/// <summary>
/// initial netlogon signature token when AES is negotiated
/// </summary>
/// <param name="sequenceNumber">sequence number</param>
/// <param name="sessionKey">session key</param>
/// <param name="requestConfidentiality">confidentiality is required or not</param>
/// <param name="isClientSideOutbound">Is client side outbound message.</param>
/// <param name="securityBuffers">
/// Security buffers, contains input plain-text; output cipher-text and signature.
/// </param>
private static void InitialNetlogonSignatureTokenWhenAesIsNegotiated(
ref ulong sequenceNumber,
byte[] sessionKey,
bool requestConfidentiality,
bool isClientSideOutbound,
SecurityBuffer[] securityBuffers)
{
byte[] plainText;
byte[] cipherText;
byte[] token;
NL_AUTH_SHA2_SIGNATURE nlAuthSha2Sign = new NL_AUTH_SHA2_SIGNATURE();
//The SignatureAlgorithm first byte MUST be set to 0x13,
//and the second byte MUST be set to 0x00.
nlAuthSha2Sign.SignatureAlgorithm =
NL_AUTH_SHA2_SIGNATURE_SignatureAlgorithm_Values.HMACSHA256;
if (requestConfidentiality)
{
//If the Confidentiality option (section 3.3.1) is
//requested from the application, then the SealAlgorithm
//first byte MUST be set to 0x1A, the second byte MUST
//be set to 0x00, and the Confounder MUST be filled with
//cryptographically random data.
nlAuthSha2Sign.SealAlgorithm =
NL_AUTH_SHA2_SIGNATURE_SealAlgorithm_Values.AES128;
nlAuthSha2Sign.Confounder = GenerateNonce(NL_AUTH_SIGNATURE_CONFOUNDER_LENGTH);
}
else
{
//If the Confidentiality option (section 3.3.1) is not
//requested, then the SealAlgorithm MUST be filled with
//two bytes of 0xff, and the Confounder is not included in the token.
nlAuthSha2Sign.SealAlgorithm =
NL_AUTH_SHA2_SIGNATURE_SealAlgorithm_Values.NotEncrypted;
nlAuthSha2Sign.Confounder = null;
}
//The Pad MUST be filled with 0xff bytes.
nlAuthSha2Sign.Pad = NL_AUTH_SHA2_SIGNATURE_Pad_Values.V1;
//The Flags MUST be filled with 0x00 bytes.
nlAuthSha2Sign.Flags = Flags_Values.V1;
//The SequenceNumber MUST be computed using the following algorithm.
nlAuthSha2Sign.SequenceNumber = ComputeCopySequenceNumber(sequenceNumber, isClientSideOutbound);
//The ClientSequenceNumber MUST be incremented by 1.
sequenceNumber += 1;
//Compute signature
plainText = ConcatenateSecurityBuffersForChecksum(securityBuffers);
nlAuthSha2Sign.Checksum = ComputeSignatureWhenAesIsNegotiated(
nlAuthSha2Sign,
sessionKey,
requestConfidentiality,
plainText);
//If the Confidentiality option is requested, the data and the Confounder
//field MUST be encrypted. If AES is negotiated then the server MUST use
//the AES-128 algorithm using the SessionKey with an initialization
//vector constructed by concatenating the sequence number with
//itself twice (thus getting 16 bytes of data)
if (requestConfidentiality)
{
byte[] aesEncryptionKey = ComputeEncryptionKeyWhenAesIsNegotiated(sessionKey);
using (BCryptAlgorithm aes = new BCryptAlgorithm("AES"))
{
aes.Mode = BCryptCipherMode.CFB;
aes.Key = aesEncryptionKey;
aes.IV = ArrayUtility.ConcatenateArrays(
nlAuthSha2Sign.SequenceNumber,
nlAuthSha2Sign.SequenceNumber);
nlAuthSha2Sign.Confounder = aes.Encrypt(nlAuthSha2Sign.Confounder);
plainText = SspiUtility.ConcatenateReadWriteSecurityBuffers(
securityBuffers,
SecurityBufferType.Data);
cipherText = aes.Encrypt(plainText);
}
SspiUtility.UpdateSecurityBuffers(securityBuffers, SecurityBufferType.Data, cipherText);
}
else
{
cipherText = null;
}
//The SequenceNumber MUST be encrypted.
