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From: mahesh_m
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[19Nov05] How Do I
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From:
mahesh_m
19 November 2005
How Do I...
_________________________________________________________________
How Do I Encrypt and Decrypt a file?
The CryptoStream class in the System.Security.Cryptography namespace is used to
easily define cryptographic transforms on any data stream. The constructor is
defined as the following: CryptoStream (Stream argument, ICryptoTransform
transform, CryptoStreamMode mode).
Stream argument - Defines the stream on which the cryptographic transform is to
be performed. Any stream that derives from System.IO.Stream can be plugged in
here. For example, pass in an instance of
System.IO.FileStream to perform a cryptographic transform on a file. Because
CryptoStream derives from Stream, it is possible to use CryptoStream to define
cryptographic transforms on other cryptographic streams. This makes it possible
to chain objects that implement CryptoStream together, for example encrypting a
file and computing the hash for the encryption in a single operation.
ICrypto Transformtransform - Defines the cryptographic transform that is to be
performed on the stream. Because every class that derives from HashAlgorithm
implements the ICryptoTransform interface, an instance of a hash algorithm can
be passed in here to take the hash of a stream. All symmetric encryption or
decryption algorithms that derive from the SymmetricAlgorithm class have
CreateEncryptor() and CreateDecryptor() functions that return an instance of an
ICryptoTransform implementation. To define a TripleDES encryption on a given
stream, call the CreateEncryptor() function on an instance of a TripleDES
implementation and pass the result into the CryptoStream constructor.
Generally, any class that implements ICryptoTransform can be passed into the
CryptoStream constructor.
CryptoStreamMode mode - Defines whether you are reading from or writing to the
stream. To write to a CryptoStream you must pass CryptoStreamMode.Write into
the CryptoStream constructor. To read from the stream,
CryptoStreamMode.Read must be passed into the constructor.
The CryptoStream class contains the standard stream member functions to either
read a byte array from the stream or write a byte array to the stream. The
CryptoStream class handles the buffering internally when reading from or
writing to the stream. Application code needs only to provide the byte buffer
and call the appropriate read or write method on the stream.
The following sample code shows the creation of a CryptoStream to encrypt a
file using the DES algorithm. First, the FileStream that will contain the
encrypted file is created. Then, an instance of a DES implementation is
created. If an instance of a symmetric or asymmetric algorithm is created
without explicit constructor arguments, a random key (or public or private key
pair) is generated and default properties are set that cover most encryption or
decryption scenarios. A DES encryptor object is created on the DES instance.
Next, a CryptoStream is created by passing the FileStream instance and the DES
encryptor into the CryptoStream constructor; the stream is set to write mode.
Finally, we write a byte array of plain text to the stream and close the
stream. The result is a file named "
EncryptedFile.txt" which contains the DES encryption of bytearrayinput.
VB.NET
Dim fs As New FileStream("EncryptedFile.txt", FileMode.Create, FileAccess.Write)
Dim des As New DESCryptoServiceProvider()
Dim desencrypt As ICryptoTransform = des.CreateEncryptor()
Dim cryptostream As New CryptoStream(fs, desencrypt, CryptoStreamMode.Write)
cryptostream.Write(bytearrayinput, 0, bytearrayinput.Length)
cryptostream.Close()
C#
FileStream fs = new
FileStream("EncryptedFile.txt",FileMode.Create,FileAccess.Write);
DESCryptoServiceProvider des = new DESCryptoServiceProvider();
ICryptoTransform desencrypt = des.CreateEncryptor
();
CryptoStream cryptostream = new
CryptoStream(fs,desencrypt,CryptoStreamMode.Write);
cryptostream.Write(bytearrayinput,0,bytearrayinput.Length);
cryptostream.Close();
_________________________________________________________________
You can also post your questions which you think are of the form "How Do I...?"
to [EMAIL PROTECTED]
. I will try to answer them in this section.
--
--
Thank You,
Regards,
m_mahesh
Mahesh Mitkari
INETA Volunteer
Asst. Manager (Pune .net User group)
Manager (PUG Student)
09890555485 ([EMAIL PROTECTED])
http://mmahesh.blogspot.com
_________________________________________________________________
Note: The information Published under this section is ONLY FOR INFORMATIVE
PURPOSE of the User Group Members. The most of the part of this section is
collected from the Microsoft .Net Framework SDK
2.0, Microsoft website, Resource kit published by the Microsoft and MSDN
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