library/pk.c

/*
 *  Public Key abstraction layer
 *
 *  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.
 */

#include "common.h"

#if defined(MBEDTLS_PK_C)
#include "mbedtls/pk.h"
#include "pk_wrap.h"

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

#if defined(MBEDTLS_RSA_C)
#include "mbedtls/rsa.h"
#endif
#if defined(MBEDTLS_ECP_C)
#include "mbedtls/ecp.h"
#endif
#if defined(MBEDTLS_ECDSA_C)
#include "mbedtls/ecdsa.h"
#endif

#if defined(MBEDTLS_USE_PSA_CRYPTO)
#include "mbedtls/psa_util.h"
#endif

#include <limits.h>
#include <stdint.h>

/* Parameter validation macros based on platform_util.h */
#define PK_VALIDATE_RET( cond )    \
    MBEDTLS_INTERNAL_VALIDATE_RET( cond, MBEDTLS_ERR_PK_BAD_INPUT_DATA )
#define PK_VALIDATE( cond )        \
    MBEDTLS_INTERNAL_VALIDATE( cond )

/*
 * Initialise a mbedtls_pk_context
 */
void mbedtls_pk_init( mbedtls_pk_context *ctx )
{
    PK_VALIDATE( ctx != NULL );

    ctx->pk_info = NULL;
    ctx->pk_ctx = NULL;
}

/*
 * Free (the components of) a mbedtls_pk_context
 */
void mbedtls_pk_free( mbedtls_pk_context *ctx )
{
    if( ctx == NULL )
        return;

    if ( ctx->pk_info != NULL )
        ctx->pk_info->ctx_free_func( ctx->pk_ctx );

    mbedtls_platform_zeroize( ctx, sizeof( mbedtls_pk_context ) );
}

#if defined(MBEDTLS_ECDSA_C) && defined(MBEDTLS_ECP_RESTARTABLE)
/*
 * Initialize a restart context
 */
void mbedtls_pk_restart_init( mbedtls_pk_restart_ctx *ctx )
{
    PK_VALIDATE( ctx != NULL );
    ctx->pk_info = NULL;
    ctx->rs_ctx = NULL;
}

/*
 * Free the components of a restart context
 */
void mbedtls_pk_restart_free( mbedtls_pk_restart_ctx *ctx )
{
    if( ctx == NULL || ctx->pk_info == NULL ||
        ctx->pk_info->rs_free_func == NULL )
    {
        return;
    }

    ctx->pk_info->rs_free_func( ctx->rs_ctx );

    ctx->pk_info = NULL;
    ctx->rs_ctx = NULL;
}
#endif /* MBEDTLS_ECDSA_C && MBEDTLS_ECP_RESTARTABLE */

/*
 * Get pk_info structure from type
 */
const mbedtls_pk_info_t * mbedtls_pk_info_from_type( mbedtls_pk_type_t pk_type )
{
    switch( pk_type ) {
#if defined(MBEDTLS_RSA_C)
        case MBEDTLS_PK_RSA:
            return( &mbedtls_rsa_info );
#endif
#if defined(MBEDTLS_ECP_C)
        case MBEDTLS_PK_ECKEY:
            return( &mbedtls_eckey_info );
        case MBEDTLS_PK_ECKEY_DH:
            return( &mbedtls_eckeydh_info );
#endif
#if defined(MBEDTLS_ECDSA_C)
        case MBEDTLS_PK_ECDSA:
            return( &mbedtls_ecdsa_info );
#endif
        /* MBEDTLS_PK_RSA_ALT omitted on purpose */
        default:
            return( NULL );
    }
}

