Botan::SRP6_Server_Session Class Reference

#include <srp6.h>

Public Member Functions
BigInt	step1 (const BigInt &v, const DL_Group &group, std::string_view hash_id, size_t b_bits, RandomNumberGenerator &rng)
BigInt	step1 (const BigInt &v, std::string_view group_id, std::string_view hash_id, RandomNumberGenerator &rng)
SymmetricKey	step2 (const BigInt &A)

Detailed Description

Represents a SRP-6a server session

Definition at line 102 of file srp6.h.

Member Function Documentation

step1() [1/2]

BigInt Botan::SRP6_Server_Session::step1	(	const BigInt &	v,
		const DL_Group &	group,
		std::string_view	hash_id,
		size_t	b_bits,
		RandomNumberGenerator &	rng )

Server side step 1 This version of step1 added in 2.11

Parameters

v	the verification value saved from client registration
group	the SRP group
Hash Function Identification	the SRP hash in use
Random Number Generators	a random number generator
b_bits	size of secret exponent in bits

Returns

SRP-6 B value

Definition at line 164 of file srp6.cpp.

                                                                                                              {
   if(v.signum() <= 0 || v >= group.get_p()) {
      throw Invalid_Argument("SRP6_Server_Session: invalid verifier");
   }
 
   BOTAN_ARG_CHECK(b_bits >= 160 && b_bits <= group.p_bits(), "Invalid b_bits");
 
   BOTAN_STATE_CHECK(!m_group);
   m_group = std::make_unique<DL_Group>(group);
   m_b_bits = b_bits;
 
   const BigInt& g = m_group->get_g();
   const BigInt& p = m_group->get_p();
 
   m_v = v;
   m_b = BigInt(rng, m_b_bits);
   m_hash_id = hash_id;
 
   auto hash_fn = HashFunction::create_or_throw(hash_id);
   if(8 * hash_fn->output_length() >= m_group->p_bits()) {
      throw Invalid_Argument(fmt("Hash function {} too large for SRP6 with this group", hash_fn->name()));
   }
 
   const BigInt k = hash_seq(*hash_fn, m_group->p_bytes(), p, g);
   m_B = m_group->mod_p(v * k + m_group->power_g_p(m_b, b_bits));
 
   return m_B;
}

References BOTAN_ARG_CHECK, BOTAN_STATE_CHECK, Botan::HashFunction::create_or_throw(), Botan::fmt(), Botan::DL_Group::get_p(), Botan::DL_Group::p_bits(), and Botan::BigInt::signum().

step1() [2/2]

BigInt Botan::SRP6_Server_Session::step1	(	const BigInt &	v,
		std::string_view	group_id,
		std::string_view	hash_id,
		RandomNumberGenerator &	rng )

Server side step 1

Parameters

v	the verification value saved from client registration
group_id	the SRP group id
Hash Function Identification	the SRP hash in use
Random Number Generators	a random number generator

Returns

SRP-6 B value

Definition at line 155 of file srp6.cpp.

                                                              {
   auto group = DL_Group::from_name(group_id);
   const size_t b_bits = group.exponent_bits();
   return this->step1(v, group, hash_id, b_bits, rng);
}

References Botan::DL_Group::from_name(), and step1().

Referenced by step1().

step2()

SymmetricKey Botan::SRP6_Server_Session::step2

(

const BigInt &

A

)

Server side step 2

Parameters

A	the client's value

Returns

shared symmetric key

Definition at line 194 of file srp6.cpp.

                                                       {
   BOTAN_STATE_CHECK(m_group);
 
   if(A <= 0 || A >= m_group->get_p()) {
      throw Decoding_Error("Invalid SRP parameter from client");
   }
 
   auto hash_fn = HashFunction::create_or_throw(m_hash_id);
   if(8 * hash_fn->output_length() >= m_group->p_bits()) {
      throw Invalid_Argument(fmt("Hash function {} too large for SRP6 with this group", hash_fn->name()));
   }
 
   const BigInt u = hash_seq(*hash_fn, m_group->p_bytes(), A, m_B);
   BOTAN_ASSERT_NOMSG(!u.is_zero());
 
   // The maximum length of u is fixed based on the chosen hash function
   const size_t u_bits = hash_fn->output_length() * 8;
   const BigInt vup = m_group->power_b_p(m_v, u, u_bits);
 
   // The size of b is chosen by either a formula or the application; either way it is public
   const BigInt S = m_group->power_b_p(m_group->multiply_mod_p(A, vup), m_b, m_b_bits);
 
   return SymmetricKey(S.serialize<secure_vector<uint8_t>>(m_group->p_bytes()));
}

References BOTAN_ASSERT_NOMSG, BOTAN_STATE_CHECK, Botan::HashFunction::create_or_throw(), Botan::fmt(), Botan::BigInt::is_zero(), and Botan::BigInt::serialize().

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The documentation for this class was generated from the following files:

• src/lib/misc/srp6/srp6.h
• src/lib/misc/srp6/srp6.cpp