library/psa_crypto_rsa.c

/*
 *  PSA RSA layer on top of Mbed TLS crypto
 */
/*
 *  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_PSA_CRYPTO_C)

#include <psa/crypto.h>
#include "psa_crypto_core.h"
#include "psa_crypto_random_impl.h"
#include "psa_crypto_rsa.h"
#include "psa_crypto_hash.h"

#include <stdlib.h>
#include <string.h>
#include "mbedtls/platform.h"

#include <mbedtls/rsa.h>
#include <mbedtls/error.h>
#include <mbedtls/pk.h>
#include <mbedtls/pk_internal.h>

#if defined(MBEDTLS_PSA_BUILTIN_ALG_RSA_PKCS1V15_CRYPT) || \
    defined(MBEDTLS_PSA_BUILTIN_ALG_RSA_OAEP) || \
    defined(MBEDTLS_PSA_BUILTIN_ALG_RSA_PKCS1V15_SIGN) || \
    defined(MBEDTLS_PSA_BUILTIN_ALG_RSA_PSS) || \
    defined(MBEDTLS_PSA_BUILTIN_KEY_TYPE_RSA_KEY_PAIR) || \
    defined(MBEDTLS_PSA_BUILTIN_KEY_TYPE_RSA_PUBLIC_KEY)

/* Mbed TLS doesn't support non-byte-aligned key sizes (i.e. key sizes
 * that are not a multiple of 8) well. For example, there is only
 * mbedtls_rsa_get_len(), which returns a number of bytes, and no
 * way to return the exact bit size of a key.
 * To keep things simple, reject non-byte-aligned key sizes. */
static psa_status_t psa_check_rsa_key_byte_aligned(
    const mbedtls_rsa_context *rsa )
{
    mbedtls_mpi n;
    psa_status_t status;
    mbedtls_mpi_init( &n );
    status = mbedtls_to_psa_error(
        mbedtls_rsa_export( rsa, &n, NULL, NULL, NULL, NULL ) );
    if( status == PSA_SUCCESS )
    {
        if( mbedtls_mpi_bitlen( &n ) % 8 != 0 )
            status = PSA_ERROR_NOT_SUPPORTED;
    }
    mbedtls_mpi_free( &n );
    return( status );
}

psa_status_t mbedtls_psa_rsa_load_representation(
    psa_key_type_t type, const uint8_t *data, size_t data_length,
    mbedtls_rsa_context **p_rsa )
{
    psa_status_t status;
    mbedtls_pk_context ctx;
    size_t bits;
    mbedtls_pk_init( &ctx );

    /* Parse the data. */
    if( PSA_KEY_TYPE_IS_KEY_PAIR( type ) )
        status = mbedtls_to_psa_error(
            mbedtls_pk_parse_key( &ctx, data, data_length, NULL, 0 ) );
    else
        status = mbedtls_to_psa_error(
            mbedtls_pk_parse_public_key( &ctx, data, data_length ) );
    if( status != PSA_SUCCESS )
        goto exit;

    /* We have something that the pkparse module recognizes. If it is a
     * valid RSA key, store it. */
    if( mbedtls_pk_get_type( &ctx ) != MBEDTLS_PK_RSA )
    {
        status = PSA_ERROR_INVALID_ARGUMENT;
        goto exit;
    }

    /* The size of an RSA key doesn't have to be a multiple of 8. Mbed TLS
     * supports non-byte-aligned key sizes, but not well. For example,
     * mbedtls_rsa_get_len() returns the key size in bytes, not in bits. */
    bits = PSA_BYTES_TO_BITS( mbedtls_rsa_get_len( mbedtls_pk_rsa( ctx ) ) );
    if( bits > PSA_VENDOR_RSA_MAX_KEY_BITS )
    {
        status = PSA_ERROR_NOT_SUPPORTED;
        goto exit;
    }
    status = psa_check_rsa_key_byte_aligned( mbedtls_pk_rsa( ctx ) );
    if( status != PSA_SUCCESS )
        goto exit;

