1 files changed, 68 insertions, 0 deletions
diff --git a/security/nss/lib/freebl/ecl/ec_naf.c b/security/nss/lib/freebl/ecl/ec_naf.c
new file mode 100644
index 0000000000..cad08cb278
--- /dev/null
+++ b/security/nss/lib/freebl/ecl/ec_naf.c
@@ -0,0 +1,68 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "ecl-priv.h"
+
+/* Returns 2^e as an integer. This is meant to be used for small powers of
+ * two. */
+int
+ec_twoTo(int e)
+{
+    int a = 1;
+    int i;
+
+    for (i = 0; i < e; i++) {
+        a *= 2;
+    }
+    return a;
+}
+
+/* Computes the windowed non-adjacent-form (NAF) of a scalar. Out should
+ * be an array of signed char's to output to, bitsize should be the number
+ * of bits of out, in is the original scalar, and w is the window size.
+ * NAF is discussed in the paper: D. Hankerson, J. Hernandez and A.
+ * Menezes, "Software implementation of elliptic curve cryptography over
+ * binary fields", Proc. CHES 2000. */
+mp_err
+ec_compute_wNAF(signed char *out, int bitsize, const mp_int *in, int w)
+{
+    mp_int k;
+    mp_err res = MP_OKAY;
+    int i, twowm1, mask;
+
+    twowm1 = ec_twoTo(w - 1);
+    mask = 2 * twowm1 - 1;
+
+    MP_DIGITS(&k) = 0;
+    MP_CHECKOK(mp_init_copy(&k, in));
+
+    i = 0;
+    /* Compute wNAF form */
+    while (mp_cmp_z(&k) > 0) {
+        if (mp_isodd(&k)) {
+            out[i] = MP_DIGIT(&k, 0) & mask;
+            if (out[i] >= twowm1)
+                out[i] -= 2 * twowm1;
+
+            /* Subtract off out[i].  Note mp_sub_d only works with
+             * unsigned digits */
+            if (out[i] >= 0) {
+                MP_CHECKOK(mp_sub_d(&k, out[i], &k));
+            } else {
+                MP_CHECKOK(mp_add_d(&k, -(out[i]), &k));
+            }
+        } else {
+            out[i] = 0;
+        }
+        MP_CHECKOK(mp_div_2(&k, &k));
+        i++;
+    }
+    /* Zero out the remaining elements of the out array. */
+    for (; i < bitsize + 1; i++) {
+        out[i] = 0;
+    }
+CLEANUP:
+    mp_clear(&k);
+    return res;
+}