Examples for Module 04



  
C# Examples:
  
How to Generate a Symmetric Key From a Password
  
How to Encrypt Data with a Symmetric Algorithm 
  
How to Decrypt Data with a Symmetric Algorithm 
  
How to Configure an Asymmetric Algorithm


  

  
How to Encrypt and Decrypt Data with an Asymmetric Algorithm
  
  
How to Hash Data
  
How to Sign Data



  
Visual Basic Examples:
  
How to Generate a Symmetric Key From a Password
  
How to Encrypt Data with a Symmetric Algorithm 
  
How to Decrypt Data with a Symmetric Algorithm 
  
How to Configure an Asymmetric Algorithm


  

  
How to Encrypt and Decrypt Data with an Asymmetric Algorithm
  
  
How to Hash Data
  
How to Sign Data


  
 



 


How to Generate a Symmetric Key From a Password


// Check the length and variety of a password
public bool IsValidPassword(string password)
{
   bool retval = false;
   Regex r = new Regex(
      @"^(?=.*[0-9])(?=.*[a-z])(?=.*[A-Z])(?=.*\W)",
      RegexOptions.Singleline);

   if ((password.Length >= 9) && (r.IsMatch(password)))
      retval = true;

   return retval;
}

// Creating a key from a password
// Generate a 16 byte salt
RandomNumberGenerator rNum = RandomNumberGenerator.Create();
byte [] salt = new byte[16];
rNum.GetBytes(salt);

// Generate a 16 byte (128 bit) key from a password and salt
PasswordDeriveBytes passDerBytes = new PasswordDeriveBytes(
   password, salt);
byte [] key = passDerBytes.GetBytes(16);


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How to Encrypt Data with a Symmetric Algorithm


// Create and configure the symmetric algorithm object
Rijndael cryptoAlg = Rijndael.Create();
// Assume key is a 16 byte array, as generated in the code
// sample in the previous topic
cryptoAlg.Key = key;
// Create the file stream for the encrypted data
// Assume filename is a string with a path to a file
FileStream fileStm = new FileStream(
   filename, FileMode.Create);

// Write the salt and initialization vector to the file
fileStm.Write(salt, 0, salt.Length);
fileStm.Write(cryptoAlg.IV, 0, cryptoAlg.IV.Length);

// Create the CryptoStream and encrypt the data
CryptoStream cryptoStm = new CryptoStream(fileStm,
   cryptoAlg.CreateEncryptor(),
   CryptoStreamMode.Write);
// Assume output is an array of bytes you want to encrypt
cryptoStm.Write(output, 0, output.Length);
cryptoStm.FlushFinalBlock();
cryptoStm.Close();


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How to Decrypt Data with a Symmetric Algorithm


// Create the symmetric algorithm object
Rijndael cryptoAlg = Rijndael.Create();
// Open the encrypted file
// Assume filename is a string with a path to a file
FileStream encFileStm = new FileStream(filename,
   FileMode.Open);

// Declare the variables and read the values from the file
byte [] salt = new byte[16];
byte [] IV = new byte[cryptoAlg.IV.Length];
encFileStm.Read(salt, 0, salt.Length);
encFileStm.Read(IV, 0, IV.Length);

// Regenerate the key and set up the algorithm
// Assume password is a string containing the password
PasswordDeriveBytes passDerBytes = new PasswordDeriveBytes(
   password, salt);
byte [] key = passDerBytes.GetBytes(16);
cryptoAlg.Key = key;
cryptoAlg.IV = IV;

// Create the CryptoStream for reading and decrypting data
CryptoStream cryptoStream = new CryptoStream(encFileStm,
   cryptoAlg.CreateDecryptor(),
   CryptoStreamMode.Read);
// Loop through the data in the file, decrypting it
int bytesRead = 0;
byte [] buffer = new byte[256];
do
{
   bytesRead = cryptoStream.Read(buffer, 0, 256);
   // buffer now contains decrypted data, code to use
   // the decrypted data goes here
}
while (bytesRead > 0);
// Close the CryptoStream
cryptoStream.Close();


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How to Configure an Asymmetric Algorithm


// Create an instance of the default RSA implementation
RSA cryptoAlg = RSA.Create();

// Create the CspParameters and pass it to the algorithm
CspParameters cspParms = new CspParameters(1, null,
   "My RSA Key");
RSACryptoServiceProvider alg = new RSACryptoServiceProvider(
   cspParms);

