diff --git a/crypto/ec/curve25519.c b/crypto/ec/curve25519.c
index ee0634fe86..d1c725fa39 100644
--- a/crypto/ec/curve25519.c
+++ b/crypto/ec/curve25519.c
@@ -1,5 +1,5 @@
 /*
- * Copyright 2016 The OpenSSL Project Authors. All Rights Reserved.
+ * Copyright 2016-2017 The OpenSSL Project Authors. All Rights Reserved.
  *
  * Licensed under the OpenSSL license (the "License").  You may not use
  * this file except in compliance with the License.  You can obtain a copy
@@ -7,15 +7,489 @@
  * https://www.openssl.org/source/license.html
  */
 
-/* This code is mostly taken from the ref10 version of Ed25519 in SUPERCOP
- * 20141124 (http://bench.cr.yp.to/supercop.html).
- *
- * The field functions are shared by Ed25519 and X25519 where possible. */
-
 #include <string.h>
 #include "ec_lcl.h"
 #include <openssl/sha.h>
 
+#if !defined(PEDANTIC) && \
+    (defined(__SIZEOF_INT128__) && __SIZEOF_INT128__==16)
+/*
+ * Base 2^51 implementation.
+ */
+# define BASE_2_51_IMPLEMENTED
+
+typedef uint64_t fe51[5];
+typedef unsigned __int128 u128;
+
+static const uint64_t MASK51 = 0x7ffffffffffff;
+
+static uint64_t load_7(const uint8_t *in)
+{
+    uint64_t result;
+
+    result = in[0];
+    result |= ((uint64_t)in[1]) << 8;
+    result |= ((uint64_t)in[2]) << 16;
+    result |= ((uint64_t)in[3]) << 24;
+    result |= ((uint64_t)in[4]) << 32;
+    result |= ((uint64_t)in[5]) << 40;
+    result |= ((uint64_t)in[6]) << 48;
+
+    return result;
+}
+
+static uint64_t load_6(const uint8_t *in)
+{
+    uint64_t result;
+
+    result = in[0];
+    result |= ((uint64_t)in[1]) << 8;
+    result |= ((uint64_t)in[2]) << 16;
+    result |= ((uint64_t)in[3]) << 24;
+    result |= ((uint64_t)in[4]) << 32;
+    result |= ((uint64_t)in[5]) << 40;
+
+    return result;
+}
+
+static void fe51_frombytes(fe51 h, const uint8_t *s)
+{
+    uint64_t h0 = load_7(s);                                /* 56 bits */
+    uint64_t h1 = load_6(s + 7) << 5;                       /* 53 bits */
+    uint64_t h2 = load_7(s + 13) << 2;                      /* 58 bits */
+    uint64_t h3 = load_6(s + 20) << 7;                      /* 55 bits */
+    uint64_t h4 = (load_6(s + 26) & 0x7fffffffffff) << 4;   /* 51 bits */
+
+    h1 |= h0 >> 51; h0 &= MASK51;
+    h2 |= h1 >> 51; h1 &= MASK51;
+    h3 |= h2 >> 51; h2 &= MASK51;
+    h4 |= h3 >> 51; h3 &= MASK51;
+
+    h[0] = h0;
+    h[1] = h1;
+    h[2] = h2;
+    h[3] = h3;
+    h[4] = h4;
+}
+
+static void fe51_tobytes(uint8_t *s, const fe51 h)
+{
+    uint64_t h0 = h[0];
+    uint64_t h1 = h[1];
+    uint64_t h2 = h[2];
+    uint64_t h3 = h[3];
+    uint64_t h4 = h[4];
+    uint64_t q;
+
+    /* compare to modulus */
+    q = (h0 + 19) >> 51;
+    q = (h1 + q) >> 51;
+    q = (h2 + q) >> 51;
