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Xors and byte arrays
Rob Bovey posted a bit of code to http://www.devx.com/tips/Tip/5676
Function szEncryptDecrypt(ByVal szData As String) As String ''' This key value can be changed to alter the ''' encryption, but it must be the same for both ''' encryption and decryption. Const KEY_TEXT As String = "ScratchItYouFool" ''' The KEY_OFFSET is optional, and may be any ''' value 0-64. ''' Likewise, it needs to be the same coming/going. Const KEY_OFFSET As Long = 38 Dim bytKey() As Byte Dim bytData() As Byte Dim lNum As Long Dim szKey As String For lNum = 1 To ((Len(szData) \ Len(KEY_TEXT)) + 1) szKey = szKey & KEY_TEXT Next lNum bytKey = Left$(szKey, Len(szData)) bytData = szData For lNum = LBound(bytData) To UBound(bytData) If lNum Mod 2 Then bytData(lNum) = bytData(lNum) Xor (bytKey(lNum) _ + KEY_OFFSET) Else bytData(lNum) = bytData(lNum) Xor (bytKey(lNum) _ - KEY_OFFSET) End If Next lNum szEncryptDecrypt = bytData End Function I'm finding that it generates an awful lot of overflow errors because the value being returned to bytData(lNum) is not in a byte range. There seem to be dozens of scenarios where varying the key and the key offset (seemingly within the expected parameters) that bytData(lNum) Xor (bytKey(lNum) - KEY_OFFSET) cannot return byte data OR that the final bytData cannot be converted back to a string. Am I missing something here? Do I need to do some preliminary checks before setting the constants and passing data into the function? Regards GPO |
Xors and byte arrays
Hi GPO,
The general rule for modifying the obfuscation constants in this function is that the KEY_OFFSET constant must be less than or equal to the lowest ASCII character value in the KEY_TEXT string. So if KEY_TEXT = "0123456789abcdefg" then KEY_OFFSET must be less than or equal to 48, because that's the ASCII value of the character "0" in the KEY_TEXT string. -- Rob Bovey, Excel MVP Application Professionals http://www.appspro.com/ * Take your Excel development skills to the next level. * Professional Excel Development http://www.appspro.com/Books/Books.htm "GPO" wrote in message ... Rob Bovey posted a bit of code to http://www.devx.com/tips/Tip/5676 Function szEncryptDecrypt(ByVal szData As String) As String ''' This key value can be changed to alter the ''' encryption, but it must be the same for both ''' encryption and decryption. Const KEY_TEXT As String = "ScratchItYouFool" ''' The KEY_OFFSET is optional, and may be any ''' value 0-64. ''' Likewise, it needs to be the same coming/going. Const KEY_OFFSET As Long = 38 Dim bytKey() As Byte Dim bytData() As Byte Dim lNum As Long Dim szKey As String For lNum = 1 To ((Len(szData) \ Len(KEY_TEXT)) + 1) szKey = szKey & KEY_TEXT Next lNum bytKey = Left$(szKey, Len(szData)) bytData = szData For lNum = LBound(bytData) To UBound(bytData) If lNum Mod 2 Then bytData(lNum) = bytData(lNum) Xor (bytKey(lNum) _ + KEY_OFFSET) Else bytData(lNum) = bytData(lNum) Xor (bytKey(lNum) _ - KEY_OFFSET) End If Next lNum szEncryptDecrypt = bytData End Function I'm finding that it generates an awful lot of overflow errors because the value being returned to bytData(lNum) is not in a byte range. There seem to be dozens of scenarios where varying the key and the key offset (seemingly within the expected parameters) that bytData(lNum) Xor (bytKey(lNum) - KEY_OFFSET) cannot return byte data OR that the final bytData cannot be converted back to a string. Am I missing something here? Do I need to do some preliminary checks before setting the constants and passing data into the function? Regards GPO |
Xors and byte arrays
By Golly that was quick! Thanks Rob.
