mbedTLS STM32F429I-Eval handshake problem

Bence Stocker · ‎2019-08-15

Hi!

We try connect to a server with STM32F4 Cube mbedTLS Client example application (on an STM324x9I_EVAL-1 board).

On the server side we use letsencrypt certifcates with nginx.

Access log: SSL_do_handshake() failed (SSL: error:1417A0C1:SSL routines:tls_post_process_client_hello:no shared cipher) while SSL handshaking

On the display of the board we got this error: "mbedtls_ssl_handshake returned -0x7780"

We spent hours to find soltion on the internet and we tried a lots of configurations but nothing changed.

Please help us!

After Forever · ‎2019-08-15

It seems that the Client and the Server don't have common ciphersuites.

I checked the code of your mentioned example, it uses TLSv1.2 and 2 AES-GCM-based ciphersuites (in Inc/mbedtls_config.h):

#define MBEDTLS_SSL_PROTO_TLS1_2
 ...
#define MBEDTLS_SSL_CIPHERSUITES                        \
    MBEDTLS_TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384,    \
    MBEDTLS_TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256

Make sure Nginx is configured to use those ciphersutes, for example this configuration options should do the trick (don't forget to restart Nginx after making changes in the configuration):

ssl_ciphers "ECDHE-ECDSA-AES256-GCM-SHA384:ECDHE-RSA-AES256-GCM-SHA384:ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES128-GCM-SHA256";
ssl_protocols TLSv1.2;

Added:

Take note that the example's default configuration will work only with ECDSA keys, most likely you have RSA, so you'll have to edit the MBEDTLS_SSL_CIPHERSUITES definition to include the RSA ciphersuites too:

#define MBEDTLS_KEY_EXCHANGE_ECDHE_RSA_ENABLED
 
#define MBEDTLS_SSL_CIPHERSUITES                        \
    MBEDTLS_TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384,    \
    MBEDTLS_TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256,    \
    MBEDTLS_TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384,      \
    MBEDTLS_TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256

Bence Stocker · ‎2019-08-16

Thanks the answer!

Now we have an other error, on the demo board: "mbedtls_ssl_handshake returned -0x3b00"

On the server side (nginx) we got this error: SSL_do_handshake() failed (SSL: error:14094412:SSL routines:ssl3_read_bytes:sslv3 alert bad certificate:SSL alert number 42

Our mbedtls_config.h:

/**

*

******************************************************************************

* @file mbedtls_config.h

* @author MCD Application Team

* @brief the mbedtls custom config header file.

******************************************************************************

* @attention

*

* Redistribution and us e in source and binary forms, with or without modification,

* are permitted provided that the following conditions are met:

* 1. Redistributions of source code must retain the above copyright notice,

* this list of conditions and the following disclaimer.

* 2. Redistributions in binary form must reproduce the above copyright notice,

* this list of conditions and the following disclaimer in the documentation

* and/or other materials provided with the distribution.

* 3. Neither the name of STMicroelectronics nor the names of its contributors

* may be used to endorse or promote products derived from this software

* without specific prior written permission.

*

* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"

* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE

* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE

* DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE

* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL

* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR

* SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER

* CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,

* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE

* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

*

******************************************************************************

*/

#ifndef MBEDTLS_CONFIG_H

#define MBEDTLS_CONFIG_H

/* System support */

#define MBEDTLS_HAVE_ASM

#define MBEDTLS_HAVE_TIME

/* mbed TLS feature support */

#define MBEDTLS_ECP_DP_SECP256R1_ENABLED

#define MBEDTLS_ECP_DP_SECP384R1_ENABLED

#define MBEDTLS_KEY_EXCHANGE_ECDHE_ECDSA_ENABLED

#define MBEDTLS_KEY_EXCHANGE_ECDHE_RSA_ENABLED

#define MBEDTLS_SSL_PROTO_TLS1_2

/* mbed TLS modules */

#define MBEDTLS_AES_C

#define MBEDTLS_ASN1_PARSE_C

#define MBEDTLS_ASN1_WRITE_C

#define MBEDTLS_BIGNUM_C

#define MBEDTLS_CIPHER_C

#define MBEDTLS_CTR_DRBG_C

#define MBEDTLS_ECDH_C

#define MBEDTLS_ECDSA_C

#define MBEDTLS_ECP_C

#define MBEDTLS_ENTROPY_C

#define MBEDTLS_GCM_C

#define MBEDTLS_MD_C

#define MBEDTLS_NET_C

#define MBEDTLS_OID_C

#define MBEDTLS_PK_C

#define MBEDTLS_PK_PARSE_C

#define MBEDTLS_SHA256_C

#define MBEDTLS_SHA512_C

#define MBEDTLS_SSL_CLI_C

#define MBEDTLS_SSL_SRV_C

#define MBEDTLS_SSL_TLS_C

#define MBEDTLS_X509_CRT_PARSE_C

#define MBEDTLS_SSL_SERVER_NAME_INDICATION

#define MBEDTLS_X509_USE_C

#define MBEDTLS_RSA_C

#define MBEDTLS_PKCS1_V15

/* For test certificates */

#define MBEDTLS_BASE64_C

#define MBEDTLS_CERTS_C

#define MBEDTLS_PEM_PARSE_C

/* Save RAM at the expense of ROM */

#define MBEDTLS_AES_ROM_TABLES

/* Disable double-width division */

#define MBEDTLS_NO_UDBL_DIVISION

/* Save RAM by adjusting to our exact needs */

#define MBEDTLS_ECP_MAX_BITS 384

#define MBEDTLS_MPI_MAX_SIZE 48 // 384 bits is 48 bytes

/* Save RAM at the expense of speed, see ecp.h */

#define MBEDTLS_ECP_WINDOW_SIZE 2

#define MBEDTLS_ECP_FIXED_POINT_OPTIM 0

/* Significant speed benefit at the expense of some ROM */

#define MBEDTLS_ECP_NIST_OPTIM

/*

* You should adjust this to the exact number of sources you're using: default

* is the "mbedtls_platform_entropy_poll" source, but you may want to add other ones.

* Minimum is 2 for the entropy test suite.

*/

#define MBEDTLS_ENTROPY_MAX_SOURCES 2

/* Save ROM and a few bytes of RAM by specifying our own ciphersuite list */

#define MBEDTLS_SSL_CIPHERSUITES \

MBEDTLS_TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384, \

MBEDTLS_TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256, \

MBEDTLS_TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384, \

MBEDTLS_TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256

/*

* Save RAM at the expense of interoperability: do this only if you control

* both ends of the connection! (See coments in "mbedtls/ssl.h".)

* The minimum size here depends on the certificate chain used as well as the

* typical size of records.

*/

//#define MBEDTLS_SSL_MAX_CONTENT_LEN 2048

#define MBEDTLS_SSL_SRV_RESPECT_CLIENT_PREFERENCE

#define MBEDTLS_CAMELLIA_C

#ifdef USE_LCD

#include "lcd_log.h"

#define MBEDTLS_PLATFORM_C

#define MBEDTLS_PLATFORM_PRINTF_MACRO LCD_UsrLog

#endif

/* Customize the entropy data generation */

#define MBEDTLS_NO_PLATFORM_ENTROPY

#define MBEDTLS_ENTROPY_HARDWARE_ALT

#include "mbedtls/check_config.h"

#endif /* MBEDTLS_CONFIG_H */

After Forever · ‎2019-08-16

Can you access your server using a standard browser with no issues? Please check your server using this tool and see if there are errors/warnings.

Bence Stocker · ‎2019-08-16

Yes,

We tested the server with browser and with an ESP32 wifi modul too. It works both way correctly.

Btw, the nginx we use is a linuxserver/letsencrypt docker image. So the config is not specific.

We run the ssl test, the server got an overall A+ everythings looks fine.

After Forever · ‎2019-08-16

The issue must be that the client doesn't recognize your server's certificate's authority. You'll have to include Let's Encrypt's CA (download from here with right-click -> save as) in your root certificates list. Here in ssl_client.c your example loads mbedTLS's test CA (from mbedTLS/library/certs.c) as root certificate, so it doesn't accept your certificate signed with a real CA:

/*
   * 0. Initialize certificates
   */
  mbedtls_printf( "  . Loading the CA root certificate ..." );
 
  ret = mbedtls_x509_crt_parse( &cacert, (const unsigned char *) mbedtls_test_cas_pem,
                        mbedtls_test_cas_pem_len );

Bence Stocker · ‎2019-08-16

Thanks,

it could be the problem. We tried to change the certificate in certs.c like this:

