libs/TinyECDH/ecdh.h

/*

  Crypto using elliptic curves defined over the finite binary field GF(2^m) where m is prime.

  The curves used are the anomalous binary curves (ABC-curves) or also called Koblitz curves.

  This class of curves was chosen because it yields efficient implementation of operations.



  Curves available - their different NIST/SECG names and eqivalent symmetric security level:

      NIST      SEC Group     strength
    ------------------------------------
      K-163     sect163k1      80 bit
      B-163     sect163r2      80 bit
      K-233     sect233k1     112 bit
      B-233     sect233r1     112 bit
      K-283     sect283k1     128 bit
      B-283     sect283r1     128 bit
      K-409     sect409k1     192 bit
      B-409     sect409r1     192 bit
      K-571     sect571k1     256 bit
      B-571     sect571r1     256 bit



  Curve parameters from:

    http://www.secg.org/sec2-v2.pdf
    http://csrc.nist.gov/publications/fips/fips186-3/fips_186-3.pdf


  Reference:

    https://www.ietf.org/rfc/rfc4492.txt
*/

#ifndef _ECDH_H__
#define _ECDH_H__


/* for size-annotated integer types: uint8_t, uint32_t etc. */
#include <stdint.h>

#ifdef __cplusplus
extern "C" {
#endif /* __cplusplus */

#define NIST_B163  1
#define NIST_K163  2
#define NIST_B233  3
#define NIST_K233  4
#define NIST_B283  5
#define NIST_K283  6
#define NIST_B409  7
#define NIST_K409  8
#define NIST_B571  9
#define NIST_K571 10

/* What is the default curve to use? */
#ifndef ECC_CURVE
 #define ECC_CURVE NIST_K571
#endif

#if defined(ECC_CURVE) && (ECC_CURVE != 0)
 #if   (ECC_CURVE == NIST_K163) || (ECC_CURVE == NIST_B163)
  #define CURVE_DEGREE       163
  #define ECC_PRV_KEY_SIZE   24
 #elif (ECC_CURVE == NIST_K233) || (ECC_CURVE == NIST_B233)
  #define CURVE_DEGREE       233
  #define ECC_PRV_KEY_SIZE   32
 #elif (ECC_CURVE == NIST_K283) || (ECC_CURVE == NIST_B283)
  #define CURVE_DEGREE       283
  #define ECC_PRV_KEY_SIZE   36
 #elif (ECC_CURVE == NIST_K409) || (ECC_CURVE == NIST_B409)
  #define CURVE_DEGREE       409
  #define ECC_PRV_KEY_SIZE   52
 #elif (ECC_CURVE == NIST_K571) || (ECC_CURVE == NIST_B571)
  #define CURVE_DEGREE       571
  #define ECC_PRV_KEY_SIZE   72
 #endif
#else
 #error Must define a curve to use
#endif

#define ECC_PUB_KEY_SIZE     (2 * ECC_PRV_KEY_SIZE)


/******************************************************************************/


/* NOTE: assumes private is filled with random data before calling */
int ecdh_generate_keys(uint8_t* public_key, uint8_t* private_key);

/* input: own private key + other party's public key, output: shared secret */
int ecdh_shared_secret(const uint8_t* private_key, const uint8_t* others_pub, uint8_t* output);


/******************************************************************************/

#ifdef __cplusplus
}
#endif /* __cplusplus */

#endif /* #ifndef _ECDH_H__ */