Byte To Hex and back again...

  • Thread starter Thread starter Jose Perez
  • Start date Start date
J

Jose Perez

Dear All,

I have the following problem. I am passing an encrypted value on the
querystring from one aspx to another. Originally I was outputing
characters such as "+, /,..." (which caused problems), so I converted
this byte array to Hex. When I come to read the string back into a
byte array to decrypt it I always get an extra value, so myByte(40)
becomes a length of 41 and I get an error relating to the length of
the byte array. If I try and force it to be myByte(39) (so the length
is 40) I get an error saying bad data!! Code below...

I don't know whether this is the correct solution but I want to
"delete" the last byte of my (hex to byte) array.

Any help is greatly appreciated.

Thanks in advance,
Jose

<code>
(Const sPassword As String)
Public Shared Function Encrypt(ByVal sToEncrypt As String) As String

Dim sEncrypted As String
Dim des As TripleDESCryptoServiceProvider
Dim hashMD5 As MD5CryptoServiceProvider
Dim pwdHash As Byte()
Dim buff As Byte()

hashMD5 = New MD5CryptoServiceProvider
pwdHash =
hashMD5.ComputeHash(ASCIIEncoding.ASCII.GetBytes(sPassword))

'Set variable to nothing.
hashMD5 = Nothing

des = New TripleDESCryptoServiceProvider
des.Key = pwdHash
des.Mode = CipherMode.ECB

buff = ASCIIEncoding.ASCII.GetBytes(sToEncrypt)
buff = des.CreateEncryptor().TransformFinalBlock(buff, 0,
buff.Length)

'Encode each byte in the binary into two hex digits.
Dim sHex As New StringBuilder(2 * buff.Length)
Dim i As Integer

For i = 0 To buff.Length - 1 Step 1
sHex.AppendFormat("{0:X2} ", buff(i))
Next

'Remove all whitespaces and return.
Return sHex.ToString().Replace(" ", String.Empty)

End Function

Public Shared Function Decrypt(ByVal sToDecrypt As String) As
String

Dim des As TripleDESCryptoServiceProvider
Dim hashMD5 As MD5CryptoServiceProvider
Dim pwdHash As Byte()
Dim buff As Byte()
Dim sDecrypted As String

hashMD5 = New MD5CryptoServiceProvider
pwdHash =
hashMD5.ComputeHash(ASCIIEncoding.ASCII.GetBytes(sPassword))

'Set variable to nothing.
hashMD5 = Nothing

des = New TripleDESCryptoServiceProvider
des.Key = pwdHash
des.Mode = CipherMode.ECB

'Change "each" Hex into byte format.
Dim i As Integer
Dim iByte As Integer = sToDecrypt.Length / 2
Dim ByteVar(iByte) As Byte

For i = 0 To iByte - 1
ByteVar(i) = Convert.ToByte(sToDecrypt.Substring(i *
2, 2), 16)
Next

buff = ByteVar '####HERE'S THE PROBLEM####

'Decrypt DES 3 encrypted byte buffer and return ASCII
string.
sDecrypted =
ASCIIEncoding.ASCII.GetString(des.CreateDecryptor().TransformFinalBlock(buff,
0, buff.Length))

'Cleanup
des = Nothing

Return sDecrypted

End Function

</code>
 
Jose Perez said:
buff = ASCIIEncoding.ASCII.GetBytes(sToEncrypt)
buff = des.CreateEncryptor().TransformFinalBlock(buff,
0,
buff.Length)
Click to expand...

You know that ASCII = 7 bits only? Means, character #128 is converted to 0,
character #129 to 1, and so on. Though, I don't know whether this is this
the reason for your problem.

Maybe you should try System.Text.Encoding.Default instead?


--
Armin

How to quote and why:
http://www.plig.net/nnq/nquote.html
http://www.netmeister.org/news/learn2quote.html
 
I have the following problem. I am passing an encrypted value on the
querystring from one aspx to another. Originally I was outputing
characters such as "+, /,..." (which caused problems), so I converted
this byte array to Hex.
Click to expand...

Just use the HttpServerUtility.UrlEncode method to properly encode the
value.
 
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