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+/* Copyright 2008, Google Inc.
+ * All rights reserved.
+ *
+ * Code released into the public domain.
+ *
+ * curve25519-donna: Curve25519 elliptic curve, public key function
+ *
+ * http://code.google.com/p/curve25519-donna/
+ *
+ * Adam Langley <agl@imperialviolet.org>
+ *
+ * Derived from public domain C code by Daniel J. Bernstein <djb@cr.yp.to>
+ *
+ * More information about curve25519 can be found here
+ * http://cr.yp.to/ecdh.html
+ *
+ * djb's sample implementation of curve25519 is written in a special assembly
+ * language called qhasm and uses the floating point registers.
+ *
+ * This is, almost, a clean room reimplementation from the curve25519 paper. It
+ * uses many of the tricks described therein. Only the crecip function is taken
+ * from the sample implementation.
+ */
+
+#include <string.h>
+#include <stdint.h>
+
+typedef uint8_t u8;
+typedef uint64_t limb;
+typedef limb felem[5];
+// This is a special gcc mode for 128-bit integers. It's implemented on 64-bit
+// platforms only as far as I know.
+typedef unsigned uint128_t __attribute__((mode(TI)));
+
+#undef force_inline
+#define force_inline __attribute__((always_inline))
+
+/* Sum two numbers: output += in */
+static inline void force_inline
+fsum(limb *output, const limb *in) {
+ output[0] += in[0];
+ output[1] += in[1];
+ output[2] += in[2];
+ output[3] += in[3];
+ output[4] += in[4];
+}
+
+/* Find the difference of two numbers: output = in - output
+ * (note the order of the arguments!)
+ *
+ * Assumes that out[i] < 2**52
+ * On return, out[i] < 2**55
+ */
+static inline void force_inline
+fdifference_backwards(felem out, const felem in) {
+ /* 152 is 19 << 3 */
+ static const limb two54m152 = (((limb)1) << 54) - 152;
+ static const limb two54m8 = (((limb)1) << 54) - 8;
+
+ out[0] = in[0] + two54m152 - out[0];
+ out[1] = in[1] + two54m8 - out[1];
+ out[2] = in[2] + two54m8 - out[2];
+ out[3] = in[3] + two54m8 - out[3];
+ out[4] = in[4] + two54m8 - out[4];
+}
+
+/* Multiply a number by a scalar: output = in * scalar */
+static inline void force_inline
+fscalar_product(felem output, const felem in, const limb scalar) {
+ uint128_t a;
+
+ a = ((uint128_t) in[0]) * scalar;
+ output[0] = ((limb)a) & 0x7ffffffffffff;
+
+ a = ((uint128_t) in[1]) * scalar + ((limb) (a >> 51));
+ output[1] = ((limb)a) & 0x7ffffffffffff;
+
+ a = ((uint128_t) in[2]) * scalar + ((limb) (a >> 51));
+ output[2] = ((limb)a) & 0x7ffffffffffff;
+
+ a = ((uint128_t) in[3]) * scalar + ((limb) (a >> 51));
+ output[3] = ((limb)a) & 0x7ffffffffffff;
+
+ a = ((uint128_t) in[4]) * scalar + ((limb) (a >> 51));
+ output[4] = ((limb)a) & 0x7ffffffffffff;
+
+ output[0] += (a >> 51) * 19;
+}
+
+/* Multiply two numbers: output = in2 * in
+ *
+ * output must be distinct to both inputs. The inputs are reduced coefficient
+ * form, the output is not.
+ *
+ * Assumes that in[i] < 2**55 and likewise for in2.
