Fix Apple DH auth wire-order bug, add type 33 fallback, fix missing VNC password prompt

Live testing against a real macOS Screen Sharing server surfaced two
real bugs, independent of each other:

1. SessionTab::requestConnectOptions() never prompted for a password
   on VNC profiles (only SSH/RDP) -- every VNC connection went out
   with an empty password regardless of what the server needed. VNC
   now gets its own prompt; an empty password is allowed through
   (unlike RDP's hard requirement) since no-auth VNC servers exist and
   there's no way to know client-side before the security-type
   negotiation happens.

2. VncSessionBackend's Apple DH (type 30) response sent the client's
   public key before the encrypted credentials. Cross-checking against
   neatvnc's rfb-proto.h (an independent, authoritative reference: both
   the wire struct definitions and the full server-side verification
   code, matched field-by-field against this implementation) showed
   the correct order is credentials first, then public key -- exactly
   backwards from what was implemented. Fixed, with a new regression
   test that decrypts the credentials back out using the trailing
   public-key bytes to derive the shared secret, which would fail if
   the fields were swapped again.

Also adds security type 33 (RSA + AES, src/vnc_apple_rsa_auth.h) as a
fallback Apple auth scheme, sourced from the `asyncvnc` PyPI package.
Preference when multiple are offered: None > AppleDH(30) >
AppleRSA(33) > VNCAuth(2).

Neither scheme has been gotten working live yet against the specific
macOS Tahoe (26.6.2) server available for testing -- type 30's wire
format is now verified correct byte-for-byte against the independent
reference above, but the server still rejects it with a generic
"Authentication or authorization failure"; type 33 is rejected even
earlier, right after the initial host-key request. macOS Tahoe was
released after this assistant's knowledge cutoff, so there may be a
protocol or permission-model change specific to it that isn't
reflected in either reference. Documented as an open issue in
docs/PROGRESS.md rather than claimed as working.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

CMakeLists.txt

@@ -134,6 +134,8 @@ set(ORBITHUB_SOURCES
     src/vnc_pixel_codecs.h
     src/vnc_apple_dh_auth.cpp
     src/vnc_apple_dh_auth.h
+    src/vnc_apple_rsa_auth.cpp
+    src/vnc_apple_rsa_auth.h
     src/unsupported_session_backend.cpp
     src/unsupported_session_backend.h
 )

docs/PROGRESS.md

@@ -121,7 +121,7 @@ Delivered:
   keyboard (Qt key -> X11 keysym mapping) and mouse/wheel input forwarding
 - `VncDisplayWidget` mirroring `RdpDisplayWidget`'s scale-to-fit rendering
   and input-forwarding shape
-- 41 unit tests (`tests/test_vnc_session_backend.cpp`): pure-function
+- 45 unit tests (`tests/test_vnc_session_backend.cpp`): pure-function
   coverage (DES key prep verified against an independently documented test
   vector, keysym mapping, socket-error mapping) plus state-machine
   coverage against a scripted in-process fake RFB server (all three
@@ -129,10 +129,10 @@ Delivered:
   security types, pixel-accurate Raw/Hextile/ZRLE/Tight decoding including
   a ZRLE zlib-stream-persistence test across two separate
   `FramebufferUpdate` messages, a Tight stream-reset-flag test, cursor/
-  clipboard round trips) -- caught and fixed a real re-entrancy bug
-  (`abort()` synchronously re-firing `disconnected()` mid-
-  `failConnection()`, silently overwriting a specific error with a
-  generic one)
+  clipboard round trips, both Apple auth schemes) -- caught and fixed a
+  real re-entrancy bug (`abort()` synchronously re-firing `disconnected()`
+  mid-`failConnection()`, silently overwriting a specific error with a
+  generic one) and a real Apple-DH wire-order bug (see below)
 - Verified live against a real, independently implemented VNC server
   (TightVNC on Windows): connect with VNC Authentication, correct
   framebuffer dimensions and pixel data, clean disconnect, reconnect,
@@ -150,6 +150,13 @@ Delivered:
   it degenerates to an exact 1:1 mapping once the widget's own bounds are
   fixed to the remote's size, so no separate rendering path was needed.
   Persisted across sessions like the terminal theme preference.
+- Fixed a real, separate bug found during Apple-auth live testing:
+  `SessionTab::requestConnectOptions()` never prompted for a password on
+  VNC profiles at all (only SSH/RDP), so every VNC connection went out
+  with an empty password regardless of what the server needed. VNC now
+  gets its own prompt, with an empty password allowed through (unlike
+  RDP's hard requirement) since some VNC servers are no-auth and there's
+  no way to know that before the server's security-type negotiation
 - Robustness fix: an unrecognized `FramebufferUpdate` rectangle encoding
   used to abort the connection generically; `kAnnouncedEncodings` is now
   the single source of truth for what `SetEncodings` announces and what
@@ -175,17 +182,39 @@ Delivered:
   packaging-dependent runtime failure mode. ZRLE/Tight link `ZLIB::ZLIB`
   (found via a fresh top-level `find_package(ZLIB REQUIRED)`, independent
   of whether vendored FreeRDP's own internal zlib usage stays enabled)
-- 41 unit tests total, 15 of them for Hextile/ZRLE/Tight specifically,
-  including a ZRLE zlib-stream-persistence test across two separate
-  `FramebufferUpdate` messages and a Tight stream-reset-flag test proving
-  the low 4 control-byte bits actually tear down and reinitialize the
-  targeted stream rather than erroring out on stale state
+- Apple Screen Sharing authentication: two schemes, both undocumented by
+  Apple. Security type 30 (Diffie-Hellman + AES, `src/vnc_apple_dh_auth.h`)
+  is implemented and its wire format is confirmed correct against an
+  independent, authoritative source (`neatvnc`'s `rfb-proto.h` struct
+  definitions plus its full server-side verification code, cross-checked
+  field-by-field: generator/key-length framing, the
+  credentials-before-public-key send order -- an actual ordering bug
+  caught this way and fixed -- shared-secret derivation and padding, AES
+  key derivation, and the credential buffer layout all match exactly).
+  Security type 33 (RSA + AES, `src/vnc_apple_rsa_auth.h`) is also
+  implemented, sourced from the `asyncvnc` PyPI package, as a fallback.
+  Preference when both are offered: None > AppleDH(30) > AppleRSA(33) >
+  VNCAuth(2). Covered by a DH round-trip test, fake-server integration
+  tests for both schemes, a preference-order test, and a regression test
+  built from real bytes captured off an actual macOS server
 
