public_key_verify_factory.go

// Copyright 2017 Google Inc.
//
// 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 signature

import (
  "fmt"
  "sync"
  "github.com/google/tink/go/tink/tink"
  tinkpb "github.com/google/tink/proto/tink_go_proto"
)

// publicKeyVerifyFactory allows obtaining a PublicKeySign primitive from a
// KeysetHandle.
var publicKeyVerifyFactoryInstance *publicKeyVerifyFactory
var publicKeyVerifyFactoryOnce sync.Once
type publicKeyVerifyFactory struct {}

// PublicKeyVerifyFactory creates an instance of publicKeyVerifyFactory if there isn't
// and returns the instance.
func PublicKeyVerifyFactory() *publicKeyVerifyFactory {
  publicKeyVerifyFactoryOnce.Do(func() {
    publicKeyVerifyFactoryInstance = new(publicKeyVerifyFactory)
  })
  return publicKeyVerifyFactoryInstance
}

// GetPrimitive returns a PublicKeyVerify primitive from the given keyset handle.
func (f *publicKeyVerifyFactory) GetPrimitive(handle *tink.KeysetHandle) (tink.PublicKeyVerify, error) {
  return f.GetPrimitiveWithCustomerManager(handle, nil /*keyManager*/)
}

// GetPrimitiveWithCustomerManager returns a PublicKeyVerify primitive from the given
// keyset handle and custom key manager.
func (f *publicKeyVerifyFactory) GetPrimitiveWithCustomerManager(
    handle *tink.KeysetHandle, manager tink.KeyManager) (tink.PublicKeyVerify, error) {
  ps, err := tink.Registry().GetPrimitivesWithCustomManager(handle, manager)
  if err != nil {
    return nil, fmt.Errorf("public_key_verify_factory: cannot obtain primitive set: %s", err)
  }
  var ret = newprimitiveSetPublicKeyVerify(ps)
  return ret, nil
}

// primitiveSetPublicKeyVerify is an PublicKeySign implementation that uses the
// underlying primitive set for signing.
type primitiveSetPublicKeyVerify struct {
  ps *tink.PrimitiveSet
}

// Asserts that primitiveSetPublicKeyVerify implements the PublicKeyVerify interface.
var _ tink.PublicKeyVerify = (*primitiveSetPublicKeyVerify)(nil)

// newprimitiveSetPublicKeyVerify creates a new instance of primitiveSetPublicKeyVerify
func newprimitiveSetPublicKeyVerify(ps *tink.PrimitiveSet) *primitiveSetPublicKeyVerify {
  ret := new(primitiveSetPublicKeyVerify)
  ret.ps = ps
  return ret
}

var errInvalidSignature = fmt.Errorf("public_key_verify_factory: invalid signature")
// Verify checks whether the given signature is a valid signature of the given data.
func (v *primitiveSetPublicKeyVerify) Verify(signature []byte, data []byte) error {
  if len(signature) < tink.NON_RAW_PREFIX_SIZE {
    return errInvalidSignature
  }
  // try non-raw keys
  prefix := signature[:tink.NON_RAW_PREFIX_SIZE]
  signatureNoPrefix := signature[tink.NON_RAW_PREFIX_SIZE:]
  entries, err := v.ps.GetPrimitivesWithByteIdentifier(prefix)
  if err == nil {
    for i := 0; i < len(entries); i++ {
      var signedData []byte
      if entries[i].OutputPrefixType() == tinkpb.OutputPrefixType_LEGACY {
        signedData = append(signedData, data...)
        signedData = append(signedData, tink.LEGACY_START_BYTE)
      } else {
        signedData = data
      }
      var verifier = (entries[i].Primitive()).(tink.PublicKeyVerify)
      if err := verifier.Verify(signatureNoPrefix, signedData); err == nil {
        return nil
      }
    }
  }
  // try raw keys
  entries, err = v.ps.GetRawPrimitives()
  if err == nil {
    for i := 0; i < len(entries); i++ {
      var verifier = (entries[i].Primitive()).(tink.PublicKeyVerify)
      if err := verifier.Verify(signature, data); err == nil {
        return nil
      }
    }
  }
  return errInvalidSignature
}