Data compression and encryption source code 1

dslaby · Feb 8, 2000

I need to compress and encrypt a replicated data set using email. I have written the code that attaches the data file to the email message, but need source code for compressing and encrypting the file, and of course, uncompressing and decrypting the file after recieved. Anybody has any source code or locations where I can get some? Likewise, I am willing to share my code for attaching and sending email using smtp from VB. Thanks.

MikeLacey · Feb 9, 2000

Do you especially need to encrupt the data? There is a windows API call that will compress it. 
 
Mike 
Mike Lacey <a href=mailto:Mike_Lacey@Cargill.Com>Mike_Lacey@Cargill.Com</a> <a href=

http://www.cargill.com/>

Cargill's Corporate Web Site</a>

Alt255 · Feb 9, 2000

Here's a link that should provide everything you need: 
<A HREF="

http://www.pkware.com/catalog/library.html"

TARGET="_new">

http://www.pkware.com/catalog/library.html</A>

These guys have been in business for years and their data compression libraries will probably provide better results than any of our meager attempts to re-invent the wheel. 
But, Mike, what's the name of that compression API? Dslaby might be a do-it-yourselfer (or unwilling to use a third party solution). If you provide the API, I'll provide a short (but hard to beat) encryption routine.

dslaby · Feb 9, 2000

If you post the API call, and alt255 posts some code, I'll be happy to post my final result for anybody's review. Thanks.

MikeLacey · Feb 11, 2000

These are the function definitions for *reading* a compressed file. Hadn't really looked at them before (just made a mental note that there was compression stuff) and I don't see calls to create lz files, just to read them. Hmmm... I'll keep on looking. 
 
Mike 
 
'********************************** 
'** Function Declarations: 
 
#if WIN32 Then 
Private Declare Function LZStart& Lib "lz32.dll" () 
Private Declare Function LZSeek& Lib "lz32.dll" (ByVal hfFile As Long, ByVal lOffset As Long, ByVal nOrigin As Long) 
Private Declare Function LZRead& Lib "lz32.dll" (ByVal hfFile As Long, ByVal lpvBuf As String, ByVal cbread As Long) 
Private Declare Function LZOpenFile& Lib "lz32.dll" Alias "LZOpenFileA" (ByVal lpszFile As String, lpOf As OFSTRUCT, ByVal style As Long) 
Private Declare Function LZInit& Lib "lz32.dll" (ByVal hfSrc As Long) 
Private Declare Sub LZDone Lib "lz32.dll" () 
Private Declare Function LZCopy& Lib "lz32.dll" (ByVal hfSource As Long, ByVal hfDest As Long) 
Private Declare Sub LZClose Lib "lz32.dll" (ByVal hfFile As Long) 
Private Declare Function GetExpandedName& Lib "lz32.dll" Alias "GetExpandedNameA" (ByVal lpszSource As String, ByVal lpszBuffer As String) 
Private Declare Function CopyLZFile& Lib "lz32.dll" (ByVal n1 As Long, ByVal n2 As Long) 
#endif 'WIN32 
Mike Lacey <a href=mailto:Mike_Lacey@Cargill.Com>Mike_Lacey@Cargill.Com</a> <a href=

http://www.cargill.com/>

Cargill's Corporate Web Site</a>

chiph · Feb 15, 2000

dslaby - 
 
For your encryption, check out Bruce Schneier's web site at <A HREF="

http://www.counterpane.com/labs.html"

TARGET="_new">

http://www.counterpane.com/labs.html</A>.

He's huge in the Crypto field (has a regular column in Dr. Dobb's Journal). Be careful where you distribute your application. 40-bit encryption is the current legal limit to export from the US. Some countries (like France) do not permit civilians to use any encryption software whatsoever. Violate the US laws, and you will get locked up under the same statutes as if you had exported a nuclear bomb or poison gas. 
 
Your safest bet would be to license a library/DLL from someone who has already jumped through the legal hurdles (like RSA or Counterpane or someone else) and can advise you on international use of their library. 
 
 
You need to get a copy of "The Data Compression Book 2nd Edition" by Mark Nelson. I've got the 1st edition, and it is very good. Only drawback is that it was written for C programmers. 
 
You might want to use the Micosoft LZW DLL like Mike Lacey suggested, but I'm not sure if you would have to pay royalties to Unisys (they hold the patent on the LZW compression algorithm -- see <A HREF="

http://www.cloanto.com/users/mcb/19950127giflzw.html"

TARGET="_new">

http://www.cloanto.com/users/mcb/19950127giflzw.html</A>).

