- mbed-tls - lists.trustedfirmware.org

by Manuel Pegourie-Gonnard

Hi Farhad, I think for this question as well as the "packets lost" question, it's important to distinguish two phases of a DTLS connection: initially there's a handshake (to negotiate and establish security parameters and session keys), and then application data can be exchanged. Application data is what's passed to `mbedtls_ssl_write()` or written by `mbedtls_ssl_read()` (depending on whether you're the sender or receiver) - this can only happen once the handshake is completed. During the handshake, there are indeed mechanisms to re-order packets that were received out of order and also retransmit packets that were lost. But that's only during the handshake (because it's a lockstep process where everything needs to happen in order), and only for data that's purely internal to the DTLS protocol and never seen by the application. Once the handshake is completed and application data starts to be exchanged, there is no longer any kind of re-ordering or retransmission mechanism. The reason is, as you guessed, DTLS aims to provide similar properties to UDP - with cryptographic security in addition. So, if you send something with `mbedtls_ssl_write()` and the record gets lost, the DTLS protocol won't even know about it, and no retransmission will happen. If record N+1 arrives before record N, the DTLS protocol will know but do nothing, and just deliver the records in the order they arrived. Again, as you said, doing otherwise would introduce latency and be contrary to the goals of DTLS - people who want reliability at the expense of latency should use TLS. The main exception to that principle that you can expect DTLS to behave like UDP is duplicated records: the DTLS protocol provide optional replay protection (that is, if record N arrives twice, the second occurrence is dropped). In Mbed TLS, this mechanism is enabled by default but can be disabled at compile-time by not defining MBEDTLS_SSL_DTLS_ANTI_REPLAY in config.h, or at runtime by calling mbedtls_ssl_conf_dtls_anti_replay(). I hope this answers your questions. Regards, Manuel. ________________________________ From: mbed-tls <mbed-tls-bounces(a)lists.trustedfirmware.org> on behalf of saghili via mbed-tls <mbed-tls(a)lists.trustedfirmware.org> Sent: 10 December 2020 18:31 To: mbed-tls(a)lists.trustedfirmware.org <mbed-tls(a)lists.trustedfirmware.org> Subject: [mbed-tls] "Reordering" in DTLS Hello, I have a question about DTLS. One thing that is not entirely clear to me from the RFC is this: suppose 2 records are received within a "short" period, e.g. seq# N+1 followed by seq# N. In this case, what does DTLS do? My understanding is that it will pass on packets in the order it was received (i.e. out of order). But it can (should?) re-order at the DTLS layer and pass them on to the upper layer in the right order. HOWEVER, this implies that the DTLS "wait" for a certain window to see if the seq#=N packet arrives or not. But doing so introduces additional delay at DTLS layer and also contradicts with the UDP principle (i.e. no concept of order). Could you please give me a hint regarding this issue? Best regards, Farhad -- mbed-tls mailing list mbed-tls(a)lists.trustedfirmware.org https://lists.trustedfirmware.org/mailman/listinfo/mbed-tls

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[Mbed-tls-announce] Mbed TLS: Release of Mbed TLS 2.25.0, 2.16.9 and 2.7.18

by Janos Follath via Mbed-tls-announce

Mbed TLS versions 2.25.0, 2.16.9 and 2.7.18 have just been released. These releases of Mbed TLS address several security issues, provide bug fixes, and bring other minor changes. Full details are available in the release notes (https://github.com/ARMmbed/mbedtls/releases/tag/v2.25.0, https://github.com/ARMmbed/mbedtls/releases/tag/v2.16.9, https://github.com/ARMmbed/mbedtls/releases/tag/v2.7.18 ). We recommend all users to consider whether they are impacted, and to upgrade appropriately. -- Mbed-tls-announce mailing list Mbed-tls-announce(a)lists.trustedfirmware.org https://lists.trustedfirmware.org/mailman/listinfo/mbed-tls-announce

