encryption padding problem with RijndaelManaged

11 May 2007 2:09 PM

Jon Jacobs

I thought the following code worked for me until I looked closer.
My first clue came when I tried to decrypt the file, and got a
CryptographicException saying:
Padding is invalid and cannot be removed.

I looked at the file sizes, and the encrypted file is a
little smaller than the source file,
the exact opposite of what I expected:
WindowsUpdate.log (a copy of the original) is 1,827,175 bytes
WindowsUpdate.txt                          is 1,827,168 bytes

What went wrong?

Thanks,
Jon

Sub Main()
        ec = New EmpCipher()
        crypt("C:\0JQJ\WindowsUpdate.log", "C:\0JQJ\WindowsUpdate.txt")
    End Sub

    Sub crypt(ByVal source As String, ByVal dest As String)
        'read in a clear file to an array of bytes
        Dim inFile As FileStream = New FileStream(source, FileMode.Open,
FileAccess.Read)
        Dim L As Int32 = inFile.Length
        Dim b(L) As Byte
        inFile.Read(b, 0, L)

        'get encrypted stream from byte array
        Dim m As MemoryStream = ec.c3(b)
        m.Seek(0, SeekOrigin.Begin)
        L = m.Length

        'write the encrypted stream to a file
        Dim buf(L - 1) As Byte
        m.Read(buf, 0, L)
        Dim fs As FileStream = New FileStream(dest, FileMode.Create,
FileAccess.Write)
        fs.Write(buf, 0, L)
        fs.Close()
    End Sub

'from the EmpCipher class, intended to encrypt any byte array, not just files
    Public Function c3(ByVal b() As Byte) As MemoryStream
        Dim e As ICryptoTransform = alg.CreateEncryptor
        Dim m As MemoryStream = New MemoryStream()
        Dim c As CryptoStream = New CryptoStream(m, e, CryptoStreamMode.Write)
        c.Write(b, 0, b.Length)
        Return m
    End Function

11 May 2007 5:53 PM

JR

From the Help:

"You should always explicitly close your CryptoStream object after you are
done using it by calling the Close method. Doing so flushes the stream and
causes all remain blocks of data to be processed by the CryptoStream
object."

This could be the reason for your bug.

JR

"Jon Jacobs" <JonJac***@discussions.microsoft.com> ëúá

áäåãòä:5C3AC9BB-C57B-45F7-9483-AA1FABF0B***@microsoft.com...
Show quote

>I thought the following code worked for me until I looked closer.
> My first clue came when I tried to decrypt the file, and got a
> CryptographicException saying:
> Padding is invalid and cannot be removed.
>
> I looked at the file sizes, and the encrypted file is a
> little smaller than the source file,
> the exact opposite of what I expected:
> WindowsUpdate.log (a copy of the original) is 1,827,175 bytes
> WindowsUpdate.txt                          is 1,827,168 bytes
>
> What went wrong?
>
> Thanks,
> Jon
>
> Sub Main()
>        ec = New EmpCipher()
>        crypt("C:\0JQJ\WindowsUpdate.log", "C:\0JQJ\WindowsUpdate.txt")
>    End Sub
>
>    Sub crypt(ByVal source As String, ByVal dest As String)
>        'read in a clear file to an array of bytes
>        Dim inFile As FileStream = New FileStream(source, FileMode.Open,
> FileAccess.Read)
>        Dim L As Int32 = inFile.Length
>        Dim b(L) As Byte
>        inFile.Read(b, 0, L)
>
>        'get encrypted stream from byte array
>        Dim m As MemoryStream = ec.c3(b)
>        m.Seek(0, SeekOrigin.Begin)
>        L = m.Length
>
>        'write the encrypted stream to a file
>        Dim buf(L - 1) As Byte
>        m.Read(buf, 0, L)
>        Dim fs As FileStream = New FileStream(dest, FileMode.Create,
> FileAccess.Write)
>        fs.Write(buf, 0, L)
>        fs.Close()
>    End Sub
>
> 'from the EmpCipher class, intended to encrypt any byte array, not just
> files
>    Public Function c3(ByVal b() As Byte) As MemoryStream
>        Dim e As ICryptoTransform = alg.CreateEncryptor
>        Dim m As MemoryStream = New MemoryStream()
>        Dim c As CryptoStream = New CryptoStream(m, e,
> CryptoStreamMode.Write)
>        c.Write(b, 0, b.Length)
>        Return m
>    End Function

11 May 2007 6:03 PM

Jon Jacobs

> "You should always explicitly close your CryptoStream object after you are
> This could be the reason for your bug.

That is very probably it. Thank you very much

11 May 2007 5:53 PM

JR

From the Help:

"You should always explicitly close your CryptoStream object after you are
done using it by calling the Close method. Doing so flushes the stream and
causes all remain blocks of data to be processed by the CryptoStream
object."