    /* Copy out the pointer to the RSA context, and reset the PK context
     * such that pk_free doesn't free the RSA context we just grabbed. */
    *p_rsa = mbedtls_pk_rsa( ctx );
    ctx.pk_info = NULL;

exit:
    mbedtls_pk_free( &ctx );
    return( status );
}
#endif /* defined(MBEDTLS_PSA_BUILTIN_ALG_RSA_PKCS1V15_CRYPT) ||
        * defined(MBEDTLS_PSA_BUILTIN_ALG_RSA_OAEP) ||
        * defined(MBEDTLS_PSA_BUILTIN_ALG_RSA_PKCS1V15_SIGN) ||
        * defined(MBEDTLS_PSA_BUILTIN_ALG_RSA_PSS) ||
        * defined(MBEDTLS_PSA_BUILTIN_KEY_TYPE_RSA_KEY_PAIR) ||
        * defined(MBEDTLS_PSA_BUILTIN_KEY_TYPE_RSA_PUBLIC_KEY) */

#if defined(MBEDTLS_PSA_BUILTIN_KEY_TYPE_RSA_KEY_PAIR) || \
    defined(MBEDTLS_PSA_BUILTIN_KEY_TYPE_RSA_PUBLIC_KEY)

psa_status_t mbedtls_psa_rsa_import_key(
    const psa_key_attributes_t *attributes,
    const uint8_t *data, size_t data_length,
    uint8_t *key_buffer, size_t key_buffer_size,
    size_t *key_buffer_length, size_t *bits )
{
    psa_status_t status;
    mbedtls_rsa_context *rsa = NULL;

    /* Parse input */
    status = mbedtls_psa_rsa_load_representation( attributes->core.type,
                                                  data,
                                                  data_length,
                                                  &rsa );
    if( status != PSA_SUCCESS )
        goto exit;

    *bits = (psa_key_bits_t) PSA_BYTES_TO_BITS( mbedtls_rsa_get_len( rsa ) );

    /* Re-export the data to PSA export format, such that we can store export
     * representation in the key slot. Export representation in case of RSA is
     * the smallest representation that's allowed as input, so a straight-up
     * allocation of the same size as the input buffer will be large enough. */
    status = mbedtls_psa_rsa_export_key( attributes->core.type,
                                         rsa,
                                         key_buffer,
                                         key_buffer_size,
                                         key_buffer_length );
exit:
    /* Always free the RSA object */
    mbedtls_rsa_free( rsa );
    mbedtls_free( rsa );

    return( status );
}

psa_status_t mbedtls_psa_rsa_export_key( psa_key_type_t type,
                                         mbedtls_rsa_context *rsa,
                                         uint8_t *data,
                                         size_t data_size,
                                         size_t *data_length )
{
#if defined(MBEDTLS_PK_WRITE_C)
    int ret;
    mbedtls_pk_context pk;
    uint8_t *pos = data + data_size;

    mbedtls_pk_init( &pk );
    pk.pk_info = &mbedtls_rsa_info;
    pk.pk_ctx = rsa;

    /* PSA Crypto API defines the format of an RSA key as a DER-encoded
     * representation of the non-encrypted PKCS#1 RSAPrivateKey for a
     * private key and of the RFC3279 RSAPublicKey for a public key. */
    if( PSA_KEY_TYPE_IS_KEY_PAIR( type ) )
        ret = mbedtls_pk_write_key_der( &pk, data, data_size );
    else
        ret = mbedtls_pk_write_pubkey( &pos, data, &pk );

    if( ret < 0 )
    {
        /* Clean up in case pk_write failed halfway through. */
        memset( data, 0, data_size );
        return( mbedtls_to_psa_error( ret ) );
    }

    /* The mbedtls_pk_xxx functions write to the end of the buffer.
     * Move the data to the beginning and erase remaining data
     * at the original location. */
    if( 2 * (size_t) ret <= data_size )
    {
        memcpy( data, data + data_size - ret, ret );
        memset( data + data_size - ret, 0, ret );
    }
    else if( (size_t) ret < data_size )
    {
        memmove( data, data + data_size - ret, ret );
        memset( data + ret, 0, data_size - ret );
    }

