HMACSHA256 クラス

定義

SHA256 ハッシュ関数を使用して、ハッシュ メッセージ認証コード (HMAC) を計算します。Computes a Hash-based Message Authentication Code (HMAC) by using the SHA256 hash function.

public ref class HMACSHA256 : System::Security::Cryptography::HMAC
[System.Runtime.InteropServices.ComVisible(true)]
public class HMACSHA256 : System.Security.Cryptography.HMAC
type HMACSHA256 = class
    inherit HMAC
Public Class HMACSHA256
Inherits HMAC
継承
属性

次の例では、 HMACSHA256オブジェクトを使用してファイルに署名する方法と、ファイルを検証する方法を示します。The following example shows how to sign a file by using the HMACSHA256 object and then how to verify the file.

using namespace System;
using namespace System::IO;
using namespace System::Security::Cryptography;

// Computes a keyed hash for a source file, creates a target file with the keyed hash
// prepended to the contents of the source file, then decodes the file and compares
// the source and the decoded files.
void EncodeFile( array<Byte>^key, String^ sourceFile, String^ destFile )
{
   
   // Initialize the keyed hash object.
   HMACSHA256^ myhmacsha256 = gcnew HMACSHA256( key );
   FileStream^ inStream = gcnew FileStream( sourceFile,FileMode::Open );
   FileStream^ outStream = gcnew FileStream( destFile,FileMode::Create );
   
   // Compute the hash of the input file.
   array<Byte>^hashValue = myhmacsha256->ComputeHash( inStream );
   
   // Reset inStream to the beginning of the file.
   inStream->Position = 0;
   
   // Write the computed hash value to the output file.
   outStream->Write( hashValue, 0, hashValue->Length );
   
   // Copy the contents of the sourceFile to the destFile.
   int bytesRead;
   
   // read 1K at a time
   array<Byte>^buffer = gcnew array<Byte>(1024);
   do
   {
      
      // Read from the wrapping CryptoStream.
      bytesRead = inStream->Read( buffer, 0, 1024 );
      outStream->Write( buffer, 0, bytesRead );
   }
   while ( bytesRead > 0 );

   myhmacsha256->Clear();
   
   // Close the streams
   inStream->Close();
   outStream->Close();
   return;
} // end EncodeFile



// Decode the encoded file and compare to original file.
bool DecodeFile( array<Byte>^key, String^ sourceFile )
{
   
   // Initialize the keyed hash object. 
   HMACSHA256^ hmacsha256 = gcnew HMACSHA256( key );
   
   // Create an array to hold the keyed hash value read from the file.
   array<Byte>^storedHash = gcnew array<Byte>(hmacsha256->HashSize / 8);
   
   // Create a FileStream for the source file.
   FileStream^ inStream = gcnew FileStream( sourceFile,FileMode::Open );
   
   // Read in the storedHash.
   inStream->Read( storedHash, 0, storedHash->Length );
   
   // Compute the hash of the remaining contents of the file.
   // The stream is properly positioned at the beginning of the content, 
   // immediately after the stored hash value.
   array<Byte>^computedHash = hmacsha256->ComputeHash( inStream );
   
   // compare the computed hash with the stored value
   bool err = false;
   for ( int i = 0; i < storedHash->Length; i++ )
   {
      if ( computedHash[ i ] != storedHash[ i ] )
      {
         err = true;
      }
   }
   if (err)
        {
            Console::WriteLine("Hash values differ! Encoded file has been tampered with!");
            return false;
        }
        else
        {
            Console::WriteLine("Hash values agree -- no tampering occurred.");
            return true;
        }

} //end DecodeFile


int main()
{
   array<String^>^Fileargs = Environment::GetCommandLineArgs();
   String^ usageText = "Usage: HMACSHA256 inputfile.txt encodedfile.hsh\nYou must specify the two file names. Only the first file must exist.\n";
   
   //If no file names are specified, write usage text.
   if ( Fileargs->Length < 3 )
   {
      Console::WriteLine( usageText );
   }
   else
   {
      try
      {
         