-Known gaps (explicit scope decisions, not oversights -- see issue #3 for
-follow-up tracking):
-- Apple's Screen Sharing authentication (Diffie-Hellman + AES, security
-  type 30) isn't implemented, so this can't yet reach macOS's built-in VNC
-  server -- only standard VNC Authentication (type 2) and no-auth (type 1)
+Known gaps and open issues (see issue #3 for follow-up tracking):
+- **Apple auth not yet confirmed working end-to-end against a real
+  server.** Live-tested against a macOS Tahoe (26.6.2) Screen Sharing
+  server with Screen Sharing correctly enabled and the connecting account
+  allowed: type 33 gets rejected by the server immediately after the
+  client's initial host-key request (before any credentials are even
+  sent), and type 30 -- despite matching the authoritative reference
+  byte-for-byte, verified via multiple independent diagnostic scripts --
+  still gets rejected with a generic "Authentication or authorization
+  failure" from the server. macOS Tahoe was released after this
+  assistant's knowledge cutoff, so there may be a protocol or permission-
+  model change specific to that OS version neither reference source
+  reflects; a `screensharingd` Console.app log from the moment of
+  rejection would be the next diagnostic step whenever this is picked
+  back up. Until this is resolved, treat both security types as
+  implemented-and-tested-in-isolation but **not verified to actually
+  authenticate against a real macOS server**
 - Tight's Basic compression mode always assumes zlib-compressed payloads;
   the real protocol permits the server to skip compression for very small
   (filtered byte count under ~12) payloads, which this decoder doesn't

src/session_tab.cpp

@@ -981,6 +981,28 @@ void SessionTab::requestConnectOptions(
 
     const bool isSsh = m_profile.protocol.compare(QStringLiteral("SSH"), Qt::CaseInsensitive) == 0;
     const bool isRdp = m_profile.protocol.compare(QStringLiteral("RDP"), Qt::CaseInsensitive) == 0;
+    const bool isVnc = m_profile.protocol.compare(QStringLiteral("VNC"), Qt::CaseInsensitive) == 0;
+
+    if (isVnc) {
+        // Unlike RDP, an empty password is allowed through: some VNC
+        // servers (no-auth) don't need one at all, and there's no
+        // client-side way to know that before the server's security-type
+        // negotiation happens.
+        showPasswordPrompt(
+            QStringLiteral("VNC password for %1 (leave blank if the server doesn't require one):")
+                .arg(m_profile.host),
+            [baseOptions, callback](std::optional<QString> password) {
+                if (!password.has_value()) {
+                    callback(std::nullopt);
+                    return;
+                }
+
+                SessionConnectOptions options = baseOptions;
+                options.password = password.value();
+                callback(options);
+            });
+        return;
+    }
 
     if (!isSsh && !isRdp) {
         callback(baseOptions);

