/// <summary>
/// Imports a specified key.
/// </summary>
/// <param name="provider">The handle of the CSP.</param>
/// <param name="algorithm">One of the <see cref="CryptoAlgorithm"/> values.</param>
/// <param name="key">The key to import.</param>
/// <returns>The handle of the symmetric key.</returns>
/// <exception cref="SecurityException">An error occurs while importing the specified key.</exception>
private int KeyFromBytes(int provider, CryptoAlgorithm algorithm, byte[] key)
{
int dwFlags = SecurityConstants.CRYPT_FIRST, dwSize, dwProvSessionKeySize = 0, dwPublicKeySize = 0, dwSessionBlob, offset = 0, hTempKey = 0, hSessionKey = 0;
IntPtr algo = new IntPtr((int)algorithm), dwPrivKeyAlg = IntPtr.Zero, pbSessionBlob = IntPtr.Zero;
IntPtr provEnum = IntPtr.Zero;
try {
// Double check to see if this provider supports this algorithm
// and key size
bool found = false;
provEnum = Marshal.AllocHGlobal(84 + IntPtr.Size);
do
{
dwSize = 84 + IntPtr.Size;
if (SspiProvider.CryptGetProvParam(provider, SecurityConstants.PP_ENUMALGS_EX, provEnum, ref dwSize, dwFlags) == 0)
{
break;
}
dwFlags = 0;
if (Marshal.ReadIntPtr(provEnum) == algo)
{
found = true;
}
} while (!found);
if (!found)
{
throw new SecurityException("CSP does not support selected algorithm.");
}
// We have to get the key size(including padding)
// from an HCRYPTKEY handle. PP_ENUMALGS_EX contains
// the key size without the padding so we can't use it.
if (SspiProvider.CryptGenKey(provider, algo, 0, ref hTempKey) == 0)
{
throw new SecurityException("Cannot generate temporary key.");
}
dwSize = 4; // sizeof(int)
if (SspiProvider.CryptGetKeyParam(hTempKey, SecurityConstants.KP_KEYLEN, ref dwProvSessionKeySize, ref dwSize, 0) == 0)
{
throw new SecurityException("Cannot retrieve key parameters.");
}
// Our key is too big, leave
if ((key.Length * 8) > dwProvSessionKeySize)
{
throw new SecurityException("Key too big.");
}
// Get private key's algorithm
dwSize = IntPtr.Size; //sizeof(ALG_ID)
if (SspiProvider.CryptGetKeyParam(m_ExponentOfOne, SecurityConstants.KP_ALGID, ref dwPrivKeyAlg, ref dwSize, 0) == 0)
{
throw new SecurityException("Unable to get the private key's algorithm.");
}
// Get private key's length in bits
dwSize = 4; // sizeof(DWORD)
if (SspiProvider.CryptGetKeyParam(m_ExponentOfOne, SecurityConstants.KP_KEYLEN, ref dwPublicKeySize, ref dwSize, 0) == 0)
{
throw new SecurityException("Unable to get the key length.");
}
// calculate Simple blob's length
dwSessionBlob = (dwPublicKeySize / 8) + IntPtr.Size /*sizeof(ALG_ID)*/ + 4 + IntPtr.Size /*sizeof(BLOBHEADER)*/;
// allocate simple blob buffer
pbSessionBlob = Marshal.AllocHGlobal(dwSessionBlob);
// SIMPLEBLOB Format is documented in SDK
// Copy header to buffer
PUBLICKEYSTRUC pks = new PUBLICKEYSTRUC();
pks.bType = SecurityConstants.SIMPLEBLOB;
pks.bVersion = 2;
pks.reserved = 0;
pks.aiKeyAlg = algo;
Marshal.StructureToPtr(pks, pbSessionBlob, false);
Marshal.WriteIntPtr(pbSessionBlob, offset = Marshal.SizeOf(pks), dwPrivKeyAlg);
offset += IntPtr.Size; // sizeof(ALG_ID)
// Place the key material in reverse order
for (int i = 0; i < key.Length; i++)
{
Marshal.WriteByte(pbSessionBlob, offset + key.Length - i - 1, key[i]);
}
// 3 is for the first reserved byte after the key material + the 2 reserved bytes at the end.
dwSize = dwSessionBlob - (IntPtr.Size /*sizeof(ALG_ID)*/ + IntPtr.Size + 4 /*sizeof(BLOBHEADER)*/ + key.Length + 3);
offset += key.Length + 1;
// Generate random data for the rest of the buffer
// (except that last two bytes)
if (SspiProvider.CryptGenRandom(provider, dwSize, new IntPtr(pbSessionBlob.ToInt64() + offset)) == 0)
{
throw new SecurityException("Could not generate random data.");
}
for (int i = 0; i < dwSize; i++)
{
if (Marshal.ReadByte(pbSessionBlob, offset) == 0)
{
Marshal.WriteByte(pbSessionBlob, offset, 1);
}
offset++;
}
Marshal.WriteByte(pbSessionBlob, dwSessionBlob - 2, 2);
if (SspiProvider.CryptImportKey(provider, pbSessionBlob, dwSessionBlob, m_ExponentOfOne, SecurityConstants.CRYPT_EXPORTABLE, ref hSessionKey) == 0)
{
throw new SecurityException("Cannot import key [key has right size?].");
}
} finally {
if (provEnum != IntPtr.Zero)
{
Marshal.FreeHGlobal(provEnum);
}
if (hTempKey != 0)
{
SspiProvider.CryptDestroyKey(hTempKey);
}
if (pbSessionBlob != IntPtr.Zero)
{
Marshal.FreeHGlobal(pbSessionBlob);
}
}
return(hSessionKey);
}