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// Copyright 2019 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 hybrid
import (
"bytes"
"fmt"
"github.com/tink-crypto/tink-go/v2/internal/internalapi"
"github.com/tink-crypto/tink-go/v2/internal/internalregistry"
"github.com/tink-crypto/tink-go/v2/internal/monitoringutil"
"github.com/tink-crypto/tink-go/v2/internal/prefixmap"
"github.com/tink-crypto/tink-go/v2/internal/primitiveset"
"github.com/tink-crypto/tink-go/v2/keyset"
"github.com/tink-crypto/tink-go/v2/monitoring"
"github.com/tink-crypto/tink-go/v2/tink"
)
// NewHybridDecrypt returns an HybridDecrypt primitive from the given keyset handle.
func NewHybridDecrypt(handle *keyset.Handle) (tink.HybridDecrypt, error) {
ps, err := keyset.Primitives[tink.HybridDecrypt](handle, internalapi.Token{})
if err != nil {
return nil, fmt.Errorf("hybrid_factory: cannot obtain primitive set: %s", err)
}
return newWrappedHybridDecrypt(ps)
}
type fullHybridDecryptAdapter struct {
rawHybridDecrypt tink.HybridDecrypt
prefix []byte
}
var _ tink.HybridDecrypt = (*fullHybridDecryptAdapter)(nil)
func (d *fullHybridDecryptAdapter) Decrypt(ciphertext, contextInfo []byte) ([]byte, error) {
// This is called by `wrappedHybridDecrypt.Decrypt`, which selects the
// correct decrypter based on the prefix; if the prefix is not correct,
// this is a bug.
if len(ciphertext) < len(d.prefix) {
return nil, fmt.Errorf("ciphertext too short")
}
if !bytes.Equal(d.prefix, ciphertext[:len(d.prefix)]) {
return nil, fmt.Errorf("ciphertext does not start with the expected prefix %x", d.prefix)
}
return d.rawHybridDecrypt.Decrypt(ciphertext[len(d.prefix):], contextInfo)
}
type decrypterAndID struct {
decrypter tink.HybridDecrypt
keyID uint32
}
var _ tink.HybridDecrypt = (*decrypterAndID)(nil)
func (d *decrypterAndID) Decrypt(ciphertext, contextInfo []byte) ([]byte, error) {
return d.decrypter.Decrypt(ciphertext, contextInfo)
}
// wrappedHybridDecrypt is an HybridDecrypt implementation that uses the underlying primitive set
// for decryption.
type wrappedHybridDecrypt struct {
decrypters *prefixmap.PrefixMap[decrypterAndID]
logger monitoring.Logger
}
// compile time assertion that wrappedHybridDecrypt implements the HybridDecrypt interface.
var _ tink.HybridDecrypt = (*wrappedHybridDecrypt)(nil)
func newWrappedHybridDecrypt(ps *primitiveset.PrimitiveSet[tink.HybridDecrypt]) (*wrappedHybridDecrypt, error) {
// Make sure the primitives do not implement tink.AEAD.
decrypters := prefixmap.New[decrypterAndID]()
if isAEAD(ps.Primary.Primitive) || isAEAD(ps.Primary.FullPrimitive) {
return nil, fmt.Errorf("hybrid_factory: primary primitive must NOT implement tink.AEAD")
}
for _, primitives := range ps.Entries {
for _, p := range primitives {
if isAEAD(p.Primitive) || isAEAD(p.FullPrimitive) {
return nil, fmt.Errorf("hybrid_factory: primitive must NOT implement tink.AEAD")
}
fullPrimitive := p.FullPrimitive
if fullPrimitive == nil {
fullPrimitive = &fullHybridDecryptAdapter{
rawHybridDecrypt: p.Primitive,
prefix: p.OutputPrefix(),
}
}
decrypters.Insert(string(p.OutputPrefix()), decrypterAndID{
decrypter: fullPrimitive,
keyID: p.KeyID,
})
}
}
logger, err := createDecryptLogger(ps)
if err != nil {
return nil, err
}
return &wrappedHybridDecrypt{
decrypters: decrypters,
logger: logger,
}, nil
}
func createDecryptLogger(ps *primitiveset.PrimitiveSet[tink.HybridDecrypt]) (monitoring.Logger, error) {
if len(ps.Annotations) == 0 {
return &monitoringutil.DoNothingLogger{}, nil
}
keysetInfo, err := monitoringutil.KeysetInfoFromPrimitiveSet(ps)
if err != nil {
return nil, err
}
return internalregistry.GetMonitoringClient().NewLogger(&monitoring.Context{
KeysetInfo: keysetInfo,
Primitive: "hybrid_decrypt",
APIFunction: "decrypt",
})
}
// Decrypt decrypts the given ciphertext, verifying the integrity of contextInfo.
// It returns the corresponding plaintext if the ciphertext is authenticated.
func (a *wrappedHybridDecrypt) Decrypt(ciphertext, contextInfo []byte) ([]byte, error) {
it := a.decrypters.PrimitivesMatchingPrefix(ciphertext)
for decrypter, ok := it.Next(); ok; decrypter, ok = it.Next() {
pt, err := decrypter.Decrypt(ciphertext, contextInfo)
if err != nil {
continue
}
a.logger.Log(decrypter.keyID, len(ciphertext))
return pt, nil
}
// Nothing worked.
a.logger.LogFailure()
return nil, fmt.Errorf("hybrid_factory: decryption failed")
}
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