claim/local_signer.h

// 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.
//

#ifndef THIRD_PARTY_CREDENTIO_CLAIM_LOCAL_SIGNER_H_
#define THIRD_PARTY_CREDENTIO_CLAIM_LOCAL_SIGNER_H_

#include <cstddef>
#include <optional>

#include "absl/base/nullability.h"
#include "absl/functional/any_invocable.h"
#include "absl/log/die_if_null.h"
#include "absl/status/statusor.h"
#include "absl/strings/string_view.h"
#include "claim/signer.h"
#include "cose/timestamp_creator.h"
#include "crypto/crypto_write_handler.h"
#include "crypto/hash.h"

namespace credentio {
// A signer to sign a Claim according to
// https://spec.c2pa.org/specifications/specifications/2.4/specs/C2PA_Specification.html#_signing_a_claim.
class LocalClaimSigner : public ClaimSigner {
 public:
  explicit LocalClaimSigner(CryptoWriteHandler* absl_nonnull crypto_writer,
                            const HasherFactory* absl_nonnull hasher_factory,
                            std::optional<size_t> pad_to_size = std::nullopt)
      : crypto_writer_(*ABSL_DIE_IF_NULL(crypto_writer)),
        hasher_factory_(*ABSL_DIE_IF_NULL(hasher_factory)),
        timestamp_creator_(&crypto_writer_, &hasher_factory_),
        pad_to_size_(pad_to_size) {}

  // Signs the serialized CBOR of the claim and returns the serialized
  // COSE_Sign1_Tagged structure that will be written into the C2PA Claim
  // Signature box. For more details, see
  // https://spec.c2pa.org/specifications/specifications/2.4/specs/C2PA_Specification.html#_signing_a_claim.
  // It guarantees that the size of the result is fixed and is a function of
  // `max_signature_bytes_size()` and `max_timestamp_byte_size()` of the
  // CryptoWriteHandler rather than of the actual signature and timestamp sizes.
  void Sign(absl::string_view claim, Options options,
            absl::AnyInvocable<void(absl::StatusOr<SignResult>) &&> cb)
      const override;

 private:
  CryptoWriteHandler& crypto_writer_;
  const HasherFactory& hasher_factory_;
  TimestampCreator timestamp_creator_;
  std::optional<size_t> pad_to_size_;
};
}  // namespace credentio

#endif  // THIRD_PARTY_CREDENTIO_CLAIM_LOCAL_SIGNER_H_