#define TEST_CA_CRT_RSA_SHA256 \

"-----BEGIN CERTIFICATE-----\r\n" \

"MIIEkjCCA3qgAwIBAgIQCgFBQgAAAVOFc2oLheynCDANBgkqhkiG9w0BAQsFADA/\r\n" \

"MSQwIgYDVQQKExtEaWdpdGFsIFNpZ25hdHVyZSBUcnVzdCBDby4xFzAVBgNVBAMT\r\n" \

"DkRTVCBSb290IENBIFgzMB4XDTE2MDMxNzE2NDA0NloXDTIxMDMxNzE2NDA0Nlow\r\n" \

"SjELMAkGA1UEBhMCVVMxFjAUBgNVBAoTDUxldCdzIEVuY3J5cHQxIzAhBgNVBAMT\r\n" \

"GkxldCdzIEVuY3J5cHQgQXV0aG9yaXR5IFgzMIIBIjANBgkqhkiG9w0BAQEFAAOC\r\n" \

"AQ8AMIIBCgKCAQEAnNMM8FrlLke3cl03g7NoYzDq1zUmGSXhvb418XCSL7e4S0EF\r\n" \

"q6meNQhY7LEqxGiHC6PjdeTm86dicbp5gWAf15Gan/PQeGdxyGkOlZHP/uaZ6WA8\r\n" \

"SMx+yk13EiSdRxta67nsHjcAHJyse6cF6s5K671B5TaYucv9bTyWaN8jKkKQDIZ0\r\n" \

"Z8h/pZq4UmEUEz9l6YKHy9v6Dlb2honzhT+Xhq+w3Brvaw2VFn3EK6BlspkENnWA\r\n" \

"a6xK8xuQSXgvopZPKiAlKQTGdMDQMc2PMTiVFrqoM7hD8bEfwzB/onkxEz0tNvjj\r\n" \

"/PIzark5McWvxI0NHWQWM6r6hCm21AvA2H3DkwIDAQABo4IBfTCCAXkwEgYDVR0T\r\n" \

"AQH/BAgwBgEB/wIBADAOBgNVHQ8BAf8EBAMCAYYwfwYIKwYBBQUHAQEEczBxMDIG\r\n" \

"CCsGAQUFBzABhiZodHRwOi8vaXNyZy50cnVzdGlkLm9jc3AuaWRlbnRydXN0LmNv\r\n" \

"bTA7BggrBgEFBQcwAoYvaHR0cDovL2FwcHMuaWRlbnRydXN0LmNvbS9yb290cy9k\r\n" \

"c3Ryb290Y2F4My5wN2MwHwYDVR0jBBgwFoAUxKexpHsscfrb4UuQdf/EFWCFiRAw\r\n" \

"VAYDVR0gBE0wSzAIBgZngQwBAgEwPwYLKwYBBAGC3xMBAQEwMDAuBggrBgEFBQcC\r\n" \

"ARYiaHR0cDovL2Nwcy5yb290LXgxLmxldHNlbmNyeXB0Lm9yZzA8BgNVHR8ENTAz\r\n" \

"MDGgL6AthitodHRwOi8vY3JsLmlkZW50cnVzdC5jb20vRFNUUk9PVENBWDNDUkwu\r\n" \

"Y3JsMB0GA1UdDgQWBBSoSmpjBH3duubRObemRWXv86jsoTANBgkqhkiG9w0BAQsF\r\n" \

"AAOCAQEA3TPXEfNjWDjdGBX7CVW+dla5cEilaUcne8IkCJLxWh9KEik3JHRRHGJo\r\n" \

"uM2VcGfl96S8TihRzZvoroed6ti6WqEBmtzw3Wodatg+VyOeph4EYpr/1wXKtx8/\r\n" \

"wApIvJSwtmVi4MFU5aMqrSDE6ea73Mj2tcMyo5jMd6jmeWUHK8so/joWUoHOUgwu\r\n" \

"X4Po1QYz+3dszkDqMp4fklxBwXRsW10KXzPMTZ+sOPAveyxindmjkW8lGy+QsRlG\r\n" \

"PfZ+G6Z6h7mjem0Y+iWlkYcV4PIWL1iwBi8saCbGS5jN2p8M+X+Q7UNKEkROb3N6\r\n" \

"KOqkqm57TH2H3eDJAkSnh6/DNFu0Qg==\r\n" \

"-----END CERTIFICATE-----\r\n"

const char mbedtls_test_ca_crt_rsa[] = TEST_CA_CRT_RSA_SHA256;

const size_t mbedtls_test_ca_crt_rsa_len = sizeof( mbedtls_test_ca_crt_rsa );

#define TEST_CA_CRT_RSA_SOME

We got this error on the board: mbedtls_x509_crt_parse returned -03b00

Could you explain where and how should we use this letsencrypt cert?

Thanks

After Forever · ‎2019-08-16

Can you debug and see where mbedTLS returns the error code? It's possible that you need to set correct date & time (and implement/define the mbedtls_time function used by mbedTLS), because mbedTLS is checking if the current datetime is within certificate signing and expiration dates in the x509_crt_verify_chain function:

/* Check time-validity (all certificates) */
        if( mbedtls_x509_time_is_past( &child->valid_to ) )
            *flags |= MBEDTLS_X509_BADCERT_EXPIRED;
 
        if( mbedtls_x509_time_is_future( &child->valid_from ) )
            *flags |= MBEDTLS_X509_BADCERT_FUTURE;

Or it can be 100 other things, debugging will make it easy to diagnose.

P.S.

I have never used mbedTLS, just skimming through the code for some clues.

P.S.2

Embedded TLS is hard (: