/// <summary>
/// Returns the bytes that represent the symmetric key.
/// </summary>
/// <returns>An array of bytes.</returns>
/// <exception cref="ObjectDisposedException">The SymmetricKey has been disposed.</exception>
public byte[] ToBytes()
{
if (m_Handle == 0)
{
throw new ObjectDisposedException(this.GetType().FullName);
}
IntPtr pbSessionBlob = IntPtr.Zero;
try {
int dwSessionBlob = 0;
if (SspiProvider.CryptExportKey(m_Handle, m_ExponentOfOne, SecurityConstants.SIMPLEBLOB, 0, IntPtr.Zero, ref dwSessionBlob) == 0)
{
throw new SecurityException("Cannot export key.");
}
pbSessionBlob = Marshal.AllocHGlobal(dwSessionBlob);
if (SspiProvider.CryptExportKey(m_Handle, m_ExponentOfOne, SecurityConstants.SIMPLEBLOB, 0, pbSessionBlob, ref dwSessionBlob) == 0)
{
throw new SecurityException("Cannot export key.");
}
// Get session key size in bits
int dwSize = 4; // sizeof(DWORD)
int dwKeyMaterial = 0;
if (SspiProvider.CryptGetKeyParam(m_Handle, SecurityConstants.KP_KEYLEN, ref dwKeyMaterial, ref dwSize, 0) == 0)
{
throw new SecurityException("Cannot retrieve key parameters.");
}
// Get the number of bytes and allocate buffer
dwKeyMaterial /= 8;
byte[] pbKeyMaterial = new byte[dwKeyMaterial];
// Skip the header
int offset = 4 + IntPtr.Size; // sizeof(BLOBHEADER);
offset += IntPtr.Size; // sizeof(ALG_ID);
Marshal.Copy(new IntPtr(pbSessionBlob.ToInt64() + offset), pbKeyMaterial, 0, pbKeyMaterial.Length);
// the key is reversed
Array.Reverse(pbKeyMaterial);
return(pbKeyMaterial);
} finally {
if (pbSessionBlob != IntPtr.Zero)
{
Marshal.FreeHGlobal(pbSessionBlob);
}
}
}
/// <summary>
/// Dynamically creates an exponent-of-one key.
/// </summary>
/// <returns>The handle of a exponent-of-one key.</returns>
/// <exception cref="SecurityException">An error occurs while creating the key.</exception>
private int CreateDynamicExponentOfOneKey()
{
int hPrivateKey = 0;
int dwKeyBlob = 0;
IntPtr keyblob = IntPtr.Zero;
int dwBitLen;
try {
if (SspiProvider.CryptGenKey(m_Provider, new IntPtr(SecurityConstants.AT_KEYEXCHANGE), SecurityConstants.CRYPT_EXPORTABLE, ref hPrivateKey) == 0)
{
throw new SecurityException("Cannot generate key pair.");
}
// Export the private key, we'll convert it to a private
// exponent of one key
if (SspiProvider.CryptExportKey(hPrivateKey, 0, SecurityConstants.PRIVATEKEYBLOB, 0, IntPtr.Zero, ref dwKeyBlob) == 0)
{
throw new SecurityException("Cannot export generated key.");
}
keyblob = Marshal.AllocHGlobal(dwKeyBlob);
if (SspiProvider.CryptExportKey(hPrivateKey, 0, SecurityConstants.PRIVATEKEYBLOB, 0, keyblob, ref dwKeyBlob) == 0)
{
throw new SecurityException("Cannot export generated key.");
}
SspiProvider.CryptDestroyKey(hPrivateKey);
hPrivateKey = 0;
// Get the bit length of the key
dwBitLen = Marshal.ReadInt32(keyblob, 12);
/* Modify the Exponent in Key BLOB format [Key BLOB format is documented in SDK] */
// Convert pubexp in rsapubkey to 1
int offset = 16;
for (int i = 0; i < 4; i++)
{
if (i == 0)
{
Marshal.WriteByte(keyblob, offset, 1);
}
else
{
Marshal.WriteByte(keyblob, offset + i, 0);
}
}
// Skip pubexp
offset += 4;
// Skip modulus, prime1, prime2
offset += dwBitLen / 8;
offset += dwBitLen / 16;
offset += dwBitLen / 16;
// Convert exponent1 to 1
for (int i = 0; i < dwBitLen / 16; i++)
{
if (i == 0)
{
Marshal.WriteByte(keyblob, offset, 1);
}
else
{
Marshal.WriteByte(keyblob, offset + i, 0);
}
}
// Skip exponent1
offset += dwBitLen / 16;
// Convert exponent2 to 1
for (int i = 0; i < dwBitLen / 16; i++)
{
if (i == 0)
{
Marshal.WriteByte(keyblob, offset, 1);
}
else
{
Marshal.WriteByte(keyblob, offset + i, 0);
}
}
// Skip exponent2, coefficient
offset += dwBitLen / 16;
offset += dwBitLen / 16;
// Convert privateExponent to 1
for (int i = 0; i < dwBitLen / 8; i++)
{
if (i == 0)
{
Marshal.WriteByte(keyblob, offset, 1);
}
else
{
Marshal.WriteByte(keyblob, offset + i, 0);
}
}
// Import the exponent-of-one private key.
if (SspiProvider.CryptImportKey(m_Provider, keyblob, dwKeyBlob, 0, SecurityConstants.CRYPT_EXPORTABLE, ref hPrivateKey) == 0)
{
throw new SecurityException("Could not import modified key.");
}
} catch (Exception e) {
if (hPrivateKey != 0)
{
SspiProvider.CryptDestroyKey(hPrivateKey);
}
throw e;
} finally {
if (keyblob != IntPtr.Zero)
{
Marshal.FreeHGlobal(keyblob);
}
}
return(hPrivateKey);
}
