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Re: [mbed-tls] 3.0 plans: remove pkcs11.c from the code base

by Manuel Pegourie-Gonnard

Hi Gilles, Thanks for this precision, as well as the reminder of the existing github issue. With no opposition here in a week, and none on github for nearly 3 months either, plus no opposition when we marked it as deprecated in 2.21 in February, I'm also moving this to the "Accepted" section on the wiki discussion tracking page: https://developer.trustedfirmware.org/w/mbed-tls/tech-plans-3.0/ - but again, it's still time to voice concerns until we've actually removed it from the code base. Regards, Manuel.

5 years, 2 months

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Re: [mbed-tls] 3.0 plans: remove havege.c from the code base

by Manuel Pegourie-Gonnard

Hi Gilles, Thanks for your feedback and for providing a link to the existing issue, which I completely forgot about - I'll reference that in the wiki as well. Since it's been a week, with one agreement and no opposition, I'm also moving this to the "Accepted" section in the summary wiki page: https://developer.trustedfirmware.org/w/mbed-tls/tech-plans-3.0/ - though again, it you have concerns it's still time to voice them. Regards, Manuel.

5 years, 2 months

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Re: [mbed-tls] 3.0 plans: remove old TLS options from the code base entirely

by Manuel Pegourie-Gonnard

Hi all, Since this list of old options was probably not controversial in the first place and there has been no opposition in more than a week (a time that was sufficient for other thread in the same series to get several reactions), I'm moving this from "Under discussion" to "Accepted" in the summary wiki page: https://developer.trustedfirmware.org/w/mbed-tls/tech-plans-3.0/ This is not meant to shut down discussion and if you disagree or have concerns it's still time to voice them - this is just to simplify tracking of the discussions. Best regards, Manuel.

5 years, 2 months

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Re: [mbed-tls] 3.0 plans: remove memory_buffer_alloc.c from the code base

by Gilles Peskine

On 09/04/2020 13:17, Janos Follath via mbed-tls wrote: > Hi, > > Based on what I read on this thread it seems an accepted point of view that the toolchain provided C standard library implementations are less trusted than the toolchains themselves. Can somebody please help me understand the reasoning behind this distinction? Well, I disagree with this statement. I trust the toolchain to implement the C standard library correctly, and with good performance for the target platform. I do not want to provide my own implementation of standard functions. I only trust the toolchain to be functionally correct. I don't know about its security. I certainly can't rely on the toolchain to have security characteristics that are not guaranteed by the language definition. For example, I do trust memset_s() to zero out sensitive memory if the toolchain provides it, but I don't trust memset() for this task. On the topic at hand, my personal opinion of memory_buffer_alloc is that it doesn't belong in Mbed TLS. I hope that when PSA crypto is a standalone product, it won't use malloc internally, and so it certainly won't provide a malloc implementation. I wouldn't necessarily say the same thing of Mbed TLS 4.0: it's difficult to design an X.509 interface that doesn't use malloc. But if we can do it, I think we should. I recognize that there are many bare-metal applications that don't use malloc themselves, but use Mbed TLS. For their sake, it does make some sense for Mbed TLS to have its own malloc implementation. But the focus is for internal use, not on serving as a general-purpose allocator for applications that also use malloc for non-mbedtls-related purposes. -- Gilles Peskine Mbed TLS developer IMPORTANT NOTICE: The contents of this email and any attachments are confidential and may also be privileged. If you are not the intended recipient, please notify the sender immediately and do not disclose the contents to any other person, use it for any purpose, or store or copy the information in any medium. Thank you.

