- mbed-tls - lists.trustedfirmware.org

by Abhilash Iyer

Hello, I am trying to do the ECDH shared secret computation using the mbedTLS library. I am referring to multiple examples such as ecdh_curve25519.c<https://github.com/ARMmbed/mbedtls/blob/development/programs/pkey/ecdh_curv…> and ecdh_main.c<https://github.com/SiliconLabs/peripheral_examples/blob/master/series2/se/s…>. In my case, in my application firmware, I already have a device _priv key and I receive a server_public key; both generated using a curve ECP_DP_SECP256R1 in the bootloader itself. So in the application firmware, I would like to do generate a shared secret from here on and preserve it for future use. The following is the steps that I do: 1. Create a new client context, entropy context, ctr_drbg context variables. 2. use mbedtls_"respective"_init() to initalize all the three variables 3. Seed a random number using mbedtls_ctr_drbg_seed() function. 4. load the P256 elliptic curve in client context using mbedtls_ecp_group_load() 5. Then use mbedtls_mpi_lset() to set Qp.Z =1 6. Then read the server pub key using mbedtls_mpi_read_binary(&ctx_cli.Qp.X, server_pub, 65); 7. Now the question is: Should I initialize the ctx_cli with my already generated device_priv key using mbedtls_mpi_read_binary(&ctx_cli.d, device_priv_key, 50) ? 8. Then I use mbedtls_ecdh_compute_shared(&ctx_cli.grp, &ctx_cli.z, &ctx_cli.Qp, &ctx_cli.d, mbedtls_ctr_drbg_random, &ctr_drbg); to compute the shared secret in z. Questions: 1. Do I need to generate a keypair for client context using mbedtls_ecdh_gen_public(&ctx_cli.grp, &ctx_cli.d, &ctx_cli.Q, mbedtls_ctr_drbg_random, &ctrDrbg)? And then set pvtkey as device priv key and pub key as service pub key? 2. I see that ctx_cli.Q has two components, Q.x and Q.y. How do I extract these two values from a public key? Do I need to separately initialize them? Please let me know if the flow is correct. In all the examples, they generate a key pair and just update the public key part (Qp.X) of the key. They do not touch the private key part (d) of the key. Please confirm if I can upload my private key directly in my case. Also if my platform is a little endian, is there a recommended step before using mbedtls_mpi_read_binary_le functions? Thanks so much for your help in advance! Thanks, Abhilash From: Abhilash Iyer Sent: Monday, April 27, 2020 11:25 AM To: mbed-tls(a)lists.trustedfirmware.org Subject: Hello, I am trying to do the ECDH shared secret computation using the mbedTLS library. I am referring to multiple examples such as ecdh_curve25519.c<https://github.com/ARMmbed/mbedtls/blob/development/programs/pkey/ecdh_curv…> and ecdh_main.c<https://github.com/SiliconLabs/peripheral_examples/blob/master/series2/se/s…>. In my case, in my application firmware, I already have a device _priv key and I receive a server_public key; both generated using a curve ECP_DP_SECP256R1 in the bootloader itself. So in the application firmware, I would like to do generate a shared secret from here on and preserve it for future use. The following is the steps that I do: 1. Create a new client context, entropy context, ctr_drbg context variables. 2. use mbedtls_"respective"_init() to initalize all the three variables 3. Seed a random number using mbedtls_ctr_drbg_seed() function. 4. load the P256 elliptic curve in client context using mbedtls_ecp_group_load() 5. Then use mbedtls_mpi_lset() to set Qp.Z =1 6. Then read the server pub key using mbedtls_mpi_read_binary(&ctx_cli.Qp.X, server_pub, 65); 7. Now the question is: Should I initialize the ctx_cli with my already generated device_priv key using mbedtls_mpi_read_binary(&ctx_cli.d, device_priv_key, 50) ? 8. Then I use mbedtls_ecdh_compute_shared(&ctx_cli.grp, &ctx_cli.z, &ctx_cli.Qp, &ctx_cli.d, mbedtls_ctr_drbg_random, &ctr_drbg); to compute the shared secret in z. Questions: 1. Do I need to generate a keypair for client context using mbedtls_ecdh_gen_public(&ctx_cli.grp, &ctx_cli.d, &ctx_cli.Q, mbedtls_ctr_drbg_random, &ctrDrbg)? And then set pvtkey as device priv key and pub key as service pub key? 2. I see that ctx_cli.Q has two components, Q.x and Q.y. How do I extract these two values from a public key? Do I need to separately initialize them? Please let me know if the flow is correct. In all the examples, they generate a key pair and just update the public key part (Qp.X) of the key. They do not touch the private key part (d) of the key. Please confirm if I can upload my private key directly in my case. Also if my platform is a little endian, is there a recommended step before using mbedtls_mpi_read_binary_le functions? Thanks so much for your help in advance! Thanks, Abhilash Sent from Mail<https://go.microsoft.com/fwlink/?LinkId=550986> for Windows 10