+    q = (h3 + q) >> 51;
+    q = (h4 + q) >> 51;
+
+    /* full reduce */
+    h0 += 19 * q;
+    h1 += h0 >> 51; h0 &= MASK51;
+    h2 += h1 >> 51; h1 &= MASK51;
+    h3 += h2 >> 51; h2 &= MASK51;
+    h4 += h3 >> 51; h3 &= MASK51;
+                    h4 &= MASK51;
+
+    /* smash */
+    s[0] = h0 >> 0;
+    s[1] = h0 >> 8;
+    s[2] = h0 >> 16;
+    s[3] = h0 >> 24;
+    s[4] = h0 >> 32;
+    s[5] = h0 >> 40;
+    s[6] = (h0 >> 48) | ((uint32_t)h1 << 3);
+    s[7] = h1 >> 5;
+    s[8] = h1 >> 13;
+    s[9] = h1 >> 21;
+    s[10] = h1 >> 29;
+    s[11] = h1 >> 37;
+    s[12] = (h1 >> 45) | ((uint32_t)h2 << 6);
+    s[13] = h2 >> 2;
+    s[14] = h2 >> 10;
+    s[15] = h2 >> 18;
+    s[16] = h2 >> 26;
+    s[17] = h2 >> 34;
+    s[18] = h2 >> 42;
+    s[19] = (h2 >> 50) | ((uint32_t)h3 << 1);
+    s[20] = h3 >> 7;
+    s[21] = h3 >> 15;
+    s[22] = h3 >> 23;
+    s[23] = h3 >> 31;
+    s[24] = h3 >> 39;
+    s[25] = (h3 >> 47) | ((uint32_t)h4 << 4);
+    s[26] = h4 >> 4;
+    s[27] = h4 >> 12;
+    s[28] = h4 >> 20;
+    s[29] = h4 >> 28;
+    s[30] = h4 >> 36;
+    s[31] = h4 >> 44;
+}
+
+static void fe51_mul(fe51 h, const fe51 f, const fe51 g)
+{
+    u128 h0, h1, h2, h3, h4;
+    uint64_t f_i, g0, g1, g2, g3, g4;
+
+    f_i = f[0];
+    h0 = (u128)f_i * (g0 = g[0]);
+    h1 = (u128)f_i * (g1 = g[1]);
+    h2 = (u128)f_i * (g2 = g[2]);
+    h3 = (u128)f_i * (g3 = g[3]);
+    h4 = (u128)f_i * (g4 = g[4]);
+
+    f_i = f[1];
+    h0 += (u128)f_i * (g4 *= 19);
+    h1 += (u128)f_i * g0;
+    h2 += (u128)f_i * g1;
+    h3 += (u128)f_i * g2;
+    h4 += (u128)f_i * g3;
+
+    f_i = f[2];
+    h0 += (u128)f_i * (g3 *= 19);
+    h1 += (u128)f_i * g4;
+    h2 += (u128)f_i * g0;
+    h3 += (u128)f_i * g1;
+    h4 += (u128)f_i * g2;
+
+    f_i = f[3];
+    h0 += (u128)f_i * (g2 *= 19);
+    h1 += (u128)f_i * g3;
+    h2 += (u128)f_i * g4;
+    h3 += (u128)f_i * g0;
+    h4 += (u128)f_i * g1;
+
+    f_i = f[4];
+    h0 += (u128)f_i * (g1 *= 19);
+    h1 += (u128)f_i * g2;
+    h2 += (u128)f_i * g3;
+    h3 += (u128)f_i * g4;
+    h4 += (u128)f_i * g0;
+
+    /* partial [lazy] reduction */
+    h3 += (uint64_t)(h2 >> 51); g2 = (uint64_t)h2 & MASK51;
+    h1 += (uint64_t)(h0 >> 51); g0 = (uint64_t)h0 & MASK51;
+
+    h4 += (uint64_t)(h3 >> 51); g3 = (uint64_t)h3 & MASK51;
+    g2 += (uint64_t)(h1 >> 51); g1 = (uint64_t)h1 & MASK51;
+
+    g0 += (uint64_t)(h4 >> 51) * 19; g4 = (uint64_t)h4 & MASK51;
+    g3 += g2 >> 51; g2 &= MASK51;
+    g1 += g0 >> 51; g0 &= MASK51;
+
+    h[0] = g0;
+    h[1] = g1;
+    h[2] = g2;
+    h[3] = g3;
+    h[4] = g4;
+}
+
+static void fe51_sq(fe51 h, const fe51 f)
+{
+# if defined(OPENSSL_SMALL_FOOTPRINT)
+    fe51_mul(h, f, f);
+# else