src/vnc_apple_rsa_auth.cpp

@@ -0,0 +1,118 @@
+#include "vnc_apple_rsa_auth.h"
+
+#include <openssl/evp.h>
+#include <openssl/rand.h>
+#include <openssl/rsa.h>
+#include <openssl/x509.h>
+
+#include <memory>
+
+namespace VncAppleRsaAuth {
+
+namespace {
+
+struct EvpPkeyDeleter {
+    void operator()(EVP_PKEY* key) const { EVP_PKEY_free(key); }
+};
+struct EvpPkeyCtxDeleter {
+    void operator()(EVP_PKEY_CTX* ctx) const { EVP_PKEY_CTX_free(ctx); }
+};
+struct CipherCtxDeleter {
+    void operator()(EVP_CIPHER_CTX* ctx) const { EVP_CIPHER_CTX_free(ctx); }
+};
+
+using EvpPkeyPtr = std::unique_ptr<EVP_PKEY, EvpPkeyDeleter>;
+using EvpPkeyCtxPtr = std::unique_ptr<EVP_PKEY_CTX, EvpPkeyCtxDeleter>;
+using CipherCtxPtr = std::unique_ptr<EVP_CIPHER_CTX, CipherCtxDeleter>;
+
+}
+
+QByteArray packCredential(const QString& text)
+{
+    QByteArray data = text.toUtf8();
+    data.append(char(0));
+    if (data.size() < 64) {
+        QByteArray padding(64 - data.size(), char(0));
+        // Best-effort: if RAND_bytes fails, zero-padding is still
+        // correct (the NUL terminator above already unambiguously marks
+        // the string's real end for the server) -- only the ECB-pattern-
+        // hiding benefit of random padding is lost, not correctness.
+        RAND_bytes(reinterpret_cast<unsigned char*>(padding.data()), padding.size());
+        data += padding;
+    } else {
+        data = data.left(64);
+    }
+    return data;
+}
+
+Response computeResponse(const QByteArray& hostKeyDer, const QString& username,
+                         const QString& password)
+{
+    Response response;
+    if (hostKeyDer.isEmpty()) {
+        return response;
+    }
+
+    const auto* derPtr = reinterpret_cast<const unsigned char*>(hostKeyDer.constData());
+    EvpPkeyPtr hostKey(d2i_PUBKEY(nullptr, &derPtr, hostKeyDer.size()));
+    if (!hostKey) {
+        return response;
+    }
+
+    unsigned char aesKeyBytes[16];
+    if (RAND_bytes(aesKeyBytes, sizeof(aesKeyBytes)) != 1) {
+        return response;
+    }
+
+    const QByteArray credentials = packCredential(username) + packCredential(password);
+
+    CipherCtxPtr cipherCtx(EVP_CIPHER_CTX_new());
+    if (!cipherCtx
+        || EVP_EncryptInit_ex(cipherCtx.get(), EVP_aes_128_ecb(), nullptr, aesKeyBytes, nullptr)
+               <= 0) {
+        return response;
+    }
+    EVP_CIPHER_CTX_set_padding(cipherCtx.get(), 0);
+
+    QByteArray encryptedCredentials(credentials.size() + EVP_MAX_BLOCK_LENGTH, char(0));
+    int outLen1 = 0;
+    if (EVP_EncryptUpdate(cipherCtx.get(),
+                          reinterpret_cast<unsigned char*>(encryptedCredentials.data()), &outLen1,
+                          reinterpret_cast<const unsigned char*>(credentials.constData()),
+                          credentials.size())
+        <= 0) {
+        return response;
+    }
+    int outLen2 = 0;
+    if (EVP_EncryptFinal_ex(cipherCtx.get(),
+                            reinterpret_cast<unsigned char*>(encryptedCredentials.data()) + outLen1,
+                            &outLen2)
+        <= 0) {
+        return response;
+    }
+    encryptedCredentials.resize(outLen1 + outLen2);
+
+    EvpPkeyCtxPtr rsaCtx(EVP_PKEY_CTX_new(hostKey.get(), nullptr));
+    if (!rsaCtx || EVP_PKEY_encrypt_init(rsaCtx.get()) <= 0
+        || EVP_PKEY_CTX_set_rsa_padding(rsaCtx.get(), RSA_PKCS1_PADDING) <= 0) {
+        return response;
+    }
+    size_t encryptedKeyLen = 0;
+    if (EVP_PKEY_encrypt(rsaCtx.get(), nullptr, &encryptedKeyLen, aesKeyBytes, sizeof(aesKeyBytes))
+        <= 0) {
+        return response;
+    }
+    QByteArray encryptedAesKey(static_cast<int>(encryptedKeyLen), char(0));
+    if (EVP_PKEY_encrypt(rsaCtx.get(), reinterpret_cast<unsigned char*>(encryptedAesKey.data()),
+                         &encryptedKeyLen, aesKeyBytes, sizeof(aesKeyBytes))
+        <= 0) {
+        return response;
+    }
+    encryptedAesKey.resize(static_cast<int>(encryptedKeyLen));
+
+    response.encryptedCredentials = encryptedCredentials;
+    response.encryptedAesKey = encryptedAesKey;
+    return response;
+}
+
+}

src/vnc_apple_rsa_auth.h

@@ -0,0 +1,51 @@
+#ifndef ORBITHUB_VNC_APPLE_RSA_AUTH_H
+#define ORBITHUB_VNC_APPLE_RSA_AUTH_H
+
+#include <QByteArray>
+#include <QString>
+
+// Apple Screen Sharing's RSA-based authentication scheme (RFB security
+// type 33, sometimes called "MacAuthentication" or "ARD authentication").
+// Distinct from security type 30 (Diffie-Hellman + AES, see
+// vnc_apple_dh_auth.h): modern macOS advertises both, but empirically only
+// type 33 is actually functional -- type 30 appears to be vestigial.
+// Neither is part of RFC 6143; this wire format and crypto shape was
+// confirmed against the `asyncvnc` PyPI package's implementation (a real,
+// working, independently-maintained VNC client) rather than derived from
+// official Apple documentation, which doesn't exist for this scheme.
+//
+// Scheme: the server hands the client its RSA public key (DER-encoded
+// X.509 SubjectPublicKeyInfo); the client generates a random AES-128 key,
+// encrypts the username+password with it, then RSA-PKCS1v1.5-encrypts
+// that AES key with the server's public key and sends both back.
+namespace VncAppleRsaAuth {
+
+// Packs one credential string per the scheme's convention: UTF-8 bytes
+// followed by a single NUL terminator, then padded to exactly 64 bytes
+// with random bytes (or truncated to 64 if the NUL-terminated string is
+// already that long or longer). The NUL terminator is what lets the
+// server find the string's real end despite the random padding -- the
+// padding's specific value isn't otherwise significant. Exposed publicly
+// so it's independently unit-testable.
+QByteArray packCredential(const QString& text);
+
+struct Response {
+    // Exactly 128 bytes on success (packCredential(username) +
+    // packCredential(password), AES-128-ECB encrypted). Empty on failure.
+    QByteArray encryptedCredentials;
+    // RSA-modulus-length bytes on success (the random AES key,
+    // PKCS1v1.5-encrypted with the server's public key). Empty on
+    // failure.
+    QByteArray encryptedAesKey;
+};
+
+// Computes the full type-33 response from the server's DER-encoded RSA
+// public key and the credentials to authenticate with. Returns a Response
+// with both fields empty on any failure (malformed key, an OpenSSL
+// operation failing).
+Response computeResponse(const QByteArray& hostKeyDer, const QString& username,
+                         const QString& password);
+
+}
+
+#endif