6 years, 1 month

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Re: [mbed-tls] Random Number Generator module in mbed TLS

by ROSHINI DEVI

Perfect! Thanks everyone for your assistance. On Tue, Apr 28, 2020 at 1:48 PM Janos Follath via mbed-tls < mbed-tls(a)lists.trustedfirmware.org> wrote: > Hi, > > > > Hanno described perfectly how it works and I just would like to add a > single remark. You mentioned that some of your platforms don’t have a > hardware entropy source. In cases like that, depending on your threat model > you might need to use the MBEDTLS_ENTROPY_NV_SEED feature to achieve > security. > > > > (This uses a stored secret value as a seed and on embedded systems without > a hardware entropy source it is more secure against a remote adversary than > trying to collect the entropy from the environment. On systems like that > NV_SEED can have an edge against physical attackers – compared to > attempting to collect entropy from the environment – if the seed is stored > in secure storage/internal flash.) > > > > Regards, > > Janos > > > > *From: *mbed-tls <mbed-tls-bounces(a)lists.trustedfirmware.org> on behalf > of Hanno Becker via mbed-tls <mbed-tls(a)lists.trustedfirmware.org> > *Reply to: *Hanno Becker <Hanno.Becker(a)arm.com> > *Date: *Tuesday, 28 April 2020 at 07:55 > *To: *"mbed-tls(a)lists.trustedfirmware.org" < > mbed-tls(a)lists.trustedfirmware.org>, ROSHINI DEVI <roshinilachi(a)gmail.com> > *Subject: *Re: [mbed-tls] Random Number Generator module in mbed TLS > > > > Hi, > > > > Mbed TLS establishes variable-length access to random data in a three step > fashion: > > > > 1) At the bottommost layer, there is a variable number of *entropy > sources *external to the library. > > Such sources are supposed to provide some true randomness, though the > exact amount of > > entropy they contain isn't yet specified (at least to my knowledge). > > > > 2) Mbed TLS' entropy module mixes those entropy sources into a single > source of randomness. > > In contrast to the entropy sources themselves, the idea here is that, > ideally, the data obtained > > from the entropy module has full entropy. This is achieved by (a) > accumulating random data > > from available entropy sources and depending on the amount of entropy each > of them offers, > > and (b) 'mixing' them by a application of hash functions. > > > > 3) Based on true randomness, Mbed TLS' provides two implementations of > pseudo random > > number generators: CTR-DRBG and HMAC-DRBG. Those build on top of an > entropy context > > and expand the underlying randomness as standardized in NIST SP 800-90. > > > > Applications should use the PRNGs from step 3) as their actual source of > randomness, > > and not directly hook into the underlying TRNGs. > > > > Take a look at the example programs such as `ssl_client2` or `ssl_server2` > to see how this > > works practically. Also see > https://tls.mbed.org/kb/how-to/add-a-random-generator. > > > > Now specifically to your question: You should register your STM32 hardware > entropy > > as an entropy source via `mbedtls_entropy_add_source()` but not (need) to > change > > anything else in your code. In particular, steps 2) and 3) above are > entirely independent > > of the exact source of true randomness. > > > > Hope this helps, > > > > Hanno > > > ------------------------------ > > *From:* mbed-tls <mbed-tls-bounces(a)lists.trustedfirmware.org> on behalf > of ROSHINI DEVI via mbed-tls <mbed-tls(a)lists.trustedfirmware.org> > *Sent:* Tuesday, April 28, 2020 6:06 AM > *To:* mbed-tls(a)lists.trustedfirmware.org < > mbed-tls(a)lists.trustedfirmware.org> > *Subject:* Re: [mbed-tls] Random Number Generator module in mbed TLS > > > > Hello, > > > > Can anyone confirm this? Its urgent. > > > > Thanks > > > > On Fri, Apr 17, 2020 at 4:50 PM ROSHINI DEVI <roshinilachi(a)gmail.com> > wrote: > > Hello, > > > > Is there any random number library available in mbedTLS? > > Right now, I am using hardware entropy in STM32 boards. > > If hardware platform changes and if there is no hardware entropy present, > then again we need to redefine the API. > > > > Thanks > > 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 >

