nRF51822 Le secure connection

[m-o]

Hello all.

I am developing a BT4.2 compliant application.
I have a question about LESC (LE Secure Connection).

devzone.nordicsemi.com/.../how-to-implement-ecc-functions-on-sdk-v12- 3-0-and-nrf51822 / 142314 # 142314
I had add the above process.

But, if you connect using "nRF Connect" on a PC, a DHKEY error (BLE_GAP_SEC_STATUS_DHKEY_FAILURE) will occur.
And connecting with "nRF Connect" on ipad pro results in unspecified error in Public key exchange.

However, I can connect with the module I created.

Any idea what might be happening?
Thanks.

【Development environment】

nRF51822

SDK12.3

[Einar Thorsrud]

Hi,

The post that you link to describes how to adapt the LESC implementation in SDK 15.3 to fix the security issue that was closed in the Erratum 10734 of the BLE spec. The code changes shown in the post describes what you need to change from the Experimental: BLE LE Secure Connections multirole example, and this is verified to be functional.

Did your LESC implementation work before you started to modify it according to the post, or did it never work? If not, I suggest you first try to implement LESC in the same way as is done in the SDK example and only modify it further once it is working. The modification itself is straight-forward (just copy-paste as described in the post), but it is better to do one step at a time.

If you still need assistance after that, please elaborate on what you have done, (show your code, describe how you have tested and how it behaves, etc.).

[m-o]

thank you for your answer.

Only the connection between modules is confirmed before modifying.
It worked correctly.

The same DHKEY error occurs in SDK 12.3 "ble_app_multirole_lesc".

The evaluation method is connected with LES (module: display only , PC: keybord).

Sorry, the code can not be disclosed.
Describes the setting value and sniffer data.
Please let us know if you have other necessary information.

[Setting value]
m_sec_params.bond = true;
m_sec_params.mitm = true;
m_sec_params.lesc = true;
m_sec_params.keypress = false;
m_sec_params.io_caps = m_io_capabilities;
m_sec_params.oob = false;
m_sec_params.min_key_size = 7;
m_sec_params.max_key_size = 16;
m_sec_params.kdist_own.enc = 1;
m_sec_params.kdist_own.id = 1;
m_sec_params.kdist_peer.enc = 1;
m_sec_params.kdist_peer.id = 1;

     err_code = pm_sec_params_set (& m_sec_params);
     APP_ERROR_CHECK (err_code);

【Sniffer data】

4111.ble_app_multirole_lesc.pcapng

[m-o]

No, I don't want to know general transplantation methods.

Confirmed that uploaded project is connected with peripheral

What I want to know is that reason DHKEY errors do not occur in IAR and DHKEY errors occur in SES.

[Einar Thorsrud]

Hi,

I see. I tested with SES and then it seems to run. What is the test procedure (how do I get the DK to connect to something)?

[m-o]

thank you for your answer.

For my test, connect the board of DK (bRF52832) and nRF51822 according to the following procedure.

1. Connect DK to PC

2. Start "nRF Connect for Desk top" and select DK.

3. Write the firmware to the nRF51822 board.

4. Connect nRF51822 board (peripheral) and DK (central).

5. Pair using LESC.
→ DHKEY error occurs

[Einar Thorsrud]

Hi,

I have been looking into this, but I do not yet understand what is going on. Is it OK for you to keep using Keil in the meantime?

[m-o]

Thank you for the survey.

Since development has ended,I cannot be changed to KEIL.

Has the symptom reproduced?

[Einar Thorsrud]

Hi,

I understand (I had a vague understanding that you were using Keil as well, but that was probably just for testing this).

I was not able to test the way you describe since for some reason I did not see the advertisement packets on air. Since you reported that the issue was specifically with the calculation of the shared secret I instead put together a simple test function that verifies the crypto operations needed for LESC, which you can see here (and run yourself by copy-pasting into your code and calling from your main function):

// Test crypto functions needed for LESC. To be used in the ble_app_multirole_lesc example in SDK 12.3.
static void crypto_test(void)
{
    ret_code_t err_code;

    // Own key structures
    __ALIGN(4) static const ble_gap_lesc_p256_sk_t sk =
    {{
        0x11, 0x11, 0x11, 0x11, 0x11, 0x11, 0x11, 0x11,
        0x11, 0x11, 0x11, 0x11, 0x11, 0x11, 0x11, 0x11,
        0x11, 0x11, 0x11, 0x11, 0x11, 0x11, 0x11, 0x11,
        0x11, 0x11, 0x11, 0x11, 0x11, 0x11, 0x11, 0x11,
    }};
    __ALIGN(4) static ble_gap_lesc_p256_pk_t lesc_pk;    /**< LESC ECC Public Key */
    __ALIGN(4) static ble_gap_lesc_dhkey_t lesc_dhkey;   /**< LESC ECC DH Key */

    static nrf_crypto_key_t own_sk =
    {
        .p_le_data = (uint8_t *) sk.sk,
        .len = sizeof(sk.sk)
    };
    static nrf_crypto_key_t own_pk =
    {
        .p_le_data = (uint8_t *) lesc_pk.pk,
        .len = sizeof(lesc_pk.pk)
    };
    static nrf_crypto_key_t key_dhkey =
    {
        .p_le_data = (uint8_t *) lesc_dhkey.key,
        .len = sizeof(lesc_dhkey.key)
    };

