wallet: add --extra-entropy command line flag

It lets the user add custom entropy to the PRNG.
It does this by hashing the new data and xoring the resulting
hash with the PRNG state.

src/crypto/crypto.cpp

@@ -88,13 +88,24 @@ namespace crypto {
     return &reinterpret_cast<const unsigned char &>(scalar);
   }
 
-  void generate_random_bytes_thread_safe(size_t N, uint8_t *bytes)
+  boost::mutex &get_random_lock()
   {
     static boost::mutex random_lock;
-    boost::lock_guard<boost::mutex> lock(random_lock);
+    return random_lock;
+  }
+
+  void generate_random_bytes_thread_safe(size_t N, uint8_t *bytes)
+  {
+    boost::lock_guard<boost::mutex> lock(get_random_lock());
     generate_random_bytes_not_thread_safe(N, bytes);
   }
 
+  void add_extra_entropy_thread_safe(const void *ptr, size_t bytes)
+  {
+    boost::lock_guard<boost::mutex> lock(get_random_lock());
+    add_extra_entropy_not_thread_safe(ptr, bytes);
+  }
+
   static inline bool less32(const unsigned char *k0, const unsigned char *k1)
   {
     for (int n = 31; n >= 0; --n)

src/crypto/crypto.h

@@ -147,6 +147,7 @@ namespace crypto {
   };
 
   void generate_random_bytes_thread_safe(size_t N, uint8_t *bytes);
+  void add_extra_entropy_thread_safe(const void *ptr, size_t bytes);
 
   /* Generate N random bytes
    */

src/crypto/random.c

@@ -146,3 +146,18 @@ void generate_random_bytes_not_thread_safe(size_t n, void *result) {
     }
   }
 }
+
+void add_extra_entropy_not_thread_safe(const void *ptr, size_t bytes)
+{
+  size_t i;
+
+  while (bytes > 0)
+  {
+    hash_permutation(&state);
+    const size_t round_bytes = bytes > HASH_DATA_AREA ? HASH_DATA_AREA : bytes;
+    for (i = 0; i < round_bytes; ++i)
+      state.b[i] ^= ((const uint8_t*)ptr)[i];
+    bytes -= round_bytes;
+    ptr = cpadd(ptr, round_bytes);
+  }
+}

src/crypto/random.h

@@ -33,3 +33,4 @@
 #include <stddef.h>
 
 void generate_random_bytes_not_thread_safe(size_t n, void *result);
+void add_extra_entropy_not_thread_safe(const void *ptr, size_t bytes);

src/wallet/wallet2.cpp

@@ -273,6 +273,7 @@ struct options {
   const command_line::arg_descriptor<std::string> tx_notify = { "tx-notify" , "Run a program for each new incoming transaction, '%s' will be replaced by the transaction hash" , "" };
   const command_line::arg_descriptor<bool> no_dns = {"no-dns", tools::wallet2::tr("Do not use DNS"), false};
   const command_line::arg_descriptor<bool> offline = {"offline", tools::wallet2::tr("Do not connect to a daemon, nor use DNS"), false};
+  const command_line::arg_descriptor<std::string> extra_entropy = {"extra-entropy", tools::wallet2::tr("File containing extra entropy to initialize the PRNG (any data, aim for 256 bits of entropy to be useful, wihch typically means more than 256 bits of data)")};
 };
 
 void do_prepare_file_names(const std::string& file_path, std::string& keys_file, std::string& wallet_file, std::string &mms_file)
@@ -474,6 +475,15 @@ std::unique_ptr<tools::wallet2> make_basic(const boost::program_options::variabl
   if (command_line::get_arg(vm, opts.offline))
     wallet->set_offline();
 
+  const std::string extra_entropy = command_line::get_arg(vm, opts.extra_entropy);
+  if (!extra_entropy.empty())
+  {
+    std::string data;
+    THROW_WALLET_EXCEPTION_IF(!epee::file_io_utils::load_file_to_string(extra_entropy, data),
+        tools::error::wallet_internal_error, "Failed to load extra entropy from " + extra_entropy);
+    add_extra_entropy_thread_safe(data.data(), data.size());
+  }
+
   try
   {
     if (!command_line::is_arg_defaulted(vm, opts.tx_notify))
@@ -1198,6 +1208,7 @@ void wallet2::init_options(boost::program_options::options_description& desc_par
   command_line::add_arg(desc_params, opts.tx_notify);
   command_line::add_arg(desc_params, opts.no_dns);
   command_line::add_arg(desc_params, opts.offline);
+  command_line::add_arg(desc_params, opts.extra_entropy);
 }
 
 std::pair<std::unique_ptr<wallet2>, tools::password_container> wallet2::make_from_json(const boost::program_options::variables_map& vm, bool unattended, const std::string& json_file, const std::function<boost::optional<tools::password_container>(const char *, bool)> &password_prompter)