5 years, 2 months

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Re: [mbed-tls] 3.0 plans: remove havege.c from the code base

by Gilles Peskine

Yes, we should remove it. Unlike other features, I think we should remove HAVEGE _especially_ if someone is using it, because unlike the rest of the library, I cannot vouch for its security. I don't even know if our havege.c is implementing the HAVEGE specification correctly. And I cannot think of a platform where HAVEGE would give a useful amount of entropy, and where there isn't already a proper hardware RNG or an OS kernel with its own entropy gathering built with knowledge of the actual platform. (Also noted on https://github.com/ARMmbed/mbedtls/issues/2599 .) -- Gilles Peskine Mbed TLS developer On 08/04/2020 12:41, Manuel Pegourie-Gonnard via mbed-tls wrote: > Hi all, > > In this new installment of "let's discuss ideas for Mbed TLS 3.0" [1]: > should we remove havege.c from the code base? > > [1]: https://developer.trustedfirmware.org/w/mbed-tls/tech-plans-3.0/ > > The crypto library currently includes an implementation of the HAVEGE entropy > gatherer [2], which is disabled in the default build (MBEDTLS_HAVEGE_C in > config.h), but used as a source by our entropy module if enabled. > > [2]: https://www.irisa.fr/caps/projects/hipsor/ > > We'd like to drop this module and remove it from the code base entirely for > the following reasons: > > - HAVEGE was designed for superscalar processors with high > microarchitectural complexity, and is unsuitable for microcontrollers (or > virtualized environments). We feel like when a complex enough CPU is used for > HAVEGE to stand a chance of being secure, it's very likely that an operating > system is also available, which probably already manages a random generator > better that what we can do in user space. > > - On a more practical note, our implementation relies on `timing_hardclock()` > provided by timing.c only for a limited number of architectures and > environments (funnily enough, not including any Arm architecture), with a > silent fallback to a definition relying on `gettimeofday()` which is clearly > not high-resolution enough to make HAVEGE secure. > > - As with any random source, it is very difficult to assess whether HAVEGE is > actually secure on any given platform. Further, the maintenance team > doesn't have any specific knowledge of HAVEGE and there hasn't been any > independent evaluation of our implementation of it. > > - As a result of the above points, we're afraid people using our HAVEGE > implementation on the wrong platforms, might be getting a false sense of > security, which might prevent them from using more secure options, such as the > OS RNG (when using an OS) or a hardware RNG (on microcontrollers). > > If you're using MBEDTLS_HAVEGE_C or know someone who does, or if for any other > reason you think we shouldn't drop it in Mbed TLS 3.0, please speak up now! > > Regards, > Manuel. IMPORTANT NOTICE: The contents of this email and any attachments are confidential and may also be privileged. If you are not the intended recipient, please notify the sender immediately and do not disclose the contents to any other person, use it for any purpose, or store or copy the information in any medium. Thank you.

5 years, 2 months

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Re: [mbed-tls] 3.0 plans: remove pkcs11.c from the code base

by Gilles Peskine

Hello, As noted in https://github.com/ARMmbed/mbedtls/issues/3006, I'm aware of only one project that is using Mbed TLS's pkcs11-helper support: OpenVPN. But this support has been removed from the development version. -- Gilles Peskine Mbed TLS developer On 08/04/2020 12:37, Manuel Pegourie-Gonnard via mbed-tls wrote: > Hi all, > > In this new installment of "let's discuss ideas for Mbed TLS 3.0" [1]: > should we remove pkcs11.c from the code base? > > [1]: https://developer.trustedfirmware.org/w/mbed-tls/tech-plans-3.0/ > > The X.509 library currently includes a module called "pkcs11", excluded from > the default build, which provides a few wrappers around libpkcs11-helper [2], > a library that "simplifies the interaction with PKCS#11 providers for end-user > applications". In practice, it supports the use of X.509 certificates > associated with an RSA key (not ECDSA) managed by libpkcs11-helper. > > [2]: https://github.com/OpenSC/pkcs11-helper > > We'd like to drop this module and remove it from the code base entirely for > the following reasons: > > - It has limited functionality, and soon PSA Crypto will provide more flexible > support for secure management of private keys (not just RSA, and not just > associated with X.509 certificates). > > - It currently has not automated tests so we're not even sure if it still > works properly. > > - The documentation is scarce and no member of the current maintenance team > knows for sure how it's supposed to work. > > - We never receive any support request about it so we're not sure if anyone is > still using it. (As a weaker signal in the same direction, we deprecated it > in 2.21.0, released 2020-02-20, and nobody complained so far.) > > If you're using MBEDTLS_PKCS11_C or know someone who does, or if for any other > reason you think we shouldn't drop it in Mbed TLS 3.0, please speak up now! > > Regards, > Manuel. > IMPORTANT NOTICE: The contents of this email and any attachments are confidential and may also be privileged. If you are not the intended recipient, please notify the sender immediately and do not disclose the contents to any other person, use it for any purpose, or store or copy the information in any medium. Thank you.

