Support generation of strong random numbers

1 files changed, 38 insertions, 1 deletions

diff --git a/lib/crypto/src/crypto.erl b/lib/crypto/src/crypto.erl
index 631af62615..4b386924cb 100644
--- a/lib/crypto/src/crypto.erl
+++ b/lib/crypto/src/crypto.erl
@@ -30,6 +30,8 @@
 -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([strong_rand_uniform/0]).
+-export([strong_rand_uniform/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]).
@@ -283,9 +285,11 @@ 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 strong_rand_uniform() -> float().
+-spec strong_rand_uniform(pos_integer()) -> pos_integer().
 -spec rand_uniform(crypto_integer(), crypto_integer()) ->
 			  crypto_integer().
 
@@ -297,6 +301,38 @@ strong_rand_bytes(Bytes) ->
 strong_rand_bytes_nif(_Bytes) -> ?nif_stub.
 
 
+strong_rand_uniform() ->
+    Sign = 0, % positive
+    Exponent = 1023, % on the interval [1.0, 2.0[
+    Fraction = strong_rand_uniform(1, 1 bsl 52), % the whole interval above (except 1.0)
+    <<Value:64/big-float>> = <<Sign:1, Exponent:11, Fraction:52>>,
+    Value - 1.0.
+
+strong_rand_uniform(N) when is_integer(N), N >= 1 ->
+    1 + strong_rand_uniform(0, N).
+
+strong_rand_uniform(From, To) when is_binary(From), is_binary(To) ->
+    case strong_rand_uniform_nif(From,To) of
+        false ->
+            erlang:error(low_entropy);
+        <<Len:32/integer, MSB, Rest/binary>> when MSB > 127 ->
+            <<(Len + 1):32/integer, 0, MSB, Rest/binary>>;
+        Whatever ->
+            Whatever
+    end;
+strong_rand_uniform(From, To) when is_integer(From), is_integer(To), From < To ->
+    BinFrom = mpint(From),
+    BinTo = mpint(To),
+    case strong_rand_uniform(BinFrom, BinTo) of
+        Result when is_binary(Result) ->
+            erlint(Result);
+        Other ->
+            Other
+    end.
+
+strong_rand_uniform_nif(_From, _To) -> ?nif_stub.
+
+
 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 ->
@@ -325,6 +361,7 @@ rand_uniform_pos(_,_) ->
 
 rand_uniform_nif(_From,_To) -> ?nif_stub.
 
+
 -spec rand_seed(binary()) -> ok.
 rand_seed(Seed) ->
     rand_seed_nif(Seed).