Blog : How to implement common file encryption and decryption between c# and php

How to implement common file encryption and decryption between c# and php

Recently I got a opportunity to work with 2 different languages(c# and php) for file encryption and decryption.

But the problem is the above solution works for string encryption and decryption.When i try to implement the same for file, the file has been corrupted for docx,xlsx formats due to padding zeros.After little research, i have sorted out the issue.

Here is the code for PHP. You can also download the live samples attached in the bottom of this post

function Encrypt($source, $destination) {
 $key="passwordDR0wSS@P6660juht";
 $iv="password";
if (extension_loaded('mcrypt') === true)
 {
  if (is_file($source) === true)
  {
  $source = file_get_contents($source);
  $encryptedSource=$this->TripleDesEncrypt($source,$key,$iv);
  if (file_put_contents($destination,$encryptedSource, LOCK_EX) !== false)
  {
  return true;
  }
  return false;
  }
 return false;
 }
return false;
 }

function Decrypt($source, $destination) {
 $key="passwordDR0wSS@P6660juht";
 $iv="password";
 if (extension_loaded('mcrypt') === true)
 {
 if (is_file($source) === true)
 {
 $source = file_get_contents($source);
 $decryptedSource=self::TripleDesDecrypt($source,$key,$iv);
 if (file_put_contents($destination,$decryptedSource, LOCK_EX) !== false)
 {
 return true;
 }
 echo "no read";
 return false;
 }
 echo "no file";
 return false;
 }
 echo "no mcrypt";

return false;
 }

/*
 Apply tripleDES algorthim for encryption, append "___EOT" to encrypted file ,
 so that we can remove it while decrpytion also padding 0's
 */
 function TripleDesEncrypt($buffer,$key,$iv) {

$cipher = mcrypt_module_open(MCRYPT_3DES, '', 'cbc', '');
 $buffer.='___EOT';
 // get the amount of bytes to pad
 $extra = 8 - (strlen($buffer) % 8);
 // add the zero padding
 if($extra > 0) {
 for($i = 0; $i < $extra; $i++) {
 $buffer .= '_';
 }
 }
 mcrypt_generic_init($cipher, $key, $iv);
 $result = mcrypt_generic($cipher, $buffer);
 mcrypt_generic_deinit($cipher);
 return base64_encode($result);
 }

/*
 Apply tripleDES algorthim for decryption, remove "___EOT" from encrypted file ,
 so that we can get the real data.
 */
 function TripleDesDecrypt($buffer,$key,$iv) {
 $buffer= base64_decode($buffer);
 $cipher = mcrypt_module_open(MCRYPT_3DES, '', 'cbc', '');
 mcrypt_generic_init($cipher, $key, $iv);
 $result = mdecrypt_generic($cipher,$buffer);
 $result=substr($result,0,strpos($result,'___EOT'));
 mcrypt_generic_deinit($cipher);
 return $result;
 }

code for C#

private byte[] Encrypt(byte[] data)
 {
 string Key = "passwordDR0wSS@P6660juht";
 string IV = "password";
 string enc1 = Encoding.Default.GetString(data);
 enc1 += "___EOT";
 data = Encoding.Default.GetBytes(enc1);
 byte[] key = Encoding.ASCII.GetBytes(Key);
 byte[] iv = Encoding.ASCII.GetBytes(IV);

byte[] enc = new byte[0];
 TripleDES tdes = TripleDES.Create();
 tdes.IV = iv;
 tdes.Key = key;
 tdes.Mode = CipherMode.CBC;
 tdes.Padding = PaddingMode.Zeros;
 ICryptoTransform ict = tdes.CreateEncryptor();
 enc = ict.TransformFinalBlock(data, 0, data.Length);
 data = Encoding.UTF8.GetBytes(Convert.ToBase64String(enc));
 return data;
 }

private byte[] Decrypt(byte[] data)
 {
 string Key = "passwordDR0wSS@P6660juht";
 string IV = "password";
 byte[] enc = new byte[0];
 byte[] key = Encoding.ASCII.GetBytes(Key);
 byte[] iv = Encoding.ASCII.GetBytes(IV);
 TripleDES tdes = TripleDES.Create();
 tdes.IV = iv;
 tdes.Key = key;
 tdes.Mode = CipherMode.CBC;
 tdes.Padding = PaddingMode.Zeros;
 ICryptoTransform ict = tdes.CreateDecryptor();
 data = Convert.FromBase64String(Encoding.UTF8.GetString(data));
 enc = ict.TransformFinalBlock(data, 0, data.Length);
 string enc1 = Encoding.Default.GetString(enc);
 enc1 = enc1.Substring(0, enc1.IndexOf("___EOT"));
 enc = Encoding.Default.GetBytes(enc1);
 return enc;
}

private byte[] ReadFile(string path)
 {
 byte[] fileContents = null;

try
 {
 FileInfo ff = new FileInfo(path);
 fileContents = new byte[ff.Length];
 using (FileStream fr = ff.OpenRead())
 {
 fr.Read(fileContents, 0, Convert.ToInt32(ff.Length));
 }

}
 catch (Exception ex)
 {
 throw;
 }
 return fileContents;
 }

private void WriteFile(string path, byte[] data)
 {
 FileStream fileStream = new FileStream(path, FileMode.Create, FileAccess.Write);
 fileStream.Write(data, 0, data.Length);
 fileStream.Close();
 }