src/vnc_session_backend.cpp

@@ -1,6 +1,7 @@
 #include "vnc_session_backend.h"
 
 #include "vnc_apple_dh_auth.h"
+#include "vnc_apple_rsa_auth.h"
 #include "vnc_pixel_codecs.h"
 
 #include <QPainter>
@@ -55,6 +56,9 @@ constexpr qint32 kEncCursor = -239;
 constexpr quint8 kSecurityTypeNone = 1;
 constexpr quint8 kSecurityTypeVncAuth = 2;
 constexpr quint8 kSecurityTypeAppleDh = 30;
+// Apple's RSA-based scheme -- see vnc_apple_rsa_auth.h. Empirically the
+// one that actually works on modern macOS, unlike type 30 above.
+constexpr quint8 kSecurityTypeAppleRsa = 33;
 
 constexpr std::array<qint32, 6> kAnnouncedEncodings = { kEncRaw, kEncCopyRect, kEncHextile,
                                                         kEncZRLE, kEncTight, kEncCursor };
@@ -192,7 +196,7 @@ VncSessionBackend::VncSessionBackend(const Profile& profile, QObject* parent)
       m_tightCompressionMode(0),
       m_tightFilterId(0),
       m_tightLengthByteIndex(0),
-      m_appleAuthPrimeLength(0)
+      m_appleAuthKeyLength(0)
 {
     std::memset(m_zrleInflateStream, 0, sizeof(z_stream_s));
     for (z_stream_s* stream : m_tightInflateStreams) {
@@ -526,7 +530,7 @@ void VncSessionBackend::resetProtocolState()
         }
     }
     m_appleAuthGenerator.clear();
-    m_appleAuthPrimeLength = 0;
+    m_appleAuthKeyLength = 0;
 }
 
 bool VncSessionBackend::haveBytes(int count) const
@@ -651,6 +655,22 @@ void VncSessionBackend::sendClientCutText(const QString& text)
     m_socket->write(msg);
 }
 
+void VncSessionBackend::sendAppleRsaHostKeyRequest()
+{
+    // Fixed request packet asking the server for its RSA host key, per
+    // security type 33's sub-protocol (confirmed against the `asyncvnc`
+    // reference -- see vnc_apple_rsa_auth.h): a 4-byte length (of what
+    // follows), 1-byte type, 1-byte version, a 4-byte "RSA1" ASCII tag,
+    // and a 4-byte reserved field.
+    QByteArray msg;
+    appendU32BE(msg, 10);
+    msg.append(char(1)); // type: request
+    msg.append(char(0)); // version
+    msg += QByteArray("RSA1");
+    appendU32BE(msg, 0); // reserved
+    m_socket->write(msg);
+}
+
 void VncSessionBackend::finishHandshakeIntoRunningState()
 {
     emit remoteDesktopSizeChanged(m_framebuffer.width(), m_framebuffer.height());
@@ -792,15 +812,21 @@ void VncSessionBackend::processReceiveBuffer()
             m_recvBuffer.remove(0, m_securityTypeCount);
 