5 years, 2 months

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Running Mbed TLS unit tests on embedded targets

by Gilles Peskine

Hello, We're planning to make some changes to the way you can run Mbed TLS unit tests on embedded platforms. We want to make it easier to run the tests on platforms that have limited space for code and don't have a filesystem to read data from. At the moment, there are two ways to build the test suites. If you run 'make test', this builds one a host executable using host_test.function for each test_suite_*.function and one “compiled” data file for each test_suite_*.data, and the executable reads the compiled data file at runtime. It's also possible to build an executable with target_test.function, which includes calls to the Mbed-tools Greentea library to communicate over the serial port, and you can use the script mbedtls_test.py to run the tests with Greentea. Neither method works directly for embedded platforms other than Mbed OS. If you've run the Mbed TLS unit tests without reading the .datax file from the filesystem, and without using Mbed OS and Greentea, how did you do it? If you haven't run the unit tests but would like to do so, what changes would you like to see what Mbed TLS provides? I have a few more specific questions: • Does Mbed TLS need to include some abstraction for serial communication? If not, what would the interface of the test functions be? (Tests can currently take inputs that are zero-terminated text string, binary string with length, or int, and we'd like to add the possibility to add other integer types such as uint64_t, but nothing more complex. The outcome of a test is pass/fail/skip, and if fail/skip location information about the failure.) • Is it useful to have a way to build the test data into the executable, so that the only interaction that the executable needs is to write out the test results? It's more convenient but doesn't work everywhere (the biggest test suite has >200kB of test data). • Should test executables be self-contained in their reporting (including error messages)? Or should they minimize code size, and then you'd need an extra host-side script to make sense of results? • The current .function-to-.c transformation script (generate_test_code.py) generates a single C file with all of the test code (but not the test data). Is this a useful requirement? We welcome any thoughts you may have on the topic. -- Gilles Peskine Mbed TLS developer IMPORTANT NOTICE: The contents of this email and any attachments are confidential and may also be privileged. If you are not the intended recipient, please notify the sender immediately and do not disclose the contents to any other person, use it for any purpose, or store or copy the information in any medium. Thank you.

5 years, 2 months

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Re: [mbed-tls] 3.0 plans: remove memory_buffer_alloc.c from the code base

