hash.h

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/*
* Hash Function Base Class
* (C) 1999-2008 Jack Lloyd
*
* Botan is released under the Simplified BSD License (see license.txt)
*/
 
#ifndef BOTAN_HASH_FUNCTION_BASE_CLASS_H_
#define BOTAN_HASH_FUNCTION_BASE_CLASS_H_
 
#include <botan/buf_comp.h>
#include <memory>
#include <string>
#include <string_view>
 
namespace Botan {
 
/**
* This class represents hash function (message digest) objects
*/
class BOTAN_PUBLIC_API(2, 0) HashFunction : public Buffered_Computation {
   public:
      /**
      * Create an instance based on a name, or return null if the
      * algo/provider combination cannot be found. If provider is
      * empty then best available is chosen.
      */
      static std::unique_ptr<HashFunction> create(std::string_view algo_spec, std::string_view provider = "");
 
      /**
      * Create an instance based on a name
      * If provider is empty then best available is chosen.
      * @param algo_spec algorithm name
      * @param provider provider implementation to use
      * Throws Lookup_Error if not found.
      */
      static std::unique_ptr<HashFunction> create_or_throw(std::string_view algo_spec, std::string_view provider = "");
 
      /**
      * List the providers available for a given hash
      * @return list of available providers for this algorithm, empty if not available
      * @param algo_spec algorithm name
      */
      static std::vector<std::string> providers(std::string_view algo_spec);
 
      /**
      * Return the name of the provider implementing this object
      * @return provider information about this implementation. Default is "base",
      * might also return "sse2", "avx2", "openssl", or some other arbitrary string.
      */
      virtual std::string provider() const { return "base"; }
 
      /**
      * Reset the state.
      */
      virtual void clear() = 0;
 
      /**
      * Return the name of this hash function
      * @return the hash function name
      */
      virtual std::string name() const = 0;
 
      /**
      * Return the internal block size of this hash function
      * @return hash block size as defined for this algorithm
      */
      virtual size_t hash_block_size() const { return 0; }
 
      /**
      * Return an estimate, in bits, of the security level of this hash
      * function, with respect to collision resistance. For most hashes this is
      * simply half the output length, matching the generic birthday attack.
      * It is lower for hash functions with a known collision attack, and zero
      * for checksums and any hash where finding collisions is trivial.
      */
      virtual size_t security_level() const { return 4 * output_length(); }
 
      /**
      * Return a new hash object with the same state as *this. This
      * allows computing the hash of several messages with a common
      * prefix more efficiently than would otherwise be possible.
      *
      * This function should be called `clone` but that was already
      * used for the case of returning an uninitialized object.
      * @return new hash object
      */
      virtual std::unique_ptr<HashFunction> copy_state() const = 0;
 
      /**
      * Create a new uninitialized object of the same type
      * @return new object representing the same algorithm as *this
      */
      virtual std::unique_ptr<HashFunction> new_object() const = 0;
 
      /**
      * Create a new uninitialized object of the same type
      * @return new object representing the same algorithm as *this
      */
      HashFunction* clone() const { return this->new_object().release(); }
};
 
}  // namespace Botan
 
#endif