Additional supported KDF func w/ HSE

[Changhawn]

Hi

I need KDF function w/HSE , which follow specification of NIST Special Publication 800-56A(The KDF shall be the “concatenation KDF”)

1. Do you have any guide or related code about this?

2. Below code is KDF function w/o HSE(all the paramters is string),  If change as KDF func w/ HSE.  parameter "sharedSecret" is changed as Key handle. In that case, could you guide and tell how to modify?

Thank u.

int concatKDF(uint8_t *key, unsigned int keyLen, const uint8_t *sharedSecret, unsigned int sharedSecretLen,

              const uint8_t *otherInfo, unsigned int otherInfoLen)

{

    const mbedtls_md_info_t *md_info = mbedtls_md_info_from_type(MBEDTLS_MD_SHA256);

    mbedtls_md_context_t md;

    uint8_t hash[32]; /* SHA256 Info Length is 32 */

    uint32_t hashLen;

    uint32_t formatted;

    uint8_t counter[4];

    uint32_t N;

    uint32_t offset;

    uint32_t amt;

    uint32_t minlen;

    int rc = 0;

    uint32_t i;

    const void *res;

    do

    {

        mbedtls_md_init(&md);

        rc = mbedtls_md_setup(&md, md_info, 1);

        if (rc != 0)

        {

            SYS_CONSOLE_PRINT("!!! mbedtls_md_init_ctx returned %d\r\n", rc);

            rc = -1;

        }

        else

        {

            hashLen = mbedtls_md_get_size(md_info);

            if (hashLen > 0u) 

            {

                N = ((unsigned int)keyLen + hashLen - 1u) / hashLen;

                offset = 0;

                amt = keyLen;

                for (i = 1; i <= N; i++)

                {

                    formatted = htonl(i);

                    counter[0] = (uint8_t)(formatted >> 0) & 0xffu;

                    counter[1] = (uint8_t)(formatted >> & 0xffu;

                    counter[2] = (uint8_t)(formatted >> 16) & 0xffu;

                    counter[3] = (uint8_t)(formatted >> 24) & 0xffu;

                    rc = mbedtls_md_starts(&md);

                    rc = mbedtls_md_update(&md, counter, sizeof(counter));

                    rc = mbedtls_md_update(&md, sharedSecret, sharedSecretLen);

                    rc = mbedtls_md_update(&md, otherInfo, otherInfoLen);

                    rc = mbedtls_md_finish(&md, hash);

                    if (rc != 0)

                    {

                        ;

                    }

                    minlen = (hashLen < amt) ? hashLen : amt;

                    res = memcpy(&key[offset], hash, (size_t)minlen);

                    offset += hashLen;

                    amt = (amt > hashLen) ? (amt - hashLen) : 0u;

                }

                mbedtls_md_free(&md);

            }

            else

            {

                SYS_CONSOLE_PRINT("!!! hash length(md_info size) is zero\r\n");

                rc = -1;

            }

        }

    } while (false);

    return rc;

}

[lukaszadrapa]

Hi @Changhawn 

Follwing algorithms are supported by HSE:

I can see in the source codes that only HSE_KDF_ALGO_TLS12PRF in HSE_Tls12Prf() is used in the NXP port.

So, you can check that function to see how to prepare descriptor to call such service.

Or "S32K344_DemoApp_SessionKeys" example in this package:
https://www.nxp.com/webapp/Download?colCode=S32K3_HSE_DemoExamples
... shows how to call HSE_SRV_ID_KEY_DERIVE.

Regards,
Lukas

[Changhawn]

Dear @lukaszadrapa 

I need to drive KEY by NIST KDF SP800 56A spec.

Like below picture, I know that HSE is not support KDF SP800 56A .

If it is possible to implement , please let me know.

Thank u.

Chang.

[Changhawn · Accepted solution]

Dear NXP guys.

In KDF,  I know that NIST 800-56A is not supported currently in NXP HSE.

So implemented it without HSE.