+ * On return, output[i] < 2**52
+ */
+static inline void force_inline
+fmul(felem output, const felem in2, const felem in) {
+ uint128_t t[5];
+ limb r0,r1,r2,r3,r4,s0,s1,s2,s3,s4,c;
+
+ r0 = in[0];
+ r1 = in[1];
+ r2 = in[2];
+ r3 = in[3];
+ r4 = in[4];
+
+ s0 = in2[0];
+ s1 = in2[1];
+ s2 = in2[2];
+ s3 = in2[3];
+ s4 = in2[4];
+
+ t[0] = ((uint128_t) r0) * s0;
+ t[1] = ((uint128_t) r0) * s1 + ((uint128_t) r1) * s0;
+ t[2] = ((uint128_t) r0) * s2 + ((uint128_t) r2) * s0 + ((uint128_t) r1) * s1;
+ t[3] = ((uint128_t) r0) * s3 + ((uint128_t) r3) * s0 + ((uint128_t) r1) * s2 + ((uint128_t) r2) * s1;
+ t[4] = ((uint128_t) r0) * s4 + ((uint128_t) r4) * s0 + ((uint128_t) r3) * s1 + ((uint128_t) r1) * s3 + ((uint128_t) r2) * s2;
+
+ r4 *= 19;
+ r1 *= 19;
+ r2 *= 19;
+ r3 *= 19;
+
+ t[0] += ((uint128_t) r4) * s1 + ((uint128_t) r1) * s4 + ((uint128_t) r2) * s3 + ((uint128_t) r3) * s2;
+ t[1] += ((uint128_t) r4) * s2 + ((uint128_t) r2) * s4 + ((uint128_t) r3) * s3;
+ t[2] += ((uint128_t) r4) * s3 + ((uint128_t) r3) * s4;
+ t[3] += ((uint128_t) r4) * s4;
+
+ r0 = (limb)t[0] & 0x7ffffffffffff; c = (limb)(t[0] >> 51);
+ t[1] += c; r1 = (limb)t[1] & 0x7ffffffffffff; c = (limb)(t[1] >> 51);
+ t[2] += c; r2 = (limb)t[2] & 0x7ffffffffffff; c = (limb)(t[2] >> 51);
+ t[3] += c; r3 = (limb)t[3] & 0x7ffffffffffff; c = (limb)(t[3] >> 51);
+ t[4] += c; r4 = (limb)t[4] & 0x7ffffffffffff; c = (limb)(t[4] >> 51);
+ r0 += c * 19; c = r0 >> 51; r0 = r0 & 0x7ffffffffffff;
+ r1 += c; c = r1 >> 51; r1 = r1 & 0x7ffffffffffff;
+ r2 += c;
+
+ output[0] = r0;
+ output[1] = r1;
+ output[2] = r2;
+ output[3] = r3;
+ output[4] = r4;
+}
+
+static inline void force_inline
+fsquare_times(felem output, const felem in, limb count) {
+ uint128_t t[5];
+ limb r0,r1,r2,r3,r4,c;
+ limb d0,d1,d2,d4,d419;
+
+ r0 = in[0];
+ r1 = in[1];
+ r2 = in[2];
+ r3 = in[3];
+ r4 = in[4];
+
+ do {
+ d0 = r0 * 2;
+ d1 = r1 * 2;
+ d2 = r2 * 2 * 19;
+ d419 = r4 * 19;
+ d4 = d419 * 2;
+
+ t[0] = ((uint128_t) r0) * r0 + ((uint128_t) d4) * r1 + (((uint128_t) d2) * (r3 ));
+ t[1] = ((uint128_t) d0) * r1 + ((uint128_t) d4) * r2 + (((uint128_t) r3) * (r3 * 19));
+ t[2] = ((uint128_t) d0) * r2 + ((uint128_t) r1) * r1 + (((uint128_t) d4) * (r3 ));
+ t[3] = ((uint128_t) d0) * r3 + ((uint128_t) d1) * r2 + (((uint128_t) r4) * (d419 ));
+ t[4] = ((uint128_t) d0) * r4 + ((uint128_t) d1) * r3 + (((uint128_t) r2) * (r2 ));
+
+ r0 = (limb)t[0] & 0x7ffffffffffff; c = (limb)(t[0] >> 51);
