blob: f141ac028b0f7bba419c218aad66275b507eb8c3 [file] [log] [blame]
 // Copyright (c) 2013 The Chromium Authors. All rights reserved. // Use of this source code is governed by a BSD-style license that can be // found in the LICENSE file. /* * curve25519-donna: Curve25519 elliptic curve, public key function * * http://code.google.com/p/curve25519-donna/ * * Adam Langley * * Derived from public domain C code by Daniel J. Bernstein * * 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 #include typedef uint8_t u8; typedef int32_t s32; typedef int64_t limb; /* Field element representation: * * Field elements are written as an array of signed, 64-bit limbs, least * significant first. The value of the field element is: * x[0] + 2^26·x[1] + x^51·x[2] + 2^102·x[3] + ... * * i.e. the limbs are 26, 25, 26, 25, ... bits wide. */ /* Sum two numbers: output += in */ static void fsum(limb *output, const limb *in) { unsigned i; for (i = 0; i < 10; i += 2) { output[0+i] = (output[0+i] + in[0+i]); output[1+i] = (output[1+i] + in[1+i]); } } /* Find the difference of two numbers: output = in - output * (note the order of the arguments!) */ static void fdifference(limb *output, const limb *in) { unsigned i; for (i = 0; i < 10; ++i) { output[i] = (in[i] - output[i]); } } /* Multiply a number my a scalar: output = in * scalar */ static void fscalar_product(limb *output, const limb *in, const limb scalar) { unsigned i; for (i = 0; i < 10; ++i) { output[i] = in[i] * scalar; } } /* Multiply two numbers: output = in2 * in * * output must be distinct to both inputs. The inputs are reduced coefficient * form, the output is not. */ static void fproduct(limb *output, const limb *in2, const limb *in) { output[0] = ((limb) ((s32) in2[0])) * ((s32) in[0]); output[1] = ((limb) ((s32) in2[0])) * ((s32) in[1]) + ((limb) ((s32) in2[1])) * ((s32) in[0]); output[2] = 2 * ((limb) ((s32) in2[1])) * ((s32) in[1]) + ((limb) ((s32) in2[0])) * ((s32) in[2]) + ((limb) ((s32) in2[2])) * ((s32) in[0]); output[3] = ((limb) ((s32) in2[1])) * ((s32) in[2]) + ((limb) ((s32) in2[2])) * ((s32) in[1]) + ((limb) ((s32) in2[0])) * ((s32) in[3]) + ((limb) ((s32) in2[3])) * ((s32) in[0]); output[4] = ((limb) ((s32) in2[2])) * ((s32) in[2]) + 2 * (((limb) ((s32) in2[1])) * ((s32) in[3]) + ((limb) ((s32) in2[3])) * ((s32) in[1])) + ((limb) ((s32) in2[0])) * ((s32) in[4]) + ((limb) ((s32) in2[4])) * ((s32) in[0]); output[5] = ((limb) ((s32) in2[2])) * ((s32) in[3]) + ((limb) ((s32) in2[3])) * ((s32) in[2]) + ((limb) ((s32) in2[1])) * ((s32) in[4]) + ((limb) ((s32) in2[4])) * ((s32) in[1]) + ((limb) ((s32) in2[0])) * ((s32) in[5]) + ((limb) ((s32) in2[5])) * ((s32) in[0]); output[6] = 2 * (((limb) ((s32) in2[3])) * ((s32) in[3]) + ((limb) ((s32) in2[1])) * ((s32) in[5]) + ((limb) ((s32) in2[5])) * ((s32) in[1])) + ((limb) ((s32) in2[2])) * ((s32) in[4]) + ((limb) ((s32) in2[4])) * ((s32) in[2]) + ((limb) ((s32) in2[0])) * ((s32) in[6]) + ((limb) ((s32) in2[6])) * ((s32) in[0]); output[7] = ((limb) ((s32) in2[3])) * ((s32) in[4]) + ((limb) ((s32) in2[4])) * ((s32) in[3]) + ((limb) ((s32) in2[2])) * ((s32) in[5]) + ((limb) ((s32) in2[5])) * ((s32) in[2]) + ((limb) ((s32) in2[1])) * ((s32) in[6]) + ((limb) ((s32) in2[6])) * ((s32) in[1]) + ((limb) ((s32) in2[0])) * ((s32) in[7]) + ((limb) ((s32) in2[7])) * ((s32) in[0]); output[8] = ((limb) ((s32) in2[4])) * ((s32) in[4]) + 2 * (((limb) ((s32) in2[3])) * ((s32) in[5]) + ((limb) ((s32) in2[5])) * ((s32) in[3]) + ((limb) ((s32) in2[1])) * ((s32) in[7]) + ((limb) ((s32) in2[7])) * ((s32) in[1])) + ((limb) ((s32) in2[2])) * ((s32) in[6]) + ((limb) ((s32) in2[6])) * ((s32) in[2]) + ((limb) ((s32) in2[0])) * ((s32) in[8]) + ((limb) ((s32) in2[8])) * ((s32) in[0]); output[9] = ((limb) ((s32) in2[4])) * ((s32) in[5]) + ((limb) ((s32) in2[5])) * ((s32) in[4]) + ((limb) ((s32) in2[3])) * ((s32) in[6]) + ((limb) ((s32) in2[6])) * ((s32) in[3]) + ((limb) ((s32) in2[2])) * ((s32) in[7]) + ((limb) ((s32) in2[7])) * ((s32) in[2]) + ((limb) ((s32) in2[1])) * ((s32) in[8]) + ((limb) ((s32) in2[8])) * ((s32) in[1]) + ((limb) ((s32) in2[0])) * ((s32) in[9]) + ((limb) ((s32) in2[9])) * ((s32) in[0]); output[10] = 2 * (((limb) ((s32) in2[5])) * ((s32) in[5]) + ((limb) ((s32) in2[3])) * ((s32) in[7]) + ((limb) ((s32) in2[7])) * ((s32) in[3]) + ((limb) ((s32) in2[1])) * ((s32) in[9]) + ((limb) ((s32) in2[9])) * ((s32) in[1])) + ((limb) ((s32) in2[4])) * ((s32) in[6]) + ((limb) ((s32) in2[6])) * ((s32) in[4]) + ((limb) ((s32) in2[2])) * ((s32) in[8]) + ((limb) ((s32) in2[8])) * ((s32) in[2]); output[11] = ((limb) ((s32) in2[5])) * ((s32) in[6]) + ((limb) ((s32) in2[6])) * ((s32) in[5]) + ((limb) ((s32) in2[4])) * ((s32) in[7]) + ((limb) ((s32) in2[7])) * ((s32) in[4]) + ((limb) ((s32) in2[3])) * ((s32) in[8]) + ((limb) ((s32) in2[8])) * ((s32) in[3]) + ((limb) ((s32) in2[2])) * ((s32) in[9]) + ((limb) ((s32) in2[9])) * ((s32) in[2]); output[12] = ((limb) ((s32) in2[6])) * ((s32) in[6]) + 2 * (((limb) ((s32) in2[5])) * ((s32) in[7]) + ((limb) ((s32) in2[7])) * ((s32) in[5]) + ((limb) ((s32) in2[3])) * ((s32) in[9]) + ((limb) ((s32) in2[9])) * ((s32) in[3])) + ((limb) ((s32) in2[4])) * ((s32) in[8]) + ((limb) ((s32) in2[8])) * ((s32) in[4]); output[13] = ((limb) ((s32) in2[6])) * ((s32) in[7]) + ((limb) ((s32) in2[7])) * ((s32) in[6]) + ((limb) ((s32) in2[5])) * ((s32) in[8]) + ((limb) ((s32) in2[8])) * ((s32) in[5]) + ((limb) ((s32) in2[4])) * ((s32) in[9]) + ((limb) ((s32) in2[9])) * ((s32) in[4]); output[14] = 