RSA encrypt/decrypt of byte array

RSA encrypt/decrypt of byte array

I'm encrypting and then decrypting a byte array using the
RSACryptoServiceProvider. The byte array is 52 bytes in length. After
encrypting I'm converting the encrypted bytes (returned from the
provider's Encrypt method) to a string using Encoding.UTF8.GetString.
I then pass this string along to the decryption function. That
function first converts the string back to a byte array using
Encoding.UTF8.GetBytes. It then calls the RSACryptoServiceProvider's
Decrypt method. I get an exception trying to make this call because
the byte array returned from Encoding.UTF8.GetBytes is too long. A max
of 128 bytes can be passed to the RSA decryption algorithm.

I've tried other encodings but can't get this to work. What am I doing
wrong? Here's some code:

client (encrypts):

        byte[] cipherBytes = rsa.Encrypt( bytesToEncrypt, false);

        string cipherText = Encoding.UTF8.GetString(cipherBytes);

server (decrypts):

        byte[] encryptedBytes = Encoding.UTF8.GetBytes(cipherText);

        byte[] clearTextBytes = provider.Decrypt(encryptedBytes,
false); <<--- GET EXCEPTION HERE

Thanks,
 Bob

date: Tue, 6 May 2008 14:28:40 -0700 (PDT) author: bobuva

Re: RSA encrypt/decrypt of byte array

You can't encrypt this much data with RSA with a key the size you are using. 
RSA is typically used to encrypt a randomly generated session key which does 
the bulk encryption.

The EnvelopedCms class in the Pkcs namespace provides a handy wrapper around 
the PKCS7 enveloped data structure which handles all this stuff for you 
although it is designed primarily for encrypting with certificates instead 
of raw RSA keys.  You can devise your own data structure to handle this 
though.

You definitely want to use UTF8 to convert your string to a byte array 
unless you are certain that it will only contain characters that fit in a 
single byte character set, in which case one of those may be smaller.  UTF8 
produces the same byte array as ASCII for ASCII characters.

You could try zipping the data before encrypting it, but you might not get 
it reduced small enough.

Joe K.
-- 
Joe Kaplan-MS MVP Directory Services Programming
Co-author of "The .NET Developer's Guide to Directory Services Programming"
http://www.directoryprogramming.net
--
"bobuva"  wrote in message 
news:014f714a-e412-42d2-83bf-e590600aa6b6@24g2000hsh.googlegroups.com...
> I'm encrypting and then decrypting a byte array using the
> RSACryptoServiceProvider. The byte array is 52 bytes in length. After
> encrypting I'm converting the encrypted bytes (returned from the
> provider's Encrypt method) to a string using Encoding.UTF8.GetString.
> I then pass this string along to the decryption function. That
> function first converts the string back to a byte array using
> Encoding.UTF8.GetBytes. It then calls the RSACryptoServiceProvider's
> Decrypt method. I get an exception trying to make this call because
> the byte array returned from Encoding.UTF8.GetBytes is too long. A max
> of 128 bytes can be passed to the RSA decryption algorithm.
>
> I've tried other encodings but can't get this to work. What am I doing
> wrong? Here's some code:
>
> client (encrypts):
>
>        byte[] cipherBytes = rsa.Encrypt( bytesToEncrypt, false);
>
>        string cipherText = Encoding.UTF8.GetString(cipherBytes);
>
> server (decrypts):
>
>        byte[] encryptedBytes = Encoding.UTF8.GetBytes(cipherText);
>
>        byte[] clearTextBytes = provider.Decrypt(encryptedBytes,
> false); <<--- GET EXCEPTION HERE
>
> Thanks,
> Bob

date: Tue, 6 May 2008 21:25:41 -0500 author: Joe Kaplan

Re: RSA encrypt/decrypt of byte array

bobuva  wrote in news:014f714a-e412-42d2-83bf-
e590600aa6b6@24g2000hsh.googlegroups.com:

> client (encrypts):
> 
>         byte[] cipherBytes = rsa.Encrypt( bytesToEncrypt, false);
> 
>         string cipherText = Encoding.UTF8.GetString(cipherBytes);
> 
> server (decrypts):
> 
>         byte[] encryptedBytes = Encoding.UTF8.GetBytes(cipherText);
> 
>         byte[] clearTextBytes = provider.Decrypt(encryptedBytes,
> false); <<--- GET EXCEPTION HERE

Bob,

The problem lies in constructing your cipherText string. Not all byte 
sequences represent a character in UTF-8, which means that you can't just 
feed the result of rsa.Encrypt() to Encoding.UTF8.GetString().

