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// Copyright 2023 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.
//
////////////////////////////////////////////////////////////////////////////////
#ifndef TINK_MAC_HMAC_PARAMETERS_H_
#define TINK_MAC_HMAC_PARAMETERS_H_
#include <memory>
#include "tink/mac/mac_parameters.h"
#include "tink/util/statusor.h"
namespace crypto {
namespace tink {
// Describes the parameters of an `HmacKey`.
class HmacParameters : public MacParameters {
public:
// Describes the details of a MAC computation.
//
// The usual HMAC key is used for variant `NO_PREFIX`. Other variants
// slightly change how the MAC is computed, or add a prefix to every
// computation depending on the key id.
enum class Variant : int {
// Prepends '0x01<big endian key id>' to tag.
kTink = 1,
// Prepends '0x00<big endian key id>' to tag.
kCrunchy = 2,
// Appends a 0-byte to input message BEFORE computing the tag, then
// prepends '0x00<big endian key id>' to tag.
kLegacy = 3,
// Does not prepend any prefix (i.e., keys must have no ID requirement).
kNoPrefix = 4,
// Added to guard from failures that may be caused by future expansions.
kDoNotUseInsteadUseDefaultWhenWritingSwitchStatements = 20,
};
// Describes the hash algorithm used.
enum class HashType : int {
kSha1 = 1,
kSha224 = 2,
kSha256 = 3,
kSha384 = 4,
kSha512 = 5,
kDoNotUseInsteadUseDefaultWhenWritingSwitchStatements = 20,
};
// Copyable and movable.
HmacParameters(const HmacParameters& other) = default;
HmacParameters& operator=(const HmacParameters& other) = default;
HmacParameters(HmacParameters&& other) = default;
HmacParameters& operator=(HmacParameters&& other) = default;
// Creates a new HMAC parameters object unless an error occurs. An error
// occurs under one of the following conditions:
// 1. `key_size_in_bytes` is a value smaller than 16 bytes
// 2. `cryptographic_tag_size_in_bytes` is either less than 10 bytes or
// greater than the maximum value accepted by the corresponding hash algorithm
static util::StatusOr<HmacParameters> Create(
int key_size_in_bytes, int cryptographic_tag_size_in_bytes,
HashType hash_type, Variant variant);
Variant GetVariant() const { return variant_; }
HashType GetHashType() const { return hash_type_; }
int KeySizeInBytes() const { return key_size_in_bytes_; }
// Returns the size of the tag, which is computed cryptographically from the
// message. Note that this may differ from the total size of the tag, as for
// some keys, Tink prefixes the tag with a key dependent output prefix.
int CryptographicTagSizeInBytes() const {
return cryptographic_tag_size_in_bytes_;
}
// Returns the size of the cryptographic tag plus the size of the prefix with
// which this key prefixes every cryptographic tag.
int TotalTagSizeInBytes() const;
bool HasIdRequirement() const override {
return variant_ != Variant::kNoPrefix;
}
bool operator==(const Parameters& other) const override;
private:
HmacParameters(int key_size_in_bytes, int cryptographic_tag_size_in_bytes,
HashType hash_type, Variant variant)
: key_size_in_bytes_(key_size_in_bytes),
cryptographic_tag_size_in_bytes_(cryptographic_tag_size_in_bytes),
hash_type_(hash_type),
variant_(variant) {}
int key_size_in_bytes_;
int cryptographic_tag_size_in_bytes_;
HashType hash_type_;
Variant variant_;
};
} // namespace tink
} // namespace crypto
#endif // TINK_MAC_HMAC_PARAMETERS_H_
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