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/**
* Wrapper for truncated hashes
* (C) 2023 Jack Lloyd
* 2023 René Meusel - Rohde & Schwarz Cybersecurity
*
* Botan is released under the Simplified BSD License (see license.txt)
*/
#ifndef BOTAN_TRUNCATED_HASH_H_
#define BOTAN_TRUNCATED_HASH_H_
#include <botan/hash.h>
namespace Botan {
/**
* Wrapper class to truncate underlying hash function output to a given number
* of bits. The leading bits are retained. Since the HashFunction interface is
* defined to return bytes, if the desired truncation length is not a multiple
* of 8, then the final byte of the output will have some number of trailing
* bits always set to zero.
*/
class Truncated_Hash final : public HashFunction {
public:
void clear() override;
std::string name() const override;
std::unique_ptr<HashFunction> new_object() const override;
std::unique_ptr<HashFunction> copy_state() const override;
size_t output_length() const override;
/**
* @param hash the underlying hash function whose output shall be truncated
* @param length the number of bits the hash shall be truncated to
*/
Truncated_Hash(std::unique_ptr<HashFunction> hash, size_t length);
private:
void add_data(std::span<const uint8_t>) override;
void final_result(std::span<uint8_t>) override;
std::unique_ptr<HashFunction> m_hash;
size_t m_output_bits;
secure_vector<uint8_t> m_buffer;
};
} // namespace Botan
#endif