Chip H.

Snaggs · Feb 15, 2000

Here's a simple XOR encryption algorithm that I use now and then. This code has been tested: 
 
Public Function Encrypt(UnEncrypted As String, ByVal Key As String) As String 
'Simple XOR Incryption With Key 
'This function takes two paramaters. One is the Encrypted or Non-Encrypted string, 
'the other is the Key to encrypt or un-encrpyt with. It returns the encrypted or 
'un-encrypted string result. EncryptedString = Encrypt(StringToEncrypt, EncryptionKey). 
'Then call the function again to decrypt the string 
'RealString = Encrypt(EncryptedSting, EncryptionKey). 
' 
'You must use the same key to decrypt the string as you do to encrypt it. 
' 
'Sample usage: 
' 
' strString = Encrypt("January 1, 2000", "ABC&quot

' Debug.Print Encrypt(strString, "ABC&quot

' 
 
Dim lngOffset As Long 
 
Do Until Len(Encrypt) = Len(UnEncrypted) 
For lngOffset = 1 To Len(Key) 
If Len(Encrypt) = Len(UnEncrypted) Then Exit For 
Encrypt = Encrypt & Chr(Asc(Mid(UnEncrypted, Len(Encrypt) + 1, 1)) Xor Asc(Mid(Key, lngOffset, 1))) 
Next lngOffset 
Loop 
End Function 
 
I also found some code that does RLE (Run Length Encoding) in VB. I can't vouch for this code as I have not used it or tested it. Use this code at your own risk. Having said that, here's the code: 
 
Option Explicit 
 
Public Sub Main() 
Dim TempArr() As Byte 
Dim TempStr As String 
TempStr = "TTTTHHHHIIIISSSS a Test" 
RLECompress TempStr, TempArr 
TempStr = TempArr 
TempStr = RLEUncompress(TempArr) 
End Sub 
 
Public Sub RLECompress(StrToCompress As String, ByteArr() As Byte) 
Dim TempArr() As Byte 
Dim I As Integer 
Dim ByteCnt As Byte 
Dim PrevAdded As Boolean 
TempArr = StrConv(StrToCompress, vbFromUnicode) 
ReDim ByteArr(0) 
ByteArr(0) = TempArr(0) 
For I = 1 To UBound(TempArr) 
If TempArr(I) = TempArr(I - 1) Then 
ByteCnt = I 
Do Until (TempArr(ByteCnt) <> TempArr(I - 1)) Or (ByteCnt - (I - 1) = 254) 
ByteCnt = ByteCnt + 1 
If ByteCnt > UBound(TempArr) Then Exit Do 
Loop 
If UBound(ByteArr) = 0 Then 
ReDim Preserve ByteArr(UBound(ByteArr) + 1) 
ElseIf PrevAdded = False Then 
ReDim Preserve ByteArr(UBound(ByteArr) + 2) 
End If 
ByteArr(UBound(ByteArr) - 1) = (ByteCnt - (I - 1)) 
ByteArr(UBound(ByteArr)) = TempArr(I) 
I = ByteCnt - 1 
PrevAdded = False 
Else 
ReDim Preserve ByteArr(UBound(ByteArr) + 2) 
ByteArr(UBound(ByteArr) - 1) = 1 
ByteArr(UBound(ByteArr)) = TempArr(I) 
PrevAdded = True 
End If 
Next I 
End Sub 
 
Public Function RLEUncompress(ByteArr() As Byte) 
Dim I As Integer 
For I = 0 To UBound(ByteArr) Step 2 
RLEUncompress = RLEUncompress & String(ByteArr(I), Chr(ByteArr(I + 1))) 
Next I 
End Function 
 
Steve Meier <a href=mailto:sdmeier@jcn1.com>sdmeier@jcn1.com</a> <a href= > </a>

Alt255 · Feb 17, 2000

There are a number of VB compression tools available here: 
<A HREF="

http://www.cgvb.com/links/lpage.boa/FILEIO"

TARGET="_new">

http://www.cgvb.com/links/lpage.boa/FILEIO</A>

Sorry, having not tried them I can't attest to their effectiveness.

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Data compression and encryption source code 1

dslaby

Programmer

MikeLacey

MIS

Alt255

Programmer

dslaby

Programmer

MikeLacey

MIS

chiph

Programmer

Snaggs

Programmer

Alt255

Programmer

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