library/ecjpake.c

/*
 *  Elliptic curve J-PAKE
 *
 *  Copyright The Mbed TLS Contributors
 *  SPDX-License-Identifier: Apache-2.0
 *
 *  Licensed under the Apache License, Version 2.0 (the "License"); you may
 *  not use this file except in compliance with the License.
 *  You may obtain a copy of the License at
 *
 *  http://www.apache.org/licenses/LICENSE-2.0
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 *  WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License.
 */

/*
 * References in the code are to the Thread v1.0 Specification,
 * available to members of the Thread Group http://threadgroup.org/
 */

#include "common.h"

#if defined(MBEDTLS_ECJPAKE_C)

#include "mbedtls/ecjpake.h"
#include "mbedtls/platform_util.h"
#include "mbedtls/error.h"

/* We use MD first if it's available (for compatibility reasons)
 * and "fall back" to PSA otherwise (which needs psa_crypto_init()). */
#if !defined(MBEDTLS_MD_C)
#include "psa/crypto.h"
#include "mbedtls/psa_util.h"
#endif /* !MBEDTLS_MD_C */

#include "hash_info.h"

#include <string.h>

#if !defined(MBEDTLS_ECJPAKE_ALT)

/*
 * Convert a mbedtls_ecjpake_role to identifier string
 */
static const char * const ecjpake_id[] = {
    "client",
    "server"
};

#define ID_MINE     ( ecjpake_id[ ctx->role ] )
#define ID_PEER     ( ecjpake_id[ 1 - ctx->role ] )

/**
  * Helper to Compute a hash from md_type
  */
static int mbedtls_ecjpake_compute_hash( mbedtls_md_type_t md_type,
                                    const unsigned char *input, size_t ilen,
                                    unsigned char *output )
{
#if defined(MBEDTLS_MD_C)
    return( mbedtls_md( mbedtls_md_info_from_type( md_type ),
                        input, ilen, output ) );
#else
    psa_algorithm_t alg = mbedtls_psa_translate_md( md_type );
    psa_status_t status;
    size_t out_size = PSA_HASH_LENGTH( alg );
    size_t out_len;

    status = psa_hash_compute( alg, input, ilen, output, out_size, &out_len );

    return( mbedtls_md_error_from_psa( status ) );
#endif /* !MBEDTLS_MD_C */
}

/*
 * Initialize context
 */
void mbedtls_ecjpake_init( mbedtls_ecjpake_context *ctx )
{
    ctx->md_type = MBEDTLS_MD_NONE;
    mbedtls_ecp_group_init( &ctx->grp );
    ctx->point_format = MBEDTLS_ECP_PF_UNCOMPRESSED;

    mbedtls_ecp_point_init( &ctx->Xm1 );
    mbedtls_ecp_point_init( &ctx->Xm2 );
    mbedtls_ecp_point_init( &ctx->Xp1 );
    mbedtls_ecp_point_init( &ctx->Xp2 );
    mbedtls_ecp_point_init( &ctx->Xp  );

    mbedtls_mpi_init( &ctx->xm1 );
    mbedtls_mpi_init( &ctx->xm2 );
    mbedtls_mpi_init( &ctx->s   );
}

/*
 * Free context
 */
void mbedtls_ecjpake_free( mbedtls_ecjpake_context *ctx )
{
    if( ctx == NULL )
        return;

    ctx->md_type = MBEDTLS_MD_NONE;
    mbedtls_ecp_group_free( &ctx->grp );

    mbedtls_ecp_point_free( &ctx->Xm1 );
    mbedtls_ecp_point_free( &ctx->Xm2 );
    mbedtls_ecp_point_free( &ctx->Xp1 );
    mbedtls_ecp_point_free( &ctx->Xp2 );
    mbedtls_ecp_point_free( &ctx->Xp  );

    mbedtls_mpi_free( &ctx->xm1 );
    mbedtls_mpi_free( &ctx->xm2 );
    mbedtls_mpi_free( &ctx->s   );
}

/*
 * Setup context
 */
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 )
{
    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;

    if( role != MBEDTLS_ECJPAKE_CLIENT && role != MBEDTLS_ECJPAKE_SERVER )
        return( MBEDTLS_ERR_ECP_BAD_INPUT_DATA );

    ctx->role = role;

#if defined(MBEDTLS_MD_C)
    if( ( mbedtls_md_info_from_type( hash ) ) == NULL )
        return( MBEDTLS_ERR_MD_FEATURE_UNAVAILABLE );
#else
    if( mbedtls_psa_translate_md( hash ) == MBEDTLS_MD_NONE )
        return( MBEDTLS_ERR_MD_FEATURE_UNAVAILABLE );
#endif

    ctx->md_type = hash;

    MBEDTLS_MPI_CHK( mbedtls_ecp_group_load( &ctx->grp, curve ) );

    MBEDTLS_MPI_CHK( mbedtls_mpi_read_binary( &ctx->s, secret, len ) );

cleanup:
    if( ret != 0 )
        mbedtls_ecjpake_free( ctx );

    return( ret );
}

int mbedtls_ecjpake_set_point_format( mbedtls_ecjpake_context *ctx,
                                      int point_format )
{
    switch( point_format )
    {
        case MBEDTLS_ECP_PF_UNCOMPRESSED:
        case MBEDTLS_ECP_PF_COMPRESSED:
            ctx->point_format = point_format;
            return( 0 );
        default:
            return( MBEDTLS_ERR_ECP_BAD_INPUT_DATA );
    }
}

/*
 * Check if context is ready for use
 */
int mbedtls_ecjpake_check( const mbedtls_ecjpake_context *ctx )
{
    if( ctx->md_type == MBEDTLS_MD_NONE ||
        ctx->grp.id == MBEDTLS_ECP_DP_NONE ||
        ctx->s.p == NULL )
    {
        return( MBEDTLS_ERR_ECP_BAD_INPUT_DATA );
    }

    return( 0 );
}

/*
 * Write a point plus its length to a buffer
 */
static int ecjpake_write_len_point( unsigned char **p,
                                    const unsigned char *end,
                                    const mbedtls_ecp_group *grp,
                                    const int pf,
                                    const mbedtls_ecp_point *P )
{
    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
    size_t len;

    /* Need at least 4 for length plus 1 for point */
    if( end < *p || end - *p < 5 )
        return( MBEDTLS_ERR_ECP_BUFFER_TOO_SMALL );

    ret = mbedtls_ecp_point_write_binary( grp, P, pf,
                                          &len, *p + 4, end - ( *p + 4 ) );
    if( ret != 0 )
        return( ret );

    MBEDTLS_PUT_UINT32_BE( len, *p, 0 );

    *p += 4 + len;

    return( 0 );
}

/*
 * Size of the temporary buffer for ecjpake_hash:
 * 3 EC points plus their length, plus ID and its length (4 + 6 bytes)
 */
#define ECJPAKE_HASH_BUF_LEN    ( 3 * ( 4 + MBEDTLS_ECP_MAX_PT_LEN ) + 4 + 6 )

