168 lines
3.8 KiB
C
168 lines
3.8 KiB
C
/* Edwards curve signature system
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* Daniel Beer <dlbeer@gmail.com>, 22 Apr 2014
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*
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* This file is in the public domain.
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*/
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#include "ed25519.h"
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#include "sha512.h"
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#include "fprime.h"
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#include "edsign.h"
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#define EXPANDED_SIZE 64
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static const uint8_t ed25519_order[FPRIME_SIZE] = {
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0xed, 0xd3, 0xf5, 0x5c, 0x1a, 0x63, 0x12, 0x58,
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0xd6, 0x9c, 0xf7, 0xa2, 0xde, 0xf9, 0xde, 0x14,
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0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
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0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x10
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};
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static void expand_key(uint8_t *expanded, const uint8_t *secret)
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{
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struct sha512_state s;
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sha512_init(&s);
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sha512_final(&s, secret, EDSIGN_SECRET_KEY_SIZE);
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sha512_get(&s, expanded, 0, EXPANDED_SIZE);
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ed25519_prepare(expanded);
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}
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static uint8_t upp(struct ed25519_pt *p, const uint8_t *packed)
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{
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uint8_t x[F25519_SIZE];
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uint8_t y[F25519_SIZE];
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uint8_t ok = ed25519_try_unpack(x, y, packed);
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ed25519_project(p, x, y);
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return ok;
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}
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static void pp(uint8_t *packed, const struct ed25519_pt *p)
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{
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uint8_t x[F25519_SIZE];
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uint8_t y[F25519_SIZE];
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ed25519_unproject(x, y, p);
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ed25519_pack(packed, x, y);
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}
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static void sm_pack(uint8_t *r, const uint8_t *k)
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{
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struct ed25519_pt p;
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ed25519_smult(&p, &ed25519_base, k);
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pp(r, &p);
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}
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void edsign_sec_to_pub(uint8_t *pub, const uint8_t *secret)
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{
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uint8_t expanded[EXPANDED_SIZE];
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expand_key(expanded, secret);
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sm_pack(pub, expanded);
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}
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static void hash_with_prefix(uint8_t *out_fp,
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uint8_t *init_block, unsigned int prefix_size,
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const uint8_t *message, size_t len)
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{
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struct sha512_state s;
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sha512_init(&s);
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if (len < SHA512_BLOCK_SIZE && len + prefix_size < SHA512_BLOCK_SIZE) {
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memcpy(init_block + prefix_size, message, len);
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sha512_final(&s, init_block, len + prefix_size);
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} else {
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size_t i;
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memcpy(init_block + prefix_size, message,
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SHA512_BLOCK_SIZE - prefix_size);
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sha512_block(&s, init_block);
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for (i = SHA512_BLOCK_SIZE - prefix_size;
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i + SHA512_BLOCK_SIZE <= len;
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i += SHA512_BLOCK_SIZE)
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sha512_block(&s, message + i);
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sha512_final(&s, message + i, len + prefix_size);
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}
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sha512_get(&s, init_block, 0, SHA512_HASH_SIZE);
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fprime_from_bytes(out_fp, init_block, SHA512_HASH_SIZE, ed25519_order);
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}
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static void generate_k(uint8_t *k, const uint8_t *kgen_key,
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const uint8_t *message, size_t len)
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{
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uint8_t block[SHA512_BLOCK_SIZE];
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memcpy(block, kgen_key, 32);
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hash_with_prefix(k, block, 32, message, len);
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}
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static void hash_message(uint8_t *z, const uint8_t *r, const uint8_t *a,
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const uint8_t *m, size_t len)
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{
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uint8_t block[SHA512_BLOCK_SIZE];
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memcpy(block, r, 32);
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memcpy(block + 32, a, 32);
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hash_with_prefix(z, block, 64, m, len);
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}
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void edsign_sign(uint8_t *signature, const uint8_t *pub,
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const uint8_t *secret,
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const uint8_t *message, size_t len)
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{
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uint8_t expanded[EXPANDED_SIZE];
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uint8_t e[FPRIME_SIZE];
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uint8_t s[FPRIME_SIZE];
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uint8_t k[FPRIME_SIZE];
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uint8_t z[FPRIME_SIZE];
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expand_key(expanded, secret);
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/* Generate k and R = kB */
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generate_k(k, expanded + 32, message, len);
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sm_pack(signature, k);
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/* Compute z = H(R, A, M) */
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hash_message(z, signature, pub, message, len);
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/* Obtain e */
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fprime_from_bytes(e, expanded, 32, ed25519_order);
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/* Compute s = ze + k */
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fprime_mul(s, z, e, ed25519_order);
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fprime_add(s, k, ed25519_order);
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memcpy(signature + 32, s, 32);
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}
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uint8_t edsign_verify(const uint8_t *signature, const uint8_t *pub,
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const uint8_t *message, size_t len)
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{
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struct ed25519_pt p;
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struct ed25519_pt q;
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uint8_t lhs[F25519_SIZE];
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uint8_t rhs[F25519_SIZE];
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uint8_t z[FPRIME_SIZE];
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uint8_t ok = 1;
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/* Compute z = H(R, A, M) */
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hash_message(z, signature, pub, message, len);
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/* sB = (ze + k)B = ... */
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sm_pack(lhs, signature + 32);
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/* ... = zA + R */
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ok &= upp(&p, pub);
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ed25519_smult(&p, &p, z);
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ok &= upp(&q, signature);
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ed25519_add(&p, &p, &q);
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pp(rhs, &p);
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/* Equal? */
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return ok & f25519_eq(lhs, rhs);
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}
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