5 years

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"Reordering" in DTLS

by saghili

Hello, I have a question about DTLS. One thing that is not entirely clear to me from the RFC is this: suppose 2 records are received within a "short" period, e.g. seq# N+1 followed by seq# N. In this case, what does DTLS do? My understanding is that it will pass on packets in the order it was received (i.e. out of order). But it can (should?) re-order at the DTLS layer and pass them on to the upper layer in the right order. HOWEVER, this implies that the DTLS "wait" for a certain window to see if the seq#=N packet arrives or not. But doing so introduces additional delay at DTLS layer and also contradicts with the UDP principle (i.e. no concept of order). Could you please give me a hint regarding this issue? Best regards, Farhad

5 years

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"packets lost" in DTLS in "Record" layer

by saghili

Hello, I have a question about DTLS. Because of the latency, I need to disable the "packets lost" feature. Does MbedTLS provide the flag that we can disable resending the packet in case of the packet lost? For instance, if I have 3 packets 42, 43, and 44, is it possible to decrypt packet 44 without receiving packets 42 and 43? It will be in the "Record" layer. Thank you. Best regards, Farhad

5 years

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Re: [mbed-tls] mbedtls undefined behaviour

by Сысоев Андрей

Thank you for quick response. > Are you using blocking or non-blocking I/O? Non-blocking IO I've preset bio_send/recv callbacks I have pair of buffers, transport buffer and application buffer, for reading and writing (4 buffers total). Application buffers are protected by mutexes. Transport buffers are written/read in bio_send/recv (if no async op pending, otherwise WANT_READ/WRITE). mbedtls_ssl_xxx work with application buffers. > Are you using TLS or DTLS? What protocol version, what cipher suite and what extensions are negotiated? TLS (over tcp, no lossy channel involved) version 1.2 > Does your application call mbedtls_ssl_write() and mbedtls_ssl_read() again with the same buffer if they return MBEDTLS_ERR_SSL_WANT_READ or MBEDTLS_ERR_SSL_WANT_WRITE? Well, actually, no. AND it's quite possible, that application outgoing buffer (std::vector) has been relocated between mbedtls_ssl_write calls, because app could push data several times while async op was pending and bio_send returned WANT_WRITE, causing these buffers to resize. So buf.data() will not be equal to that from previous mbedtls_ssl_write call. Is this what causes trouble? It's somehow connected to partial sends? I do call ssl_write inside while-loop, counting sent and unsent bytes - thought this was enough. But if mbedtls somehow remembers addresses from previos calls - that might cause problems. > Do you close the TLS connection if mbedtls_ssl_xxx() returns an error other than WANT_XXX (or XXX_IN_PROGRESS if you use these features)? Yes, but that never happens (from handshake to until problem appears) > What is the value of MBEDTLS_SSL_MAX_CONTENT_LEN (or MBEDTLS_SSL_OUT_CONTENT_LEN if it's defined)? Not defined in config, looks like both 16834 >What operating system are you using? Ubuntu 20, Kali 20 > Is this a client or a server? What TLS stack does the other side run? Both are written same way, both using same library. I'll try to prepare test-case code, that reproduces the problem, and logs, but that will require some time. 10.12.2020 1:07, Gilles Peskine via mbed-tls пишет: > Hi Андрей, > > The behavior you describe is a bug. But there isn't enough information > to tell whether the bug is in Mbed TLS, in asio-standalone, in some > other third-party code, or in your application. > > Some things to consider: > > * Are you using blocking or non-blocking I/O? > * Are you using TLS or DTLS? What protocol version, what cipher suite > and what extensions are negotiated? > * Does your application call mbedtls_ssl_write() and mbedtls_ssl_read() > again with the same buffer if they return MBEDTLS_ERR_SSL_WANT_READ or > MBEDTLS_ERR_SSL_WANT_WRITE? > * Do you close the TLS connection if mbedtls_ssl_xxx() returns an error > other than WANT_XXX (or XXX_IN_PROGRESS if you use these features)? > * What is the value of MBEDTLS_SSL_MAX_CONTENT_LEN (or > MBEDTLS_SSL_OUT_CONTENT_LEN if it's defined)? > * What operating system are you using? > * Is this a client or a server? What TLS stack does the other side run? > > You'll give others the most chance to help you if you post small, > complete code to reproduce the problem. I realize this may be difficult. > A good intermediate way to see what is going on would be to post debug > logs. To get debug logs, make sure that MBEDTLS_DEBUG_C is enabled and > call these functions before opening the TLS connection: > > mbedtls_ssl_conf_dbg(&ssl_conf, my_debug, stdout); > mbedtls_debug_set_threshold(2); > > See https://tls.mbed.org/kb/how-to/mbedtls-tutorial for a sample version > of my_debug(). > > Calls to bio_send() are shown in the logs as > > => flush output > message length: %d, out_left: %d > ssl->f_send() returned %d > <= flush output > > If they don't show expected numbers, the rest of the logs should give a > clue as to why. > > Hope this helps, >