by Janos Follath

Hi Dan, Thank you for explaining, I see it now. I think we definitely should leave the choice open for Mbed TLS users and I agree that such a joint stdlib implementation project would be a much better place for a toolchain independent memory allocator. Regards, Janos On 09/04/2020, 14:31, "mbed-tls on behalf of Dan Handley via mbed-tls" <mbed-tls-bounces(a)lists.trustedfirmware.org on behalf of mbed-tls(a)lists.trustedfirmware.org> wrote: Hi Janos It's not so much that the toolchain stdlib implementations are less trusted from a security point of view, it's that there is variation in their non-functional characteristics, e.g. * security * robustness * code size * performance * open-ness * ... If you remove this variation it's easier to reason about the non-functional characteristics of the code. This is perhaps more important for projects that build final executable images but may also be important for libraries, especially ones that export executable link libraries like Mbed TLS. On the other hand, Mbed TLS is deployed in many other places than Trusted Firmware and it may be hard to choose a stdlib implementation that works for all users. Perhaps the compromise is to create a shared stdlib implementation for Trusted Firmware deployments but leave the choice open for other Mbed TLS users? Regards Dan > -----Original Message----- > From: mbed-tls <mbed-tls-bounces(a)lists.trustedfirmware.org> On Behalf Of > Janos Follath via mbed-tls > Sent: 09 April 2020 12:18 > To: mbed-tls(a)lists.trustedfirmware.org > Subject: Re: [mbed-tls] 3.0 plans: remove memory_buffer_alloc.c from the code > base > > Hi, > > Based on what I read on this thread it seems an accepted point of view that > the toolchain provided C standard library implementations are less trusted > than the toolchains themselves. Can somebody please help me understand the > reasoning behind this distinction? > > Regards, > Janos > > On 09/04/2020, 12:07, "Dan Handley via mbed-tls" <mbed- > tls(a)lists.trustedfirmware.org> wrote: > > Hi > > There has already been some discussion about a shared C standard library > implementation, at least for TF-A and TF-M. So far there's been general > agreement that this is a good idea but no actual commitment from anyone to > make this happen, since each project is reasonably happy with what they've > got. > > Regarding MBEDTLS_MEMORY_BUFFER_ALLOC_C, TF-A at least enables this so > removing this from the codebase would be an issue there. Memory allocators > are probably not the core expertise of other Trusted Firmware projects either > but it needs to be if they're going to use them! > > I propose that we move this allocator into a new shared > TrustedFirmware.org standard C library project and work with the other > projects to ensure it has the correct initial maintainers. This will probably > have to be driven by the maintainers of whichever project is most motivated > to make this happen. It sounds like that could be Mbed TLS and this will need > to be done before any separation of the PSA Crypto implementation. In the > short term, as we move C stdlib functionality out of the other projects and > into this new project, we will need to support multiple implementations of > some functions. Eventually we should move towards a common implementation, > and I agree we should look at what security-oriented implementations are > already available. > > I also agree it would make sense for Mbed TLS to not use the toolchain- > provided stdlib implementation by default, but only once it uses a default > implementation it trusts. > > Regards > > Dan. > > > -----Original Message----- > > From: mbed-tls <mbed-tls-bounces(a)lists.trustedfirmware.org> On Behalf > Of > > Ronald Cron via mbed-tls > > Sent: 09 April 2020 08:47 > > To: mbed-tls(a)lists.trustedfirmware.org > > Subject: Re: [mbed-tls] 3.0 plans: remove memory_buffer_alloc.c from > the code > > base > > > > Hi, I think this is related to the more general need for an > implementation of > > the C standard library for trusted firmware projects. As far as I know > TF-A > > and TF-M don't use the standard library provided by compilation > toolchains. > > The rationale is to have complete control over the trusted firmware > code. > > Currently they both have their own partial implementation of the parts > of the > > C standard library they need. > > > > This memory_buffer_alloc.c module in question here is another partial > > implementation of the C standard library. Currently TF-A and TF-M don't > > use/provide dynamic memory allocations but PSA-FF explicitly mentions > that an > > SPM implementation may support dynamic memory allocation. Thus it is > possible > > that TF-M at some point consider providing dynamic memory allocation > support. > > > > All of this to say that a possible way forward may be to remove > > memory_buffer_alloc.c from