/*
 * Initialise context
 */
int mbedtls_pk_setup( mbedtls_pk_context *ctx, const mbedtls_pk_info_t *info )
{
    PK_VALIDATE_RET( ctx != NULL );
    if( info == NULL || ctx->pk_info != NULL )
        return( MBEDTLS_ERR_PK_BAD_INPUT_DATA );

    if( ( ctx->pk_ctx = info->ctx_alloc_func() ) == NULL )
        return( MBEDTLS_ERR_PK_ALLOC_FAILED );

    ctx->pk_info = info;

    return( 0 );
}

#if defined(MBEDTLS_USE_PSA_CRYPTO)
/*
 * Initialise a PSA-wrapping context
 */
int mbedtls_pk_setup_opaque( mbedtls_pk_context *ctx,
                             const mbedtls_svc_key_id_t key )
{
    const mbedtls_pk_info_t * const info = &mbedtls_pk_opaque_info;
    psa_key_attributes_t attributes = PSA_KEY_ATTRIBUTES_INIT;
    mbedtls_svc_key_id_t *pk_ctx;
    psa_key_type_t type;

    if( ctx == NULL || ctx->pk_info != NULL )
        return( MBEDTLS_ERR_PK_BAD_INPUT_DATA );

    if( PSA_SUCCESS != psa_get_key_attributes( key, &attributes ) )
        return( MBEDTLS_ERR_PK_BAD_INPUT_DATA );
    type = psa_get_key_type( &attributes );
    psa_reset_key_attributes( &attributes );

    /* Current implementation of can_do() relies on this. */
    if( ! PSA_KEY_TYPE_IS_ECC_KEY_PAIR( type ) )
        return( MBEDTLS_ERR_PK_FEATURE_UNAVAILABLE) ;

    if( ( ctx->pk_ctx = info->ctx_alloc_func() ) == NULL )
        return( MBEDTLS_ERR_PK_ALLOC_FAILED );

    ctx->pk_info = info;

    pk_ctx = (mbedtls_svc_key_id_t *) ctx->pk_ctx;
    *pk_ctx = key;

    return( 0 );
}
#endif /* MBEDTLS_USE_PSA_CRYPTO */

#if defined(MBEDTLS_PK_RSA_ALT_SUPPORT)
/*
 * Initialize an RSA-alt context
 */
int mbedtls_pk_setup_rsa_alt( mbedtls_pk_context *ctx, void * key,
                         mbedtls_pk_rsa_alt_decrypt_func decrypt_func,
                         mbedtls_pk_rsa_alt_sign_func sign_func,
                         mbedtls_pk_rsa_alt_key_len_func key_len_func )
{
    mbedtls_rsa_alt_context *rsa_alt;
    const mbedtls_pk_info_t *info = &mbedtls_rsa_alt_info;

    PK_VALIDATE_RET( ctx != NULL );
    if( ctx->pk_info != NULL )
        return( MBEDTLS_ERR_PK_BAD_INPUT_DATA );

    if( ( ctx->pk_ctx = info->ctx_alloc_func() ) == NULL )
        return( MBEDTLS_ERR_PK_ALLOC_FAILED );

    ctx->pk_info = info;

    rsa_alt = (mbedtls_rsa_alt_context *) ctx->pk_ctx;

    rsa_alt->key = key;
    rsa_alt->decrypt_func = decrypt_func;
    rsa_alt->sign_func = sign_func;
    rsa_alt->key_len_func = key_len_func;

    return( 0 );
}
#endif /* MBEDTLS_PK_RSA_ALT_SUPPORT */

/*
 * Tell if a PK can do the operations of the given type
 */
int mbedtls_pk_can_do( const mbedtls_pk_context *ctx, mbedtls_pk_type_t type )
{
    /* A context with null pk_info is not set up yet and can't do anything.
     * For backward compatibility, also accept NULL instead of a context
     * pointer. */
    if( ctx == NULL || ctx->pk_info == NULL )
        return( 0 );

    return( ctx->pk_info->can_do( type ) );
}

/*
 * Helper for mbedtls_pk_sign and mbedtls_pk_verify
 */
static inline int pk_hashlen_helper( mbedtls_md_type_t md_alg, size_t *hash_len )
{
    const mbedtls_md_info_t *md_info;

    if( *hash_len != 0 )
        return( 0 );

    if( ( md_info = mbedtls_md_info_from_type( md_alg ) ) == NULL )
        return( -1 );