/*
 * Compute hash for ZKP (7.4.2.2.2.1)
 */
static int ecjpake_hash( const mbedtls_md_type_t md_type,
                         const mbedtls_ecp_group *grp,
                         const int pf,
                         const mbedtls_ecp_point *G,
                         const mbedtls_ecp_point *V,
                         const mbedtls_ecp_point *X,
                         const char *id,
                         mbedtls_mpi *h )
{
    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
    unsigned char buf[ECJPAKE_HASH_BUF_LEN];
    unsigned char *p = buf;
    const unsigned char *end = buf + sizeof( buf );
    const size_t id_len = strlen( id );
    unsigned char hash[MBEDTLS_MD_MAX_SIZE];

    /* Write things to temporary buffer */
    MBEDTLS_MPI_CHK( ecjpake_write_len_point( &p, end, grp, pf, G ) );
    MBEDTLS_MPI_CHK( ecjpake_write_len_point( &p, end, grp, pf, V ) );
    MBEDTLS_MPI_CHK( ecjpake_write_len_point( &p, end, grp, pf, X ) );

    if( end - p < 4 )
        return( MBEDTLS_ERR_ECP_BUFFER_TOO_SMALL );

    MBEDTLS_PUT_UINT32_BE( id_len, p, 0 );
    p += 4;

    if( end < p || (size_t)( end - p ) < id_len )
        return( MBEDTLS_ERR_ECP_BUFFER_TOO_SMALL );

    memcpy( p, id, id_len );
    p += id_len;

    /* Compute hash */
    MBEDTLS_MPI_CHK( mbedtls_ecjpake_compute_hash( md_type,
                                                   buf, p - buf, hash ) );

    /* Turn it into an integer mod n */
    MBEDTLS_MPI_CHK( mbedtls_mpi_read_binary( h, hash,
                                    mbedtls_hash_info_get_size( md_type ) ) );
    MBEDTLS_MPI_CHK( mbedtls_mpi_mod_mpi( h, h, &grp->N ) );

cleanup:
    return( ret );
}

/*
 * Parse a ECShnorrZKP (7.4.2.2.2) and verify it (7.4.2.3.3)
 */
static int ecjpake_zkp_read( const mbedtls_md_type_t md_type,
                             const mbedtls_ecp_group *grp,
                             const int pf,
                             const mbedtls_ecp_point *G,
                             const mbedtls_ecp_point *X,
                             const char *id,
                             const unsigned char **p,
                             const unsigned char *end )
{
    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
    mbedtls_ecp_point V, VV;
    mbedtls_mpi r, h;
    size_t r_len;

    mbedtls_ecp_point_init( &V );
    mbedtls_ecp_point_init( &VV );
    mbedtls_mpi_init( &r );
    mbedtls_mpi_init( &h );

    /*
     * struct {
     *     ECPoint V;
     *     opaque r<1..2^8-1>;
     * } ECSchnorrZKP;
     */
    if( end < *p )
        return( MBEDTLS_ERR_ECP_BAD_INPUT_DATA );

    MBEDTLS_MPI_CHK( mbedtls_ecp_tls_read_point( grp, &V, p, end - *p ) );

    if( end < *p || (size_t)( end - *p ) < 1 )
    {
        ret = MBEDTLS_ERR_ECP_BAD_INPUT_DATA;
        goto cleanup;
    }

    r_len = *(*p)++;

    if( end < *p || (size_t)( end - *p ) < r_len || r_len == 0 )
    {
        ret = MBEDTLS_ERR_ECP_BAD_INPUT_DATA;
        goto cleanup;
    }

    MBEDTLS_MPI_CHK( mbedtls_mpi_read_binary( &r, *p, r_len ) );
    *p += r_len;

    /*
     * Verification
     */
    MBEDTLS_MPI_CHK( ecjpake_hash( md_type, grp, pf, G, &V, X, id, &h ) );
    MBEDTLS_MPI_CHK( mbedtls_ecp_muladd( (mbedtls_ecp_group *) grp,
                     &VV, &h, X, &r, G ) );

    if( mbedtls_ecp_point_cmp( &VV, &V ) != 0 )
    {
        ret = MBEDTLS_ERR_ECP_VERIFY_FAILED;
        goto cleanup;
    }

cleanup:
    mbedtls_ecp_point_free( &V );
    mbedtls_ecp_point_free( &VV );
    mbedtls_mpi_free( &r );
    mbedtls_mpi_free( &h );

    return( ret );
}

/*
 * Generate ZKP (7.4.2.3.2) and write it as ECSchnorrZKP (7.4.2.2.2)
 */
static int ecjpake_zkp_write( const mbedtls_md_type_t md_type,
                              const mbedtls_ecp_group *grp,
                              const int pf,
                              const mbedtls_ecp_point *G,
                              const mbedtls_mpi *x,
                              const mbedtls_ecp_point *X,
                              const char *id,
                              unsigned char **p,
                              const unsigned char *end,
                              int (*f_rng)(void *, unsigned char *, size_t),
                              void *p_rng )
{
    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
    mbedtls_ecp_point V;
    mbedtls_mpi v;
    mbedtls_mpi h; /* later recycled to hold r */
    size_t len;

    if( end < *p )
        return( MBEDTLS_ERR_ECP_BUFFER_TOO_SMALL );

    mbedtls_ecp_point_init( &V );
    mbedtls_mpi_init( &v );
    mbedtls_mpi_init( &h );

    /* Compute signature */
    MBEDTLS_MPI_CHK( mbedtls_ecp_gen_keypair_base( (mbedtls_ecp_group *) grp,
                                                   G, &v, &V, f_rng, p_rng ) );
    MBEDTLS_MPI_CHK( ecjpake_hash( md_type, grp, pf, G, &V, X, id, &h ) );
    MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mpi( &h, &h, x ) ); /* x*h */
    MBEDTLS_MPI_CHK( mbedtls_mpi_sub_mpi( &h, &v, &h ) ); /* v - x*h */
    MBEDTLS_MPI_CHK( mbedtls_mpi_mod_mpi( &h, &h, &grp->N ) ); /* r */

    /* Write it out */
    MBEDTLS_MPI_CHK( mbedtls_ecp_tls_write_point( grp, &V,
                pf, &len, *p, end - *p ) );
    *p += len;

    len = mbedtls_mpi_size( &h ); /* actually r */
    if( end < *p || (size_t)( end - *p ) < 1 + len || len > 255 )
    {
        ret = MBEDTLS_ERR_ECP_BUFFER_TOO_SMALL;
        goto cleanup;
    }

