SecureString.Clear メソッドとは何？わかりやすく解説 Weblio辞書

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.NET Framework クラスライブラリリファレンス

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SecureString.Clear メソッド

メモ : このメソッドは、.NET Framework version 2.0 で新しく追加されたものです。

現在のセキュリティ文字列の値を削除します。

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

Visual Basic (宣言)

Public Sub Clear

Visual Basic (使用法)

Dim instance As SecureString

instance.Clear

public void Clear ()

C++

public:
void Clear ()

public void Clear ()

JScript

public function Clear ()

例外

例外の種類	条件
ObjectDisposedException	このセキュリティ文字列は、既に破棄されています。
InvalidOperationException	このセキュリティ文字列は読み取り専用です。

解説

このセキュリティ文字列の値を格納するコンピュータメモリが 0 に設定された後、このセキュリティ文字列の長さが 0 に設定されます。

使用例

AppendChar、InsertAt、RemoveAt、SetAt、Clear の各メソッドが SecureString オブジェクトの値にどのような影響を与えるかをデモンストレーションするコード例を次に示します。

Visual Basic

' This example demonstrates the AppendChar, 
' InsertAt, RemoveAt, SetAt, and Clear methods.
Imports System
Imports System.Security

Class Sample
   Public Shared Sub Main()
      Dim msg1 As String
 = "   SecureString = {0}" & vbCrLf & "
   Length = {1}" & vbCrLf
      Dim msg2 As String
 = "This example demonstrates the effect of the AppendChar, InsertAt,"
 & vbCrLf & _
                           "RemoveAt, SetAt, and Clear methods
 on the value of a SecureString" & vbCrLf & _
                           "object. This example simulates the
 value of the object because the" & vbCrLf & _
                           "actual value is encrypted."
 & vbCrLf
      Dim ss As New SecureString()
' 
'  This sample modifies the contents of a SecureString, ss, in
'  several steps. After each step, the length and simulated value of
 ss 
'  are displayed. The actual value of ss is encrypted.
'
      Console.WriteLine(msg2)
      
      Console.WriteLine("1) The initial value of the SecureString
 object:")
      Console.WriteLine(msg1, """""",
 ss.Length)
      
      Console.WriteLine("2) AppendChar: Append 'a' to the value:")
      ss.AppendChar("a"c)
      Console.WriteLine(msg1, """a""",
 ss.Length)
      
      Console.WriteLine("3) AppendChar: Append 'X' to the value:")
      ss.AppendChar("X"c)
      Console.WriteLine(msg1, """aX""",
 ss.Length)
      
      Console.WriteLine("4) AppendChar: Append 'c' to the value:")
      ss.AppendChar("c"c)
      Console.WriteLine(msg1, """aXc""",
 ss.Length)
      
      Console.WriteLine(("5) InsertAt: Insert 'd' at the end of
 the value (equivalent" & vbCrLf & "     to AppendChar):"))
      ss.InsertAt(ss.Length, "d"c)
      Console.WriteLine(msg1, """aXcd""",
 ss.Length)
      
      Console.WriteLine("6) RemoveAt: Remove the last character ('d')
 from the value:")
      ss.RemoveAt(3)
      Console.WriteLine(msg1, """aXc""",
 ss.Length)
      
      Console.WriteLine("7) SetAt: Set the second character
 ('X') of the value to 'b':")
      ss.SetAt(1, "b"c)
      Console.WriteLine(msg1, """abc""",
 ss.Length)
      