    *hash_len = mbedtls_md_get_size( md_info );
    return( 0 );
}

#if defined(MBEDTLS_ECDSA_C) && defined(MBEDTLS_ECP_RESTARTABLE)
/*
 * Helper to set up a restart context if needed
 */
static int pk_restart_setup( mbedtls_pk_restart_ctx *ctx,
                             const mbedtls_pk_info_t *info )
{
    /* Don't do anything if already set up or invalid */
    if( ctx == NULL || ctx->pk_info != NULL )
        return( 0 );

    /* Should never happen when we're called */
    if( info->rs_alloc_func == NULL || info->rs_free_func == NULL )
        return( MBEDTLS_ERR_PK_BAD_INPUT_DATA );

    if( ( ctx->rs_ctx = info->rs_alloc_func() ) == NULL )
        return( MBEDTLS_ERR_PK_ALLOC_FAILED );

    ctx->pk_info = info;

    return( 0 );
}
#endif /* MBEDTLS_ECDSA_C && MBEDTLS_ECP_RESTARTABLE */

/*
 * Verify a signature (restartable)
 */
int mbedtls_pk_verify_restartable( mbedtls_pk_context *ctx,
               mbedtls_md_type_t md_alg,
               const unsigned char *hash, size_t hash_len,
               const unsigned char *sig, size_t sig_len,
               mbedtls_pk_restart_ctx *rs_ctx )
{
    PK_VALIDATE_RET( ctx != NULL );
    PK_VALIDATE_RET( ( md_alg == MBEDTLS_MD_NONE && hash_len == 0 ) ||
                     hash != NULL );
    PK_VALIDATE_RET( sig != NULL );

    if( ctx->pk_info == NULL ||
        pk_hashlen_helper( md_alg, &hash_len ) != 0 )
        return( MBEDTLS_ERR_PK_BAD_INPUT_DATA );

#if defined(MBEDTLS_ECDSA_C) && defined(MBEDTLS_ECP_RESTARTABLE)
    /* optimization: use non-restartable version if restart disabled */
    if( rs_ctx != NULL &&
        mbedtls_ecp_restart_is_enabled() &&
        ctx->pk_info->verify_rs_func != NULL )
    {
        int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;

        if( ( ret = pk_restart_setup( rs_ctx, ctx->pk_info ) ) != 0 )
            return( ret );

        ret = ctx->pk_info->verify_rs_func( ctx->pk_ctx,
                   md_alg, hash, hash_len, sig, sig_len, rs_ctx->rs_ctx );

        if( ret != MBEDTLS_ERR_ECP_IN_PROGRESS )
            mbedtls_pk_restart_free( rs_ctx );

        return( ret );
    }
#else /* MBEDTLS_ECDSA_C && MBEDTLS_ECP_RESTARTABLE */
    (void) rs_ctx;
#endif /* MBEDTLS_ECDSA_C && MBEDTLS_ECP_RESTARTABLE */

    if( ctx->pk_info->verify_func == NULL )
        return( MBEDTLS_ERR_PK_TYPE_MISMATCH );

    return( ctx->pk_info->verify_func( ctx->pk_ctx, md_alg, hash, hash_len,
                                       sig, sig_len ) );
}

/*
 * Verify a signature
 */
int mbedtls_pk_verify( mbedtls_pk_context *ctx, mbedtls_md_type_t md_alg,
               const unsigned char *hash, size_t hash_len,
               const unsigned char *sig, size_t sig_len )
{
    return( mbedtls_pk_verify_restartable( ctx, md_alg, hash, hash_len,
                                           sig, sig_len, NULL ) );
}

