# AES Encryption Padding Problem

**URL:** <https://community.particle.io/t/aes-encryption-padding-problem/26869>\
**Category:** Firmware\
**Created:** [October 29, 2016, 4:07pm UTC](https://community.particle.io/t/aes-encryption-padding-problem/26869 "2016-10-29T16:07:51Z")\
**Posts on this page:** 1\
**Page:** 1

<div class="post-metadata">

**Author:** ![skasat](https://avatars.discourse-cdn.com/v4/letter/s/f14d63/32.png) [@skasat](https://community.particle.io/u/skasat)\
**Post date:** [October 29, 2016, 4:07pm UTC](https://community.particle.io/t/aes-encryption-padding-problem/26869/1 "2016-10-29T16:07:51Z")

</div>

Hello,

I am using AES-128\_ECB encryption and I have imported the tropicssl library. I am encrypting it and then encoding it to Base64. But I am having a lot of extra padding. Is there any way to remove the padding, or customise the padding? Like I want to pad it with b’\x10’.

Here is the Base64 Output that I am getting- Ouril+UTDF8htLzEhiRj7wAPDw9PdXJpbCtVVERGOGg=  
Converted- b’0123456789012345\xde8\x1d\xea\xc0\xc2d\x10z\xed0\xf6\x88\xaa\t\xfb’  
And I should have got- b’Ouril+UTDF8htLzEhiRj7w==‘  
Original Message- b’0123456789012345’

See the extra padding is something which I want to avoid/ remove/ customise… Any of those will work!  
Here is the code-

```
size_t pad(unsigned char *buf, size_t messageLength) {
  size_t paddedLength = (messageLength & ~15) + 16;
  char pad = paddedLength - messageLength;
  memset(buf + messageLength, pad, pad);
  return paddedLength;
}

void demoAES() {
  aes_context aes;
  unsigned char key[17]="2222222222222222";
  
  unsigned char buf[17];

  Serial.println("Key:");
  Serial.println((const char *)key);

  // Our super secret message goes into buf
  const char *original = "0123456789012345";
  int length = strlen(original) + 1; // include null terminating byte
  memcpy(buf, original, length);
  unsigned char ta[]= "0000000000000000";
  unsigned char *encoded= ta;
  // Esoterica: add PKCS #7 padding
  size_t paddedLength = pad(buf, length);
  char *temp="0123456789012345";
  // Print the plaintext directly
  Serial.println("\nPlaintext:");
  Serial.println((const char *)buf);

  // buf is unsigned char[]
  // encoded is char*
  // original is const char*
  // Encrypt
  aes_setkey_enc(&aes, key, 128); // aes_context * ctx, const unsigned char *key, int keysize
  aes_crypt_ecb(&aes, AES_ENCRYPT, buf, buf); // aes_context * ctx, int mode, const unsigned char input[16], unsigned char output[16]
  base64_encode(encoded,buf,paddedLength); // char *output, char *input, int inputLen
  // Print the ciphertext directly
  Serial.println("\nBase64text:");
  Serial.println((const char *)encoded);

  // Decrypt
  // IV has been modified, so use original copy
  base64_decode(buf,encoded,16); // char * output, char * input, int inputLen
  Serial.println("\nDECODED");
  Serial.println((const char *)buf);
  aes_setkey_dec(&aes, key, 128); // aes_context * ctx, const unsigned char *key, int keysize
  aes_crypt_ecb(&aes, AES_DECRYPT, buf, buf); // aes_context * ctx, int mode, const unsigned char input[16], unsigned char output[16]

  // Print the plaintext directly
  Serial.println("\nPlaintext (after decrypting):");
  Serial.println((const char *)buf);

  Serial.println("\n-------------\n");
}
```