// Creating and loading test keys
private void createTestKey(string filename)
{
   // Create a new instance of an RSA algorithm with a
   // random key and save the key to an XML file
   RSA alg = RSA.Create();
   string key = alg.ToXmlString(true);
   FileStream fs = new FileStream(filename, FileMode.Create);
   StreamWriter sw = new StreamWriter(fs);
   sw.Write(key);
   sw.Close();
}

private RSA loadTestKey(string filename)
{
   // Load an XML string with key information from a
   // file and set it on a new RSA algorithm object
   FileStream fs = new FileStream(filename, FileMode.Open);
   StreamReader sr = new StreamReader(fs);
   string key = sr.ReadToEnd();
   sr.Close();
   RSA alg = RSA.Create();
   alg.FromXmlString(key);
   return alg;
}


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How to Encrypt and Decrypt Data with an Asymmetric Algorithm


// This method takes an instance of an RSA algorithm and
// some data and returns the encrypted data with padding
private byte[] encryptRSA(RSA cryptoAlg, byte[] data)
{
   RSAPKCS1KeyExchangeFormatter formatter = new
      RSAPKCS1KeyExchangeFormatter(cryptoAlg);
   byte[] encData = formatter.CreateKeyExchange(data);
   return encData;
}

// This method takes an instance of an RSA algorithm and
// some encrypted data and returns the decrypted data
// Note: the key information set on the RSA algorithm must
// include a private key
private byte[] decryptRSA(RSA cryptoAlg, byte[] encData)
{
   RSAPKCS1KeyExchangeDeformatter deformatter = new
      RSAPKCS1KeyExchangeDeformatter(cryptoAlg);
   byte[] data = deformatter.DecryptKeyExchange(encData);
   return data;
}

// Create a new instance of an RSA algorithm with a random
// key
RSACryptoServiceProvider cryptoAlg = new 
   RSACryptoServiceProvider();
// Encrypt the data, the second argument to the Encrypt
// method determines the type of padding used
// Assume data is an array of bytes
byte[] encData = cryptoAlg.Encrypt(data, false);
// Decrypt the encrypted data
byte[] decData = cryptoAlg.Decrypt(encData, false);


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How to Hash Data


// This method takes some data as an array of bytes and
// computes the SHA1 hash of the data
private byte[] computeSHA1HashFromBytes(byte[] data)
{
   SHA1 hashAlg = SHA1.Create();
   byte[] hashValue = hashAlg.ComputeHash(data);
   return hashValue;
}

// This method takes some data as a stream and
// computes the SHA1 hash of the data
private byte[] computeSHA1HashFromStream(Stream stream)
{
   SHA1 hashAlg = SHA1.Create();
   byte[] hashValue = hashAlg.ComputeHash(stream);
   return hashValue;
}

// This method takes two file names, a source file and
// a destination file, copies the contents of the source
// file to the destination file, and then writes the hash
// value of the data to the end of the destination file
private void writeFileWithSHA512Hash(string sourceFile,
   string destFile)
{
   // Create the Hash and FileStream objects
   SHA512 hashAlg = SHA512.Create();
   FileStream sourceStream = new FileStream(sourceFile,
      FileMode.Open);
   FileStream destStream = new FileStream (destFile,
      FileMode.Create);
   // Create a CryptoStream that will hash the source
   // data as we read it
   CryptoStream hashedSourceStream = new CryptoStream(
      sourceStream, hashAlg, CryptoStreamMode.Read);
   // Loop through the data 1K at a time, hashing the input
   // data as it is read and writing it to the output file
   int bytesRead = 0;
   byte[] buffer = new byte[1024];
   do
   {
      bytesRead = hashedSourceStream.Read(buffer, 0, 1024);
      destStream.Write(buffer, 0, bytesRead);
   }
   while
   (bytesRead > 0);
   hashedSourceStream.Close();
   // Write the hash value to the end of the output file
   destStream.Write(hashAlg.Hash, 0, hashAlg.Hash.Length);
   destStream.Close();
}


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How to Sign Data


// Using RSA's SignHash and VerifyHash
// This method takes some data as an array of bytes and
// generates an RSA signature for the data
private byte[] computeRSASignatureWithSHA1(byte[] data)
{
   SHA1 hashAlg = SHA1.Create();
   RSACryptoServiceProvider cryptoAlg = new
      RSACryptoServiceProvider();
   byte[] hashValue = hashAlg.ComputeHash(data);
   byte[] signature = cryptoAlg.SignHash(hashValue,
      "1.3.14.3.2.26");
   return signature;
}