/*
 * Verify a signature with options
 */
int mbedtls_pk_verify_ext( mbedtls_pk_type_t type, const void *options,
                   mbedtls_pk_context *ctx, mbedtls_md_type_t md_alg,
                   const unsigned char *hash, size_t hash_len,
                   const unsigned char *sig, size_t sig_len )
{
    PK_VALIDATE_RET( ctx != NULL );
    PK_VALIDATE_RET( ( md_alg == MBEDTLS_MD_NONE && hash_len == 0 ) ||
                     hash != NULL );
    PK_VALIDATE_RET( sig != NULL );

    if( ctx->pk_info == NULL )
        return( MBEDTLS_ERR_PK_BAD_INPUT_DATA );

    if( ! mbedtls_pk_can_do( ctx, type ) )
        return( MBEDTLS_ERR_PK_TYPE_MISMATCH );

    if( type != MBEDTLS_PK_RSASSA_PSS )
    {
        /* General case: no options */
        if( options != NULL )
            return( MBEDTLS_ERR_PK_BAD_INPUT_DATA );

        return( mbedtls_pk_verify( ctx, md_alg, hash, hash_len, sig, sig_len ) );
    }

#if defined(MBEDTLS_RSA_C) && defined(MBEDTLS_PKCS1_V21)
    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
    const mbedtls_pk_rsassa_pss_options *pss_opts;

#if SIZE_MAX > UINT_MAX
    if( md_alg == MBEDTLS_MD_NONE && UINT_MAX < hash_len )
        return( MBEDTLS_ERR_PK_BAD_INPUT_DATA );
#endif /* SIZE_MAX > UINT_MAX */

    if( options == NULL )
        return( MBEDTLS_ERR_PK_BAD_INPUT_DATA );

    pss_opts = (const mbedtls_pk_rsassa_pss_options *) options;

#if defined(MBEDTLS_USE_PSA_CRYPTO)
    psa_status_t status;
    if( pss_opts->mgf1_hash_id == md_alg &&
        ( (size_t) pss_opts->expected_salt_len == hash_len ||
            pss_opts->expected_salt_len  == MBEDTLS_RSA_SALT_LEN_ANY ) )
    {
        /* see RSA_PUB_DER_MAX_BYTES in pkwrite.c */
        unsigned char buf[ 38 + 2 * MBEDTLS_MPI_MAX_SIZE ];
        unsigned char *p;
        int key_len;
        psa_algorithm_t psa_md_alg = mbedtls_psa_translate_md( md_alg );
        mbedtls_svc_key_id_t key_id = MBEDTLS_SVC_KEY_ID_INIT;
        psa_key_attributes_t attributes = PSA_KEY_ATTRIBUTES_INIT;
        psa_algorithm_t psa_sig_alg =
            ( pss_opts->expected_salt_len == MBEDTLS_RSA_SALT_LEN_ANY ?
                                 PSA_ALG_RSA_PSS_ANY_SALT(psa_md_alg) :
                                 PSA_ALG_RSA_PSS(psa_md_alg) );
        p = buf + sizeof( buf );
        key_len = mbedtls_pk_write_pubkey( &p, buf, ctx );

        if( key_len < 0 )
            return( key_len );

        psa_set_key_type( &attributes, PSA_KEY_TYPE_RSA_PUBLIC_KEY );
        psa_set_key_usage_flags( &attributes, PSA_KEY_USAGE_VERIFY_HASH );
        psa_set_key_algorithm( &attributes, psa_sig_alg );

        status = psa_import_key( &attributes,
                                 buf + sizeof( buf ) - key_len, key_len,
                                 &key_id );
        if( status != PSA_SUCCESS )
        {
            psa_destroy_key( key_id );
            return( mbedtls_psa_err_translate_pk( status ) );
        }

        status = psa_verify_hash( key_id, psa_sig_alg, hash,
                                  hash_len, sig, sig_len );
        psa_destroy_key( key_id );

