SMTPS MbedTLS TLS not working

Hi Franc,

Thanks for the help, I finally got the email to go through using SMTPS. For the most part, I had to change the configuration file and increase the heap size. I also increased the MBEDTLS_SSL_MAX_CONTENT_LEN which fixed my last issue of mbedTLs not sending the TLS "Client Hello".

Another thing I wanted to do is move this SMTPS code over to an older board, lpc3250 Arm9, which is not supported by Keilv5. The Arm9 project is a bare metal environment with no operating system. Currently, the Arm9 application does have a bare metal SMTP protocol hand written, but I want to switch it to SMTPS. I am working on the lpc3250 processor using Keilv4 whcih does not include all the new software packs and run-time environment.

My questions are:
1. Will this mbedTLS SMTPS application work on a bare metal environment without a RTOS?
2. Does mbedTLS require an outside API, such as Windows API, to run TLS?
3. Is it possible to move over all the source code to the Arm9 Keilv4 project and get it to work with mbedTLS SMTPS?
4. I read that some TLS certificates require a date verification and my Arm9 embedded system does not keep track of the current date and time, is this involved in SMTPS?

-Kamal

Hi Franc,

Thanks for the help, I finally got the email to go through using SMTPS. For the most part, I had to change the configuration file and increase the heap size. I also increased the MBEDTLS_SSL_MAX_CONTENT_LEN which fixed my last issue of mbedTLs not sending the TLS "Client Hello".

Another thing I wanted to do is move this SMTPS code over to an older board, lpc3250 Arm9, which is not supported by Keilv5. The Arm9 project is a bare metal environment with no operating system. Currently, the Arm9 application does have a bare metal SMTP protocol hand written, but I want to switch it to SMTPS. I am working on the lpc3250 processor using Keilv4 whcih does not include all the new software packs and run-time environment.

My questions are:
1. Will this mbedTLS SMTPS application work on a bare metal environment without a RTOS?
2. Does mbedTLS require an outside API, such as Windows API, to run TLS?
3. Is it possible to move over all the source code to the Arm9 Keilv4 project and get it to work with mbedTLS SMTPS?
4. I read that some TLS certificates require a date verification and my Arm9 embedded system does not keep track of the current date and time, is this involved in SMTPS?

-Kamal

Also,

I can send the mbed SMTPS TLS1.2 using ports 587 and 25 successfully, is that how it is supposed to work?

My mbedTLS SMTPS program does not work every single run. Sometimes the program will hang or fail. Why is the program not running the same every time?
Most of the time when it does hang, it will hang right after:

 39, 4.21519186, Net_SMTP, ConnectIp4, ip=10.0.1.2  port=587

Even in the successful email cases, I sometimes receive events like:

 19, 2.21033839, Net_ETH, LinkDownError, no-link

 39, 4.21497440, Net_DNS, RecordTypeNotSupported, rr_type=TYPE_CNAME

 41, 4.21587020, Net_TCP, FrameUnrecognised, sock=1

 42, 4.89372711, Net_TCP, NoRetriesLeft, sock=1

 43, 4.89384738, Net_SMTP, SocketAborted, sock=1

One example of a failed SMTPS email Keil event recorder:

