Trouble creating a create a certificate signing request on nrf5340 for BLE Mesh Certificate based provisioning.

RE: Trouble creating a create a certificate signing request on nrf5340 for BLE Mesh Certificate based provisioning.

Sigurd Hellesvik — Tue, 10 Sep 2024 05:48:43 GMT

[quote user="Utkarsh-"]The above mentioned error is thrown when I assign life time as PSA_KEY_LIFETIME_PERSISTENT instead of PSA_KEY_LIFETIME_VOLATILE and use psa_set_key_id[/quote]

Yes in the case of persistent lifetime you will need to enable some more settings.

[quote user="Utkarsh-"]One final question, how can I add TF-M support ?[/quote]

Our TF-M implementation does not support CSR yet, so this sample will not work with TF-M in v2.7.0.
I specifically asked our devs about this when I created the sample.

I cannot give any timeline as to when our TF-M implementation will support this.

RE: Trouble creating a create a certificate signing request on nrf5340 for BLE Mesh Certificate based provisioning.

Utkarsh — Tue, 10 Sep 2024 05:21:19 GMT

One final question, how can I add TF-M support ?

RE: Trouble creating a create a certificate signing request on nrf5340 for BLE Mesh Certificate based provisioning.

Utkarsh — Mon, 09 Sep 2024 09:33:31 GMT

My apologies it is working now on ncs v2.6.1. The above mentioned error is thrown when I assign life time as PSA_KEY_LIFETIME_PERSISTENT instead of PSA_KEY_LIFETIME_VOLATILE and use psa_set_key_id

RE: Trouble creating a create a certificate signing request on nrf5340 for BLE Mesh Certificate based provisioning.

Sigurd Hellesvik — Mon, 09 Sep 2024 07:37:12 GMT

As in your code or my sample?
If my sample, can you list which board target and NCS version you built for?

RE: Trouble creating a create a certificate signing request on nrf5340 for BLE Mesh Certificate based provisioning.

Utkarsh — Mon, 09 Sep 2024 03:48:51 GMT

The code now builds fine but throws a psa_generate_key failed (-134) error after flashing

RE: Trouble creating a create a certificate signing request on nrf5340 for BLE Mesh Certificate based provisioning.

Sigurd Hellesvik — Fri, 06 Sep 2024 12:35:24 GMT

I had a bug in my patch, which by chance caused this very random error.
I fixed it in a commit now

RE: Trouble creating a create a certificate signing request on nrf5340 for BLE Mesh Certificate based provisioning.

Utkarsh — Wed, 04 Sep 2024 05:23:24 GMT

Yes it is persisting in v2.7.0 as well

RE: Trouble creating a create a certificate signing request on nrf5340 for BLE Mesh Certificate based provisioning.

Utkarsh — Tue, 03 Sep 2024 10:00:57 GMT

okay will check as soon as possible

RE: Trouble creating a create a certificate signing request on nrf5340 for BLE Mesh Certificate based provisioning.

Sigurd Hellesvik — Tue, 03 Sep 2024 09:13:43 GMT

Try on v2.7.0. Does the new patch work there?

RE: Trouble creating a create a certificate signing request on nrf5340 for BLE Mesh Certificate based provisioning.

Utkarsh — Tue, 03 Sep 2024 05:53:30 GMT

Also it is breaking my other codes with the error:

#error "MBEDTLS_PEM_WRITE_C defined, but not all prerequisites"

RE: Trouble creating a create a certificate signing request on nrf5340 for BLE Mesh Certificate based provisioning.

Utkarsh — Tue, 03 Sep 2024 05:16:21 GMT

Hi, I have tried using the newer patch but it isnt working for me. This is the error that I get