5 years

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Re: [mbed-tls] mbedtls undefined behaviour

by Gilles Peskine

By the way, I notice you're using Mbed TLS 2.16.3. This version has known bugs, including security issues. Please upgrade to the latest Mbed TLS 2.16.x (currently 2.16.8, very soon 2.16.9) which is a security and bugfix update, or to the latest release (2.24.0, soon 2.25.0) which has all the latest bugfixes and features. Looking at the changelog, I don't see any mention of a bug that could explain your problem, but I might have missed something. -- Gilles Peskine Mbed TLS developer On 09/12/2020 22:17, Сысоев Андрей via mbed-tls wrote: > Hello. > > I need a little help with mbedtls 2.16.3. > I'm using it under x86-64 with asio-standalone. > > Here's a standard situation: > - I call mbedtls_ssl_write() to write let's say 8192 bytes of payload > - it calls my own bio_send() with (8192+21) bytes as len parameter > - bio_send() returns len=(8192+21), indicating transport data > correctly written > - mbedtls_ssl_write() returns 8192, indicating payload send > GOOD: next I use this value to shift application buffer (erase first > 8192 bytes), then send next chunk > > BUT after some time of running this situation happens: > - once again, a call to mbedtls_ssl_write() to write let's say 8192 > bytes of payload > - it calls bio_send() with smaller number, about 5500 bytes as len > parameter (?? but OK) > - bio_send() returns len=5500, indicating transport data correctly > written > - mbedtls_ssl_write() returns 8192 (??? why not 5500 ???), indicating > payload send > BAD: next I use this value to shift application buffer (erase first > 8192 bytes), this leads to data loss of (8192-5500)=2692 bytes and > ruins protocol > > As you can see, mbedtls_ssl_write() incorrectly reports about sent > application data (8192 instead of 5500) - is this a bug? How can such > situation happen under normal operation? > > Thanks in advance. >

5 years

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Re: [mbed-tls] mbedtls undefined behaviour

by Gilles Peskine

Hi Андрей, The behavior you describe is a bug. But there isn't enough information to tell whether the bug is in Mbed TLS, in asio-standalone, in some other third-party code, or in your application. Some things to consider: * Are you using blocking or non-blocking I/O? * Are you using TLS or DTLS? What protocol version, what cipher suite and what extensions are negotiated? * Does your application call mbedtls_ssl_write() and mbedtls_ssl_read() again with the same buffer if they return MBEDTLS_ERR_SSL_WANT_READ or MBEDTLS_ERR_SSL_WANT_WRITE? * Do you close the TLS connection if mbedtls_ssl_xxx() returns an error other than WANT_XXX (or XXX_IN_PROGRESS if you use these features)? * What is the value of MBEDTLS_SSL_MAX_CONTENT_LEN (or MBEDTLS_SSL_OUT_CONTENT_LEN if it's defined)? * What operating system are you using? * Is this a client or a server? What TLS stack does the other side run? You'll give others the most chance to help you if you post small, complete code to reproduce the problem. I realize this may be difficult. A good intermediate way to see what is going on would be to post debug logs. To get debug logs, make sure that MBEDTLS_DEBUG_C is enabled and call these functions before opening the TLS connection: mbedtls_ssl_conf_dbg(&ssl_conf, my_debug, stdout); mbedtls_debug_set_threshold(2); See https://tls.mbed.org/kb/how-to/mbedtls-tutorial for a sample version of my_debug(). Calls to bio_send() are shown in the logs as => flush output message length: %d, out_left: %d ssl->f_send() returned %d <= flush output If they don't show expected numbers, the rest of the logs should give a clue as to why. Hope this helps, -- Gilles Peskine Mbed TLS developer On 09/12/2020 22:17, Сысоев Андрей via mbed-tls wrote: > Hello. > > I need a little help with mbedtls 2.16.3. > I'm using it under x86-64 with asio-standalone. > > Here's a standard situation: > - I call mbedtls_ssl_write() to write let's say 8192 bytes of payload > - it calls my own bio_send() with (8192+21) bytes as len parameter > - bio_send() returns len=(8192+21), indicating transport data > correctly written > - mbedtls_ssl_write() returns 8192, indicating payload send > GOOD: next I use this value to shift application buffer (erase first > 8192 bytes), then send next chunk > > BUT after some time of running this situation happens: > - once again, a call to mbedtls_ssl_write() to write let's say 8192 > bytes of payload > - it calls bio_send() with smaller number, about 5500 bytes as len > parameter (?? but OK) > - bio_send() returns len=5500, indicating transport data correctly > written > - mbedtls_ssl_write() returns 8192 (??? why not 5500 ???), indicating > payload send > BAD: next I use this value to shift application buffer (erase first > 8192 bytes), this leads to data loss of (8192-5500)=2692 bytes and > ruins protocol > > As you can see, mbedtls_ssl_write() incorrectly reports about sent > application data (8192 instead of 5500) - is this a bug? How can such > situation happen under normal operation? > > Thanks in advance. >

