CryptoStream Class
Defines a stream that links data streams to cryptographic transformations.
Assembly: mscorlib (in mscorlib.dll)
The common language runtime uses a stream-oriented design for cryptography. The core of this design is CryptoStream. Any cryptographic objects that implement CryptoStream can be chained together with any objects that implement Stream, so the streamed output from one object can be fed into the input of another object. The intermediate result (the output from the first object) does not need to be stored separately.
You should always explicitly close your CryptoStream object after you are done using it by calling the Close method. Doing so flushes the stream and causes all remain blocks of data to be processed by the CryptoStream object. However, if an exception occurs before you call the Close method, the CryptoStream object might not be closed. To ensure that the Close method always gets called, place your call to the Close method within the finally block of a try/catch statement.
The following example demonstrates how to use a CryptoStream to encrypt a string. This method uses RijndaelManaged class with the specified Key and initialization vector (IV).
Imports System Imports System.IO Imports System.Security.Cryptography Class RijndaelExample Public Shared Sub Main() Try Dim original As String = "Here is some data to encrypt!" ' Create a new instance of the Rijndael ' class. This generates a new key and initialization ' vector (IV). Using myRijndael = Rijndael.Create() ' Encrypt the string to an array of bytes. Dim encrypted As Byte() = EncryptStringToBytes(original, myRijndael.Key, myRijndael.IV) ' Decrypt the bytes to a string. Dim roundtrip As String = DecryptStringFromBytes(encrypted, myRijndael.Key, myRijndael.IV) 'Display the original data and the decrypted data. Console.WriteLine("Original: {0}", original) Console.WriteLine("Round Trip: {0}", roundtrip) End Using Catch e As Exception Console.WriteLine("Error: {0}", e.Message) End Try End Sub 'Main Shared Function EncryptStringToBytes(ByVal plainText As String, ByVal Key() As Byte, ByVal IV() As Byte) As Byte() ' Check arguments. If plainText Is Nothing OrElse plainText.Length <= 0 Then Throw New ArgumentNullException("plainText") End If If Key Is Nothing OrElse Key.Length <= 0 Then Throw New ArgumentNullException("Key") End If If IV Is Nothing OrElse IV.Length <= 0 Then Throw New ArgumentNullException("Key") End If Dim encrypted() As Byte ' Create an Rijndael object ' with the specified key and IV. Using rijAlg = Rijndael.Create() rijAlg.Key = Key rijAlg.IV = IV ' Create a decrytor to perform the stream transform. Dim encryptor As ICryptoTransform = rijAlg.CreateEncryptor(rijAlg.Key, rijAlg.IV) ' Create the streams used for encryption. Using msEncrypt As New MemoryStream() Using csEncrypt As New CryptoStream(msEncrypt, encryptor, CryptoStreamMode.Write) Using swEncrypt As New StreamWriter(csEncrypt) 'Write all data to the stream. swEncrypt.Write(plainText) End Using encrypted = msEncrypt.ToArray() End Using End Using End Using ' Return the encrypted bytes from the memory stream. Return encrypted End Function 'EncryptStringToBytes Shared Function DecryptStringFromBytes(ByVal cipherText() As Byte, ByVal Key() As Byte, ByVal IV() As Byte) As String ' Check arguments. If cipherText Is Nothing OrElse cipherText.Length <= 0 Then Throw New ArgumentNullException("cipherText") End If If Key Is Nothing OrElse Key.Length <= 0 Then Throw New ArgumentNullException("Key") End If If IV Is Nothing OrElse IV.Length <= 0 Then Throw New ArgumentNullException("Key") End If ' Declare the string used to hold ' the decrypted text. Dim plaintext As String = Nothing ' Create an Rijndael object ' with the specified key and IV. Using rijAlg = Rijndael.Create() rijAlg.Key = Key rijAlg.IV = IV ' Create a decrytor to perform the stream transform. Dim decryptor As ICryptoTransform = rijAlg.CreateDecryptor(rijAlg.Key, rijAlg.IV) ' Create the streams used for decryption. Using msDecrypt As New MemoryStream(cipherText) Using csDecrypt As New CryptoStream(msDecrypt, decryptor, CryptoStreamMode.Read) Using srDecrypt As New StreamReader(csDecrypt) ' Read the decrypted bytes from the decrypting stream ' and place them in a string. plaintext = srDecrypt.ReadToEnd() End Using End Using End Using End Using Return plaintext End Function 'DecryptStringFromBytes End Class
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