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Feedback requested: Mbed TLS builds with PSA and legacy implementations of the same algorithm with different characteristics

by Gilles Peskine

Hello, Summary: I am soliciting feedback about builds of Mbed TLS where *there is both a PSA implementation and the built-in software implementation of the same algorithm, by design, *and the PSA implementation isn't just calling the built-in implementation because the two have different characteristics, each desirable in some context. Please read this message if you are doing this or considering it. Feel free to ignore otherwise. For example, both MBEDTLS_SHA256_C and MBEDTLS_PSA_ACCEL_ALG_SHA_256 are enabled, so that calls to mbedtls_md_xxx() use the software implementation and calls to psa_hash_xxx() use the hardware accelerator via the PSA driver. And this is deliberate: there is a reason why mbedtls_md_xxx() must not call the PSA driver. In most cases, this is not desirable: if there's an accelerator, why not use it? And we're working to allow getting rid of the software implementation in more and more cases. Ultimately, PSA will be the only crypto interface in Mbed TLS, so all interfaces to calculate SHA-256 will go through psa_hash_xxx() and therefore will dispatch the call to the driver if there is one. This will be an API break, since it will require calling psa_crypto_init() before performing any cryptography. Currently we are planning to introduce this requirement in Mbed TLS 4.0. But it is currently possible to have dual algorithm support, and I can think of unusual cases where it might desirable. Scenario 1, with accelerator drivers: there is a driver, but it can only be used after some initialization. The application needs to use the algorithm before calling psa_crypto_init(), so it calls the legacy interface. After psa_crypto_init() has been called, the application would like to use the driver as much as possible. A typical use case is a bootloader which wants to verify a signature before initializing the random generator, so it calls mbedtls_md_xxx() and mbedtls_rsa_xxx(). Scenario 1 is clearly desirable, and for that we have a planned solution, which is staged initialization. The bootloader will be able to (1) initialize drivers, (2) perform a hash calculation, (3) initialize the keystore, (4) verify a signature, all without initializing the RNG. We won't make psa_crypto_init() mandatory until this feature is implemented. Scenario 2: with a cryptography service. This is a build of Mbed TLS with MBEDTLS_PSA_CRYPTO_CLIENT, so all psa_xxx() calls call the service. But, for some reason, there is also a local implementation of some cryptography algorithms. So you can call mbedtls_md() to calculate a hash even before the connection to the service has been established. Or maybe you want to call mbedtls_md() for short messages and psa_hash_compute() for long messages, because the crypto service has a faster implementation but the communication overhead offsets the gain for short messages. We are currently working on improving support for PSA drivers, and in particular, saving code size by eliminating more unnecessary code when a driver is present, and increasing the set of APIs that benefit from drivers. The obvious way to do that is to make all cryptography calls (especially from X.509 and TLS) go via the PSA interface, but we can't do that yet due to the need to have initialized the keystore and RNG. We are considering routing /certain/ crypto calls via PSA, in a way that would break scenario 2, and would also break scenario 1 in some cases, but not for hashes or signature verification. If, for example, in Mbed TLS 3.4, mbedtls_md() starts calling psa_hash_(), would this break your code? Are you in scenario 1, scenario 2, or some other variant I haven't thought of? If so, *please reply to this message and let us know what your needs are*. Feel free to reply to me in private if you don't want to discuss this publicly (I won't share directly outside Arm, but the eventual design might leak information about the unusual scenario). If we don't hear objections, there is a chance that a future Mbed TLS 3.x will break scenarios 1 and 2. If we do hear objections, we'll work to keep the current behavior or arrange a migration path. Best regards, -- Gilles Peskine Mbed TLS developer

1 year, 11 months

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problem PSA_CRYPTO (Mbedtls 2.28.0)

by xlin＠murata.com

I have port mbedtls 2.28.0 into my platform and am able to connect to a few websites in PKI mode. But after enabling MBEDTLS_USE_PSA_CRYPTO & MBEDTLS_PSA_CRYPTO_EXTERNAL_RNG, with everything else stay the same, I can't connect to the same websites anymore. in the working case (no MBEDTLS_USE_PSA_CRYPTO), after the client (my app) sends "Certificate, Client Key Exchange, Certificate Verify, Change Cipher Spec, Encrypted Handshake Message", the server responds with "Change Cipher Spec, Encrypted Handshake Message". In the broken case (with MBEDTLS_USE_PSA_CRYPTO), after the client (my app) sends "Certificate, Client Key Exchange, Certificate Verify, Change Cipher Spec, Encrypted Handshake Message", the server doesn't respond with "Change Cipher Spec, Encrypted Handshake Message". I don't know how to debug the issue, any suggestion what my cause the server to drop off at the last step?

