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Where is the AES 128 GCM key expansion/generate round key performed?

by Mbed TLS

Hi, I'm using AES 128 GCM with TLS 1.2 and trying to understand the AES key expansion code for decrypting received SSL records. I'm not an expert on AES but as I understand it, we use the IV (4 byte salt + 8 byte explicit nonce in the received message), pad to 16 bytes, increment and use this as input to the AES key expansion for the first block of ciphertext. This produces a round key per AES round (10 rounds for AES 128). We then increment our IV as input to the key expansion and generate the rounding keys for the next block. I noticed aesni_setkey_enc_128 in aesni.c contains the Intel AES-NI instruction AESKEYGENASSIST which helps with key expansion. However, what's confusing me is when I add a breakpoint in GDB, this function is only called once, via mbedtls_ctr_drbg_seed in ctr_drbg.c. I thought we need to do the key expansion on every block, to generate the round keys? I kept looking at the code and I noticed mbedtls_aesni_crypt_ecb, which contains the Intel AES-NI instructions for performing decryption. This loads the round key via ctx->buf + ctx->rk_offset but I do not see any code updating this round key per block. Could someone please explain where the round keys are generated for each round, per block? Thanks,

2 years, 8 months

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Should TLS be blocking all FreeRTOS tasks which use LWIP, during its RSA/EC phase, regardless of priorities?

by Peter

Hi All, I have a couple of tasks which use LWIP and which get suspended for a few seconds during TLS RSA/EC crypto. One (a primitive http server) uses Netconn and the other (a serial to TCP data copy process) uses sockets. I also have a number of tasks which don't do any networking and which run as they should, throughout. Experimentation of what priority these need is difficult but it looks like it needs to be at/above the tasks which invoke TLS. If their priority is 0 then TLS hangs them up as well. After much experimentation with RTOS priorities, this is what I found, and I wonder if it is right: TCP/IP applications (whether using the LWIP Netconn API or the LWIP socket API) should run at a priority equal to or lower than that of LWIP itself which [in this project] is osPriorityHigh (40). TCP/IP applications can be run with a priority all the way down to tskIDLE_PRIORITY (0). The exception is if TLS is in use. TLS does not yield to the RTOS; you get a solid CPU time lump of ~3 secs (STM 32F417, hardware AES only). TLS starts in the priority of the task which invokes it, but subsequent TLS-driven TCP/IP operations run at the priority of LWIP. So when TLS is doing the session setup crypto, tasks of a priority lower than LWIP get suspended. If this gap is an issue, the priority of the relevant tasks should be equal to LWIP's. Furthermore, due to the structure of LWIP, the priority of a task using it should not be higher than LWIP (24) since it might cause blocking on socket (or netconn) writes. Does this make sense? It looks like LWIP blocks all netconn and socket ops when TLS is using it. Is that possible? I am running with #define LWIP_TCPIP_CORE_LOCKING 0 #define LWIP_ALLOW_MEM_FREE_FROM_OTHER_CONTEXT 1 #define SYS_LIGHTWEIGHT_PROT 1 as this was found to have much better granularity for task switching. With LWIP_TCPIP_CORE_LOCKING=1 you end up with a crude mutex across the entire API call, which is fine in a single RTOS task. Thank you in advance for any pointers. Peter

2 years, 8 months

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Generating self signed certificate

by Prithvi Pai

Hi Team, I have a requirement to generate self signed certificate programmatically. I have raw EDCSA key pairs generated via OP-TEE APIs. I m trying to generate self signed certificate. I tried the example as shown in programs/x509/cert_write.c. This doesn't work for me as I have raw key pairs where as this expects the key pairs to be in either pem/der format. I tried the following code but it throws error "0xffffdd00" when I call mbedtls_x509write_crt_der Code to set the raw key pairs: mbedtls_ecdh_context issuer_ctx; mbedtls_ecdh_init(&issuer_ctx); ret = mbedtls_ecdh_setup(&issuer_ctx, MBEDTLS_ECP_DP_SECP384R1); if (ret != 0) { goto exit; } res = TA_ECSetPublicKey(&issuer_ctx, public_keyX, public_key_Y, 48); if (res != TEE_SUCCESS) { goto exit; } res = TA_ECSetPrivateKey(&issuer_ctx, private_key, 48); if (res != TEE_SUCCESS) { goto exit; } Am I doing something wrong ? Please help It would be very helpful if some working example of generating certificate programmatically is shared for my reference Thanks, Prithvi