This could be the reason for your bug.

JR

"Jon Jacobs" <JonJac***@discussions.microsoft.com> ëúá

áäåãòä:5C3AC9BB-C57B-45F7-9483-AA1FABF0B***@microsoft.com...
Show quote

>I thought the following code worked for me until I looked closer.
> My first clue came when I tried to decrypt the file, and got a
> CryptographicException saying:
> Padding is invalid and cannot be removed.
>
> I looked at the file sizes, and the encrypted file is a
> little smaller than the source file,
> the exact opposite of what I expected:
> WindowsUpdate.log (a copy of the original) is 1,827,175 bytes
> WindowsUpdate.txt                          is 1,827,168 bytes
>
> What went wrong?
>
> Thanks,
> Jon
>
> Sub Main()
>        ec = New EmpCipher()
>        crypt("C:\0JQJ\WindowsUpdate.log", "C:\0JQJ\WindowsUpdate.txt")
>    End Sub
>
>    Sub crypt(ByVal source As String, ByVal dest As String)
>        'read in a clear file to an array of bytes
>        Dim inFile As FileStream = New FileStream(source, FileMode.Open,
> FileAccess.Read)
>        Dim L As Int32 = inFile.Length
>        Dim b(L) As Byte
>        inFile.Read(b, 0, L)
>
>        'get encrypted stream from byte array
>        Dim m As MemoryStream = ec.c3(b)
>        m.Seek(0, SeekOrigin.Begin)
>        L = m.Length
>
>        'write the encrypted stream to a file
>        Dim buf(L - 1) As Byte
>        m.Read(buf, 0, L)
>        Dim fs As FileStream = New FileStream(dest, FileMode.Create,
> FileAccess.Write)
>        fs.Write(buf, 0, L)
>        fs.Close()
>    End Sub
>
> 'from the EmpCipher class, intended to encrypt any byte array, not just
> files
>    Public Function c3(ByVal b() As Byte) As MemoryStream
>        Dim e As ICryptoTransform = alg.CreateEncryptor
>        Dim m As MemoryStream = New MemoryStream()
>        Dim c As CryptoStream = New CryptoStream(m, e,
> CryptoStreamMode.Write)
>        c.Write(b, 0, b.Length)
>        Return m
>    End Function

11 May 2007 6:05 PM

JR

From the Help:

"You should always explicitly close your CryptoStream object after you are
done using it by calling the Close method. Doing so flushes the stream and
causes all remain blocks of data to be processed by the CryptoStream
object."

This could be the reason for your bug.

JR

"Jon Jacobs" <JonJac***@discussions.microsoft.com> ëúá

áäåãòä:5C3AC9BB-C57B-45F7-9483-AA1FABF0B***@microsoft.com...
Show quote

>I thought the following code worked for me until I looked closer.
> My first clue came when I tried to decrypt the file, and got a
> CryptographicException saying:
> Padding is invalid and cannot be removed.
>
> I looked at the file sizes, and the encrypted file is a
> little smaller than the source file,
> the exact opposite of what I expected:
> WindowsUpdate.log (a copy of the original) is 1,827,175 bytes
> WindowsUpdate.txt                          is 1,827,168 bytes
>
> What went wrong?
>
> Thanks,
> Jon
>
> Sub Main()
>        ec = New EmpCipher()
>        crypt("C:\0JQJ\WindowsUpdate.log", "C:\0JQJ\WindowsUpdate.txt")
>    End Sub
>
>    Sub crypt(ByVal source As String, ByVal dest As String)
>        'read in a clear file to an array of bytes
>        Dim inFile As FileStream = New FileStream(source, FileMode.Open,
> FileAccess.Read)
>        Dim L As Int32 = inFile.Length
>        Dim b(L) As Byte
>        inFile.Read(b, 0, L)
>
>        'get encrypted stream from byte array
>        Dim m As MemoryStream = ec.c3(b)
>        m.Seek(0, SeekOrigin.Begin)
>        L = m.Length
>
>        'write the encrypted stream to a file
>        Dim buf(L - 1) As Byte
>        m.Read(buf, 0, L)
>        Dim fs As FileStream = New FileStream(dest, FileMode.Create,
> FileAccess.Write)
>        fs.Write(buf, 0, L)
>        fs.Close()
>    End Sub
>
> 'from the EmpCipher class, intended to encrypt any byte array, not just
> files
>    Public Function c3(ByVal b() As Byte) As MemoryStream
>        Dim e As ICryptoTransform = alg.CreateEncryptor
>        Dim m As MemoryStream = New MemoryStream()
>        Dim c As CryptoStream = New CryptoStream(m, e,
> CryptoStreamMode.Write)
>        c.Write(b, 0, b.Length)
>        Return m
>    End Function