1 year, 11 months

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How much bigger is MbedTLS 2.28.1 relative to 2.16.2? (STM 32F417 GCC)

by Peter

I may need TLS 1.3 support which I believe arrived in 2.28, or maybe a bit later. I don't want to change to TLS 3 just yet. It looks like many changes. My target is "OK" on FLASH (150k of the 350k total code size) but is tight on RAM (after allocating 50k for the MbedTLS heap, we have just 20k RAM left). Ideally I would like the very last version of v2. The problem just found is that Cloudflare is asking for TLS 1.3 which MbedTLS 2.16 does not support. But it may be that Cloudflare can fall back and the problem is elsewhere. Many thanks for any input.

1 year, 11 months

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Performance tuning of SHA256 on big files

by Liu James

Hi, This is an updated post from https://github.com/Mbed-TLS/mbedtls/issues/6464, which should be posted in mbedtls mail list. My question is how to significantly improve SHA256 performance on big files (regardless of architectures). *=== Updates* I use same code with mbedtls-3.1.0 to run tests in x86, and performance is still downgraded. Mbed TLS version (number or commit id): *3.1.0* Operating system and version: * Centos-8.5, CPU 11900K* Configuration (if not default, please attach mbedtls_config.h): Compiler and options (if you used a pre-built binary, please indicate how you obtained it): *gcc/g++ 8.5* Additional environment information: *Test files and performance* CentOS-8.5.2111-x86_64-boot.iso (827.3 MB): sha256 *5 sec* CentOS-8.5.2111-x86_64-boot.iso (10.79 GB): sha256 *66 sec* Also, as advised I try to turn on "MBEDTLS_SHA256_USE_A64_CRYPTO_IF_PRESENT " and "MBEDTLS_SHA512_USE_A64_CRYPTO_IF_PRESENT" using mbedtls-3.2.0 in M1, but compiler reported the following error: CMake Error at library/CMakeLists.txt:257 (add_library): Cannot find source file: psa_crypto_driver_wrappers.c Tried extensions .c .C .c++ .cc .cpp .cxx .cu .mpp .m .M .mm .ixx .cppm .h .hh .h++ .hm .hpp .hxx .in .txx .f .F .for .f77 .f90 .f95 .f03 .hip .ispc CMake Error at library/CMakeLists.txt:257 (add_library): No SOURCES given to target: mbedcrypto Thanks for your help. *=== Original message at github* Summary sha256() and sha1() incurs significant overhead on big files(~1G above). *This might not be an issue*, and I'm looking for an efficient way to calculate hash on big files. System information Mbed TLS version (number or commit id): 3.1.0 Operating system and version: M1 OSX Configuration (if not default, please attach mbedtls_config.h): Compiler and options (if you used a pre-built binary, please indicate how you obtained it): Clang++ Additional environment information: Expected behavior Fast calculation of big files in less than 1 second Actual behavior Test files: CentOS-8.5.2111-x86_64-boot.iso (827.3 MB): sha1 *3.3 sec*, sha256 *5.9 sec* CentOS-8.5.2111-x86_64-boot.iso (10.79 GB): sha1 *40 sec*, sha256 *78 sec* Steps to reproduce ISO files can be downloaded at: http://ftp.iij.ad.jp/pub/linux/centos-vault/8.5.2111/isos/x86_64/ Make sure use fast disk, say nvme, to store ISO files, or else loading big files could take lots of time. Also use user from time command to measure performance. Workable code of sha256: string test_sha256(string file_path) { mbedtls_sha256_context ctx; FILE *fp; string output; int BUFFER_SIZE = 4096; uint8_t buffer[BUFFER_SIZE]; size_t read, k_bytes; uint8_t hash[32]; mbedtls_sha256_init(&ctx); mbedtls_sha256_starts(&ctx, 0); fp = fopen(file_path.c_str(), "r"); if (fp == NULL) { mbedtls_sha256_free(&ctx); return output; } while ((read = fread(buffer, 1, BUFFER_SIZE, fp))) { mbedtls_sha256_update(&ctx, buffer, read); } mbedtls_sha256_finish(&ctx, hash); mbedtls_sha256_free(&ctx); fclose(fp); // update hash string, omit here return output; }