+ t[1] += c; r1 = (limb)t[1] & 0x7ffffffffffff; c = (limb)(t[1] >> 51);
+ t[2] += c; r2 = (limb)t[2] & 0x7ffffffffffff; c = (limb)(t[2] >> 51);
+ t[3] += c; r3 = (limb)t[3] & 0x7ffffffffffff; c = (limb)(t[3] >> 51);
+ t[4] += c; r4 = (limb)t[4] & 0x7ffffffffffff; c = (limb)(t[4] >> 51);
+ r0 += c * 19; c = r0 >> 51; r0 = r0 & 0x7ffffffffffff;
+ r1 += c; c = r1 >> 51; r1 = r1 & 0x7ffffffffffff;
+ r2 += c;
+ } while(--count);
+
+ output[0] = r0;
+ output[1] = r1;
+ output[2] = r2;
+ output[3] = r3;
+ output[4] = r4;
+}
+
+/* Load a little-endian 64-bit number */
+static limb
+load_limb(const u8 *in) {
+ return
+ ((limb)in[0]) |
+ (((limb)in[1]) << 8) |
+ (((limb)in[2]) << 16) |
+ (((limb)in[3]) << 24) |
+ (((limb)in[4]) << 32) |
+ (((limb)in[5]) << 40) |
+ (((limb)in[6]) << 48) |
+ (((limb)in[7]) << 56);
+}
+
+static void
+store_limb(u8 *out, limb in) {
+ out[0] = in & 0xff;
+ out[1] = (in >> 8) & 0xff;
+ out[2] = (in >> 16) & 0xff;
+ out[3] = (in >> 24) & 0xff;
+ out[4] = (in >> 32) & 0xff;
+ out[5] = (in >> 40) & 0xff;
+ out[6] = (in >> 48) & 0xff;
+ out[7] = (in >> 56) & 0xff;
+}
+
+/* Take a little-endian, 32-byte number and expand it into polynomial form */
+static void
+fexpand(limb *output, const u8 *in) {
+ output[0] = load_limb(in) & 0x7ffffffffffff;
+ output[1] = (load_limb(in+6) >> 3) & 0x7ffffffffffff;
+ output[2] = (load_limb(in+12) >> 6) & 0x7ffffffffffff;
+ output[3] = (load_limb(in+19) >> 1) & 0x7ffffffffffff;
+ output[4] = (load_limb(in+24) >> 12) & 0x7ffffffffffff;
+}
+
+/* Take a fully reduced polynomial form number and contract it into a
+ * little-endian, 32-byte array
+ */
+static void
+fcontract(u8 *output, const felem input) {
+ uint128_t t[5];
+
+ t[0] = input[0];
+ t[1] = input[1];
+ t[2] = input[2];
+ t[3] = input[3];
+ t[4] = input[4];
+
+ t[1] += t[0] >> 51; t[0] &= 0x7ffffffffffff;
+ t[2] += t[1] >> 51; t[1] &= 0x7ffffffffffff;
+ t[3] += t[2] >> 51; t[2] &= 0x7ffffffffffff;
+ t[4] += t[3] >> 51; t[3] &= 0x7ffffffffffff;
+ t[0] += 19 * (t[4] >> 51); t[4] &= 0x7ffffffffffff;
+
+ t[1] += t[0] >> 51; t[0] &= 0x7ffffffffffff;
+ t[2] += t[1] >> 51; t[1] &= 0x7ffffffffffff;
+ t[3] += t[2] >> 51; t[2] &= 0x7ffffffffffff;
+ t[4] += t[3] >> 51; t[3] &= 0x7ffffffffffff;
+ t[0] += 19 * (t[4] >> 51); t[4] &= 0x7ffffffffffff;
+
+ /* now t is between 0 and 2^255-1, properly carried. */
+ /* case 1: between 0 and 2^255-20. case 2: between 2^255-19 and 2^255-1. */
+
+ t[0] += 19;
+
+ t[1] += t[0] >> 51; t[0] &= 0x7ffffffffffff;