"Rob Bovey" wrote: Hi GPO, The general rule for modifying the obfuscation constants in this function is that the KEY_OFFSET constant must be less than or equal to the lowest ASCII character value in the KEY_TEXT string. So if KEY_TEXT = "0123456789abcdefg" then KEY_OFFSET must be less than or equal to 48, because that's the ASCII value of the character "0" in the KEY_TEXT string. -- Rob Bovey, Excel MVP Application Professionals http://www.appspro.com/ * Take your Excel development skills to the next level. * Professional Excel Development http://www.appspro.com/Books/Books.htm "GPO" wrote in message ... Rob Bovey posted a bit of code to http://www.devx.com/tips/Tip/5676 Function szEncryptDecrypt(ByVal szData As String) As String ''' This key value can be changed to alter the ''' encryption, but it must be the same for both ''' encryption and decryption. Const KEY_TEXT As String = "ScratchItYouFool" ''' The KEY_OFFSET is optional, and may be any ''' value 0-64. ''' Likewise, it needs to be the same coming/going. Const KEY_OFFSET As Long = 38 Dim bytKey() As Byte Dim bytData() As Byte Dim lNum As Long Dim szKey As String For lNum = 1 To ((Len(szData) \ Len(KEY_TEXT)) + 1) szKey = szKey & KEY_TEXT Next lNum bytKey = Left$(szKey, Len(szData)) bytData = szData For lNum = LBound(bytData) To UBound(bytData) If lNum Mod 2 Then bytData(lNum) = bytData(lNum) Xor (bytKey(lNum) _ + KEY_OFFSET) Else bytData(lNum) = bytData(lNum) Xor (bytKey(lNum) _ - KEY_OFFSET) End If Next lNum szEncryptDecrypt = bytData End Function I'm finding that it generates an awful lot of overflow errors because the value being returned to bytData(lNum) is not in a byte range. There seem to be dozens of scenarios where varying the key and the key offset (seemingly within the expected parameters) that bytData(lNum) Xor (bytKey(lNum) - KEY_OFFSET) cannot return byte data OR that the final bytData cannot be converted back to a string. Am I missing something here? Do I need to do some preliminary checks before setting the constants and passing data into the function? Regards GPO |
Xors and byte arrays
Hi again,
Even controlling for the prev issue, it also seems to fall over where the offset is 0 and they key and data both start with the same char. Cheers GPO |
Xors and byte arrays
"GPO" wrote in message
... Hi again, Even controlling for the prev issue, it also seems to fall over where the offset is 0 and they key and data both start with the same char. Hi GPO, I'm not seeing this. Can you give me an example where it happens? I set KEY_OFFSET to zero and used various identical strings for both KEY_TEXT and the data without any problem. -- Rob Bovey, Excel MVP Application Professionals http://www.appspro.com/ * Take your Excel development skills to the next level. * Professional Excel Development http://www.appspro.com/Books/Books.htm |
Xors and byte arrays
Hi Rob.
I confirm that your fine UDF work properly, but not with the KEY_OFFSET = 0 Fine in all the other situation i tried. Try: oggi piove ma forse domani sarą bel tempo; il futuro comunque č nelle mani di Zeus 0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMN OPQRSTUVWXYZ ScratchItYouFool S.O = XP Office = XL2003 Regards Eliano On 25 Giu, 04:18, "Rob Bovey" wrote: "GPO" wrote in message ... Hi again, Even controlling for the prev issue, it also seems to fall over where the offset is 0 and they key and data both start with the same char. Hi GPO, * * I'm not seeing this. Can you give me an example where it happens? I set KEY_OFFSET to zero and used various identical strings for both KEY_TEXT and the data without any problem. -- Rob Bovey, Excel MVP Application Professionalshttp://www.appspro.com/ * Take your Excel development skills to the next level. * Professional Excel Developmenthttp://www.appspro.com/Books/Books.htm |
Xors and byte arrays
<<--------------
Try: oggi piove ma forse domani sarą bel tempo; il futuro comunque č nelle mani di Zeus 0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMN OPQRSTUVWXYZ ScratchItYouFool S.O = XP Office = XL2003 ------------------------ Hi Eliano, This seems to work fine for me. I wonder if the problem has something to do with code page differences in different language versions of Windows? The test code that works correctly for me in US English Windows XP/Excel 2003 is shown below: Sub Test() Dim szTest As String szTest = "oggi piove ma forse domani sarą bel tempo; il futuro comunque č nelle mani di Zeus" szTest = szEncryptDecrypt(szTest) Debug.Print szTest ''' Encrypted string szTest = szEncryptDecrypt(szTest) Debug.Print szTest ''' Decrypted string End Sub Function szEncryptDecrypt(ByVal szData As String) As String Const KEY_TEXT As String = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLM NOPQRSTUVWXYZ" Const KEY_OFFSET As Long = 0 Dim bytKey() As Byte Dim bytData() As Byte Dim lNum As Long Dim szKey As String For lNum = 1 To ((Len(szData) \ Len(KEY_TEXT)) + 1) szKey = szKey & KEY_TEXT Next lNum bytKey = Left$(szKey, Len(szData)) bytData = szData For lNum = LBound(bytData) To UBound(bytData) If lNum Mod 2 Then bytData(lNum) = bytData(lNum) Xor (bytKey(lNum) + KEY_OFFSET) Else bytData(lNum) = bytData(lNum) Xor (bytKey(lNum) - KEY_OFFSET) End If Next lNum szEncryptDecrypt = bytData End Function ------------------------------------------ Output in Immediate Window: ------------------------------------------- _VUZE_XN\AD J Q?V Z5'.4*}g!%j-99;=?q1<9 8&-<zŲ\VXYSUX C F= oggi piove ma forse domani sarą bel tempo; il futuro comunque č nelle mani di Zeus -- Rob Bovey, Excel MVP Application Professionals http://www.appspro.com/ * Take your Excel development skills to the next level. * Professional Excel Development http://www.appspro.com/Books/Books.htm "eliano" wrote in message ... Hi Rob. I confirm that your fine UDF work properly, but not with the KEY_OFFSET = 0 Fine in all the other situation i tried. Try: oggi piove ma forse domani sarą bel tempo; il futuro comunque č nelle mani di Zeus 0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMN OPQRSTUVWXYZ ScratchItYouFool S.O = XP Office = XL2003 Regards Eliano On 25 Giu, 04:18, "Rob Bovey" wrote: "GPO" wrote in message ... Hi again, Even controlling for the prev issue, it also seems to fall over where the offset is 0 and they key and data both start with the same char. Hi GPO, I'm not seeing this. Can you give me an example where it happens? I set KEY_OFFSET to zero and used various identical strings for both KEY_TEXT and the data without any problem. -- Rob Bovey, Excel MVP Application Professionalshttp://www.appspro.com/ * Take your Excel development skills to the next level. * Professional Excel Developmenthttp://www.appspro.com/Books/Books.htm |
Xors and byte arrays
Hi Rob.
