ESP32 Forum

Posted: **Fri Nov 24, 2017 10:34 am**

My aim is to load a 2048-bit RSA public key from a file which was generated using OpenSSL and then use this to encrypt a message. To do this I'm using mbedTLS functions, specifically as laid out in this tutorial: https://tls.mbed.org/kb/how-to/encrypt- ... t-with-rsa.

The key is being loaded into memory (or at least, the parsing function returns a success) but I'm getting the following error when calling the encrypt function:

Code: Select all

Guru Meditation Error of type InstrFetchProhibited occurred on core  1. Exception was unhandled.
Register dump:
PC      : 0x00000000  PS      : 0x00060030  A0      : 0x80101b10  A1      : 0x3ffd02a0
A2      : 0x3ffb64e8  A3      : 0x00000000  A4      : 0x00000000  A5      : 0x00000000
A6      : 0x00000180  A7      : 0x0000000a  A8      : 0x80101a12  A9      : 0x3ffd0290
A10     : 0x00000000  A11     : 0x3ffd02a0  A12     : 0x00000000  A13     : 0x3ffd0420
A14     : 0xacb68920  A15     : 0x00000018  SAR     : 0x00000004  EXCCAUSE: 0x00000014
EXCVADDR: 0x00000000  LBEG    : 0x4000c46c  LEND    : 0x4000c477  LCOUNT  : 0x00000000

Backtrace: 0x00000000:0x3ffd02a0 0x40101b10:0x3ffd0440 0x40101ba4:0x3ffd04a0 0x400fc985:0x3ffd04c0 0x400fca4c:0x3ffd04f0 0x40109f66:0x3ffd0520 0x40101c60:0x3ffd0550 0x400f6ae0:0x3ffd0580 0x400f6992:0x3ffd1180
0x40101b10: mbedtls_ctr_drbg_random_with_add at C:/msys32/home/esp-idf/components/mbedtls/library/ctr_drbg.c:355

0x40101ba4: mbedtls_ctr_drbg_random at C:/msys32/home/esp-idf/components/mbedtls/library/ctr_drbg.c:416

0x400fc985: mbedtls_rsa_rsaes_pkcs1_v15_encrypt at C:/msys32/home/esp-idf/components/mbedtls/library/rsa.c:1613

0x400fca4c: mbedtls_rsa_pkcs1_encrypt at C:/msys32/home/esp-idf/components/mbedtls/library/rsa.c:1613

0x40109f66: rsa_encrypt_wrap at C:/msys32/home/esp-idf/components/mbedtls/library/pk_wrap.c:56

0x40101c60: mbedtls_pk_encrypt at C:/msys32/home/esp-idf/components/mbedtls/library/pk.c:296

0x400f6ae0: rsaTest at C:/Users/aaquilina.ESDL/Desktop/Projects/ESP32/msys32/msys32/home/TG_MODEM2/main/tls_cipher.c:135

0x400f6992: sslTask at C:/Users/aaquilina.ESDL/Desktop/Projects/ESP32/msys32/msys32/home/TG_MODEM2/main/network.c:325 (discriminator 1)

The code I'm using is the following:

Code: Select all

mbedtls_pk_init( &pk );
	
	if((mbedtls_pk_parse_public_keyfile(&pk, "/spiffs/pubkey.pem")) != 0)
	{
		ESP_LOGE(TAG, "rsaInit: Public key could not be found!");
	}
	else
	{
		ESP_LOGI(TAG, "rsaInit: Public key loaded");
	}
	
	unsigned char plaintext[15] = "123456789abcde";
	unsigned char enctext[3000] = {0};
	size_t olen = 0;
	ret = 0;
	
	ret = mbedtls_pk_encrypt(&pk, plaintext, strlen("123456789abcde"),
                                    enctext, &olen, 3000,
                                    mbedtls_ctr_drbg_random, &ctr_drbg);
	 if(ret != 0 )
    {
       ESP_LOGE(TAG, "Failure to encrypt message with error value%d", ret);
    }

Can anyone tell me why this is occuring?

Posted: **Sun Mar 11, 2018 12:15 am**

Looking at your trace, the failure appears to be occurring within the ctr_drbg module. In your snippet, you aren't showing the initialization of ctr_drbg. Are you doing that correctly?

When I get errors like this, I have found that spending time with JTAG debugging and stepping into the source to identify the actual source statement and contextual data has helped me well.

Posted: **Tue Oct 09, 2018 11:55 pm**

Hi, mpulis! Did you find a way to make it work? I'm just trying to do the same thing.

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