Make cache size configurable

4 files changed, 62 insertions, 10 deletions

diff --git a/lib/crypto/doc/src/crypto.xml b/lib/crypto/doc/src/crypto.xml
index 5afab632cd..c32e3430ab 100644
--- a/lib/crypto/doc/src/crypto.xml
+++ b/lib/crypto/doc/src/crypto.xml
@@ -800,6 +800,7 @@ _FloatValue = rand:uniform().     % [0.0; 1.0[</pre>
         <v>Alg = crypto | crypto_cache</v>
       </type>
       <desc>
+	<marker id="rand_seed_alg-1" />
 	<p>
           Creates state object for
 	  <seealso marker="stdlib:rand">random number generation</seealso>,
@@ -814,6 +815,12 @@ _FloatValue = rand:uniform().     % [0.0; 1.0[</pre>
 	  may throw exception <c>low_entropy</c> in case the random generator
 	  failed due to lack of secure "randomness".
 	</p>
+	<p>
+	  The cache size can be changed from its default value using the
+	  <seealso marker="crypto_app">
+	    crypto app's
+	  </seealso> configuration parameter <c>rand_cache_size</c>.
+	</p>
         <p><em>Example</em></p>
         <pre>
 _ = crypto:rand_seed_alg(crypto_cache),
@@ -829,6 +836,7 @@ _FloatValue = rand:uniform().     % [0.0; 1.0[</pre>
         <v>Alg = crypto | crypto_cache</v>
       </type>
       <desc>
+	<marker id="rand_seed_alg_s-1" />
 	<p>
           Creates state object for
 	  <seealso marker="stdlib:rand">random number generation</seealso>,
@@ -852,6 +860,12 @@ _FloatValue = rand:uniform().     % [0.0; 1.0[</pre>
 	  may throw exception <c>low_entropy</c> in case the random generator
 	  failed due to lack of secure "randomness".
 	</p>
+	<p>
+	  The cache size can be changed from its default value using the
+	  <seealso marker="crypto_app">
+	    crypto app's
+	  </seealso> configuration parameter <c>rand_cache_size</c>.
+	</p>
 	<note>
 	  <p>
 	    The state returned from this function can not be used
diff --git a/lib/crypto/doc/src/crypto_app.xml b/lib/crypto/doc/src/crypto_app.xml
index ba22557480..8296b1bc77 100644
--- a/lib/crypto/doc/src/crypto_app.xml
+++ b/lib/crypto/doc/src/crypto_app.xml
@@ -68,6 +68,24 @@
         thus the crypto module will fail to load. This mechanism
         prevents the accidental use of non-validated algorithms.</p>
       </item>
+      <tag><c>rand_cache_size = integer()</c></tag>
+      <item>
+        <p>
+	  Sets the cache size in bytes to use by
+	  <seealso marker="crypto#rand_seed_alg-1">
+	    <c>crypto:rand_seed_alg(crypto_cache)</c>
+	  </seealso> and
+	  <seealso marker="crypto#rand_seed_alg_s-1">
+	    <c>crypto:rand_seed_alg_s(crypto_cache)</c>
+	  </seealso>.
+	  This parameter is read when a seed function is called,
+	  and then kept in generators state object.  It has a rather
+	  small default value that causes reads of strong random bytes
+	  about once per hundred calls for a random value.
+	  The set value is rounded up to an integral number of words
+	  of the size these seed functions use.
+	</p>
+      </item>
     </taglist>
   </section>
 
diff --git a/lib/crypto/src/crypto.app.src b/lib/crypto/src/crypto.app.src
index 1d3f35e465..492aa10e51 100644
--- a/lib/crypto/src/crypto.app.src
+++ b/lib/crypto/src/crypto.app.src
@@ -24,7 +24,7 @@
 	       crypto_ec_curves]},
     {registered, []},
     {applications, [kernel, stdlib]},
-    {env, [{fips_mode, false}]},
+    {env, [{fips_mode, false}, {rand_cache_size, 896}]},
     {runtime_dependencies, ["erts-9.0","stdlib-3.4","kernel-5.3"]}]}.
 