6 years, 1 month

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Re: [mbed-tls] Random Number Generator module in mbed TLS

by Janos Follath

Hi, Hanno described perfectly how it works and I just would like to add a single remark. You mentioned that some of your platforms don’t have a hardware entropy source. In cases like that, depending on your threat model you might need to use the MBEDTLS_ENTROPY_NV_SEED feature to achieve security. (This uses a stored secret value as a seed and on embedded systems without a hardware entropy source it is more secure against a remote adversary than trying to collect the entropy from the environment. On systems like that NV_SEED can have an edge against physical attackers – compared to attempting to collect entropy from the environment – if the seed is stored in secure storage/internal flash.) Regards, Janos From: mbed-tls <mbed-tls-bounces(a)lists.trustedfirmware.org> on behalf of Hanno Becker via mbed-tls <mbed-tls(a)lists.trustedfirmware.org> Reply to: Hanno Becker <Hanno.Becker(a)arm.com> Date: Tuesday, 28 April 2020 at 07:55 To: "mbed-tls(a)lists.trustedfirmware.org" <mbed-tls(a)lists.trustedfirmware.org>, ROSHINI DEVI <roshinilachi(a)gmail.com> Subject: Re: [mbed-tls] Random Number Generator module in mbed TLS Hi, Mbed TLS establishes variable-length access to random data in a three step fashion: 1) At the bottommost layer, there is a variable number of entropy sources external to the library. Such sources are supposed to provide some true randomness, though the exact amount of entropy they contain isn't yet specified (at least to my knowledge). 2) Mbed TLS' entropy module mixes those entropy sources into a single source of randomness. In contrast to the entropy sources themselves, the idea here is that, ideally, the data obtained from the entropy module has full entropy. This is achieved by (a) accumulating random data from available entropy sources and depending on the amount of entropy each of them offers, and (b) 'mixing' them by a application of hash functions. 3) Based on true randomness, Mbed TLS' provides two implementations of pseudo random number generators: CTR-DRBG and HMAC-DRBG. Those build on top of an entropy context and expand the underlying randomness as standardized in NIST SP 800-90. Applications should use the PRNGs from step 3) as their actual source of randomness, and not directly hook into the underlying TRNGs. Take a look at the example programs such as `ssl_client2` or `ssl_server2` to see how this works practically. Also see https://tls.mbed.org/kb/how-to/add-a-random-generator. Now specifically to your question: You should register your STM32 hardware entropy as an entropy source via `mbedtls_entropy_add_source()` but not (need) to change anything else in your code. In particular, steps 2) and 3) above are entirely independent of the exact source of true randomness. Hope this helps, Hanno ________________________________ From: mbed-tls <mbed-tls-bounces(a)lists.trustedfirmware.org> on behalf of ROSHINI DEVI via mbed-tls <mbed-tls(a)lists.trustedfirmware.org> Sent: Tuesday, April 28, 2020 6:06 AM To: mbed-tls(a)lists.trustedfirmware.org <mbed-tls(a)lists.trustedfirmware.org> Subject: Re: [mbed-tls] Random Number Generator module in mbed TLS Hello, Can anyone confirm this? Its urgent. Thanks On Fri, Apr 17, 2020 at 4:50 PM ROSHINI DEVI <roshinilachi(a)gmail.com<mailto:roshinilachi@gmail.com>> wrote: Hello, Is there any random number library available in mbedTLS? Right now, I am using hardware entropy in STM32 boards. If hardware platform changes and if there is no hardware entropy present, then again we need to redefine the API. Thanks 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.