2 * (((limb) ((s32) in2[7])) * ((s32) in[7]) + ((limb) ((s32) in2[5])) * ((s32) in[9]) + ((limb) ((s32) in2[9])) * ((s32) in[5])) + ((limb) ((s32) in2[6])) * ((s32) in[8]) + ((limb) ((s32) in2[8])) * ((s32) in[6]); output[15] = ((limb) ((s32) in2[7])) * ((s32) in[8]) + ((limb) ((s32) in2[8])) * ((s32) in[7]) + ((limb) ((s32) in2[6])) * ((s32) in[9]) + ((limb) ((s32) in2[9])) * ((s32) in[6]); output[16] = ((limb) ((s32) in2[8])) * ((s32) in[8]) + 2 * (((limb) ((s32) in2[7])) * ((s32) in[9]) + ((limb) ((s32) in2[9])) * ((s32) in[7])); output[17] = ((limb) ((s32) in2[8])) * ((s32) in[9]) + ((limb) ((s32) in2[9])) * ((s32) in[8]); output[18] = 2 * ((limb) ((s32) in2[9])) * ((s32) in[9]); } /* Reduce a long form to a short form by taking the input mod 2^255 - 19. */ static void freduce_degree(limb *output) { /* Each of these shifts and adds ends up multiplying the value by 19. */ output[8] += output[18] << 4; output[8] += output[18] << 1; output[8] += output[18]; output[7] += output[17] << 4; output[7] += output[17] << 1; output[7] += output[17]; output[6] += output[16] << 4; output[6] += output[16] << 1; output[6] += output[16]; output[5] += output[15] << 4; output[5] += output[15] << 1; output[5] += output[15]; output[4] += output[14] << 4; output[4] += output[14] << 1; output[4] += output[14]; output[3] += output[13] << 4; output[3] += output[13] << 1; output[3] += output[13]; output[2] += output[12] << 4; output[2] += output[12] << 1; output[2] += output[12]; output[1] += output[11] << 4; output[1] += output[11] << 1; output[1] += output[11]; output[0] += output[10] << 4; output[0] += output[10] << 1; output[0] += output[10]; } /* Reduce all coefficients of the short form input so that |x| < 2^26. * * On entry: |output[i]| < 2^62 */ static void freduce_coefficients(limb *output) { unsigned i; do { output[10] = 0; for (i = 0; i < 10; i += 2) { limb over = output[i] / 0x4000000l; output[i+1] += over; output[i] -= over * 0x4000000l; over = output[i+1] / 0x2000000; output[i+2] += over; output[i+1] -= over * 0x2000000; } output[0] += 19 * output[10]; } while (output[10]); } /* A helpful wrapper around fproduct: output = in * in2. * * output must be distinct to both inputs. The output is reduced degree and * reduced coefficient. */ static void fmul(limb *output, const limb *in, const limb *in2) { limb t[19]; fproduct(t, in, in2); freduce_degree(t); freduce_coefficients(t); memcpy(output, t, sizeof(limb) * 10); } static void fsquare_inner(limb *output, const limb *in) { output[0] = ((limb) ((s32) in[0])) * ((s32) in[0]); output[1] = 2 * ((limb) ((s32) in[0])) * ((s32) in[1]); output[2] = 2 * (((limb) ((s32) in[1])) * ((s32) in[1]) + ((limb) ((s32) in[0])) * ((s32) in[2])); output[3] = 