[2/228] Generating include/generated/version.h
-- Zephyr version: 3.5.99 (C:/ncs/v2.6.1/zephyr), build: v3.5.99-ncs1-1
[8/228] Building C object modules/nrf/subsys/nrf_security/src/CMakeFiles/mbedcrypto_base.dir/C_/ncs/v2.6.1/modules/crypto/mbedtls/library/base64.c.obj
FAILED: modules/nrf/subsys/nrf_security/src/CMakeFiles/mbedcrypto_base.dir/C_/ncs/v2.6.1/modules/crypto/mbedtls/library/base64.c.obj 
C:\ncs\toolchains\cf2149caf2\opt\zephyr-sdk\arm-zephyr-eabi\bin\arm-zephyr-eabi-gcc.exe -DKERNEL -DMBEDTLS_CONFIG_FILE=\"nrf-config.h\" -DMBEDTLS_PSA_CRYPTO_CONFIG_FILE=\"nrf-psa-crypto-want-config.h\" -DMBEDTLS_PSA_CRYPTO_USER_CONFIG_FILE=\"nrf-psa-crypto-config.h\" -DNRF5340_XXAA_APPLICATION -DNRF_SKIP_FICR_NS_COPY_TO_RAM -DPICOLIBC_LONG_LONG_PRINTF_SCANF -D_FORTIFY_SOURCE=1 -D_POSIX_C_SOURCE=200809 -D__LINUX_ERRNO_EXTENSIONS__ -D__PROGRAM_START -D__ZEPHYR__=1 -IC:/ncs/v2.6.1/zephyr/include -IC:/Users/Dell/Nordic_Projects/csr_ecdsa/build_1/zephyr/include/generated -IC:/ncs/v2.6.1/zephyr/soc/arm/nordic_nrf/nrf53 -IC:/ncs/v2.6.1/zephyr/lib/libc/common/include -IC:/ncs/v2.6.1/zephyr/soc/common/nordic_nrf/. -IC:/ncs/v2.6.1/zephyr/soc/arm/nordic_nrf/common/. -IC:/ncs/v2.6.1/nrf/include -IC:/ncs/v2.6.1/nrfxlib/crypto/nrf_cc312_mbedcrypto/include -IC:/ncs/v2.6.1/nrfxlib/crypto/nrf_cc312_mbedcrypto/include/mbedtls -IC:/ncs/v2.6.1/nrf/tests/include -IC:/ncs/v2.6.1/modules/hal/cmsis/CMSIS/Core/Include -IC:/ncs/v2.6.1/zephyr/modules/cmsis/. -IC:/ncs/v2.6.1/modules/hal/nordic/nrfx -IC:/ncs/v2.6.1/modules/hal/nordic/nrfx/drivers/include -IC:/ncs/v2.6.1/modules/hal/nordic/nrfx/mdk -IC:/ncs/v2.6.1/zephyr/modules/hal_nordic/nrfx/. -IC:/ncs/v2.6.1/nrfxlib/crypto/nrf_cc312_platform/include -IC:/Users/Dell/Nordic_Projects/csr_ecdsa/build_1/modules/nrf/subsys/nrf_security/src/include/generated -IC:/ncs/v2.6.1/nrf/subsys/nrf_security/include -IC:/ncs/v2.6.1/nrf/ext/oberon/psa/core/include -IC:/ncs/v2.6.1/nrf/ext/oberon/psa/core/library -IC:/ncs/v2.6.1/modules/crypto/mbedtls/include -IC:/ncs/v2.6.1/modules/crypto/mbedtls/library -IC:/ncs/v2.6.1/nrf/subsys/nrf_security/src/drivers/nrf_cc3xx/include -fno-strict-aliasing -Os -imacros C:/Users/Dell/Nordic_Projects/csr_ecdsa/build_1/zephyr/include/generated/autoconf.h -fno-printf-return-value -fno-common -g -gdwarf-4 -fdiagnostics-color=always -mcpu=cortex-m33 -mthumb -mabi=aapcs -mfp16-format=ieee -mtp=soft --sysroot=C:/ncs/toolchains/cf2149caf2/opt/zephyr-sdk/arm-zephyr-eabi/arm-zephyr-eabi -imacros C:/ncs/v2.6.1/zephyr/include/zephyr/toolchain/zephyr_stdint.h -Wall -Wformat -Wformat-security -Wno-format-zero-length -Wno-pointer-sign -Wpointer-arith -Wexpansion-to-defined -Wno-unused-but-set-variable -Werror=implicit-int -fno-pic -fno-pie -fno-asynchronous-unwind-tables -ftls-model=local-exec -fno-reorder-functions --param=min-pagesize=0 -fno-defer-pop -fmacro-prefix-map=C:/Users/Dell/Nordic_Projects/csr_ecdsa=CMAKE_SOURCE_DIR -fmacro-prefix-map=C:/ncs/v2.6.1/zephyr=ZEPHYR_BASE -fmacro-prefix-map=C:/ncs/v2.6.1=WEST_TOPDIR -ffunction-sections -fdata-sections --specs=picolibc.specs -std=c99 -MD -MT modules/nrf/subsys/nrf_security/src/CMakeFiles/mbedcrypto_base.dir/C_/ncs/v2.6.1/modules/crypto/mbedtls/library/base64.c.obj -MF modules\nrf\subsys\nrf_security\src\CMakeFiles\mbedcrypto_base.dir\C_\ncs\v2.6.1\modules\crypto\mbedtls\library\base64.c.obj.d -o modules/nrf/subsys/nrf_security/src/CMakeFiles/mbedcrypto_base.dir/C_/ncs/v2.6.1/modules/crypto/mbedtls/library/base64.c.obj -c C:/ncs/v2.6.1/modules/crypto/mbedtls/library/base64.c
C:/ncs/v2.6.1/modules/crypto/mbedtls/library/base64.c: In function 'mbedtls_base64_encode':
C:/ncs/v2.6.1/modules/crypto/mbedtls/library/base64.c:77:16: error: 'MBEDTLS_ERR_BASE64_BUFFER_TOO_SMALL' undeclared (first use in this function); did you mean 'MBEDTLS_ERR_MPI_BUFFER_TOO_SMALL'?
   77 |         return MBEDTLS_ERR_BASE64_BUFFER_TOO_SMALL;
      |                ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
      |                MBEDTLS_ERR_MPI_BUFFER_TOO_SMALL
C:/ncs/v2.6.1/modules/crypto/mbedtls/library/base64.c:77:16: note: each undeclared identifier is reported only once for each function it appears in
C:/ncs/v2.6.1/modules/crypto/mbedtls/library/base64.c: In function 'mbedtls_base64_decode':
C:/ncs/v2.6.1/modules/crypto/mbedtls/library/base64.c:164:20: error: 'MBEDTLS_ERR_BASE64_INVALID_CHARACTER' undeclared (first use in this function); did you mean 'MBEDTLS_ERR_MPI_INVALID_CHARACTER'?
  164 |             return MBEDTLS_ERR_BASE64_INVALID_CHARACTER;
      |                    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
      |                    MBEDTLS_ERR_MPI_INVALID_CHARACTER
C:/ncs/v2.6.1/modules/crypto/mbedtls/library/base64.c:200:16: error: 'MBEDTLS_ERR_BASE64_BUFFER_TOO_SMALL' undeclared (first use in this function); did you mean 'MBEDTLS_ERR_MPI_BUFFER_TOO_SMALL'?
  200 |         return MBEDTLS_ERR_BASE64_BUFFER_TOO_SMALL;
      |                ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
      |                MBEDTLS_ERR_MPI_BUFFER_TOO_SMALL
[21/228] Building C object modules/nrf/subsys/nrf_security/src/CMakeFiles/mbedcrypto_base.dir/C_/ncs/v2.6.1/modules/crypto/mbedtls/library/bignum.c.obj
ninja: build stopped: subcommand failed.
FATAL ERROR: command exited with status 1: 'C:\ncs\toolchains\cf2149caf2\opt\bin\cmake.EXE' --build 'c:\Users\Dell\Nordic_Projects\csr_ecdsa\build_1'

