dl_group.h

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/*
* Discrete Logarithm Group
* (C) 1999-2008 Jack Lloyd
*
* Distributed under the terms of the Botan license
*/
 
#ifndef BOTAN_DL_PARAM_H__
#define BOTAN_DL_PARAM_H__
 
#include <botan/bigint.h>
#include <botan/data_src.h>
 
namespace Botan {
 
/**
* This class represents discrete logarithm groups. It holds a prime p,
* a prime q = (p-1)/2 and g = x^((p-1)/q) mod p.
*/
class BOTAN_DLL DL_Group
   {
   public:
      /**
      * Get the prime p.
      * @return prime p
      */
      const BigInt& get_p() const;
 
      /**
      * Get the prime q.
      * @return prime q
      */
      const BigInt& get_q() const;
 
      /**
      * Get the base g.
      * @return base g
      */
      const BigInt& get_g() const;
 
      /**
      * The DL group encoding format variants.
      */
      enum Format {
         ANSI_X9_42,
         ANSI_X9_57,
         PKCS_3,
 
         DSA_PARAMETERS = ANSI_X9_57,
         DH_PARAMETERS = ANSI_X9_42,
         X942_DH_PARAMETERS = ANSI_X9_42,
         PKCS3_DH_PARAMETERS = PKCS_3
      };
 
      /**
      * Determine the prime creation for DL groups.
      */
      enum PrimeType { Strong, Prime_Subgroup, DSA_Kosherizer };
 
      /**
      * Perform validity checks on the group.
      * @param rng the rng to use
      * @param strong whether to perform stronger by lengthier tests
      * @return true if the object is consistent, false otherwise
      */
      bool verify_group(RandomNumberGenerator& rng, bool strong) const;
 
      /**
      * Encode this group into a string using PEM encoding.
      * @param format the encoding format
      * @return string holding the PEM encoded group
      */
      std::string PEM_encode(Format format) const;
 
      /**
      * Encode this group into a string using DER encoding.
      * @param format the encoding format
      * @return string holding the DER encoded group
      */
      SecureVector<byte> DER_encode(Format format) const;
 
      /**
      * Decode a DER/BER encoded group into this instance.
      * @param src a DataSource providing the encoded group
      * @param format the format of the encoded group
      */
      void BER_decode(DataSource& src, Format format);
 
      /**
      * Decode a PEM encoded group into this instance.
      * @param src a DataSource providing the encoded group
      */
      void PEM_decode(DataSource& src);
 
      /**
      * Construct a DL group with uninitialized internal value.
      * Use this constructor is you wish to set the groups values
      * from a DER or PEM encoded group.
      */
      DL_Group();
 
      /**
      * Construct a DL group that is registered in the configuration.
      * @param name the name that is configured in the global configuration
      * for the desired group. If no configuration file is specified,
      * the default values from the file policy.cpp will be used. For instance,
      * use "modp/ietf/768" as name.
      */
      DL_Group(const std::string& name);
 
      /**
      * Create a new group randomly.
      * @param rng the random number generator to use
      * @param type specifies how the creation of primes p and q shall
      * be performed. If type=Strong, then p will be determined as a
      * safe prime, and q will be chosen as (p-1)/2. If
      * type=Prime_Subgroup and qbits = 0, then the size of q will be
      * determined according to the estimated difficulty of the DL
      * problem. If type=DSA_Kosherizer, DSA primes will be created.
      * @param pbits the number of bits of p
      * @param qbits the number of bits of q. Leave it as 0 to have
      * the value determined according to pbits.
      */
      DL_Group(RandomNumberGenerator& rng, PrimeType type,
               size_t pbits, size_t qbits = 0);
 
      /**
      * Create a DSA group with a given seed.
      * @param rng the random number generator to use
      * @param seed the seed to use to create the random primes
      * @param pbits the desired bit size of the prime p
      * @param qbits the desired bit size of the prime q.
      */
      DL_Group(RandomNumberGenerator& rng, const MemoryRegion<byte>& seed,
               size_t pbits = 1024, size_t qbits = 0);
 
      /**
      * Create a DL group. The prime q will be determined according to p.
      * @param p the prime p
      * @param g the base g
      */
      DL_Group(const BigInt& p, const BigInt& g);
 
      /**
      * Create a DL group.
      * @param p the prime p
      * @param q the prime q
      * @param g the base g
      */
      DL_Group(const BigInt& p, const BigInt& q, const BigInt& g);
   private:
      static BigInt make_dsa_generator(const BigInt&, const BigInt&);
 
      void init_check() const;
      void initialize(const BigInt&, const BigInt&, const BigInt&);
      bool initialized;
      BigInt p, q, g;
   };
 
}
 
#endif