Encryption using X509Certificate

[rawCoder]

Hi All,

I have a *.cer file, a public key of some one and I want to encrypt some
thing using this public key.

Can someone point me to a sample code for Encrypting some file using
X509Certificate ( *.cer file ) so that it can be used to email as
attachment.

The real part is Encrypting using X509Certificate and CryptoServicePr ovider.

Am I one the right track ?

Any help is appreciated.

Thanx in advance

rawCoder

[rawCoder]

Re: Encryption using X509Certificate

Incase someone else is also interested i found the following code snippet
useful from some newsgroup post.

// Usage
string certFile = @"c:\mycert.cer ";
X509Certificate cert = X509Certificate .CreateFromCert File(certFile) ;
RSACryptoServic eProvider rsa = CertUtil.GetCer tPublicKey(cert );
Console.WriteLi ne(rsa.ToXmlStr ing(false));

/// CertUtil helper Class.
using System;
using System.Security .Cryptography;
using System.Runtime. InteropServices ;
using System.Security .Cryptography.X 509Certificate s;


namespace WSESimpleTCPDLL
{
[StructLayout(La youtKind.Seque ntial)]
public struct PUBKEYBLOBHEADE RS
{
public byte bType; //BLOBHEADER
public byte bVersion; //BLOBHEADER
public short reserved; //BLOBHEADER
public uint aiKeyAlg; //BLOBHEADER
public uint magic; //RSAPUBKEY
public uint bitlen; //RSAPUBKEY
public uint pubexp; //RSAPUBKEY
}


/// <summary>
/// Summary description for CertUtil.
/// </summary>
public sealed class CertUtil
{
const uint CERT_SYSTEM_STO RE_CURRENT_USER = 0x00010000;
const uint CERT_STORE_READ ONLY_FLAG = 0x00008000;
const uint CERT_STORE_OPEN _EXISTING_FLAG = 0x00004000;
const uint CERT_FIND_SUBJE CT_STR = 0x00080007;
const uint X509_ASN_ENCODI NG = 0x00000001;
const uint PKCS_7_ASN_ENCO DING = 0x00010000;
const uint RSA_CSP_PUBLICK EYBLOB = 19;
const int AT_KEYEXCHANGE = 1; //keyspec values
const int AT_SIGNATURE = 2;
static uint ENCODING_TYPE = PKCS_7_ASN_ENCO DING | X509_ASN_ENCODI NG ;


private CertUtil()
{
}


public static RSACryptoServic eProvider GetCertPublicKe y(X509Certifica te
cert)
{
byte[] publickeyblob ;
byte[] encodedpubkey = cert.GetPublicK ey(); //asn.1 encoded public key


uint blobbytes = 0;


if(Win32.CryptD ecodeObject(ENC ODING_TYPE, RSA_CSP_PUBLICK EYBLOB,
encodedpubkey, (uint)encodedpu bkey.Length, 0, null, ref blobbytes))
{
publickeyblob = new byte[blobbytes];
Win32.CryptDeco deObject(ENCODI NG_TYPE, RSA_CSP_PUBLICK EYBLOB,
encodedpubkey, (uint)encodedpu bkey.Length, 0, publickeyblob, ref blobbytes);
}
else
{
throw new Exception("Coul d not decode publickeyblob from certificate
publickey") ;
}


PUBKEYBLOBHEADE RS pkheaders = new PUBKEYBLOBHEADE RS() ;
int headerslength = Marshal.SizeOf( pkheaders);
IntPtr buffer = Marshal.AllocHG lobal( headerslength);
Marshal.Copy( publickeyblob, 0, buffer, headerslength );
pkheaders = (PUBKEYBLOBHEAD ERS) Marshal.PtrToSt ructure( buffer,
typeof(PUBKEYBL OBHEADERS) );
Marshal.FreeHGl obal( buffer );


//----- Get public exponent -------------
byte[] exponent = BitConverter.Ge tBytes(pkheader s.pubexp);
//little-endian ordered
Array.Reverse(e xponent); //convert to big-endian order


//----- Get modulus -------------
int modulusbytes = (int)pkheaders. bitlen/8 ;
byte[] modulus = new byte[modulusbytes];
try
{
Array.Copy(publ ickeyblob, headerslength, modulus, 0, modulusbytes);
Array.Reverse(m odulus); //convert from little to big-endian ordering.
}
catch(Exception )
{
throw new Exception("Prob lem getting modulus from publickeyblob") ;
}


RSAParameters parms = new RSAParameters() ;
parms.Modulus = modulus;
parms.Exponent = exponent;
RSACryptoServic eProvider rsa = new RSACryptoServic eProvider();
rsa.ImportParam eters(parms);
return rsa;
}
}



}


//// Win32 Helpers
using System;
using System.Runtime. InteropServices ;
using System.Componen tModel;
using System.Collecti ons;
using System.Text;

namespace WSESimpleTCPDLL
{
public class Win32
{
[DllImport("cryp t32.dll")]
public static extern bool CryptDecodeObje ct(
uint CertEncodingTyp e,
uint lpszStructType,
byte[] pbEncoded,
uint cbEncoded,
uint flags,
[In, Out] byte[] pvStructInfo,
ref uint cbStructInfo);


[DllImport("cryp t32.dll", SetLastError=tr ue)]
public static extern IntPtr CertFindCertifi cateInStore(
IntPtr hCertStore,
uint dwCertEncodingT ype,
uint dwFindFlags,
uint dwFindType,
[In, MarshalAs(Unman agedType.LPWStr )]String pszFindString,
IntPtr pPrevCertCntxt) ;


[DllImport("cryp t32.dll", SetLastError=tr ue)]
public static extern bool CertFreeCertifi cateContext(
IntPtr hCertStore) ;


[DllImport("cryp t32.dll", CharSet=CharSet .Auto, SetLastError=tr ue)]
//overloaded
public static extern IntPtr CertOpenStore(
[MarshalAs(Unman agedType.LPStr )] String storeProvider,
uint dwMsgAndCertEnc odingType,
IntPtr hCryptProv,
uint dwFlags,
String cchNameString) ;


[DllImport("cryp t32.dll", SetLastError=tr ue)]
public static extern bool CertCloseStore(
IntPtr hCertStore,
uint dwFlags) ;
}



}

HTH
rawCoder
"rawCoder" <rawCoder@hotma il.com> wrote in message
news:O2VLKRJVFH A.3076@TK2MSFTN GP12.phx.gbl...[color=blue]
> Hi All,
>
> I have a *.cer file, a public key of some one and I want to encrypt some
> thing using this public key.
>
> Can someone point me to a sample code for Encrypting some file using
> X509Certificate ( *.cer file ) so that it can be used to email as
> attachment.
>
> The real part is Encrypting using X509Certificate and[/color]
CryptoServicePr ovider.[color=blue]
>
> Am I one the right track ?
>
> Any help is appreciated.
>
> Thanx in advance
>
> rawCoder
>
>[/color]

[Klassy]

Re: Encryption using X509Certificate

In case you are still interested. Here is an article and some sample code

http://www.codeproject.com/useritems/X509Certificate.asp