5 years

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mbedtls undefined behaviour

by Сысоев Андрей

Hello. I need a little help with mbedtls 2.16.3. I'm using it under x86-64 with asio-standalone. Here's a standard situation: - I call mbedtls_ssl_write() to write let's say 8192 bytes of payload - it calls my own bio_send() with (8192+21) bytes as len parameter - bio_send() returns len=(8192+21), indicating transport data correctly written - mbedtls_ssl_write() returns 8192, indicating payload send GOOD: next I use this value to shift application buffer (erase first 8192 bytes), then send next chunk BUT after some time of running this situation happens: - once again, a call to mbedtls_ssl_write() to write let's say 8192 bytes of payload - it calls bio_send() with smaller number, about 5500 bytes as len parameter (?? but OK) - bio_send() returns len=5500, indicating transport data correctly written - mbedtls_ssl_write() returns 8192 (??? why not 5500 ???), indicating payload send BAD: next I use this value to shift application buffer (erase first 8192 bytes), this leads to data loss of (8192-5500)=2692 bytes and ruins protocol As you can see, mbedtls_ssl_write() incorrectly reports about sent application data (8192 instead of 5500) - is this a bug? How can such situation happen under normal operation? Thanks in advance.

5 years

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Re: [mbed-tls] Implementing MbedTLS on "xilinx zu7 zynq ultrascale+soc"

by Gilles Peskine

Hi Farhad, Mbed TLS currently supports hardware acceleration through alternative implementations of the corresponding modules or functions. See https://tls.mbed.org/kb/development/hw_acc_guidelines . This mechanism is available for symmetric cryptography and partially for RSA and ECC. There is some work in progress on a new mechanism for hardware acceleration through the psa_xxx() API, which will be available for all algorithms. You can follow the work in progress on the “Unified driver interface: API design and prototype” epic at https://github.com/ARMmbed/mbedtls/projects/2#column-8543266 . Hope this helps, -- Gilles Peskine Mbed TLS developer On 04/12/2020 11:20, saghili via mbed-tls wrote: > Dear Sir/Madam, > > Our platform is a quad core Cortex A53 running PetaLinux. > In our hardware, "AF_ALG" module has performance accelerations > available through the Linux crypto drivers. > Is it possible that we have "AF_ALG" for offloading crypto operations? > > Best regards, > Farhad

5 years

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Implementing MbedTLS on "xilinx zu7 zynq ultrascale+soc"

by saghili

Dear Sir/Madam, Our platform is a quad core Cortex A53 running PetaLinux. In our hardware, "AF_ALG" module has performance accelerations available through the Linux crypto drivers. Is it possible that we have "AF_ALG" for offloading crypto operations? Best regards, Farhad

5 years

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