Develop Reference

Length of the key to encrypt a file

Many years ago I used this code to encrypt an entire file:
public static void CryptFile(string sInputFilename, string sOutputFilename, string sKey)
{
FileStream fsInput = new FileStream(sInputFilename, FileMode.Open, FileAccess.Read);
FileStream fsEncrypted = new FileStream(sOutputFilename, FileMode.Create, FileAccess.Write);
DESCryptoServiceProvider DES = new DESCryptoServiceProvider();
DES.Key = ASCIIEncoding.ASCII.GetBytes(sKey);
DES.IV = ASCIIEncoding.ASCII.GetBytes(sKey);
ICryptoTransform desencrypt = DES.CreateEncryptor();
CryptoStream cryptostream = new CryptoStream(fsEncrypted,desencrypt,CryptoStreamMode.Write);
byte[] bytearrayinput = new byte[fsInput.Length];
fsInput.Read(bytearrayinput, 0, bytearrayinput.Length);
cryptostream.Write(bytearrayinput, 0, bytearrayinput.Length);
cryptostream.Close();
fsInput.Close();
fsEncrypted.Close();
}
Today I tried to use it again but I always get this error:
the specified key size is not valid for this algorithm.
I have tried with many strings of varying length but cannot understand which is the correct length to use.

The correct length is 8 characters, such as "12345678"

C# encryption and decryption IV issue

My code performs encryption but not decryption. I wanted it to generate random IV so made some changes, but now it's not decrypting. I think I am messing up with IV. It doesn't seem that it is able to decrypt properly.
The IV is not getting prefixed to the encrypted file or the decrypt method is unable to find IV. I can't understand how to solve it. The file is produced for example I encrypted a text file which had "hello world", after encryption it produced some gibberish. After decryption it produced a empty text file.
encryption method:
private const ushort ITERATIONS = 1300;
private static readonly byte[] SALT = new byte[] { 0x26, 0xdc, 0xff, 0x00, 0xad, 0xed, 0x7a, 0xee, 0xc5, 0xfe, 0x07, 0xaf, 0x4d, 0x08, 0x22, 0x3c };
private static byte[] CreateKey(string password, int keySize)
{
DeriveBytes derivedKey = new Rfc2898DeriveBytes(password, SALT, ITERATIONS);
return derivedKey.GetBytes(keySize >> 3);
}
public static void EncryptFile(string file, string password)
{
// First we are going to open the file streams
FileStream fsIn = new FileStream(file, FileMode.Open, FileAccess.Read);
FileStream fsOut = new FileStream(file+"enc", FileMode.OpenOrCreate, FileAccess.Write);
// Then we are going to derive a Key and an IV from the
// Password and create an algorithm
byte[] passwordBytes = Encoding.UTF8.GetBytes(password);
// passwordBytes = SHA256.Create().ComputeHash(passwordBytes);
RijndaelManaged AES = new RijndaelManaged();
AES.KeySize = AES.LegalKeySizes[0].MaxSize;
AES.BlockSize = AES.LegalBlockSizes[0].MaxSize;
AES.Padding = PaddingMode.Zeros;
AES.GenerateIV();
AES.Key = CreateKey(password, AES.KeySize);
AES.Mode = CipherMode.CBC;
using (MemoryStream memStream = new MemoryStream(file.Length))
memStream.Write(AES.IV, 0, 16);
CryptoStream cs = new CryptoStream(fsOut, AES.CreateEncryptor(), CryptoStreamMode.Write);
int bufferLen = 4096;
byte[] buffer = new byte[bufferLen];
int bytesRead;
do
{
// read a chunk of data from the input file
bytesRead = fsIn.Read(buffer, 0, bufferLen);
// encrypt it
cs.Write(buffer, 0, bytesRead);
} while (bytesRead != 0);
// close everything
// this will also close the unrelying fsOut stream
cs.Close();
fsIn.Close();
}
decryption method:
private const ushort ITERATIONS = 1300;
private static readonly byte[] SALT = new byte[] { 0x26, 0xdc, 0xff, 0x00, 0xad, 0xed, 0x7a, 0xee, 0xc5, 0xfe, 0x07, 0xaf, 0x4d, 0x08, 0x22, 0x3c };
private static byte[] CreateKey(string password, int keySize)
{
DeriveBytes derivedKey = new Rfc2898DeriveBytes(password, SALT, ITERATIONS);
return derivedKey.GetBytes(keySize >> 3);
}
public static void DecryptFile(string fileIn, string Password)
{
// First we are going to open the file streams
FileStream fsIn = new FileStream(fileIn,FileMode.Open, FileAccess.Read);
string extension = System.IO.Path.GetExtension(fileIn);
string result = fileIn.Substring(0, fileIn.Length - extension.Length);
FileStream fsOut = new FileStream(result,FileMode.OpenOrCreate, FileAccess.Write);
// passwordBytes = SHA256.Create().ComputeHash(passwordBytes);
RijndaelManaged AES = new RijndaelManaged();
AES.KeySize = AES.LegalKeySizes[0].MaxSize;
AES.BlockSize = AES.LegalBlockSizes[0].MaxSize;
AES.Padding = PaddingMode.Zeros;
byte[] iv = new byte[16];
fsIn.Read(iv, 0, 16);
AES.IV=iv;
AES.Key = CreateKey(Password, AES.KeySize);
AES.Mode = CipherMode.CBC;
// Now create a crypto stream through which we are going
// to be pumping data.
// Our fileOut is going to be receiving the Decrypted bytes.
CryptoStream cs = new CryptoStream(fsOut,
AES.CreateDecryptor(), CryptoStreamMode.Write);
// Now will will initialize a buffer and will be
// processing the input file in chunks.
// This is done to avoid reading the whole file (which can be
// huge) into memory.
int bufferLen = 4096;
byte[] buffer = new byte[bufferLen];
int bytesRead;
do
{
// read a chunk of data from the input file
bytesRead = fsIn.Read(buffer, 0, bufferLen);
// Decrypt it
cs.Write(buffer, 0, bytesRead);
} while (bytesRead != 0);
// close everything
cs.Close(); // this will also close the unrelying fsOut stream
fsIn.Close();
}