the code base when there is a C standard > library > > implementation common to trustedfirmware.org projects (is there already > a > > security oriented open source implementation out there ?). > > > > In Mbed TLS, it would also make sense to me to, by default, not use C > > standard libraries provided by compilation toolchains > > (MBEDTLS_PLATFORM_NO_STD_FUNCTIONS defined by default). > > > > Thanks, Ronald. > > > > > > -----Original Message----- > > From: mbed-tls <mbed-tls-bounces(a)lists.trustedfirmware.org> On Behalf > Of > > Manuel Pegourie-Gonnard via mbed-tls > > Sent: 08 April 2020 12:42 > > To: mbed-tls(a)lists.trustedfirmware.org > > Cc: nd <nd(a)arm.com> > > Subject: [mbed-tls] 3.0 plans: remove memory_buffer_alloc.c from the > code > > base > > > > Hi all, > > > > In this new installment of "let's discuss ideas for Mbed TLS 3.0" [1]: > > should we remove memory_buffer_alloc.c from the code base? > > > > [1]: https://developer.trustedfirmware.org/w/mbed-tls/tech-plans-3.0/ > > > > Currently the crypto library includes a module called > memory_buffer_alloc.c, > > disabled in the default build (config.h option > MBEDTLS_MEMORY_BUFFER_ALLOC_C), > > which provides implementations of calloc() and free() based on a user- > > provided buffer (which could be static or on the stack), suitable for > use in > > the rest of the crypto, X.509 and TLS libraries as replacements to the > > standard functions. > > > > In addition to providing replacement calloc() and free(), the module > also > > offers some facilities for measurement and debugging. > > > > We're considering dropping this module and removing it from the code > base > > entirely for the following reasons: > > > > - Memory allocators are not our core area of expertise. > > > > - This allocator is pretty basic and has a large allocation overhead. > For > > example for ECC computations, the overhead can be as large as the > actual > > memory used. > > > > - Using this allocator also tends to slow things down, so we don't run > many > > tests with it enabled. > > > > - In the future when we split between PSA Crypto on one side and Mbed > TLS and > > X.509 on the other, it's unclear on which side this allocator should > fall. > > Which can be taken as a sign that it doesn't really belong here. > > > > On the other hand, we're hesitating for the following reasons: > > > > - We know from bug reports and questions that some people are using it. > > > > - Unlike other modules we'd like to drop, there isn't a strong security > > incentive to dropping this allocator, it's merely a matter of how we > spend > > our maintenance resources. > > > > What do you think? Should we keep maintaining this allocator as part of > Mbed > > TLS? Should we drop it and focus on our core instead? If you're using > this > > allocator, why did you pick it over other alternatives? > > > > Regards, > > Manuel. > > -- > > mbed-tls mailing list > > mbed-tls(a)lists.trustedfirmware.org > > https://lists.trustedfirmware.org/mailman/listinfo/mbed-tls > > IMPORTANT NOTICE: The contents of this email and any attachments are > > confidential and may also be privileged. If you are not the intended > > recipient, please notify the sender immediately and do not disclose the > > contents to any other person, use it for any purpose, or store or copy > the > > information in any medium. Thank you. > > -- > > mbed-tls mailing list > > mbed-tls(a)lists.trustedfirmware.org > > https://lists.trustedfirmware.org/mailman/listinfo/mbed-tls > IMPORTANT NOTICE: The contents of this email and any attachments are > confidential and may also be privileged. If you are not the intended > recipient, please notify the sender immediately and do not disclose the > contents to any other person, use it for any purpose, or store or copy the > information in any medium. Thank you. > -- > mbed-tls mailing list > mbed-tls(a)lists.trustedfirmware.org > https://lists.trustedfirmware.org/mailman/listinfo/mbed-tls > > > IMPORTANT NOTICE: The contents of this email and any attachments are > confidential and may also be privileged. If you are not the intended > recipient, please notify the sender immediately and do not disclose the > contents to any other person, use it for any purpose, or store or copy the > information in any medium. Thank you. > -- > mbed-tls mailing list > mbed-tls(a)lists.trustedfirmware.org > https://lists.trustedfirmware.org/mailman/listinfo/mbed-tls -- mbed-tls mailing list mbed-tls(a)lists.trustedfirmware.org https://lists.trustedfirmware.org/mailman/listinfo/mbed-tls IMPORTANT NOTICE: The contents of this email and any attachments are confidential and may also be privileged. If you are not the intended recipient, please notify the sender immediately and do not disclose the contents to any other person, use it for any purpose, or store or copy the information in any medium. Thank you.

