[Cryptech-Commits] [core/rng/trng] 01/01: Adding a stat counter for number of CSPRNG reseeds.

[git at cryptech.is]

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joachim at secworks.se pushed a commit to branch master
in repository core/rng/trng.

commit 173d61b457da53a4dec607113df76ebd35a56d40
Author: Joachim Strömbergson <joachim at secworks.se>
Date:   Thu Aug 20 15:20:54 2015 +0200

    Adding a stat counter for number of CSPRNG reseeds.
---
 src/rtl/trng_csprng.v | 46 +++++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 41 insertions(+), 5 deletions(-)

diff --git a/src/rtl/trng_csprng.v b/src/rtl/trng_csprng.v
index ce5c89c..208feb1 100644
--- a/src/rtl/trng_csprng.v
+++ b/src/rtl/trng_csprng.v
@@ -78,6 +78,7 @@ module trng_csprng(
 
   localparam ADDR_STAT_BLOCKS_LOW  = 8'h14;
   localparam ADDR_STAT_BLOCKS_HIGH = 8'h15;
+  localparam ADDR_STAT_RESEEDS     = 8'h16;
 
   localparam ADDR_RND_DATA         = 8'h20;
 
@@ -153,6 +154,11 @@ module trng_csprng(
   reg [63 : 0]  block_stat_ctr_reg;
   reg [63 : 0]  block_stat_ctr_new;
 
+  reg [31 : 0]  reseed_stat_ctr_reg;
+  reg [31 : 0]  reseed_stat_ctr_new;
+  reg           reseed_stat_ctr_inc;
+  reg           reseed_stat_ctr_we;
+
   reg           ready_reg;
   reg           ready_new;
   reg           ready_we;
@@ -279,6 +285,7 @@ module trng_csprng(
           cipher_block_reg    <= {16{32'h00000000}};
           block_ctr_reg       <= {2{32'h00000000}};
           block_stat_ctr_reg  <= {2{32'h00000000}};
+          reseed_stat_ctr_reg <= 32'h00000000;
           more_seed_reg       <= 0;
           seed_ack_reg        <= 0;
           ready_reg           <= 0;
@@ -316,6 +323,9 @@ module trng_csprng(
               block_stat_ctr_reg <= block_stat_ctr_new;
             end
 
+          if (reseed_stat_ctr_we)
+            reseed_stat_ctr_reg <= reseed_stat_ctr_new;
+
           if (ready_we)
             ready_reg <= ready_new;
 
@@ -421,6 +431,9 @@ module trng_csprng(
                 ADDR_STAT_BLOCKS_HIGH:
                     tmp_read_data = block_stat_ctr_reg[63 : 32];
 
+                ADDR_STAT_RESEEDS:
+                    tmp_read_data = reseed_stat_ctr_reg;
+
                 ADDR_RND_DATA:
                   begin
                     tmp_read_data = rnd_data;
@@ -453,7 +466,7 @@ module trng_csprng(
   // ability to detect that maximum allowed number of blocks
   // has been reached. Either as defined by the application
   // or the hard coded CIPHER_MAX_BLOCKS value.
-
+  //
   // The stat counter is a sepatate block counter updated in
   // sync with the block counter. It is only used to track the
   // number of blocks generated from the cipher as a metric
@@ -488,6 +501,27 @@ module trng_csprng(
 
 
   //----------------------------------------------------------------
+  // reseed_ctr
+  //
+  // A simple monotonically increasing counter that counts the
+  // number of times the CSPRNG has been reseeded. is reseeded.
+  // Note that the counter is 32-bit and it is up to SW to handle
+  // wrap around issues.
+  //----------------------------------------------------------------
+  always @*
+    begin : reseed_ctr
+      reseed_stat_ctr_new = 32'h00000000;
+      reseed_stat_ctr_we  = 0;
+
+      if (reseed_stat_ctr_inc)
+        begin
+          reseed_stat_ctr_new = reseed_stat_ctr_reg + 1'b1;
+          reseed_stat_ctr_we  = 1;
+        end
+    end // reseed_ctr
+
+
+  //----------------------------------------------------------------
   // csprng_ctrl_fsm
   //
   // Control FSM for the CSPRNG.
@@ -512,6 +546,7 @@ module trng_csprng(
       more_seed_new          = 0;
       fifo_discard           = 0;
       fifo_cipher_data_valid = 0;
+      reseed_stat_ctr_inc    = 0;
       csprng_ctrl_new        = CTRL_IDLE;
       csprng_ctrl_we         = 0;
 
@@ -597,10 +632,11 @@ module trng_csprng(
               end
             else
               begin
-                cipher_init     = 1;
-                block_ctr_rst   = 1;
-                csprng_ctrl_new = CTRL_INIT1;
-                csprng_ctrl_we  = 1;
+                reseed_stat_ctr_inc = 1;
+                cipher_init         = 1;
+                block_ctr_rst       = 1;
+                csprng_ctrl_new     = CTRL_INIT1;
+                csprng_ctrl_we      = 1;
               end
           end