    *(*p)++ = MBEDTLS_BYTE_0( len );
    MBEDTLS_MPI_CHK( mbedtls_mpi_write_binary( &h, *p, len ) ); /* r */
    *p += len;

cleanup:
    mbedtls_ecp_point_free( &V );
    mbedtls_mpi_free( &v );
    mbedtls_mpi_free( &h );

    return( ret );
}

/*
 * Parse a ECJPAKEKeyKP (7.4.2.2.1) and check proof
 * Output: verified public key X
 */
static int ecjpake_kkp_read( const mbedtls_md_type_t md_type,
                             const mbedtls_ecp_group *grp,
                             const int pf,
                             const mbedtls_ecp_point *G,
                             mbedtls_ecp_point *X,
                             const char *id,
                             const unsigned char **p,
                             const unsigned char *end )
{
    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;

    if( end < *p )
        return( MBEDTLS_ERR_ECP_BAD_INPUT_DATA );

    /*
     * struct {
     *     ECPoint X;
     *     ECSchnorrZKP zkp;
     * } ECJPAKEKeyKP;
     */
    MBEDTLS_MPI_CHK( mbedtls_ecp_tls_read_point( grp, X, p, end - *p ) );
    if( mbedtls_ecp_is_zero( X ) )
    {
        ret = MBEDTLS_ERR_ECP_INVALID_KEY;
        goto cleanup;
    }

    MBEDTLS_MPI_CHK( ecjpake_zkp_read( md_type, grp, pf, G, X, id, p, end ) );

cleanup:
    return( ret );
}

/*
 * Generate an ECJPAKEKeyKP
 * Output: the serialized structure, plus private/public key pair
 */
static int ecjpake_kkp_write( const mbedtls_md_type_t md_type,
                              const mbedtls_ecp_group *grp,
                              const int pf,
                              const mbedtls_ecp_point *G,
                              mbedtls_mpi *x,
                              mbedtls_ecp_point *X,
                              const char *id,
                              unsigned char **p,
                              const unsigned char *end,
                              int (*f_rng)(void *, unsigned char *, size_t),
                              void *p_rng )
{
    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
    size_t len;

    if( end < *p )
        return( MBEDTLS_ERR_ECP_BUFFER_TOO_SMALL );

    /* Generate key (7.4.2.3.1) and write it out */
    MBEDTLS_MPI_CHK( mbedtls_ecp_gen_keypair_base( (mbedtls_ecp_group *) grp, G, x, X,
                                                   f_rng, p_rng ) );
    MBEDTLS_MPI_CHK( mbedtls_ecp_tls_write_point( grp, X,
                pf, &len, *p, end - *p ) );
    *p += len;

    /* Generate and write proof */
    MBEDTLS_MPI_CHK( ecjpake_zkp_write( md_type, grp, pf, G, x, X, id,
                                        p, end, f_rng, p_rng ) );

cleanup:
    return( ret );
}

/*
 * Read a ECJPAKEKeyKPPairList (7.4.2.3) and check proofs
 * Outputs: verified peer public keys Xa, Xb
 */
static int ecjpake_kkpp_read( const mbedtls_md_type_t md_type,
                              const mbedtls_ecp_group *grp,
                              const int pf,
                              const mbedtls_ecp_point *G,
                              mbedtls_ecp_point *Xa,
                              mbedtls_ecp_point *Xb,
                              const char *id,
                              const unsigned char *buf,
                              size_t len )
{
    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
    const unsigned char *p = buf;
    const unsigned char *end = buf + len;

    /*
     * struct {
     *     ECJPAKEKeyKP ecjpake_key_kp_pair_list[2];
     * } ECJPAKEKeyKPPairList;
     */
    MBEDTLS_MPI_CHK( ecjpake_kkp_read( md_type, grp, pf, G, Xa, id, &p, end ) );
    MBEDTLS_MPI_CHK( ecjpake_kkp_read( md_type, grp, pf, G, Xb, id, &p, end ) );

    if( p != end )
        ret = MBEDTLS_ERR_ECP_BAD_INPUT_DATA;

cleanup:
    return( ret );
}

/*
 * Generate a ECJPAKEKeyKPPairList
 * Outputs: the serialized structure, plus two private/public key pairs
 */
static int ecjpake_kkpp_write( const mbedtls_md_type_t md_type,
                               const mbedtls_ecp_group *grp,
                               const int pf,
                               const mbedtls_ecp_point *G,
                               mbedtls_mpi *xm1,
                               mbedtls_ecp_point *Xa,
                               mbedtls_mpi *xm2,
                               mbedtls_ecp_point *Xb,
                               const char *id,
                               unsigned char *buf,
                               size_t len,
                               size_t *olen,
                               int (*f_rng)(void *, unsigned char *, size_t),
                               void *p_rng )
{
    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
    unsigned char *p = buf;
    const unsigned char *end = buf + len;

    MBEDTLS_MPI_CHK( ecjpake_kkp_write( md_type, grp, pf, G, xm1, Xa, id,
                &p, end, f_rng, p_rng ) );
    MBEDTLS_MPI_CHK( ecjpake_kkp_write( md_type, grp, pf, G, xm2, Xb, id,
                &p, end, f_rng, p_rng ) );

    *olen = p - buf;

cleanup:
    return( ret );
}

/*
 * Read and process the first round message
 */
int mbedtls_ecjpake_read_round_one( mbedtls_ecjpake_context *ctx,
                                    const unsigned char *buf,
                                    size_t len )
{
    return( ecjpake_kkpp_read( ctx->md_type, &ctx->grp, ctx->point_format,
                               &ctx->grp.G,
                               &ctx->Xp1, &ctx->Xp2, ID_PEER,
                               buf, len ) );
}

/*
 * Generate and write the first round message
 */
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 )
{
    return( ecjpake_kkpp_write( ctx->md_type, &ctx->grp, ctx->point_format,
                                &ctx->grp.G,
                                &ctx->xm1, &ctx->Xm1, &ctx->xm2, &ctx->Xm2,
                                ID_MINE, buf, len, olen, f_rng, p_rng ) );
}

/*
 * Compute the sum of three points R = A + B + C
 */
static int ecjpake_ecp_add3( mbedtls_ecp_group *grp, mbedtls_ecp_point *R,
                             const mbedtls_ecp_point *A,
                             const mbedtls_ecp_point *B,
                             const mbedtls_ecp_point *C )
{
    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
    mbedtls_mpi one;

    mbedtls_mpi_init( &one );

    MBEDTLS_MPI_CHK( mbedtls_mpi_lset( &one, 1 ) );
    MBEDTLS_MPI_CHK( mbedtls_ecp_muladd( grp, R, &one, A, &one, B ) );
    MBEDTLS_MPI_CHK( mbedtls_ecp_muladd( grp, R, &one, R, &one, C ) );

cleanup:
    mbedtls_mpi_free( &one );

    return( ret );
}

/*
 * Read and process second round message (C: 7.4.2.5, S: 7.4.2.6)
 */
int mbedtls_ecjpake_read_round_two( mbedtls_ecjpake_context *ctx,
                                            const unsigned char *buf,
                                            size_t len )
{
    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
    const unsigned char *p = buf;
    const unsigned char *end = buf + len;
    mbedtls_ecp_group grp;
    mbedtls_ecp_point G;    /* C: GB, S: GA */

    mbedtls_ecp_group_init( &grp );
    mbedtls_ecp_point_init( &G );