         // Create a random key using a random number generator. This would be the
         //  secret key shared by sender and receiver.
         array<Byte>^secretkey = gcnew array<Byte>(64);
         
         //RNGCryptoServiceProvider is an implementation of a random number generator.
         RNGCryptoServiceProvider^ rng = gcnew RNGCryptoServiceProvider;
         
         // The array is now filled with cryptographically strong random bytes.
         rng->GetBytes( secretkey );
         
         // Use the secret key to encode the message file.
         EncodeFile( secretkey, Fileargs[ 1 ], Fileargs[ 2 ] );
         
         // Take the encoded file and decode
         DecodeFile( secretkey, Fileargs[ 2 ] );
      }
      catch ( IOException^ e ) 
      {
         Console::WriteLine( "Error: File not found", e );
      }

   }
} //end main


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

public class HMACSHA256example
{

    public static void Main(string[] Fileargs)
    {
        string dataFile;
        string signedFile;
        //If no file names are specified, create them.
        if (Fileargs.Length < 2)
        {
            dataFile = @"text.txt";
            signedFile = "signedFile.enc";

            if (!File.Exists(dataFile))
            {
                // Create a file to write to.
                using (StreamWriter sw = File.CreateText(dataFile))
                {
                    sw.WriteLine("Here is a message to sign");
                }
            }

        }
        else
        {
            dataFile = Fileargs[0];
            signedFile = Fileargs[1];
        }
        try
        {
            // Create a random key using a random number generator. This would be the
            //  secret key shared by sender and receiver.
            byte[] secretkey = new Byte[64];
            //RNGCryptoServiceProvider is an implementation of a random number generator.
            using (RNGCryptoServiceProvider rng = new RNGCryptoServiceProvider())
            {
                // The array is now filled with cryptographically strong random bytes.
                rng.GetBytes(secretkey);

                // Use the secret key to sign the message file.
                SignFile(secretkey, dataFile, signedFile);

                // Verify the signed file
                VerifyFile(secretkey, signedFile);
            }
        }
        catch (IOException e)
        {
            Console.WriteLine("Error: File not found", e);
        }

    }  //end main
    // Computes a keyed hash for a source file and creates a target file with the keyed hash
    // prepended to the contents of the source file. 
    public static void SignFile(byte[] key, String sourceFile, String destFile)
    {
        // Initialize the keyed hash object.
        using (HMACSHA256 hmac = new HMACSHA256(key))
        {
            using (FileStream inStream = new FileStream(sourceFile, FileMode.Open))
            {
                using (FileStream outStream = new FileStream(destFile, FileMode.Create))
                {
                    // Compute the hash of the input file.
                    byte[] hashValue = hmac.ComputeHash(inStream);
                    // Reset inStream to the beginning of the file.
                    inStream.Position = 0;
                    // Write the computed hash value to the output file.
                    outStream.Write(hashValue, 0, hashValue.Length);
                    // Copy the contents of the sourceFile to the destFile.
                    int bytesRead;
                    // read 1K at a time
                    byte[] buffer = new byte[1024];
                    do
                    {
                        // Read from the wrapping CryptoStream.
                        bytesRead = inStream.Read(buffer, 0, 1024);
                        outStream.Write(buffer, 0, bytesRead);
                    } while (bytesRead > 0);
                }
            }
        }
        return;
    } // end SignFile


    // Compares the key in the source file with a new key created for the data portion of the file. If the keys 
    // compare the data has not been tampered with.
    public static bool VerifyFile(byte[] key, String sourceFile)
    {
        bool err = false;
        // Initialize the keyed hash object. 
        using (HMACSHA256 hmac = new HMACSHA256(key))
        {
            // Create an array to hold the keyed hash value read from the file.
            byte[] storedHash = new byte[hmac.HashSize / 8];
            // Create a FileStream for the source file.
            using (FileStream inStream = new FileStream(sourceFile, FileMode.Open))
            {
                // Read in the storedHash.
                inStream.Read(storedHash, 0, storedHash.Length);
                // Compute the hash of the remaining contents of the file.
                // The stream is properly positioned at the beginning of the content, 
                // immediately after the stored hash value.
                byte[] computedHash = hmac.ComputeHash(inStream);
                // compare the computed hash with the stored value