+ t[2] += t[1] >> 51; t[1] &= 0x7ffffffffffff;
+ t[3] += t[2] >> 51; t[2] &= 0x7ffffffffffff;
+ t[4] += t[3] >> 51; t[3] &= 0x7ffffffffffff;
+ t[0] += 19 * (t[4] >> 51); t[4] &= 0x7ffffffffffff;
+
+ /* now between 19 and 2^255-1 in both cases, and offset by 19. */
+
+ t[0] += 0x8000000000000 - 19;
+ t[1] += 0x8000000000000 - 1;
+ t[2] += 0x8000000000000 - 1;
+ t[3] += 0x8000000000000 - 1;
+ t[4] += 0x8000000000000 - 1;
+
+ /* now between 2^255 and 2^256-20, and offset by 2^255. */
+
+ t[1] += t[0] >> 51; t[0] &= 0x7ffffffffffff;
+ t[2] += t[1] >> 51; t[1] &= 0x7ffffffffffff;
+ t[3] += t[2] >> 51; t[2] &= 0x7ffffffffffff;
+ t[4] += t[3] >> 51; t[3] &= 0x7ffffffffffff;
+ t[4] &= 0x7ffffffffffff;
+
+ store_limb(output, t[0] | (t[1] << 51));
+ store_limb(output+8, (t[1] >> 13) | (t[2] << 38));
+ store_limb(output+16, (t[2] >> 26) | (t[3] << 25));
+ store_limb(output+24, (t[3] >> 39) | (t[4] << 12));
+}
+
+/* Input: Q, Q', Q-Q'
+ * Output: 2Q, Q+Q'
+ *
+ * x2 z3: long form
+ * x3 z3: long form
+ * x z: short form, destroyed
+ * xprime zprime: short form, destroyed
+ * qmqp: short form, preserved
+ */
+static void
+fmonty(limb *x2, limb *z2, /* output 2Q */
+ limb *x3, limb *z3, /* output Q + Q' */
+ limb *x, limb *z, /* input Q */
+ limb *xprime, limb *zprime, /* input Q' */
+ const limb *qmqp /* input Q - Q' */) {
+ limb origx[5], origxprime[5], zzz[5], xx[5], zz[5], xxprime[5],
+ zzprime[5], zzzprime[5];
+
+ memcpy(origx, x, 5 * sizeof(limb));
+ fsum(x, z);
+ fdifference_backwards(z, origx); // does x - z
+
+ memcpy(origxprime, xprime, sizeof(limb) * 5);
+ fsum(xprime, zprime);
+ fdifference_backwards(zprime, origxprime);
+ fmul(xxprime, xprime, z);
+ fmul(zzprime, x, zprime);
+ memcpy(origxprime, xxprime, sizeof(limb) * 5);
+ fsum(xxprime, zzprime);
+ fdifference_backwards(zzprime, origxprime);
+ fsquare_times(x3, xxprime, 1);
+ fsquare_times(zzzprime, zzprime, 1);
+ fmul(z3, zzzprime, qmqp);
+
+ fsquare_times(xx, x, 1);
+ fsquare_times(zz, z, 1);
+ fmul(x2, xx, zz);
+ fdifference_backwards(zz, xx); // does zz = xx - zz
+ fscalar_product(zzz, zz, 121665);
+ fsum(zzz, xx);
+ fmul(z2, zz, zzz);
+}
+
+// -----------------------------------------------------------------------------
+// Maybe swap the contents of two limb arrays (@a and @b), each @len elements
+// long. Perform the swap iff @swap is non-zero.
+//
+// This function performs the swap without leaking any side-channel
+// information.