    /*
     * Server: GA = X3  + X4  + X1      (7.4.2.6.1)
     * Client: GB = X1  + X2  + X3      (7.4.2.5.1)
     * Unified: G = Xm1 + Xm2 + Xp1
     * We need that before parsing in order to check Xp as we read it
     */
    MBEDTLS_MPI_CHK( ecjpake_ecp_add3( &ctx->grp, &G,
                                       &ctx->Xm1, &ctx->Xm2, &ctx->Xp1 ) );

    /*
     * struct {
     *     ECParameters curve_params;   // only client reading server msg
     *     ECJPAKEKeyKP ecjpake_key_kp;
     * } Client/ServerECJPAKEParams;
     */
    if( ctx->role == MBEDTLS_ECJPAKE_CLIENT )
    {
        MBEDTLS_MPI_CHK( mbedtls_ecp_tls_read_group( &grp, &p, len ) );
        if( grp.id != ctx->grp.id )
        {
            ret = MBEDTLS_ERR_ECP_FEATURE_UNAVAILABLE;
            goto cleanup;
        }
    }

    MBEDTLS_MPI_CHK( ecjpake_kkp_read( ctx->md_type, &ctx->grp,
                            ctx->point_format,
                            &G, &ctx->Xp, ID_PEER, &p, end ) );

    if( p != end )
    {
        ret = MBEDTLS_ERR_ECP_BAD_INPUT_DATA;
        goto cleanup;
    }

cleanup:
    mbedtls_ecp_group_free( &grp );
    mbedtls_ecp_point_free( &G );

    return( ret );
}

/*
 * Compute R = +/- X * S mod N, taking care not to leak S
 */
static int ecjpake_mul_secret( mbedtls_mpi *R, int sign,
                               const mbedtls_mpi *X,
                               const mbedtls_mpi *S,
                               const mbedtls_mpi *N,
                               int (*f_rng)(void *, unsigned char *, size_t),
                               void *p_rng )
{
    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
    mbedtls_mpi b; /* Blinding value, then s + N * blinding */

    mbedtls_mpi_init( &b );

    /* b = s + rnd-128-bit * N */
    MBEDTLS_MPI_CHK( mbedtls_mpi_fill_random( &b, 16, f_rng, p_rng ) );
    MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mpi( &b, &b, N ) );
    MBEDTLS_MPI_CHK( mbedtls_mpi_add_mpi( &b, &b, S ) );

    /* R = sign * X * b mod N */
    MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mpi( R, X, &b ) );
    R->s *= sign;
    MBEDTLS_MPI_CHK( mbedtls_mpi_mod_mpi( R, R, N ) );

cleanup:
    mbedtls_mpi_free( &b );

    return( ret );
}

/*
 * Generate and write the second round message (S: 7.4.2.5, C: 7.4.2.6)
 */
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 ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
    mbedtls_ecp_point G;    /* C: GA, S: GB */
    mbedtls_ecp_point Xm;   /* C: Xc, S: Xs */
    mbedtls_mpi xm;         /* C: xc, S: xs */
    unsigned char *p = buf;
    const unsigned char *end = buf + len;
    size_t ec_len;

    mbedtls_ecp_point_init( &G );
    mbedtls_ecp_point_init( &Xm );
    mbedtls_mpi_init( &xm );

    /*
     * First generate private/public key pair (S: 7.4.2.5.1, C: 7.4.2.6.1)
     *
     * Client:  GA = X1  + X3  + X4  | xs = x2  * s | Xc = xc * GA
     * Server:  GB = X3  + X1  + X2  | xs = x4  * s | Xs = xs * GB
     * Unified: G  = Xm1 + Xp1 + Xp2 | xm = xm2 * s | Xm = xm * G
     */
    MBEDTLS_MPI_CHK( ecjpake_ecp_add3( &ctx->grp, &G,
                                       &ctx->Xp1, &ctx->Xp2, &ctx->Xm1 ) );
    MBEDTLS_MPI_CHK( ecjpake_mul_secret( &xm, 1, &ctx->xm2, &ctx->s,
                                         &ctx->grp.N, f_rng, p_rng ) );
    MBEDTLS_MPI_CHK( mbedtls_ecp_mul( &ctx->grp, &Xm, &xm, &G, f_rng, p_rng ) );

    /*
     * Now write things out
     *
     * struct {
     *     ECParameters curve_params;   // only server writing its message
     *     ECJPAKEKeyKP ecjpake_key_kp;
     * } Client/ServerECJPAKEParams;
     */
    if( ctx->role == MBEDTLS_ECJPAKE_SERVER )
    {
        if( end < p )
        {
            ret = MBEDTLS_ERR_ECP_BUFFER_TOO_SMALL;
            goto cleanup;
        }
        MBEDTLS_MPI_CHK( mbedtls_ecp_tls_write_group( &ctx->grp, &ec_len,
                                                      p, end - p ) );
        p += ec_len;
    }

    if( end < p )
    {
        ret = MBEDTLS_ERR_ECP_BUFFER_TOO_SMALL;
        goto cleanup;
    }
    MBEDTLS_MPI_CHK( mbedtls_ecp_tls_write_point( &ctx->grp, &Xm,
                     ctx->point_format, &ec_len, p, end - p ) );
    p += ec_len;

    MBEDTLS_MPI_CHK( ecjpake_zkp_write( ctx->md_type, &ctx->grp,
                                        ctx->point_format,
                                        &G, &xm, &Xm, ID_MINE,
                                        &p, end, f_rng, p_rng ) );

    *olen = p - buf;

cleanup:
    mbedtls_ecp_point_free( &G );
    mbedtls_ecp_point_free( &Xm );
    mbedtls_mpi_free( &xm );

    return( ret );
}

/*
 * Derive PMS (7.4.2.7 / 7.4.2.8)
 */
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 )
{
    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
    mbedtls_ecp_point K;
    mbedtls_mpi m_xm2_s, one;
    unsigned char kx[MBEDTLS_ECP_MAX_BYTES];
    size_t x_bytes;

    *olen = mbedtls_hash_info_get_size( ctx->md_type );
    if( len < *olen )
        return( MBEDTLS_ERR_ECP_BUFFER_TOO_SMALL );

    mbedtls_ecp_point_init( &K );
    mbedtls_mpi_init( &m_xm2_s );
    mbedtls_mpi_init( &one );

    MBEDTLS_MPI_CHK( mbedtls_mpi_lset( &one, 1 ) );