You must specify a block size of 128-bits (16-bytes) for the encryption to be AES, see options below:
Generally the iv is the same size as the block size. You are supplying a 16-byte iv and the Rijndael maximum block size is 32-bytes so there is a very good chance that the encryption routines are using an additional 16-bytes of junk bytes following the iv.
There are a few problems: The class is Rijndael and AES is a subset of Rijndael so allowable parameters of Rijndael may not be allowable for AES.
LegalBlockSizes[0].MaxSize will return the maximum Rijndael block size of 256-bits but AES has a fixed block size of 128-bits. Thus you are not actually using AES. You must specify a block size of 128-bits (16-bytes).
PaddingMode.Zeros will not work if the last byte of the data to be encrypted is a 0x00 byte. Generally PKCS#7 (archaically PKCS#5) is used, PHP mcrypt excepted. -- Thanks to ArtjomB.
As prompted by ArtjomB.
If I am correct there are two options,choose one of the options:
1: Change the block size to 16-bytes as required by AES:
Change to encryption and decryption:
AES.BlockSize = 128;
2: Use a 32-byte iv (note that this will not produce AES encryption):
Change to encryption:
memStream.Write(AES.IV, 0, 32);
Change to decryption:
byte[] iv = new byte[32];
fsIn.Read(iv, 0, 32

Building on the results of zaph's answer...
You need to write the IV to the file, not to some temporary MemoryStream that you're never using:
fsOut.Write(AES.IV, 0, 32);
And completely remove the line using (MemoryStream memStream = new MemoryStream(file.Length)).
This seems be the issue when reading in the comments:
the file is produced for example I encrypted a text file which had "hello world" , after encryption it produced some gibberish. after decryption it produced a empty text file
This means that the actual ciphertext is empty and there is nothing to decrypt. The happens, because the IV wasn't actually written to the ciphertext file and therefore the decryption method thought that the single block that is present in there is actually the IV.
Don't forget to read the full IV from the ciphertext file during decryption:
byte[] iv = new byte[32];
fsIn.Read(iv, 0, 32)

