java的扩展包很好的实现了你需要的功能。这个包在java.security.*当然了还有很多好的加密方法，在sun的第三方jar包中有。目前密码加密使用用的是MD5加密，这个是单向加密，不可以解密。要想实现加密和解密，那么就需要学习密码学的知识。
希望对你有所帮助。
最简单的就一个FOR循环要加密的文件 再声明一个字符串 遍历要加密的文件和字符串进行位与操作或之类操作类似这样->
import java.util.Arrays
public class Test {
public static void main(String[] args) {
String str = "hello"
byte[] strCode = str.getBytes()
System.out.println("原始信息字节码："+Arrays.toString(strCode))
String key = "abcde"
byte[] keyCode = key.getBytes()
System.out.println("密钥字节码："+Arrays.toString(keyCode))
byte[] finallyCode = new byte[strCode.length]
for(int i=0i<str.length()i++){
finallyCode[i] = (byte) (strCode[i] ^ keyCode[i])
}
System.out.println("加密后的字节码："+Arrays.toString(finallyCode))
System.out.println("加密后的字符串："+new String(finallyCode))
//============解密
for(int i=0i<str.length()i++){
finallyCode[i] = (byte) (finallyCode[i] ^ keyCode[i])
}
System.out.println("解密后的字节码："+Arrays.toString(finallyCode))
System.out.println("解密后的字符串："+new String(finallyCode))
}
}
哈哈!不会是老师留给你的作业吧!在网上做牛!VERSION 4.00
Begin VB.Form Form1
Caption = "Sample"
ClientHeight= 705
ClientLeft = 3915
ClientTop = 3315
ClientWidth = 1800
ControlBox = 0 'False
Height = 1110
Left= 3855
LinkTopic = "Form1"
MaxButton = 0 'False
MinButton = 0 'False
ScaleHeight = 705
ScaleWidth = 1800
Top = 2970
Width = 1920
Begin VB.CommandButton Command1
Caption = "Command1"
Height = 495
Left= 240
TabIndex= 0
Top = 120
Width = 1215
End
End
Attribute VB_Name = "Form1"
Attribute VB_Creatable = False
Attribute VB_Exposed = False
Sub FileEncodeAndDecode(InputFile As String, OutputFile As String, PasswordKey As String)
Dim temp As Single
Dim Char As String * 1
Dim XORMask As Single
Dim temp1 As Integer
Open InputFile For Binary As #1
Open OutputFile For Binary As #2
For x = 1 To Len(PasswordKey)
temp = Asc(Mid$(PasswordKey, x, 1))
For y = 1 To temp
temp1 = Rnd
Next y
' Re-seed to throw off prying eyes
Randomize temp1
Next x
Counter = 0
For z = 1 To FileLen(InputFile)
'Generate random mask
XORMask = Int(Rnd * 256)
'Get the char &change it
Get 1, , Char
Char = Chr$((Asc(Char) Xor XORMask))
Put 2, , Char
Counter = Counter + 1
If Counter >Len(PasswordKey) Then Counter = 1
' Pull random numbers from the hat
For x = 1 To (Asc(Mid$(PasswordKey, Counter, 1)) * 2)
temp = Rnd
Next x
Next z
Close #1
Close #2
End Sub
Private Sub Command1_Click()
Dim InputFile As String
Dim OutputFile As String
Dim PasswordKey As String
InputFile = InputBox("Enter a filename to encode")
OutputFile = InputBox("Enter the new filename this will become ")
PasswordKey = InputBox("Enter the password (key)")
Call FileEncodeAndDecode(InputFile, OutputFile, PasswordKey)
MsgBox "File written to " + OutputFile
End
End Sub
Private Sub Form_Load()
Command1.Caption = "Code/Decode"
End Sub
Form=enc-dec.frm
Reference=*\G{BEF6E001-A874-101A-8BBA-00AA00300CAB}#2.0#0#D:\WINDOWS\SYSTEM\OLEPRO32.DLL#Standard OLE Types
Reference=*\G{00025E01-0000-0000-C000-000000000046}#3.0#0#D:\PROGRAM FILES\COMMON FILES\MICROSOFT SHARED\DD:\PROGRAM FIL#Microsoft DAO 3.0 Object Library
ProjWinSize=113,438,221,107
ProjWinShow=2
Name="Project1"
HelpContextID="0"
StartMode=0
VersionCompatible32="0"
MajorVer=1
MinorVer=0
RevisionVer=0
AutoIncrementVer=0
ServerSupportFiles=0
VersionCompanyName="Southern Cross Software"
