v1.1.0

Changelog

All notable changes to this project are documented in this file.

The format is based on Keep a Changelog,
and this project adheres to Semantic Versioning.

[1.1.0] - 2026-10-16

External Security Protocol work. TLS now completes against a real RDP host; the
NTLM exchange that CredSSP needs is implemented but does not yet complete.

Added

• TLS channel (Security/TlsChannel.cs): the handshake MS-RDPEA 3.1.5.1
  places on the same TCP connection, with TERMSRV/<host> SNI. The self-signed
  host certificate is accepted and then reported, because RDP does not
  chain-validate and the default policy would reject every real host.
• Security mode selection (Security/RdpSecurity.cs): maps the negotiated
  SelectedProtocol to TLS, CredSSP or none, and refuses an unknown protocol
  rather than downgrading.
• NTLM (Security/Ntlm.cs, Security/Md4.cs, Security/NtlmAuthenticator.cs):
  NEGOTIATE, CHALLENGE and AUTHENTICATE messages with an NTLMv2 response. MD4 is
  implemented because .NET does not ship it and NTLM specifies it.
• SPNEGO (Security/Spnego.cs): BER encoding and decoding for the
  GSS-API NegTokenInit / NegTokenTarg wrappers, plus SPNEGO error decoding.
• CredSSP renegotiation (RdpConnection.RenegotiateInsideCredSspAsync): the
  second RDP_NEG_REQ that MS-RDPEA 3.2.1.5.1.5 requires inside the
  authenticated channel.
• rdpprobe flags --tls12, --tls-only and --credssp-only to pin the
  security mode while diagnosing a host.
• Wrapped TLS and SPNEGO failures now report their root cause instead of the
  outermost message.

Verified

Against a Windows Server 2025 host (fDenyTSConnections=0, port 3389):

• RDP negotiation selects PROTOCOL_HYBRID_EX and the client reports CredSSP.
• The TLS handshake completes on both TLS 1.3 and TLS 1.2, presenting the
  server's self-signed certificate.
• Requesting PROTOCOL_SSL alone is refused with RDP_NEG_FAILURE code 5
  (SSL_REQUIRED_BY_SERVER), so the host mandates NLA.

Not working

The SPNEGO/NTLM exchange does not complete. The first token write is followed by
a TLS decryption failure, which indicates the host answered with an alert rather
than a challenge. The cause is not yet identified, so this is reported as a
failure rather than papered over.

Not implemented

Unchanged from 1.0.0, and all still ahead of the login screen:

• CredSSP RSA key exchange and session key derivation (MS-RDPBCGR 5.3.2)
• Encryption of MCS traffic (RC4 / AES)
• Capability exchange (2.2.7), including the Demand Active / Confirm Active
  pairs that begin the connection
• Early User Authorization (2.2.10.2) and the logon-information PDUs
• The graphics pipeline and input needed to draw a framebuffer at all

Fixed

• The SPNEGO mechanism OID was double-wrapped and declared a five-octet length
  for six octets of content, which made every token malformed.
• thisMech in the GSS-API wrapper is tagged APPLICATION (0x60), not
  CONTEXT-specific; the two are not interchangeable.

1.0.0 - 2026-10-16

First release. The RDP connection sequence, implemented from Microsoft's public
Open Specifications, verified byte-for-byte against a live Windows RDP server.

Added

• X.224 / T.125 connection request (MS-RDPBCGR 2.2.1.1) with TPKT framing.
• RDP negotiation exchange (2.2.1.1.1, 2.2.1.2.1): RDP_NEG_REQ / RDP_NEG_RSP,
  optional correlation block with CORRELATION_INFO_PRESENT.
• MCS Connect Initial / Connect Response (2.2.1.3.4, 2.2.1.3.5) including the
  GCC Conference Create Request.
• Client data blocks (2.2.1.3.4.1–.5): TS_UD_CS_CORE, TS_UD_CS_SECURITY,
  TS_UD_CS_NET, TS_UD_CS_CLUSTER, TS_UD_CS_USER.
• MCS domain and channel setup (2.2.1.3.6–.8): Erect Domain Request,
  Attach User Request, Channel Join Request, Send Data Request framing.
• T.125 Disconnect Request for orderly close.
• WinUI 3 desktop app with a connection form and a timestamped handshake log.
• rdpprobe console harness for exercising the handshake without the GUI;
  reads the password from RDP_PASSWORD and never echoes it.
• Protocol-layer unit tests pinned to bytes captured from mstsc.exe.
• Documentation site, logo, and application icon set.

