AES CFB 256 bit encrypt the output is longer than the input?

Question

I want to ask something, what makes a difference in the output below that these two programs vb.net 2010 and the dynamic c? Why the length of the encrypted data different results (vb.net - 16 byte = 0x878e086ec00cbfeaafc9fc91edc8294c and dynamic C - 10 byte = 0x878e086ec00cbfeaafc9), although using key, initial vector(IV) and plaint text the same. Which is correct output? THANKYOU

I am trying to Encrypt Decrypt using AES CFB 256 BIT used vb.net 2010, the result like this:

Key : 0x603deb1015ca71be2b73aef0857d77811f352c073b6108d72d9810a30914dff4 (256 bit = 32 BYTE)

IV : 0x000102030405060708090A0B0C0D0E0F (16 byte)

Plaintext : 0123456789 (10 byte)

Encrypt : 0x878e086ec00cbfeaafc9fc91edc8294c (16 byte) ????? longer 6byte than Plaintext = fc91edc8294c

Decrypt : 0123456789 (10 byte)

And Encrypt Decrypt using AES CFB 256 BIT used Dynamic C, the result like this:

Key : 0x603deb1015ca71be2b73aef0857d77811f352c073b6108d72d9810a30914dff4 (256 bit = 32 BYTE)

IV : 0x000102030405060708090A0B0C0D0E0F (16 byte)

Plaintext : 0123456789 (10 byte)

Encrypt : 0x878e086ec00cbfeaafc9 (10 byte) ????? length same equal with Plaintext

Decrypt : 0123456789 (10 byte)

---

' VB.NET

Imports System
Imports System.IO
Imports System.Security.Cryptography
Imports System.Text

Public Class Form1

Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load

    Dim original As String = "0123456789"
    Dim roundtrip As String
    Dim textConverter As New ASCIIEncoding()
    Dim myRijndael As New RijndaelManaged()
    Dim fromEncrypt() As Byte
    Dim encrypted() As Byte
    Dim toEncrypt() As Byte
    Dim key() As Byte
    Dim IV() As Byte

    'Create a new key and initialization vector.
    'myRijndael.GenerateKey()
    'myRijndael.GenerateIV()

    Debug.Print("Original:   " & original)

    myRijndael.Mode = CipherMode.CFB
    myRijndael.BlockSize = 128
    myRijndael.KeySize = 256
    myRijndael.Key = StringToByteArray("603deb1015ca71be2b73aef0857d77811f352c073b6108d72d9810a30914dff4")
    myRijndael.IV = StringToByteArray("000102030405060708090A0B0C0D0E0F")


    'Get the key and IV.
    key = myRijndael.Key
    IV = myRijndael.IV

    'Get an encryptor.
    Dim encryptor As ICryptoTransform = myRijndael.CreateEncryptor(key, IV)

    'Encrypt the data.
    Dim msEncrypt As New MemoryStream()
    Dim csEncrypt As New CryptoStream(msEncrypt, encryptor, CryptoStreamMode.Write)

    'Convert the data to a byte array.
    toEncrypt = textConverter.GetBytes(original)

    'Write all data to the crypto stream and flush it.
    csEncrypt.Write(toEncrypt, 0, toEncrypt.Length)
    csEncrypt.FlushFinalBlock()

    'Get encrypted array of bytes.
    encrypted = msEncrypt.ToArray()
    Debug.Print("Encrypted:  " & ByteArrayToString(encrypted))

    'This is where the message would be transmitted to a recipient
    ' who already knows your secret key. Optionally, you can
    ' also encrypt your secret key using a public key algorithm
    ' and pass it to the mesage recipient along with the RijnDael
    ' encrypted message.            
    'Get a decryptor that uses the same key and IV as the encryptor.
    Dim decryptor As ICryptoTransform = myRijndael.CreateDecryptor(key, IV)

    'Now decrypt the previously encrypted message using the decryptor
    ' obtained in the above step.
    Dim msDecrypt As New MemoryStream(encrypted)
    Dim csDecrypt As New CryptoStream(msDecrypt, decryptor, CryptoStreamMode.Read)

    fromEncrypt = New Byte(encrypted.Length) {}

    'Read the data out of the crypto stream.
    csDecrypt.Read(fromEncrypt, 0, fromEncrypt.Length)

    'Convert the byte array back into a string.
    roundtrip = textConverter.GetString(fromEncrypt)

    'Display the original data and the decrypted data.
    Debug.Print("Decrypt:    " & roundtrip)
    Debug.Print("")

