1 files changed, 133 insertions, 0 deletions
diff --git a/comm/third_party/botan/src/lib/math/mp/mp_monty.cpp b/comm/third_party/botan/src/lib/math/mp/mp_monty.cpp
new file mode 100644
index 0000000000..433d3ff358
--- /dev/null
+++ b/comm/third_party/botan/src/lib/math/mp/mp_monty.cpp
@@ -0,0 +1,133 @@
+/*
+* Montgomery Reduction
+* (C) 1999-2011 Jack Lloyd
+*     2006 Luca Piccarreta
+*     2016 Matthias Gierlings
+*
+* Botan is released under the Simplified BSD License (see license.txt)
+*/
+
+#include <botan/internal/mp_core.h>
+#include <botan/internal/mp_monty.h>
+#include <botan/internal/mp_madd.h>
+#include <botan/internal/mp_asmi.h>
+#include <botan/internal/ct_utils.h>
+#include <botan/mem_ops.h>
+#include <botan/exceptn.h>
+
+namespace Botan {
+
+namespace {
+
+/*
+* Montgomery reduction - product scanning form
+*
+* https://www.iacr.org/archive/ches2005/006.pdf
+* https://eprint.iacr.org/2013/882.pdf
+* https://www.microsoft.com/en-us/research/wp-content/uploads/1996/01/j37acmon.pdf
+*/
+void bigint_monty_redc_generic(word z[], size_t z_size,
+                               const word p[], size_t p_size, word p_dash,
+                               word ws[])
+   {
+   word w2 = 0, w1 = 0, w0 = 0;
+
+   w0 = z[0];
+
+   ws[0] = w0 * p_dash;
+
+   word3_muladd(&w2, &w1, &w0, ws[0], p[0]);
+
+   w0 = w1;
+   w1 = w2;
+   w2 = 0;
+
+   for(size_t i = 1; i != p_size; ++i)
+      {
+      for(size_t j = 0; j < i; ++j)
+         {
+         word3_muladd(&w2, &w1, &w0, ws[j], p[i-j]);
+         }
+
+      word3_add(&w2, &w1, &w0, z[i]);
+
+      ws[i] = w0 * p_dash;
+
+      word3_muladd(&w2, &w1, &w0, ws[i], p[0]);
+
+      w0 = w1;
+      w1 = w2;
+      w2 = 0;
+      }
+
+   for(size_t i = 0; i != p_size; ++i)
+      {
+      for(size_t j = i + 1; j != p_size; ++j)
+         {
+         word3_muladd(&w2, &w1, &w0, ws[j], p[p_size + i-j]);
+         }
+
+      word3_add(&w2, &w1, &w0, z[p_size+i]);
+
+      ws[i] = w0;
+      w0 = w1;
+      w1 = w2;
+      w2 = 0;
+      }
+
+   word3_add(&w2, &w1, &w0, z[z_size-1]);
+
+   ws[p_size] = w0;
+   ws[p_size+1] = w1;
+
+   /*
+   * The result might need to be reduced mod p. To avoid a timing
+   * channel, always perform the subtraction. If in the compution
+   * of x - p a borrow is required then x was already < p.
+   *
+   * x starts at ws[0] and is p_size+1 bytes long.
+   * x - p starts at ws[p_size+1] and is also p_size+1 bytes log
+   *
+   * Select which address to copy from indexing off of the final
+   * borrow.
+   */
+
+   // word borrow = bigint_sub3(ws + p_size + 1, ws, p_size + 1, p, p_size);
+   word borrow = 0;
+   for(size_t i = 0; i != p_size; ++i)
+      ws[p_size + 1 + i] = word_sub(ws[i], p[i], &borrow);
+   ws[2*p_size+1] = word_sub(ws[p_size], 0, &borrow);
+
+   BOTAN_DEBUG_ASSERT(borrow == 0 || borrow == 1);
+
+   CT::conditional_copy_mem(borrow, z, ws, ws + (p_size + 1), (p_size + 1));
+   clear_mem(z + p_size, z_size - p_size - 2);
+   }
+
+}
+
+void bigint_monty_redc(word z[],
+                       const word p[], size_t p_size, word p_dash,
+                       word ws[], size_t ws_size)
+   {
+   const size_t z_size = 2*(p_size+1);
+
+   BOTAN_ARG_CHECK(ws_size >= z_size, "workspace too small");
+
+   if(p_size == 4)
+      bigint_monty_redc_4(z, p, p_dash, ws);
+   else if(p_size == 6)
+      bigint_monty_redc_6(z, p, p_dash, ws);
+   else if(p_size == 8)
+      bigint_monty_redc_8(z, p, p_dash, ws);
+   else if(p_size == 16)
+      bigint_monty_redc_16(z, p, p_dash, ws);
+   else if(p_size == 24)
+      bigint_monty_redc_24(z, p, p_dash, ws);
+   else if(p_size == 32)
+      bigint_monty_redc_32(z, p, p_dash, ws);
+   else
+      bigint_monty_redc_generic(z, z_size, p, p_size, p_dash, ws);
+   }
+
+}