5 years, 2 months

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Some thoughts towards mbed TLS 3.0

by Torsten Schuetze

Hi all, this will be a long mail. Sorry for that. In the past weeks I've been using mbedTLS 2.16.5 for implementing crypto on an ARM Cortex M4 (STM32F479). This was my first experience with mbedTLS, but I have some (almost 20 years) experience with applied and high-assurance crypto. So maybe the following thoughts fit into the discussion of plans for version 3.0 of Mbed TLS. In the end, I achieved everything that was required for my project with mbedTLS, but some things surprised me or it took a while to find out. I'll enumerate the following points for easier reference. Nothing of the following is meant to embarrass anyone, just my personal thoughts. 1. I really missed an Initialize, Update, Finalize (IUF) interface for CCM. For GCM, we have mbedtls_gcm_init(), mbedtls_gcm_setkey(), mbedtls_gcm_starts(), mbedtls_gcm_update() iterated, mbedtls_gcm_finish(), mbedtls_gcm_free() or the comfort functions mbedtls_gcm_crypt_and_tag() and mbedtls_gcm_auth_decrypt(). For CCM, only mbedtls_ccm_init(), mbedtls_ccm_setkey(), mbedtls_ccm_encrypt_and_tag() or mbedtls_ccm_auth_decrypt() and mbedtls_ccm_free(). With this interface it was only possible to encrypt and tag 128 kByte on my target system, while with GCM I could encrypt much larger files. see Github issue #662 and my comment there 2. The next step, of course, is to integrate this into the higher mbedtls_cipher layer. Regarding higher, abstract layers: I often didn't understand which interface I was supposed to use. In general, I like to use the lowest available interface, for example, #include "mbedtls/sha512.h" when I want to use sha512. However, if I need HMAC-SHA-512 or HKDF-HMAC-SHA-512 then I have to use the interface in md.h. For hash functions this is fine. Almost all hash functions are supported via md.h. (I missed SHA-512/256 which is sometimes preferable to SHA-256 on 64bit systems). But with cipher.h, I can only access Chacha20Poly1305 and AES-GCM, not AES-CCM. 3. For certification and evaluation purposes I need some test vectors for each crypto function on target. While I know about the comprehensive self-test program I'm now talking about built-in functions like mbedtls_sha512_self_test(), etc to be enabled with #define MBEDTLS_SELF_TEST. These self-tests are very different in coverage. For SHA-384 and SHA-512 they are fine, for HMAC-SHA-384 and HMAC-SHA-512 I couldn't find any as well as for HKDF-HMAC-SHA-256 (in RFC 5869) or HKDF-HMAC-SHA-384/512 (official test vectors difficult to find). AES-CTR and AES-XTS are only tested with key length 128 bit, not with 256 bit. AES-CCM is not tested with 256 bit and even for 128 bit, the test vector from the standard NIST SP 800-38C with long additional data is not used. The builtin self-test for GCM is the best I've seen with mbedtls: all three key lengths are tested as well as the IUF-interface and the comfort function. Bravo! 4. That I couldn't configure AES-256 only, i.e. without AES-128 and AES-192, was to be expected (and the code overhead is not that much). But in modern modes of operations nobody needs AES decryption, only the forward direction. Sometimes modern publications as Schwabe/Stoffelen "All the AES you need on Cortex-M3 and M4" provide only the forward direction. So, it would be fine if one could configure an AES (ECB) encryption only without decryption. Of course, this is only possible if we don't use CBC mode, etc. This wouldn't only save the AES decryption code but also the rather large T-tables for decryption. 5. Regarding AES or better the AES context-type definition typedef struct mbedtls_aes_context { int nr; /*!< The number of rounds. */ uint32_t *rk; /*!< AES round keys. */ uint32_t buf[68]; /*!< Unaligned data buffer. This buffer can hold 32 extra Bytes, which can be used for one of the following purposes: <ul><li>Alignment if VIA padlock is used.