Merge branch 'g-andrade/strong-random-numbers/PR-1367/OTP-14317'

* g-andrade/strong-random-numbers/PR-1367/OTP-14317:
  Clean up documentation and test cases
  Attempt faster approach to strong random floats
  Allow for crypto upgrades when using rand plugin
  fixup! Support cryptographically strong rand plugin
  fixup! Support cryptographically strong rand plugin
  fixup! Support cryptographically strong rand plugin
  fixup! Support cryptographically strong rand plugin
  No longer expose strong_rand_(range|float)
  Support cryptographically strong rand plugin
  Restyle crypto strong numeric generators for usage in rand
  Support generation of strong random numbers

7 files changed, 351 insertions, 64 deletions

diff --git a/lib/crypto/c_src/crypto.c b/lib/crypto/c_src/crypto.c
index b2f31870b9..b8ef08410c 100644
--- a/lib/crypto/c_src/crypto.c
+++ b/lib/crypto/c_src/crypto.c
@@ -429,6 +429,7 @@ static ERL_NIF_TERM aes_ige_crypt_nif(ErlNifEnv* env, int argc, const ERL_NIF_TE
 static ERL_NIF_TERM aes_ctr_stream_init(ErlNifEnv* env, int argc, const ERL_NIF_TERM argv[]);
 static ERL_NIF_TERM aes_ctr_stream_encrypt(ErlNifEnv* env, int argc, const ERL_NIF_TERM argv[]);
 static ERL_NIF_TERM strong_rand_bytes_nif(ErlNifEnv* env, int argc, const ERL_NIF_TERM argv[]);
+static ERL_NIF_TERM strong_rand_range_nif(ErlNifEnv* env, int argc, const ERL_NIF_TERM argv[]);
 static ERL_NIF_TERM rand_uniform_nif(ErlNifEnv* env, int argc, const ERL_NIF_TERM argv[]);
 static ERL_NIF_TERM mod_exp_nif(ErlNifEnv* env, int argc, const ERL_NIF_TERM argv[]);
 static ERL_NIF_TERM dss_verify_nif(ErlNifEnv* env, int argc, const ERL_NIF_TERM argv[]);
@@ -501,6 +502,7 @@ static ErlNifFunc nif_funcs[] = {
     {"aes_ctr_stream_encrypt", 2, aes_ctr_stream_encrypt},
     {"aes_ctr_stream_decrypt", 2, aes_ctr_stream_encrypt},
     {"strong_rand_bytes_nif", 1, strong_rand_bytes_nif},
+    {"strong_rand_range_nif", 1, strong_rand_range_nif},
     {"rand_uniform_nif", 2, rand_uniform_nif},
     {"mod_exp_nif", 4, mod_exp_nif},
     {"dss_verify_nif", 4, dss_verify_nif},
@@ -2331,6 +2333,27 @@ static ERL_NIF_TERM bin_from_bn(ErlNifEnv* env, const BIGNUM *bn)
     return term;
 }
 
+static ERL_NIF_TERM strong_rand_range_nif(ErlNifEnv* env, int argc, const ERL_NIF_TERM argv[])
+{/* (Range) */
+    BIGNUM *bn_range, *bn_rand;
+    ERL_NIF_TERM ret;
+
+    if(!get_bn_from_bin(env, argv[0], &bn_range)) {
+        return enif_make_badarg(env);
+    }
+
+    bn_rand = BN_new();
+    if (BN_rand_range(bn_rand, bn_range) != 1) {
+        ret = atom_false;
+    }
+    else {
+        ret = bin_from_bn(env, bn_rand);
+    }
+    BN_free(bn_rand);
+    BN_free(bn_range);
+    return ret;
+}
+
 static ERL_NIF_TERM rand_uniform_nif(ErlNifEnv* env, int argc, const ERL_NIF_TERM argv[])
 {/* (Lo,Hi) */
     BIGNUM *bn_from = NULL, *bn_to, *bn_rand;
diff --git a/lib/crypto/doc/src/crypto.xml b/lib/crypto/doc/src/crypto.xml
index d0deaceaaf..552d95d7dc 100644
--- a/lib/crypto/doc/src/crypto.xml
+++ b/lib/crypto/doc/src/crypto.xml
@@ -658,10 +658,11 @@
       </type>
       <desc>
         <p>Set the seed for PRNG to the given binary. This calls the
-	RAND_seed function from openssl. Only use this if the system
-	you are running on does not have enough "randomness" built in.
-	Normally this is when <seealso marker="#strong_rand_bytes/1">
-	strong_rand_bytes/1</seealso> returns <c>low_entropy</c></p>
+        RAND_seed function from openssl. Only use this if the system
+        you are running on does not have enough "randomness" built in.
+        Normally this is when
+        <seealso marker="#strong_rand_bytes/1">strong_rand_bytes/1</seealso>
+        throws <c>low_entropy</c></p>
       </desc>
     </func>
 
