Symmetric encryption and asymmetric encryption are performed using different processes. Symmetric encryption is performed on streams and is therefore useful to encrypt large amounts of data. Asymmetric encryption is performed on a small number of bytes and is therefore useful only for small amounts of data. The managed symmetric cryptography classes are used with a special stream class called a CryptoStream that encrypts data read into the stream.
The CryptoStream class is initialized with a managed stream class, a class that implements the ICryptoTransform interface created from a class that implements a cryptographic algorithm , and a CryptoStreamMode enumeration that describes the type of access permitted to the CryptoStream. Using these classes, you can perform symmetric encryption on a variety of stream objects. The following example illustrates how to create a new instance of the default implementation class for the Aes algorithm.
The instance is used to perform encryption on a CryptoStream class. In this example, the CryptoStream is initialized with a stream object called fileStream that can be any type of managed stream. In this case, the default key and IV generated from aes are used. After this code is executed, any data written to the CryptoStream object is encrypted using the AES algorithm. The following example shows the entire process of creating a stream, encrypting the stream, writing to the stream, and closing the stream.
This example creates a file stream that is encrypted using the CryptoStream class and the Aes class. Generated IV is written to beginning of FileStream , so it can be read and used for decryption. Anyone that you allow to decrypt your data must possess the same key and IV and use the same algorithm. Generally, a new key and IV should be created for every session, and neither the key nor IV should be stored for use in a later session.
To communicate a symmetric key and IV to a remote party, you would usually encrypt the symmetric key by using asymmetric encryption. Sending the key across an insecure network without encrypting it is unsafe, because anyone who intercepts the key and IV can then decrypt your data. The following example shows the creation of a new instance of the default implementation class for the Aes algorithm.
When the previous code is executed, a new key and IV are generated and placed in the Key and IV properties, respectively. Sometimes you might need to generate multiple keys. In this situation, you can create a new instance of a class that implements a symmetric algorithm and then create a new key and IV by calling the GenerateKey and GenerateIV methods.
The following code example illustrates how to create new keys and IVs after a new instance of the symmetric cryptographic class has been made. When the preceding code is executed, a key and IV are generated when the new instance of Aes is made.
Asymmetric keys can be either stored for use in multiple sessions or generated for one session only. While the public key can be made generally available, the private key should be closely guarded. After a new instance of the class is created, the key information can be extracted using the ExportParameters method, which returns an RSAParameters structure that holds the key information. The method accepts a Boolean value that indicates whether to return only the public key information or to return both the public-key and the private-key information.
Net this class seems to generate a new key with every app restart so doesn't work. With a quick peek in ILSpy it looks to me like it generates its own defaults if the appropriate app.
So you may actually be able to set it up outside ASP. BouncyCastle is a great Crypto library for. NET, it's available as a Nuget package for install into your projects. I like it a lot more than what's currently available in the System.
Cryptography library. It gives you a lot more options in terms of available algorithms, and provides more modes for those algorithms. This is an example of an implementation of TwoFish , which was written by Bruce Schneier hero to all us paranoid people out there.
It's a symmetric algorithm like the Rijndael aka AES. It was one of the three finalists for the AES standard and sibling to another famous algorithm written by Bruce Schneier called BlowFish. First thing with bouncycastle is to create an encryptor class, this will make it easier to implement other block ciphers within the library.
The following encryptor class takes in a generic argument T where T implements IBlockCipher and has a default constructor.
Although from a style perspective this goes against the SOLID principle of single responsibility, because of the nature of what this class does I reniged. This class will now take two generic parameters, one for the cipher and one for the digest. Next just call the encrypt and decrypt methods on the new class, here's the example using twofish:.
The hardest part about encryption actually deals with the keys and not the algorithms. You'll have to think about where you store your keys, and if you have to, how you exchange them. These algorithms have all withstood the test of time, and are extremely hard to break. Someone who wants to steal information from you isn't going to spend eternity doing cryptanalysis on your messages, they're going to try to figure out what or where your key is.
So 1 choose your keys wisely, 2 store them in a safe place, if you use a web. Update 2 Changed compare method to mitigate against timing attacks.
Also updated to default to PKCS7 padding and added new constructor to allow end user the ability to choose which padding they would like to use. Thanks CodesInChaos for the suggestions. HOW TO? ID : viewed : 56 Tags : c.
Also too much work to alter this answer otherwise. The sharedSecret parameters must match. GetBytes aesAlg. CreateEncryptor aesAlg. Key, aesAlg. Write BitConverter.
Length , 0, sizeof int ; msEncrypt. Write aesAlg. IV, 0, aesAlg. ToBase64String msEncrypt. CreateDecryptor aesAlg. Read rawLength, 0, rawLength. ToInt32 rawLength, 0 ]; if s. Read buffer, 0, buffer. Modern Examples of Symmetric Authenticated Encryption of a string.
IO; using System. Cryptography; using System. Write cipherText ; binaryWriter.
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