 Event, Time (sec), Component, Event Property, Value
0, 0.00391493, EvCtrl, EventRecorderInitialize, Restart Count = 2
1, 0.00393650, EvCtrl, EventRecorderStart,
2, 0.00445639, Net_SYS, InitSystem, ver=7.10.0
3, 0.00548874, Net_DHCP, InitClient, vcid=0  opt=0
4, 0.00549881, Net_DHCP, StartClient,
5, 0.00554865, Net_SMTP, InitClient, smtp
6, 0.00562303, Net_SYS, InitComplete, success
7, 0.00579318, STDIO, stdout, 0x4D 0x57 0x20 0x4E 0x65 0x74 0x77 0x6F
8, 0.00582144, STDIO, stdout, 0x72 0x6B 0x20 0x20 0x20 0x20 0x20 0x20
9, 0.00582199, STDIO, stdout, 0x0A 0x00 0x00 0x00 0x00 0x00 0x00 0x00
10, 0.00587034, STDIO, stdout, 0x0D 0x53 0x4D 0x54 0x50 0x20 0x43 0x6C
11, 0.00587143, STDIO, stdout, 0x69 0x65 0x6E 0x74 0x20 0x20 0x20 0x20
12, 0.00587204, STDIO, stdout, 0x20 0x0A 0x00 0x00 0x00 0x00 0x00 0x00
13, 0.00588006, STDIO, stdout, 0x0D 0x53 0x65 0x6E 0x64 0x69 0x6E 0x67
14, 0.00588113, STDIO, stdout, 0x20 0x65 0x6D 0x61 0x69 0x6C 0x2E 0x2E
15, 0.00588173, STDIO, stdout, 0x2E 0x0A 0x00 0x00 0x00 0x00 0x00 0x00
16, 0.00593655, Net_SMTP, SendMail, recipients=1
17, 0.00626456, Net_ETH, LinkDownError, no-link
18, 0.21044865, Net_ETH, LinkDownError, no-link
19, 2.21036563, Net_ETH, LinkDownError, no-link
20, 2.91042894, Net_DHCP, ClientState, state=INIT
21, 2.91045321, Net_DHCP, SendDhcpMessage, type=DHCP_DISCOVER  bcast=1
22, 2.91066462, Net_DHCP, NextState, state=SELECTING
23, 2.91300110, Net_DHCP, ReceiveFrame, server=10.0.2.17  len=300
24, 2.91304104, Net_DHCP, ClientState, state=SELECTING
25, 2.91308409, Net_DHCP, DhcpOfferReceived,
26, 2.91309079, Net_DHCP, ShowServerId, server_id=10.0.2.17
27, 2.91311357, Net_DHCP, ShowOfferedIpAddress, ip=10.0.2.157
28, 2.91311873, Net_DHCP, SendDhcpMessage, type=DHCP_REQUEST  bcast=1
29, 2.91328019, Net_DHCP, NextState, state=REQUESTING
30, 2.91706581, Net_DHCP, ReceiveFrame, server=10.0.2.17  len=300
31, 2.91708329, Net_DHCP, ClientState, state=REQUESTING
32, 2.91709156, Net_DHCP, DhcpAckReceived,
33, 2.91709607, Net_DHCP, ShowAssignedAddress, ip=10.0.2.157
34, 2.91711923, Net_DHCP, ShowLeaseTime, time=171072
35, 2.91715024, Net_DHCP, ShowNetMask, mask=255.255.0.0
36, 2.91716467, Net_DHCP, ShowGatewayAddress, gateway=10.0.2.2
37, 2.91716525, Net_DHCP, ShowDnsServers, pri=8.8.8.8  sec=8.8.4.4
38, 2.91718709, Net_DHCP, NextState, state=BOUND
39, 4.21523585, Net_DNS, RecordTypeNotSupported, rr_type=TYPE_CNAME
40, 4.21535812, Net_SMTP, ConnectIp4, ip=74.125.141.108  port=587
41, 4.89372711, Net_TCP, NoRetriesLeft, sock=1
42, 4.89384738, Net_SMTP, SocketAborted, sock=1
43, 4.89390436, Net_SMTP, ClientCloseSocket, sock=1
44, 4.99372952, Net_SMTP, ClientDone, cb_event=Error
45, 4.99384296, STDIO, stdout, 0x0D 0x53 0x65 0x6E 0x64 0x20 0x65 0x6D
46, 4.99384931, STDIO, stdout, 0x61 0x69 0x6C 0x20 0x66 0x61 0x69 0x6C
47, 4.99385004, STDIO, stdout, 0x65 0x64 0x2E 0x0A 0x00 0x00 0x00 0x00

It looks like you have an invalid system clock configuration. Message 40 starts the TCP connection. If the remote host does not respond, TCP resends the SYN packet. It takes 15 seconds before the message 41 is recorded.

If I calculate the delay, the kernel clock is 25 Mhz, but it is likely to be set at 600 MHz. The errors you mention are the result of invalid clock settings.

Thanks for letting me know about the clock settings. Do you have any advise on my earlier message about the bare metal environment?

My questions are:
1. Will this mbedTLS SMTPS application work on a bare metal environment without a RTOS?
2. Does mbedTLS require an outside API, such as Windows API, to run TLS?
3. Is it possible to move over all the source code to the Arm9 Keilv4 project and get it to work with mbedTLS SMTPS?
4. I read that some TLS certificates require a date verification and my Arm9 embedded system does not keep track of the current date and time, is this involved in SMTPS?
5. Can I just copy over all the source and header files from my working SMTPS Arm Cortex 7 project to my bare metal Arm9 project, including all the RTOS and mbedTLS files?

For a bare metal implementation, mbedTLS requires a socket API. It does not matter on which platform. The network socket interface is in the "net_socket.c".

For MDK middleware, the interface is in:

C:\Keil\ARM\PACK\ARM\mbedTLS\1.6.0\MDK\library\mw_network\net_sockets.c

The SMTPS client demo example is in:

C:\Keil\ARM\PACK\ARM\mbedTLS\1.6.0\programs\ssl\ssl_mail_client.c

You can use those as a reference. However the SMTPS client demo example from mbedTLS pack is only a basic implementation and does not support attachments, multiple recipients, address friendly names and different character encodings.

Note that MDK Middleware version 7 uses a different mbedTLS interface, which allows integration into the MDK MW as an external component.

The latest version of the MDK MW that supports ARM9 devices is Version 4. Subsequent versions only support Cortex-M devices.

And NO, you can not simply move the code to ARM9 device and expect it to work. The SMTP client in MDK MW version 4 is very limited, has a different API, and does not support SMTPS.