@@ -728,6 +729,43 @@
 	failed due to lack of secure "randomness".</p>
       </desc>
     </func>
+
+    <func>
+      <name>rand_seed() -> rand:state()</name>
+      <fsummary>Strong random number generation plugin state</fsummary>
+      <desc>
+	<p>
+          Creates state object for
+	  <seealso marker="stdlib:rand">random number generation</seealso>,
+          in order to generate cryptographically strong random numbers
+          (based on OpenSSL's <c>BN_rand_range</c>),
+          and saves it on process dictionary before returning it as well.
+          See also
+	  <seealso marker="stdlib:rand#seed-1">rand:seed/1</seealso>.
+	</p>
+        <p><em>Example</em></p>
+        <pre>
+_ = crypto:rand_seed(),
+_IntegerValue = rand:uniform(42), % [1; 42]
+_FloatValue = rand:uniform().     % [0.0; 1.0[</pre>
+      </desc>
+    </func>
+
+    <func>
+      <name>rand_seed_s() -> rand:state()</name>
+      <fsummary>Strong random number generation plugin state</fsummary>
+      <desc>
+	<p>
+          Creates state object for
+	  <seealso marker="stdlib:rand">random number generation</seealso>,
+          in order to generate cryptographically strongly random numbers
+          (based on OpenSSL's <c>BN_rand_range</c>).
+          See also
+	  <seealso marker="stdlib:rand#seed_s-1">rand:seed_s/1</seealso>.
+	</p>
+      </desc>
+    </func>
+
     <func>
       <name>stream_init(Type, Key) -> State</name>
       <fsummary></fsummary>
diff --git a/lib/crypto/src/crypto.erl b/lib/crypto/src/crypto.erl
index d322765dff..1287ec6176 100644
--- a/lib/crypto/src/crypto.erl
+++ b/lib/crypto/src/crypto.erl
@@ -30,6 +30,12 @@
 -export([hmac/3, hmac/4, hmac_init/2, hmac_update/2, hmac_final/1, hmac_final_n/2]).
 -export([cmac/3, cmac/4]).
 -export([exor/2, strong_rand_bytes/1, mod_pow/3]).
+-export([rand_seed/0]).
+-export([rand_seed_s/0]).
+-export([rand_plugin_next/1]).
+-export([rand_plugin_uniform/1]).
+-export([rand_plugin_uniform/2]).
+-export([rand_plugin_jump/1]).
 -export([rand_uniform/2]).
 -export([block_encrypt/3, block_decrypt/3, block_encrypt/4, block_decrypt/4]).
 -export([next_iv/2, next_iv/3]).
@@ -45,6 +51,9 @@
 %% This should correspond to the similar macro in crypto.c
 -define(MAX_BYTES_TO_NIF, 20000). %%  Current value is: erlang:system_info(context_reductions) * 10
 
+%% Used by strong_rand_float/0
+-define(HALF_DBL_EPSILON, 1.1102230246251565e-16). % math:pow(2, -53)
+
 %%-type ecdsa_digest_type() :: 'md5' | 'sha' | 'sha256' | 'sha384' | 'sha512'.
 -type crypto_integer() :: binary() | integer().
 %%-type ec_named_curve() :: atom().
@@ -286,9 +295,11 @@ stream_decrypt(State, Data0) ->
     stream_crypt(fun do_stream_decrypt/2, State, Data, erlang:byte_size(Data), MaxByts, []).
 
