cipher50.txt

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//  CIPHER50.FLL
//
//  Character encryption routine for VFP 5.0
//
//  Usage:    ENCRYPT(plaintext,password)
//
//            Plaintext can be a character string or a memo field (memo fields
//            must be passed by reference -- encrypt(@memo,password) ).  
//            If a memo field is passed to this function, it will not 
//            be modified, even though it is nominally passed by reference.
//            A character string passed by reference will be modified.  A
//            variable (other than a character string or memo field) that 
//            is passed by reference will be unchanged (and the function return
//            value will be the same value as the variable).
//
//            Also, password must be at least 3 characters in length or the
//            function will return the character string unchanged.
//
//            To decrypt a string, just run it through this function again.
//            Thus:  ENCRYPT(ENCRYPT(plaintext,password),password) = plaintext
//
//  Returns:  Encrypted string of same length as plaintext
//
//
//  History:  Produced as CIPHER50.FLL for VFP 5.0 API by Guy Pardoe, 1/6/97
//            Produced as CIPHER30.FLL for VFP 3.0 API by Roy Gerber, 8/95
//            Modified by Walt Kennamer for FoxPro 2.0 API, 8/19/91
//            Encryption logic originally written by Tom Rettig and Leonard Zerman,
//              and placed in the public domain by Tom Rettig Associates, 10/22/1990
//
//  CIPHER50.FLL is public domain software.
//
//  Produced with MS VC++ 4.2.  CIPHER50 has been successfully tested on plaintext
//  strings (memo fields) in excess of 150,000 characters with snappy performance.
//
//
//  Contact Guy Pardoe 73552,2477 if you have questions.
//
//
//  DISCLAIMER:	Not responsible for direct, indirect, incidental, or
//              consequential damages resulting from any defect, error, or
//              failure to perform. No other warranty expressed or implied.
//
//              All Trademarks Recognized.
//
//
//
//  Tech Note:	On some Windows 95 PCs when you issue the command:
//
//		       SET LIBRARY TO cipher50.fll
//
//		you may experience an error similar to:
//
//		       Error 1691 - Library file Cipher50.FLL is invalid.
//
//		The error is a result of the Windows PC not having MSVCRT.DLL installed
//		in its SYSTEM directory.  The problem does not occur with Windows NT.
//		Microsoft states that MSVCRT.DLL is required with multithreaded .DLLs
//		[or .FLLs] by design.  However, it is not shipped with all O/S products.
//
//		Microsoft ships this .DLL with Windows NT 4.0, OEM Service Release 2 of
//		Windows 95 (OSR 2), and MS VC++ 4.2 and higher.  It does NOT ship with
//		the original version of Windows 95, the Windows 95 Upgrade, the Win95
//		Service Pack 1, or VFP 5.0.
//
//		MSVCRT.DLL [version 5.0.7022] is now included with CIPHER50.ZIP.  If you
//		distribute CIPHER50 enabled applications with the VFP 5.0 Setup Wizard,
//		remember to direct MSVCRT.DLL to WinSysDir in step 6 of the Setup Wizard.
//
//		Occassionally, there may be difficulty installing a .DLL in the SYSTEM
//		directory due to the .DLL being in use at the time of a new install.
//		However, installing this particular .DLL should be fairly painless since
//		it is not one of the active .DLLs that is always [or often] running.  The
//		fact that it is not part of the original version of Windows testifies to
//		this.
//
//		As another work around for a Windows 95 PC that does not have MSVCRT.DLL,
//		copying MSVCRT40.DLL to MSVCRT.DLL in the SYSTEM directory has been known
//		to work.
//
//		Refer to the MS Knowledge Base Article Q157317 for additional information
//		regarding .FLLs and MSVCRT.DLL.