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_id	the SRP hash in use
rng	a random number generator
b_bits	size of secret exponent in bits

Returns

SRP-6 B value

Definition at line 160 of file srp6.cpp.

                                                                                                              {
   BOTAN_ARG_CHECK(b_bits <= group.p_bits(), "Invalid b_bits");
 
   m_group = group;
 
   const BigInt& g = group.get_g();
   const BigInt& p = group.get_p();
 
   m_v = v;
   m_b = BigInt(rng, b_bits);
   m_hash_id = hash_id;
 
   auto hash_fn = HashFunction::create_or_throw(hash_id);
   if(8 * hash_fn->output_length() >= 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 = group.mod_p(v * k + group.power_g_p(m_b, b_bits));
 
   return m_B;
}

References BOTAN_ARG_CHECK, Botan::HashFunction::create_or_throw(), Botan::fmt(), Botan::DL_Group::get_g(), Botan::DL_Group::get_p(), Botan::DL_Group::mod_p(), Botan::DL_Group::p_bits(), Botan::DL_Group::p_bytes(), and Botan::DL_Group::power_g_p().

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_id	the SRP hash in use
rng	a random number generator

Returns

SRP-6 B value

Definition at line 151 of file srp6.cpp.

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

References Botan::DL_Group::exponent_bits(), 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 184 of file srp6.cpp.

                                                       {
   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);
 
   const BigInt vup = m_group.power_b_p(m_v, u, m_group.p_bits());
   const BigInt S = m_group.power_b_p(m_group.multiply_mod_p(A, vup), m_b, m_group.p_bits());
 
   return SymmetricKey(BigInt::encode_1363(S, m_group.p_bytes()));
}

References Botan::HashFunction::create_or_throw(), Botan::BigInt::encode_1363(), Botan::fmt(), Botan::DL_Group::get_p(), Botan::DL_Group::multiply_mod_p(), Botan::DL_Group::p_bits(), Botan::DL_Group::p_bytes(), and Botan::DL_Group::power_b_p().

---

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

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