 %%
-%% RAND - pseudo random numbers using RN_ functions in crypto lib
+%% RAND - pseudo random numbers using RN_ and BN_ functions in crypto lib
 %%
 -spec strong_rand_bytes(non_neg_integer()) -> binary().
+-spec rand_seed() -> rand:state().
+-spec rand_seed_s() -> rand:state().
 -spec rand_uniform(crypto_integer(), crypto_integer()) ->
 			  crypto_integer().
 
@@ -300,6 +311,46 @@ strong_rand_bytes(Bytes) ->
 strong_rand_bytes_nif(_Bytes) -> ?nif_stub.
 
 
+rand_seed() ->
+    rand:seed(rand_seed_s()).
+
+rand_seed_s() ->
+    {#{ type => ?MODULE,
+        max => infinity,
+        next => fun ?MODULE:rand_plugin_next/1,
+        uniform => fun ?MODULE:rand_plugin_uniform/1,
+        uniform_n => fun ?MODULE:rand_plugin_uniform/2,
+        jump => fun ?MODULE:rand_plugin_jump/1},
+     no_seed}.
+
+rand_plugin_next(Seed) ->
+    {bytes_to_integer(strong_rand_range(1 bsl 64)), Seed}.
+
+rand_plugin_uniform(State) ->
+    {strong_rand_float(), State}.
+
+rand_plugin_uniform(Max, State) ->
+    {bytes_to_integer(strong_rand_range(Max)) + 1, State}.
+
+rand_plugin_jump(State) ->
+    State.
+
+strong_rand_range(Range) when is_integer(Range), Range > 0 ->
+    BinRange = int_to_bin(Range),
+    strong_rand_range(BinRange);
+strong_rand_range(BinRange) when is_binary(BinRange) ->
+    case strong_rand_range_nif(BinRange) of
+        false ->
+            erlang:error(low_entropy);
+        <<BinResult/binary>> ->
+            BinResult
+    end.
+strong_rand_range_nif(_BinRange) -> ?nif_stub.
+
+strong_rand_float() ->
+    WholeRange = strong_rand_range(1 bsl 53),
+    ?HALF_DBL_EPSILON * bytes_to_integer(WholeRange).
+
 rand_uniform(From,To) when is_binary(From), is_binary(To) ->
     case rand_uniform_nif(From,To) of
 	<<Len:32/integer, MSB, Rest/binary>> when MSB > 127 ->
@@ -328,6 +379,7 @@ rand_uniform_pos(_,_) ->
 
 rand_uniform_nif(_From,_To) -> ?nif_stub.
 
+
 -spec rand_seed(binary()) -> ok.
 rand_seed(Seed) ->
     rand_seed_nif(Seed).
diff --git a/lib/crypto/test/crypto_SUITE.erl b/lib/crypto/test/crypto_SUITE.erl
index 1d7037d003..1b7456af18 100644
--- a/lib/crypto/test/crypto_SUITE.erl
+++ b/lib/crypto/test/crypto_SUITE.erl
@@ -36,7 +36,9 @@ all() ->
      {group, non_fips},
      mod_pow,
      exor,
-     rand_uniform
+     rand_uniform,
+     rand_plugin,
+     rand_plugin_s
     ].
 
 groups() ->
@@ -486,6 +488,17 @@ rand_uniform(Config) when is_list(Config) ->
     10 = byte_size(crypto:strong_rand_bytes(10)).
 
 %%--------------------------------------------------------------------
+rand_plugin() ->
+    [{doc, "crypto rand plugin testing (implicit state / process dictionary)"}].
+rand_plugin(Config) when is_list(Config) ->
+    rand_plugin_aux(implicit_state).
+
+rand_plugin_s() ->
+    [{doc, "crypto rand plugin testing (explicit state)"}].
+rand_plugin_s(Config) when is_list(Config) ->
+    rand_plugin_aux(explicit_state).
+
+%%--------------------------------------------------------------------
 %% Internal functions ------------------------------------------------
 %%--------------------------------------------------------------------
 hash(_, [], []) ->
@@ -951,6 +964,101 @@ crypto_rand_uniform(L,H) ->
 	    ct:fail({"Not in interval", R1, L, H})
     end.
 
