CryptoStream クラスとは何？わかりやすく解説 Weblio辞書

.NET Framework クラスライブラリリファレンス

索引トップ用語の索引ランキング

CryptoStream クラス

データストリームを暗号変換にリンクするストリームを定義します。

名前空間: System.Security.Cryptography
アセンブリ: mscorlib (mscorlib.dll 内)
構文

Visual Basic (宣言)

<ComVisibleAttribute(True)> _
Public Class CryptoStream
    Inherits Stream
    Implements IDisposable

Visual Basic (使用法)

Dim instance As CryptoStream

[ComVisibleAttribute(true)] 
public class CryptoStream : Stream, IDisposable

C++

[ComVisibleAttribute(true)] 
public ref class CryptoStream : public
 Stream, IDisposable

/** @attribute ComVisibleAttribute(true) */ 
public class CryptoStream extends Stream implements
 IDisposable

JScript

ComVisibleAttribute(true) 
public class CryptoStream extends
 Stream implements IDisposable

解説

共通言語ランタイムは、ストリーム指向の暗号デザインを採用しています。このデザインの中核となっているのが CryptoStream です。CryptoStream を実装するすべての暗号オブジェクトは、Stream を実装する任意のオブジェクトと一緒にチェインにまとめることができるため、あるオブジェクトからの出力をストリーム経由で別のオブジェクトの入力に転送できます。このとき、中間結果 (最初のオブジェクトからの出力) を別個に格納する必要はありません。

CryptoStream オブジェクトを使用した場合は、必ず Close メソッドを呼び出して明示的に閉じる必要があります。これによりストリームがフラッシュされ、残りのデータブロックが CryptoStream オブジェクトによってすべて処理されます。ただし、Close メソッドを呼び出す前に例外が発生した場合、CryptoStream オブジェクトを閉じることができない場合もあります。Close メソッドが常に呼び出されるようにするには、Close メソッド呼び出しを try/catch ステートメントの finally ブロックに記述します。

使用例

CryptoStream を使用して文字列を暗号化する方法を次の例に示します。このメソッドでは、RijndaelManaged クラスで Key と初期化ベクタ (IV) が指定されています。

Visual Basic

Imports System.Security.Cryptography
Imports System.Text
Imports System.IO

Module RijndaelSample

    Sub Main()
        Try
            ' Create a new Rijndael object to generate a key
            ' and initialization vector (IV).
            Dim RijndaelAlg As Rijndael = Rijndael.Create

            ' Create a string to encrypt.
            Dim sData As String
 = "Here is some data to encrypt."
            Dim FileName As String
 = "CText.txt"

            ' Encrypt text to a file using the file name, key, and IV.
            EncryptTextToFile(sData, FileName, RijndaelAlg.Key, RijndaelAlg.IV)

            ' Decrypt the text from a file using the file name, key,
 and IV.
            Dim Final As String
 = DecryptTextFromFile(FileName, RijndaelAlg.Key, RijndaelAlg.IV)

            ' Display the decrypted string to the console.
            Console.WriteLine(Final)
        Catch e As Exception
            Console.WriteLine(e.Message)
        End Try

        Console.ReadLine()

    End Sub


    Sub EncryptTextToFile(ByVal Data As
 String, ByVal FileName As
 String, ByVal Key() As Byte, ByVal IV() As Byte)
        Try
            ' Create or open the specified file.
            Dim fStream As FileStream = File.Open(FileName,
 FileMode.OpenOrCreate)

            ' Create a new Rijndael object.
            Dim RijndaelAlg As Rijndael = Rijndael.Create

            ' Create a CryptoStream using the FileStream 
            ' and the passed key and initialization vector (IV).
            Dim cStream As New
 CryptoStream(fStream, _
                                           RijndaelAlg.CreateEncryptor(Key, IV),
 _
                                           CryptoStreamMode.Write)

            ' Create a StreamWriter using the CryptoStream.
            Dim sWriter As New
 StreamWriter(cStream)

            Try

                ' Write the data to the stream 
                ' to encrypt it.
                sWriter.WriteLine(Data)
            Catch e As Exception

                Console.WriteLine("An error occurred: {0}",
 e.Message)

            Finally

                ' Close the streams and
                ' close the file.
                sWriter.Close()
                cStream.Close()
                fStream.Close()

            End Try
        Catch e As CryptographicException
            Console.WriteLine("A Cryptographic error occurred:
 {0}", e.Message)
        Catch e As UnauthorizedAccessException
            Console.WriteLine("A file error occurred: {0}",
 e.Message)
        End Try
    End Sub


    Function DecryptTextFromFile(ByVal FileName
 As String, ByVal Key()
 As Byte, ByVal IV() As Byte) As String
        Try
            ' Create or open the specified file. 
            Dim fStream As FileStream = File.Open(FileName,
 FileMode.OpenOrCreate)

