How to get the 64-byte signature from secure element (ATECC608B) in esp-idf

Question

I'm trying to get the 64-byte signature after signing (ATECC608B) from buf, but the returned size is 72, and sometimes varies between 70-72, depending on the size of hash. Any ideas on how I can get hold of the 64-byte signature?

ESP_LOGI(TAG, " Generating ECDSA Signature...");
ret = mbedtls_pk_sign(&pkey, MBEDTLS_MD_SHA256, hash, 0, buf, MBEDTLS_MPI_MAX_SIZE, &olen,
                          mbedtls_ctr_drbg_random, &ctr_drbg);
if (ret != 0)
{
  ESP_LOGI(TAG, " failed ! mbedtls_pk_sign returned -0x%04x", -ret);
  goto exit;
}
ESP_LOGI(TAG, " ok");

and here is how i'm trying to print it:

ESP_LOGI(TAG, "Signature:");
ESP_LOGW(TAG, "%i", olen);
ESP_LOG_BUFFER_HEX_LEVEL(TAG, buf, olen, ESP_LOG_WARN);

I (649) atecc_example: Signature:
W (649) atecc_example: 72
W (649) atecc_example: 30 46 02 21 00 f6 8b 21 9f 60 47 d3 f7 99 e0 a4 
W (649) atecc_example: a1 0b df 4d d3 78 36 3e d1 0c 2c 34 4c 14 39 6d 
W (659) atecc_example: 2f 5c cb 43 bc 02 21 00 bd 20 87 ed fa fa 81 db 
W (669) atecc_example: 02 df 82 0e 3c 3d 5a 35 c3 6b c5 0d cb 35 d2 e1 
W (679) atecc_example: 7b 3a 3a ca 21 59 6b cc 

The example seems to sign and verify the message successfully, but my problem is getting the 64-byte signature.

Appreciate any advice!

Links: Example code Datasheet