+foldallmap(_Fun, AccN, []) ->
+    {true, AccN};
+foldallmap(Fun, AccN, [H|T]) ->
+    case Fun(H, AccN) of
+        {true, AccM} -> foldallmap(Fun, AccM, T);
+        {{false, Result}, AccM} -> {Result, AccM}
+    end.
+
+allmap(_Fun, []) ->
+    true;
+allmap(Fun, [H|T]) ->
+    case Fun(H) of
+        true -> allmap(Fun, T);
+        {false, Result} -> Result
+    end.
+
+rand_plugin_aux(StateType) ->
+    {Seeder, SeedExporter, FloatGenerator, IntegerGenerator} = rand_plugin_functions(StateType),
+    State0 = Seeder(),
+    {crypto, no_seed} = SeedExporter(State0),
+    {FloatTestResult, State1} = rand_plugin_aux_floats(State0, FloatGenerator),
+    case FloatTestResult of
+        true ->
+            {IntegerTestResult, _State2} = rand_plugin_aux_integers(State1, IntegerGenerator),
+            IntegerTestResult;
+        {false, _} ->
+            FloatTestResult
+    end.
+
+% returns {Seeder, SeedExporter, FloatGenerator, IntegerGenerator} with consistent signatures
+rand_plugin_functions(implicit_state) ->
+    {fun () -> crypto:rand_seed(), implicit_state end,
+     fun (implicit_state) -> rand:export_seed() end,
+     fun (implicit_state) -> {rand:uniform(), implicit_state} end,
+     fun (N, implicit_state) -> {rand:uniform(N), implicit_state} end};
+rand_plugin_functions(explicit_state) ->
+    {fun crypto:rand_seed_s/0,
+     fun rand:export_seed_s/1,
+     fun rand:uniform_s/1,
+     fun rand:uniform_s/2}.
+
+rand_plugin_aux_floats(State0, FloatGenerator) ->
+    {FloatSamples, State1} =
+        lists:mapfoldl(
+          fun (_, StateAcc) ->
+                  FloatGenerator(StateAcc)
+          end,
+          State0,
+          lists:seq(1, 10000)),
+
+    {allmap(
+       fun (V) ->
+               (V >= 0.0 andalso V < 1.0)
+               orelse {false, ct:fail({"Float sample not in interval", V, 0.0, 1.0})}
+       end,
+       FloatSamples),
+     State1}.
+
+rand_plugin_aux_integers(State0, IntegerGenerator) ->
+    MaxIntegerCeiling = 1 bsl 32,
+    {IntegerCeilings, State1} =
+        lists:mapfoldl(
+          fun (_, StateAcc) ->
+                  IntegerGenerator(MaxIntegerCeiling, StateAcc)
+          end,
+          State0,
+          lists:seq(1, 100)),
+
+    foldallmap(
+      fun (Ceiling, StateAcc) ->
+              case Ceiling >= 1 andalso Ceiling =< MaxIntegerCeiling of
+                  false ->
+                      {{false, ct:fail({"Integer ceiling not in interval",
+                                        Ceiling, 1, MaxIntegerCeiling})},
+                       StateAcc};
+                  true ->
+                      foldallmap(
+                        fun (_, SubStateAcc) ->
+                                {Sample, NewSubStateAcc} = IntegerGenerator(Ceiling, SubStateAcc),
+                                case Sample >= 1 andalso Sample =< Ceiling of
+                                    false ->
+                                        {{false, ct:fail({"Integer sample not in interval",
+                                                          Sample, 1, Ceiling})},
+                                         NewSubStateAcc};
+                                    true ->
+                                        {true, NewSubStateAcc}
+                                end
+                        end,
+                        StateAcc,
+                        lists:seq(1, 100))
+              end
+      end,
+      State1,
+      IntegerCeilings).
+
 %%--------------------------------------------------------------------
 %% Test data ------------------------------------------------
 %%--------------------------------------------------------------------
diff --git a/lib/stdlib/doc/src/rand.xml b/lib/stdlib/doc/src/rand.xml
index 8745e16908..2ddf3021ac 100644
--- a/lib/stdlib/doc/src/rand.xml
+++ b/lib/stdlib/doc/src/rand.xml
@@ -120,27 +120,50 @@ S0 = rand:seed_s(exsplus),
 {SND0, S2} = rand:normal_s(S1),</pre>
 