//If AES is negotiated, then the server MUST use the AES-128
//algorithm using the SessionKey with an initialization vector
//constructed by concatenating the first 8 bytes of the
//checksum with itself twice (thus getting 16 bytes of data)
using (BCryptAlgorithm aes = new BCryptAlgorithm("AES"))
{
aes.Mode = BCryptCipherMode.CFB;
aes.Key = sessionKey;
aes.IV = ArrayUtility.ConcatenateArrays(
nlAuthSha2Sign.Checksum, // Checksum is only 8 bytes
nlAuthSha2Sign.Checksum);
nlAuthSha2Sign.SequenceNumber = aes.Encrypt(nlAuthSha2Sign.SequenceNumber);
}
nlAuthSha2Sign.Dummy = GenerateNonce(NL_AUTH_SHA2_SIGNATURE_DUMMY_LENGTH); // 24 == size of dummy
token = TypeMarshal.ToBytes(nlAuthSha2Sign);
SspiUtility.UpdateSecurityBuffers(securityBuffers, SecurityBufferType.Token, token);
}
/// <summary>
/// Compute signature when AES is negotiated
/// </summary>
/// <param name="nlAuthSha2Sign">NL_AUTH_SHA2_SIGNATURE struct</param>
/// <param name="sessionKey">session key</param>
/// <param name="requestConfidentiality">confidentiality is required or not</param>
/// <param name="plainText">plain-text message to make signature</param>
/// <returns>signature</returns>
private static byte[] ComputeSignatureWhenAesIsNegotiated(
NL_AUTH_SHA2_SIGNATURE nlAuthSha2Sign,
byte[] sessionKey,
bool requestConfidentiality,
byte[] plainText)
{
//If AES is negotiated, then a signature MUST be computed using
//the following algorithm:
//CALL SHA256Reset(&HashContext, Sk, sizeof(Sk));
//CALL SHA256Input(HashContext, NL_AUTH_SHA2_SIGNATURE, [8 bytes]);
//IF Confidentiality requested
//CALL SHA256Input(HashContext, Confounder, [8 bytes]);
//CALL SHA256FinalBits(HashContext, Message, size of Message;
//CALL SHA256Result(HashContext, output);
//SET Signature to output
//Note: In the first call to SHA256Input, only the first 8-bytes
//of the NL_AUTH_SHA2_SIGNATURE structure are used.
byte[] signature;
byte[] buf = ArrayUtility.ConcatenateArrays(
BitConverter.GetBytes((ushort)nlAuthSha2Sign.SignatureAlgorithm),
BitConverter.GetBytes((ushort)nlAuthSha2Sign.SealAlgorithm),
BitConverter.GetBytes((ushort)nlAuthSha2Sign.Pad),
BitConverter.GetBytes((ushort)nlAuthSha2Sign.Flags));
if (requestConfidentiality)
{
buf = ArrayUtility.ConcatenateArrays(
buf,
nlAuthSha2Sign.Confounder);
}
buf = ArrayUtility.ConcatenateArrays(
buf,
plainText);
using (HMACSHA256 hmacSha256 = new HMACSHA256(sessionKey))
{
signature = hmacSha256.ComputeHash(buf);
}
//After the signature is computed, the signature MUST be truncated,
//with only the first 8 bytes being copied into the Checksum field
//of NL_AUTH_SHA2_SIGNATURE.
signature = ArrayUtility.SubArray(signature, 0, NL_AUTH_SIGNATURE_CHECKSUM_LENGTH);
return signature;
}