</li> <li>Simplifying key expansion in the 256-bit case by generating an extra round key. </li></ul> */ } mbedtls_aes_context; I really don't understand why we need additional 2176 bit in EVERY AES context. I would understand 128 bit (one block size) or even 512 bit (for example for CTR optimization which is not used!). But 2176 bit in every AES context? The VIA padlock is not very common, I suppose. But even if it were, this doesn't justify such memory overhead. How wasteful this is, one can see in the next type definition /** * \brief The AES XTS context-type definition. */ typedef struct mbedtls_aes_xts_context { mbedtls_aes_context crypt; /*!< The AES context to use for AES block encryption or decryption. */ mbedtls_aes_context tweak; /*!< The AES context used for tweak computation. */ } mbedtls_aes_xts_context; The tweak context is for the encryption of exactly 128 bit, not more. 6. In general, the contexts of mbedTLS are rather full of implementation specific details. Most extreme is mbedtls_ecp_group in ecp.h. Wouldn't it be clearer if one separates the standard things (domain parameters in this case) from implementation specific details? 7. While at Elliptic Curve Cryptography: I assume that some of you know that projectives coordinates as outer interface to ECC are dangerous, see David Naccache, Nigel P. Smart, Jacques Stern: Projective Coordinates Leak, Eurocrypt 2004, pp. 257–267. Therefore, the usual interface in ECC standards are either affine points or compressed affine points (Okay, with the modern curves Curve25519 and Curve 448 it's X only.). Now with /** * \brief The ECP point structure, in Jacobian coordinates. * * \note All functions expect and return points satisfying * the following condition: <code>Z == 0</code> or * <code>Z == 1</code>. Other values of \p Z are * used only by internal functions. * The point is zero, or "at infinity", if <code>Z == 0</code>. * Otherwise, \p X and \p Y are its standard (affine) * coordinates. */ typedef struct mbedtls_ecp_point { mbedtls_mpi X; /*!< The X coordinate of the ECP point. */ mbedtls_mpi Y; /*!< The Y coordinate of the ECP point. */ mbedtls_mpi Z; /*!< The Z coordinate of the ECP point. */ } mbedtls_ecp_point; you have Jacobian coordinates, i.e. projective coordinates, as outer interface. In the comment, its is noted that only the affine part is used, but can this be assured? In all circumstances? 8. In my personal opinion the definition /** * \brief The ECP key-pair structure. * * A generic key-pair that may be used for ECDSA and fixed ECDH, for example. * * \note Members are deliberately in the same order as in the * ::mbedtls_ecdsa_context structure. */ typedef struct mbedtls_ecp_keypair { mbedtls_ecp_group grp; /*!< Elliptic curve and base point */ mbedtls_mpi d; /*!< our secret value */ mbedtls_ecp_point Q; /*!< our public value */ } mbedtls_ecp_keypair; is dangerous. Why not differentiate between private and public key and domain parameters? How often does it happen by accident with this structure that you give the private key (unneeded and dangerous) together with the public key to ECDSA signature verification? Obviously this was known (and perhaps it happened) to the authors of programs\ecdsa.c with the following comment /* * Transfer public information to verifying context * * We could use the same context for verification and signatures, but we * chose to use a new one in order to make it clear that the verifying * context only needs the public key (Q), and not the private key (d). */ What is sometimes useful, is to have the public key at hand when you have performed a private key operation (as countermeasure against fault attacks, verify after signing). But for ECC the verification procedure if often too expensive (in contrast to cheap RSA verify). 