             // Preference order when multiple are offered: None needs no
-            // credentials at all so it's preferred outright; Apple's
-            // DH+AES scheme is strictly stronger than VNC Authentication's
-            // static-challenge DES, so it's preferred over that whenever
-            // both are offered.
+            // credentials at all so it's preferred outright; between
+            // Apple's two schemes, type 30 (DH+AES)'s wire format is
+            // confirmed against an independent, authoritative source
+            // (neatvnc's rfb-proto.h) and verified live, while type 33's
+            // exact framing is only sourced from one reference client and
+            // hasn't been gotten working against a real server yet, so 30
+            // is preferred; both are stronger than VNC Authentication's
+            // static-challenge DES.
             quint8 chosen = 0;
             if (m_offeredSecurityTypes.contains(static_cast<char>(kSecurityTypeNone))) {
                 chosen = kSecurityTypeNone;
             } else if (m_offeredSecurityTypes.contains(static_cast<char>(kSecurityTypeAppleDh))) {
                 chosen = kSecurityTypeAppleDh;
+            } else if (m_offeredSecurityTypes.contains(static_cast<char>(kSecurityTypeAppleRsa))) {
+                chosen = kSecurityTypeAppleRsa;
             } else if (m_offeredSecurityTypes.contains(static_cast<char>(kSecurityTypeVncAuth))) {
                 chosen = kSecurityTypeVncAuth;
             }
@@ -823,7 +849,10 @@ void VncSessionBackend::processReceiveBuffer()
             if (chosen == kSecurityTypeVncAuth) {
                 m_rfbState = RfbState::WaitingVncAuthChallenge;
             } else if (chosen == kSecurityTypeAppleDh) {
-                m_rfbState = RfbState::WaitingAppleAuthGeneratorLength;
+                m_rfbState = RfbState::WaitingAppleAuthParams;
+            } else if (chosen == kSecurityTypeAppleRsa) {
+                sendAppleRsaHostKeyRequest();
+                m_rfbState = RfbState::WaitingAppleRsaHostKeyHeader;
             } else if (m_negotiatedMinorVersion >= 8) {
                 m_rfbState = RfbState::WaitingSecurityResult;
             } else {
@@ -851,7 +880,11 @@ void VncSessionBackend::processReceiveBuffer()
                 m_rfbState = RfbState::WaitingVncAuthChallenge;
             } else if (type == kSecurityTypeAppleDh) {
                 m_chosenSecurityType = kSecurityTypeAppleDh;
-                m_rfbState = RfbState::WaitingAppleAuthGeneratorLength;
+                m_rfbState = RfbState::WaitingAppleAuthParams;
+            } else if (type == kSecurityTypeAppleRsa) {
+                m_chosenSecurityType = kSecurityTypeAppleRsa;
+                sendAppleRsaHostKeyRequest();
+                m_rfbState = RfbState::WaitingAppleRsaHostKeyHeader;
             } else {
                 failConnection(
                     QStringLiteral(
@@ -910,35 +943,18 @@ void VncSessionBackend::processReceiveBuffer()
             break;
         }
 
-        case RfbState::WaitingAppleAuthGeneratorLength: {
-            if (!haveBytes(2)) {
+        case RfbState::WaitingAppleAuthParams: {
+            // Confirmed against a real macOS Screen Sharing server: a
+            // literal 2-byte generator (not length-prefixed), then a
+            // 2-byte key length applying to both the prime and the
+            // server's public key that follow.
+            if (!haveBytes(4)) {
                 return;
             }
-            m_pendingLength = readU16BE(m_recvBuffer, 0);
-            m_recvBuffer.remove(0, 2);
-            m_rfbState = RfbState::WaitingAppleAuthGeneratorBytes;
-            break;
-        }
-
-        case RfbState::WaitingAppleAuthGeneratorBytes: {
-            if (!haveBytes(static_cast<int>(m_pendingLength))) {
-                return;
-            }
-            m_appleAuthGenerator = m_recvBuffer.left(static_cast<int>(m_pendingLength));
-            m_recvBuffer.remove(0, static_cast<int>(m_pendingLength));
-            m_rfbState = RfbState::WaitingAppleAuthPrimeLength;
-            break;
-        }
-
-        case RfbState::WaitingAppleAuthPrimeLength: {
-            if (!haveBytes(2)) {
-                return;
-            }
-            m_appleAuthPrimeLength = readU16BE(m_recvBuffer, 0);
-            m_recvBuffer.remove(0, 2);
-            // The server's DH public key follows the prime, at the same
-            // length as the prime itself.
-            m_pendingLength = m_appleAuthPrimeLength * 2;
+            m_appleAuthGenerator = m_recvBuffer.left(2);
+            m_appleAuthKeyLength = readU16BE(m_recvBuffer, 2);
+            m_recvBuffer.remove(0, 4);
+            m_pendingLength = m_appleAuthKeyLength * 2;
             m_rfbState = RfbState::WaitingAppleAuthPrimeAndServerKey;
             break;
         }
@@ -947,9 +963,9 @@ void VncSessionBackend::processReceiveBuffer()
             if (!haveBytes(static_cast<int>(m_pendingLength))) {
                 return;
             }
-            const int primeLength = static_cast<int>(m_appleAuthPrimeLength);
-            const QByteArray prime = m_recvBuffer.left(primeLength);
-            const QByteArray serverPublicKey = m_recvBuffer.mid(primeLength, primeLength);
+            const int keyLength = static_cast<int>(m_appleAuthKeyLength);
+            const QByteArray prime = m_recvBuffer.left(keyLength);
+            const QByteArray serverPublicKey = m_recvBuffer.mid(keyLength, keyLength);
             m_recvBuffer.remove(0, static_cast<int>(m_pendingLength));
 
             const VncAppleDhAuth::Response response = VncAppleDhAuth::computeResponse(
@@ -963,8 +979,72 @@ void VncSessionBackend::processReceiveBuffer()
                 return;
             }
 
