha384Digest: digest,
},
}, nil
} else if (signatureAlgorithm == s2av2pb.SignatureAlgorithm_S2A_SSL_SIGN_RSA_PKCS1_SHA512) || (signatureAlgorithm == s2av2pb.SignatureAlgorithm_S2A_SSL_SIGN_ECDSA_SECP521R1_SHA512) || (signatureAlgorithm == s2av2pb.SignatureAlgorithm_S2A_SSL_SIGN_RSA_PSS_RSAE_SHA512) || (signatureAlgorithm == s2av2pb.SignatureAlgorithm_S2A_SSL_SIGN_ED25519) {
return &s2av2pb.OffloadPrivateKeyOperationReq{
Operation: s2av2pb.OffloadPrivateKeyOperationReq_SIGN,
SignatureAlgorithm: signatureAlgorithm,
InBytes: &s2av2pb.OffloadPrivateKeyOperationReq_Sha512Digest{
Sha512Digest: digest,
},
}, nil
} else {
return nil, fmt.Errorf("unknown signature algorithm: %v", signatureAlgorithm)
}
}
// getSignatureAlgorithm returns the signature algorithm that S2A must use when
// performing a signing operation that has been offloaded by an application
// using the crypto/tls libraries.
func getSignatureAlgorithm(opts crypto.SignerOpts, leafCert *x509.Certificate) (s2av2pb.SignatureAlgorithm, error) {
if opts == nil || leafCert == nil {
return s2av2pb.SignatureAlgorithm_S2A_SSL_SIGN_UNSPECIFIED, fmt.Errorf("unknown signature algorithm")
}
switch leafCert.PublicKeyAlgorithm {
case x509.RSA:
if rsaPSSOpts, ok := opts.(*rsa.PSSOptions); ok {
return rsaPSSAlgorithm(rsaPSSOpts)
}
return rsaPPKCS1Algorithm(opts)
case x509.ECDSA:
return ecdsaAlgorithm(opts)
case x509.Ed25519:
return s2av2pb.SignatureAlgorithm_S2A_SSL_SIGN_ED25519, nil
default:
return s2av2pb.SignatureAlgorithm_S2A_SSL_SIGN_UNSPECIFIED, fmt.Errorf("unknown signature algorithm: %q", leafCert.PublicKeyAlgorithm)
}
}
func rsaPSSAlgorithm(opts *rsa.PSSOptions) (s2av2pb.SignatureAlgorithm, error) {
switch opts.HashFunc() {
case crypto.SHA256:
return s2av2pb.SignatureAlgorithm_S2A_SSL_SIGN_RSA_PSS_RSAE_SHA256, nil
case crypto.SHA384:
return s2av2pb.SignatureAlgorithm_S2A_SSL_SIGN_RSA_PSS_RSAE_SHA384, nil
case crypto.SHA512:
return s2av2pb.SignatureAlgorithm_S2A_SSL_SIGN_RSA_PSS_RSAE_SHA512, nil
default:
return s2av2pb.SignatureAlgorithm_S2A_SSL_SIGN_UNSPECIFIED, fmt.Errorf("unknown signature algorithm")
}
}
func rsaPPKCS1Algorithm(opts crypto.SignerOpts) (s2av2pb.SignatureAlgorithm, error) {
switch opts.HashFunc() {
case crypto.SHA256:
return s2av2pb.SignatureAlgorithm_S2A_SSL_SIGN_RSA_PKCS1_SHA256, nil
case crypto.SHA384:
return s2av2pb.SignatureAlgorithm_S2A_SSL_SIGN_RSA_PKCS1_SHA384, nil
case crypto.SHA512:
return s2av2pb.SignatureAlgorithm_S2A_SSL_SIGN_RSA_PKCS1_SHA512, nil
default:
return s2av2pb.SignatureAlgorithm_S2A_SSL_SIGN_UNSPECIFIED, fmt.Errorf("unknown signature algorithm")
}
}
func ecdsaAlgorithm(opts crypto.SignerOpts) (s2av2pb.SignatureAlgorithm, error) {
switch opts.HashFunc() {
case crypto.SHA256:
return s2av2pb.SignatureAlgorithm_S2A_SSL_SIGN_ECDSA_SECP256R1_SHA256, nil
case crypto.SHA384:
return s2av2pb.SignatureAlgorithm_S2A_SSL_SIGN_ECDSA_SECP384R1_SHA384, nil
case crypto.SHA512:
return s2av2pb.SignatureAlgorithm_S2A_SSL_SIGN_ECDSA_SECP521R1_SHA512, nil
default:
return s2av2pb.SignatureAlgorithm_S2A_SSL_SIGN_UNSPECIFIED, fmt.Errorf("unknown signature algorithm")
}
}
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