I checked one you recommended and looks like it is very complicated.
Do you have any sample project(SSH client) based on MbedTLS+LWIP?
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1. Problem with decrypt aes 128 in ecb mode. HELP ME! (email@example.com) 2. Re: SSH client sample (Gilles Peskine) 3. Re: patches for low memory (Gilles Peskine)
Message: 1 Date: Wed, 22 Jul 2020 14:42:33 +0000 (UTC) From: "firstname.lastname@example.org" email@example.com To: firstname.lastname@example.org Subject: [mbed-tls] Problem with decrypt aes 128 in ecb mode. HELP ME! Message-ID: email@example.com Content-Type: text/plain; charset="utf-8"
I developed a server application that obtains the data from a dht11 sensor, I encrypt it with aes 128 and publish it on the server. The client application makes a request to the server, and I would like to decrypt the answer. When I want to display decrypted message, it shows garbage
The message retrieved from the server is in hex. I think that must to convert hex in binary, but i don’t know how can do it…
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Message: 2 Date: Wed, 22 Jul 2020 17:10:18 +0200 From: Gilles Peskine firstname.lastname@example.org To: email@example.com Subject: Re: [mbed-tls] SSH client sample Message-ID: firstname.lastname@example.org Content-Type: text/plain; charset=windows-1252
Libssh2 (https://github.com/libssh2/libssh2) supports Mbed TLS.
I've never used it or investigated it, so I can't vouch for it, I just know that it's there.
-- Gilles Peskine Mbed TLS developer
On 21/07/2020 18:40, Christie Su via mbed-tls wrote:
I am using FRDM-K64F with LWIP+mbedTLS for our control system. Now, I want to develop the SSH client(or telnet 22) to access my SSH server.
Could you give me some indications how to do it? Or do you have any sample project?
Message: 3 Date: Wed, 22 Jul 2020 17:34:44 +0200 From: Gilles Peskine email@example.com To: firstname.lastname@example.org Subject: Re: [mbed-tls] patches for low memory Message-ID: email@example.com Content-Type: text/plain; charset=utf-8
A TLS stack in 6kB of RAM sounds impressive, congratulations!
We'd certainly be interested in all the improvements you can contribute. The process is documented in CONTRIBUTING.md (https://github.com/ARMmbed/mbedtls/blob/development/CONTRIBUTING.md). I just need to warn you that the limiting factor is reviewers' time. For a significant contribution, it may take a while before the Mbed TLS team can look at it in detail. Small patches are usually easier than large ones: if something only takes half an hour to review, someone will probably do it when they're stuck on some other task. If a review takes several days, it needs to be scheduled.
It would probably be better to discuss the general nature of the changes on this mailing list first. Is a new compilation option needed? Is an API change needed? What is the risk that the change might break existing code? How is the new code tested? etc.
Which version of Mbed TLS have you been using? We've made a few changes that are of interest to low-memory platforms recently, such as the option MBEDTLS_SSL_VARIABLE_BUFFER_LENGTH to resize SSL buffers after the handshake (new in 2.22).
I don't know what the issue with the incoming SSL packet header length could be. If you could give precise steps to reproduce the issue, this would be very helpful. Eventually we'd want to construct a test in tests/ssl-opt.sh for this.
-- Gilles Peskine Mbed TLS developer
On 17/07/2020 21:00, Nick Setzer via mbed-tls wrote:
Hi, I have been working with Mbed TLS for the last 6 months in an extremely low memory use case. This library has been an absolute joy to work with because of how flexible it is. I have an interesting use case with how little RAM I have to work with (around 6kb on one microprocessor) and I have made some changes that I thought would be of interest. I'm not sure if I should submit them as a single changeset or a set of changes. I'll describe the changes and if there is interest I can clean them up for submission.
The first change that I made was for a scenario with two microprocessors communicating over a UART. I was already using TLS offloading so that the private key was on one processor (with only 6kb of RAM free) and the SSL context stored on the other. I required generating a CSR and thus made some changes to the CSR code to be able to generate the CSR using a similar private key offloading strategy.
I found an issue with downloading firmware for OTA from openssl web servers. This is a little tricky to describe. The server was not responsive to requests for reducing the max fragment length, which forced me to use MBEDTLS_SSL_MAX_CONTENT_LEN set to 16384. But I needed to have multiple ssl sessions open for other activities and did not have enough RAM to hold multiple large buffers. I have made a set of changes to allow setting the content length when the ssl context is initialized, as well as setting different IN and OUT content lengths to save memory. This change allowed me to set up one session with 16kb for the IN content length, and then 4kb for OUT content length, while a second session could use 2kb for a total of 24kb instead of 64kb.
Related to the openssl issue, I found that the incoming ssl packet header length can sometimes be 8 or 16 bytes larger than expected depending on which AES method is selected. I'm not actually sure what the best way to solve this is. One way may be to change MBEDTLS_SSL_HEADER_LEN from 13 to 29 bytes. However I ended up solving it by adding 16 to both MBEDTLS_SSL_IN_BUFFER_LEN and MBEDTLS_SSL_OUT_BUFFER_LEN. This way I could handle the larger ssl header as well as receive the content body.
If these three changes sound interesting I can start work on cleaning up the code to be less specific to my company and then submit the changes. Also I would like to know if there is any process I should be following when submitting these changes.
Nick Setzer SimpliSafe, Inc. 294 Washington Street, 9th Floor Boston, MA 02108
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