Botan::Scrypt_Family Class Reference

#include <scrypt.h>

Inheritance diagram for Botan::Scrypt_Family:

Public Member Functions
std::unique_ptr< PasswordHash >	default_params () const override
std::unique_ptr< PasswordHash >	from_iterations (size_t iter) const override
std::unique_ptr< PasswordHash >	from_params (size_t N, size_t r, size_t p) const override
std::string	name () const override
std::unique_ptr< PasswordHash >	tune (size_t output_length, std::chrono::milliseconds msec, size_t max_memory, std::chrono::milliseconds tune_msec) const override

Static Public Member Functions
static std::unique_ptr< PasswordHashFamily >	create (std::string_view algo_spec, std::string_view provider="")
static std::unique_ptr< PasswordHashFamily >	create_or_throw (std::string_view algo_spec, std::string_view provider="")
static std::vector< std::string >	providers (std::string_view algo_spec)

Detailed Description

Definition at line 52 of file scrypt.h.

Member Function Documentation

create()

std::unique_ptr< PasswordHashFamily > Botan::PasswordHashFamily::create ( std::string_view algo_spec, std::string_view provider = "" )

staticinherited

Create an instance based on a name If provider is empty then best available is chosen.

Parameters

algo_spec	algorithm name
provider	provider implementation to choose

Returns

a null pointer if the algo/provider combination cannot be found

Definition at line 53 of file pwdhash.cpp.

                                                                                                              {
   const SCAN_Name req(algo_spec);
 
#if defined(BOTAN_HAS_PBKDF2)
   if(req.algo_name() == "PBKDF2") {
      if(provider.empty() || provider == "base") {
         if(auto mac = MessageAuthenticationCode::create("HMAC(" + req.arg(0) + ")")) {
            return std::make_unique<PBKDF2_Family>(std::move(mac));
         }
 
         if(auto mac = MessageAuthenticationCode::create(req.arg(0))) {
            return std::make_unique<PBKDF2_Family>(std::move(mac));
         }
      }
 
      return nullptr;
   }
#endif
 
#if defined(BOTAN_HAS_SCRYPT)
   if(req.algo_name() == "Scrypt") {
      return std::make_unique<Scrypt_Family>();
   }
#endif
 
#if defined(BOTAN_HAS_ARGON2)
   if(req.algo_name() == "Argon2d") {
      return std::make_unique<Argon2_Family>(static_cast<uint8_t>(0));
   } else if(req.algo_name() == "Argon2i") {
      return std::make_unique<Argon2_Family>(static_cast<uint8_t>(1));
   } else if(req.algo_name() == "Argon2id") {
      return std::make_unique<Argon2_Family>(static_cast<uint8_t>(2));
   }
#endif
 
#if defined(BOTAN_HAS_PBKDF_BCRYPT)
   if(req.algo_name() == "Bcrypt-PBKDF") {
      return std::make_unique<Bcrypt_PBKDF_Family>();
   }
#endif
 
#if defined(BOTAN_HAS_PGP_S2K)
   if(req.algo_name() == "OpenPGP-S2K" && req.arg_count() == 1) {
      if(auto hash = HashFunction::create(req.arg(0))) {
         return std::make_unique<RFC4880_S2K_Family>(std::move(hash));
      }
   }
#endif
 
   BOTAN_UNUSED(req);
   BOTAN_UNUSED(provider);
 
   return nullptr;
}

References Botan::SCAN_Name::algo_name(), Botan::SCAN_Name::arg(), Botan::SCAN_Name::arg_count(), BOTAN_UNUSED, Botan::HashFunction::create(), and Botan::MessageAuthenticationCode::create().

Referenced by botan_pwdhash(), botan_pwdhash_timed(), and Botan::PasswordHashFamily::create_or_throw().

create_or_throw()

std::unique_ptr< PasswordHashFamily > Botan::PasswordHashFamily::create_or_throw ( std::string_view algo_spec, std::string_view provider = "" )

staticinherited

Create an instance based on a name, or throw if the algo/provider combination cannot be found. If provider is empty then best available is chosen.

Definition at line 109 of file pwdhash.cpp.

                                                                                                 {
   if(auto pbkdf = PasswordHashFamily::create(algo, provider)) {
      return pbkdf;
   }
   throw Lookup_Error("PasswordHashFamily", algo, provider);
}

References Botan::PasswordHashFamily::create().

Referenced by Botan::argon2_check_pwhash(), Botan::argon2_generate_pwhash(), Botan::CryptoBox::decrypt_bin(), and Botan::CryptoBox::encrypt().

default_params()

std::unique_ptr< PasswordHash > Botan::Scrypt_Family::default_params ( ) const

overridevirtual

Return some default parameter set for this PBKDF that should be good enough for most users. The value returned may change over time as processing power and attacks improve.

Implements Botan::PasswordHashFamily.

Definition at line 32 of file scrypt.cpp.

                                                                {
   return std::make_unique<Scrypt>(32768, 8, 1);
}

Referenced by tune().

from_iterations()

std::unique_ptr< PasswordHash > Botan::Scrypt_Family::from_iterations ( size_t iterations ) const

overridevirtual

Return a parameter chosen based on a rough approximation with the specified iteration count. The exact value this returns for a particular algorithm may change from over time. Think of it as an alternative to tune, where time is expressed in terms of PBKDF2 iterations rather than milliseconds.

Implements Botan::PasswordHashFamily.

Definition at line 118 of file scrypt.cpp.

                                                                            {
   const size_t r = 8;
   const size_t p = 1;
 
   size_t N = 8192;
 
   if(iter > 50000) {
      N = 16384;
   }
   if(iter > 100000) {
      N = 32768;
   }
   if(iter > 150000) {
      N = 65536;
   }
 
   return std::make_unique<Scrypt>(N, r, p);
}

from_params()

std::unique_ptr< PasswordHash > Botan::Scrypt_Family::from_params ( size_t i1, size_t i2, size_t i3 ) const

overridevirtual

Create a password hash using some scheme specific format. Parameters are as follows:

• For PBKDF2, PGP-S2K, and Bcrypt-PBKDF, i1 is iterations
• Scrypt uses N, r, p for i{1-3}
• Argon2 family uses memory (in KB), iterations, and parallelism for i{1-3}

All unneeded parameters should be set to 0 or left blank.

Implements Botan::PasswordHashFamily.

Definition at line 114 of file scrypt.cpp.

                                                                                         {
   return std::make_unique<Scrypt>(N, r, p);
}

Referenced by tune().

name()

std::string Botan::Scrypt_Family::name ( ) const

overridevirtual

Returns

name of this PasswordHash

Implements Botan::PasswordHashFamily.

Definition at line 28 of file scrypt.cpp.

                                    {
   return "Scrypt";
}

providers()

std::vector< std::string > Botan::PasswordHashFamily::providers ( std::string_view algo_spec )

staticinherited

Returns

list of available providers for this algorithm, empty if not available

Definition at line 117 of file pwdhash.cpp.

                                                                           {
   return probe_providers_of<PasswordHashFamily>(algo_spec);
}

References Botan::probe_providers_of().

tune()

std::unique_ptr< PasswordHash > Botan::Scrypt_Family::tune ( size_t output_length, std::chrono::milliseconds msec, size_t max_memory_usage_mb, std::chrono::milliseconds tuning_msec ) const

overridevirtual

Return a new parameter set tuned for this machine

Return a password hash instance tuned to run for approximately msec milliseconds when producing an output of length output_length. (Accuracy may vary, use the command line utility botan pbkdf_tune to check.)

The parameters will be selected to use at most max_memory_usage_mb megabytes of memory, or if left as zero any size is allowed.

This function works by runing a short tuning loop to estimate the performance of the algorithm, then scaling the parameters appropriately to hit the target size. The length of time the tuning loop runs can be controlled using the tuning_msec parameter.

Parameters

output_length	how long the output length will be
msec	the desired execution time in milliseconds
max_memory_usage_mb	some password hash functions can use a tunable amount of memory, in this case max_memory_usage limits the amount of RAM the returned parameters will require, in mebibytes (2**20 bytes). It may require some small amount above the request. Set to zero to place no limit at all.
tuning_msec	how long to run the tuning loop

Implements Botan::PasswordHashFamily.

Definition at line 36 of file scrypt.cpp.

                                                                                         {
   BOTAN_UNUSED(output_length);
 
   /*
   * Some rough relations between scrypt parameters and runtime.
   * Denote here by stime(N,r,p) the msec it takes to run scrypt.
   *
   * Emperically for smaller sizes:
   * stime(N,8*r,p) / stime(N,r,p) is ~ 6-7
   * stime(N,r,8*p) / stime(N,r,8*p) is ~ 7
   * stime(2*N,r,p) / stime(N,r,p) is ~ 2
   *
   * Compute stime(8192,1,1) as baseline and extrapolate
   */
 
   // This is zero if max_memory_usage_mb == 0 (unbounded)
   const size_t max_memory_usage = max_memory_usage_mb * 1024 * 1024;
 
   // Starting parameters
   size_t N = 8 * 1024;
   size_t r = 1;
   size_t p = 1;
 
   Timer timer("Scrypt");
 
   auto pwdhash = this->from_params(N, r, p);
 
   timer.run_until_elapsed(tune_time, [&]() {
      uint8_t output[32] = {0};
      pwdhash->derive_key(output, sizeof(output), "test", 4, nullptr, 0);
   });
 
   // No timer events seems strange, perhaps something is wrong - give
   // up on this and just return default params
   if(timer.events() == 0) {
      return default_params();
   }
 
   // nsec per eval of scrypt with initial params
   const uint64_t measured_time = timer.value() / timer.events();
 
   const uint64_t target_nsec = msec.count() * static_cast<uint64_t>(1000000);
 
   uint64_t est_nsec = measured_time;
 
   // In below code we invoke scrypt_memory_usage with p == 0 as p contributes
   // (very slightly) to memory consumption, but N is the driving factor.
   // Including p leads to using an N half as large as what the user would expect.
 
   // First increase r by 8x if possible
   if(max_memory_usage == 0 || scrypt_memory_usage(N, r * 8, 0) <= max_memory_usage) {
      if(target_nsec / est_nsec >= 5) {
         r *= 8;
         est_nsec *= 5;
      }
   }
 
   // Now double N as many times as we can
   while(max_memory_usage == 0 || scrypt_memory_usage(N * 2, r, 0) <= max_memory_usage) {
      if(target_nsec / est_nsec >= 2) {
         N *= 2;
         est_nsec *= 2;
      } else {
         break;
      }
   }
 
   // If we have extra runtime budget, increment p
   if(target_nsec / est_nsec >= 2) {
      p *= std::min<size_t>(1024, static_cast<size_t>(target_nsec / est_nsec));
   }
 
   return std::make_unique<Scrypt>(N, r, p);
}

References BOTAN_UNUSED, default_params(), Botan::Timer::events(), from_params(), Botan::Timer::run_until_elapsed(), and Botan::Timer::value().

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

• src/lib/pbkdf/scrypt/scrypt.h
• src/lib/pbkdf/scrypt/scrypt.cpp