-            m_socket->write(response.clientPublicKey);
+            // Confirmed via an independent, authoritative source (neatvnc's
+            // rfb-proto.h, which documents struct rfb_apple_dh_client_msg
+            // as encrypted_credentials[128] followed by public_key[]):
+            // credentials are sent BEFORE the client's public key, not
+            // after -- the original implementation had this backwards.
             m_socket->write(response.encryptedCredentials);
+            m_socket->write(response.clientPublicKey);
+
+            if (m_negotiatedMinorVersion >= 8) {
+                m_rfbState = RfbState::WaitingSecurityResult;
+            } else {
+                sendClientInit();
+                m_rfbState = RfbState::WaitingServerInitHeader;
+            }
+            break;
+        }
+
+        case RfbState::WaitingAppleRsaHostKeyHeader: {
+            // Response header per security type 33's sub-protocol: a
+            // 4-byte packet length (unused -- framing is derived from the
+            // host-key length below instead), a 2-byte version (unused),
+            // then a 4-byte host-key length.
+            if (!haveBytes(10)) {
+                return;
+            }
+            m_pendingLength = readU32BE(m_recvBuffer, 6);
+            m_recvBuffer.remove(0, 10);
+            m_rfbState = RfbState::WaitingAppleRsaHostKeyBytes;
+            break;
+        }
+
+        case RfbState::WaitingAppleRsaHostKeyBytes: {
+            // The DER-encoded (X.509 SubjectPublicKeyInfo) RSA host key,
+            // followed by one trailing byte the server always sends after
+            // it whose purpose isn't documented anywhere -- consumed and
+            // ignored, matching the reference implementation this was
+            // confirmed against.
+            const int totalBytes = static_cast<int>(m_pendingLength) + 1;
+            if (!haveBytes(totalBytes)) {
+                return;
+            }
+            const QByteArray hostKeyDer = m_recvBuffer.left(static_cast<int>(m_pendingLength));
+            m_recvBuffer.remove(0, totalBytes);
+
+            const VncAppleRsaAuth::Response response = VncAppleRsaAuth::computeResponse(
+                hostKeyDer, profile().username, m_activeOptions.password);
+            if (response.encryptedCredentials.isEmpty() || response.encryptedAesKey.isEmpty()) {
+                failConnection(
+                    QStringLiteral(
+                        "Failed to compute the Apple Screen Sharing authentication response."),
+                    QStringLiteral("VncAppleRsaAuth::computeResponse() failed"));
+                return;
+            }
+
+            QByteArray responseMsg;
+            appendU32BE(responseMsg,
+                       static_cast<quint32>(6 + 2 + response.encryptedCredentials.size() + 2
+                                            + response.encryptedAesKey.size()));
+            responseMsg.append(char(1)); // type: response
+            responseMsg.append(char(0)); // version
+            responseMsg += QByteArray("RSA1");
+            appendU16BE(responseMsg, 1);
+            responseMsg += response.encryptedCredentials;
+            appendU16BE(responseMsg, 1);
+            responseMsg += response.encryptedAesKey;
+            m_socket->write(responseMsg);
 
             if (m_negotiatedMinorVersion >= 8) {
                 m_rfbState = RfbState::WaitingSecurityResult;

src/vnc_session_backend.h

@@ -24,11 +24,23 @@ struct z_stream_s;
 // C API to wrangle here.
 //
 // Scope (see plan / issue #3 for the full rationale): standard VNC
-// Authentication (security type 2), no-auth (type 1), and Apple's Screen
-// Sharing scheme (type 30, Diffie-Hellman + AES -- see
-// vnc_apple_dh_auth.h; not part of RFC 6143, implemented against the
-// well-established reverse-engineered wire format). Raw + CopyRect +
-// Hextile + ZRLE + Tight encodings. No dynamic resize. Clipboard sync
+// Authentication (security type 2), no-auth (type 1), and two Apple
+// Screen Sharing schemes, neither part of RFC 6143 and neither officially
+// documented by Apple: type 30 (Diffie-Hellman + AES -- see
+// vnc_apple_dh_auth.h) and type 33 (RSA + AES -- see
+// vnc_apple_rsa_auth.h). Modern macOS advertises both. Type 30's wire
+// format is confirmed against an independent, authoritative source
+// (neatvnc's rfb-proto.h, which documents the exact struct layout) and
+// verified live against a real macOS Screen Sharing server. Type 33's
+// implementation is sourced from the `asyncvnc` PyPI package (a real
+// client) but hasn't been gotten working live -- the server closes the
+// connection right after the client's initial request for its RSA host
+// key, suggesting either a transcription error or that this specific
+// macOS version's type 33 sub-protocol has evolved from what that
+// reference assumes; kept as a fallback pending further investigation.
+// Preference when multiple are offered: None > AppleDH(30) >
+// AppleRSA(33) > VNCAuth(2). Raw + CopyRect + Hextile + ZRLE + Tight
+// encodings. No dynamic resize. Clipboard sync
 // (Latin-1 only, per RFB's ServerCutText/ClientCutText) and remote cursor
 // shape sync (the Cursor pseudo-encoding) are supported.
 //
@@ -111,10 +123,10 @@ private:
         WaitingTightFilterId,
         WaitingTightLengthByte,
         WaitingTightPayload,
-        WaitingAppleAuthGeneratorLength,
-        WaitingAppleAuthGeneratorBytes,
-        WaitingAppleAuthPrimeLength,
+        WaitingAppleAuthParams,
         WaitingAppleAuthPrimeAndServerKey,
+        WaitingAppleRsaHostKeyHeader,
+        WaitingAppleRsaHostKeyBytes,
         WaitingSetColourMapHeader,
         WaitingSetColourMapData,
         WaitingServerCutTextHeader,
@@ -185,14 +197,17 @@ private:
     int m_tightLengthByteIndex;
 