     <note>
-      <p>This random number generator is not cryptographically
-        strong. If a strong cryptographic random number generator is
-        needed, use one of functions in the
-        <seealso marker="crypto:crypto"><c>crypto</c></seealso>
-        module, for example, <seealso marker="crypto:crypto">
-        <c>crypto:strong_rand_bytes/1</c></seealso>.</p>
+      <p>The builtin random number generator algorithms are not
+        cryptographically strong. If a cryptographically strong
+        random number generator is needed, use something like
+        <seealso marker="crypto:crypto#rand_seed-0"><c>crypto:rand_seed/0</c></seealso>.
+      </p>
     </note>
 
   </description>
   <datatypes>
     <datatype>
+      <name name="builtin_alg"/>
+    </datatype>
+    <datatype>
       <name name="alg"/>
     </datatype>
     <datatype>
+      <name name="alg_handler"/>
+    </datatype>
+    <datatype>
+      <name name="alg_state"/>
+    </datatype>
+    <datatype>
+      <name name="exs64_state"/>
+      <desc><p>Algorithm specific internal state</p></desc>
+    </datatype>
+    <datatype>
+      <name name="exsplus_state"/>
+      <desc><p>Algorithm specific internal state</p></desc>
+    </datatype>
+    <datatype>
+      <name name="exs1024_state"/>
+      <desc><p>Algorithm specific internal state</p></desc>
+    </datatype>
+    <datatype>
       <name name="state"/>
       <desc><p>Algorithm-dependent state.</p></desc>
     </datatype>
     <datatype>
       <name name="export_state"/>
-      <desc><p>Algorithm-dependent state that can be printed or saved to
-        file.</p></desc>
+      <desc>
+	<p>
+	  Algorithm-dependent state that can be printed or saved to file.
+	</p>
+      </desc>
     </datatype>
   </datatypes>
 
@@ -215,8 +238,11 @@ S0 = rand:seed_s(exsplus),
       <fsummary>Seed random number generator.</fsummary>
       <desc>
         <marker id="seed-1"/>
-        <p>Seeds random number generation with the specifed algorithm and
-          time-dependent data if <anno>AlgOrExpState</anno> is an algorithm.</p>
+        <p>
+	  Seeds random number generation with the specifed algorithm and
+          time-dependent data if <c><anno>AlgOrStateOrExpState</anno></c>
+	  is an algorithm.
+	</p>
         <p>Otherwise recreates the exported seed in the process dictionary,
           and returns the state. See also
           <seealso marker="#export_seed-0"><c>export_seed/0</c></seealso>.</p>
@@ -236,8 +262,11 @@ S0 = rand:seed_s(exsplus),
       <name name="seed_s" arity="1"/>
       <fsummary>Seed random number generator.</fsummary>
       <desc>
-        <p>Seeds random number generation with the specifed algorithm and
-          time-dependent data if <anno>AlgOrExpState</anno> is an algorithm.</p>
+        <p>
+	  Seeds random number generation with the specifed algorithm and
+          time-dependent data if <c><anno>AlgOrStateOrExpState</anno></c>
+	  is an algorithm.
+	</p>
         <p>Otherwise recreates the exported seed and returns the state.
           See also <seealso marker="#export_seed-0">
           <c>export_seed/0</c></seealso>.</p>
@@ -258,7 +287,7 @@ S0 = rand:seed_s(exsplus),
       <fsummary>Return a random float.</fsummary>
       <desc><marker id="uniform-0"/>
         <p>Returns a random float uniformly distributed in the value
-          range <c>0.0 &lt; <anno>X</anno> &lt; 1.0</c> and
+          range <c>0.0 =&lt; <anno>X</anno> &lt; 1.0</c> and
           updates the state in the process dictionary.</p>
       </desc>
     </func>
@@ -269,7 +298,7 @@ S0 = rand:seed_s(exsplus),
       <desc><marker id="uniform-1"/>
         <p>Returns, for a specified integer <c><anno>N</anno> >= 1</c>,
           a random integer uniformly distributed in the value range
-          <c>1 &lt;= <anno>X</anno> &lt;= <anno>N</anno></c> and
+          <c>1 =&lt; <anno>X</anno> =&lt; <anno>N</anno></c> and
           updates the state in the process dictionary.</p>
       </desc>
     </func>
@@ -279,7 +308,7 @@ S0 = rand:seed_s(exsplus),
       <fsummary>Return a random float.</fsummary>
       <desc>
         <p>Returns, for a specified state, random float
-          uniformly distributed in the value range <c>0.0 &lt;
+          uniformly distributed in the value range <c>0.0 =&lt;
           <anno>X</anno> &lt; 1.0</c> and a new state.</p>
       </desc>
     </func>
@@ -290,7 +319,7 @@ S0 = rand:seed_s(exsplus),
       <desc>
         <p>Returns, for a specified integer <c><anno>N</anno> >= 1</c>
           and a state, a random integer uniformly distributed in the value
-          range <c>1 &lt;= <anno>X</anno> &lt;= <anno>N</anno></c> and a
+          range <c>1 =&lt; <anno>X</anno> =&lt; <anno>N</anno></c> and a
           new state.</p>
       </desc>
     </func>
diff --git a/lib/stdlib/src/rand.erl b/lib/stdlib/src/rand.erl
index 1f457b9e0e..dfd102f9ef 100644
--- a/lib/stdlib/src/rand.erl
+++ b/lib/stdlib/src/rand.erl
@@ -45,20 +45,31 @@
 %% =====================================================================
 
