- mbed-tls - lists.trustedfirmware.org

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

4 years, 4 months

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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

4 years, 4 months

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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, >

4 years, 4 months

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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. >

4 years, 4 months

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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. >

4 years, 4 months

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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.

4 years, 4 months

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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

4 years, 4 months

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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

4 years, 4 months

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Mbed TLS on ESP32

by Radim Kohout

Hello, I am using ESP32 Dev Module, which supports MbedTLS. I have two questions, but I can't find the answer on the forum: 1.Is there any way to import RSA keys from string(ideally from PEM format) to mbedtls_pk context? 2.How to encrypt with RSA private key and decrypt with RSA public key? Thanks Radim Kohout

4 years, 5 months

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Re: [mbed-tls] Invalid ECDSA signature created

by ROSHINI DEVI

Thanks Gilles. I have use mbedtls_ecdsa_sign and got the raw buffer output of R & S values. On Sun, Nov 22, 2020, 9:26 PM Gilles Peskine via mbed-tls < mbed-tls(a)lists.trustedfirmware.org> wrote: > Hi Roshini, > > Mathematically, an ES256 (ECDSA over the curve P256R1) signature is a > pair of numbers (r,s) between 1 and an upper bound which is very > slightly less than 2^256. There are two common representations for this > signature. JWA uses the “raw” representation: two big-endian numbers > represented each with exactly 32 bytes, concatenated together. > mbedtls_ecdsa_write_signature uses the ASN.1 DER representation, which > as you noticed represents each number in a type+length+value format. > > The DER format removes leading zeros from the number, then adds a > leading 0 bit to each number which is a sign bit (the numbers in an > ECDSA signature are always positive, but DER can also represent negative > numbers). Therefore each number has a roughly 1/2 chance of using 33 > value bytes with a leading 0 byte (1 sign bit + 7 value bits, all 0), a > 63/128 chance of using 32 value bytes, and a 1/128 chance of using 31 > value bytes or less because the 7 most significant bits of the number > were 0. A shorter number in an ECDSA signature is not invalid, it's a > 1/128 chance (independently for each of r and s). > > To get the signature in raw format with Mbed TLS, the easiest way is to > use the PSA API, where the output of psa_sign_hash() for ECDSA is the > raw format. With the classic Mbed TLS API, the easiest way is to call > mbedtls_ecdsa_sign() or mbedtls_ecdsa_sign_det_ext() to get r and s as > bignums, then use mbedtls_mpi_write_binary() to write r and s with their > exact size into the output buffer. You can find an example in the > internal function psa_ecdsa_sign(): > > https://github.com/ARMmbed/mbedtls/blob/mbedtls-2.24.0/library/psa_crypto.c… > > Hope this helps, > > -- > Gilles Peskine > Mbed TLS developer > > On 22/11/2020 10:12, ROSHINI DEVI via mbed-tls wrote: > > Hello all, > > > > I need to sign the message using ES256 algorithm. After doing > > necessary initializations, I called API > > - mbedtls_ecdsa_write_signature() API and it gave me signature in ASN1 > > encoded form and there was no error generated by this API. > > After getting the signature, I need the r & s values to create JWT > > Token. So, I wrote my custom function to parse the signature buffer > > and get the R & S values of it. > > It was working fine. Sometimes, I am getting an invalid signature as > > shown below signature DER buffer - > > > > 30 43 02 1f 31 92 8d 22 10 41 86 25 68 7f 42 81 26 0f 37 bc 7f 38 b7 > > d5 1a 6b 69 31 07 34 11 a6 04 e5 90 02 20 23 26 f8 b9 80 cf 2c 25 c8 > > 04 b4 ac 43 51 6a 04 a6 af 8f 94 36 f8 cf 35 c2 94 cc df de db 92 b2 > > > > The reason for invalid is - > > 1st byte represents ASN1 sequence, followed by length and 3rd byter > > indicates it is an integer. > > Ideally, 4th byte indicates length of r-value, it should have been 32 > > or 33 bytes ( in case of padding with 00 ). You can see in the above > > buffer it is 0x1F ( 31 bytes ). It is really weird how it is possible > > to get the signature length of 31 bytes. > > > > It is blocking me for generation of JWT token, where in RFC 7518 > > - https://tools.ietf.org/html/rfc7518#page-9 , it says R & S must be > > 32 bytes long. And, the generation is failing. > > > > It is of high priority for me. If anyone can provide your suggestions > > on this issue, it would be really great. Thanks in advance > > > > Thanks, > > Roshini > > > > > -- > mbed-tls mailing list > mbed-tls(a)lists.trustedfirmware.org > https://lists.trustedfirmware.org/mailman/listinfo/mbed-tls >

4 years, 5 months

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