2 years, 8 months

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Can the same mbedtls_ssl_context be used simultaneously for send and receive from different tasks?

by pascal.haefliger＠schweizer-electronic.com

Hello, In our project we use mbedTLS together with freeRTOS. mbedTLS requires an mbedtls_ssl_context (let's say `ssl_context`) for the send (`mbedtls_ssl_write(...)`) and receive (`mbedtls_ssl_read(...)`) functions. In our project we have a freeRTOS task `A` to send data with mbedTLS and a freeRTOS task `B`to receive data with mbedTLS over the same session/interface. Both tasks use the same `ssl_context` instance. Potentially sending and receiving can happen at the same time. Is it safe to use the same `ssl_context` instance from both taks? Or should only one task access the `ssl_context`? At the moment we are using `mbedtls_ssl_read(...)` in blocking mode and hence the `ssl_context` cannot be protected against multiple access with a mutex because then the sending task cannot obtain the mutex as long as the receiving task is the blocked receiving state (holding the mutext). Thank you for your help. Best regards, Pascal

2 years, 8 months

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Intent to remove DES in Mbed TLS 4.0

by Gilles Peskine

Hello, We intend to remove DES (including Triple-DES) in the next major version of Mbed TLS, i.e. Mbed TLS 4.0. We do not yet have a release date, but at the moment it seems likely that there will be a new major version in 2024. As usual, the Mbed TLS 3.x series will keep the current support for DES, and we intend to maintain the last 3.x minor release as a long-term support branch for 3 years. Rationale: Most security standards deprecate DES if they do not forbid it already. Tooling is widely available to switch to AES or other cipher. In particular, NIST will forbid Triple-DES except to decrypt legacy data after 31 December 2023 (following SP 800-131A <https://nvlpubs.nist.gov/nistpubs/SpecialPublications/NIST.SP.800-131Ar2.pdf>). We would like to remove the last 64-bit block cipher from Mbed TLS to simplify some parts of the code and reduce the maintenance burden. If you wish for Mbed TLS to keep supporting DES longer, please let us know what your business case is, either by replying to this email or on the GitHub issue: https://github.com/Mbed-TLS/mbedtls/issues/7024 Best regards, -- Gilles Peskine Mbed TLS developer

2 years, 8 months

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Builtin keys and Opaque driver wrappers.

by Rehan Malak

Dear MbedTLS dev, I am writing an opaque driver (equivalent of PSA_CRYPTO_TEST_DRIVER_LOCATION/PSA_KEY_PERSISTENCE_READ_ONLY in the test suite) with the PSA API compiled with MBEDTLS_PSA_CRYPTO_BUILTIN_KEYS. But I am not sure if I have to use "psa_import_key" before "psa_driver_wrapper_sign_message" or if I have to "read/generate" the builtin key on the fly, at each psa_driver_wrapper_* operation ? Would it be possible to add this example in the test suite ? Or explain how builtin key + opaque driver is supposed to be used with, for example, "psa_driver_wrapper_sign_message" ? I put more details below. Thank you in advance, Best regards, Rehan ############################################################################# I would like to write an example doing : I) psa_sign_message (ECDSA SECP256R1 SHA-256) II) psa_export_public_key III) psa_verify_message (with the public key from II) I am following the examples provided by the test suite, especially : 1) sign_message transparent driver: calculate in driver ECDSA SECP256R1 SHA-256 using the API : - psa_import_key - psa_sign_message with the attributes : - key_type = PSA_KEY_TYPE_ECC_KEY_PAIR(PSA_ECC_FAMILY_SECP_R1) 2) PSA opaque driver builtin pubkey export: secp256r1 using the API : - psa_export_public_key with the attributes : - key_id = MBEDTLS_PSA_KEY_ID_BUILTIN_MIN + 1 - key_type = PSA_KEY_TYPE_ECC_KEY_PAIR(PSA_ECC_FAMILY_SECP_R1) and the driver code : - platform_builtin_keys.c : mbedtls_psa_platform_get_builtin_key() (PSA_KEY_PERSISTENCE_READ_ONLY, PSA_CRYPTO_TEST_DRIVER_LOCATION) - test_driver_key_management.c : mbedtls_test_opaque_export_public_key() 3) verify_message transparent driver: calculate in driver ECDSA SECP256R1 SHA-256 using the API : - psa_import_key - psa_verify_message with the attributes : - key_type = PSA_KEY_TYPE_ECC_KEY_PAIR(PSA_ECC_FAMILY_SECP_R1) It seems to me that II)=2) and 3) should be pretty similar to III) because I assume that neither transparent vs opaque, nor PSA_KEY_TYPE_ECC_KEY_PAIR vs PSA_KEY_TYPE_ECC_PUBLIC_KEY_BASE, is gonna change much here. But the signature I) is less clear... Has the built-in key feature been thought such that the read-only key is read each time we call a different PSA API function ? Long story short, an "opaque driver + builtin keys" equivalent of the "sign_message transparent driver: calculate in driver ECDSA SECP256R1 SHA-256" example in the test-suite would be really helpful :)