 %% This depends on the algorithm handler function
--type alg_seed() :: exs64_state() | exsplus_state() | exs1024_state().
+-type alg_state() ::
+        exs64_state() | exsplus_state() | exs1024_state() | term().
+
 %% This is the algorithm handler function within this module
--type alg_handler() :: #{type      := alg(),
-			 max       := integer(),
-			 next      := fun(),
-			 uniform   := fun(),
-			 uniform_n := fun(),
-			 jump      := fun()}.
-
-%% Internal state
--opaque state() :: {alg_handler(), alg_seed()}.
--type alg() :: exs64 | exsplus | exs1024.
--opaque export_state() :: {alg(), alg_seed()}.
--export_type([alg/0, state/0, export_state/0]).
+-type alg_handler() ::
+        #{type := alg(),
+          max  := integer() | infinity,
+          next :=
+              fun((alg_state()) -> {non_neg_integer(), alg_state()}),
+          uniform :=
+              fun((state()) -> {float(), state()}),
+          uniform_n :=
+              fun((pos_integer(), state()) -> {pos_integer(), state()}),
+          jump :=
+              fun((state()) -> state())}.
+
+%% Algorithm state
+-type state() :: {alg_handler(), alg_state()}.
+-type builtin_alg() :: exs64 | exsplus | exs1024.
+-type alg() :: builtin_alg() | atom().
+-type export_state() :: {alg(), alg_state()}.
+-export_type(
+   [builtin_alg/0, alg/0, alg_handler/0, alg_state/0,
+    state/0, export_state/0]).
+-export_type([exs64_state/0, exsplus_state/0, exs1024_state/0]).
 
 %% =====================================================================
 %% API
@@ -72,7 +83,7 @@ export_seed() ->
 	_ -> undefined
     end.
 
--spec export_seed_s(state()) -> export_state().
+-spec export_seed_s(State :: state()) -> export_state().
 export_seed_s({#{type:=Alg}, Seed}) -> {Alg, Seed}.
 
 %% seed(Alg) seeds RNG with runtime dependent values
@@ -81,27 +92,37 @@ export_seed_s({#{type:=Alg}, Seed}) -> {Alg, Seed}.
 %% seed({Alg,Seed}) setup RNG with a previously exported seed
 %% and return the NEW state
 
--spec seed(AlgOrExpState::alg() | export_state()) -> state().
+-spec seed(
+        AlgOrStateOrExpState :: builtin_alg() | state() | export_state()) ->
+                  state().
 seed(Alg) ->
     seed_put(seed_s(Alg)).
 