    /*
     * Client:  K = ( Xs - X4  * x2  * s ) * x2
     * Server:  K = ( Xc - X2  * x4  * s ) * x4
     * Unified: K = ( Xp - Xp2 * xm2 * s ) * xm2
     */
    MBEDTLS_MPI_CHK( ecjpake_mul_secret( &m_xm2_s, -1, &ctx->xm2, &ctx->s,
                                         &ctx->grp.N, f_rng, p_rng ) );
    MBEDTLS_MPI_CHK( mbedtls_ecp_muladd( &ctx->grp, &K,
                                         &one, &ctx->Xp,
                                         &m_xm2_s, &ctx->Xp2 ) );
    MBEDTLS_MPI_CHK( mbedtls_ecp_mul( &ctx->grp, &K, &ctx->xm2, &K,
                                      f_rng, p_rng ) );

    /* PMS = SHA-256( K.X ) */
    x_bytes = ( ctx->grp.pbits + 7 ) / 8;
    MBEDTLS_MPI_CHK( mbedtls_mpi_write_binary( &K.X, kx, x_bytes ) );
    MBEDTLS_MPI_CHK( mbedtls_ecjpake_compute_hash( ctx->md_type,
                                                   kx, x_bytes, buf ) );

cleanup:
    mbedtls_ecp_point_free( &K );
    mbedtls_mpi_free( &m_xm2_s );
    mbedtls_mpi_free( &one );

    return( ret );
}

#undef ID_MINE
#undef ID_PEER

#endif /* ! MBEDTLS_ECJPAKE_ALT */

#if defined(MBEDTLS_SELF_TEST)

#if defined(MBEDTLS_PLATFORM_C)
#include "mbedtls/platform.h"
#else
#include <stdio.h>
#define mbedtls_printf     printf
#endif

#if !defined(MBEDTLS_ECP_DP_SECP256R1_ENABLED) || \
    !defined(MBEDTLS_SHA256_C)
int mbedtls_ecjpake_self_test( int verbose )
{
    (void) verbose;
    return( 0 );
}
#else

static const unsigned char ecjpake_test_password[] = {
    0x74, 0x68, 0x72, 0x65, 0x61, 0x64, 0x6a, 0x70, 0x61, 0x6b, 0x65, 0x74,
    0x65, 0x73, 0x74
};

#if !defined(MBEDTLS_ECJPAKE_ALT)

static const unsigned char ecjpake_test_x1[] = {
    0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0x0a, 0x0b, 0x0c,
    0x0d, 0x0e, 0x0f, 0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17, 0x18,
    0x19, 0x1a, 0x1b, 0x1c, 0x1d, 0x1e, 0x1f, 0x21
};

static const unsigned char ecjpake_test_x2[] = {
    0x61, 0x62, 0x63, 0x64, 0x65, 0x66, 0x67, 0x68, 0x69, 0x6a, 0x6b, 0x6c,
    0x6d, 0x6e, 0x6f, 0x70, 0x71, 0x72, 0x73, 0x74, 0x75, 0x76, 0x77, 0x78,
    0x79, 0x7a, 0x7b, 0x7c, 0x7d, 0x7e, 0x7f, 0x81
};

static const unsigned char ecjpake_test_x3[] = {
    0x61, 0x62, 0x63, 0x64, 0x65, 0x66, 0x67, 0x68, 0x69, 0x6a, 0x6b, 0x6c,
    0x6d, 0x6e, 0x6f, 0x70, 0x71, 0x72, 0x73, 0x74, 0x75, 0x76, 0x77, 0x78,
    0x79, 0x7a, 0x7b, 0x7c, 0x7d, 0x7e, 0x7f, 0x81
};

static const unsigned char ecjpake_test_x4[] = {
    0xc1, 0xc2, 0xc3, 0xc4, 0xc5, 0xc6, 0xc7, 0xc8, 0xc9, 0xca, 0xcb, 0xcc,
    0xcd, 0xce, 0xcf, 0xd0, 0xd1, 0xd2, 0xd3, 0xd4, 0xd5, 0xd6, 0xd7, 0xd8,
    0xd9, 0xda, 0xdb, 0xdc, 0xdd, 0xde, 0xdf, 0xe1
};

static const unsigned char ecjpake_test_cli_one[] = {
    0x41, 0x04, 0xac, 0xcf, 0x01, 0x06, 0xef, 0x85, 0x8f, 0xa2, 0xd9, 0x19,
    0x33, 0x13, 0x46, 0x80, 0x5a, 0x78, 0xb5, 0x8b, 0xba, 0xd0, 0xb8, 0x44,
    0xe5, 0xc7, 0x89, 0x28, 0x79, 0x14, 0x61, 0x87, 0xdd, 0x26, 0x66, 0xad,
    0xa7, 0x81, 0xbb, 0x7f, 0x11, 0x13, 0x72, 0x25, 0x1a, 0x89, 0x10, 0x62,
    0x1f, 0x63, 0x4d, 0xf1, 0x28, 0xac, 0x48, 0xe3, 0x81, 0xfd, 0x6e, 0xf9,
    0x06, 0x07, 0x31, 0xf6, 0x94, 0xa4, 0x41, 0x04, 0x1d, 0xd0, 0xbd, 0x5d,
    0x45, 0x66, 0xc9, 0xbe, 0xd9, 0xce, 0x7d, 0xe7, 0x01, 0xb5, 0xe8, 0x2e,
    0x08, 0xe8, 0x4b, 0x73, 0x04, 0x66, 0x01, 0x8a, 0xb9, 0x03, 0xc7, 0x9e,
    0xb9, 0x82, 0x17, 0x22, 0x36, 0xc0, 0xc1, 0x72, 0x8a, 0xe4, 0xbf, 0x73,
    0x61, 0x0d, 0x34, 0xde, 0x44, 0x24, 0x6e, 0xf3, 0xd9, 0xc0, 0x5a, 0x22,
    0x36, 0xfb, 0x66, 0xa6, 0x58, 0x3d, 0x74, 0x49, 0x30, 0x8b, 0xab, 0xce,
    0x20, 0x72, 0xfe, 0x16, 0x66, 0x29, 0x92, 0xe9, 0x23, 0x5c, 0x25, 0x00,
    0x2f, 0x11, 0xb1, 0x50, 0x87, 0xb8, 0x27, 0x38, 0xe0, 0x3c, 0x94, 0x5b,
    0xf7, 0xa2, 0x99, 0x5d, 0xda, 0x1e, 0x98, 0x34, 0x58, 0x41, 0x04, 0x7e,
    0xa6, 0xe3, 0xa4, 0x48, 0x70, 0x37, 0xa9, 0xe0, 0xdb, 0xd7, 0x92, 0x62,
    0xb2, 0xcc, 0x27, 0x3e, 0x77, 0x99, 0x30, 0xfc, 0x18, 0x40, 0x9a, 0xc5,
    0x36, 0x1c, 0x5f, 0xe6, 0x69, 0xd7, 0x02, 0xe1, 0x47, 0x79, 0x0a, 0xeb,
    0x4c, 0xe7, 0xfd, 0x65, 0x75, 0xab, 0x0f, 0x6c, 0x7f, 0xd1, 0xc3, 0x35,
    0x93, 0x9a, 0xa8, 0x63, 0xba, 0x37, 0xec, 0x91, 0xb7, 0xe3, 0x2b, 0xb0,
    0x13, 0xbb, 0x2b, 0x41, 0x04, 0xa4, 0x95, 0x58, 0xd3, 0x2e, 0xd1, 0xeb,
    0xfc, 0x18, 0x16, 0xaf, 0x4f, 0xf0, 0x9b, 0x55, 0xfc, 0xb4, 0xca, 0x47,
    0xb2, 0xa0, 0x2d, 0x1e, 0x7c, 0xaf, 0x11, 0x79, 0xea, 0x3f, 0xe1, 0x39,
    0x5b, 0x22, 0xb8, 0x61, 0x96, 0x40, 0x16, 0xfa, 0xba, 0xf7, 0x2c, 0x97,
    0x56, 0x95, 0xd9, 0x3d, 0x4d, 0xf0, 0xe5, 0x19, 0x7f, 0xe9, 0xf0, 0x40,
    0x63, 0x4e, 0xd5, 0x97, 0x64, 0x93, 0x77, 0x87, 0xbe, 0x20, 0xbc, 0x4d,
    0xee, 0xbb, 0xf9, 0xb8, 0xd6, 0x0a, 0x33, 0x5f, 0x04, 0x6c, 0xa3, 0xaa,
    0x94, 0x1e, 0x45, 0x86, 0x4c, 0x7c, 0xad, 0xef, 0x9c, 0xf7, 0x5b, 0x3d,
    0x8b, 0x01, 0x0e, 0x44, 0x3e, 0xf0
};

