SHA256 Sample not working

[ColinC]

Hello, 

While developping firmware I wanted to use the PSA API psa_hash_compute() to compute a hash over 8 bytes but to no avail. The function returns -134 and the out parameter holding the hash value is all 0s. 

I Tried running the sample from nrf/samples/crypto/sha256 and got the same results. I setup the sample on SDK v2.7.0 with nrf5340dk/nrf5340/cpuapp/ns as Board Target. I removed the return statements in the main.c function to let also verify_sha256() and the following functions execute, otherwise the code would return on line 178 after hash_singlepart_sha256 had failed. 

Here is the log output: 

*** Booting nRF Connect SDK v2.7.0-5cb85570ca43 ***
*** Using Zephyr OS v3.6.99-100befc70c74 ***
[00:00:00.260,742] <inf> sha256: Starting SHA256 example...
[00:00:00.260,772] <inf> sha256: ---- Plaintext to hash (len: 150): ----
[00:00:00.260,803] <inf> sha256: Content:
                                 45 78 61 6d 70 6c 65 20  73 74 72 69 6e 67 20 74 |Example  string t
                                 6f 20 64 65 6d 6f 6e 73  74 72 61 74 65 20 62 61 |o demons trate ba
                                 73 69 63 20 75 73 61 67  65 20 6f 66 20 53 48 41 |sic usag e of SHA
                                 32 35 36 2e 54 68 61 74  20 75 73 65 73 20 73 69 |256.That  uses si
                                 6e 67 6c 65 20 61 6e 64  20 6d 75 6c 74 69 2d 70 |ngle and  multi-p
                                 61 72 74 20 50 53 41 20  63 72 79 70 74 6f 20 41 |art PSA  crypto A
                                 50 49 27 73 20 74 6f 20  70 65 72 66 6f 72 6d 20 |PI's to  perform 
                                 61 20 53 48 41 2d 32 35  36 20 68 61 73 68 69 6e |a SHA-25 6 hashin
                                 67 20 6f 70 65 72 61 74  69 6f 6e 2e 00 00 00 00 |g operat ion.....
                                 00 00 00 00 00 00                                |......           
[00:00:00.260,833] <inf> sha256: ---- Plaintext to hash end  ----
[00:00:00.260,833] <inf> sha256: Hashing using SHA256...
[00:00:00.260,925] <inf> sha256: psa_hash_compute failed! (Error: -134)
[00:00:00.260,925] <inf> sha256: Example exited with error!
[00:00:00.260,955] <inf> sha256: Verifying the SHA256 hash...
[00:00:00.261,016] <inf> sha256: psa_hash_compare failed! (Error: -134)
[00:00:00.261,016] <inf> sha256: Example exited with error!
[00:00:00.261,047] <inf> sha256: Hashing using multi-part SHA256...
[00:00:00.261,108] <err> sha256: Could not setup the hash operation! Error -134
[00:00:00.261,108] <inf> sha256: Example exited with error!
[00:00:00.261,108] <inf> sha256: Verifying the SHA256 hash...
[00:00:00.261,199] <inf> sha256: psa_hash_compare failed! (Error: -134)
[00:00:00.261,199] <inf> sha256: Example exited with error!
[00:00:00.261,199] <inf> sha256: Example finished successfully!

What am I missing? Can you try to run the sample on a DK to confirm the behaviour that I get? Could it be possible to add rudimentary explanations on how to interact with the PSA API in the README of the sample? 

Regards 

Colin 

[Charlie]

Hi Colin,

Thanks for reaching out about this issue.

I’ll set aside some time to test it and will update you once I find something.

Best regards,
Charlie

[Charlie]

Hi Colin,

I did a try the sha256 sample built with latest NCS 2.9.0 and NCS 2.7.0 on a nRF5340DK v2.0.0, and they all worked as expected.

