FromBase64Transform.TransformBlock Method

Definition

Namespace:

System.Security.Cryptography

Assemblies:

netstandard.dll, System.Security.Cryptography.dll

Source:

Base64Transforms.cs

Converts the specified region of the input byte array from base 64 and copies the result to the specified region of the output byte array.

C#

public int TransformBlock(byte[] inputBuffer, int inputOffset, int inputCount, byte[] outputBuffer, int outputOffset);

Parameters

inputBuffer

Byte[]

The input to compute from base 64.

inputOffset

Int32

The offset into the input byte array from which to begin using data.

inputCount

Int32

The number of bytes in the input byte array to use as data.

outputBuffer

Byte[]

The output to which to write the result.

outputOffset

Int32

The offset into the output byte array from which to begin writing data.

Returns

Int32

The number of bytes written.

Implements

TransformBlock(Byte[], Int32, Int32, Byte[], Int32)

Exceptions

ObjectDisposedException

The current FromBase64Transform object has already been disposed.

ArgumentException

inputCount uses an invalid value.

-or-

inputBuffer has an invalid offset length.

ArgumentOutOfRangeException

inputOffset is out of range. This parameter requires a non-negative number.

ArgumentNullException

inputBuffer is null.

Examples

The following example decrypts a base 64-encoded file to an output text file.

C#

using System;
using System.IO;
using System.Security.Cryptography;

class Members
{
    [STAThread]
    static void Main(string[] args)
    {
        string appPath = (System.IO.Directory.GetCurrentDirectory() );
        appPath = appPath + "..\\\\..\\\\..\\";
        // Insert your file names into this method call.
        EncodeFromFile(appPath + "program.cs", appPath + "code.enc");
        DecodeFromFile(appPath + "code.enc", appPath + "roundtrip.txt");
    }

    // Read in the specified source file and write out an encoded target file.
    private static void EncodeFromFile(string sourceFile, string targetFile) 
    {
        // Verify members.cs exists at the specified directory.
        if (!File.Exists(sourceFile))
        {
            Console.Write("Unable to locate source file located at ");
            Console.WriteLine(sourceFile + ".");
            Console.Write("Please correct the path and run the ");
            Console.WriteLine("sample again.");
            return;
        }

        // Retrieve the input and output file streams.
        using (FileStream inputFileStream =
            new FileStream(sourceFile, FileMode.Open, FileAccess.Read))
        {
            using (FileStream outputFileStream =
                new FileStream(targetFile, FileMode.Create, FileAccess.Write))
            {

                // Create a new ToBase64Transform object to convert to base 64.
                ToBase64Transform base64Transform = new ToBase64Transform();

                // Create a new byte array with the size of the output block size.
                byte[] outputBytes = new byte[base64Transform.OutputBlockSize];

                // Retrieve the file contents into a byte array.
                byte[] inputBytes = new byte[inputFileStream.Length];
                inputFileStream.Read(inputBytes, 0, inputBytes.Length);

                // Verify that multiple blocks can not be transformed.
                if (!base64Transform.CanTransformMultipleBlocks)
                {
                    // Initialize the offset size.
                    int inputOffset = 0;

                    // Iterate through inputBytes transforming by blockSize.
                    int inputBlockSize = base64Transform.InputBlockSize;

                    while (inputBytes.Length - inputOffset > inputBlockSize)
                    {
                        base64Transform.TransformBlock(
                            inputBytes,
                            inputOffset,
                            inputBytes.Length - inputOffset,
                            outputBytes,
                            0);

                        inputOffset += base64Transform.InputBlockSize;
                        outputFileStream.Write(
                            outputBytes,
                            0,
                            base64Transform.OutputBlockSize);
                    }

                    // Transform the final block of data.
                    outputBytes = base64Transform.TransformFinalBlock(
                        inputBytes,
                        inputOffset,
                        inputBytes.Length - inputOffset);

                    outputFileStream.Write(outputBytes, 0, outputBytes.Length);
                    Console.WriteLine("Created encoded file at " + targetFile);
                }

                // Determine if the current transform can be reused.
                if (!base64Transform.CanReuseTransform)
                {
                    // Free any used resources.
                    base64Transform.Clear();
                }
            }
        }
    }

        public static void DecodeFromFile(string inFileName, string outFileName)
        {
            using (FromBase64Transform myTransform = new FromBase64Transform(FromBase64TransformMode.IgnoreWhiteSpaces))
            {

                byte[] myOutputBytes = new byte[myTransform.OutputBlockSize];

                // Open the input and output files.
                using (FileStream myInputFile = new FileStream(inFileName, FileMode.Open, FileAccess.Read))
                {
                    using (FileStream myOutputFile = new FileStream(outFileName, FileMode.Create, FileAccess.Write))
                    {

                        // Retrieve the file contents into a byte array. 
                        byte[] myInputBytes = new byte[myInputFile.Length];
                        myInputFile.Read(myInputBytes, 0, myInputBytes.Length);

                        // Transform the data in chunks the size of InputBlockSize. 
                        int i = 0;
                        while (myInputBytes.Length - i > 4/*myTransform.InputBlockSize*/)
                        {
                            int bytesWritten = myTransform.TransformBlock(myInputBytes, i, 4/*myTransform.InputBlockSize*/, myOutputBytes, 0);
                            i += 4/*myTransform.InputBlockSize*/;
                            myOutputFile.Write(myOutputBytes, 0, bytesWritten);
                        }

                        // Transform the final block of data.
                        myOutputBytes = myTransform.TransformFinalBlock(myInputBytes, i, myInputBytes.Length - i);
                        myOutputFile.Write(myOutputBytes, 0, myOutputBytes.Length);

                        // Free up any used resources.
                        myTransform.Clear();
                    }
                }
            }
        }
}

Applies to

See also

• Cryptographic Services