1 year, 11 months

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Is there a server somewhere which can be used for testing various MbedTLS client cipher suites

by Peter

Hi All, There are machines out there for testing servers but I don't know of one which can be used for testing a client. This is a tricky area. For example I have a board running, LWIP and MbedTLS, uploading little test files to two sites. One was running EC and AES256. It worked fine. The other was running RSA and AES256 but didn't work, and after some work it was found that its certificate chain was running SHA-1 on the top level certificate, dated 2006. This is actually a major name on the internet! And we didn't have SHA-1 enabled because it is supposed to be deprecated. I wonder if there is some practical way to test out all this. We can probably enable all the MbedTLS crypto options (TLS is taking up 150k out of 350k of code for the whole product, but we can probably throw in some more) but testing them is something else. There is a test suite in TLS but it needs to be embedded in the product itself. Has someone implemented that code on a server somewhere? Thank you in advance for any pointers. Peter

1 year, 11 months

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Error about psa_crypto_init

by 韩轾

I meet a problem when I call function `psa_crypto_init`, it return error code -148 that was PSA_ERROR_INSUFFICIENT_ENTROPY. I track this function step by step and found it caused by MBEDTLS_ERR_ENTROPY_NO_SOURCES_DEFINED. Code in entropy.c, if( ctx->source_count == 0 ), return this error. My question: I run code on Ubuntu, it runs well. But in some arm board, it returns this error. Why this count will be 0 sometimes? What is the root cause of this error.

1 year, 11 months

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Reminder: MBed TLS Technical Forum - US/Europe

by Don Harbin

Hi All, A gentle reminder that the US-Europe timezone-friendly MBed TLS Tech forum is next Monday at 4:30 PM UK time. Invite details can be found on the online calendar here <https://www.trustedfirmware.org/meetings/>. If you have any topics, please let Dave Rodgman know. :) Best regards, Don Harbin TrustedFirmware Community Manager don.harbin(a)linaro.org

1 year, 11 months

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PKCS#7 format of certificate

by Subramanian Gopi Krishnan

Hi, I have developed a TLS and EST client application. Where the EST server issues the certificate in PKCS#7 format. It seems mbedtls library not support certificates in PKCS#7 format. Is there any plan to support PKCS#7 in future? Thanks, Gopi Krishnan

1 year, 11 months

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Reminder: MBed TLS Technical Forum - Asia

by Don Harbin

Hi All, A gentle reminder that the Asia-Europe timezone-friendly MBed TLS Tech forum is next *Monday, Oct 10 at 10:00am UK time*. Invite details can be found on the online calendar here <https://www.trustedfirmware.org/meetings/>. If you have any topics, please let Dave Rodgman, cc'd, know. :) Best regards, Don Harbin TrustedFirmware Community Manager don.harbin(a)linaro.org

1 year, 11 months

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Re: Writing mbedtls_x509_crt chain to PEM ?

by Nicolas Pillot

Hello Please note that this is a repost from my previous message from yesterday as it seemd to have bugged (empty text + html attachement) when viewed from the archive. Apologies. Short question : how do i output an in-memory mbedtls_x509_crt chain to PEM text ? Context : I have a project where the user provides a PEM bundle to be used for HTTPS As it is provided by a user, may be incomplete or malformed : - no private key - more than 1 private key - no certificate at all - duplicate certificates - no certificate matching the private key - broken chain - extraneous certificates not part of the chain… So i want to full validate user input. Here is what i have succeeded so far : - parse the bundle into atomic parts, based on « BEGIN/END » labels - try to mbedtls_x509_crt_parse / mbedtls_pk_parse_key each part (no chain) - check that i only have one private key in the bundle - search for the certificat C matching the private key - starting from that atomic certificate, verify it against each other candidate certificate - if it validates, add it to the chain of C, and repeat until no candidate validates - then check that there are no remaining certificate (which never validated anything) - finally print and store the chain (as it’s now deemed correct and minimal) Now i want to store it in PEM format for later use. But i do not understand the way to do it : - there are no write functions for mbedtls_x509_crt - the mbedtls_x509write_cert structure shares few members with mbedtls_x509_crt - i have not found yet how to get/convert many of the missing members - as memory is tight i have have cleaned the « atomic parts » text buffers (but if there is no other way, i'll keep and reuse them) I guess it should be pretty simple, but i cannot wrap my head around it. Thanks in advance for your help Nicolas PS : if steps 1-8 could be done more elegantly, please do not hesitate to point me in the right direction.

1 year, 12 months

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