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// Copyright 2020 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef CHROME_BROWSER_NEARBY_SHARING_CERTIFICATES_NEARBY_SHARE_PRIVATE_CERTIFICATE_H_
#define CHROME_BROWSER_NEARBY_SHARING_CERTIFICATES_NEARBY_SHARE_PRIVATE_CERTIFICATE_H_
#include <array>
#include <memory>
#include <optional>
#include <set>
#include <vector>
#include "base/containers/queue.h"
#include "base/containers/span.h"
#include "base/gtest_prod_util.h"
#include "base/time/time.h"
#include "base/values.h"
#include "chrome/browser/nearby_sharing/certificates/constants.h"
#include "chrome/browser/nearby_sharing/certificates/nearby_share_encrypted_metadata_key.h"
#include "chromeos/ash/services/nearby/public/mojom/nearby_share_settings.mojom.h"
#include "crypto/keypair.h"
#include "third_party/nearby/sharing/proto/encrypted_metadata.pb.h"
#include "third_party/nearby/sharing/proto/rpc_resources.pb.h"
// Stores metadata and crypto keys for the local device. This certificate
// can be converted to a public certificate and sent to select contacts, who
// will then use the certificate for authenticating the local device before
// transferring data. Provides method for signing a payload during
// authentication with a remote device. Provides method for encrypting the
// metadata encryption key, which can then be advertised.
class NearbySharePrivateCertificate {
public:
// Inverse operation of ToDictionary(). Returns std::nullopt if the
// conversion is not successful
static std::optional<NearbySharePrivateCertificate> FromDictionary(
const base::Value::Dict& dict);
// Generates a random EC key pair, secret key, and metadata encryption
// key. Derives the certificate ID from the secret key. Derives the
// not-after time from |not_before| and the certificate validity period fixed
// by the Nearby Share protocol. Visibility cannot be "no one".
NearbySharePrivateCertificate(
nearby_share::mojom::Visibility visibility,
base::Time not_before,
nearby::sharing::proto::EncryptedMetadata unencrypted_metadata);
NearbySharePrivateCertificate(
nearby_share::mojom::Visibility visibility,
base::Time not_before,
base::Time not_after,
crypto::keypair::PrivateKey private_key,
base::span<const uint8_t, kNearbyShareNumBytesSecretKey> secret_key,
base::span<const uint8_t, kNearbyShareNumBytesMetadataEncryptionKey>
metadata_encryption_key,
base::span<const uint8_t, kNearbyShareNumBytesCertificateId> id,
nearby::sharing::proto::EncryptedMetadata unencrypted_metadata,
std::set<
std::array<uint8_t, kNearbyShareNumBytesMetadataEncryptionKeySalt>>
consumed_salts);
NearbySharePrivateCertificate(const NearbySharePrivateCertificate& other);
NearbySharePrivateCertificate& operator=(
const NearbySharePrivateCertificate& other);
NearbySharePrivateCertificate(NearbySharePrivateCertificate&& other);
NearbySharePrivateCertificate& operator=(
NearbySharePrivateCertificate&& other);
virtual ~NearbySharePrivateCertificate();
base::span<const uint8_t> id() const { return id_; }
nearby_share::mojom::Visibility visibility() const { return visibility_; }
base::Time not_before() const { return not_before_; }
base::Time not_after() const { return not_after_; }
const nearby::sharing::proto::EncryptedMetadata& unencrypted_metadata()
const {
return unencrypted_metadata_;
}
// Encrypts |metadata_encryption_key_| with the |secret_key_|, using a
// randomly generated 2-byte salt that has not already been consumed. Returns
// std::nullopt if the encryption failed or if there are no remaining salts.
// Note: Due to the generation and storage of an unconsumed salt, this method
// is not thread safe.
std::optional<NearbyShareEncryptedMetadataKey> EncryptMetadataKey();
// Signs the input |payload| with |private_key_|.
std::vector<uint8_t> Sign(base::span<const uint8_t> payload) const;
// Creates a hash of the |authentication_token|, using |secret_key_|. The use
// of HKDF and the output vector size is part of the Nearby Share protocol and
// conforms with the GmsCore implementation.
std::array<uint8_t, kNearbyShareNumBytesAuthenticationTokenHash>
HashAuthenticationToken(base::span<const uint8_t> authentication_token) const;
// Converts this private certificate to a public certificate proto that can be
// shared with select contacts. Returns std::nullopt if the conversion was
// unsuccessful.
std::optional<nearby::sharing::proto::PublicCertificate> ToPublicCertificate()
const;
// Converts this private certificate to a dictionary value for storage
// in Prefs.
base::Value::Dict ToDictionary() const;
// For testing only.
base::queue<
std::array<uint8_t, kNearbyShareNumBytesMetadataEncryptionKeySalt>>&
next_salts_for_testing() {
return next_salts_for_testing_;
}
std::optional<base::TimeDelta>& offset_for_testing() {
return offset_for_testing_;
}
private:
// Generates a random 2-byte salt used for encrypting the metadata encryption
// key. Adds returned salt to |consumed_salts_|. Returns std::nullopt if the
// maximum number of salts have been exhausted or if an unconsumed salt cannot
// be found in a fixed number of attempts, though this is highly improbably.
// Note: This function is not thread safe.
std::optional<
std::array<uint8_t, kNearbyShareNumBytesMetadataEncryptionKeySalt>>
GenerateUnusedSalt();
// Encrypts |unencrypted_metadata_| with the |metadata_encryption_key_|, using
// the |secret_key_| as salt.
std::optional<std::vector<uint8_t>> EncryptMetadata() const;
// Specifies which contacts can receive the public certificate corresponding
// to this private certificate.
nearby_share::mojom::Visibility visibility_;
// The begin/end times of the certificate's validity period. Note: An offset
// is not yet applied to these values. To avoid issues with clock skew,
// offsets should be applied during conversion to a public certificate.
base::Time not_before_;
base::Time not_after_;
// The private key used for this certificate. The public key derived from it
// will be included in the certificate; the private key stays on device.
crypto::keypair::PrivateKey private_key_;
// A 32-byte AES key used, along with a salt, to encrypt the
// |metadata_encryption_key_|, after which it can be safely advertised. Also,
// used to generate an authentication token hash. Included in the public
// certificate.
std::array<uint8_t, kNearbyShareNumBytesSecretKey> secret_key_;
// A 14-byte symmetric key used to encrypt |unencrypted_metadata_|. Not
// included in public certificate.
std::array<uint8_t, kNearbyShareNumBytesMetadataEncryptionKey>
metadata_encryption_key_;
// An ID for the certificate, generated from the secret key.
std::array<uint8_t, kNearbyShareNumBytesCertificateId> id_;
// Unencrypted device metadata. The proto name is misleading; it holds data
// that will eventually be serialized and encrypted.
nearby::sharing::proto::EncryptedMetadata unencrypted_metadata_;
// The set of 2-byte salts already used to encrypt the metadata key.
std::set<std::array<uint8_t, kNearbyShareNumBytesMetadataEncryptionKeySalt>>
consumed_salts_;
// For testing only.
base::queue<
std::array<uint8_t, kNearbyShareNumBytesMetadataEncryptionKeySalt>>
next_salts_for_testing_;
std::optional<base::TimeDelta> offset_for_testing_;
FRIEND_TEST_ALL_PREFIXES(NearbySharePrivateCertificateTest, ToFromDictionary);
};
#endif // CHROME_BROWSER_NEARBY_SHARING_CERTIFICATES_NEARBY_SHARE_PRIVATE_CERTIFICATE_H_
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