static const unsigned char ecjpake_test_srv_one[] = {
    0x41, 0x04, 0x7e, 0xa6, 0xe3, 0xa4, 0x48, 0x70, 0x37, 0xa9, 0xe0, 0xdb,
    0xd7, 0x92, 0x62, 0xb2, 0xcc, 0x27, 0x3e, 0x77, 0x99, 0x30, 0xfc, 0x18,
    0x40, 0x9a, 0xc5, 0x36, 0x1c, 0x5f, 0xe6, 0x69, 0xd7, 0x02, 0xe1, 0x47,
    0x79, 0x0a, 0xeb, 0x4c, 0xe7, 0xfd, 0x65, 0x75, 0xab, 0x0f, 0x6c, 0x7f,
    0xd1, 0xc3, 0x35, 0x93, 0x9a, 0xa8, 0x63, 0xba, 0x37, 0xec, 0x91, 0xb7,
    0xe3, 0x2b, 0xb0, 0x13, 0xbb, 0x2b, 0x41, 0x04, 0x09, 0xf8, 0x5b, 0x3d,
    0x20, 0xeb, 0xd7, 0x88, 0x5c, 0xe4, 0x64, 0xc0, 0x8d, 0x05, 0x6d, 0x64,
    0x28, 0xfe, 0x4d, 0xd9, 0x28, 0x7a, 0xa3, 0x65, 0xf1, 0x31, 0xf4, 0x36,
    0x0f, 0xf3, 0x86, 0xd8, 0x46, 0x89, 0x8b, 0xc4, 0xb4, 0x15, 0x83, 0xc2,
    0xa5, 0x19, 0x7f, 0x65, 0xd7, 0x87, 0x42, 0x74, 0x6c, 0x12, 0xa5, 0xec,
    0x0a, 0x4f, 0xfe, 0x2f, 0x27, 0x0a, 0x75, 0x0a, 0x1d, 0x8f, 0xb5, 0x16,
    0x20, 0x93, 0x4d, 0x74, 0xeb, 0x43, 0xe5, 0x4d, 0xf4, 0x24, 0xfd, 0x96,
    0x30, 0x6c, 0x01, 0x17, 0xbf, 0x13, 0x1a, 0xfa, 0xbf, 0x90, 0xa9, 0xd3,
    0x3d, 0x11, 0x98, 0xd9, 0x05, 0x19, 0x37, 0x35, 0x14, 0x41, 0x04, 0x19,
    0x0a, 0x07, 0x70, 0x0f, 0xfa, 0x4b, 0xe6, 0xae, 0x1d, 0x79, 0xee, 0x0f,
    0x06, 0xae, 0xb5, 0x44, 0xcd, 0x5a, 0xdd, 0xaa, 0xbe, 0xdf, 0x70, 0xf8,
    0x62, 0x33, 0x21, 0x33, 0x2c, 0x54, 0xf3, 0x55, 0xf0, 0xfb, 0xfe, 0xc7,
    0x83, 0xed, 0x35, 0x9e, 0x5d, 0x0b, 0xf7, 0x37, 0x7a, 0x0f, 0xc4, 0xea,
    0x7a, 0xce, 0x47, 0x3c, 0x9c, 0x11, 0x2b, 0x41, 0xcc, 0xd4, 0x1a, 0xc5,
    0x6a, 0x56, 0x12, 0x41, 0x04, 0x36, 0x0a, 0x1c, 0xea, 0x33, 0xfc, 0xe6,
    0x41, 0x15, 0x64, 0x58, 0xe0, 0xa4, 0xea, 0xc2, 0x19, 0xe9, 0x68, 0x31,
    0xe6, 0xae, 0xbc, 0x88, 0xb3, 0xf3, 0x75, 0x2f, 0x93, 0xa0, 0x28, 0x1d,
    0x1b, 0xf1, 0xfb, 0x10, 0x60, 0x51, 0xdb, 0x96, 0x94, 0xa8, 0xd6, 0xe8,
    0x62, 0xa5, 0xef, 0x13, 0x24, 0xa3, 0xd9, 0xe2, 0x78, 0x94, 0xf1, 0xee,
    0x4f, 0x7c, 0x59, 0x19, 0x99, 0x65, 0xa8, 0xdd, 0x4a, 0x20, 0x91, 0x84,
    0x7d, 0x2d, 0x22, 0xdf, 0x3e, 0xe5, 0x5f, 0xaa, 0x2a, 0x3f, 0xb3, 0x3f,
    0xd2, 0xd1, 0xe0, 0x55, 0xa0, 0x7a, 0x7c, 0x61, 0xec, 0xfb, 0x8d, 0x80,
    0xec, 0x00, 0xc2, 0xc9, 0xeb, 0x12
};

