ESP_AES.cpp

#include <Arduino.h>
#include <mbedtls/aes.h>

#define PROCESS_FAIL -1

int encrypt(uint8_t *input, uint8_t size, uint8_t key[16], uint8_t *encrypt) {
  mbedtls_aes_context encryptContext;
  uint8_t iv[16] = {0};
  int ret = 0;
  
  uint8_t msgBuff[size];
  memset(msgBuff, 0, size);
  memcpy(msgBuff, input, size);

  // initial context
  mbedtls_aes_init(&encryptContext);
  ret = mbedtls_aes_setkey_enc(&encryptContext, key, 256);
  if (ret) return PROCESS_FAIL;

  // encryption
  ret = mbedtls_aes_crypt_cbc(&encryptContext, ESP_AES_ENCRYPT, size, iv, msgBuff, encrypt);
  if (ret) return PROCESS_FAIL;

  return size;
}

int decrypt(uint8_t *input, size_t size, uint8_t key[16], uint8_t *decrypt) {
  mbedtls_aes_context decryptContext;
  uint8_t iv[16] = {0};
  int ret = 0;

  if (size % 16) return PROCESS_FAIL;

  uint8_t msgBuff[size];
  memset(msgBuff, 0, size);
  memcpy(msgBuff, input, size);

  // initial context
  mbedtls_aes_init(&decryptContext);
  ret = mbedtls_aes_setkey_dec(&decryptContext, key, 256);
  if (ret) return PROCESS_FAIL;

  // decryption
  ret = mbedtls_aes_crypt_cbc(&decryptContext, ESP_AES_DECRYPT, size, iv, msgBuff, decrypt);
  if (ret) return PROCESS_FAIL;

  return size;
}

size_t calAESBlockSize(size_t size) {
  int blockSizeRemain = (size % 16 == 0) ? 0 : 16 - (size % 16);
  int totalMsgBuffSize = size + blockSizeRemain;
  return totalMsgBuffSize;
}

void setup() {
  // put your setup code here, to run once:
  Serial.begin(115200);

  const char key[16] = "this is a key";
  String plaintext = "Welcome to I AM {TEAM}";
  int ret = PROCESS_FAIL;
  size_t buffSize = calAESBlockSize(plaintext.length());
  uint8_t buffEncrypt[buffSize] = {0};
  uint8_t buffDecrypt[buffSize] = {0};


  ret = encrypt((uint8_t *)plaintext.c_str(), buffSize, (uint8_t *)key, buffEncrypt);
  if (ret == PROCESS_FAIL) return;

  ret = decrypt(buffEncrypt, buffSize, (uint8_t *)key, buffDecrypt);
  if (ret == PROCESS_FAIL) return;

  Serial.printf("before encrypt %s \nAfter encrypt ", plaintext.c_str());
  for (uint8_t buff : buffEncrypt) {
    Serial.print((char)buff);
  } Serial.println();

  Serial.printf("After decrypt ");
  for (uint8_t buff : buffDecrypt) {
    Serial.print((char)buff);
  } Serial.println();
  
}

void loop() {
  // put your main code here, to run repeatedly:
}