edsign.h

   1 /* Edwards curve signature system
   2  * Daniel Beer <dlbeer@gmail.com>, 22 Apr 2014
   3  *
   4  * This file is in the public domain.
   5  */
   6
   7 #ifndef EDSIGN_H_
   8 #define EDSIGN_H_
   9
  10 #include <stdint.h>
  11 #include <stdbool.h>
  12 #include "sha512.h"
  13
  14 /* This is the Ed25519 signature system, as described in:
  15  *
  16  *     Daniel J. Bernstein, Niels Duif, Tanja Lange, Peter Schwabe, Bo-Yin
  17  *     Yang. High-speed high-security signatures. Journal of Cryptographic
  18  *     Engineering 2 (2012), 77–89. Document ID:
  19  *     a1a62a2f76d23f65d622484ddd09caf8. URL:
  20  *     http://cr.yp.to/papers.html#ed25519. Date: 2011.09.26.
  21  *
  22  * The format and calculation of signatures is compatible with the
  23  * Ed25519 implementation in SUPERCOP. Note, however, that our secret
  24  * keys are half the size: we don't store a copy of the public key in
  25  * the secret key (we generate it on demand).
  26  */
  27
  28 /* Any string of 32 random bytes is a valid secret key. There is no
  29  * clamping of bits, because we don't use the key directly as an
  30  * exponent (the exponent is derived from part of a key expansion).
  31  */
  32 #define EDSIGN_SECRET_KEY_SIZE          32
  33
  34 /* Given a secret key, produce the public key (a packed Edwards-curve
  35  * point).
  36  */
  37 #define EDSIGN_PUBLIC_KEY_SIZE          32
  38
  39 void edsign_sec_to_pub(void *pub, const void *secret);
  40
  41 /* Produce a signature for a message. */
  42 #define EDSIGN_SIGNATURE_SIZE           64
  43
  44 void edsign_sign(uint8_t *signature, const uint8_t *pub,
  45                  const uint8_t *secret,
  46                  const uint8_t *message, size_t len);
  47
  48 struct edsign_verify_state {
  49         struct sha512_state sha;
  50 };
  51
  52 void edsign_verify_init(struct edsign_verify_state *st, const void *sig,
  53                         const void *pub);
  54
  55 static inline void
  56 edsign_verify_add(struct edsign_verify_state *st, const void *data, int len)
  57 {
  58         sha512_add(&st->sha, data, len);
  59 }
  60
  61 /* Verify a message signature. Returns non-zero if ok. */
  62 bool edsign_verify(struct edsign_verify_state *st, const void *sig, const void *pub);
  63
  64 #endif