End Sub

Public Function ByteArrayToString(ByVal ba As Byte()) As String
    Dim hex As New StringBuilder(ba.Length * 2)
    For Each b As Byte In ba
        hex.AppendFormat("{0:x2}", b)
    Next
    Return hex.ToString()
End Function

Public Function StringToByteArray(ByVal hex As [String]) As Byte()
    Dim NumberChars As Integer = hex.Length
    Dim bytes As Byte() = New Byte(NumberChars \ 2 - 1) {}
    For i As Integer = 0 To NumberChars - 1 Step 2
        bytes(i \ 2) = Convert.ToByte(hex.Substring(i, 2), 16)
    Next
    Return bytes
End Function

End Class

---

//////////////////////////////////////
//DYNAMIC C
//////////////////////////////////////
#use AES_CRYPT.LIB
#define AES_BLOCK_SIZE 16
#define BUFFER_SIZE 128

const char AES_KEY[AES_BLOCK_SIZE * 2] = {
  '\x60', '\x3d', '\xeb', '\x10', '\x15', '\xca', '\x71', '\xbe',
  '\x2b', '\x73', '\xae', '\xf0', '\x85', '\x7d', '\x77', '\x81',
  '\x1f', '\x35', '\x2c', '\x07', '\x3b', '\x61', '\x08', '\xd7',
  '\x2d', '\x98', '\x10', '\xa3', '\x09', '\x14', '\xdf', '\xf4',
};

const char AES_IV[AES_BLOCK_SIZE] = {
  '\x00', '\x01', '\x02', '\x03', '\x04', '\x05', '\x06', '\x07',
  '\x08', '\x09', '\x0A', '\x0B', '\x0C', '\x0D', '\x0E', '\x0F',
};


void ENC_AES_CFB_256(char data_in[], char data_out[]){
  static char buffer[BUFFER_SIZE];
  AESstreamState state;

  memset(buffer,'\0',sizeof(buffer));
  AESinitStream256(&state, AES_KEY, AES_IV);
  memcpy(buffer, data_in, strlen(data_in));
  AESencryptStream(&state, buffer, strlen(buffer));
  strcpy(data_out, buffer);
}

void DEC_AES_CFB_256(char data_in[], char data_out[]){
  static char buffer[BUFFER_SIZE];
  AESstreamState state;

  memset(buffer,'\0',sizeof(buffer));
  AESinitStream256(&state, AES_KEY, AES_IV);
  memcpy(buffer, data_in, strlen(data_in));
  AESdecryptStream(&state, buffer, strlen(buffer));
  strcpy(data_out, buffer);
}


int main(void) {
  static char ot[128], buf1[128];
  int i;

  memset(ot,'\0',sizeof(ot));
  memset(buf1,'\0',sizeof(buf1));

  ENC_AES_CFB_256("0123456789", ot);
  for (i = 0; i < strlen(ot); i++) {
    printf("%02x", ot[i]);
  }
  printf("\n");

  DEC_AES_CFB_256(ot, buf1);
  for (i = 0; i < strlen(buf1); i++) {
    printf(" %c ", buf1[i]);
  }
  printf("\n");

  return 0;
}

/////////////////////////////////////// UPDATE FOR DYNAMIC C //////////////////////////////////////

    #class auto

    #use AES_CRYPT.LIB

    #define AES_BLOCK_SIZE    16  // BYTE
    #define MD5_BLOCK_SIZE    16  // BYTE
    #define AES_BUFFER_SIZE   128 // BYTE

    const char AES_KEY[AES_BLOCK_SIZE * 2] = {
      '\x60', '\x3d', '\xeb', '\x10', '\x15', '\xca', '\x71', '\xbe',
      '\x2b', '\x73', '\xae', '\xf0', '\x85', '\x7d', '\x77', '\x81',
      '\x1f', '\x35', '\x2c', '\x07', '\x3b', '\x61', '\x08', '\xd7',
      '\x2d', '\x98', '\x10', '\xa3', '\x09', '\x14', '\xdf', '\xf4',
    };

    const char AES_IV[AES_BLOCK_SIZE] = {
      '\x00', '\x01', '\x02', '\x03', '\x04', '\x05', '\x06', '\x07',
      '\x08', '\x09', '\x0A', '\x0B', '\x0C', '\x0D', '\x0E', '\x0F',
    };


    /////////////////// AES CFB - KEY: 32 Byte (256 bit) and BLOCK: 16 byte (128 bit) ///////////////////

    void ENC_AES_CFB_32(char data_in[], char data_out[], int count) { 
       AESstreamState enc_state;
       static char enc_buffer[AES_BUFFER_SIZE];

       memset(enc_buffer,'\0', sizeof(enc_buffer));
       memcpy(enc_buffer, data_in, count);
       enc_buffer[count]='\0';