    *data_length = ret;
    return( PSA_SUCCESS );
#else
    (void) type;
    (void) rsa;
    (void) data;
    (void) data_size;
    (void) data_length;
    return( PSA_ERROR_NOT_SUPPORTED );
#endif /* MBEDTLS_PK_WRITE_C */
}

psa_status_t mbedtls_psa_rsa_export_public_key(
    const psa_key_attributes_t *attributes,
    const uint8_t *key_buffer, size_t key_buffer_size,
    uint8_t *data, size_t data_size, size_t *data_length )
{
    psa_status_t status = PSA_ERROR_CORRUPTION_DETECTED;
    mbedtls_rsa_context *rsa = NULL;

    status = mbedtls_psa_rsa_load_representation(
                 attributes->core.type, key_buffer, key_buffer_size, &rsa );
    if( status != PSA_SUCCESS )
        return( status );

    status = mbedtls_psa_rsa_export_key( PSA_KEY_TYPE_RSA_PUBLIC_KEY,
                                         rsa,
                                         data,
                                         data_size,
                                         data_length );

    mbedtls_rsa_free( rsa );
    mbedtls_free( rsa );

    return( status );
}
#endif /* defined(MBEDTLS_PSA_BUILTIN_KEY_TYPE_RSA_KEY_PAIR) ||
        * defined(MBEDTLS_PSA_BUILTIN_KEY_TYPE_RSA_PUBLIC_KEY) */

#if defined(MBEDTLS_PSA_BUILTIN_KEY_TYPE_RSA_KEY_PAIR) && \
    defined(MBEDTLS_GENPRIME)
static psa_status_t psa_rsa_read_exponent( const uint8_t *domain_parameters,
                                           size_t domain_parameters_size,
                                           int *exponent )
{
    size_t i;
    uint32_t acc = 0;

    if( domain_parameters_size == 0 )
    {
        *exponent = 65537;
        return( PSA_SUCCESS );
    }

    /* Mbed TLS encodes the public exponent as an int. For simplicity, only
     * support values that fit in a 32-bit integer, which is larger than
     * int on just about every platform anyway. */
    if( domain_parameters_size > sizeof( acc ) )
        return( PSA_ERROR_NOT_SUPPORTED );
    for( i = 0; i < domain_parameters_size; i++ )
        acc = ( acc << 8 ) | domain_parameters[i];
    if( acc > INT_MAX )
        return( PSA_ERROR_NOT_SUPPORTED );
    *exponent = acc;
    return( PSA_SUCCESS );
}

psa_status_t mbedtls_psa_rsa_generate_key(
    const psa_key_attributes_t *attributes,
    uint8_t *key_buffer, size_t key_buffer_size, size_t *key_buffer_length )
{
    psa_status_t status;
    mbedtls_rsa_context rsa;
    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
    int exponent;

    status = psa_rsa_read_exponent( attributes->domain_parameters,
                                    attributes->domain_parameters_size,
                                    &exponent );
    if( status != PSA_SUCCESS )
        return( status );

    mbedtls_rsa_init( &rsa, MBEDTLS_RSA_PKCS_V15, MBEDTLS_MD_NONE );
    ret = mbedtls_rsa_gen_key( &rsa,
                               mbedtls_psa_get_random,
                               MBEDTLS_PSA_RANDOM_STATE,
                               (unsigned int)attributes->core.bits,
                               exponent );
    if( ret != 0 )
        return( mbedtls_to_psa_error( ret ) );

    status = mbedtls_psa_rsa_export_key( attributes->core.type,
                                         &rsa, key_buffer, key_buffer_size,
                                         key_buffer_length );
    mbedtls_rsa_free( &rsa );

    return( status );
}
#endif /* defined(MBEDTLS_PSA_BUILTIN_KEY_TYPE_RSA_KEY_PAIR)
        * defined(MBEDTLS_GENPRIME) */

/****************************************************************/
/* Sign/verify hashes */
/****************************************************************/

#if defined(MBEDTLS_PSA_BUILTIN_ALG_RSA_PKCS1V15_SIGN) || \
    defined(MBEDTLS_PSA_BUILTIN_ALG_RSA_PSS)

/* Decode the hash algorithm from alg and store the mbedtls encoding in
 * md_alg. Verify that the hash length is acceptable. */
static psa_status_t psa_rsa_decode_md_type( psa_algorithm_t alg,
                                            size_t hash_length,
                                            mbedtls_md_type_t *md_alg )
{
    psa_algorithm_t hash_alg = PSA_ALG_SIGN_GET_HASH( alg );
    const mbedtls_md_info_t *md_info = mbedtls_md_info_from_psa( hash_alg );
    *md_alg = mbedtls_md_get_type( md_info );