Decrypt file have bad data if wrong key

I've code to decrypt file in DES Encryption, I try I keep getting the file even though I enter the key at the time when the key decrypt the encrypted differently. But i've get the error.
while ((data = cryptostreamDecr.ReadByte()) != -1) // Message Error : Bad Data.
Which code should I add or change in order to keep the process running decrypt?
private static void DecryptFile(string sInputFilename, string sKey)
{
var DES = new DESCryptoServiceProvider();
DES.Key = Encoding.ASCII.GetBytes(sKey);
DES.IV = Encoding.ASCII.GetBytes(sKey);
ICryptoTransform desdecrypt = DES.CreateDecryptor();
using (var fsread = new FileStream(sInputFilename, FileMode.Open,
FileAccess.ReadWrite))
{
using (var cryptostreamDecr = new CryptoStream(fsread,
desdecrypt,
CryptoStreamMode.Read))
{
int data;
fsread.Flush();
using (var ms = new MemoryStream())
{
while ((data = cryptostreamDecr.ReadByte()) != -1)
{
ms.WriteByte((byte)data);
}
cryptostreamDecr.Close();
using (var fsWrite = new FileStream(sInputFilename, FileMode.Truncate))
{
ms.WriteTo(fsWrite);
ms.Flush();
}
}
}
}
}
Encrypt Code :
public static void EncryptFile(string sInputFilename, string sKey)
{
FileStream fsInput = new FileStream(sInputFilename,
FileMode.Open,
FileAccess.ReadWrite);
DESCryptoServiceProvider DES = new DESCryptoServiceProvider();
DES.Key = ASCIIEncoding.ASCII.GetBytes(sKey);
DES.IV = ASCIIEncoding.ASCII.GetBytes(sKey);
ICryptoTransform desencrypt = DES.CreateEncryptor();
CryptoStream cryptostream = new CryptoStream(fsInput,
desencrypt,
CryptoStreamMode.Write);
byte[] bytearrayinput = new byte[fsInput.Length];
fsInput.Read(bytearrayinput, 0, bytearrayinput.Length);
fsInput.SetLength(0);
cryptostream.Write(bytearrayinput, 0, bytearrayinput.Length);
cryptostream.FlushFinalBlock();
cryptostream.Close();
fsInput.Close();
}
[EDIT] : remove in Encypt :
cryptostream.FlushFinalBlock();
And add in decrypt
DES.Padding = PaddingMode.None;

64 bits is the only valid key size for the DES encryption algorithm.
8 bits is equal to one ASCII character means 64 bits is equal to 8 Characters.
If you send 8 characters only then check this (C# "Bad Data" exception when decrypting encrypted file). It may solve your problem.
[Edit]
Add DES.Padding = PaddingMode.None; in DecryptFile.

How to Protect a File? [duplicate]

This question already has answers here:
How to create a password protected file in C#
(2 answers)
Closed 9 years ago.
Am having a FILE named Sample. It may be of any type(.txt/.doc/.docx/.pdf/....). Now I want to set a password for that file. If it is possible just help me with code's.

You can Encrypt the file using your own passwort or with generated keys (See the documentation)
Example from MSDN:
class Class1
{
// Call this function to remove the key from memory after use for security
[System.Runtime.InteropServices.DllImport("KERNEL32.DLL", EntryPoint="RtlZeroMemory")]
public static extern bool ZeroMemory(IntPtr Destination, int Length);
// Function to Generate a 64 bits Key.
static string GenerateKey()
{
// Create an instance of Symetric Algorithm. Key and IV is generated automatically.
DESCryptoServiceProvider desCrypto =(DESCryptoServiceProvider)DESCryptoServiceProvider.Create();
// Use the Automatically generated key for Encryption.
return ASCIIEncoding.ASCII.GetString(desCrypto.Key);
}
static void EncryptFile(string sInputFilename,
string sOutputFilename,
string sKey)
{
FileStream fsInput = new FileStream(sInputFilename,
FileMode.Open,
FileAccess.Read);
FileStream fsEncrypted = new FileStream(sOutputFilename,
FileMode.Create,
FileAccess.Write);
DESCryptoServiceProvider DES = new DESCryptoServiceProvider();
DES.Key = ASCIIEncoding.ASCII.GetBytes(sKey);
DES.IV = ASCIIEncoding.ASCII.GetBytes(sKey);
ICryptoTransform desencrypt = DES.CreateEncryptor();
CryptoStream cryptostream = new CryptoStream(fsEncrypted,
desencrypt,
CryptoStreamMode.Write);
byte[] bytearrayinput = new byte[fsInput.Length];
fsInput.Read(bytearrayinput, 0, bytearrayinput.Length);
cryptostream.Write(bytearrayinput, 0, bytearrayinput.Length);
cryptostream.Close();
fsInput.Close();
fsEncrypted.Close();
}
static void DecryptFile(string sInputFilename,
string sOutputFilename,
string sKey)
{
DESCryptoServiceProvider DES = new DESCryptoServiceProvider();
//A 64 bit key and IV is required for this provider.
//Set secret key For DES algorithm.
DES.Key = ASCIIEncoding.ASCII.GetBytes(sKey);
//Set initialization vector.
DES.IV = ASCIIEncoding.ASCII.GetBytes(sKey);
//Create a file stream to read the encrypted file back.
FileStream fsread = new FileStream(sInputFilename,
FileMode.Open,
FileAccess.Read);
//Create a DES decryptor from the DES instance.
ICryptoTransform desdecrypt = DES.CreateDecryptor();
//Create crypto stream set to read and do a
//DES decryption transform on incoming bytes.
CryptoStream cryptostreamDecr = new CryptoStream(fsread,
desdecrypt,
CryptoStreamMode.Read);
//Print the contents of the decrypted file.
StreamWriter fsDecrypted = new StreamWriter(sOutputFilename);
fsDecrypted.Write(new StreamReader(cryptostreamDecr).ReadToEnd());
fsDecrypted.Flush();
fsDecrypted.Close();
}
static void Main()
{
// Must be 64 bits, 8 bytes.
// Distribute this key to the user who will decrypt this file.
string sSecretKey;
// Get the Key for the file to Encrypt.
sSecretKey = GenerateKey();
// For additional security Pin the key.
GCHandle gch = GCHandle.Alloc( sSecretKey,GCHandleType.Pinned );
// Encrypt the file.
EncryptFile(#"C:\MyData.txt",
#"C:\Encrypted.txt",
sSecretKey);
// Decrypt the file.
DecryptFile(#"C:\Encrypted.txt",
#"C:\Decrypted.txt",
sSecretKey);
// Remove the Key from memory.
ZeroMemory(gch.AddrOfPinnedObject(), sSecretKey.Length * 2);
gch.Free();
}
}
}

