ECP multiplication using windowed algorithm

CHANGELOG.md

@@ -26,6 +26,8 @@ Given a version number MAJOR.MINOR.PATCH
 
 - ECP core arithmetic (add,dbl,mul)
 - Load NIST-P256 EC parameters
+- DSA end ECDSA digital signature
+- ECP multiplication with windowed algorithm
 
 [0.0.5] - 2016-10-02
 --------------------

README.md

@@ -42,6 +42,12 @@ Public key algorithms
 
 - Diffie-Hellman
 
+### Digital signature
+
+- RSA (PKCS#1 v1.5)
+- DSA
+- ECDSA
+
 
 Elliptic Curve
 --------------

config.mk

@@ -26,7 +26,7 @@ CRY_DEBUG=y
 
 # Use one octet digit in place of sizeof(unsigned long) octets.
 # Warning: NO ADVANTAGES, just for testing purposes
-CRY_MPI_SMALL_DIGIT=y
+#CRY_MPI_SMALL_DIGIT=y
 
 # Options: aes|weak|posix|win
 CRY_PRNG=aes
@@ -44,3 +44,6 @@ CRY_MPI_MUL_COMBA=y
 # Karatsuba multiplier enabled, see the mpi_mul.c to set the CUTOFF
 CRY_MPI_MUL_KARATSUBA=y
 
+# Elliptic curve point multiplication with windowed algorithm (faster)
+CRY_ECP_MUL_WIN=y
+

src/ecp/ecp_mul.c

@@ -19,6 +19,94 @@
 
 #include "cry/ecp.h"
 #include "mpi/mpi_pvt.h" /* CRY_MPI_DIGIT_BITS */
+#include <stdlib.h>      /* malloc() */
+
+#define CHK(exp) do { if ((res = (exp)) != 0) goto e; } while (0)
+
+#ifdef CRY_ECP_MUL_WIN
+
+#define WINSIZ      4
+#define WINPTS      (1 << WINSIZ)
+#define WINMSK      (WINPTS-1)
+
+int cry_ecp_mul(cry_ecp *pr, const cry_ecp *p1, const cry_mpi *k,
+                const cry_mpi *a, const cry_mpi *p)
+{
+    int res, i, j, w, paf = 1;
+    struct cry_ecp r, *win = NULL;
+    cry_mpi_digit msk;
+
+    if ((res = cry_ecp_init(&r)) != 0)
+        return res;
+
+    /*
+     * BEGIN window generation
+     */
+    win = malloc(sizeof(cry_ecp) * WINPTS);
+    if (win == NULL)
+        goto e0;
+    for (i = 0; i < WINPTS; i++) {
+        if ((res = cry_ecp_init(&win[i])) != 0) {  // 0P
+            while (i-- > 0) /* rollback */
+                cry_ecp_clear(&win[i]);
+            goto e1;
+        }
+    }
+    CHK(cry_ecp_copy(&win[1], p1));                     // 1P
+    CHK(cry_ecp_dbl(&win[2],  &win[1], a, p));          // 2P
+    CHK(cry_ecp_add(&win[3],  &win[2], &win[1], p));    // 3P
+    CHK(cry_ecp_dbl(&win[4],  &win[2], a, p));          // 4P
+    CHK(cry_ecp_add(&win[5],  &win[4], &win[1], p));    // 5P
+    CHK(cry_ecp_add(&win[6],  &win[5], &win[1], p));    // 6P
+    CHK(cry_ecp_add(&win[7],  &win[6], &win[1], p));    // 7P
+    CHK(cry_ecp_dbl(&win[8],  &win[4], a, p));          // 8P
+    CHK(cry_ecp_add(&win[9],  &win[8], &win[1], p));    // 9P
+    CHK(cry_ecp_add(&win[10], &win[9], &win[1], p));    // 10P
+    CHK(cry_ecp_add(&win[11], &win[10], &win[1], p));   // 11P
+    CHK(cry_ecp_add(&win[12], &win[11], &win[1], p));   // 12P
+    CHK(cry_ecp_add(&win[13], &win[12], &win[1], p));   // 13P
+    CHK(cry_ecp_add(&win[14], &win[13], &win[1], p));   // 14P
+    CHK(cry_ecp_add(&win[15], &win[14], &win[1], p));   // 15P
+    /*
+     * END window generation
+     */
+
+    i = k->used;
+    while (i > 0) {
+        i--;
+        w = (CRY_MPI_DIGIT_BITS - WINSIZ);
+        msk = ((cry_mpi_digit)WINMSK) << w;
+        j = CRY_MPI_DIGIT_BITS;
+        while (j > 0) {
+            if (!paf) {
+                for (w = 0; w < WINSIZ; w++)
+                    CHK(cry_ecp_dbl(&r, &r, a, p));
+            }
+
+            j -= WINSIZ;
+            w = (k->data[i] & msk) >> j;
+            if (w > 0) {
+                if (!paf) {
+                    CHK(cry_ecp_add(&r, &r, &win[w], p));
+                } else {
+                    paf = 0; /* First addition */
+                    CHK(cry_ecp_copy(&r, &win[w]));
+                }
+            }
+            msk >>= WINSIZ;
+        }
+    }
+    /* Success */
+    cry_ecp_swap(pr, &r);
+
+e:  for (i = 0; i < WINPTS; i++)
+        cry_ecp_clear(&win[i]);
+e1: free(win);
+e0: cry_ecp_clear(&r);
+    return res;
+}
+
+#else /* !CRY_ECP_MUL_WIN */
 
 int cry_ecp_mul(cry_ecp *pr, const cry_ecp *p1, const cry_mpi *k,
                 const cry_mpi *a, const cry_mpi *p)
@@ -58,3 +146,5 @@ e:  cry_mpi_clear_list(&dp.x, &dp.y, &r.x, &r.y, 0);
     return res;
 }
 
+#endif /* CRY_ECP_MUL_WIN */
+