+// -----------------------------------------------------------------------------
+static void
+swap_conditional(limb a[5], limb b[5], limb iswap) {
+ unsigned i;
+ const limb swap = -iswap;
+
+ for (i = 0; i < 5; ++i) {
+ const limb x = swap & (a[i] ^ b[i]);
+ a[i] ^= x;
+ b[i] ^= x;
+ }
+}
+
+/* Calculates nQ where Q is the x-coordinate of a point on the curve
+ *
+ * resultx/resultz: the x coordinate of the resulting curve point (short form)
+ * n: a little endian, 32-byte number
+ * q: a point of the curve (short form)
+ */
+static void
+cmult(limb *resultx, limb *resultz, const u8 *n, const limb *q) {
+ limb a[5] = {0}, b[5] = {1}, c[5] = {1}, d[5] = {0};
+ limb *nqpqx = a, *nqpqz = b, *nqx = c, *nqz = d, *t;
+ limb e[5] = {0}, f[5] = {1}, g[5] = {0}, h[5] = {1};
+ limb *nqpqx2 = e, *nqpqz2 = f, *nqx2 = g, *nqz2 = h;
+
+ unsigned i, j;
+
+ memcpy(nqpqx, q, sizeof(limb) * 5);
+
+ for (i = 0; i < 32; ++i) {
+ u8 byte = n[31 - i];
+ for (j = 0; j < 8; ++j) {
+ const limb bit = byte >> 7;
+
+ swap_conditional(nqx, nqpqx, bit);
+ swap_conditional(nqz, nqpqz, bit);
+ fmonty(nqx2, nqz2,
+ nqpqx2, nqpqz2,
+ nqx, nqz,
+ nqpqx, nqpqz,
+ q);
+ swap_conditional(nqx2, nqpqx2, bit);
+ swap_conditional(nqz2, nqpqz2, bit);
+
+ t = nqx;
+ nqx = nqx2;
+ nqx2 = t;
+ t = nqz;
+ nqz = nqz2;
+ nqz2 = t;
+ t = nqpqx;
+ nqpqx = nqpqx2;
+ nqpqx2 = t;
+ t = nqpqz;
+ nqpqz = nqpqz2;
+ nqpqz2 = t;
+
+ byte <<= 1;
+ }
+ }
+
+ memcpy(resultx, nqx, sizeof(limb) * 5);
+ memcpy(resultz, nqz, sizeof(limb) * 5);
+}
+
+
+// -----------------------------------------------------------------------------
+// Shamelessly copied from djb's code, tightened a little
+// -----------------------------------------------------------------------------
+static void
+crecip(felem out, const felem z) {
+ felem a,t0,b,c;
+
+ /* 2 */ fsquare_times(a, z, 1); // a = 2
+ /* 8 */ fsquare_times(t0, a, 2);
+ /* 9 */ fmul(b, t0, z); // b = 9
+ /* 11 */ fmul(a, b, a); // a = 11
+ /* 22 */ fsquare_times(t0, a, 1);
+ /* 2^5 - 2^0 = 31 */ fmul(b, t0, b);
+ /* 2^10 - 2^5 */ fsquare_times(t0, b, 5);
+ /* 2^10 - 2^0 */ fmul(b, t0, b);
+ /* 2^20 - 2^10 */ fsquare_times(t0, b, 10);
+ /* 2^20 - 2^0 */ fmul(c, t0, b);
+ /* 2^40 - 2^20 */ fsquare_times(t0, c, 20);
+ /* 2^40 - 2^0 */ fmul(t0, t0, c);
+ /* 2^50 - 2^10 */ fsquare_times(t0, t0, 10);
+ /* 2^50 - 2^0 */ fmul(b, t0, b);
+ /* 2^100 - 2^50 */ fsquare_times(t0, b, 50);
+ /* 2^100 - 2^0 */ fmul(c, t0, b);
+ /* 2^200 - 2^100 */ fsquare_times(t0, c, 100);
+ /* 2^200 - 2^0 */ fmul(t0, t0, c);
+ /* 2^250 - 2^50 */ fsquare_times(t0, t0, 50);
+ /* 2^250 - 2^0 */ fmul(t0, t0, b);
+ /* 2^255 - 2^5 */ fsquare_times(t0, t0, 5);
+ /* 2^255 - 21 */ fmul(out, t0, a);
+}
+
+int curve25519_donna(u8 *, const u8 *, const u8 *);
+
+int
+curve25519_donna(u8 *mypublic, const u8 *secret, const u8 *basepoint) {
+ limb bp[5], x[5], z[5], zmone[5];
+ uint8_t e[32];
+ int i;
+
+ for (i = 0;i < 32;++i) e[i] = secret[i];
+ e[0] &= 248;
+ e[31] &= 127;
+ e[31] |= 64;
+
+ fexpand(bp, basepoint);
+ cmult(x, z, e, bp);
+ crecip(zmone, z);
+ fmul(z, x, zmone);
+ fcontract(mypublic, z);
+ return 0;
+}
generated by cgit v1.2.3 (git 2.45.0) at 2024-11-20 09:44:07 +0000