You cannot set a password on every file in order to restrict it from opening. However, you can protect file contents by using encryption.
See this link for Encryption & Decryption in C# http://support.microsoft.com/kb/307010

"Specified initialization vector (IV) does not match the block size for this algorithm" using an CryptoStream

I've had troubles using an CryptoStream for my file encryption..
Code:
public static void EncryptFile(string inputFile, string outputFile)
{
int num;
string s = "PUPlr";
byte[] bytes = new UnicodeEncoding().GetBytes(s);
string path = outputFile;
FileStream stream = new FileStream(path, FileMode.Create);
RijndaelManaged managed = new RijndaelManaged();
CryptoStream crpytStream = new CryptoStream(stream, managed.CreateEncryptor(bytes, bytes), CryptoStreamMode.Write);
FileStream stream2 = new FileStream(inputFile, FileMode.Open);
while ((num = stream2.ReadByte()) != -1)
{
crpytStream.WriteByte((byte)num);
}
stream2.Close();
crpytStream.Close();
stream.Close();
}
Trying "managed.BlockSize = 16;" or "= 128;" doesn't seem to work, so how could I fix my error?

Block cyphers like Rijndael require keys and IVs of length equal to the block size, typically 256 bits.
In addition, the IV must be unique for each message, or your data will not be secure.

The error is:
managed.CreateEncryptor(bytes, bytes)
where the bytes needs to be either 128 bits (16 bytes), 192 bits (24 bytes) or 256 bits (32 bytes) for the first (Key) and second parameter.
Notes:
for AES interoperability you should use Rijndael with a BlockSize of 128 bits (16 bytes).
UnicodeEncoding will (often) give you weak password. Look at using PKCS#5 to create a strong key (and IV) from a password. For .NET look at RFC2898DeriveBytes;
avoid using the same data for both the key and IV;

This line here:
managed.CreateEncryptor(bytes, bytes)
Doesn't work. The first parameter is a key, and the second parameter is an initialization vector. If your intention was to use the string s as a "password" or key, try using Rfc2898DeriveBytes to generate a key from a password.

public static void EncryptFile(string input, string output)
{
string theKey = "urKey";
byte[] salt = new byte[] { 0x26, 0xdc, 0xff, 0x00, 0xad, 0xed, 0x7a, 0xee, 0xc5, 0xfe, 0x07, 0xaf, 0x4d, 0x08, 0x22, 0x3c };
Rfc2898DeriveBytes pdb = new Rfc2898DeriveBytes(theKey, salt);
RijndaelManaged RMCrypto = new RijndaelManaged();
using (var inputStream=new FileStream(input))
using (var outputStream = new FileStream(output))
using (CryptoStream cs = new CryptoStream(inputStream, RMCrypto.CreateEncryptor(pdb.GetBytes(32), pdb.GetBytes(16)), CryptoStreamMode.Read))
{
byte[] buffer = new byte[1024];
int bytesRead = 0;
do
{
bytesRead = cs.Read(buffer, 0, buffer.Length);
outputStream.Write(buffer, 0, bytesRead);
} while (bytesRead > 0);
}
}