Random bytes on the beginning of encrypted file

[Lech Migdal]

Hi all

I am having a problem with decrypting files using TripleDES. Every time I
decrypt something, first 8 bytes are random. The rest of the file is a'ok.

Maybe someone has encountered such a issue ? I would appreciate any help.

Here is the code for decrypting:

FileStream fin = new FileStream(inName, FileMode.Open, FileAccess.Read);
FileStream fout = new FileStream(outName, FileMode.Create,
FileAccess.Write);
fout.SetLength(0);
char[] tempKey = tdesKeyText.ToCharArray();
byte[] tdesKey = new byte[tempKey.Length];

for (int i=0; i<tdesKey.Length; i++) {
tdesKey=Convert.ToByte(tempKey);
}

TripleDESCryptoServiceProvider tdes = new TripleDESCryptoServiceProvider();
CryptoStream decStream = new CryptoStream(fout,
tdes.CreateDecryptor(tdesKey, tdesIV), CryptoStreamMode.Write);

int data;
while ((data=fin.ReadByte())!=-1)
decStream.WriteByte((byte) data);

Thank you in advance

Leszek Migdal

 

[Guest]

Try the code at the following link, this works fine for me

http://www.pocketnerd.net/CodeSampl...ocumentID=7556B9FF-D2C9-429D-ADB4-D26203A6436

HT

RS

 

[Jon Skeet [C# MVP]]

I am having a problem with decrypting files using TripleDES. Every time I
decrypt something, first 8 bytes are random. The rest of the file is a'ok.

<snip>

Could you show the code which writes the encrypted file to start with?

 

[Lech Migdal]

a'ok.

<snip>

Could you show the code which writes the encrypted file to start with?

Here it's :

FileStream fin = new FileStream(inName, FileMode.Open, FileAccess.Read);
FileStream fout = new FileStream(outName, FileMode.Create,
FileAccess.Write);
fout.SetLength(0);
char[] tempKey = tdesKeyText.ToCharArray();
byte[] tdesKey = new byte[tempKey.Length];
for (int i=0; i<tdesKey.Length; i++) {
tdesKey=Convert.ToByte(tempKey);
}

TripleDESCryptoServiceProvider tdes = new TripleDESCryptoServiceProvider();
CryptoStream encStream = new CryptoStream(fout,
tdes.CreateEncryptor(tdesKey, tdesIV), CryptoStreamMode.Write);

int data;
while ((data=fin.ReadByte())!=-1)
encStream.WriteByte((byte) data);

encStream.Close();
fin.Close();
fout.Close();

regards
Leszek Migdal

 

[Jon Skeet [C# MVP]]

Could you show the code which writes the encrypted file to start with?

Here it's :

FileStream fin = new FileStream(inName, FileMode.Open, FileAccess.Read);
FileStream fout = new FileStream(outName, FileMode.Create,
FileAccess.Write);
fout.SetLength(0);
char[] tempKey = tdesKeyText.ToCharArray();
byte[] tdesKey = new byte[tempKey.Length];
for (int i=0; i<tdesKey.Length; i++) {
tdesKey=Convert.ToByte(tempKey);
}

TripleDESCryptoServiceProvider tdes = new TripleDESCryptoServiceProvider();
CryptoStream encStream = new CryptoStream(fout,
tdes.CreateEncryptor(tdesKey, tdesIV), CryptoStreamMode.Write);

Hmm.

It's not as nice as it might be in various ways, but I can't see any
reason why it shouldn't work.

Could you combine those two bits of code as a short but complete sample
application which we could very easily test?

 

[Guest]

Was there ever a resolution to this issue? I am experiencing the same problem. Thanks

----- Lech Migdal wrote: ----

Hi al

I am having a problem with decrypting files using TripleDES. Every time
decrypt something, first 8 bytes are random. The rest of the file is a'ok

Maybe someone has encountered such a issue ? I would appreciate any help

Here is the code for decrypting

FileStream fin = new FileStream(inName, FileMode.Open, FileAccess.Read)
FileStream fout = new FileStream(outName, FileMode.Create
FileAccess.Write)
fout.SetLength(0)
char[] tempKey = tdesKeyText.ToCharArray()
byte[] tdesKey = new byte[tempKey.Length]

for (int i=0; i<tdesKey.Length; i++)
tdesKey=Convert.ToByte(tempKey)


TripleDESCryptoServiceProvider tdes = new TripleDESCryptoServiceProvider()
CryptoStream decStream = new CryptoStream(fout
tdes.CreateDecryptor(tdesKey, tdesIV), CryptoStreamMode.Write)

int data
while ((data=fin.ReadByte())!=-1
decStream.WriteByte((byte) data)

Thank you in advanc

Leszek Migda

 

[Jon Skeet [C# MVP]]

Was there ever a resolution to this issue? I am experiencing the same
problem. Thanks.

Yes, we resolved it over email. The problem was that Leszek was
specifying null as the initialisation vector, which meant that it took
a random value. So long as you use the same initialisation vector (and
key, obviously) for encryption and decryption, you should be okay.