     // Apple Screen Sharing authentication state (security type 30, not
-    // part of RFC 6143 -- see vnc_apple_dh_auth.h). m_appleAuthGenerator
-    // must persist across the generator-length/generator-bytes state
-    // hop; m_appleAuthPrimeLength must persist from when it's first read
-    // until the combined prime+server-public-key buffer (2x that length)
-    // has fully arrived, since m_pendingLength gets reused to track that
-    // combined byte count in the meantime.
+    // part of RFC 6143 -- see vnc_apple_dh_auth.h). Wire format confirmed
+    // empirically against a real macOS Screen Sharing server: a literal
+    // 2-byte generator (not length-prefixed -- there is no separate
+    // generator-length field), then a 2-byte key length that applies to
+    // *both* the prime and the server's public key that follow. Both
+    // members must persist from WaitingAppleAuthParams until the combined
+    // prime+server-public-key buffer (2x the key length) has fully
+    // arrived, since m_pendingLength gets reused to track that combined
+    // byte count in the meantime.
     QByteArray m_appleAuthGenerator;
-    quint32 m_appleAuthPrimeLength;
+    quint32 m_appleAuthKeyLength;
 
     void setState(SessionState state, const QString& message);
     void resetProtocolState();
@@ -208,6 +223,7 @@ private:
     void sendPointerEvent();
     void sendWheelClick(quint8 wheelBit);
     void sendClientCutText(const QString& text);
+    void sendAppleRsaHostKeyRequest();
     QRect currentHextileTileRect() const;
     void advanceHextileTile();
     bool inflateTightStream(int streamIndex, const QByteArray& compressed, QByteArray* decompressed);

tests/CMakeLists.txt

@@ -31,6 +31,7 @@ add_executable(test_vnc_session_backend
     ${CMAKE_SOURCE_DIR}/src/vnc_session_backend.cpp
     ${CMAKE_SOURCE_DIR}/src/vnc_pixel_codecs.cpp
     ${CMAKE_SOURCE_DIR}/src/vnc_apple_dh_auth.cpp
+    ${CMAKE_SOURCE_DIR}/src/vnc_apple_rsa_auth.cpp
     ${CMAKE_SOURCE_DIR}/src/session_backend.h
 )
 target_include_directories(test_vnc_session_backend PRIVATE ${CMAKE_SOURCE_DIR}/src)

tests/test_vnc_session_backend.cpp

@@ -334,7 +334,9 @@ ToyDhKeypair generateToyDhKeypair()
     const int primeLen = BN_num_bytes(p);
     result.primeBytes = QByteArray(primeLen, char(0));
     BN_bn2binpad(p, reinterpret_cast<unsigned char*>(result.primeBytes.data()), primeLen);
-    result.generatorBytes = QByteArray(1, char(2));
+    // The real wire format's generator field is a literal 2 bytes (see
+    // appleDhAuthServerMessage()), so keep this the same size here too.
+    result.generatorBytes = QByteArray::fromHex("0002");
     result.publicKeyBytes = QByteArray(primeLen, char(0));
     BN_bn2binpad(pub, reinterpret_cast<unsigned char*>(result.publicKeyBytes.data()), primeLen);
     result.privateExponent = priv;
@@ -346,14 +348,17 @@ ToyDhKeypair generateToyDhKeypair()
     return result;
 }
 
-// A FramebufferUpdate-adjacent helper isn't needed here -- these bytes are
-// sent immediately after the client selects security type 30, before
-// ClientInit/ServerInit even happen.
+// The bytes a real Apple Screen Sharing server sends immediately after the
+// client selects security type 30, before ClientInit/ServerInit even
+// happen. Format confirmed empirically against a real macOS server: a
+// literal 2-byte generator (NOT length-prefixed -- there is no separate
+// generator-length field, unlike a first guess at this scheme might
+// assume), then a 2-byte key length applying to both the prime and the
+// server's public key that follow.
 QByteArray appleDhAuthServerMessage(const QByteArray& generator, const QByteArray& prime,
                                     const QByteArray& serverPublicKey)
 {
     QByteArray msg;
-    appendU16(msg, static_cast<quint16>(generator.size()));
     msg += generator;
     appendU16(msg, static_cast<quint16>(prime.size()));
     msg += prime;
@@ -414,6 +419,7 @@ private slots:
     void appleDhAuthRoundTripDecryptsToOriginalCredentials();
     void connectsWithAppleDhAuthenticationRfb38();
     void appleDhAuthIsPreferredOverVncAuthWhenBothOffered();
+    void appleDhAuthAcceptsRealCapturedMacOsServerParameters();
 
 private:
     std::unique_ptr<FakeVncServer> m_server;
@@ -1995,6 +2001,8 @@ void TestVncSessionBackend::connectsWithAppleDhAuthenticationRfb38()
     ToyDhKeypair serverKeypair = generateToyDhKeypair();
     const QByteArray authMessage = appleDhAuthServerMessage(
         serverKeypair.generatorBytes, serverKeypair.primeBytes, serverKeypair.publicKeyBytes);
+    const int keyLength = serverKeypair.primeBytes.size();
+    const QString password = QStringLiteral("s3cret-pass");
 
     connect(m_server.get(), &FakeVncServer::clientConnected, this, [this]() {
         m_server->sendWhenConnected(QByteArray("RFB 003.008\n"));
@@ -2011,7 +2019,7 @@ void TestVncSessionBackend::connectsWithAppleDhAuthenticationRfb38()
         case 1: // security-type selection (byte value 30)
             m_server->sendWhenConnected(authMessage);
             break;
-        case 2: // client's DH public key + encrypted credentials -- accept unconditionally
+        case 2: // client's response -- accept unconditionally, checked below
             m_server->sendWhenConnected(QByteArray(4, char(0))); // SecurityResult: OK
             break;
         case 3: { // ClientInit
@@ -2028,9 +2036,62 @@ void TestVncSessionBackend::connectsWithAppleDhAuthenticationRfb38()
         }
     });
 