       AESinitStream256(&enc_state, AES_KEY, AES_IV);
       AESencryptStream(&enc_state, enc_buffer, sizeof(enc_buffer));

       memcpy(data_out, enc_buffer, count);
       data_out[count]='\0';
    }

    void DEC_AES_CFB_32(char data_in[], char data_out[], int count){
       AESstreamState dec_state;
       static char dec_buffer[AES_BUFFER_SIZE];

       memset(dec_buffer,'\0', sizeof(dec_buffer));
       memcpy(dec_buffer, data_in, count);
       dec_buffer[count]='\0';

       AESinitStream256(&dec_state, AES_KEY, AES_IV);
       AESdecryptStream(&dec_state, dec_buffer, sizeof(dec_buffer));

       memcpy(data_out, dec_buffer, count);
       data_out[count]='\0';
    }


    ////////////// MAIN PROGRAM ////////////////////

    int main(void) {

       static char in[AES_BUFFER_SIZE], ot[AES_BUFFER_SIZE], buf[AES_BUFFER_SIZE];
       int i, cnt;

       ////////////// INITIALIZE INPUT CFB ////////////////////

       memset(in,'\0',sizeof(in));          // CLEAR INPUT BUFFER

       //// DATA INPUT (TEST 1)  ////
       //cnt = 10;                           // DATA INPUT LENGTH
       //sprintf(in,"%s","0123496785");      // DATA INPUT

       //// DATA INPUT (TEST 2) ////
      cnt = 82;                            // DATA INPUT LENGTH
      sprintf(in,"%s","0123456789abcdefghijklmnopqrstuvwxyz!@#$%^&*()_+{}|:L<>?ABCDEFGHIJKLMNOPQRSTUVWXYZ"); // DATA INPUT   

      printf("PLAINT TEXT : %s", in);      // PRINT INPUT
      printf("\n\n");


      ////////////// TEST ENCRYPT WITH CFB ////////////////////

      memset(ot,'\0',sizeof(ot));     // CLEAR OUTPUT BUFFER

      ENC_AES_CFB_32(in, ot, cnt);    // CALL ENCRYPT FUNCTION

      printf("ENCRYPT     : ");       // PRINT OUTPUT
      for (i = 0; i < cnt; i++){
         printf("%02x", ot[i]);
      }
      printf("\n\n");


      ////////////// TEST DECRYPT WITH CFB ////////////////////

      memset(buf,'\0',sizeof(buf));     // CLEAR OUTPUT BUFFER

      DEC_AES_CFB_32(ot, buf, cnt);     // CALL DECRYPT FUNCTION

      printf("DECRYPT     : ");         // PRINT OUTPUT
      for (i = 0; i < cnt; i++) {
         printf("%c", buf[i]);
      }
      printf("\n\n");

      return 0;

    }


    /////////////  OUTPUT TEST 1 ////////////

    // PLAINT TEXT : 0123496785
    // ENCRYPT     : 878e086ec000bfeaafc5
    // DECRYPT     : 0123496785

     /////////////  OUTPUT TEST 2 ////////////

     // PLAINT TEXT : 0123456789abcdefghijklmnopqrstuvwxyz!@#$%^&*()_+{}|:L<>?ABCDEFGHIJKLMNOPQRSTUVWXYZ
     // ENCRYPT     : 878e086ec00cbfeaafc99bf588aa4a2cbefd574850365f17d882f1dd19fa601e80bbcf845a5f213800d72a5ab8b1aafc87df077ed8695c92e38ce8d3b54071d87274349f806b8afae15f6f3730dbaf8dc4c5
     // DECRYPT     : 0123456789abcdefghijklmnopqrstuvwxyz!@#$%^&*()_+{}|:L<>?ABCDEFGHIJKLMNOPQRSTUVWXYZ

Answer 1

The problem is that your VB code is using PKCS #5 padding (PKCS7 in .NET).

You shouldn't use padding with CFB; as a stream mode, there's never a partial block that needs padding. .NET, however, sets PKCS7 padding as the default. Explicitly override it like this:

…
myRijndael.Mode = CipherMode.CFB
myRijndael.Padding = PaddingMode.None
…

Answer 2

Using strlen and strcpy on the cipher text in the C program may be part of the problem. The encrypted data could easily have zeros in it, so it would not be reliable to use those C functions which expect NULL terminated strings. That may not be the issue in this particular situation, but eventually it would likely cause a problem and result in a bug.