6 years, 1 month

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Re: [mbed-tls] Random Number Generator module in mbed TLS

by Hanno Becker

Hi, Mbed TLS establishes variable-length access to random data in a three step fashion: 1) At the bottommost layer, there is a variable number of entropy sources external to the library. Such sources are supposed to provide some true randomness, though the exact amount of entropy they contain isn't yet specified (at least to my knowledge). 2) Mbed TLS' entropy module mixes those entropy sources into a single source of randomness. In contrast to the entropy sources themselves, the idea here is that, ideally, the data obtained from the entropy module has full entropy. This is achieved by (a) accumulating random data from available entropy sources and depending on the amount of entropy each of them offers, and (b) 'mixing' them by a application of hash functions. 3) Based on true randomness, Mbed TLS' provides two implementations of pseudo random number generators: CTR-DRBG and HMAC-DRBG. Those build on top of an entropy context and expand the underlying randomness as standardized in NIST SP 800-90. Applications should use the PRNGs from step 3) as their actual source of randomness, and not directly hook into the underlying TRNGs. Take a look at the example programs such as `ssl_client2` or `ssl_server2` to see how this works practically. Also see https://tls.mbed.org/kb/how-to/add-a-random-generator. Now specifically to your question: You should register your STM32 hardware entropy as an entropy source via `mbedtls_entropy_add_source()` but not (need) to change anything else in your code. In particular, steps 2) and 3) above are entirely independent of the exact source of true randomness. Hope this helps, Hanno ________________________________ From: mbed-tls <mbed-tls-bounces(a)lists.trustedfirmware.org> on behalf of ROSHINI DEVI via mbed-tls <mbed-tls(a)lists.trustedfirmware.org> Sent: Tuesday, April 28, 2020 6:06 AM To: mbed-tls(a)lists.trustedfirmware.org <mbed-tls(a)lists.trustedfirmware.org> Subject: Re: [mbed-tls] Random Number Generator module in mbed TLS Hello, Can anyone confirm this? Its urgent. Thanks On Fri, Apr 17, 2020 at 4:50 PM ROSHINI DEVI <roshinilachi(a)gmail.com<mailto:roshinilachi@gmail.com>> wrote: Hello, Is there any random number library available in mbedTLS? Right now, I am using hardware entropy in STM32 boards. If hardware platform changes and if there is no hardware entropy present, then again we need to redefine the API. Thanks 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.

6 years, 1 month

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Random Number Generator module in mbed TLS

by ROSHINI DEVI

Hello, Is there any random number library available in mbedTLS? Right now, I am using hardware entropy in STM32 boards. If hardware platform changes and if there is no hardware entropy present, then again we need to redefine the API. Thanks

6 years, 1 month

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Edwards curve support (#3245): fixing mbedtls_ecp_get_type

by Aurelien Jarno

Hi all, I have submitted PR#3245 in order to add Edwards curves support to Mbed TLS, with the eventual goal to add support for the EdDSA algorithm. There are still a few things to fix that require discussion. Let's start the discussion with the first one. Adding a new curve type requires to add a new entry to the mbedtls_ecp_curve_type enum. The curve type used by a group is returned by the mbedtls_ecp_get_type function. It currently uses the coordinates type of the base point to determine the curve type. Montgomery curves are lacking the y coordinate, and the Short Weierstrass curves use the three x, y and z coordinates. The Edwards arithmetic implementation in this PR uses the projective coordinates. As such it also uses the x, y and z coordinates and this gives no way to differentiate a Short Weierstrass from an Edwards curve. I have currently implemented that by checking if the curves are the Ed25519 or Ed448 ones using the group id [1]. I am not sure it's very clean and it won't scale if more curves are added later. Another alternative would be to add another entry to mbedtls_ecp_group to hold the curve type. What do you think is the best option? Any other idea? Thanks, Aurelien [1] https://github.com/ARMmbed/mbedtls/pull/3245/commits/aa20cf122a1a54cfa23624… -- Aurelien Jarno GPG: 4096R/1DDD8C9B aurelien(a)aurel32.net http://www.aurel32.net

6 years, 1 month

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Re: [mbed-tls] Development environment: minimum tool versions

by Steffan Karger

Hi, I maintain OpenVPN-NL (https://openvpn.fox-it.com), which uses mbedtls as it's crypto library. On 24-04-2020 00:25, Gilles Peskine via mbed-tls wrote: > 1. Is there any interest in the community for making sure that the build > keeps (or starts) working on RHEL 6? Yes, we support RHEL6 until it's retirement (30 November 2020). > 2. Is there any interest in the community for making sure that the build > keeps working on Ubuntu 16.04? Yes, we support all Ubuntu LTS versions until their standard support ends (April 2021 for 16.04). > 3. Are there any other "old" platforms that we should consider? All Debian and SLES versions that are still in regular maintance (ie, not including any "extended security maintenance" support). It would be nice if it's at least possible to build mbedtls on/for these platforms until they go out of regular support. Preferably with their default packages compilers. SLES/RHEL are the most demanding, with their 10 year support cycle. Thanks, -Steffan

