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- MeshCore-based Simple Sensor firmware - Heltec T114 without display - BME280 sensor support (temp/humidity/pressure) - Radio: 868.856018 MHz, SF7, BW62.5 kHz, CR4/7 - 2-byte path hash - PlatformIO project
80 lines
1.8 KiB
C
80 lines
1.8 KiB
C
#include "ed_25519.h"
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#include "fe.h"
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void ed25519_key_exchange(unsigned char *shared_secret, const unsigned char *public_key, const unsigned char *private_key) {
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unsigned char e[32];
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unsigned int i;
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fe x1;
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fe x2;
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fe z2;
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fe x3;
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fe z3;
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fe tmp0;
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fe tmp1;
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int pos;
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unsigned int swap;
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unsigned int b;
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/* copy the private key and make sure it's valid */
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for (i = 0; i < 32; ++i) {
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e[i] = private_key[i];
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}
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e[0] &= 248;
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e[31] &= 63;
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e[31] |= 64;
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/* unpack the public key and convert edwards to montgomery */
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/* due to CodesInChaos: montgomeryX = (edwardsY + 1)*inverse(1 - edwardsY) mod p */
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fe_frombytes(x1, public_key);
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fe_1(tmp1);
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fe_add(tmp0, x1, tmp1);
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fe_sub(tmp1, tmp1, x1);
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fe_invert(tmp1, tmp1);
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fe_mul(x1, tmp0, tmp1);
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fe_1(x2);
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fe_0(z2);
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fe_copy(x3, x1);
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fe_1(z3);
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swap = 0;
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for (pos = 254; pos >= 0; --pos) {
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b = e[pos / 8] >> (pos & 7);
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b &= 1;
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swap ^= b;
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fe_cswap(x2, x3, swap);
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fe_cswap(z2, z3, swap);
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swap = b;
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/* from montgomery.h */
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fe_sub(tmp0, x3, z3);
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fe_sub(tmp1, x2, z2);
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fe_add(x2, x2, z2);
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fe_add(z2, x3, z3);
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fe_mul(z3, tmp0, x2);
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fe_mul(z2, z2, tmp1);
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fe_sq(tmp0, tmp1);
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fe_sq(tmp1, x2);
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fe_add(x3, z3, z2);
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fe_sub(z2, z3, z2);
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fe_mul(x2, tmp1, tmp0);
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fe_sub(tmp1, tmp1, tmp0);
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fe_sq(z2, z2);
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fe_mul121666(z3, tmp1);
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fe_sq(x3, x3);
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fe_add(tmp0, tmp0, z3);
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fe_mul(z3, x1, z2);
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fe_mul(z2, tmp1, tmp0);
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}
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fe_cswap(x2, x3, swap);
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fe_cswap(z2, z3, swap);
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fe_invert(z2, z2);
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fe_mul(x2, x2, z2);
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fe_tobytes(shared_secret, x2);
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}
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