What you could do instead, is converting your bytes to and from Base64:

   // On the client
   string cipherText = Convert.ToBase64String(cipherBytes);

   // On the server
   byte[] encryptedBytes = Convert.FromBase64String(cipherText);


-- 
Arnout.

date: Wed, 07 May 2008 08:22:52 -0700 author: Arnout Grootveld am

Re: RSA encrypt/decrypt of byte array

On May 7, 8:22 am, Arnout Grootveld <arn...@newsgroup.nospam> wrote:
> bobuva  wrote in news:014f714a-e412-42d2-83bf-
> e590600aa...@24g2000hsh.googlegroups.com:
>
> > client (encrypts):
>
> >         byte[] cipherBytes = rsa.Encrypt( bytesToEncrypt, false);
>
> >         string cipherText = Encoding.UTF8.GetString(cipherBytes);
>
> > server (decrypts):
>
> >         byte[] encryptedBytes = Encoding.UTF8.GetBytes(cipherText);
>
> >         byte[] clearTextBytes = provider.Decrypt(encryptedBytes,
> > false); <<--- GET EXCEPTION HERE
>
> Bob,
>
> The problem lies in constructing your cipherText string. Not all byte
> sequences represent a character in UTF-8, which means that you can't just
> feed the result of rsa.Encrypt() to Encoding.UTF8.GetString().
>
> What you could do instead, is converting your bytes to and from Base64:
>
>    // On the client
>    string cipherText = Convert.ToBase64String(cipherBytes);
>
>    // On the server
>    byte[] encryptedBytes = Convert.FromBase64String(cipherText);
>
> --
> Arnout.

I did try converting to/from base-64 string but got a "Bad Data" error
from the Decrypt call. I'll look at what Joe K. recommended. Although
it looks like I may be switching to WCF for the utility I'm working on
instead of doing the encryption myself.

Bob

date: Wed, 7 May 2008 13:36:39 -0700 (PDT) author: bobuva

Re: RSA encrypt/decrypt of byte array

On 7 íÁÊ, 23:36, bobuva  wrote:
>
> I did try converting to/from base-64 string but got a "Bad Data" error
> from the Decrypt call. I'll look at what Joe K. recommended. Although
> it looks like I may be switching to WCF for the utility I'm working on
> instead of doing the encryption myself.
>
> Bob

Hi,
you probably using hardware CSP (smart card). RSACryptoServiceProvider
in .NET Framework 2.0 have a problem with hardware CSP. If you use for
example "Microsoft base cryptographic provider" then your code will
not generate exception. For more information see this:

http://forums.microsoft.com/msdn/ShowPost.aspx?postid=2033926&siteid=1
http://lab.msdn.microsoft.com/ProductFeedback/viewFeedback.aspx?feedbackid=0022f1de-c89d-435c-b8dd-1372d67d1ab9

In .NET Framework 1.1 in VS2003 RSACryptoServiceProvider class work
ok.

Ivan Blagoev

date: Thu, 8 May 2008 01:53:42 -0700 (PDT) author: unknown

Re: RSA encrypt/decrypt of byte array

On 7 íÁÊ, 23:36, bobuva  wrote:
> On May 7, 8:22 am, Arnout Grootveld <arn...@newsgroup.nospam> wrote:
>
>
>
> > bobuva  wrote in news:014f714a-e412-42d2-83bf-
> > e590600aa...@24g2000hsh.googlegroups.com:
>
> > > client (encrypts):
>
> > >         byte[] cipherBytes = rsa.Encrypt( bytesToEncrypt, false);
>
> > >         string cipherText = Encoding.UTF8.GetString(cipherBytes);
>
> > > server (decrypts):
>
> > >         byte[] encryptedBytes = Encoding.UTF8.GetBytes(cipherText);
>
> > >         byte[] clearTextBytes = provider.Decrypt(encryptedBytes,
> > > false); <<--- GET EXCEPTION HERE
>
> > Bob,
>
> > The problem lies in constructing your cipherText string. Not all byte
> > sequences represent a character in UTF-8, which means that you can't just
> > feed the result of rsa.Encrypt() to Encoding.UTF8.GetString().
>
> > What you could do instead, is converting your bytes to and from Base64:
>
> >    // On the client
> >    string cipherText = Convert.ToBase64String(cipherBytes);
>
> >    // On the server
> >    byte[] encryptedBytes = Convert.FromBase64String(cipherText);
>
> > --
> > Arnout.
>
> I did try converting to/from base-64 string but got a "Bad Data" error
> from the Decrypt call. I'll look at what Joe K. recommended. Although
> it looks like I may be switching to WCF for the utility I'm working on
> instead of doing the encryption myself.
>
> Bob

Hi,
you probably using hardware CSP (smart card). RSACryptoServiceProvider
in .NET Framework 2.0 have a problem with hardware CSP. If you use for
example "Microsoft base cryptographic provider" then your code will
not generate exception. For more information see this:

http://forums.microsoft.com/msdn/ShowPost.aspx?postid=2033926&siteid=1
http://lab.msdn.microsoft.com/ProductFeedback/viewFeedback.aspx?feedb...

In .NET Framework 1.1 in VS2003 RSACryptoServiceProvider class work
ok.

Ivan Blagoev

date: Fri, 9 May 2008 00:17:24 -0700 (PDT) author: unknown