// This method takes some data as an array of bytes and
// and a signature and verifies the signature against the
// data, returning true if the signature is verified
private bool verifyRSASignatureWithSHA1(byte[] data,
   byte[] signature)
{
   SHA1 hashAlg = SHA1.Create();
   RSACryptoServiceProvider cryptoAlg = new
      RSACryptoServiceProvider();
   byte[] hashValue = hashAlg.ComputeHash(data);
   bool sigsMatch = cryptoAlg.VerifyHash(hashValue,
      "1.3.14.3.2.26", signature);
   return sigsMatch;
}


// Using RSA's SignData and VerifyData
// This method takes some data as an array of bytes and
// generates an RSA signature for the data
private byte[] computeRSASignatureWithSHA1(byte[] data)
{
   RSACryptoServiceProvider cryptoAlg = new
      RSACryptoServiceProvider();
   byte[] signature = cryptoAlg.SignData(data, "SHA1");
   return signature;
}

// This method takes some data as an array of bytes and
// and a signature and verifies the signature against the
// data, returning true if the signature is verified
private bool verifyRSASignatureWithSHA1(byte[] data,
   byte[] signature)
{
   RSACryptoServiceProvider cryptoAlg = new
      RSACryptoServiceProvider();
   bool sigsMatch = cryptoAlg.VerifyData(data, "SHA1",
      signature);
   return sigsMatch;
}


// Using DSA's CreateSignature and VerifySignature
// This method takes some data as an array of bytes and
// generates a DSA signature for the data
private byte[] computeDSASignature(byte[] data)
{
   SHA1 hashAlg = SHA1.Create();
   DSACryptoServiceProvider cryptoAlg = new
      DSACryptoServiceProvider();
   byte[] hashValue = hashAlg.ComputeHash(data);
   byte[] signature = cryptoAlg.CreateSignature(hashValue);
   return signature;
}

// This method takes some data as an array of bytes and
// and a signature and verifies the signature against the
// data, returning true if the signature is verified
private bool verifyDSASignature(byte[] data,
   byte[] signature)
{
   SHA1 hashAlg = SHA1.Create();
   DSACryptoServiceProvider cryptoAlg = new
      DSACryptoServiceProvider();
   byte[] hashValue = hashAlg.ComputeHash(data);
   bool sigsMatch = cryptoAlg.VerifySignature(hashValue,
      signature);
   return sigsMatch;
}

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How to Generate a Symmetric Key From a Password


' Check the length and variety of a password
Public Function IsValidPassword(ByVal password As String) _
   As Boolean

   Dim retval As Boolean = false
   Dim r As Regex = New Regex( _
      "^(?=.*[0-9])(?=.*[a-z])(?=.*[A-Z])(?=.*\W)", _
      RegexOptions.Singleline)

   If ((password.Length >= 9) And (r.IsMatch(password))) Then
      retval = True
   End If

   Return retval
End Function

' Generate a 16 byte salt
Dim rNum As RandomNumberGenerator = _
   RandomNumberGenerator.Create()
Dim salt(15) As Byte
rNum.GetBytes(salt)

' Generate a 16 byte (128 bit) key from a password and salt
Dim passDerBytes As New PasswordDeriveBytes(password, salt)
Dim key() As Byte = passDerBytes.GetBytes(16)


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How to Encrypt Data with a Symmetric Algorithm


' Create and configure the symmetric algorithm object
Dim cryptoAlg As Rijndael = Rijndael.Create()
' Assume key is a 16 byte array, as generated in the code
' sample in the previous topic
cryptoAlg.Key = key
' Create the file stream for the encrypted data
' Assume filename is a string with a path to a file
Dim fileStm As New FileStream(filename, FileMode.Create)

' Write the salt and initialization vector to the file
fileStm.Write(salt, 0, salt.Length)
fileStm.Write(cryptoAlg.IV, 0, cryptoAlg.IV.Length)

' Create the CryptoStream and encrypt the data
Dim cryptoStm As New CryptoStream(fileStm, _
   cryptoAlg.CreateEncryptor(), _
   CryptoStreamMode.Write)
' Assume output is an array of bytes you want to encrypt
cryptoStm.Write(output, 0, output.Length)
cryptoStm.FlushFinalBlock()
cryptoStm.Close()


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How to Decrypt Data with a Symmetric Algorithm