 *  The terminal process terminated with exit code: 1. 
 *  Terminal will be reused by tasks, press any key to close it.

RE: Trouble creating a create a certificate signing request on nrf5340 for BLE Mesh Certificate based provisioning.

Sigurd Hellesvik — Wed, 21 Aug 2024 10:42:05 GMT

[quote user="Utkarsh-"]Thank you very much for adding TF-M support![/quote]

The sample itself does not support TF-M. But the patch from before was breaking TF-M globally so I fixed that.

[quote user="Utkarsh-"]Is there a reason why patch was required and not included in the NCS release?[/quote]

We are currently working on converting our crypto libraries, and not everything has been moved yet. This will be added to NCS at some point, but in the meantime I created a patch as a workaround. The patch is not "clean", so the final solution at some later point will probably be different.

RE: Trouble creating a create a certificate signing request on nrf5340 for BLE Mesh Certificate based provisioning.

Utkarsh — Wed, 21 Aug 2024 10:09:11 GMT

Thank you very much for adding TF-M support!

Is there a reason why patch was required and not included in the NCS release?

RE: Trouble creating a create a certificate signing request on nrf5340 for BLE Mesh Certificate based provisioning.

Sigurd Hellesvik — Wed, 21 Aug 2024 08:17:29 GMT

Happy to hear that!
Btw, I just added a new commit to the project, so you might want to check that one out.

RE: Trouble creating a create a certificate signing request on nrf5340 for BLE Mesh Certificate based provisioning.

Utkarsh — Wed, 21 Aug 2024 04:54:42 GMT

It is working now.

Thank you for all the help over the past few weeks!

RE: Trouble creating a create a certificate signing request on nrf5340 for BLE Mesh Certificate based provisioning.

Sigurd Hellesvik — Tue, 20 Aug 2024 11:37:12 GMT

yes

RE: Trouble creating a create a certificate signing request on nrf5340 for BLE Mesh Certificate based provisioning.

Utkarsh — Tue, 20 Aug 2024 10:44:34 GMT

Should I remove the previously applied patch on mbedtls?

RE: Trouble creating a create a certificate signing request on nrf5340 for BLE Mesh Certificate based provisioning.

Utkarsh — Tue, 20 Aug 2024 08:50:22 GMT

I am still getting the above mentioned errors

RE: Trouble creating a create a certificate signing request on nrf5340 for BLE Mesh Certificate based provisioning.

Sigurd Hellesvik — Tue, 20 Aug 2024 07:43:10 GMT

I just changed it to ECDSA. See the git sample again now.

RE: Trouble creating a create a certificate signing request on nrf5340 for BLE Mesh Certificate based provisioning.

Utkarsh — Tue, 20 Aug 2024 05:15:33 GMT

Thank you very much!
Can the same be done using ECDSA? I have changed the code to accommodate the same but I get the following error:

FAILED: modules/nrf/subsys/nrf_security/src/CMakeFiles/mbedcrypto.dir/C_/ncs/v2.6.1/modules/crypto/mbedtls/library/pk_wrap.c.obj 
C:\ncs\toolchains\cf2149caf2\opt\zephyr-sdk\arm-zephyr-eabi\bin\arm-zephyr-eabi-gcc.exe -DKERNEL -DMBEDTLS_CONFIG_FILE=\"nrf-config.h\" -DMBEDTLS_PSA_CRYPTO_CONFIG_FILE=\"nrf-psa-crypto-want-config.h\" -DMBEDTLS_PSA_CRYPTO_USER_CONFIG_FILE=\"nrf-psa-crypto-config.h\" -DNRF5340_XXAA_APPLICATION -DNRF_SKIP_FICR_NS_COPY_TO_RAM -DPICOLIBC_LONG_LONG_PRINTF_SCANF -D_FORTIFY_SOURCE=1 -D_POSIX_C_SOURCE=200809 -D__LINUX_ERRNO_EXTENSIONS__ -D__PROGRAM_START -D__ZEPHYR__=1 -IC:/ncs/v2.6.1/zephyr/include -IC:/Users/Dell/Nordic_Projects/psa_csr_ecc/build_1/zephyr/include/generated -IC:/ncs/v2.6.1/zephyr/soc/arm/nordic_nrf/nrf53 -IC:/ncs/v2.6.1/zephyr/lib/libc/common/include -IC:/ncs/v2.6.1/zephyr/soc/common/nordic_nrf/. -IC:/ncs/v2.6.1/zephyr/soc/arm/nordic_nrf/common/. -IC:/ncs/v2.6.1/nrf/include -IC:/ncs/v2.6.1/nrf/tests/include -IC:/ncs/v2.6.1/modules/hal/cmsis/CMSIS/Core/Include -IC:/ncs/v2.6.1/zephyr/modules/cmsis/. -IC:/ncs/v2.6.1/modules/hal/nordic/nrfx -IC:/ncs/v2.6.1/modules/hal/nordic/nrfx/drivers/include -IC:/ncs/v2.6.1/modules/hal/nordic/nrfx/mdk -IC:/ncs/v2.6.1/zephyr/modules/hal_nordic/nrfx/. -IC:/Users/Dell/Nordic_Projects/psa_csr_ecc/build_1/modules/nrf/subsys/nrf_security/src/include/generated -IC:/ncs/v2.6.1/nrf/subsys/nrf_security/include -IC:/ncs/v2.6.1/nrf/ext/oberon/psa/core/include -IC:/ncs/v2.6.1/nrf/ext/oberon/psa/core/library -IC:/ncs/v2.6.1/modules/crypto/mbedtls/include -IC:/ncs/v2.6.1/modules/crypto/mbedtls/library -IC:/ncs/v2.6.1/nrf/ext/oberon/psa/drivers -isystem C:/ncs/v2.6.1/nrfxlib/crypto/nrf_cc312_platform/include -isystem C:/ncs/v2.6.1/nrfxlib/crypto/nrf_oberon/include -isystem C:/ncs/v2.6.1/nrfxlib/crypto/nrf_oberon/include/mbedtls -fno-strict-aliasing -Os -imacros C:/Users/Dell/Nordic_Projects/psa_csr_ecc/build_1/zephyr/include/generated/autoconf.h -fno-printf-return-value -fno-common -g -gdwarf-4 -fdiagnostics-color=always -mcpu=cortex-m33 -mthumb -mabi=aapcs -mfp16-format=ieee -mtp=soft --sysroot=C:/ncs/toolchains/cf2149caf2/opt/zephyr-sdk/arm-zephyr-eabi/arm-zephyr-eabi -imacros C:/ncs/v2.6.1/zephyr/include/zephyr/toolchain/zephyr_stdint.h -Wall -Wformat -Wformat-security -Wno-format-zero-length -Wno-pointer-sign -Wpointer-arith -Wexpansion-to-defined -Wno-unused-but-set-variable -Werror=implicit-int -fno-pic -fno-pie -fno-asynchronous-unwind-tables -ftls-model=local-exec -fno-reorder-functions --param=min-pagesize=0 -fno-defer-pop -fmacro-prefix-map=C:/Users/Dell/Nordic_Projects/psa_csr_ecc=CMAKE_SOURCE_DIR -fmacro-prefix-map=C:/ncs/v2.6.1/zephyr=ZEPHYR_BASE -fmacro-prefix-map=C:/ncs/v2.6.1=WEST_TOPDIR -ffunction-sections -fdata-sections --specs=picolibc.specs -std=c99 -Wno-unused-function -Wno-unused-variable -Wno-stringop-overflow -Wno-stringop-overread -Wno-strict-aliasing -Wno-uninitialized -Wno-maybe-uninitialized -MD -MT modules/nrf/subsys/nrf_security/src/CMakeFiles/mbedcrypto.dir/C_/ncs/v2.6.1/modules/crypto/mbedtls/library/pk_wrap.c.obj -MF modules\nrf\subsys\nrf_security\src\CMakeFiles\mbedcrypto.dir\C_\ncs\v2.6.1\modules\crypto\mbedtls\library\pk_wrap.c.obj.d -o modules/nrf/subsys/nrf_security/src/CMakeFiles/mbedcrypto.dir/C_/ncs/v2.6.1/modules/crypto/mbedtls/library/pk_wrap.c.obj -c C:/ncs/v2.6.1/modules/crypto/mbedtls/library/pk_wrap.c
In file included from C:/ncs/v2.6.1/modules/crypto/mbedtls/library/pk_internal.h:25,
                 from C:/ncs/v2.6.1/modules/crypto/mbedtls/library/pk_wrap.c:14:
C:/ncs/v2.6.1/modules/crypto/mbedtls/library/pk_wrap.c: In function 'rsa_opaque_sign_wrap':
C:/ncs/v2.6.1/modules/crypto/mbedtls/library/pk_internal.h:28:67: error: 'psa_to_pk_rsa_errors' undeclared (first use in this function); did you mean 'psa_to_pk_ecdsa_errors'?
   28 |                                                                   psa_to_pk_rsa_errors,            \
      |                                                                   ^~~~~~~~~~~~~~~~~~~~
C:/ncs/v2.6.1/nrf/ext/oberon/psa/core/library/psa_util_internal.h:103:35: note: in definition of macro 'PSA_TO_MBEDTLS_ERR_LIST'
  103 |     psa_status_to_mbedtls(status, error_list,                         \
      |                                   ^~~~~~~~~~
C:/ncs/v2.6.1/modules/crypto/mbedtls/library/pk_wrap.c:1784:20: note: in expansion of macro 'PSA_PK_RSA_TO_MBEDTLS_ERR'
 1784 |             return PSA_PK_RSA_TO_MBEDTLS_ERR(status);
      |                    ^~~~~~~~~~~~~~~~~~~~~~~~~
C:/ncs/v2.6.1/modules/crypto/mbedtls/library/pk_internal.h:28:67: note: each undeclared identifier is reported only once for each function it appears in
   28 |                                                                   psa_to_pk_rsa_errors,            \
      |                                                                   ^~~~~~~~~~~~~~~~~~~~
C:/ncs/v2.6.1/nrf/ext/oberon/psa/core/library/psa_util_internal.h:103:35: note: in definition of macro 'PSA_TO_MBEDTLS_ERR_LIST'
  103 |     psa_status_to_mbedtls(status, error_list,                         \
      |                                   ^~~~~~~~~~
C:/ncs/v2.6.1/modules/crypto/mbedtls/library/pk_wrap.c:1784:20: note: in expansion of macro 'PSA_PK_RSA_TO_MBEDTLS_ERR'
 1784 |             return PSA_PK_RSA_TO_MBEDTLS_ERR(status);
      |                    ^~~~~~~~~~~~~~~~~~~~~~~~~
[64/257] Building C object modules/nrf/subsys/nrf_security/src/CMakeFiles/mbedcrypto.dir/C_/ncs/v2.6.1/modules/crypto/mbedtls/library/ccm.c.obj
ninja: build stopped: subcommand failed.
FATAL ERROR: command exited with status 1: 'C:\ncs\toolchains\cf2149caf2\opt\bin\cmake.EXE' --build 'c:\Users\Dell\Nordic_Projects\psa_csr_ecc\build_1'