+    /* dedicated squaring gives 16-25% overall improvement */
+    uint64_t g0 = f[0];
+    uint64_t g1 = f[1];
+    uint64_t g2 = f[2];
+    uint64_t g3 = f[3];
+    uint64_t g4 = f[4];
+    u128 h0, h1, h2, h3, h4;
+
+    h0 = (u128)g0 * g0;     g0 *= 2;
+    h1 = (u128)g0 * g1;
+    h2 = (u128)g0 * g2;
+    h3 = (u128)g0 * g3;
+    h4 = (u128)g0 * g4;
+
+    g0 = g4;                /* borrow g0 */
+    h3 += (u128)g0 * (g4 *= 19);
+
+    h2 += (u128)g1 * g1;    g1 *= 2;
+    h3 += (u128)g1 * g2;
+    h4 += (u128)g1 * g3;
+    h0 += (u128)g1 * g4;
+
+    g0 = g3;                /* borrow g0 */
+    h1 += (u128)g0 * (g3 *= 19);
+    h2 += (u128)(g0 * 2) * g4;
+
+    h4 += (u128)g2 * g2;    g2 *= 2;
+    h0 += (u128)g2 * g3;
+    h1 += (u128)g2 * g4;
+
+    /* partial [lazy] reduction */
+    h3 += (uint64_t)(h2 >> 51); g2 = (uint64_t)h2 & MASK51;
+    h1 += (uint64_t)(h0 >> 51); g0 = (uint64_t)h0 & MASK51;
+
+    h4 += (uint64_t)(h3 >> 51); g3 = (uint64_t)h3 & MASK51;
+    g2 += (uint64_t)(h1 >> 51); g1 = (uint64_t)h1 & MASK51;
+
+    g0 += (uint64_t)(h4 >> 51) * 19; g4 = (uint64_t)h4 & MASK51;
+    g3 += g2 >> 51; g2 &= MASK51;
+    g1 += g0 >> 51; g0 &= MASK51;
+
+    h[0] = g0;
+    h[1] = g1;
+    h[2] = g2;
+    h[3] = g3;
+    h[4] = g4;
+# endif
+}
+
+static void fe51_add(fe51 h, const fe51 f, const fe51 g)
+{
+    h[0] = f[0] + g[0];
+    h[1] = f[1] + g[1];
+    h[2] = f[2] + g[2];
+    h[3] = f[3] + g[3];
+    h[4] = f[4] + g[4];
+}
+
+static void fe51_sub(fe51 h, const fe51 f, const fe51 g)
+{
+    /*
+     * Add 2*modulus to ensure that result remains positive
+     * even if subtrahend is partially reduced.
+     */
+    h[0] = (f[0] + 0xfffffffffffda) - g[0];
+    h[1] = (f[1] + 0xffffffffffffe) - g[1];
+    h[2] = (f[2] + 0xffffffffffffe) - g[2];
+    h[3] = (f[3] + 0xffffffffffffe) - g[3];
+    h[4] = (f[4] + 0xffffffffffffe) - g[4];
+}
+
+static void fe51_0(fe51 h)
+{
+    h[0] = 0;
+    h[1] = 0;
+    h[2] = 0;
+    h[3] = 0;
+    h[4] = 0;
+}
+
+static void fe51_1(fe51 h)
+{
+    h[0] = 1;
+    h[1] = 0;
+    h[2] = 0;
+    h[3] = 0;
+    h[4] = 0;
+}
+
+static void fe51_copy(fe51 h, const fe51 f)
+{
+    h[0] = f[0];
+    h[1] = f[1];
+    h[2] = f[2];
+    h[3] = f[3];
+    h[4] = f[4];
+}
+
+static void fe51_cswap(fe51 f, fe51 g, unsigned int b)
+{
+    int i;
+    uint64_t mask = 0 - (uint64_t)b;
+
+    for (i = 0; i < 5; i++) {
+        int64_t x = f[i] ^ g[i];
+        x &= mask;
+        f[i] ^= x;
+        g[i] ^= x;
+    }
+}
+
+static void fe51_invert(fe51 out, const fe51 z)
+{
+    fe51 t0;
+    fe51 t1;
+    fe51 t2;
+    fe51 t3;
+    int i;
+
+    /*
+     * Compute z ** -1 = z ** (2 ** 255 - 19 - 2) with the exponent as
+     * 2 ** 255 - 21 = (2 ** 5) * (2 ** 250 - 1) + 11.