--spec seed_s(AlgOrExpState::alg() | export_state()) -> state().
-seed_s(Alg) when is_atom(Alg) ->
-    seed_s(Alg, {erlang:phash2([{node(),self()}]),
-		 erlang:system_time(),
-		 erlang:unique_integer()});
+-spec seed_s(
+        AlgOrStateOrExpState :: builtin_alg() | state() | export_state()) ->
+                    state().
+seed_s({AlgHandler, _Seed} = State) when is_map(AlgHandler) ->
+    State;
 seed_s({Alg0, Seed}) ->
     {Alg,_SeedFun} = mk_alg(Alg0),
-    {Alg, Seed}.
+    {Alg, Seed};
+seed_s(Alg) ->
+    seed_s(Alg, {erlang:phash2([{node(),self()}]),
+		 erlang:system_time(),
+		 erlang:unique_integer()}).
 
 %% seed/2: seeds RNG with the algorithm and given values
 %% and returns the NEW state.
 
--spec seed(Alg :: alg(), {integer(), integer(), integer()}) -> state().
+-spec seed(
+        Alg :: builtin_alg(), Seed :: {integer(), integer(), integer()}) ->
+                  state().
 seed(Alg0, S0) ->
     seed_put(seed_s(Alg0, S0)).
 
--spec seed_s(Alg :: alg(), {integer(), integer(), integer()}) -> state().
+-spec seed_s(
+        Alg :: builtin_alg(), Seed :: {integer(), integer(), integer()}) ->
+                    state().
 seed_s(Alg0, S0 = {_, _, _}) ->
     {Alg, Seed} = mk_alg(Alg0),
     AS = Seed(S0),
@@ -113,7 +134,7 @@ seed_s(Alg0, S0 = {_, _, _}) ->
 %% uniform/0: returns a random float X where 0.0 < X < 1.0,
 %% updating the state in the process dictionary.
 
--spec uniform() -> X::float().
+-spec uniform() -> X :: float().
 uniform() ->
     {X, Seed} = uniform_s(seed_get()),
     _ = seed_put(Seed),
@@ -123,7 +144,7 @@ uniform() ->
 %% uniform/1 returns a random integer X where 1 =< X =< N,
 %% updating the state in the process dictionary.
 
--spec uniform(N :: pos_integer()) -> X::pos_integer().
+-spec uniform(N :: pos_integer()) -> X :: pos_integer().
 uniform(N) ->
     {X, Seed} = uniform_s(N, seed_get()),
     _ = seed_put(Seed),
@@ -133,7 +154,7 @@ uniform(N) ->
 %% returns a random float X where 0.0 < X < 1.0,
 %% and a new state.
 
--spec uniform_s(state()) -> {X::float(), NewS :: state()}.
+-spec uniform_s(State :: state()) -> {X :: float(), NewState :: state()}.
 uniform_s(State = {#{uniform:=Uniform}, _}) ->
     Uniform(State).
 
@@ -141,7 +162,8 @@ uniform_s(State = {#{uniform:=Uniform}, _}) ->
 %% uniform_s/2 returns a random integer X where 1 =< X =< N,
 %% and a new state.
 
--spec uniform_s(N::pos_integer(), state()) -> {X::pos_integer(), NewS::state()}.
+-spec uniform_s(N :: pos_integer(), State :: state()) ->
+                       {X :: pos_integer(), NewState :: state()}.
 uniform_s(N, State = {#{uniform_n:=Uniform, max:=Max}, _})
   when 0 < N, N =< Max ->
     Uniform(N, State);
@@ -155,7 +177,7 @@ uniform_s(N, State0 = {#{uniform:=Uniform}, _})
 %% after a large number of call defined for each algorithm.
 %% The large number is algorithm dependent.
 
--spec jump(state()) -> NewS :: state().
+-spec jump(state()) -> NewState :: state().
 jump(State = {#{jump:=Jump}, _}) ->
     Jump(State).
 
@@ -164,7 +186,7 @@ jump(State = {#{jump:=Jump}, _}) ->
 %% and write back the new value to the internal state,
 %% then returns the new value.
 