static const unsigned char ecjpake_test_srv_two[] = {
    0x03, 0x00, 0x17, 0x41, 0x04, 0x0f, 0xb2, 0x2b, 0x1d, 0x5d, 0x11, 0x23,
    0xe0, 0xef, 0x9f, 0xeb, 0x9d, 0x8a, 0x2e, 0x59, 0x0a, 0x1f, 0x4d, 0x7c,
    0xed, 0x2c, 0x2b, 0x06, 0x58, 0x6e, 0x8f, 0x2a, 0x16, 0xd4, 0xeb, 0x2f,
    0xda, 0x43, 0x28, 0xa2, 0x0b, 0x07, 0xd8, 0xfd, 0x66, 0x76, 0x54, 0xca,
    0x18, 0xc5, 0x4e, 0x32, 0xa3, 0x33, 0xa0, 0x84, 0x54, 0x51, 0xe9, 0x26,
    0xee, 0x88, 0x04, 0xfd, 0x7a, 0xf0, 0xaa, 0xa7, 0xa6, 0x41, 0x04, 0x55,
    0x16, 0xea, 0x3e, 0x54, 0xa0, 0xd5, 0xd8, 0xb2, 0xce, 0x78, 0x6b, 0x38,
    0xd3, 0x83, 0x37, 0x00, 0x29, 0xa5, 0xdb, 0xe4, 0x45, 0x9c, 0x9d, 0xd6,
    0x01, 0xb4, 0x08, 0xa2, 0x4a, 0xe6, 0x46, 0x5c, 0x8a, 0xc9, 0x05, 0xb9,
    0xeb, 0x03, 0xb5, 0xd3, 0x69, 0x1c, 0x13, 0x9e, 0xf8, 0x3f, 0x1c, 0xd4,
    0x20, 0x0f, 0x6c, 0x9c, 0xd4, 0xec, 0x39, 0x22, 0x18, 0xa5, 0x9e, 0xd2,
    0x43, 0xd3, 0xc8, 0x20, 0xff, 0x72, 0x4a, 0x9a, 0x70, 0xb8, 0x8c, 0xb8,
    0x6f, 0x20, 0xb4, 0x34, 0xc6, 0x86, 0x5a, 0xa1, 0xcd, 0x79, 0x06, 0xdd,
    0x7c, 0x9b, 0xce, 0x35, 0x25, 0xf5, 0x08, 0x27, 0x6f, 0x26, 0x83, 0x6c
};

static const unsigned char ecjpake_test_cli_two[] = {
    0x41, 0x04, 0x69, 0xd5, 0x4e, 0xe8, 0x5e, 0x90, 0xce, 0x3f, 0x12, 0x46,
    0x74, 0x2d, 0xe5, 0x07, 0xe9, 0x39, 0xe8, 0x1d, 0x1d, 0xc1, 0xc5, 0xcb,
    0x98, 0x8b, 0x58, 0xc3, 0x10, 0xc9, 0xfd, 0xd9, 0x52, 0x4d, 0x93, 0x72,
    0x0b, 0x45, 0x54, 0x1c, 0x83, 0xee, 0x88, 0x41, 0x19, 0x1d, 0xa7, 0xce,
    0xd8, 0x6e, 0x33, 0x12, 0xd4, 0x36, 0x23, 0xc1, 0xd6, 0x3e, 0x74, 0x98,
    0x9a, 0xba, 0x4a, 0xff, 0xd1, 0xee, 0x41, 0x04, 0x07, 0x7e, 0x8c, 0x31,
    0xe2, 0x0e, 0x6b, 0xed, 0xb7, 0x60, 0xc1, 0x35, 0x93, 0xe6, 0x9f, 0x15,
    0xbe, 0x85, 0xc2, 0x7d, 0x68, 0xcd, 0x09, 0xcc, 0xb8, 0xc4, 0x18, 0x36,
    0x08, 0x91, 0x7c, 0x5c, 0x3d, 0x40, 0x9f, 0xac, 0x39, 0xfe, 0xfe, 0xe8,
    0x2f, 0x72, 0x92, 0xd3, 0x6f, 0x0d, 0x23, 0xe0, 0x55, 0x91, 0x3f, 0x45,
    0xa5, 0x2b, 0x85, 0xdd, 0x8a, 0x20, 0x52, 0xe9, 0xe1, 0x29, 0xbb, 0x4d,
    0x20, 0x0f, 0x01, 0x1f, 0x19, 0x48, 0x35, 0x35, 0xa6, 0xe8, 0x9a, 0x58,
    0x0c, 0x9b, 0x00, 0x03, 0xba, 0xf2, 0x14, 0x62, 0xec, 0xe9, 0x1a, 0x82,
    0xcc, 0x38, 0xdb, 0xdc, 0xae, 0x60, 0xd9, 0xc5, 0x4c
};

static const unsigned char ecjpake_test_pms[] = {
    0xf3, 0xd4, 0x7f, 0x59, 0x98, 0x44, 0xdb, 0x92, 0xa5, 0x69, 0xbb, 0xe7,
    0x98, 0x1e, 0x39, 0xd9, 0x31, 0xfd, 0x74, 0x3b, 0xf2, 0x2e, 0x98, 0xf9,
    0xb4, 0x38, 0xf7, 0x19, 0xd3, 0xc4, 0xf3, 0x51
};

/*
 * PRNG for test - !!!INSECURE NEVER USE IN PRODUCTION!!!
 *
 * This is the linear congruential generator from numerical recipes,
 * except we only use the low byte as the output. See
 * https://en.wikipedia.org/wiki/Linear_congruential_generator#Parameters_in_common_use
 */
static int self_test_rng( void *ctx, unsigned char *out, size_t len )
{
    static uint32_t state = 42;

    (void) ctx;

    for( size_t i = 0; i < len; i++ )
    {
        state = state * 1664525u + 1013904223u;
        out[i] = (unsigned char) state;
    }

    return( 0 );
}

/* Load my private keys and generate the corresponding public keys */
static int ecjpake_test_load( mbedtls_ecjpake_context *ctx,
                              const unsigned char *xm1, size_t len1,
                              const unsigned char *xm2, size_t len2 )
{
    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;

    MBEDTLS_MPI_CHK( mbedtls_mpi_read_binary( &ctx->xm1, xm1, len1 ) );
    MBEDTLS_MPI_CHK( mbedtls_mpi_read_binary( &ctx->xm2, xm2, len2 ) );
    MBEDTLS_MPI_CHK( mbedtls_ecp_mul( &ctx->grp, &ctx->Xm1, &ctx->xm1,
                                      &ctx->grp.G, self_test_rng, NULL ) );
    MBEDTLS_MPI_CHK( mbedtls_ecp_mul( &ctx->grp, &ctx->Xm2, &ctx->xm2,
                                      &ctx->grp.G, self_test_rng, NULL ) );

cleanup:
    return( ret );
}

#endif /* ! MBEDTLS_ECJPAKE_ALT */

/* For tests we don't need a secure RNG;
 * use the LGC from Numerical Recipes for simplicity */
static int ecjpake_lgc( void *p, unsigned char *out, size_t len )
{
    static uint32_t x = 42;
    (void) p;

    while( len > 0 )
    {
        size_t use_len = len > 4 ? 4 : len;
        x = 1664525 * x + 1013904223;
        memcpy( out, &x, use_len );
        out += use_len;
        len -= use_len;
    }

    return( 0 );
}

#define TEST_ASSERT( x )    \
    do {                    \
        if( x )             \
            ret = 0;        \
        else                \
        {                   \
            ret = 1;        \
            goto cleanup;   \
        }                   \
    } while( 0 )