        if( status == PSA_SUCCESS && sig_len > mbedtls_pk_get_len( ctx ) )
            return( MBEDTLS_ERR_PK_SIG_LEN_MISMATCH );

        return( status == PSA_ERROR_INVALID_SIGNATURE?
                              MBEDTLS_ERR_RSA_VERIFY_FAILED :
                              mbedtls_psa_err_translate_pk( status ) );
    }
    else
#endif
    {
        if( sig_len < mbedtls_pk_get_len( ctx ) )
            return( MBEDTLS_ERR_RSA_VERIFY_FAILED );

        ret = mbedtls_rsa_rsassa_pss_verify_ext( mbedtls_pk_rsa( *ctx ),
                                                 md_alg, (unsigned int) hash_len, hash,
                                                 pss_opts->mgf1_hash_id,
                                                 pss_opts->expected_salt_len,
                                                 sig );
        if( ret != 0 )
            return( ret );

        if( sig_len > mbedtls_pk_get_len( ctx ) )
            return( MBEDTLS_ERR_PK_SIG_LEN_MISMATCH );

        return( 0 );
    }
#else
    return( MBEDTLS_ERR_PK_FEATURE_UNAVAILABLE );
#endif /* MBEDTLS_RSA_C && MBEDTLS_PKCS1_V21 */
}

/*
 * Make a signature (restartable)
 */
int mbedtls_pk_sign_restartable( mbedtls_pk_context *ctx,
             mbedtls_md_type_t md_alg,
             const unsigned char *hash, size_t hash_len,
             unsigned char *sig, size_t sig_size, size_t *sig_len,
             int (*f_rng)(void *, unsigned char *, size_t), void *p_rng,
             mbedtls_pk_restart_ctx *rs_ctx )
{
    PK_VALIDATE_RET( ctx != NULL );
    PK_VALIDATE_RET( ( md_alg == MBEDTLS_MD_NONE && hash_len == 0 ) ||
                     hash != NULL );
    PK_VALIDATE_RET( sig != NULL );

    if( ctx->pk_info == NULL ||
        pk_hashlen_helper( md_alg, &hash_len ) != 0 )
        return( MBEDTLS_ERR_PK_BAD_INPUT_DATA );

#if defined(MBEDTLS_ECDSA_C) && defined(MBEDTLS_ECP_RESTARTABLE)
    /* optimization: use non-restartable version if restart disabled */
    if( rs_ctx != NULL &&
        mbedtls_ecp_restart_is_enabled() &&
        ctx->pk_info->sign_rs_func != NULL )
    {
        int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;

        if( ( ret = pk_restart_setup( rs_ctx, ctx->pk_info ) ) != 0 )
            return( ret );

        ret = ctx->pk_info->sign_rs_func( ctx->pk_ctx, md_alg,
                                          hash, hash_len,
                                          sig, sig_size, sig_len,
                                          f_rng, p_rng, rs_ctx->rs_ctx );

        if( ret != MBEDTLS_ERR_ECP_IN_PROGRESS )
            mbedtls_pk_restart_free( rs_ctx );

        return( ret );
    }
#else /* MBEDTLS_ECDSA_C && MBEDTLS_ECP_RESTARTABLE */
    (void) rs_ctx;
#endif /* MBEDTLS_ECDSA_C && MBEDTLS_ECP_RESTARTABLE */

    if( ctx->pk_info->sign_func == NULL )
        return( MBEDTLS_ERR_PK_TYPE_MISMATCH );

    return( ctx->pk_info->sign_func( ctx->pk_ctx, md_alg,
                                     hash, hash_len,
                                     sig, sig_size, sig_len,
                                     f_rng, p_rng ) );
}