+     */
+
+    /* t0 = z ** 2 */
+    fe51_sq(t0, z);
+
+    /* t1 = t0 ** (2 ** 2) = z ** 8 */
+    fe51_sq(t1, t0);
+    fe51_sq(t1, t1);
+
+    /* t1 = z * t1 = z ** 9 */
+    fe51_mul(t1, z, t1);
+    /* t0 = t0 * t1 = z ** 11 -- stash t0 away for the end. */
+    fe51_mul(t0, t0, t1);
+
+    /* t2 = t0 ** 2 = z ** 22 */
+    fe51_sq(t2, t0);
+
+    /* t1 = t1 * t2 = z ** (2 ** 5 - 1) */
+    fe51_mul(t1, t1, t2);
+
+    /* t2 = t1 ** (2 ** 5) = z ** ((2 ** 5) * (2 ** 5 - 1)) */
+    fe51_sq(t2, t1);
+    for (i = 1; i < 5; ++i)
+        fe51_sq(t2, t2);
+
+    /* t1 = t1 * t2 = z ** ((2 ** 5 + 1) * (2 ** 5 - 1)) = z ** (2 ** 10 - 1) */
+    fe51_mul(t1, t2, t1);
+
+    /* Continuing similarly... */
+
+    /* t2 = z ** (2 ** 20 - 1) */
+    fe51_sq(t2, t1);
+    for (i = 1; i < 10; ++i)
+        fe51_sq(t2, t2);
+
+    fe51_mul(t2, t2, t1);
+
+    /* t2 = z ** (2 ** 40 - 1) */
+    fe51_sq(t3, t2);
+    for (i = 1; i < 20; ++i)
+        fe51_sq(t3, t3);
+
+    fe51_mul(t2, t3, t2);
+
+    /* t2 = z ** (2 ** 10) * (2 ** 40 - 1) */
+    for (i = 0; i < 10; ++i)
+        fe51_sq(t2, t2);
+
+    /* t1 = z ** (2 ** 50 - 1) */
+    fe51_mul(t1, t2, t1);
+
+    /* t2 = z ** (2 ** 100 - 1) */
+    fe51_sq(t2, t1);
+    for (i = 1; i < 50; ++i)
+        fe51_sq(t2, t2);
+
+    fe51_mul(t2, t2, t1);
+
+    /* t2 = z ** (2 ** 200 - 1) */
+    fe51_sq(t3, t2);
+    for (i = 1; i < 100; ++i)
+        fe51_sq(t3, t3);
+
+    fe51_mul(t2, t3, t2);
+
+    /* t2 = z ** ((2 ** 50) * (2 ** 200 - 1) */
+    for (i = 0; i < 50; ++i)
+        fe51_sq(t2, t2);
+
+    /* t1 = z ** (2 ** 250 - 1) */
+    fe51_mul(t1, t2, t1);
+
+    /* t1 = z ** ((2 ** 5) * (2 ** 250 - 1)) */
+    for (i = 0; i < 5; ++i)
+        fe51_sq(t1, t1);
+
+    /* Recall t0 = z ** 11; out = z ** (2 ** 255 - 21) */
+    fe51_mul(out, t1, t0);
+}
+
+static void fe51_mul121666(fe51 h, fe51 f)
+{
+    u128 h0 = f[0] * (u128)121666;
+    u128 h1 = f[1] * (u128)121666;
+    u128 h2 = f[2] * (u128)121666;
+    u128 h3 = f[3] * (u128)121666;
+    u128 h4 = f[4] * (u128)121666;
+    uint64_t g0, g1, g2, g3, g4;
+
+    h3 += (uint64_t)(h2 >> 51); g2 = (uint64_t)h2 & MASK51;
+    h1 += (uint64_t)(h0 >> 51); g0 = (uint64_t)h0 & MASK51;
+
+    h4 += (uint64_t)(h3 >> 51); g3 = (uint64_t)h3 & MASK51;
+    g2 += (uint64_t)(h1 >> 51); g1 = (uint64_t)h1 & MASK51;
+
+    g0 += (uint64_t)(h4 >> 51) * 19; g4 = (uint64_t)h4 & MASK51;
+    g3 += g2 >> 51; g2 &= MASK51;
+    g1 += g0 >> 51; g0 &= MASK51;
+
+    h[0] = g0;
+    h[1] = g1;
+    h[2] = g2;
+    h[3] = g3;
+    h[4] = g4;
+}
+
+/*
+ * Duplicate of original x25519_scalar_mult_generic, but using
+ * fe51_* subroutines.