      Console.WriteLine("8) Clear: Delete the value of the SecureString
 object:")
      ss.Clear()
      Console.WriteLine(msg1, """""",
 ss.Length)
   End Sub 'Main
End Class 'Sample
'
'This code example produces the following results:
'
'This example demonstrates the effect of the AppendChar, InsertAt,
'RemoveAt, SetAt, and Clear methods on the value of a SecureString
'object. This example simulates the value of the object because the
'actual value is encrypted.
'
'1) The initial value of the SecureString object:
'   SecureString = ""
'   Length = 0
'
'2) AppendChar: Append 'a' to the value:
'   SecureString = "a"
'   Length = 1
'
'3) AppendChar: Append 'X' to the value:
'   SecureString = "aX"
'   Length = 2
'
'4) AppendChar: Append 'c' to the value:
'   SecureString = "aXc"
'   Length = 3
'
'5) InsertAt: Insert 'd' at the end of the value (equivalent
'     to AppendChar):
'   SecureString = "aXcd"
'   Length = 4
'
'6) RemoveAt: Remove the last character ('d') from the value:
'   SecureString = "aXc"
'   Length = 3
'
'7) SetAt: Set the second character ('X') of the value to 'b':
'   SecureString = "abc"
'   Length = 3
'
'8) Clear: Delete the value of the SecureString object:
'   SecureString = ""
'   Length = 0
'

// This example demonstrates the AppendChar, 
// InsertAt, RemoveAt, SetAt, and Clear methods.

using System;
using System.Security;

class Sample 
{
    public static void Main()
 
    {
    string msg1 = "   SecureString = {0}\n   Length = {1}\n";
    string msg2 = "This example demonstrates the effect of
 the AppendChar, InsertAt,\n" +
                  "RemoveAt, SetAt, and Clear methods on the value of a SecureString\n"
 +
                  "object. This example simulates the value of the object because
 the\n" +
                  "actual value is encrypted.\n";
    SecureString ss = new SecureString();
/* 
  This sample modifies the contents of a SecureString, ss, in
  several steps. After each step, the length and simulated value of ss 
  are displayed. The actual value of ss is encrypted.
*/
    Console.WriteLine(msg2);

    Console.WriteLine("1) The initial value of the SecureString object:");
    Console.WriteLine(msg1, "\"\"", ss.Length);

    Console.WriteLine("2) AppendChar: Append 'a' to the value:");
    ss.AppendChar('a');
    Console.WriteLine(msg1, "\"a\"", ss.Length);

    Console.WriteLine("3) AppendChar: Append 'X' to the value:");
    ss.AppendChar('X');
    Console.WriteLine(msg1, "\"aX\"", ss.Length);

    Console.WriteLine("4) AppendChar: Append 'c' to the value:");
    ss.AppendChar('c');
    Console.WriteLine(msg1, "\"aXc\"", ss.Length);

    Console.WriteLine("5) InsertAt: Insert 'd' at the end of the value (equivalent\n"
 +
                      "     to AppendChar):");
    ss.InsertAt(ss.Length, 'd');
    Console.WriteLine(msg1, "\"aXcd\"", ss.Length);

    Console.WriteLine("6) RemoveAt: Remove the last character ('d') from the
 value:");
    ss.RemoveAt(3);
    Console.WriteLine(msg1, "\"aXc\"", ss.Length);

    Console.WriteLine("7) SetAt: Set the second character ('X') of the value
 to 'b':");
    ss.SetAt(1, 'b');
    Console.WriteLine(msg1, "\"abc\"", ss.Length);

    Console.WriteLine("8) Clear: Delete the value of the SecureString object:");
    ss.Clear();
    Console.WriteLine(msg1, "\"\"", ss.Length);
    }
}
/*
This code example produces the following results:

This example demonstrates the effect of the AppendChar, InsertAt,
RemoveAt, SetAt, and Clear methods on the value of a SecureString
object. This example simulates the value of the object because the
actual value is encrypted.

1) The initial value of the SecureString object:
   SecureString = ""
   Length = 0

2) AppendChar: Append 'a' to the value:
   SecureString = "a"
   Length = 1

3) AppendChar: Append 'X' to the value:
   SecureString = "aX"
   Length = 2

4) AppendChar: Append 'c' to the value:
   SecureString = "aXc"
   Length = 3

5) InsertAt: Insert 'd' at the end of the value (equivalent
     to AppendChar):
   SecureString = "aXcd"
   Length = 4

6) RemoveAt: Remove the last character ('d') from the value:
   SecureString = "aXc"
   Length = 3