 
diff --git a/lib/crypto/src/crypto.erl b/lib/crypto/src/crypto.erl
index 69c98c651f..69ca884471 100644
--- a/lib/crypto/src/crypto.erl
+++ b/lib/crypto/src/crypto.erl
@@ -297,11 +297,17 @@ stream_decrypt(State, Data0) ->
 %%
 %% RAND - pseudo random numbers using RN_ and BN_ functions in crypto lib
 %%
+-type rand_cache_seed() ::
+        nonempty_improper_list(non_neg_integer(), binary()).
 -spec strong_rand_bytes(non_neg_integer()) -> binary().
 -spec rand_seed() -> rand:state().
 -spec rand_seed_s() -> rand:state().
--spec rand_seed_alg(Alg :: atom()) -> rand:state().
--spec rand_seed_alg_s(Alg :: atom()) -> rand:state().
+-spec rand_seed_alg(Alg :: atom()) ->
+                           {rand:alg_handler(),
+                            atom() | rand_cache_seed()}.
+-spec rand_seed_alg_s(Alg :: atom()) ->
+                             {rand:alg_handler(),
+                              atom() | rand_cache_seed()}.
 -spec rand_uniform(crypto_integer(), crypto_integer()) ->
 			  crypto_integer().
 
@@ -319,10 +325,12 @@ rand_seed() ->
 rand_seed_s() ->
     rand_seed_alg_s(?MODULE).
 
+-dialyzer({no_improper_lists, rand_seed_alg/1}).
 rand_seed_alg(Alg) ->
     rand:seed(rand_seed_alg_s(Alg)).
-    
+
 -define(CRYPTO_CACHE_BITS, 56).
+-dialyzer({no_improper_lists, rand_seed_alg_s/1}).
 rand_seed_alg_s(?MODULE) ->
     {#{ type => ?MODULE,
         bits => 64,
@@ -331,10 +339,22 @@ rand_seed_alg_s(?MODULE) ->
         uniform_n => fun ?MODULE:rand_plugin_uniform/2},
      no_seed};
 rand_seed_alg_s(crypto_cache) ->
+    EnvCacheSize =
+        application:get_env(
+          crypto, rand_cache_size,
+          ?CRYPTO_CACHE_BITS * 16), % Cache 16 * 8 words
+    Bytes = (?CRYPTO_CACHE_BITS + 7) div 8,
+    CacheSize =
+        case ((EnvCacheSize + (Bytes - 1)) div Bytes) * Bytes of
+            Sz when is_integer(Sz), Bytes =< Sz ->
+                Sz;
+            _ ->
+                Bytes
+        end,
     {#{ type => crypto_cache,
         bits => ?CRYPTO_CACHE_BITS,
         next => fun ?MODULE:rand_cache_plugin_next/1},
-     <<>>}.
+     [CacheSize|<<>>]}.
 
 rand_plugin_next(Seed) ->
     {bytes_to_integer(strong_rand_range(1 bsl 64)), Seed}.
@@ -345,11 +365,11 @@ rand_plugin_uniform(State) ->
 rand_plugin_uniform(Max, State) ->
     {bytes_to_integer(strong_rand_range(Max)) + 1, State}.
 
-rand_cache_plugin_next(<<>>) ->
-    rand_cache_plugin_next(
-      strong_rand_bytes(?CRYPTO_CACHE_BITS * 16)); % Cache 16 * 8 words
-rand_cache_plugin_next(<<I:?CRYPTO_CACHE_BITS,Cache/binary>>) ->
-    {I, Cache}.
+-dialyzer({no_improper_lists, rand_cache_plugin_next/1}).
+rand_cache_plugin_next([CacheSize|<<>>]) ->
+    rand_cache_plugin_next([CacheSize|strong_rand_bytes(CacheSize)]);
+rand_cache_plugin_next([CacheSize|<<I:?CRYPTO_CACHE_BITS,Cache/binary>>]) ->
+    {I, [CacheSize|Cache]}.
 
 strong_rand_range(Range) when is_integer(Range), Range > 0 ->
     BinRange = int_to_bin(Range),