    // Valid own public key
    __ALIGN(4) static const uint8_t valid_own_pk[] =
    {
        0x02, 0x17, 0xE6, 0x17, 0xF0, 0xB6, 0x44, 0x39,
        0x28, 0x27, 0x8F, 0x96, 0x99, 0x9E, 0x69, 0xA2,
        0x3A, 0x4F, 0x2C, 0x15, 0x2B, 0xDF, 0x6D, 0x6C,
        0xDF, 0x66, 0xE5, 0xB8, 0x02, 0x82, 0xD4, 0xED,
        0x19, 0x4A, 0x7D, 0xEB, 0xCB, 0x97, 0x71, 0x2D,
        0x2D, 0xDA, 0x3C, 0xA8, 0x5A, 0xA8, 0x76, 0x5A,
        0x56, 0xF4, 0x5F, 0xC7, 0x58, 0x59, 0x96, 0x52,
        0xF2, 0x89, 0x7C, 0x65, 0x30, 0x6E, 0x57, 0x94,
    };

    // Peer public key structures
    __ALIGN(4) static const uint8_t peer_raw_public_key[] =
    {
        0xA5, 0x62, 0xBD, 0x02, 0x60, 0x88, 0x81, 0x2E,
        0x0A, 0x26, 0xE6, 0xA3, 0x55, 0x0E, 0xFA, 0xC6,
        0x06, 0xE6, 0x91, 0xDE, 0xB5, 0x6F, 0xA2, 0x1B,
        0x19, 0x8F, 0x2E, 0xFD, 0x0B, 0xD5, 0xCB, 0x25,
        0x9B, 0x4A, 0x96, 0x09, 0x12, 0xFD, 0x30, 0xD8,
        0x79, 0xA4, 0x52, 0x47, 0xF8, 0x05, 0x08, 0xE1,
        0x33, 0x3C, 0xA2, 0x5A, 0x4B, 0x83, 0x26, 0x23,
        0x3A, 0xE8, 0x26, 0x82, 0x46, 0x5A, 0x21, 0xCD,
    };

    static nrf_crypto_key_t peer_pk =
    {
        .p_le_data = (uint8_t *) peer_raw_public_key,
        .len = sizeof(peer_raw_public_key)
    };

    // Compare shared secret with valid shared secret
        __ALIGN(4) static const uint8_t valid_shared_secret[] =
    {
        0x6C, 0x21, 0xB1, 0xAB, 0xCF, 0x65, 0xFC, 0xB7,
        0x50, 0x48, 0xF2, 0x1B, 0x43, 0xA5, 0x31, 0x22,
        0xF8, 0x13, 0x65, 0x17, 0x02, 0x71, 0x5E, 0xBE,
        0xD2, 0x77, 0xFD, 0xB8, 0xA2, 0x4C, 0x5E, 0x73,
    };

    // -------------------------------- Begin test --------------------------------

    NRF_LOG_INFO("Test crypto operations used for LESC...\r\n");

    // Calculate own public key (not really needed in this test since we will not pass to a peer in
    // this test) but it is done to verify that it works since it is used in the real LESC procedure.
    nrf_crypto_init();
    err_code = nrf_crypto_public_key_compute(NRF_CRYPTO_CURVE_SECP256R1, &own_sk, &own_pk);
    APP_ERROR_CHECK(err_code);

    NRF_LOG_INFO("Calculated public key:\r\n");
    NRF_LOG_HEXDUMP_INFO(own_pk.p_le_data, own_pk.len);

    // Compare with valid public key
    if (memcmp(own_pk.p_le_data, valid_own_pk, 64) == 0)
    {
        NRF_LOG_INFO("Calculated public key is correct.\r\n");
    }
    else
    {
        NRF_LOG_ERROR("Fail: Calculated public key is INCORRECT!\r\n");
    }

    // Calculate shared secret
    err_code = nrf_crypto_shared_secret_compute(NRF_CRYPTO_CURVE_SECP256R1, &own_sk, &peer_pk, &key_dhkey);
    APP_ERROR_CHECK(err_code);

    NRF_LOG_INFO("Calculated shared secret:\r\n");
    NRF_LOG_HEXDUMP_INFO(key_dhkey.p_le_data, key_dhkey.len);

    // Compare with valid shared secret
    if (memcmp(key_dhkey.p_le_data, valid_shared_secret, 32) == 0)
    {
        NRF_LOG_INFO("Calculated shared secret is correct.\r\n");
    }
    else
    {
        NRF_LOG_ERROR("Fail: Calculated shared secret is INCORRECT!\r\n");
    }
}

Interestingly this test passes in your SES project, so there does not seem to be any problems with mciro-ecc. I don't know why LESC files when you test, nor do I know why I don't even see the advertisement packets on air on my side. Everything else looks OK to me. So it is a bit of a mystery for now.

[m-o]

Thank you for the test function.

I will check it.

Have you changed thumb_crt0.s?

[Einar Thorsrud]

No. Why do you ask?

[m-o]

Sorry, the above was unnecessary.

The cause has been found.
uECC.c was not working because it was included in the compilation.

Thank you for your cooperation.