2 * (((limb) ((s32) in[1])) * ((s32) in[2]) + ((limb) ((s32) in[0])) * ((s32) in[3])); output[4] = ((limb) ((s32) in[2])) * ((s32) in[2]) + 4 * ((limb) ((s32) in[1])) * ((s32) in[3]) + 2 * ((limb) ((s32) in[0])) * ((s32) in[4]); output[5] = 2 * (((limb) ((s32) in[2])) * ((s32) in[3]) + ((limb) ((s32) in[1])) * ((s32) in[4]) + ((limb) ((s32) in[0])) * ((s32) in[5])); output[6] = 2 * (((limb) ((s32) in[3])) * ((s32) in[3]) + ((limb) ((s32) in[2])) * ((s32) in[4]) + ((limb) ((s32) in[0])) * ((s32) in[6]) + 2 * ((limb) ((s32) in[1])) * ((s32) in[5])); output[7] = 2 * (((limb) ((s32) in[3])) * ((s32) in[4]) + ((limb) ((s32) in[2])) * ((s32) in[5]) + ((limb) ((s32) in[1])) * ((s32) in[6]) + ((limb) ((s32) in[0])) * ((s32) in[7])); output[8] = ((limb) ((s32) in[4])) * ((s32) in[4]) + 2 * (((limb) ((s32) in[2])) * ((s32) in[6]) + ((limb) ((s32) in[0])) * ((s32) in[8]) + 2 * (((limb) ((s32) in[1])) * ((s32) in[7]) + ((limb) ((s32) in[3])) * ((s32) in[5]))); output[9] = 2 * (((limb) ((s32) in[4])) * ((s32) in[5]) + ((limb) ((s32) in[3])) * ((s32) in[6]) + ((limb) ((s32) in[2])) * ((s32) in[7]) + ((limb) ((s32) in[1])) * ((s32) in[8]) + ((limb) ((s32) in[0])) * ((s32) in[9])); output[10] = 2 * (((limb) ((s32) in[5])) * ((s32) in[5]) + ((limb) ((s32) in[4])) * ((s32) in[6]) + ((limb) ((s32) in[2])) * ((s32) in[8]) + 2 * (((limb) ((s32) in[3])) * ((s32) in[7]) + ((limb) ((s32) in[1])) * ((s32) in[9]))); output[11] = 2 * (((limb) ((s32) in[5])) * ((s32) in[6]) + ((limb) ((s32) in[4])) * ((s32) in[7]) + ((limb) ((s32) in[3])) * ((s32) in[8]) + ((limb) ((s32) in[2])) * ((s32) in[9])); output[12] = ((limb) ((s32) in[6])) * ((s32) in[6]) + 2 * (((limb) ((s32) in[4])) * ((s32) in[8]) + 2 * (((limb) ((s32) in[5])) * ((s32) in[7]) + ((limb) ((s32) in[3])) * ((s32) in[9]))); output[13] = 2 * (((limb) ((s32) in[6])) * ((s32) in[7]) + ((limb) ((s32) in[5])) * ((s32) in[8]) + ((limb) ((s32) in[4])) * ((s32) in[9])); output[14] = 2 * (((limb) ((s32) in[7])) * ((s32) in[7]) + ((limb) ((s32) in[6])) * ((s32) in[8]) + 2 * ((limb) ((s32) in[5])) * ((s32) in[9])); output[15] = 2 * (((limb) ((s32) in[7])) * ((s32) in[8]) + ((limb) ((s32) in[6])) * ((s32) in[9])); output[16] = ((limb) ((s32) in[8])) * ((s32) in[8]) + 4 * ((limb) ((s32) in[7])) * ((s32) in[9]); output[17] = 2 * ((limb) ((s32) in[8])) * ((s32) in[9]); output[18] = 2 * ((limb) ((s32) in[9])) * ((s32) in[9]); } static void fsquare(limb *output, const limb *in) { limb t[19]; fsquare_inner(t, in); freduce_degree(t); freduce_coefficients(t); memcpy(output, t, sizeof(limb) * 10); } /* Take a little-endian, 32-byte number and expand it into polynomial form */ static void fexpand(limb *output, const u8 *input) { #define F(n,start,shift,mask) \ output[n] = ((((limb) input[start + 0]) | \ ((limb) input[start + 1]) << 8 | \ ((limb) input[start + 2]) << 16 | \ ((limb) input[start + 3]) << 24) >> shift) & mask; F(0, 0, 0, 0x3ffffff); F(1, 3, 2, 0x1ffffff); F(2, 6, 3, 0x3ffffff); F(3, 9, 5, 0x1ffffff); F(4, 12, 6, 0x3ffffff); F(5, 16, 0, 0x1ffffff); F(6, 19, 1, 0x3ffffff); F(7, 22, 3, 0x1ffffff); F(8, 25, 4, 0x3ffffff); F(9, 28, 6, 0x1ffffff); #undef F } /* Take a fully reduced polynomial form number and contract it into a * little-endian, 32-byte array */ static void fcontract(u8 *output, limb *input) { int i; do { for (i = 0; i < 9; ++i) { if ((i & 1) == 1) { while (input[i] < 0) { input[i] += 0x2000000; input[i + 1]--; } } else { while (input[i] < 0) { input[i] += 0x4000000; input[i + 1]--; } } } while (input[9] < 0) { input[9] += 0x2000000; input[0] -= 19; } } while (input[0] < 0); input[1] <<= 2; input[2] <<= 3; input[3] <<= 5; input[4] <<= 6; input[6] <<= 1; input[7] <<= 3; input[8] <<= 4; input[9] <<= 6; #define F(i, s) \ output[s+0] |= input[i] & 0xff; \ output[s+1] = (input[i] >> 8) & 0xff; \ output[s+2] = (input[i] >> 16) & 0xff; \ output[s+3] = (input[i] >> 24) & 0xff; output[0] = 0; output[16] = 0; F(0,0); F(1,3); F(2,6); F(3,9); F(4,12); F(5,16); F(6,19); F(7,22); F(8,25); F(9,28); #undef F } /* 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[10], origxprime[10], zzz[19], xx[19], zz[19], xxprime[19], zzprime[19], zzzprime[19], xxxprime[19]; memcpy(origx, x, 10 * sizeof(limb)); fsum(x, z); fdifference(z, origx); // does x - z memcpy(origxprime, xprime, sizeof(limb) * 10); fsum(xprime, zprime); fdifference(zprime, origxprime); fproduct(xxprime, xprime, z); fproduct(zzprime, x, zprime); freduce_degree(xxprime); freduce_coefficients(xxprime); freduce_degree(zzprime); freduce_coefficients(zzprime); memcpy(origxprime, xxprime, sizeof(limb) * 10); fsum(xxprime, zzprime); fdifference(zzprime, origxprime); fsquare(xxxprime, xxprime); fsquare(zzzprime, zzprime); fproduct(zzprime, zzzprime, qmqp); freduce_degree(zzprime); freduce_coefficients(zzprime); memcpy(x3, xxxprime, sizeof(limb) * 10); memcpy(z3, zzprime, sizeof(limb) * 10); fsquare(xx, x); fsquare(zz, z); fproduct(x2, xx, zz); freduce_degree(x2); freduce_coefficients(x2); fdifference(zz, xx); // does zz = xx - zz memset(zzz + 10, 0, sizeof(limb) * 9); fscalar_product(zzz, zz, 121665); freduce_degree(zzz); freduce_coefficients(zzz); fsum(zzz, xx); fproduct(z2, zz, zzz); freduce_degree(z2); freduce_coefficients(z2); } /* 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[19] = {0}, b[19] = {1}, c[19] = {1}, d[19] = {0}; limb *nqpqx = a, *nqpqz = b, *nqx = c, *nqz = d, *t; limb e[19] = {0}, f[19] = {1}, g[19] = {0}, h[19] = {1}; limb *nqpqx2 = e, *nqpqz2 = f, *nqx2 = g, *nqz2 = h; unsigned i, j; memcpy(nqpqx, q, sizeof(limb) * 10); for (i = 0; i < 32; ++i) { u8 byte = n[31 - i]; for (j = 0; j < 8; ++j) { if (byte & 0x80) { fmonty(nqpqx2, nqpqz2, nqx2, nqz2, nqpqx, nqpqz, nqx, nqz, q); } else { fmonty(nqx2, nqz2, nqpqx2, nqpqz2, nqx, nqz, nqpqx, nqpqz, q); } 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) * 10); memcpy(resultz, nqz, sizeof(limb) * 10); } // ----------------------------------------------------------------------------- // Shamelessly copied from djb's code // ----------------------------------------------------------------------------- static void crecip(limb *out, const limb *z) { limb z2[10]; limb z9[10]; limb z11[10]; limb z2_5_0[10]; limb z2_10_0[10]; limb z2_20_0[10]; limb z2_50_0[10]; limb z2_100_0[10]; limb t0[10]; limb t1[10]; int i; /* 2 */ fsquare(z2,z); /* 4 */ fsquare(t1,z2); /* 8 */ fsquare(t0,t1); /* 9 */ fmul(z9,t0,z); /* 11 */ fmul(z11,z9,z2); /* 22 */ fsquare(t0,z11); /* 2^5 - 2^0 = 31 */ fmul(z2_5_0,t0,z9); /* 2^6 - 2^1 */ fsquare(t0,z2_5_0); /* 2^7 - 2^2 */ fsquare(t1,t0); /* 2^8 - 2^3 */ fsquare(t0,t1); /* 2^9 - 2^4 */ fsquare(t1,t0); /* 2^10 - 2^5 */ fsquare(t0,t1); /* 2^10 - 2^0 */ fmul(z2_10_0,t0,z2_5_0); /* 2^11 - 2^1 */ fsquare(t0,z2_10_0); /* 2^12 - 2^2 */ fsquare(t1,t0); /* 2^20 - 2^10 */ for (i = 2;i < 10;i += 2) { fsquare(t0,t1); fsquare(t1,t0); } /* 2^20 - 2^0 */ fmul(z2_20_0,t1,z2_10_0); /* 2^21 - 2^1 */ fsquare(t0,z2_20_0); /* 2^22 - 2^2 */ fsquare(t1,t0); /* 2^40 - 2^20 */ for (i = 2;i < 20;i += 2) { fsquare(t0,t1); fsquare(t1,t0); } /* 2^40 - 2^0 */ fmul(t0,t1,z2_20_0); /* 2^41 - 2^1 */ fsquare(t1,t0); /* 2^42 - 2^2 */ fsquare(t0,t1); /* 2^50 - 2^10 */ for (i = 2;i < 10;i += 2) { fsquare(t1,t0); fsquare(t0,t1); } /* 2^50 - 2^0 */ fmul(z2_50_0,t0,z2_10_0); /* 2^51 - 2^1 */ fsquare(t0,z2_50_0); /* 2^52 - 2^2 */ fsquare(t1,t0); /* 2^100 - 2^50 */ for (i = 2;i < 50;i += 2) { fsquare(t0,t1); fsquare(t1,t0); } /* 2^100 - 2^0 */ fmul(z2_100_0,t1,z2_50_0); /* 2^101 - 2^1 */ fsquare(t1,z2_100_0); /* 2^102 - 2^2 */ fsquare(t0,t1); /* 2^200 - 2^100 */ for (i = 2;i < 100;i += 2) { fsquare(t1,t0); fsquare(t0,t1); } /* 2^200 - 2^0 */ fmul(t1,t0,z2_100_0); /* 2^201 - 2^1 */ fsquare(t0,t1); /* 2^202 - 2^2 */ fsquare(t1,t0); /* 2^250 - 2^50 */ for (i = 2;i < 50;i += 2) { fsquare(t0,t1); fsquare(t1,t0); } /* 2^250 - 2^0 */ fmul(t0,t1,z2_50_0); /* 2^251 - 2^1 */ fsquare(t1,t0); /* 2^252 - 2^2 */ fsquare(t0,t1); /* 2^253 - 2^3 */ fsquare(t1,t0); /* 2^254 - 2^4 */ fsquare(t0,t1); /* 2^255 - 2^5 */ fsquare(t1,t0); /* 2^255 - 21 */ fmul(out,t1,z11); } int curve25519_donna(u8 *mypublic, const u8 *secret, const u8 *basepoint) { limb bp[10], x[10], z[10], zmone[10]; 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; }