c# print barcode font // Step 1: Create a secret key in .NET

Creation QR in .NET // Step 1: Create a secret key

// Step 1: Create a secret key
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byte[] saltValueBytes = Encoding.ASCII.GetBytes( This is my sa1t );
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PasswordDeriveBytes passwordKey = new PasswordDeriveBytes
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(args[0], saltValueBytes, SHA1", 3);
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byte[] secretKey = passwordKey.GetBytes(16);
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// Step 2: Create the hash algorithm object
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HMACSHA1 myHash = new HMACSHA1(secretKey);
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// Step 3: Store the data to be hashed in a byte array
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FileStream file = new FileStream(args[1], FileMode.Open, FileAccess.Read);
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BinaryReader reader = new BinaryReader(file);
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// Step 4: Call the HashAlgorithm.ComputeHash method
myHash.ComputeHash(reader.ReadBytes((int)file.Length));
// Step 5: Retrieve the HashAlgorithm.Hash byte array
Console.WriteLine(Convert.ToBase64String(myHash.Hash));
Sub Main(ByVal args As String())
Step 1: Create a secret key
Dim saltValueBytes As Byte() = Encoding.ASCII.GetBytes( This is my sa1t )
Dim passwordKey As PasswordDeriveBytes = New PasswordDeriveBytes
(args(0), saltValueBytes, SHA1", 3)
Dim secretKey As Byte() = passwordKey.GetBytes(16)
Step 2: Create the hash algorithm object
Dim myHash As HMACSHA1 = New HMACSHA1 (secretKey)
Lesson 3: Validating Data Integrity with Hashes
Step 3: Store the data to be hashed in a byte array Dim file As FileStream = New FileStream (args(1), FileMode.Open, FileAccess.Read) Dim reader As BinaryReader = New BinaryReader (file) Step 4: Call the HashAlgorithm.ComputeHash method myHash.ComputeHash(reader.ReadBytes(CType(file.Length, Integer))) Step 5: Retrieve the HashAlgorithm.Hash byte array Console.WriteLine(Convert.ToBase64String(myHash.Hash))
End Sub
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If either the file contents or the password changes, the computed hash will also change. This ensures both the sender and recipient used the same password to generate the hash, which prevents an attacker from modifying the hash. Consider the following console output, which creates a new text file, computes the hash repeatedly, and then modifies the file. After either the file or the password (and key) is modified, the hash also changes:
C:\>echo Hello, World! > HashThis.txt C:\>KeyedHashExample SomePassword HashThis.txt
t04kYA9Z2ki+JbzUqe7llE6EjN4=
C:\>KeyedHashExample SomePassword HashThis.txt
t04kYA9Z2ki+JbzUqe7llE6EjN4=
C:\>KeyedHashExample NotSomePassword HashThis.txt
TFNPh9TspBobOvixy1yJ0fX/+vo=
C:\>echo Hello, again. >> HashThis.txt C:\>KeyedHashExample SomePassword HashThis.txt
yW6K6G7diJEV3bV2nNttgtcCM0o=
Either HMACSHA1 or MACTripleDES can be used for the previous example. However, whereas HMACSHA1 accepts a secret key of any length, MACTripleDES accepts only secret keys of 8, 16, or 24 bytes.
Practice: Validating Data Integrity with Hashes
In this practice, you will create two console applications that create and validate hashes for files. Read the scenario and then complete the exercise that follows. If you are unable to answer a question, review the lesson and try the question again. You can find answers to the questions in the Questions and Answers section at the end of this chapter.
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8
Protecting Data by Using Cryptography
Scenario
You are a consultant for Proseware, Inc., a small software development company whose encyclopedia software has suddenly become extremely popular. Proseware just received their Web site bandwidth bill from their Internet service provider (ISP), and it was much higher than they expected. They want to find ways to distribute their software and data files other than having users download it directly from their Web site. However, they are concerned that users will not trust that the files have not been modified, because they were generated by Proseware. They hired you to recommend a method to allow users to verify the integrity of their files. You interview key personnel and review technical requirements before making your recommendations. Interviews
Following is a list of company personnel interviewed and their statements:
Dick Dievendorff, Development Manager We ve been looking at using a software download service, or distributing our data files using peer-to-peer networks. I m concerned about data integrity, though. Our users rely on the accuracy of our encyclopedia data. If they download it from someone else, what prevents it from being modified We use an SSL certificate for our Web site, so our users know that when they connect to our site, the files are genuine. I d be satisfied if we could post some kind of checksum on the Web site, and allow users to download an application that verifies the checksum of the data file after they ve downloaded it. Can you recommend a way to generate that checksum, and create a simple console application to validate the checksum Oh, and use as many bits as possible for the checksum. That makes people feel safer. Create two console applications:
Technical Requirements
ComputeHash This application must take a single command-line argument: a filename. It should create output to the console that is a Base64-encoded hash of the file. VerifyHash This application must take two command-line arguments: a filename and a Base64-encoded hash of the file. It must verify the checksum and display the results to the console.
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