RE: How to do key derivation with PBKDF2 with HMAC with ARM PSA Crypto

Hieu — Wed, 03 Apr 2024 11:25:44 GMT

Hi Max,

It looks like you haven't setup the key correctly and haven't imported it yet.

Error 137 is PSA_ERROR_BAD_STATE, and the documentation for psa_key_derivation_output_key() suggests it could be that issue.

Could you please refer to this documentation and see if it helps?
https://mbed-tls.readthedocs.io/en/latest/getting_started/psa/#deriving-a-new-key-from-an-existing-key.

Hieu

RE: How to do key derivation with PBKDF2 with HMAC with ARM PSA Crypto

Max Peter — Tue, 02 Apr 2024 22:26:26 GMT

I tried following the ARM Crypto API documentation:
https://arm-software.github.io/psa-api/crypto/1.2/api/ops/kdf.html#c.PSA_ALG_PBKDF2_HMAC

Still failing with "psa_key_derivation_output_key failed! (Error: -137)"
(code tested inside Thread CLI sample)

Am I missing am Kconfig setting?
Notably, CONFIG_PSA_WANT_ALG_PBKDF2_HMAC cannot be set in prj.conf (unknown symbol) and setting it in later in build/zephyr/.config with nRF Kconfig GUI didn't help either.

#include <psa/crypto.h>

#include <psa/crypto_extra.h>

#define PRINT_HEX(p_label, p_text, len)\

({\

LOG_INF("---- %s (len: %u): ----", p_label, len);\

LOG_HEXDUMP_INF(p_text, len, "Content:");\

LOG_INF("---- %s end ----", p_label);\

})

void testPBKDF()

{

const uint8_t password[] = "my_secret_password";

const size_t password_length = sizeof(password) - 1;

const uint8_t salt[] = { 0x12, 0x34, 0x56, 0x78 };

const size_t salt_length = sizeof(salt);

const size_t iteration_count = 1000;

const size_t key_length = 32; // Desired key length in bytes

uint8_t key[32];

psa_status_t status;

psa_key_attributes_t key_attributes = PSA_KEY_ATTRIBUTES_INIT;

psa_key_id_t output_key_id;

size_t olen;

/* Initialize PSA Crypto */

status = psa_crypto_init();

if(status != PSA_SUCCESS) goto error;

psa_key_derivation_operation_t operation = PSA_KEY_DERIVATION_OPERATION_INIT;

psa_set_key_lifetime(&key_attributes, PSA_KEY_LIFETIME_VOLATILE);

psa_set_key_type(&key_attributes, PSA_KEY_TYPE_RAW_DATA);

psa_set_key_usage_flags(&key_attributes, PSA_KEY_USAGE_EXPORT); /* DONT USE IN PRODUCTION */

psa_set_key_bits(&key_attributes, key_length * 8);

/* Set the derivation algorithm */

status = psa_key_derivation_setup(&operation, PSA_ALG_PBKDF2_HMAC(PSA_ALG_SHA_256));

if (status != PSA_SUCCESS) { LOG_INF("psa_key_derivation_setup failed! (Error: %d)", status);

goto error; }

status = psa_key_derivation_input_integer(&operation, PSA_KEY_DERIVATION_INPUT_COST, iteration_count);

if (status != PSA_SUCCESS) { LOG_INF("psa_key_derivation_input_integer failed! (Error: %d)", status);

goto error; }

/* Set the salt for the operation */

status = psa_key_derivation_input_bytes(&operation, PSA_KEY_DERIVATION_INPUT_SALT, salt, salt_length);

if (status != PSA_SUCCESS) { LOG_INF("psa_key_derivation_input_bytes (salt) failed! (Error: %d)", status);

goto error; }

/* Set the password for the operation */

status = psa_key_derivation_input_bytes(&operation, PSA_KEY_DERIVATION_INPUT_SALT, password, password_length);

if (status != PSA_SUCCESS) { LOG_INF("psa_key_derivation_input_bytes (password) failed! (Error: %d)", status);

goto error; }

/* Store the derived key in the keystore slot pointed by out_key_id */

status = psa_key_derivation_output_key(&key_attributes, &operation, &output_key_id);

if (status != PSA_SUCCESS) { LOG_INF("psa_key_derivation_output_key failed! (Error: %d)", status);

goto error; }

/* Clean up the context */

status = psa_key_derivation_abort(&operation);

if (status != PSA_SUCCESS) { LOG_INF("psa_key_derivation_abort failed! (Error: %d)", status);

goto error; }

status = psa_export_key(output_key_id, key, key_length, &olen);

if (status != PSA_SUCCESS) { LOG_INF("psa_export_key failed! (Error: %d)", status);

goto error; }

status = psa_destroy_key(output_key_id);

if (status != PSA_SUCCESS) { LOG_INF("psa_destroy_key failed! (Error: %d)", status);

goto error; }

LOG_INF("Key derivation successful len=%d!", olen);

PRINT_HEX("Output key", key, key_length);

return;

error:

LOG_INF("PSA Error %d", status);

}