2 years, 9 months

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PSA crypto support for RH850 Microcontroller

by Tambe, Ujjwal (TCS)

Hello, Is it possible to use PSA crypto APIs for SHA256 and RSA signature verification for RH850F1KMS1 microcontroller from renesas which has G3KH cpu core. Let me know your thoughts. Thank you in advance. Regards, Ujjwal

2 years, 9 months

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Mbed TLS support for Renesas RH850 microcontroller

by Tambe, Ujjwal (TCS)

Hello, I am writing this mail in order to get support. I am using RH850-F1KMS1 microcontroller from Renesas, and I need to integrate mbed to perform SHA256 and RSA-1024 digital signature verification. The controller is bare metal and does not have any OS like freeRTOS. Just want to understand how to integrate mbed code in our project. Thank you in advance for the help. Regards, Ujjwal

2 years, 9 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. :) Dave, Please keep in mind that next Monday is a Federal Holiday in the US, so this may impact attendance. Best regards, Don Harbin TrustedFirmware Community Manager don.harbin(a)linaro.org

2 years, 9 months

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[Mbed-tls-announce] Coding style change in Mbed TLS

by Gilles Peskine via Mbed-tls-announce

Hello, You are concerned if: you contribute to Mbed TLS, or you maintain local patches to Mbed TLS. You are not concerned if: you just use Mbed TLS. We are going to change the C coding style in Mbed TLS. The new style is mostly what you'd find in The C Programming Language, 2nd edition, by Brian Kernighan and Dennis Ritchie (K&R2). The main changes compared to the current style are: * Spaces outside parentheses, not inside. No space in f(x). * Opening braces on the same line as if(), for(), etc., but on a separate line for functions. Indentation remains 4 spaces. The recommended maximum line length remains 80 columns. There are a few deviations from K&R2, documentation will be available shortly. The new code style will be enforced by the CI testing. This means that style that's rejected by the tool will not be merged, full stop. This also means that sometimes we'll have code that looks a bit less good to humans because the tool insists on it. We're doing this to avoid wasting reviewers' and contributors' time with style violations in code review. The tool we're using is uncrustify<https://github.com/uncrustify/uncrustify>. You can see how your code will look like by installing uncrustify 0.75.1 and running scripts/code_style.py from mbedtls-3.3.0 or mbedtls-2.28.2. There are previews of the rewritten branches at https://github.com/Mbed-TLS/mbedtls/tree/features/new-code-style/development and https://github.com/Mbed-TLS/mbedtls/tree/features/new-code-style/mbedtls-2.… (updated every few days until the real branches are rewritten). If you're now starting work on a new feature or bugfix, it will probably be easier to start from those branches, and do an easy rebase once they become official. If you've been working on a branch, we will provide a script to rebase the branch and rewrite it to the new style commit by commit. You'll need to have uncrustify 0.75.1. Concretely, when we change the code style: * If you've started to work on a branch but review has not started yet, we'll ask you to adapt your branch to the new code style. * If your work is under review, you'll need to adapt your branch to the new code style before it can be merged. Rebasing a branch is disruptive for reviews, so please synchronize with the reviewers to decide on a good time. We plan to do the switch during the first week of January 2023. Best regards, -- 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. -- Mbed-tls-announce mailing list -- mbed-tls-announce(a)lists.trustedfirmware.org To unsubscribe send an email to mbed-tls-announce-leave(a)lists.trustedfirmware.org

2 years, 9 months

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