' Create the symmetric algorithm object
Dim cryptoAlg As Rijndael = Rijndael.Create()
' Open the encrypted file
' Assume filename is a string with a path to a file
Dim encFileStm As New FileStream(filename, FileMode.Open)

' Declare the variables and read the values from the file
Dim salt(15) As Byte
Dim IV(cryptoAlg.IV.Length - 1) As Byte
encFileStm.Read(salt, 0, salt.Length)
encFileStm.Read(IV, 0, IV.Length)

' Regenerate the key and set up the algorithm
' Assume password is a string containing the password
Dim passDerBytes As New PasswordDeriveBytes(password, salt)
Dim key() As Byte = passDerBytes.GetBytes(16)
cryptoAlg.Key = key
cryptoAlg.IV = IV

' Create the CryptoStream for reading and decrypting data
Dim cryptoStream As New CryptoStream(encFileStm, _
   cryptoAlg.CreateDecryptor(), _
   CryptoStreamMode.Read)
' Loop through the data in the file, decrypting it
Dim bytesRead As Integer = 0
Dim buffer(255) As Byte
Do
   bytesRead = cryptoStream.Read(buffer, 0, 256)
   ' buffer now contains decrypted data, code to use
   ' the decrypted data goes here
Loop While bytesRead > 0
' Close the CryptoStream
cryptoStream.Close()


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How to Configure an Asymmetric Algorithm


' Create an instance of the default RSA implementation
Dim cryptoAlg As RSA = RSA.Create()

' Create the CspParameters and pass it to the algorithm
Dim cspParms As New CspParameters(1, Nothing, "My RSA Key")
Dim alg As New RSACryptoServiceProvider(cspParms)

' Creating and loading test keys
Private Sub createTestKey(ByVal filename As String)
   ' Create a new instance of an RSA algorithm with a
   ' random key and save the key to an XML file
   Dim alg As RSA = RSA.Create()
   Dim key As String = alg.ToXmlString(True)
   Dim fs As New FileStream(filename, FileMode.Create)
   Dim sw As New StreamWriter(fs)
   sw.Write(key)
   sw.Close()
End Sub

Private Function loadTestKey(ByVal filename As String) As RSA
   ' Load an XML string with key information from a
   ' file and set it on a new RSA algorithm object
   Dim fs As New FileStream(filename, FileMode.Open)
   Dim sr As New StreamReader(fs)
   Dim key As String = sr.ReadToEnd()
   sr.Close()
   Dim alg As RSA = RSA.Create()
   alg.FromXmlString(key)
   Return alg
End Function


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How to Encrypt and Decrypt Data with an Asymmetric Algorithm


' This method takes an instance of an RSA algorithm and
' some data and returns the encrypted data with padding
Private Function encryptRSA(ByVal cryptoAlg As RSA, _
   ByVal data() As Byte) As Byte()

   Dim formatter As New RSAPKCS1KeyExchangeFormatter( _
      cryptoAlg)
   Dim encData As Byte() = formatter.CreateKeyExchange(data)
   Return encData
End Function

' This method takes an instance of an RSA algorithm and
' some encrypted data and returns the decrypted data
' Note: the key information set on the RSA algorithm must
' include a private key
Private Function decryptRSA(ByVal cryptoAlg As RSA, _
   ByVal encData() As Byte) As Byte()

   Dim deformatter As New RSAPKCS1KeyExchangeDeformatter( _
      cryptoAlg)
   Dim data() As Byte = deformatter.DecryptKeyExchange( _
      encData)
   Return data
End Function

' Create a new instance of an RSA algorithm with a random
' key
Dim cryptoAlg As New RSACryptoServiceProvider()
' Encrypt the data, the second argument to the Encrypt
' method determines the type of padding used
' Assume data is an array of bytes
Dim encData As Byte() = cryptoAlg.Encrypt(data, False)
' Decrypt the encrypted data
Dim decData As Byte() = cryptoAlg.Decrypt(encData, False)


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How to Hash Data


' This method takes some data as an array of bytes and
' computes the SHA1 hash of the data
Private Function computeSHA1HashFromBytes( _
   ByVal data() As Byte) As Byte()

   Dim hashAlg As SHA1 = SHA1.Create()
   Dim hashValue() As Byte = hashAlg.ComputeHash(data)
   Return hashValue
End Function

' This method takes some data as a stream and
' computes the SHA1 hash of the data
Private Function computeSHA1HashFromStream( _
   ByVal stream As Stream) As Byte()