    /* The Mbed TLS RSA module uses an unsigned int for hash length
     * parameters. Validate that it fits so that we don't risk an
     * overflow later. */
#if SIZE_MAX > UINT_MAX
    if( hash_length > UINT_MAX )
        return( PSA_ERROR_INVALID_ARGUMENT );
#endif

    /* For signatures using a hash, the hash length must be correct. */
    if( alg != PSA_ALG_RSA_PKCS1V15_SIGN_RAW )
    {
        if( md_info == NULL )
            return( PSA_ERROR_NOT_SUPPORTED );
        if( mbedtls_md_get_size( md_info ) != hash_length )
            return( PSA_ERROR_INVALID_ARGUMENT );
    }

    return( PSA_SUCCESS );
}

psa_status_t mbedtls_psa_rsa_sign_hash(
    const psa_key_attributes_t *attributes,
    const uint8_t *key_buffer, size_t key_buffer_size,
    psa_algorithm_t alg, const uint8_t *hash, size_t hash_length,
    uint8_t *signature, size_t signature_size, size_t *signature_length )
{
    psa_status_t status = PSA_ERROR_CORRUPTION_DETECTED;
    mbedtls_rsa_context *rsa = NULL;
    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
    mbedtls_md_type_t md_alg;

    status = mbedtls_psa_rsa_load_representation( attributes->core.type,
                                                  key_buffer,
                                                  key_buffer_size,
                                                  &rsa );
    if( status != PSA_SUCCESS )
        return( status );

    status = psa_rsa_decode_md_type( alg, hash_length, &md_alg );
    if( status != PSA_SUCCESS )
        goto exit;

    if( signature_size < mbedtls_rsa_get_len( rsa ) )
    {
        status = PSA_ERROR_BUFFER_TOO_SMALL;
        goto exit;
    }

#if defined(MBEDTLS_PSA_BUILTIN_ALG_RSA_PKCS1V15_SIGN)
    if( PSA_ALG_IS_RSA_PKCS1V15_SIGN( alg ) )
    {
        mbedtls_rsa_set_padding( rsa, MBEDTLS_RSA_PKCS_V15,
                                 MBEDTLS_MD_NONE );
        ret = mbedtls_rsa_pkcs1_sign( rsa,
                                      mbedtls_psa_get_random,
                                      MBEDTLS_PSA_RANDOM_STATE,
                                      MBEDTLS_RSA_PRIVATE,
                                      md_alg,
                                      (unsigned int) hash_length,
                                      hash,
                                      signature );
    }
    else
#endif /* MBEDTLS_PSA_BUILTIN_ALG_RSA_PKCS1V15_SIGN */
#if defined(MBEDTLS_PSA_BUILTIN_ALG_RSA_PSS)
    if( PSA_ALG_IS_RSA_PSS( alg ) )
    {
        mbedtls_rsa_set_padding( rsa, MBEDTLS_RSA_PKCS_V21, md_alg );
        ret = mbedtls_rsa_rsassa_pss_sign( rsa,
                                           mbedtls_psa_get_random,
                                           MBEDTLS_PSA_RANDOM_STATE,
                                           MBEDTLS_RSA_PRIVATE,
                                           MBEDTLS_MD_NONE,
                                           (unsigned int) hash_length,
                                           hash,
                                           signature );
    }
    else
#endif /* MBEDTLS_PSA_BUILTIN_ALG_RSA_PSS */
    {
        status = PSA_ERROR_INVALID_ARGUMENT;
        goto exit;
    }

    if( ret == 0 )
        *signature_length = mbedtls_rsa_get_len( rsa );
    status = mbedtls_to_psa_error( ret );

exit:
    mbedtls_rsa_free( rsa );
    mbedtls_free( rsa );

