library/x509write_csr.c

/*
 *  X.509 Certificate Signing Request writing
 *
 *  Copyright The Mbed TLS Contributors
 *  SPDX-License-Identifier: Apache-2.0 OR GPL-2.0-or-later
 *
 *  This file is provided under the Apache License 2.0, or the
 *  GNU General Public License v2.0 or later.
 *
 *  **********
 *  Apache License 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.
 *
 *  **********
 *
 *  **********
 *  GNU General Public License v2.0 or later:
 *
 *  This program is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation; either version 2 of the License, or
 *  (at your option) any later version.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License along
 *  with this program; if not, write to the Free Software Foundation, Inc.,
 *  51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 *  **********
 */
/*
 * References:
 * - CSRs: PKCS#10 v1.7 aka RFC 2986
 * - attributes: PKCS#9 v2.0 aka RFC 2985
 */

#if !defined(MBEDTLS_CONFIG_FILE)
#include "mbedtls/config.h"
#else
#include MBEDTLS_CONFIG_FILE
#endif

#if defined(MBEDTLS_X509_CSR_WRITE_C)

#include "mbedtls/x509_csr.h"
#include "mbedtls/oid.h"
#include "mbedtls/asn1write.h"
#include "mbedtls/platform_util.h"

#include <string.h>
#include <stdlib.h>

#if defined(MBEDTLS_PEM_WRITE_C)
#include "mbedtls/pem.h"
#endif

/*
 * For the currently used signature algorithms the buffer to store any signature
 * must be at least of size MAX(MBEDTLS_ECDSA_MAX_LEN, MBEDTLS_MPI_MAX_SIZE)
 */
#if MBEDTLS_ECDSA_MAX_LEN > MBEDTLS_MPI_MAX_SIZE
#define SIGNATURE_MAX_SIZE MBEDTLS_ECDSA_MAX_LEN
#else
#define SIGNATURE_MAX_SIZE MBEDTLS_MPI_MAX_SIZE
#endif

#if defined(MBEDTLS_PLATFORM_C)
#include "mbedtls/platform.h"
#else
#include <stdlib.h>
#define mbedtls_calloc    calloc
#define mbedtls_free      free
#endif

void mbedtls_x509write_csr_init( mbedtls_x509write_csr *ctx )
{
    memset( ctx, 0, sizeof( mbedtls_x509write_csr ) );
}

void mbedtls_x509write_csr_free( mbedtls_x509write_csr *ctx )
{
    mbedtls_asn1_free_named_data_list( &ctx->subject );
    mbedtls_asn1_free_named_data_list( &ctx->extensions );

    mbedtls_platform_zeroize( ctx, sizeof( mbedtls_x509write_csr ) );
}

void mbedtls_x509write_csr_set_md_alg( mbedtls_x509write_csr *ctx, mbedtls_md_type_t md_alg )
{
    ctx->md_alg = md_alg;
}

void mbedtls_x509write_csr_set_key( mbedtls_x509write_csr *ctx, mbedtls_pk_context *key )
{
    ctx->key = key;
}

int mbedtls_x509write_csr_set_subject_name( mbedtls_x509write_csr *ctx,
                                    const char *subject_name )
{
    return mbedtls_x509_string_to_names( &ctx->subject, subject_name );
}

int mbedtls_x509write_csr_set_extension( mbedtls_x509write_csr *ctx,
                                 const char *oid, size_t oid_len,
                                 const unsigned char *val, size_t val_len )
{
    return mbedtls_x509_set_extension( &ctx->extensions, oid, oid_len,
                               0, val, val_len );
}

static size_t csr_get_unused_bits_for_named_bitstring( unsigned char bitstring,
                                                       size_t bit_offset )
{
    size_t unused_bits;

     /* Count the unused bits removing trailing 0s */
    for( unused_bits = bit_offset; unused_bits < 8; unused_bits++ )
        if( ( ( bitstring >> unused_bits ) & 0x1 ) != 0 )
            break;

     return( unused_bits );
}

int mbedtls_x509write_csr_set_key_usage( mbedtls_x509write_csr *ctx, unsigned char key_usage )
{
    unsigned char buf[4];
    unsigned char *c;
    size_t unused_bits;
    int ret;

    c = buf + 4;

    unused_bits = csr_get_unused_bits_for_named_bitstring( key_usage, 0 );
    ret = mbedtls_asn1_write_bitstring( &c, buf, &key_usage, 8 - unused_bits );

