Hello world example of a TLS client: fetch an HTTPS page. The canonical source for this example lives at https://github.com/ARMmbed/mbed-os-example-tls
HTTPS File Download Example for TLS Client on mbed OS
This application downloads a file from an HTTPS server (developer.mbed.org) and looks for a specific string in that file.
Building with mbed CLI
If you'd like to use mbed CLI to build this, then you should set up your environment if you have not done so already. For instructions, refer to the main readme. The instructions here relate to using the developer.mbed.org Online Compiler
Import the program in to the Online Compiler, select your board from the drop down in the top right hand corner and then compile the application. Once it has built, you can drag and drop the binary onto your device.
This example also requires an Ethernet cable an connection to the internet additional to the hardware requirements in the main readme.
Monitoring the application
NOTE: Make sure that the Ethernet cable is plugged in correctly before running the application.
The output in the terminal window should be similar to this:
Using Ethernet LWIP Client IP Address is 10.2.203.43 Connecting with developer.mbed.org Starting the TLS handshake... TLS connection to developer.mbed.org established Server certificate: cert. version : 3 serial number : 11:21:B8:47:9B:21:6C:B1:C6:AF:BC:5D:0C:19:52:DC:D7:C3 issuer name : C=BE, O=GlobalSign nv-sa, CN=GlobalSign Organization Validation CA - SHA256 - G2 subject name : C=GB, ST=Cambridgeshire, L=Cambridge, O=ARM Ltd, CN=*.mbed.com issued on : 2016-03-03 12:26:08 expires on : 2017-04-05 10:31:02 signed using : RSA with SHA-256 RSA key size : 2048 bits basic constraints : CA=false subject alt name : *.mbed.com, mbed.org, *.mbed.org, mbed.com key usage : Digital Signature, Key Encipherment ext key usage : TLS Web Server Authentication, TLS Web Client Authentication Certificate verification passed HTTPS: Received 439 chars from server HTTPS: Received 200 OK status ... [OK] HTTPS: Received 'Hello world!' status ... [OK] HTTPS: Received message: HTTP/1.1 200 OK Server: nginx/1.7.10 Date: Wed, 20 Jul 2016 10:00:35 GMT Content-Type: text/plain Content-Length: 14 Connection: keep-alive Last-Modified: Fri, 27 Jul 2012 13:30:34 GMT Accept-Ranges: bytes Cache-Control: max-age=36000 Expires: Wed, 20 Jul 2016 20:00:35 GMT X-Upstream-L3: 172.17.0.3:80 X-Upstream-L2: developer-sjc-indigo-1-nginx Strict-Transport-Security: max-age=31536000; includeSubdomains Hello world!
Debugging the TLS connection
To print out more debug information about the TLS connection, edit the file `main.cpp` and change the definition of `DEBUG_LEVEL` (near the top of the file) from 0 to a positive number:
- Level 1 only prints non-zero return codes from SSL functions and information about the full certificate chain being verified.
- Level 2 prints more information about internal state updates.
- Level 3 is intermediate.
- Level 4 (the maximum) includes full binary dumps of the packets.
The TLS connection can fail with an error similar to:
mbedtls_ssl_write() failed: -0x2700 (-9984): X509 - Certificate verification failed, e.g. CRL, CA or signature check failed Failed to fetch /media/uploads/mbed_official/hello.txt from developer.mbed.org:443
This probably means you need to update the contents of the
SSL_CA_PEM constant (this can happen if you modify
HTTPS_SERVER_NAME, or when
developer.mbed.org switches to a new CA when updating its certificate).
Another possible reason for this error is a proxy providing a different certificate. Proxies can be used in some network configurations or for performing man-in-the-middle attacks. If you choose to ignore this error and proceed with the connection anyway, you can change the definition of
UNSAFE near the top of the file from 0 to 1.
Warning: this removes all security against a possible active attacker, so use at your own risk or for debugging only!