                for (int i = 0; i < storedHash.Length; i++)
                {
                    if (computedHash[i] != storedHash[i])
                    {
                        err = true;
                    }
                }
            }
        }
        if (err)
        {
            Console.WriteLine("Hash values differ! Signed file has been tampered with!");
            return false;
        }
        else
        {
            Console.WriteLine("Hash values agree -- no tampering occurred.");
            return true;
        }

    } //end VerifyFile

} //end class
Imports System.IO
Imports System.Security.Cryptography

Public Class HMACSHA256example

    Public Shared Sub Main(ByVal Fileargs() As String)
        Dim dataFile As String
        Dim signedFile As String
        'If no file names are specified, create them.
        If Fileargs.Length < 2 Then
            dataFile = "text.txt"
            signedFile = "signedFile.enc"

            If Not File.Exists(dataFile) Then
                ' Create a file to write to.
                Using sw As StreamWriter = File.CreateText(dataFile)
                    sw.WriteLine("Here is a message to sign")
                End Using
            End If

        Else
            dataFile = Fileargs(0)
            signedFile = Fileargs(1)
        End If
        Try
            ' Create a random key using a random number generator. This would be the
            '  secret key shared by sender and receiver.
            Dim secretkey() As Byte = New [Byte](63) {}
            'RNGCryptoServiceProvider is an implementation of a random number generator.
            Using rng As New RNGCryptoServiceProvider()
                ' The array is now filled with cryptographically strong random bytes.
                rng.GetBytes(secretkey)

                ' Use the secret key to encode the message file.
                SignFile(secretkey, dataFile, signedFile)

                ' Take the encoded file and decode
                VerifyFile(secretkey, signedFile)
            End Using
        Catch e As IOException
            Console.WriteLine("Error: File not found", e)
        End Try

    End Sub

    ' Computes a keyed hash for a source file and creates a target file with the keyed hash
    ' prepended to the contents of the source file. 
    Public Shared Sub SignFile(ByVal key() As Byte, ByVal sourceFile As String, ByVal destFile As String)
        ' Initialize the keyed hash object.
        Using myhmac As New HMACSHA256(key)
            Using inStream As New FileStream(sourceFile, FileMode.Open)
                Using outStream As New FileStream(destFile, FileMode.Create)
                    ' Compute the hash of the input file.
                    Dim hashValue As Byte() = myhmac.ComputeHash(inStream)
                    ' Reset inStream to the beginning of the file.
                    inStream.Position = 0
                    ' Write the computed hash value to the output file.
                    outStream.Write(hashValue, 0, hashValue.Length)
                    ' Copy the contents of the sourceFile to the destFile.
                    Dim bytesRead As Integer
                    ' read 1K at a time
                    Dim buffer(1023) As Byte
                    Do
                        ' Read from the wrapping CryptoStream.
                        bytesRead = inStream.Read(buffer, 0, 1024)
                        outStream.Write(buffer, 0, bytesRead)
                    Loop While bytesRead > 0
                End Using
            End Using
        End Using
        Return