    if( ret < 0 )
        return( ret );
    else if( ret < 3 || ret > 4 )
        return( MBEDTLS_ERR_X509_INVALID_FORMAT );

    ret = mbedtls_x509write_csr_set_extension( ctx, MBEDTLS_OID_KEY_USAGE,
                                       MBEDTLS_OID_SIZE( MBEDTLS_OID_KEY_USAGE ),
                                       c, (size_t)ret );
    if( ret != 0 )
        return( ret );

    return( 0 );
}

int mbedtls_x509write_csr_set_ns_cert_type( mbedtls_x509write_csr *ctx,
                                    unsigned char ns_cert_type )
{
    unsigned char buf[4];
    unsigned char *c;
    size_t unused_bits;
    int ret;

    c = buf + 4;

    unused_bits = csr_get_unused_bits_for_named_bitstring( ns_cert_type, 0 );
    ret = mbedtls_asn1_write_bitstring( &c,
                                        buf,
                                        &ns_cert_type,
                                        8 - unused_bits );

    if( ret < 0 )
        return( ret );
    else if( ret < 3 || ret > 4 )
        return( ret );

    ret = mbedtls_x509write_csr_set_extension( ctx, MBEDTLS_OID_NS_CERT_TYPE,
                                       MBEDTLS_OID_SIZE( MBEDTLS_OID_NS_CERT_TYPE ),
                                       c, (size_t)ret );
    if( ret != 0 )
        return( ret );

    return( 0 );
}

static int x509write_csr_der_internal( mbedtls_x509write_csr *ctx,
                                 unsigned char *buf,
                                 size_t size,
                                 unsigned char *sig,
                                 int (*f_rng)(void *, unsigned char *, size_t),
                                 void *p_rng )
{
    int ret;
    const char *sig_oid;
    size_t sig_oid_len = 0;
    unsigned char *c, *c2;
    unsigned char hash[64];
    size_t pub_len = 0, sig_and_oid_len = 0, sig_len;
    size_t len = 0;
    mbedtls_pk_type_t pk_alg;

    /* Write the CSR backwards starting from the end of buf */
    c = buf + size;

    MBEDTLS_ASN1_CHK_ADD( len, mbedtls_x509_write_extensions( &c, buf,
                                                           ctx->extensions ) );

    if( len )
    {
        MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_len( &c, buf, len ) );
        MBEDTLS_ASN1_CHK_ADD( len,
            mbedtls_asn1_write_tag(
                &c, buf,
                MBEDTLS_ASN1_CONSTRUCTED | MBEDTLS_ASN1_SEQUENCE ) );

        MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_len( &c, buf, len ) );
        MBEDTLS_ASN1_CHK_ADD( len,
            mbedtls_asn1_write_tag(
                &c, buf,
                MBEDTLS_ASN1_CONSTRUCTED | MBEDTLS_ASN1_SET ) );

        MBEDTLS_ASN1_CHK_ADD( len,
            mbedtls_asn1_write_oid(
                &c, buf, MBEDTLS_OID_PKCS9_CSR_EXT_REQ,
                MBEDTLS_OID_SIZE( MBEDTLS_OID_PKCS9_CSR_EXT_REQ ) ) );

        MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_len( &c, buf, len ) );
        MBEDTLS_ASN1_CHK_ADD( len,
            mbedtls_asn1_write_tag(
                &c, buf,
                MBEDTLS_ASN1_CONSTRUCTED | MBEDTLS_ASN1_SEQUENCE ) );
    }

    MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_len( &c, buf, len ) );
    MBEDTLS_ASN1_CHK_ADD( len,
        mbedtls_asn1_write_tag(
            &c, buf,
            MBEDTLS_ASN1_CONSTRUCTED | MBEDTLS_ASN1_CONTEXT_SPECIFIC ) );

    MBEDTLS_ASN1_CHK_ADD( pub_len, mbedtls_pk_write_pubkey_der( ctx->key,
                                                              buf, c - buf ) );
    c -= pub_len;
    len += pub_len;

    /*
     *  Subject  ::=  Name
     */
    MBEDTLS_ASN1_CHK_ADD( len, mbedtls_x509_write_names( &c, buf,
                                                         ctx->subject ) );

    /*
     *  Version  ::=  INTEGER  {  v1(0), v2(1), v3(2)  }
     */
    MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_int( &c, buf, 0 ) );

    MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_len( &c, buf, len ) );
    MBEDTLS_ASN1_CHK_ADD( len,
        mbedtls_asn1_write_tag(
            &c, buf,
            MBEDTLS_ASN1_CONSTRUCTED | MBEDTLS_ASN1_SEQUENCE ) );

    /*
     * Sign the written CSR data into the sig buffer
     * Note: hash errors can happen only after an internal error
     */
    ret = mbedtls_md( mbedtls_md_info_from_type( ctx->md_alg ), c, len, hash );
    if( ret != 0 )
        return( ret );

    if( ( ret = mbedtls_pk_sign( ctx->key, ctx->md_alg, hash, 0, sig, &sig_len,
                                 f_rng, p_rng ) ) != 0 )
    {
        return( ret );
    }

    if( mbedtls_pk_can_do( ctx->key, MBEDTLS_PK_RSA ) )
        pk_alg = MBEDTLS_PK_RSA;
    else if( mbedtls_pk_can_do( ctx->key, MBEDTLS_PK_ECDSA ) )
        pk_alg = MBEDTLS_PK_ECDSA;
    else
        return( MBEDTLS_ERR_X509_INVALID_ALG );

    if( ( ret = mbedtls_oid_get_oid_by_sig_alg( pk_alg, ctx->md_alg,
                                              &sig_oid, &sig_oid_len ) ) != 0 )
    {
        return( ret );
    }

    /*
     * Move the written CSR data to the start of buf to create space for
     * writing the signature into buf.
     */
    memmove( buf, c, len );

    /*
     * Write sig and its OID into buf backwards from the end of buf.
     * Note: mbedtls_x509_write_sig will check for c2 - ( buf + len ) < sig_len
     * and return MBEDTLS_ERR_ASN1_BUF_TOO_SMALL if needed.
     */
    c2 = buf + size;
    MBEDTLS_ASN1_CHK_ADD( sig_and_oid_len,
        mbedtls_x509_write_sig( &c2, buf + len, sig_oid, sig_oid_len,
                                sig, sig_len ) );

    /*
     * Compact the space between the CSR data and signature by moving the
     * CSR data to the start of the signature.
     */
    c2 -= len;
    memmove( c2, buf, len );

    /* ASN encode the total size and tag the CSR data with it. */
    len += sig_and_oid_len;
    MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_len( &c2, buf, len ) );
    MBEDTLS_ASN1_CHK_ADD( len,
        mbedtls_asn1_write_tag(
            &c2, buf,
            MBEDTLS_ASN1_CONSTRUCTED | MBEDTLS_ASN1_SEQUENCE ) );

    /* Zero the unused bytes at the start of buf */
    memset( buf, 0, c2 - buf);

    return( (int) len );
}

int mbedtls_x509write_csr_der( mbedtls_x509write_csr *ctx, unsigned char *buf,
                               size_t size,
                               int (*f_rng)(void *, unsigned char *, size_t),
                               void *p_rng )
{
    int ret;
    unsigned char *sig;

    if( ( sig = mbedtls_calloc( 1, SIGNATURE_MAX_SIZE ) ) == NULL )
    {
        return( MBEDTLS_ERR_X509_ALLOC_FAILED );
    }

    ret = x509write_csr_der_internal( ctx, buf, size, sig, f_rng, p_rng );

    mbedtls_free( sig );

    return( ret );
}

#define PEM_BEGIN_CSR           "-----BEGIN CERTIFICATE REQUEST-----\n"
#define PEM_END_CSR             "-----END CERTIFICATE REQUEST-----\n"

#if defined(MBEDTLS_PEM_WRITE_C)
int mbedtls_x509write_csr_pem( mbedtls_x509write_csr *ctx, unsigned char *buf, size_t size,
                       int (*f_rng)(void *, unsigned char *, size_t),
                       void *p_rng )
{
    int ret;
    unsigned char output_buf[4096];
    size_t olen = 0;

    if( ( ret = mbedtls_x509write_csr_der( ctx, output_buf, sizeof(output_buf),
                                   f_rng, p_rng ) ) < 0 )
    {
        return( ret );
    }

    if( ( ret = mbedtls_pem_write_buffer( PEM_BEGIN_CSR, PEM_END_CSR,
                                  output_buf + sizeof(output_buf) - ret,
                                  ret, buf, size, &olen ) ) != 0 )
    {
        return( ret );
    }

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

#endif /* MBEDTLS_X509_CSR_WRITE_C */