6 years, 1 month

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Re: [mbed-tls] RSA key generation issue

by Gilles Peskine

Hi Nazar, On 24/04/2020 10:22, Nazar Chornenkyy via mbed-tls wrote: > > On the PSoC6 device we are using mbedtls_rsa_gen_key function with a > good hardware TRNG passed FIPS 140-2 verification. > > This function verifies generated random pair and requests new pair if > they don’t follow FIPS 186-4 criteria. > > The number of verification loops is between 1 and 6 in worst case. > > Is it expected behavior? > > The arithmetic of one loop takes a lots of time. > > How can we improve the random number to have always pass FIPS 186-4 in > a one loop? > I'm not sure what you're doing. Are you calling mbedtls_rsa_gen_key() multiple times and rejecting the key if it doesn't pass additional checks? Or are you just calling it once? As far as I know, mbedtls_rsa_gen_key() follows the procedure described in FIPS 186-4 (which is compatible with previous versions of FIPS 186), and no additional checks should be needed. If you're calling it once and observing that it tries multiple values of p and q before finding a suitable one, this is expected behavior. There's no way to "improve" the random numbers to make it faster: the probability that a pair of (probabilistic) primes can work together as an RSA key is less than 1. I don't know the math off the top of my head, but 1–6 tries seems reasonable. Key generation is the slowest of the RSA operations. If that's a problem in your application, consider using elliptic curve cryptography instead. ECC has very fast key generation, faster private key operations (signature, decryption) than RSA, and smaller keys. The main benefit of RSA is that public key operations (verification, encryption) are faster. -- 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.

6 years, 1 month

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Development environment: minimum tool versions

by Gilles Peskine

Hello, I'm starting this thread to get input from the community about what versions of compilers and other build tools Mbed TLS should support. We of course strive to remain compatible with the latest versions, so this discussion is about support for older versions. We currently don't really have an official version range for the build dependencies of Mbed TLS: * C compilers (GCC, Clang, Arm Compiler, IAR, Visual Studio) * Build tools (GNU make, CMake) * Scripting tools (shell, Perl, Python) In practice, for the past three years or so, most of our continuous integration has been running on Ubuntu 16.04, so we mostly test with GCC 5.4.0, Clang 3.8, GNU make 4.1, CMake 3.5.1 and Python 3.5. (For shell and Perl, even pretty ancient version should work.) For Arm Compiler (armcc/armclang) and IAR, we use the same version as Mbed OS. On Windows, we currently test Visual Studio 2013, 2015 and 2017, as well as a version of Mingw that's changed more quickly than most of the rest of our CI. We also run some tests on FreeBSD (a bit more recent that the Ubuntu machines). The top-level CMakeLists.txt has conditionals that detect much older versions of CMake, GCC and Clang, but we haven't tested those in ages and we don't really know if, for example, the library still builds with CMake 2.8 and GCC 4.2. As part of the move of the project from Arm to Trusted Firmware, we'll change our CI infrastructure, and this may or may not mean we end up testing with different versions. In https://github.com/ARMmbed/mbedtls/issues/2896 I looked at the software versions in some common "slow updating" operating systems: RHEL/Centos, Ubuntu LTS. 1. Is there any interest in the community for making sure that the build keeps (or starts) working on RHEL 6? 2. Is there any interest in the community for making sure that the build keeps working on Ubuntu 16.04? 3. Are there any other "old" platforms that we should consider? 4. Should we consider older compilers (maybe some platforms are stuck with older versions of GCC)? 5. On Windows, what's the oldest version of Visual Studio we should keep compatibility with? -- 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.

6 years, 1 month

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RSA key generation issue

by Nazar Chornenkyy

Hi I found this email on ARM MBED support forum. Could you help to resolve our issue? On the PSoC6 device we are using mbedtls_rsa_gen_key function with a good hardware TRNG passed FIPS 140-2 verification. This function verifies generated random pair and requests new pair if they don't follow FIPS 186-4 criteria. The number of verification loops is between 1 and 6 in worst case. Is it expected behavior? The arithmetic of one loop takes a lots of time. How can we improve the random number to have always pass FIPS 186-4 in a one loop? Thanks Nazar This message and any attachments may contain confidential information from Cypress or its subsidiaries. If it has been received in error, please advise the sender and immediately delete this message.

6 years, 1 month

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