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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
//
// 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 internalregistry
import (
"fmt"
"io"
"sync"
"google.golang.org/protobuf/proto"
"github.com/tink-crypto/tink-go/v2/core/registry"
tinkpb "github.com/tink-crypto/tink-go/v2/proto/tink_go_proto"
)
var (
derivableKeyManagersMu sync.RWMutex
// derivableKeyManagers is the set of all key managers allowed to derive keys.
// It is keyed by the key manager's type URL, i.e. typeURL -> true. All type
// URLs in this map correspond to key managers that are
// - in the registry and
// - implement key derivation.
//
// This exists because of Golang's weak type system and the desire to keep key
// derivation non-public. If we do not explicitly restrict derivable key
// managers, users would be able to register any custom key manager that
// implements DeriveKey() and be able to derive keys with it, even without
// access to this library, internalregistry.
derivableKeyManagers = make(map[string]bool)
)
// AllowKeyDerivation adds the type URL to derivableKeyManagers if the
// corresponding key manager is in the registry and implements key derivation.
func AllowKeyDerivation(typeURL string) error {
km, err := registry.GetKeyManager(typeURL)
if err != nil {
return err
}
if _, ok := km.(DerivableKeyManager); !ok {
return fmt.Errorf("key manager for type %s does not implement key derivation", typeURL)
}
derivableKeyManagersMu.Lock()
derivableKeyManagers[typeURL] = true
derivableKeyManagersMu.Unlock()
return nil
}
// CanDeriveKeys returns true if typeURL is in derivableKeyManagers.
func CanDeriveKeys(typeURL string) bool {
derivableKeyManagersMu.Lock()
defer derivableKeyManagersMu.Unlock()
return derivableKeyManagers[typeURL]
}
// DeriveKey derives a new key from template and pseudorandomness.
func DeriveKey(keyTemplate *tinkpb.KeyTemplate, pseudorandomness io.Reader) (*tinkpb.KeyData, error) {
if !CanDeriveKeys(keyTemplate.GetTypeUrl()) {
return nil, fmt.Errorf("key manager for type %s is not allowed to derive keys", keyTemplate.GetTypeUrl())
}
km, err := registry.GetKeyManager(keyTemplate.GetTypeUrl())
if err != nil {
return nil, err
}
keyManager, ok := km.(DerivableKeyManager)
if !ok {
return nil, fmt.Errorf("key manager for type %s does not implement key derivation", keyTemplate.GetTypeUrl())
}
key, err := keyManager.DeriveKey(keyTemplate.GetValue(), pseudorandomness)
if err != nil {
return nil, err
}
serializedKey, err := proto.Marshal(key)
if err != nil {
return nil, fmt.Errorf("failed to serialize derived key: %v", err)
}
return &tinkpb.KeyData{
TypeUrl: keyTemplate.GetTypeUrl(),
Value: serializedKey,
KeyMaterialType: keyManager.KeyMaterialType(),
}, nil
}
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