ecjpake.h

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#ifndef MBEDTLS_ECJPAKE_H
#define MBEDTLS_ECJPAKE_H

/*
 * J-PAKE is a password-authenticated key exchange that allows deriving a
 * strong shared secret from a (potentially low entropy) pre-shared
 * passphrase, with forward secrecy and mutual authentication.
 * https://en.wikipedia.org/wiki/Password_Authenticated_Key_Exchange_by_Juggling
 *
 * This file implements the Elliptic Curve variant of J-PAKE,
 * as defined in Chapter 7.4 of the Thread v1.0 Specification,
 * available to members of the Thread Group http://threadgroup.org/
 *
 * As the J-PAKE algorithm is inherently symmetric, so is our API.
 * Each party needs to send its first round message, in any order, to the
 * other party, then each sends its second round message, in any order.
 * The payloads are serialized in a way suitable for use in TLS, but could
 * also be use outside TLS.
 */

#include "ecp.h"
#include "md.h"

#ifdef __cplusplus
extern "C" {
#endif

typedef enum {
    MBEDTLS_ECJPAKE_CLIENT = 0,         
    MBEDTLS_ECJPAKE_SERVER,             
} mbedtls_ecjpake_role;

typedef struct
{
    const mbedtls_md_info_t *md_info;   
    mbedtls_ecp_group grp;              
    mbedtls_ecjpake_role role;          
    int point_format;                   
    mbedtls_ecp_point Xm1;              
    mbedtls_ecp_point Xm2;              
    mbedtls_ecp_point Xp1;              
    mbedtls_ecp_point Xp2;              
    mbedtls_ecp_point Xp;               
    mbedtls_mpi xm1;                    
    mbedtls_mpi xm2;                    
    mbedtls_mpi s;                      
} mbedtls_ecjpake_context;

void mbedtls_ecjpake_init( mbedtls_ecjpake_context *ctx );

int mbedtls_ecjpake_setup( mbedtls_ecjpake_context *ctx,
                           mbedtls_ecjpake_role role,
                           mbedtls_md_type_t hash,
                           mbedtls_ecp_group_id curve,
                           const unsigned char *secret,
                           size_t len );

/*
 * \brief           Check if a context is ready for use
 *
 * \param ctx       Context to check
 *
 * \return          0 if the context is ready for use,
 *                  MBEDTLS_ERR_ECP_BAD_INPUT_DATA otherwise
 */
int mbedtls_ecjpake_check( const mbedtls_ecjpake_context *ctx );

int mbedtls_ecjpake_write_round_one( mbedtls_ecjpake_context *ctx,
                            unsigned char *buf, size_t len, size_t *olen,
                            int (*f_rng)(void *, unsigned char *, size_t),
                            void *p_rng );

int mbedtls_ecjpake_read_round_one( mbedtls_ecjpake_context *ctx,
                                    const unsigned char *buf,
                                    size_t len );

int mbedtls_ecjpake_write_round_two( mbedtls_ecjpake_context *ctx,
                            unsigned char *buf, size_t len, size_t *olen,
                            int (*f_rng)(void *, unsigned char *, size_t),
                            void *p_rng );

int mbedtls_ecjpake_read_round_two( mbedtls_ecjpake_context *ctx,
                                    const unsigned char *buf,
                                    size_t len );

int mbedtls_ecjpake_derive_secret( mbedtls_ecjpake_context *ctx,
                            unsigned char *buf, size_t len, size_t *olen,
                            int (*f_rng)(void *, unsigned char *, size_t),
                            void *p_rng );

void mbedtls_ecjpake_free( mbedtls_ecjpake_context *ctx );

#if defined(MBEDTLS_SELF_TEST)

int mbedtls_ecjpake_self_test( int verbose );
#endif

#ifdef __cplusplus
}
#endif

#endif /* ecjpake.h */