Many thanks for the attention. I am Italian and i use an Italian Office. Up tomorrow i cannot try your UDF, but be sure that as soon as possible i will reply to your courtesy. Thanks again and regards. Eliano On 26 Giu, 01:36, "Rob Bovey" wrote: <<-------------- Try: oggi piove ma forse domani sarą bel tempo; il futuro comunque č nelle mani di Zeus 0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMN OPQRSTUVWXYZ ScratchItYouFool S.O = XP *Office = XL2003 ------------------------ Hi Eliano, * * This seems to work fine for me. I wonder if the problem has something to do with code page differences in different language versions of Windows? The test code that works correctly for me in US English Windows XP/Excel 2003 is shown below: Sub Test() * * Dim szTest As String * * szTest = "oggi piove ma forse domani sarą bel tempo; il futuro comunque č nelle mani di Zeus" * * szTest = szEncryptDecrypt(szTest) * * Debug.Print szTest *''' Encrypted string * * szTest = szEncryptDecrypt(szTest) * * Debug.Print szTest *''' Decrypted string End Sub Function szEncryptDecrypt(ByVal szData As String) As String * * Const KEY_TEXT As String = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLM NOPQRSTUVWXYZ" * * Const KEY_OFFSET As Long = 0 * * Dim bytKey() As Byte * * Dim bytData() As Byte * * Dim lNum As Long * * Dim szKey As String * * For lNum = 1 To ((Len(szData) \ Len(KEY_TEXT)) + 1) * * * * szKey = szKey & KEY_TEXT * * Next lNum * * bytKey = Left$(szKey, Len(szData)) * * bytData = szData * * For lNum = LBound(bytData) To UBound(bytData) * * * * If lNum Mod 2 Then * * * * * * bytData(lNum) = bytData(lNum) Xor (bytKey(lNum) + KEY_OFFSET) * * * * Else * * * * * * bytData(lNum) = bytData(lNum) Xor (bytKey(lNum) - KEY_OFFSET) * * * * End If * * Next lNum * * szEncryptDecrypt = bytData End Function ------------------------------------------ Output in Immediate Window: ------------------------------------------- _VUZ E_XN\A *D * * J * * *Q * ?V * Z5'.4*}g!%j-99;=?q1<9 8&-<zŲ \VXYS UX *C *F= oggi piove ma forse domani sarą bel tempo; il futuro comunque č nelle mani di Zeus -- Rob Bovey, Excel MVP Application Professionalshttp://www.appspro.com/ * Take your Excel development skills to the next level. * Professional Excel Developmenthttp://www.appspro.com/Books/Books.htm "eliano" wrote in ... Hi Rob. I confirm that your fine UDF work properly, but not with the KEY_OFFSET = 0 Fine in all the other situation i tried. Try: oggi piove ma forse domani sarą bel tempo; il futuro comunque č nelle mani di Zeus 0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMN OPQRSTUVWXYZ ScratchItYouFool S.O = XP *Office = XL2003 Regards Eliano On 25 Giu, 04:18, "Rob Bovey" wrote: "GPO" wrote in message ... Hi again, Even controlling for the prev issue, it also seems to fall over where the offset is 0 and they key and data both start with the same char. Hi GPO, I'm not seeing this. Can you give me an example where it happens? I set KEY_OFFSET to zero and used various identical strings for both KEY_TEXT and the data without any problem. -- Rob Bovey, Excel MVP Application Professionalshttp://www.appspro.com/ * Take your Excel development skills to the next level. * Professional Excel Developmenthttp://www.appspro.com/Books/Books.htm- Nascondi testo citato - Mostra testo citato |
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