HMACSHA256 类
定义
重要
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使用 SHA256 哈希函数计算基于哈希值的消息验证代码 (HMAC)。
public ref class HMACSHA256 : System::Security::Cryptography::HMAC[System.Runtime.Versioning.UnsupportedOSPlatform("browser")]
public class HMACSHA256 : System.Security.Cryptography.HMACpublic class HMACSHA256 : System.Security.Cryptography.HMAC[System.Runtime.InteropServices.ComVisible(true)]
public class HMACSHA256 : System.Security.Cryptography.HMAC[<System.Runtime.Versioning.UnsupportedOSPlatform("browser")>]
type HMACSHA256 = class
inherit HMACtype HMACSHA256 = class
inherit HMAC[<System.Runtime.InteropServices.ComVisible(true)>]
type HMACSHA256 = class
inherit HMACPublic Class HMACSHA256
Inherits HMAC- 继承
- 属性
示例
以下示例演示如何使用 HMACSHA256 对象对文件进行签名，然后如何验证该文件。
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
注解
HMACSHA256 是一种键控哈希算法，它由 SHA-256 哈希函数构造，用作基于哈希的消息身份验证代码 (HMAC) 。 HMAC 进程将密钥与消息数据混合，使用哈希函数对结果进行哈希处理，再次将哈希值与密钥混合，然后再次应用哈希函数。 输出哈希的长度为 256 位。
HMAC 可用于确定通过不安全通道发送的消息是否已被篡改，前提是发送方和接收方共享密钥。 发送方计算原始数据的哈希值，并将原始数据和哈希值作为单个消息发送。 接收方重新计算收到的消息的哈希值，并检查计算的 HMAC 是否与传输的 HMAC 匹配。
对数据或哈希值的任何更改都会导致不匹配，因为需要知道密钥才能更改消息并重现正确的哈希值。 因此，如果原始哈希值和计算的哈希值匹配，则会对消息进行身份验证。
HMACSHA256 接受任何大小的密钥，并生成长度为 256 位的哈希序列。
构造函数
| HMACSHA256() |
使用随机生成的密钥初始化 HMACSHA256 类的新实例。 |
| HMACSHA256(Byte[]) |
使用指定的密钥数据初始化 HMACSHA256 类的新实例。 |
字段
| HashSizeInBits |
HMAC SHA256 算法生成的哈希大小（以位为单位）。 |
| HashSizeInBytes |
HMAC SHA256 算法生成的哈希大小（以字节为单位）。 |
| HashSizeValue |
表示计算所得的哈希代码的大小（以位为单位）。 (继承自 HashAlgorithm) |
| HashValue |
表示计算所得的哈希代码的值。 (继承自 HashAlgorithm) |
| KeyValue |
用于哈希算法的密钥。 (继承自 KeyedHashAlgorithm) |
| State |
表示哈希计算的状态。 (继承自 HashAlgorithm) |
属性
| BlockSizeValue |
获取或设置哈希值中使用的块大小。 (继承自 HMAC) |
| CanReuseTransform |
获取一个值，该值指示是否可重复使用当前转换。 (继承自 HashAlgorithm) |
| CanTransformMultipleBlocks |
当在派生类中重写时，获取一个值，该值指示是否可以转换多个块。 (继承自 HashAlgorithm) |
| Hash |
获取计算所得的哈希代码的值。 (继承自 HashAlgorithm) |
| HashName |
获取或设置用于哈希计算的哈希算法的名称。 (继承自 HMAC) |
| HashSize |
获取计算得到的 HMAC 的大小（以位为单位）。 |
| HashSize |
获取计算所得的哈希代码的大小（以位为单位）。 (继承自 HashAlgorithm) |
| InputBlockSize |
当在派生类中重写时，获取输入块的大小。 (继承自 HashAlgorithm) |
| Key |
获取或设置要在 HMAC 计算中使用的密钥。 |
| Key |
获取或设置要在 HMAC 计算中使用的密钥。 (继承自 HMAC) |
| OutputBlockSize |
当在派生类中重写时，获取输出块的大小。 (继承自 HashAlgorithm) |
方法
显式接口实现
| IDisposable.Dispose() |
释放由 HashAlgorithm 占用的非托管资源，还可以另外再释放托管资源。 (继承自 HashAlgorithm) |