*** Booting nRF Connect SDK v2.7.0-5cb85570ca43 ***
*** Using Zephyr OS v3.6.99-100befc70c74 ***
[00:00:00.267,181] <inf> sha256: Starting SHA256 example...
[00:00:00.267,211] <inf> sha256: ---- Plaintext to hash (len: 150): ----
[00:00:00.267,242] <inf> sha256: Content:
                                 45 78 61 6d 70 6c 65 20  73 74 72 69 6e 67 20 74 |Example  string t
                                 6f 20 64 65 6d 6f 6e 73  74 72 61 74 65 20 62 61 |o demons trate ba
                                 73 69 63 20 75 73 61 67  65 20 6f 66 20 53 48 41 |sic usag e of SHA
                                 32 35 36 2e 54 68 61 74  20 75 73 65 73 20 73 69 |256.That  uses si
                                 6e 67 6c 65 20 61 6e 64  20 6d 75 6c 74 69 2d 70 |ngle and  multi-p
                                 61 72 74 20 50 53 41 20  63 72 79 70 74 6f 20 41 |art PSA  crypto A
                                 50 49 27 73 20 74 6f 20  70 65 72 66 6f 72 6d 20 |PI's to  perform 
                                 61 20 53 48 41 2d 32 35  36 20 68 61 73 68 69 6e |a SHA-25 6 hashin
                                 67 20 6f 70 65 72 61 74  69 6f 6e 2e 00 00 00 00 |g operat ion.....
                                 00 00 00 00 00 00                                |......           
[00:00:00.267,272] <inf> sha256: ---- Plaintext to hash end  ----
[00:00:00.267,272] <inf> sha256: Hashing using SHA256...
[00:00:00.267,486] <inf> sha256: Hashing successful!
[00:00:00.267,517] <inf> sha256: ---- SHA256 hash (len: 32): ----
[00:00:00.267,547] <inf> sha256: Content:
                                 95 6e 6a 15 b9 5e 76 65  3a 4a 4a a7 71 62 63 b9 |.nj..^ve :JJ.qbc.
                                 d2 24 8a 88 95 e0 f5 3e  82 94 2f 2a 1d ba c9 d5 |.$.....> ../*....
[00:00:00.267,547] <inf> sha256: ---- SHA256 hash end  ----
[00:00:00.267,547] <inf> sha256: Verifying the SHA256 hash...
[00:00:00.267,761] <inf> sha256: SHA256 verification successful!
[00:00:00.267,791] <inf> sha256: Hashing using multi-part SHA256...
[00:00:00.268,035] <inf> sha256: Added 42 bytes
[00:00:00.268,188] <inf> sha256: Added 58 bytes
[00:00:00.268,310] <inf> sha256: Added 50 bytes
[00:00:00.268,524] <inf> sha256: Hashing successful!
[00:00:00.268,524] <inf> sha256: ---- SHA256 hash (len: 32): ----
[00:00:00.268,554] <inf> sha256: Content:
                                 95 6e 6a 15 b9 5e 76 65  3a 4a 4a a7 71 62 63 b9 |.nj..^ve :JJ.qbc.
                                 d2 24 8a 88 95 e0 f5 3e  82 94 2f 2a 1d ba c9 d5 |.$.....> ../*....
[00:00:00.268,585] <inf> sha256: ---- SHA256 hash end  ----
[00:00:00.268,585] <inf> sha256: Verifying the SHA256 hash...
[00:00:00.268,798] <inf> sha256: SHA256 verification successful!
[00:00:00.268,798] <inf> sha256: Example finished successfully!

I do not quite understand the change you have made, did you expect to see the errors when your modifcation is applied?

If you see the error with original sample, please have a try with the fimware I buildt on NCS 2.9.0. This firmware using ns so TF-M is enabled.

ncs290_sha256_nrf5340dk_ns.hex

Best regards,

Charlie

[ColinC]

Hi Charlie, 

Thanks  for looking into it. Basically I commented out the return statements in the main function to let also hash_multipart_sha256 be executed in case only hash_singlepart_sha256 was failing. Otherwise I have not touched the SDK nor any other part of the sample. 

int main(void)
{
	int status;

	LOG_INF("Starting SHA256 example...");

	status = crypto_init();
	if (status != APP_SUCCESS) {
		LOG_INF(APP_ERROR_MESSAGE);
		//return APP_ERROR;
	}

	PRINT_HEX("Plaintext to hash", m_plain_text, sizeof(m_plain_text));

	status = hash_singlepart_sha256();
	if (status != APP_SUCCESS) {
		LOG_INF(APP_ERROR_MESSAGE);
		//return APP_ERROR;
	}

	status = verify_sha256();
	if (status != APP_SUCCESS) {
		LOG_INF(APP_ERROR_MESSAGE);
		//return APP_ERROR;
	}

	/* Reset the hash */
	memset(m_hash, 0, sizeof(m_hash));

	status = hash_multipart_sha256();
	if (status != APP_SUCCESS) {
		LOG_INF(APP_ERROR_MESSAGE);
		return APP_ERROR;
	}

	status = verify_sha256();
	if (status != APP_SUCCESS) {
		LOG_INF(APP_ERROR_MESSAGE);
		//return APP_ERROR;
	}

	LOG_INF(APP_SUCCESS_MESSAGE);

	//return APP_SUCCESS;
}

Here is the build configuration I used: 

I will try with SDK 2.9 next.