    End Sub
    ' end SignFile

    ' Compares the key in the source file with a new key created for the data portion of the file. If the keys 
    ' compare the data has not been tampered with.
    Public Shared Function VerifyFile(ByVal key() As Byte, ByVal sourceFile As String) As Boolean
        Dim err As Boolean = False
        ' Initialize the keyed hash object. 
        Using hmac As New HMACSHA256(key)
            ' Create an array to hold the keyed hash value read from the file.
            Dim storedHash(hmac.HashSize / 8 - 1) As Byte
            ' Create a FileStream for the source file.
            Using inStream As New FileStream(sourceFile, FileMode.Open)
                ' Read in the storedHash.
                inStream.Read(storedHash, 0, storedHash.Length - 1)
                ' Compute the hash of the remaining contents of the file.
                ' The stream is properly positioned at the beginning of the content, 
                ' immediately after the stored hash value.
                Dim computedHash As Byte() = hmac.ComputeHash(inStream)
                ' compare the computed hash with the stored value
                Dim i As Integer
                For i = 0 To storedHash.Length - 2
                    If computedHash(i) <> storedHash(i) Then
                        err = True
                    End If
                Next i
            End Using
        End Using
        If err Then
            Console.WriteLine("Hash values differ! Signed file has been tampered with!")
            Return False
        Else
            Console.WriteLine("Hash values agree -- no tampering occurred.")
            Return True
        End If

    End Function 'VerifyFile 
End Class
'end class

注釈

HMACSHA256は、SHA-256 ハッシュ関数から構築され、ハッシュベースのメッセージ認証コード (HMAC) として使用される、キー付きハッシュアルゴリズムの一種です。HMACSHA256 is a type of keyed hash algorithm that is constructed from the SHA-256 hash function and used as a Hash-based Message Authentication Code (HMAC). HMAC プロセスでは、秘密キーをメッセージデータと組み合わせ、ハッシュ関数を使用して結果をハッシュし、そのハッシュ値を秘密キーで再びミックスして、もう一度ハッシュ関数を適用します。The HMAC process mixes a secret key with the message data, hashes the result with the hash function, mixes that hash value with the secret key again, and then applies the hash function a second time. 出力ハッシュの長さは256ビットです。The output hash is 256 bits in length.

HMAC は、送信側と受信側が秘密キーを共有している場合に、セキュリティで保護されていないチャネルを介して送信されたメッセージが改ざんされていないかどうかを判断するために使用できます。An HMAC can be used to determine whether a message sent over an insecure channel has been tampered with, provided that the sender and receiver share a secret key. 送信側は元のデータのハッシュ値を計算し、元のデータとハッシュ値の両方を1つのメッセージとして送信します。The sender computes the hash value for the original data and sends both the original data and hash value as a single message. 受信側は、受信したメッセージのハッシュ値を再計算し、計算された HMAC が送信された HMAC と一致することを確認します。The receiver recalculates the hash value on the received message and checks that the computed HMAC matches the transmitted HMAC.

データまたはハッシュ値を変更した場合、メッセージを変更し、正しいハッシュ値を再現するために秘密鍵の知識が必要になるため、不一致が発生します。Any change to the data or the hash value results in a mismatch, because knowledge of the secret key is required to change the message and reproduce the correct hash value. したがって、元のハッシュ値と計算されたハッシュ値が一致する場合、メッセージは認証されます。Therefore, if the original and computed hash values match, the message is authenticated.

HMACSHA256任意のサイズのキーを受け入れ、ハッシュシーケンス256ビットの長さを生成します。HMACSHA256 accepts keys of any size, and produces a hash sequence 256 bits in length.

コンストラクター

HMACSHA256()

ランダムに生成されたキーを指定して、HMACSHA256 クラスの新しいインスタンスを初期化します。Initializes a new instance of the HMACSHA256 class with a randomly generated key.

HMACSHA256(Byte[])

キー データを指定して、HMACSHA256 クラスの新しいインスタンスを初期化します。Initializes a new instance of the HMACSHA256 class with the specified key data.

フィールド

HashSizeValue

計算されたハッシュ コードのサイズをビット単位で表します。Represents the size, in bits, of the computed hash code.

(継承元 HashAlgorithm)
HashValue

計算されたハッシュ コードの値を表します。Represents the value of the computed hash code.

(継承元 HashAlgorithm)
KeyValue

ハッシュ アルゴリズムで使用するキー。The key to use in the hash algorithm.

(継承元 KeyedHashAlgorithm)
State

ハッシュ計算の状態を表します。Represents the state of the hash computation.

(継承元 HashAlgorithm)

プロパティ

BlockSizeValue

ハッシュ値で使用するブロック サイズを取得または設定します。Gets or sets the block size to use in the hash value.

