使用雜湊程式碼確定資料完整性
雜湊值是唯一識別資料的固定長度數值。 由於雜湊值將大量資料表示成較小的數值，因此雜湊值可用於數位簽章。 簽署雜湊值比簽署較大的值更有效率。 雜湊值也可用來驗證經由不安全通道傳送之資料的完整性。 收到之資料的雜湊值可以和所送出的資料的雜湊值比對，決定資料是否有更改。
本主題說明如何使用 System.Security.Cryptography 命名空間中的類別，產生及驗證雜湊程式碼。
產生雜湊
Managed 雜湊類別可雜湊位元組陣列或 Managed 資料流物件。 以下範例使用 SHA1 雜湊演算法來建立字串的雜湊值。 這個範例會使用 UnicodeEncoding 類別，將字串轉換成使用 SHA1Managed 類別雜湊的位元組陣列。 接著這個雜湊值會顯示在主控台上。
Imports System
Imports System.Security.Cryptography
Imports System.Text
Module Program
Sub Main()
Dim HashValue() As Byte
Dim MessageString As String = "This is the original message!"
'Create a new instance of the UnicodeEncoding class to
'convert the string into an array of Unicode bytes.
Dim UE As New UnicodeEncoding()
'Convert the string into an array of bytes.
Dim MessageBytes As Byte() = UE.GetBytes(MessageString)
'Create a new instance of the SHA1Managed class to create
'the hash value.
Dim SHhash As New SHA1Managed()
'Create the hash value from the array of bytes.
HashValue = SHhash.ComputeHash(MessageBytes)
'Display the hash value to the console.
Dim b As Byte
For Each b In HashValue
Console.Write("{0} ", b)
Next b
End Sub
End Module
using System;
using System.IO;
using System.Security.Cryptography;
using System.Text;
class Class1
{
static void Main(string[] args)
{
byte[] HashValue;
string MessageString = "This is the original message!";
//Create a new instance of the UnicodeEncoding class to
//convert the string into an array of Unicode bytes.
UnicodeEncoding UE = new UnicodeEncoding();
//Convert the string into an array of bytes.
byte[] MessageBytes = UE.GetBytes(MessageString);
//Create a new instance of the SHA1Managed class to create
//the hash value.
SHA1Managed SHhash = new SHA1Managed();
//Create the hash value from the array of bytes.
HashValue = SHhash.ComputeHash(MessageBytes);
//Display the hash value to the console.
foreach (byte b in HashValue)
{
Console.Write("{0} ", b);
}
}
}
這個程式碼會對主控台顯示以下字串：
59 4 248 102 77 97 142 201 210 12 224 93 25 41 100 197 213 134 130 135
驗證雜湊
可比對資料與雜湊值決定其完整性。 通常，資料是在某個時間雜湊並以某種方式來保護雜湊值。 稍後，可再雜湊資料一次並與受到保護的值相比對。 如果雜湊值相符，則資料未被更改。 如果值不相符，則資料已損毀。 若要讓這個系統運作順利，受保護的雜湊必須加密或對所有未受信任者保密。
以下範例比對字串之前的雜湊值和新雜湊值。 這個範例以迴圈 (Loop) 方式比較雜湊值的每個位元組。
Imports System
Imports System.Security.Cryptography
Imports System.Text
Module Module1
Sub Main()
'This hash value is produced from "This is the original message!"
'using SHA1Managed.
Dim SentHashValue As Byte() = {59, 4, 248, 102, 77, 97, 142, 201, 210, 12, 224, 93, 25, 41, 100, 197, 213, 134, 130, 135}
'This is the string that corresponds to the previous hash value.
Dim MessageString As String = "This is the original message!"
Dim CompareHashValue() As Byte
'Create a new instance of the UnicodeEncoding class to
'convert the string into an array of Unicode bytes.
Dim UE As New UnicodeEncoding()
'Convert the string into an array of bytes.
Dim MessageBytes As Byte() = UE.GetBytes(MessageString)
'Create a new instance of the SHA1Managed class to create
'the hash value.
Dim SHhash As New SHA1Managed()
'Create the hash value from the array of bytes.
CompareHashValue = SHhash.ComputeHash(MessageBytes)
Dim Same As Boolean = True
'Compare the values of the two byte arrays.
Dim x As Integer
For x = 0 To SentHashValue.Length - 1
If SentHashValue(x) <> CompareHashValue(x) Then
Same = False
End If
Next x
'Display whether or not the hash values are the same.
If Same Then
Console.WriteLine("The hash codes match.")
Else
Console.WriteLine("The hash codes do not match.")
End If
End Sub
End Module
using System;
using System.Security.Cryptography;
using System.Text;
class Class1
{
static void Main()
{
//This hash value is produced from "This is the original message!"
//using SHA1Managed.
byte[] SentHashValue = { 59, 4, 248, 102, 77, 97, 142, 201, 210, 12, 224, 93, 25, 41, 100, 197, 213, 134, 130, 135 };
//This is the string that corresponds to the previous hash value.
string MessageString = "This is the original message!";
byte[] CompareHashValue;
//Create a new instance of the UnicodeEncoding class to
//convert the string into an array of Unicode bytes.
UnicodeEncoding UE = new UnicodeEncoding();
//Convert the string into an array of bytes.
byte[] MessageBytes = UE.GetBytes(MessageString);
//Create a new instance of the SHA1Managed class to create
//the hash value.
SHA1Managed SHhash = new SHA1Managed();
//Create the hash value from the array of bytes.
CompareHashValue = SHhash.ComputeHash(MessageBytes);
bool Same = true;
//Compare the values of the two byte arrays.
for (int x = 0; x < SentHashValue.Length; x++)
{
if (SentHashValue[x] != CompareHashValue[x])
{
Same = false;
}
}
//Display whether or not the hash values are the same.
if (Same)
{
Console.WriteLine("The hash codes match.");
}
else
{
Console.WriteLine("The hash codes do not match.");
}
}
}
如果兩個雜湊值相符，這個程式碼就會對主控台顯示以下內容：
The hash codes match.
如果不相符，程式碼將顯示以下內容：
The hash codes do not match.