Your answer showed that the psa_hash API should be callable even with TFM activated. Could you point me to a documentation that explains how all elements work together?

I've spent time reading on TFM and the crypto libraries separately but I don't understand how the hierarchy is built and what the dependencies are between them. I understand there are several moving parts: 

• TF-M
• PSA API  
• Legacy Mbed TLS 
• Mbed TLS
• Drivers: Oberon Driver / c3xx 

Somehow they are intertwined by Kconfig flags but I don't really get how. A dependency diagram of some sorts would be great. 

Thank you for the support

Kind regards 

Colin 

[ColinC]

Hi Charlie,

I Tested it with SDK v2.9 with the same build settings as your screenshot, it worked. Then I updated SDK v2.7 to make sure I hadn't alered it by mistake and it also worked. 

Then I found the real discrepancy: In my original buld config I had added prj.conf as base configuration file. I tried it again with prj.conf added and it failed. The build command looks like this : 

"west build --build-dir e:/BLE_Nordic/ncs/v2.7.0/nrf/samples/crypto/sha256/build e:/BLE_Nordic/ncs/v2.7.0/nrf/samples/crypto/sha256 --pristine --board nrf5340dk/nrf5340/cpuapp/ns --sysbuild -- -DNCS_TOOLCHAIN_VERSION=NONE -DCONF_FILE=e:/BLE_Nordic/ncs/v2.7.0/nrf/samples/crypto/sha256/prj.conf -DBOARD_ROOT=e:/ble_nordic/ncs/v2.7.0/nrf/samples/crypto/sha256"

Without explicit usage of prj.conf in the build config the build command looks like this : 

"west build --build-dir e:/BLE_Nordic/ncs/v2.7.0/nrf/samples/crypto/sha256/build e:/BLE_Nordic/ncs/v2.7.0/nrf/samples/crypto/sha256 --pristine --board nrf5340dk/nrf5340/cpuapp/ns --sysbuild -- -DNCS_TOOLCHAIN_VERSION=NONE -DBOARD_ROOT=e:/ble_nordic/ncs/v2.7.0/nrf/samples/crypto/sha256"

 

I will try comparing the .config output in both cases to understand the differences. 

Cheers 

Colin 

[Charlie]

Hi Colin,

Thank you for your question. The integration of TF-M, PSA, MbedTLS, and Oberon Driver/c3xx is quite complex, so it's difficult to explain in simple terms here.

A colleague of mine has written a blog post, (+) Securing IoT products with PSA Certified APIs - Blogs - Nordic Blog - Nordic DevZone, which partially explains PSA and TF-M. I recommend reading it, and feel free to ask more specific questions if anything remains unclear.

Best regards,
Charlie

[ColinC]

Hi Charlie, 

Thank you for the link. Regarding my previous answer, could you confirm that building with prj.conf included leads to the psa_hash_compute function failing. If so, could you explain what the reason for this is? 

[Charlie]

Hi Colin,

I was able to reproduce this issue. After comparing the build logs, I noticed that the line:
"Merged configuration 'C:/ncs/v2.9.0/nrf/samples/crypto/sha256/boards/nrf5340dk_nrf5340_cpuapp_ns.conf'." is missing.

It seems that the NS board configuration is not merged into the build when setting CONF_FILE in the build command. You also need to manually specify the location of nrf5340dk_nrf5340_cpuapp_ns.conf in the Extra Kconfig fragment.

I'll check with our build system experts to determine whether this is expected behavior or a potential bug. I'll get back to you once I have their feedback.

Best regards,
Charlie

[Charlie]

Hi Colin,

I had a chance to discuss this with our build system expert.

If you refer to the following section in  Setting Kconfig configuration values — Zephyr Project Documentation, you’ll see that the build behavior is exactly as described in the documentation. Therefore, we will not be making any changes.

1. If CONF_FILE is set, the configuration file(s) specified in it are merged and used as the application configuration. CONF_FILE can be set in various ways:

   1. In CMakeLists.txt, before calling find_package(Zephyr)

   2. By passing -DCONF_FILE=<conf file(s)>, either directly or via west

   3. From the CMake variable cache

2. Otherwise, if boards/<BOARD>.conf exists in the application configuration directory, the result of merging it with prj.conf is used.

Best regards,

Charlie

[ColinC]

Hi Charlie, 

Thanks for looking into it. Your explanation makes sense, I guess I wasn't expecting the board specific config files not being included if CONF_FILE is set. 

Many Thanks, that solves the issue for me. 

Best 

Colin 

[Charlie]

You are welcome. Good luck to you development.

Feel free to check with us if you have further questions.

Best regards,

Charlie