/*
 * Checkup routine
 */
int mbedtls_ecjpake_self_test( int verbose )
{
    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
    mbedtls_ecjpake_context cli;
    mbedtls_ecjpake_context srv;
    unsigned char buf[512], pms[32];
    size_t len, pmslen;

    mbedtls_ecjpake_init( &cli );
    mbedtls_ecjpake_init( &srv );

    if( verbose != 0 )
        mbedtls_printf( "  ECJPAKE test #0 (setup): " );

    TEST_ASSERT( mbedtls_ecjpake_setup( &cli, MBEDTLS_ECJPAKE_CLIENT,
                    MBEDTLS_MD_SHA256, MBEDTLS_ECP_DP_SECP256R1,
                    ecjpake_test_password,
            sizeof( ecjpake_test_password ) ) == 0 );

    TEST_ASSERT( mbedtls_ecjpake_setup( &srv, MBEDTLS_ECJPAKE_SERVER,
                    MBEDTLS_MD_SHA256, MBEDTLS_ECP_DP_SECP256R1,
                    ecjpake_test_password,
            sizeof( ecjpake_test_password ) ) == 0 );

    if( verbose != 0 )
        mbedtls_printf( "passed\n" );

    if( verbose != 0 )
        mbedtls_printf( "  ECJPAKE test #1 (random handshake): " );

    TEST_ASSERT( mbedtls_ecjpake_write_round_one( &cli,
                 buf, sizeof( buf ), &len, ecjpake_lgc, NULL ) == 0 );

    TEST_ASSERT( mbedtls_ecjpake_read_round_one( &srv, buf, len ) == 0 );

    TEST_ASSERT( mbedtls_ecjpake_write_round_one( &srv,
                 buf, sizeof( buf ), &len, ecjpake_lgc, NULL ) == 0 );

    TEST_ASSERT( mbedtls_ecjpake_read_round_one( &cli, buf, len ) == 0 );

    TEST_ASSERT( mbedtls_ecjpake_write_round_two( &srv,
                 buf, sizeof( buf ), &len, ecjpake_lgc, NULL ) == 0 );

    TEST_ASSERT( mbedtls_ecjpake_read_round_two( &cli, buf, len ) == 0 );

    TEST_ASSERT( mbedtls_ecjpake_derive_secret( &cli,
                 pms, sizeof( pms ), &pmslen, ecjpake_lgc, NULL ) == 0 );

    TEST_ASSERT( mbedtls_ecjpake_write_round_two( &cli,
                 buf, sizeof( buf ), &len, ecjpake_lgc, NULL ) == 0 );

    TEST_ASSERT( mbedtls_ecjpake_read_round_two( &srv, buf, len ) == 0 );

    TEST_ASSERT( mbedtls_ecjpake_derive_secret( &srv,
                 buf, sizeof( buf ), &len, ecjpake_lgc, NULL ) == 0 );

    TEST_ASSERT( len == pmslen );
    TEST_ASSERT( memcmp( buf, pms, len ) == 0 );

    if( verbose != 0 )
        mbedtls_printf( "passed\n" );

#if !defined(MBEDTLS_ECJPAKE_ALT)
    /* 'reference handshake' tests can only be run against implementations
     * for which we have 100% control over how the random ephemeral keys
     * are generated. This is only the case for the internal mbed TLS
     * implementation, so these tests are skipped in case the internal
     * implementation is swapped out for an alternative one. */
    if( verbose != 0 )
        mbedtls_printf( "  ECJPAKE test #2 (reference handshake): " );

    /* Simulate generation of round one */
    MBEDTLS_MPI_CHK( ecjpake_test_load( &cli,
                ecjpake_test_x1, sizeof( ecjpake_test_x1 ),
                ecjpake_test_x2, sizeof( ecjpake_test_x2 ) ) );

    MBEDTLS_MPI_CHK( ecjpake_test_load( &srv,
                ecjpake_test_x3, sizeof( ecjpake_test_x3 ),
                ecjpake_test_x4, sizeof( ecjpake_test_x4 ) ) );

    /* Read round one */
    TEST_ASSERT( mbedtls_ecjpake_read_round_one( &srv,
                                    ecjpake_test_cli_one,
                            sizeof( ecjpake_test_cli_one ) ) == 0 );

    TEST_ASSERT( mbedtls_ecjpake_read_round_one( &cli,
                                    ecjpake_test_srv_one,
                            sizeof( ecjpake_test_srv_one ) ) == 0 );

    /* Skip generation of round two, read round two */
    TEST_ASSERT( mbedtls_ecjpake_read_round_two( &cli,
                                    ecjpake_test_srv_two,
                            sizeof( ecjpake_test_srv_two ) ) == 0 );

    TEST_ASSERT( mbedtls_ecjpake_read_round_two( &srv,
                                    ecjpake_test_cli_two,
                            sizeof( ecjpake_test_cli_two ) ) == 0 );

    /* Server derives PMS */
    TEST_ASSERT( mbedtls_ecjpake_derive_secret( &srv,
                 buf, sizeof( buf ), &len, ecjpake_lgc, NULL ) == 0 );

    TEST_ASSERT( len == sizeof( ecjpake_test_pms ) );
    TEST_ASSERT( memcmp( buf, ecjpake_test_pms, len ) == 0 );

    memset( buf, 0, len ); /* Avoid interferences with next step */

    /* Client derives PMS */
    TEST_ASSERT( mbedtls_ecjpake_derive_secret( &cli,
                 buf, sizeof( buf ), &len, ecjpake_lgc, NULL ) == 0 );

    TEST_ASSERT( len == sizeof( ecjpake_test_pms ) );
    TEST_ASSERT( memcmp( buf, ecjpake_test_pms, len ) == 0 );

    if( verbose != 0 )
        mbedtls_printf( "passed\n" );
#endif /* ! MBEDTLS_ECJPAKE_ALT */

cleanup:
    mbedtls_ecjpake_free( &cli );
    mbedtls_ecjpake_free( &srv );

    if( ret != 0 )
    {
        if( verbose != 0 )
            mbedtls_printf( "failed\n" );

        ret = 1;
    }

    if( verbose != 0 )
        mbedtls_printf( "\n" );

    return( ret );
}

#undef TEST_ASSERT

#endif /* MBEDTLS_ECP_DP_SECP256R1_ENABLED && MBEDTLS_SHA256_C */

#endif /* MBEDTLS_SELF_TEST */

#endif /* MBEDTLS_ECJPAKE_C */