/*
 * Make a signature
 */
int mbedtls_pk_sign( mbedtls_pk_context *ctx, mbedtls_md_type_t md_alg,
             const unsigned char *hash, size_t hash_len,
             unsigned char *sig, size_t sig_size, size_t *sig_len,
             int (*f_rng)(void *, unsigned char *, size_t), void *p_rng )
{
    return( mbedtls_pk_sign_restartable( ctx, md_alg, hash, hash_len,
                                         sig, sig_size, sig_len,
                                         f_rng, p_rng, NULL ) );
}

/*
 * Decrypt message
 */
int mbedtls_pk_decrypt( mbedtls_pk_context *ctx,
                const unsigned char *input, size_t ilen,
                unsigned char *output, size_t *olen, size_t osize,
                int (*f_rng)(void *, unsigned char *, size_t), void *p_rng )
{
    PK_VALIDATE_RET( ctx != NULL );
    PK_VALIDATE_RET( input != NULL || ilen == 0 );
    PK_VALIDATE_RET( output != NULL || osize == 0 );
    PK_VALIDATE_RET( olen != NULL );

    if( ctx->pk_info == NULL )
        return( MBEDTLS_ERR_PK_BAD_INPUT_DATA );

    if( ctx->pk_info->decrypt_func == NULL )
        return( MBEDTLS_ERR_PK_TYPE_MISMATCH );

    return( ctx->pk_info->decrypt_func( ctx->pk_ctx, input, ilen,
                output, olen, osize, f_rng, p_rng ) );
}

/*
 * Encrypt message
 */
int mbedtls_pk_encrypt( mbedtls_pk_context *ctx,
                const unsigned char *input, size_t ilen,
                unsigned char *output, size_t *olen, size_t osize,
                int (*f_rng)(void *, unsigned char *, size_t), void *p_rng )
{
    PK_VALIDATE_RET( ctx != NULL );
    PK_VALIDATE_RET( input != NULL || ilen == 0 );
    PK_VALIDATE_RET( output != NULL || osize == 0 );
    PK_VALIDATE_RET( olen != NULL );

    if( ctx->pk_info == NULL )
        return( MBEDTLS_ERR_PK_BAD_INPUT_DATA );

    if( ctx->pk_info->encrypt_func == NULL )
        return( MBEDTLS_ERR_PK_TYPE_MISMATCH );

    return( ctx->pk_info->encrypt_func( ctx->pk_ctx, input, ilen,
                output, olen, osize, f_rng, p_rng ) );
}

/*
 * Check public-private key pair
 */
int mbedtls_pk_check_pair( const mbedtls_pk_context *pub,
                           const mbedtls_pk_context *prv,
                           int (*f_rng)(void *, unsigned char *, size_t),
                           void *p_rng )
{
    PK_VALIDATE_RET( pub != NULL );
    PK_VALIDATE_RET( prv != NULL );

    if( pub->pk_info == NULL ||
        prv->pk_info == NULL )
    {
        return( MBEDTLS_ERR_PK_BAD_INPUT_DATA );
    }

    if( f_rng == NULL )
        return( MBEDTLS_ERR_PK_BAD_INPUT_DATA );

    if( prv->pk_info->check_pair_func == NULL )
        return( MBEDTLS_ERR_PK_FEATURE_UNAVAILABLE );

    if( prv->pk_info->type == MBEDTLS_PK_RSA_ALT )
    {
        if( pub->pk_info->type != MBEDTLS_PK_RSA )
            return( MBEDTLS_ERR_PK_TYPE_MISMATCH );
    }
    else
    {
        if( pub->pk_info != prv->pk_info )
            return( MBEDTLS_ERR_PK_TYPE_MISMATCH );
    }

    return( prv->pk_info->check_pair_func( pub->pk_ctx, prv->pk_ctx, f_rng, p_rng ) );
}

