一款简单实用的加密算法：RC4，其源代码如下：

'RC4加密算法
'RC4是对称加密算法，其中：
' Expression 是待加密的明文或要解密的密文
' Password 是密钥
'返回：明文或密文
Public Function RC4(ByVal Expression As String,ByVal Password As String) As String

On Error Resume Next
Dim RB(0 To 255) As Integer,X As Long,Y As Long,Z As Long,Key() As Byte,ByteArray() As Byte,Temp As Byte
If Len(Password) = 0 Then
Exit Function
End If
If Len(Expression) = 0 Then
Exit Function
End If
If Len(Password) > 256 Then
Key() = StrConv(Left$(Password,256),vbFromUnicode)
Else
Key() = StrConv(Password,vbFromUnicode)
End If
For X = 0 To 255
RB(X) = X
Next X
X = 0
Y = 0
Z = 0
For X = 0 To 255
Y = (Y + RB(X) + Key(X Mod Len(Password))) Mod 256
Temp = RB(X)
RB(X) = RB(Y)
RB(Y) = Temp
Next X
X = 0
Y = 0
Z = 0
ByteArray() = StrConv(Expression,vbFromUnicode)
For X = 0 To Len(Expression)
Y = (Y + 1) Mod 256
Z = (Z + RB(Y)) Mod 256
Temp = RB(Y)
RB(Y) = RB(Z)
RB(Z) = Temp
ByteArray(X) = ByteArray(X) Xor (RB((RB(Y) + RB(Z)) Mod 256))
Next X
RC4 = StrConv(ByteArray,vbUnicode)

End Function

平常保密性不是很高的情况下，用它，我觉得也差不多了。

RSA/DES的源代码暂时未找到，此代码来源于http://freevbcode.com

在问专家找到的DES/3DES的加、解密源代码。