    return( status );
}

#if defined(MBEDTLS_PSA_BUILTIN_ALG_RSA_PSS)
static int rsa_pss_expected_salt_len( psa_algorithm_t alg,
                                      const mbedtls_rsa_context *rsa,
                                      size_t hash_length )
{
    if( PSA_ALG_IS_RSA_PSS_ANY_SALT( alg ) )
        return( MBEDTLS_RSA_SALT_LEN_ANY );
    /* Otherwise: standard salt length, i.e. largest possible salt length
     * up to the hash length. */
    int klen = (int) mbedtls_rsa_get_len( rsa ); // known to fit
    int hlen = (int) hash_length; // known to fit
    int room = klen - 2 - hlen;
    if( room < 0 )
        return( 0 ); // there is no valid signature in this case anyway
    else if( room > hlen )
        return( hlen );
    else
        return( room );
}
#endif /* MBEDTLS_PSA_BUILTIN_ALG_RSA_PSS */

psa_status_t mbedtls_psa_rsa_verify_hash(
    const psa_key_attributes_t *attributes,
    const uint8_t *key_buffer, size_t key_buffer_size,
    psa_algorithm_t alg, const uint8_t *hash, size_t hash_length,
    const uint8_t *signature, size_t signature_length )
{
    psa_status_t status = PSA_ERROR_CORRUPTION_DETECTED;
    mbedtls_rsa_context *rsa = NULL;
    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
    mbedtls_md_type_t md_alg;

    status = mbedtls_psa_rsa_load_representation( attributes->core.type,
                                                  key_buffer,
                                                  key_buffer_size,
                                                  &rsa );
    if( status != PSA_SUCCESS )
        goto exit;

    status = psa_rsa_decode_md_type( alg, hash_length, &md_alg );
    if( status != PSA_SUCCESS )
        goto exit;

    if( signature_length != mbedtls_rsa_get_len( rsa ) )
    {
        status = PSA_ERROR_INVALID_SIGNATURE;
        goto exit;
    }

#if defined(MBEDTLS_PSA_BUILTIN_ALG_RSA_PKCS1V15_SIGN)
    if( PSA_ALG_IS_RSA_PKCS1V15_SIGN( alg ) )
    {
        mbedtls_rsa_set_padding( rsa, MBEDTLS_RSA_PKCS_V15,
                                 MBEDTLS_MD_NONE );
        ret = mbedtls_rsa_pkcs1_verify( rsa,
                                        mbedtls_psa_get_random,
                                        MBEDTLS_PSA_RANDOM_STATE,
                                        MBEDTLS_RSA_PUBLIC,
                                        md_alg,
                                        (unsigned int) hash_length,
                                        hash,
                                        signature );
    }
    else
#endif /* MBEDTLS_PSA_BUILTIN_ALG_RSA_PKCS1V15_SIGN */
#if defined(MBEDTLS_PSA_BUILTIN_ALG_RSA_PSS)
    if( PSA_ALG_IS_RSA_PSS( alg ) )
    {
        int slen = rsa_pss_expected_salt_len( alg, rsa, hash_length );
        mbedtls_rsa_set_padding( rsa, MBEDTLS_RSA_PKCS_V21, md_alg );
        ret = mbedtls_rsa_rsassa_pss_verify_ext( rsa,
                                                 mbedtls_psa_get_random,
                                                 MBEDTLS_PSA_RANDOM_STATE,
                                                 MBEDTLS_RSA_PUBLIC,
                                                 md_alg,
                                                 (unsigned int) hash_length,
                                                 hash,
                                                 md_alg,
                                                 slen,
                                                 signature );
    }
    else
#endif /* MBEDTLS_PSA_BUILTIN_ALG_RSA_PSS */
    {
        status = PSA_ERROR_INVALID_ARGUMENT;
        goto exit;
    }

    /* Mbed TLS distinguishes "invalid padding" from "valid padding but
     * the rest of the signature is invalid". This has little use in
     * practice and PSA doesn't report this distinction. */
    status = ( ret == MBEDTLS_ERR_RSA_INVALID_PADDING ) ?
             PSA_ERROR_INVALID_SIGNATURE :
             mbedtls_to_psa_error( ret );

exit:
    mbedtls_rsa_free( rsa );
    mbedtls_free( rsa );

    return( status );
}

#endif /* defined(MBEDTLS_PSA_BUILTIN_ALG_RSA_PKCS1V15_SIGN) ||
        * defined(MBEDTLS_PSA_BUILTIN_ALG_RSA_PSS) */

#endif /* MBEDTLS_PSA_CRYPTO_C */