cose/timestamp_creator.cc

// Copyright 2026 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.
//

#include "cose/timestamp_creator.h"

#include <memory>
#include <optional>
#include <string>
#include <utility>

#include "absl/functional/any_invocable.h"
#include "absl/status/status_macros.h"
#include "absl/status/statusor.h"
#include "absl/strings/string_view.h"
#include "async/async_context.h"
#include "cose/sig_structure.h"
#include "cppbor/cppbor.h"
#include "crypto/hash.h"
#include "crypto/timestamp_write_handler.h"

namespace credentio {
namespace {

absl::StatusOr<std::string> MessageImprintForTimestamp(
    const HasherFactory& hasher_factory, absl::string_view body_protected,
    absl::string_view message) {
  // https://spec.c2pa.org/specifications/specifications/2.4/specs/C2PA_Specification.html#_obtaining_the_time_stamp
  std::string encoded_message = EncodeSig1Structure({
      .context = "CounterSignature",
      .body_protected = std::string(body_protected),
      .external_aad = "",
      .payload = std::string(message),
  });
  ABSL_ASSIGN_OR_RETURN(auto hasher, hasher_factory.Create());
  hasher->Update(encoded_message);
  return hasher->Digest();
}
}  // namespace

void TimestampCreator::CreateTimestamp(
    const CoseSign1TaggedStructure& cose_sign1, Options options,
    absl::AnyInvocable<void(absl::StatusOr<std::string>) &&> cb) const {
  auto signature = cppbor::Bstr(cose_sign1.signature).toString();
  auto hashed_message = MessageImprintForTimestamp(
      hasher_factory_, cose_sign1.protected_header, std::move(signature));
  if (!hashed_message.ok()) {
    AsyncResolver<std::string>(options.async_context, std::move(cb))
        .Return(hashed_message.status());
    return;
  }
  TimestampWriteHandler::Options timestamp_handler_options;
  timestamp_handler_options.async_context = std::move(options.async_context);

  timestamp_handler_.CreateTimestamp(hasher_factory_.algorithm(),
                                     std::move(*hashed_message),
                                     timestamp_handler_options, std::move(cb));
}

}  // namespace credentio