/*
 * Get key size in bits
 */
size_t mbedtls_pk_get_bitlen( const mbedtls_pk_context *ctx )
{
    /* For backward compatibility, accept NULL or a context that
     * isn't set up yet, and return a fake value that should be safe. */
    if( ctx == NULL || ctx->pk_info == NULL )
        return( 0 );

    return( ctx->pk_info->get_bitlen( ctx->pk_ctx ) );
}

/*
 * Export debug information
 */
int mbedtls_pk_debug( const mbedtls_pk_context *ctx, mbedtls_pk_debug_item *items )
{
    PK_VALIDATE_RET( ctx != NULL );
    if( ctx->pk_info == NULL )
        return( MBEDTLS_ERR_PK_BAD_INPUT_DATA );

    if( ctx->pk_info->debug_func == NULL )
        return( MBEDTLS_ERR_PK_TYPE_MISMATCH );

    ctx->pk_info->debug_func( ctx->pk_ctx, items );
    return( 0 );
}

/*
 * Access the PK type name
 */
const char *mbedtls_pk_get_name( const mbedtls_pk_context *ctx )
{
    if( ctx == NULL || ctx->pk_info == NULL )
        return( "invalid PK" );

    return( ctx->pk_info->name );
}

/*
 * Access the PK type
 */
mbedtls_pk_type_t mbedtls_pk_get_type( const mbedtls_pk_context *ctx )
{
    if( ctx == NULL || ctx->pk_info == NULL )
        return( MBEDTLS_PK_NONE );

    return( ctx->pk_info->type );
}

#if defined(MBEDTLS_USE_PSA_CRYPTO)
/*
 * Load the key to a PSA key slot,
 * then turn the PK context into a wrapper for that key slot.
 *
 * Currently only works for EC private keys.
 */
int mbedtls_pk_wrap_as_opaque( mbedtls_pk_context *pk,
                               mbedtls_svc_key_id_t *key,
                               psa_algorithm_t hash_alg )
{
#if !defined(MBEDTLS_ECP_C)
    ((void) pk);
    ((void) key);
    ((void) hash_alg);
    return( MBEDTLS_ERR_PK_TYPE_MISMATCH );
#else
    const mbedtls_ecp_keypair *ec;
    unsigned char d[MBEDTLS_ECP_MAX_BYTES];
    size_t d_len;
    psa_ecc_family_t curve_id;
    psa_key_attributes_t attributes = PSA_KEY_ATTRIBUTES_INIT;
    psa_key_type_t key_type;
    size_t bits;
    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;

    /* export the private key material in the format PSA wants */
    if( mbedtls_pk_get_type( pk ) != MBEDTLS_PK_ECKEY )
        return( MBEDTLS_ERR_PK_TYPE_MISMATCH );

    ec = mbedtls_pk_ec( *pk );
    d_len = ( ec->grp.nbits + 7 ) / 8;
    if( ( ret = mbedtls_mpi_write_binary( &ec->d, d, d_len ) ) != 0 )
        return( ret );

    curve_id = mbedtls_ecc_group_to_psa( ec->grp.id, &bits );
    key_type = PSA_KEY_TYPE_ECC_KEY_PAIR( curve_id );

    /* prepare the key attributes */
    psa_set_key_type( &attributes, key_type );
    psa_set_key_bits( &attributes, bits );
    psa_set_key_usage_flags( &attributes, PSA_KEY_USAGE_SIGN_HASH );
    psa_set_key_algorithm( &attributes, PSA_ALG_ECDSA(hash_alg) );

    /* import private key into PSA */
    if( PSA_SUCCESS != psa_import_key( &attributes, d, d_len, key ) )
        return( MBEDTLS_ERR_PLATFORM_HW_ACCEL_FAILED );

    /* make PK context wrap the key slot */
    mbedtls_pk_free( pk );
    mbedtls_pk_init( pk );

    return( mbedtls_pk_setup_opaque( pk, *key ) );
#endif /* MBEDTLS_ECP_C */
}
#endif /* MBEDTLS_USE_PSA_CRYPTO */
#endif /* MBEDTLS_PK_C */