Platform

• Windows on x64, ARM64 and x86.
• Windows only: WinUI 3 has no macOS or Linux implementation. The protocol core
  targets plain .NET and carries no UI dependency, so it can be reused from a
  cross-platform front end if one is written.

Not implemented

Stated plainly so nobody mistakes this for a working desktop viewer:

• RSA key exchange and RC4/AES session keys (2.2.1.4.3, 5.3.2)
• CredSSP / NLA — TLS + SPNEGO + NTLM (MS-RDPEA)
• Capability set exchange (2.2.7)
• Bitmap, pointer and order graphics pipeline (2.2.9)
• Keyboard and pointer input (2.2.8)
• Virtual channel data: clipboard, drive, audio (2.2.6)

Security

Credentials are transmitted as UTF-16 in TS_UD_CS_USER over the classic RDP
handshake, in clear. CredSSP is not implemented, so use only against hosts you
control or over a trusted, encrypted transport.

Fixed during development

These were found by comparing emitted bytes against a recorded mstsc.exe
exchange; each produced a malformed PDU that a server answered with an immediate
reset.

• TPKT length is big-endian while the rest of the connection sequence is
  little-endian.
• The X.224 length indicator precedes the TPDU code; TPKT orders its length last.
• TS_UD_CS_* headers are 16-bit little-endian values, not single bytes.
• TS_UD_CS_* TLV headers are 6 bytes: type(2), flags(2), length(2).
• MCS integers are plain fixed-width values with no T.125 selector bits.
• The GCC conference name length is counted in UTF-16 code units, not bytes.

v1.0.0

Changelog

All notable changes to this project are documented in this file.

The format is based on Keep a Changelog,
and this project adheres to Semantic Versioning.

1.0.0 - 2026-10-16

First release. The RDP connection sequence, implemented from Microsoft's public
Open Specifications, verified byte-for-byte against a live Windows RDP server.

Added

• X.224 / T.125 connection request (MS-RDPBCGR 2.2.1.1) with TPKT framing.
• RDP negotiation exchange (2.2.1.1.1, 2.2.1.2.1): RDP_NEG_REQ / RDP_NEG_RSP,
  optional correlation block with CORRELATION_INFO_PRESENT.
• MCS Connect Initial / Connect Response (2.2.1.3.4, 2.2.1.3.5) including the
  GCC Conference Create Request.
• Client data blocks (2.2.1.3.4.1–.5): TS_UD_CS_CORE, TS_UD_CS_SECURITY,
  TS_UD_CS_NET, TS_UD_CS_CLUSTER, TS_UD_CS_USER.
• MCS domain and channel setup (2.2.1.3.6–.8): Erect Domain Request,
  Attach User Request, Channel Join Request, Send Data Request framing.
• T.125 Disconnect Request for orderly close.
• WinUI 3 desktop app with a connection form and a timestamped handshake log.
• rdpprobe console harness for exercising the handshake without the GUI;
  reads the password from RDP_PASSWORD and never echoes it.
• Protocol-layer unit tests pinned to bytes captured from mstsc.exe.
• Documentation site, logo, and application icon set.

Platform

• Windows on x64, ARM64 and x86.
• Windows only: WinUI 3 has no macOS or Linux implementation. The protocol core
  targets plain .NET and carries no UI dependency, so it can be reused from a
  cross-platform front end if one is written.

Not implemented

Stated plainly so nobody mistakes this for a working desktop viewer:

• RSA key exchange and RC4/AES session keys (2.2.1.4.3, 5.3.2)
• CredSSP / NLA — TLS + SPNEGO + NTLM (MS-RDPEA)
• Capability set exchange (2.2.7)
• Bitmap, pointer and order graphics pipeline (2.2.9)
• Keyboard and pointer input (2.2.8)
• Virtual channel data: clipboard, drive, audio (2.2.6)

Security

Credentials are transmitted as UTF-16 in TS_UD_CS_USER over the classic RDP
handshake, in clear. CredSSP is not implemented, so use only against hosts you
control or over a trusted, encrypted transport.

Fixed during development

These were found by comparing emitted bytes against a recorded mstsc.exe
exchange; each produced a malformed PDU that a server answered with an immediate
reset.

• TPKT length is big-endian while the rest of the connection sequence is
  little-endian.
• The X.224 length indicator precedes the TPDU code; TPKT orders its length last.
• TS_UD_CS_* headers are 16-bit little-endian values, not single bytes.
• TS_UD_CS_* TLV headers are 6 bytes: type(2), flags(2), length(2).
• MCS integers are plain fixed-width values with no T.125 selector bits.
• The GCC conference name length is counted in UTF-16 code units, not bytes.