+ */
+static void x25519_scalar_mult(uint8_t out[32], const uint8_t scalar[32],
+                               const uint8_t point[32])
+{
+    fe51 x1, x2, z2, x3, z3, tmp0, tmp1;
+    uint8_t e[32];
+    unsigned swap = 0;
+    int pos;
+
+    memcpy(e, scalar, 32);
+    e[0]  &= 0xf8;
+    e[31] &= 0x7f;
+    e[31] |= 0x40;
+    fe51_frombytes(x1, point);
+    fe51_1(x2);
+    fe51_0(z2);
+    fe51_copy(x3, x1);
+    fe51_1(z3);
+
+    for (pos = 254; pos >= 0; --pos) {
+        unsigned int b = 1 & (e[pos / 8] >> (pos & 7));
+
+        swap ^= b;
+        fe51_cswap(x2, x3, swap);
+        fe51_cswap(z2, z3, swap);
+        swap = b;
+        fe51_sub(tmp0, x3, z3);
+        fe51_sub(tmp1, x2, z2);
+        fe51_add(x2, x2, z2);
+        fe51_add(z2, x3, z3);
+        fe51_mul(z3, tmp0, x2);
+        fe51_mul(z2, z2, tmp1);
+        fe51_sq(tmp0, tmp1);
+        fe51_sq(tmp1, x2);
+        fe51_add(x3, z3, z2);
+        fe51_sub(z2, z3, z2);
+        fe51_mul(x2, tmp1, tmp0);
+        fe51_sub(tmp1, tmp1, tmp0);
+        fe51_sq(z2, z2);
+        fe51_mul121666(z3, tmp1);
+        fe51_sq(x3, x3);
+        fe51_add(tmp0, tmp0, z3);
+        fe51_mul(z3, x1, z2);
+        fe51_mul(z2, tmp1, tmp0);
+    }
+    fe51_cswap(x2, x3, swap);
+    fe51_cswap(z2, z3, swap);
+
+    fe51_invert(z2, z2);
+    fe51_mul(x2, x2, z2);
+    fe51_tobytes(out, x2);
+
+    OPENSSL_cleanse(e, sizeof(e));
+}
+#endif
+
+/*
+ * Reference base 2^25.5 implementation.
+ */
+/*
+ * This code is mostly taken from the ref10 version of Ed25519 in SUPERCOP
+ * 20141124 (http://bench.cr.yp.to/supercop.html).
+ *
+ * The field functions are shared by Ed25519 and X25519 where possible.
+ */
 
 /* fe means field element. Here the field is \Z/(2^255-19). An element t,
  * entries t[0]...t[9], represents the integer t[0]+2^26 t[1]+2^51 t[2]+2^77
@@ -3452,6 +3926,7 @@ static void ge_scalarmult_base(ge_p3 *h, const uint8_t *a) {
   OPENSSL_cleanse(e, sizeof(e));
 }
 
+#if !defined(BASE_2_51_IMPLEMENTED)
 /* Replace (f,g) with (g,f) if b == 1;
  * replace (f,g) with (f,g) if b == 0.
  *
@@ -3588,6 +4063,7 @@ static void x25519_scalar_mult(uint8_t out[32], const uint8_t scalar[32],
                                const uint8_t point[32]) {
   x25519_scalar_mult_generic(out, scalar, point);
 }
+#endif
 
 static void slide(signed char *r, const uint8_t *a) {
   int i;