// 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.
//
///////////////////////////////////////////////////////////////////////////////

#ifndef TINK_HYBRID_DECRYPT_H_
#define TINK_HYBRID_DECRYPT_H_

#include <string>

#include "absl/strings/string_view.h"
#include "tink/util/statusor.h"

namespace crypto {
namespace tink {

///////////////////////////////////////////////////////////////////////////////
// The interface for hybrid decryption.
//
// Implementations of this interface are secure against adaptive
// chosen ciphertext attacks.  In addition to 'plaintext' the
// encryption takes an extra parameter 'context_info', which usually
// is public data implicit from the context, but should be bound to
// the resulting ciphertext: upon decryption the ciphertext allows for
// checking the integrity of 'context_info' (but there are no
// guarantees wrt. to secrecy or authenticity of 'context_info').
//
// WARNING: hybrid encryption does not provide authenticity, that is the
// recipient of an encrypted message does not know the identity of the sender.
// Similar to general public-key encryption schemes the security goal of
// hybrid encryption is to provide privacy only. In other words, hybrid
// encryption is secure if and only if the recipient can accept anonymous
// messages or can rely on other mechanisms to authenticate the sender.
//
// 'context_info' can be empty or null, but to ensure the correct
// decryption of the ciphertext the same value must be provided
// as was used during encryption operation (cf. HybridEncrypt-interface).
//
// A concrete instantiation of this interface can implement the
// binding of 'context_info' to the ciphertext in various ways, for
// example:
//
// - use 'context_info' as "associated data"-input for the employed
//   AEAD symmetric encryption (cf. https://tools.ietf.org/html/rfc5116).
// - use 'context_info' as "CtxInfo"-input for HKDF (if the implementation uses
//   HKDF as key derivation function, cf. https://tools.ietf.org/html/rfc5869).
class HybridDecrypt {
 public:
  // Decrypts 'ciphertext' verifying the integrity of 'context_info'.
  virtual crypto::tink::util::StatusOr<std::string> Decrypt(
      absl::string_view ciphertext, absl::string_view context_info) const = 0;

  virtual ~HybridDecrypt() {}
};

}  // namespace tink
}  // namespace crypto

#endif  // TINK_HYBRID_DECRYPT_H_