            ' Create a new Rijndael object.
            Dim RijndaelAlg As Rijndael = Rijndael.Create

            ' Create a CryptoStream using the FileStream 
            ' and the passed key and initialization vector (IV).
            Dim cStream As New
 CryptoStream(fStream, _
                                            RijndaelAlg.CreateDecryptor(Key, IV),
 _
                                            CryptoStreamMode.Read)

            ' Create a StreamReader using the CryptoStream.
            Dim sReader As New
 StreamReader(cStream)

            ' Read the data from the stream 
            ' to decrypt it.
            Dim val As String
 = Nothing

            Try

                val = sReader.ReadLine()

            Catch e As Exception
                Console.WriteLine("An Cerror occurred: {0}",
 e.Message)
            Finally
                ' Close the streams and
                ' close the file.
                sReader.Close()
                cStream.Close()
                fStream.Close()


            End Try

            ' Return the string. 
            Return val

        Catch e As CryptographicException
            Console.WriteLine("A Cryptographic error occurred:
 {0}", e.Message)
            Return Nothing
        Catch e As UnauthorizedAccessException
            Console.WriteLine("A file error occurred: {0}",
 e.Message)
            Return Nothing
        End Try
    End Function
End Module

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

class RijndaelSample
{

    static void Main()
    {
        try
        {
            // Create a new Rijndael object to generate a key
            // and initialization vector (IV).
            Rijndael RijndaelAlg = Rijndael.Create();

            // Create a string to encrypt.
            string sData = "Here is some data to encrypt.";
            string FileName = "CText.txt";

            // Encrypt text to a file using the file name, key, and
 IV.
            EncryptTextToFile(sData, FileName, RijndaelAlg.Key, RijndaelAlg.IV);

            // Decrypt the text from a file using the file name, key,
 and IV.
            string Final = DecryptTextFromFile(FileName, RijndaelAlg.Key,
 RijndaelAlg.IV);

            // Display the decrypted string to the console.
            Console.WriteLine(Final);
        }
        catch (Exception e)
        {
            Console.WriteLine(e.Message);
        }

        Console.ReadLine();
    }

    public static void EncryptTextToFile(String
 Data, String FileName, byte[] Key, byte[] IV)
    {
        try
        {
            // Create or open the specified file.
            FileStream fStream = File.Open(FileName, FileMode.OpenOrCreate);

            // Create a new Rijndael object.
            Rijndael RijndaelAlg = Rijndael.Create();

            // Create a CryptoStream using the FileStream 
            // and the passed key and initialization vector (IV).
            CryptoStream cStream = new CryptoStream(fStream,
                RijndaelAlg.CreateEncryptor(Key, IV),
                CryptoStreamMode.Write);

            // Create a StreamWriter using the CryptoStream.
            StreamWriter sWriter = new StreamWriter(cStream);

            try
            {
                // Write the data to the stream 
                // to encrypt it.
                sWriter.WriteLine(Data);
            }
            catch (Exception e)
            {
                Console.WriteLine("An error occurred: {0}", e.Message);
            }
            finally
            {
                // Close the streams and
                // close the file.
                sWriter.Close();
                cStream.Close();
                fStream.Close();
            }
        }
        catch (CryptographicException e)
        {
            Console.WriteLine("A Cryptographic error occurred: {0}", e.Message);
        }
        catch (UnauthorizedAccessException e)
        {
            Console.WriteLine("A file error occurred: {0}", e.Message);
        }

    }

    public static string
 DecryptTextFromFile(String FileName, byte[] Key, byte[] IV)
    {
        try
        {
            // Create or open the specified file. 
            FileStream fStream = File.Open(FileName, FileMode.OpenOrCreate);

            // Create a new Rijndael object.
            Rijndael RijndaelAlg = Rijndael.Create();

            // Create a CryptoStream using the FileStream 
            // and the passed key and initialization vector (IV).
            CryptoStream cStream = new CryptoStream(fStream,
                RijndaelAlg.CreateDecryptor(Key, IV),
                CryptoStreamMode.Read);

            // Create a StreamReader using the CryptoStream.
            StreamReader sReader = new StreamReader(cStream);

            string val = null;

            try
            {
                // Read the data from the stream 
                // to decrypt it.
                val = sReader.ReadLine();


            }
            catch (Exception e)
            {
                Console.WriteLine("An error occurred: {0}", e.Message);
            }
            finally
            {

                // Close the streams and
                // close the file.
                sReader.Close();
                cStream.Close();
                fStream.Close();
            }

            // Return the string. 
            return val;
        }
        catch (CryptographicException e)
        {
            Console.WriteLine("A Cryptographic error occurred: {0}", e.Message);
            return null;
        }
        catch (UnauthorizedAccessException e)
        {
            Console.WriteLine("A file error occurred: {0}", e.Message);
            return null;
        }
    }
}