   Dim hashAlg As SHA1 = SHA1.Create()
   Dim hashValue() As Byte = hashAlg.ComputeHash(stream)
   Return hashValue
End Function

' This method takes two file names, a source file and
' a destination file, copies the contents of the source
' file to the destination file, and then writes the hash
' value of the data to the end of the destination file
Private Sub writeFileWithSHA512Hash( _
   ByVal sourceFile As String, ByVal destFile As String)

   ' Create the Hash and FileStream objects
   Dim hashAlg As SHA512 = SHA512.Create()
   Dim sourceStream As New FileStream(sourceFile, _
      FileMode.Open)
   Dim destStream As New FileStream(destFile, FileMode.Create)
   ' Create a CryptoStream that will hash the source
   ' data as we read it
   Dim hashedSourceStream As New CryptoStream(sourceStream, _
      hashAlg, CryptoStreamMode.Read)
   ' Loop through the data 1K at a time, hashing the input
   ' data as it is read and writing it to the output file
   Dim bytesRead As Integer = 0
   Dim buffer(1023) As Byte
   Do
      bytesRead = hashedSourceStream.Read(buffer, 0, 1024)
      destStream.Write(buffer, 0, bytesRead)
   Loop While bytesRead > 0
   hashedSourceStream.Close()
   ' Write the hash value to the end of the output file
   destStream.Write(hashAlg.Hash, 0, hashAlg.Hash.Length)
   destStream.Close()
End Sub


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How to Sign Data


' This method takes some data as an array of bytes and
' generates an RSA signature for the data
Private Function computeRSASignatureWithSHA1( _
   ByVal data() As Byte) As Byte()

   Dim hashAlg As SHA1 = SHA1.Create()
   Dim cryptoAlg As New RSACryptoServiceProvider()
   Dim hashValue() As Byte = hashAlg.ComputeHash(data)
   Dim signature() As Byte = cryptoAlg.SignHash(hashValue, _
      "1.3.14.3.2.26")
   Return signature
End Function

' This method takes some data as an array of bytes and
' and a signature and verifies the signature against the
' data, returning true if the signature is verified
Private Function verifyRSASignatureWithSHA1( _
   ByVal data() As Byte, ByVal signature() As Byte) As Boolean

   Dim hashAlg As SHA1 = SHA1.Create()
   Dim cryptoAlg As New RSACryptoServiceProvider()
   Dim hashValue() As Byte = hashAlg.ComputeHash(data)
   Dim sigsMatch As Boolean = cryptoAlg.VerifyHash( _
      hashValue, "1.3.14.3.2.26", signature)
   Return sigsMatch
End Function


' This method takes some data as an array of bytes and
' generates an RSA signature for the data
Private Function computeRSASignatureWithSHA1( _
   ByVal data() As Byte) As Byte()

   Dim cryptoAlg As New RSACryptoServiceProvider()
   Dim signature() As Byte = cryptoAlg.SignData(data, "SHA1")
   Return signature
End Function

' This method takes some data as an array of bytes and
' and a signature and verifies the signature against the
' data, returning true if the signature is verified
Private Function verifyRSASignatureWithSHA1( _
   ByVal data() As Byte, ByVal signature() As Byte) As Boolean

   Dim cryptoAlg As New RSACryptoServiceProvider()
   Dim sigsMatch As Boolean = cryptoAlg.VerifyData(data, _
      "SHA1", signature)
   Return sigsMatch
End Function


' This method takes some data as an array of bytes and
' generates a DSA signature for the data
Private Function computeDSASignature(ByVal data() As Byte) _
   As Byte()

   Dim hashAlg As SHA1 = SHA1.Create()
   Dim cryptoAlg As New DSACryptoServiceProvider()
   Dim hashValue() As Byte = hashAlg.ComputeHash(data)
   Dim signature() As Byte = cryptoAlg.CreateSignature( _
      hashValue)
   Return signature
End Function 'computeDSASignature


' This method takes some data as an array of bytes and
' and a signature and verifies the signature against the
' data, returning true if the signature is verified
Private Function verifyDSASignature(ByVal data() As Byte, _
   ByVal signature() As Byte) As Boolean

   Dim hashAlg As SHA1 = SHA1.Create()
   Dim cryptoAlg As New DSACryptoServiceProvider()
   Dim hashValue() As Byte = hashAlg.ComputeHash(data)
   Dim sigsMatch As Boolean = cryptoAlg.VerifySignature( _
      hashValue, signature)
   Return sigsMatch
End Function


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