9. Regarding ECC examples: I found it very difficult that there isn't a single example with known test vectors as in the relevant crypto standards, i.e. FIPS 186-4 and ANSI X9.62-2005, with raw public keys. What I mean are (defined) curves, public key value Q=(Qx,Qy) and known signature values r and s. In the example ecdsa.c you generate your own key pair and read/write the signature in serialized form. In the example programs/pkey/pk_sign.c and pk_verify.c you use a higher interface pk.h and keys in PEM format. So, it took me a while for a program to verify (all) known answer tests in the standards (old standards as ANSI X9.62 1998 have more detailed known answer tests). One needs this interface with raw public keys for example for CAVP tests, see The FIPS 186-4 Elliptic Curve Digital Signature Algorithm Validation System (ECDSA2VS). 10. While debugging mbedtls_ecdsa_verify() in my example program, I found out, that the ECDSA, ECC and MPI operations are very, let's say, nested. So, IMHO there is a lot of function call overhead and special cases. It would be interesting to see what's the performance impact of a clean, straight-forward mbedtls_ecdsa_verify without restartable code, etc. to the current one. 11. In the moment, there is no single known answer tests for ECDSA (which could be activated with #define MBEDTLS_SELF_TEST). I wouldn't say that you need an example for every curve and hash combination, as it is done in ECDSA2VS CAVP, but one example for one of the NIST curves and one for Curve25519 and - if I have a wish free - one for Brainpool would be fine. And this would solve #9 above. 12. Just a minor issue: I only needed ECDSA signature verification, therefore I only included MBEDTLS_ASN1_PARSE_C. But it is not possible to compile without MBEDTLS_ASN1_WRITE_C needed for ECDSA signature generation. 13. Feature request: Since it was irrelevant for my task (only verification, no generation) I didn't have a detailed look a your ECC side-channel countermeasures. But obviously you use the same protected code for scalar multiplication in verify and sign, right? Wouldn't it be possible to use Shamir's trick in verification with fast unprotected multi-scalar multiplication. In the moment, mbedtls_ecdsa_verify is a factor 4-5 slower than mbedtls_ecdsa_sign, while OpenSSLs verify is faster than sign. 14. Design question: In the moment, both GCM and CCM use their own implementation of CTR encryption which is very simple. But then we have mbedtls_aes_crypt_ctr() in aes.h which is very simple, too. Let's assume at one day we have a performance optimized CTR encryption (for example from Schwabe & Stoffelen) with all fancy stuff like counter-mode caching etc. Then this would have to be replaced at three places at minimum. While isn't the code at this point more modularized? Is this a dedicated design decision? Why do I find at so many places for( i = 0; i < 16; i++ ) y[i] ^= b[i]; instead of a fast 128-bit XOR macro with 32bit aligned data? So, that's it for the moment. I hope I could give some hints for the further development of mbedTLS. Feel free to discuss any of the above points. It's clear to me that we cannot have both: clear and simple to understand code and performance records. Ciao, Torsten

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Security Advisory and Release of Mbed TLS 2.16.6 and 2.7.15

by Janos Follath

Hi, An Mbed TLS Security Advisory has been issued to accompany the release of Mbed TLS versions 2.16.6 and 2.7.15, which 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://tls.mbed.org/techupdates/releases/mbedtls-2.16.6-and-2.7.15-released> and in the 2020-04 security advisory<https://tls.mbed.org/tech-updates/security-advisories/mbedtls-security-advi…>. We recommend all users to consider whether they are impacted, and to upgrade appropriately. -- Janos Follath Mbed TLS Developer IMPORTANT NOTICE: The contents of this email and any attachments are confidential and may also be privileged. If you are not the intended recipient, please notify the sender immediately and do not disclose the contents to any other person, use it for any purpose, or store or copy the information in any medium. Thank you.

5 years, 2 months

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