RE: Trouble creating a create a certificate signing request on nrf5340 for BLE Mesh Certificate based provisioning.

Utkarsh — Tue, 20 Aug 2024 04:00:39 GMT

[deleted]

RE: Trouble creating a create a certificate signing request on nrf5340 for BLE Mesh Certificate based provisioning.

Sigurd Hellesvik — Mon, 19 Aug 2024 11:26:41 GMT

This one looks like it works for the nRF5340DK, without TF-M.
https://github.com/hellesvik-nordic/samples_for_nrf_connect_sdk/tree/main/crypto/psa_csr

I did not check the output, so that would be for you.

Can you give the sample a roll and let me know how it goes?

EDIT: I was told that ECC would be a better idea than RSA here so I will change it relatively soon

RE: Trouble creating a create a certificate signing request on nrf5340 for BLE Mesh Certificate based provisioning.

Utkarsh — Thu, 15 Aug 2024 18:25:08 GMT

That would be great !

RE: Trouble creating a create a certificate signing request on nrf5340 for BLE Mesh Certificate based provisioning.

Sigurd Hellesvik — Wed, 14 Aug 2024 12:37:28 GMT

How about this?

I will try to make a CSR sample myself.
Then you can use that as a reference to check your project.
It will take some time, but I got direct access to our crypto devs so I should be able to get all potential issues I have with this figured out pretty fast.
Im guessing I will be done with such a sample next week.

How does that sound to you?

RE: Trouble creating a create a certificate signing request on nrf5340 for BLE Mesh Certificate based provisioning.

Utkarsh — Wed, 14 Aug 2024 02:54:42 GMT

Yes I followed this guide to write my code for generating CSR but it resulted in the following error: Implicit declaration of function : mbedtls_pk_setup_opaque. I further looked into it and found out that even after enabling CONFIG_MBEDTLS_USE_PSA_CRYPTO it was not defined in the nrf-config.h header file, so I defined it there. This led to the code building successfully but after flashing the code onto the board, the psa_generate_key() started failing with the error -134 which stands for PSA_ERROR_NOT_SUPPORTED.

I further looked into why was this happening, and I found out that this happens whenever CONFIG_MBEDTLS_LEGACY_CRYPTO_C is enabled. But without enabling this my code doesn't build.

My problem is very similar to this and I know that there is a solution as that question was solved. Please help me in this regard