bool derive_key()

in samplecode/psi/SMCClient/worker/ecp.cpp [144:225]

• 64 lines of code
• 8 McCabe index (conditional complexity)

bool derive_key(
    const sample_ec_dh_shared_t *p_shared_key,
    uint8_t key_id,
    sample_ec_key_128bit_t* derived_key) {
    sample_status_t sample_ret = SAMPLE_SUCCESS;
    uint8_t cmac_key[MAC_KEY_SIZE];
    sample_ec_key_128bit_t key_derive_key;

    memset(&cmac_key, 0, MAC_KEY_SIZE);

    sample_ret = sample_rijndael128_cmac_msg(
                     (sample_cmac_128bit_key_t *)&cmac_key,
                     (uint8_t*)p_shared_key,
                     sizeof(sample_ec_dh_shared_t),
                     (sample_cmac_128bit_tag_t *)&key_derive_key);
    if (sample_ret != SAMPLE_SUCCESS) {
        // memset here can be optimized away by compiler, so please use memset_s on
        // windows for production code and similar functions on other OSes.
        memset(&key_derive_key, 0, sizeof(key_derive_key));
        return false;
    }

    const char *label = NULL;
    uint32_t label_length = 0;
    switch (key_id) {
    case SAMPLE_DERIVE_KEY_SMK:
        label = str_SMK;
        label_length = sizeof(str_SMK) -1;
        break;
    case SAMPLE_DERIVE_KEY_SK:
        label = str_SK;
        label_length = sizeof(str_SK) -1;
        break;
    case SAMPLE_DERIVE_KEY_MK:
        label = str_MK;
        label_length = sizeof(str_MK) -1;
        break;
    case SAMPLE_DERIVE_KEY_VK:
        label = str_VK;
        label_length = sizeof(str_VK) -1;
        break;
    default:
        // memset here can be optimized away by compiler, so please use memset_s on
        // windows for production code and similar functions on other OSes.
        memset(&key_derive_key, 0, sizeof(key_derive_key));
        return false;
        break;
    }
    /* derivation_buffer = counter(0x01) || label || 0x00 || output_key_len(0x0080) */
    uint32_t derivation_buffer_length = EC_DERIVATION_BUFFER_SIZE(label_length);
    uint8_t *p_derivation_buffer = (uint8_t *)malloc(derivation_buffer_length);
    if (p_derivation_buffer == NULL) {
        // memset here can be optimized away by compiler, so please use memset_s on
        // windows for production code and similar functions on other OSes.
        memset(&key_derive_key, 0, sizeof(key_derive_key));
        return false;
    }
    memset(p_derivation_buffer, 0, derivation_buffer_length);

    /*counter = 0x01 */
    p_derivation_buffer[0] = 0x01;
    /*label*/
    memcpy(&p_derivation_buffer[1], label, label_length);
    /*output_key_len=0x0080*/
    uint16_t *key_len = (uint16_t *)(&(p_derivation_buffer[derivation_buffer_length - 2]));
    *key_len = 0x0080;


    sample_ret = sample_rijndael128_cmac_msg(
                     (sample_cmac_128bit_key_t *)&key_derive_key,
                     p_derivation_buffer,
                     derivation_buffer_length,
                     (sample_cmac_128bit_tag_t *)derived_key);
    free(p_derivation_buffer);
    // memset here can be optimized away by compiler, so please use memset_s on
    // windows for production code and similar functions on other OSes.
    memset(&key_derive_key, 0, sizeof(key_derive_key));
    if (sample_ret != SAMPLE_SUCCESS) {
        return false;
    }
    return true;
}