--spec jump() -> NewS :: state().
+-spec jump() -> NewState :: state().
 
 jump() ->
     seed_put(jump(seed_get())).
@@ -182,7 +204,7 @@ normal() ->
 %% The Ziggurat Method for generating random variables - Marsaglia and Tsang
 %% Paper and reference code: http://www.jstatsoft.org/v05/i08/
 
--spec normal_s(state()) -> {float(), NewS :: state()}.
+-spec normal_s(State :: state()) -> {float(), NewState :: state()}.
 normal_s(State0) ->
     {Sign, R, State} = get_52(State0),
     Idx = R band 16#FF,
@@ -245,7 +267,7 @@ mk_alg(exs1024) ->
 %% Reference URL: http://xorshift.di.unimi.it/
 %% =====================================================================
 
--type exs64_state() :: uint64().
+-opaque exs64_state() :: uint64().
 
 exs64_seed({A1, A2, A3}) ->
     {V1, _} = exs64_next(((A1 band ?UINT32MASK) * 4294967197 + 1)),
@@ -280,7 +302,7 @@ exs64_jump(_) ->
 %% Modification of the original Xorshift128+ algorithm to 116
 %% by Sebastiano Vigna, a lot of thanks for his help and work.
 %% =====================================================================
--type exsplus_state() :: nonempty_improper_list(uint58(), uint58()).
+-opaque exsplus_state() :: nonempty_improper_list(uint58(), uint58()).
 
 -dialyzer({no_improper_lists, exsplus_seed/1}).
 
@@ -349,7 +371,7 @@ exsplus_jump(S, [AS0|AS1], J, N) ->
 %% Reference URL: http://xorshift.di.unimi.it/
 %% =====================================================================
 
--type exs1024_state() :: {list(uint64()), list(uint64())}.
+-opaque exs1024_state() :: {list(uint64()), list(uint64())}.
 
 exs1024_seed({A1, A2, A3}) ->
     B1 = (((A1 band ?UINT21MASK) + 1) * 2097131) band ?UINT21MASK,
diff --git a/lib/stdlib/test/rand_SUITE.erl b/lib/stdlib/test/rand_SUITE.erl
index fe5eaccda5..098eefeb61 100644
--- a/lib/stdlib/test/rand_SUITE.erl
+++ b/lib/stdlib/test/rand_SUITE.erl
@@ -356,14 +356,23 @@ basic_normal_1(0, {#{type:=Alg}, _}, Sum, SumSq) ->
 
 %% Test that the user can write algorithms.
 plugin(Config) when is_list(Config) ->
-    _ = lists:foldl(fun(_, S0) ->
-			    {V1, S1} = rand:uniform_s(10000, S0),
-			    true = is_integer(V1),
-			    {V2, S2} = rand:uniform_s(S1),
-			    true = is_float(V2),
-			    S2
-		    end, crypto_seed(), lists:seq(1, 200)),
-    ok.
+    try crypto:strong_rand_bytes(1) of
+        <<_>> ->
+            _ = lists:foldl(
+                  fun(_, S0) ->
+                          {V1, S1} = rand:uniform_s(10000, S0),
+                          true = is_integer(V1),
+                          {V2, S2} = rand:uniform_s(S1),
+                          true = is_float(V2),
+                          S2
+                  end, crypto_seed(), lists:seq(1, 200)),
+            ok
+    catch
+        error:low_entropy ->
+            {skip,low_entropy};
+        error:undef ->
+            {skip,no_crypto}
+    end.
 
 %% Test implementation
 crypto_seed() ->
@@ -397,7 +406,13 @@ crypto_uniform_n(N, State0) ->
 measure(Suite) when is_atom(Suite) -> [];
 measure(_Config) ->
     ct:timetrap({minutes,15}), %% valgrind needs a lot of time
-    Algos = [crypto64|algs()],
+    Algos =
+        try crypto:strong_rand_bytes(1) of
+            <<_>> -> [crypto64]
+        catch
+            error:low_entropy -> [];
+            error:undef -> []
+        end ++ algs(),
     io:format("RNG uniform integer performance~n",[]),
     _ = measure_1(random, fun(State) -> {int, random:uniform_s(10000, State)} end),
     _ = [measure_1(Algo, fun(State) -> {int, rand:uniform_s(10000, State)} end) || Algo <- Algos],