(継承元 HMAC)
CanReuseTransform

現在の変換を再利用できるかどうかを示す値を取得します。Gets a value indicating whether the current transform can be reused.

(継承元 HashAlgorithm)
CanTransformMultipleBlocks

派生クラスでオーバーライドされると、複数のブロックを変換できるかどうかを示す値を取得します。When overridden in a derived class, gets a value indicating whether multiple blocks can be transformed.

(継承元 HashAlgorithm)
Hash

計算されたハッシュ コードの値を取得します。Gets the value of the computed hash code.

(継承元 HashAlgorithm)
HashName

ハッシュに使用するハッシュ アルゴリズムの名前を取得または設定します。Gets or sets the name of the hash algorithm to use for hashing.

(継承元 HMAC)
HashSize
InputBlockSize

派生クラスでオーバーライドされると、入力ブロック サイズを取得します。When overridden in a derived class, gets the input block size.

(継承元 HashAlgorithm)
Key
OutputBlockSize

派生クラスでオーバーライドされると、出力ブロック サイズを取得します。When overridden in a derived class, gets the output block size.

(継承元 HashAlgorithm)

メソッド

Clear()

HashAlgorithm クラスによって使用されているすべてのリソースを解放します。Releases all resources used by the HashAlgorithm class.

(継承元 HashAlgorithm)
ComputeHash(Byte[])

指定したバイト配列のハッシュ値を計算します。Computes the hash value for the specified byte array.

(継承元 HashAlgorithm)
ComputeHash(Byte[], Int32, Int32)

指定したバイト配列の指定した領域のハッシュ値を計算します。Computes the hash value for the specified region of the specified byte array.

(継承元 HashAlgorithm)
ComputeHash(Stream)

指定された Stream オブジェクトのハッシュ値を計算します。Computes the hash value for the specified Stream object.

(継承元 HashAlgorithm)
Dispose()

HashAlgorithm クラスの現在のインスタンスによって使用されているすべてのリソースを解放します。Releases all resources used by the current instance of the HashAlgorithm class.

(継承元 HashAlgorithm)
Dispose(Boolean)
Equals(Object)

指定されたオブジェクトが現在のオブジェクトと等しいかどうかを判定します。Determines whether the specified object is equal to the current object.

(継承元 Object)
GetHashCode()

既定のハッシュ関数として機能します。Serves as the default hash function.

(継承元 Object)
GetType()

現在のインスタンスの Type を取得します。Gets the Type of the current instance.

(継承元 Object)
HashCore(Byte[], Int32, Int32)
HashCore(ReadOnlySpan<Byte>)
HashFinal()
Initialize()
MemberwiseClone()

現在の Object の簡易コピーを作成します。Creates a shallow copy of the current Object.

(継承元 Object)
ToString()

現在のオブジェクトを表す string を返します。Returns a string that represents the current object.

(継承元 Object)
TransformBlock(Byte[], Int32, Int32, Byte[], Int32)

入力バイト配列の指定した領域のハッシュ値を計算し、入力バイト配列の指定した領域を出力バイト配列の指定した領域にコピーします。Computes the hash value for the specified region of the input byte array and copies the specified region of the input byte array to the specified region of the output byte array.

(継承元 HashAlgorithm)
TransformFinalBlock(Byte[], Int32, Int32)

指定したバイト配列の指定した領域のハッシュ値を計算します。Computes the hash value for the specified region of the specified byte array.

(継承元 HashAlgorithm)
TryComputeHash(ReadOnlySpan<Byte>, Span<Byte>, Int32) (継承元 HashAlgorithm)
TryHashFinal(Span<Byte>, Int32)

明示的なインターフェイスの実装

IDisposable.Dispose()

HashAlgorithm によって使用されているアンマネージド リソースを解放し、オプションでマネージド リソースも解放します。Releases the unmanaged resources used by the HashAlgorithm and optionally releases the managed resources.

(継承元 HashAlgorithm)

適用対象

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