ESP32: AES-CBC library

[gandalfthegray]

Hi all
Any library to encrypt and decrypt (easily) with AES-256 CBC ? (a 128 should be ok too, but I prefere 256).

I've tried a couple of libs without success. What I need is something that takes a base64 encoded string as input, decode, decrypt and put the decrypted content (a json) in a string/char array.

[johnwasser]

Did your Google serach turn up this project?

https://gist.github.com/cnlohr/96128ef4126bcc878b1b5a7586c624ef

See "!!!!" marks for the two changes needed.

#include <string.h>
#include <stdio.h>
#include <aes/esp_aes.h>  // !!!! Was <hwcrypto/es.h>

/*
  For  Encryption time: 1802.40us  (9.09 MB/s) at 16kB blocks.
*/

static inline int32_t _getCycleCount(void)
{
  int32_t ccount;
  __asm__ __volatile__("rsr %0,ccount":"=a" (ccount));
  return ccount;
}

char plaintext[16384];
char encrypted[16384];


void encodetest()  // !!!! Was 'int encodetest()'
{
  uint8_t key[32];
  uint8_t iv[16];

  //If you have cryptographically random data in the start of your payload, you do not need
  //an IV.  If you start a plaintext payload, you will need an IV.
  memset( iv, 0, sizeof( iv ) );

  //Right now, I am using a key of all zeroes.  This should change.  You should fill the key
  //out with actual data.
  memset( key, 0, sizeof( key ) );

  memset( plaintext, 0, sizeof( plaintext ) );
  strcpy( plaintext, "Hello, world, how are you doing today?" );

  //Just FYI - you must be encrypting/decrypting data that is in BLOCKSIZE chunks!!!

  esp_aes_context ctx;
  esp_aes_init( &ctx );
  esp_aes_setkey( &ctx, key, 256 );
  int32_t start = _getCycleCount();
  esp_aes_crypt_cbc( &ctx, ESP_AES_ENCRYPT, sizeof(plaintext), iv, (uint8_t*)plaintext, (uint8_t*)encrypted );
  int32_t end = _getCycleCount();
  float enctime = (end - start) / 240.0;
  printf( "Encryption time: %.2fus  (%f MB/s)\n", enctime, (sizeof(plaintext) * 1.0) / enctime );

  //See encrypted payload, and wipe out plaintext.
  memset( plaintext, 0, sizeof( plaintext ) );
  int i;
  for ( i = 0; i < 128; i++ )
  {
    printf( "%02x[%c]%c", encrypted[i], (encrypted[i] > 31) ? encrypted[i] : ' ', ((i & 0xf) != 0xf) ? ' ' : '\n' );
  }
  printf( "\n" );
  //Must reset IV.
  //XXX TODO: Research further: I found out if you don't reset the IV, the first block will fail
  //but subsequent blocks will pass.  Is there some strange cryptoalgebra going on that permits this?
  printf( "IV: %02x %02x\n", iv[0], iv[1] );
  memset( iv, 0, sizeof( iv ) );


  //Use the ESP32 to decrypt the CBC block.
  esp_aes_crypt_cbc( &ctx, ESP_AES_DECRYPT, sizeof(encrypted), iv, (uint8_t*)encrypted, (uint8_t*)plaintext );


  //Verify output
  for ( i = 0; i < 128; i++ )
  {
    printf( "%02x[%c]%c", plaintext[i],  (plaintext[i] > 31) ? plaintext[i] : ' ', ((i & 0xf) != 0xf) ? ' ' : '\n' );
  }
  printf( "\n" );


  esp_aes_free( &ctx );
}