7) SetAt: Set the second character ('X') of the value to 'b':
   SecureString = "abc"
   Length = 3

8) Clear: Delete the value of the SecureString object:
   SecureString = ""
   Length = 0
*/

C++

// This example demonstrates the AppendChar,
// InsertAt, RemoveAt, SetAt, and Clear methods.

using namespace System;
using namespace System::Security;

int main()
{
    String^ msg1 = L"   SecureString = {0}\n   Length = {1}\n";
    String^ msg2 = L"This example demonstrates the effect of the AppendChar,
 InsertAt,\n"
    L"RemoveAt, SetAt, and Clear methods on the value of a SecureString\n"
    L"object. This example simulates the value of the object because the\n"
    L"actual value is encrypted.\n";
    SecureString ^ ss = gcnew SecureString;

    // This sample modifies the contents of a SecureString, ss, in
    // several steps. After each step, the length and simulated value
 of ss
    // are displayed. The actual value of ss is encrypted.
    Console::WriteLine( msg2 );
    Console::WriteLine( L"1) The initial value of the SecureString object:"
 );
    Console::WriteLine( msg1, L"\"\"", ss->Length );
    Console::WriteLine( L"2) AppendChar: Append 'a' to the value:" );

    ss->AppendChar( 'a' );
    Console::WriteLine( msg1, L"\"a\"", ss->Length );
    Console::WriteLine( L"3) AppendChar: Append 'X' to the value:" );

    ss->AppendChar( 'X' );
    Console::WriteLine( msg1, L"\"aX\"", ss->Length );
    Console::WriteLine( L"4) AppendChar: Append 'c' to the value:" );

    ss->AppendChar( 'c' );
    Console::WriteLine( msg1, L"\"aXc\"", ss->Length );
    Console::WriteLine( L"5) InsertAt: Insert 'd' at the end of the value (equivalent\n"
                        L"     to AppendChar):" );

    ss->InsertAt( ss->Length, 'd' );
    Console::WriteLine( msg1, L"\"aXcd\"", ss->Length );
    Console::WriteLine( L"6) RemoveAt: Remove the last character ('d') from
 the value:" );

    ss->RemoveAt( 3 );
    Console::WriteLine( msg1, L"\"aXc\"", ss->Length );
    Console::WriteLine( L"7) SetAt: Set the second character ('X') of the value
 to 'b':" );

    ss->SetAt( 1, 'b' );
    Console::WriteLine( msg1, L"\"abc\"", ss->Length );
    Console::WriteLine( L"8) Clear: Delete the value of the SecureString object:"
 );

    ss->Clear();
    Console::WriteLine( msg1, L"\"\"", ss->Length );

    return 0;
}

/*
This code example produces the following results:

This example demonstrates the effect of the AppendChar, InsertAt,
RemoveAt, SetAt, and Clear methods on the value of a SecureString
object. This example simulates the value of the object because the
actual value is encrypted.

1) The initial value of the SecureString object:
   SecureString = ""
   Length = 0

2) AppendChar: Append 'a' to the value:
   SecureString = "a"
   Length = 1

3) AppendChar: Append 'X' to the value:
   SecureString = "aX"
   Length = 2

4) AppendChar: Append 'c' to the value:
   SecureString = "aXc"
   Length = 3

5) InsertAt: Insert 'd' at the end of the value (equivalent
     to AppendChar):
   SecureString = "aXcd"
   Length = 4

6) RemoveAt: Remove the last character ('d') from the value:
   SecureString = "aXc"
   Length = 3

7) SetAt: Set the second character ('X') of the value to 'b':
   SecureString = "abc"
   Length = 3

8) Clear: Delete the value of the SecureString object:
   SecureString = ""
   Length = 0
*/

プラットフォーム

バージョン情報

.NET Framework
サポート対象 : 2.0

参照

関連項目
SecureString クラス
SecureString メンバ
System.Security 名前空間
Length

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SecureString.Clear メソッドとは？ わかりやすく解説

SecureString.Clear メソッド

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SecureString.Clear メソッドとは？わかりやすく解説