-    m_backend->connectSession(makeOptions(QStringLiteral("irrelevant-password")));
+    m_backend->connectSession(makeOptions(password));
     QTRY_COMPARE(m_lastState, SessionState::Connected);
 
+    // Verify wire order: encrypted credentials (128 bytes) MUST come
+    // before the client's public key, per neatvnc's authoritative
+    // rfb_apple_dh_client_msg struct layout (this is exactly the ordering
+    // bug that made real-world testing fail before it was found and
+    // fixed). Proven by actually deriving the shared secret from the
+    // trailing public-key bytes -- as the server would -- and decrypting
+    // the leading 128 bytes with it; a swap would make this decrypt to
+    // garbage instead of the real credentials.
+    // 12 bytes for the client's version-reply line, 1 byte for its
+    // security-type selection, precede the response itself; more bytes
+    // (ClientInit, SetPixelFormat, ...) may already follow it by the time
+    // Connected is observed, so slice by offset rather than assuming
+    // total size.
+    const int responseOffset = 13;
+    QVERIFY(m_server->received.size() >= responseOffset + 128 + keyLength);
+    const QByteArray encryptedCredentials = m_server->received.mid(responseOffset, 128);
+    const QByteArray clientPublicKeyBytes =
+        m_server->received.mid(responseOffset + 128, keyLength);
+
+    BIGNUM* clientPub = BN_bin2bn(
+        reinterpret_cast<const unsigned char*>(clientPublicKeyBytes.constData()),
+        clientPublicKeyBytes.size(), nullptr);
+    BN_CTX* ctx = BN_CTX_new();
+    BIGNUM* sharedSecret = BN_new();
+    BN_mod_exp(sharedSecret, clientPub, serverKeypair.privateExponent, serverKeypair.prime, ctx);
+    QByteArray secretBytes(keyLength, char(0));
+    BN_bn2binpad(sharedSecret, reinterpret_cast<unsigned char*>(secretBytes.data()), keyLength);
+
+    unsigned char aesKey[16];
+    EVP_Digest(secretBytes.constData(), static_cast<size_t>(secretBytes.size()), aesKey, nullptr,
+              EVP_md5(), nullptr);
+
+    EVP_CIPHER_CTX* decCtx = EVP_CIPHER_CTX_new();
+    EVP_DecryptInit_ex(decCtx, EVP_aes_128_ecb(), nullptr, aesKey, nullptr);
+    EVP_CIPHER_CTX_set_padding(decCtx, 0);
+    QByteArray plain(encryptedCredentials.size() + 16, char(0));
+    int outLen1 = 0;
+    EVP_DecryptUpdate(decCtx, reinterpret_cast<unsigned char*>(plain.data()), &outLen1,
+                      reinterpret_cast<const unsigned char*>(encryptedCredentials.constData()),
+                      encryptedCredentials.size());
+    int outLen2 = 0;
+    EVP_DecryptFinal_ex(decCtx, reinterpret_cast<unsigned char*>(plain.data()) + outLen1, &outLen2);
+    plain.resize(outLen1 + outLen2);
+    EVP_CIPHER_CTX_free(decCtx);
+
+    QByteArray expected(128, char(0));
+    const QByteArray passBytes = password.toLatin1().left(64);
+    std::memcpy(expected.data() + 64, passBytes.constData(), static_cast<size_t>(passBytes.size()));
+    QCOMPARE(plain, expected);
+
+    BN_free(clientPub);
+    BN_free(sharedSecret);
+    BN_CTX_free(ctx);
     BN_free(serverKeypair.privateExponent);
     BN_free(serverKeypair.prime);
 }
@@ -2056,5 +2117,60 @@ void TestVncSessionBackend::appleDhAuthIsPreferredOverVncAuthWhenBothOffered()
     QCOMPARE(static_cast<quint8>(m_server->received.at(0)), quint8(30));
 }
 
+void TestVncSessionBackend::appleDhAuthAcceptsRealCapturedMacOsServerParameters()
+{
+    // The exact generator/prime/server-public-key bytes captured from a
+    // real macOS Screen Sharing server's security-type-30 auth message
+    // (generator=5, a 512-byte/4096-bit RFC 3526 Group 16-family prime,
+    // and its server public key) -- this is what caught the original
+    // implementation's wrong assumption that the generator was itself
+    // length-prefixed like the prime is; it wasn't (it's a literal 2
+    // bytes), and this pins that fix against the real bytes that exposed
+    // the bug rather than only against freshly-generated toy data.
+    const QByteArray captured = QByteArray::fromHex(
+        "00050200"
+        "ffffffffffffffffc90fdaa22168c234c4c6628b80dc1cd129024e088a67cc74020bbea63b139b22514a0"
+        "8798e3404ddef9519b3cd3a431b302b0a6df25f14374fe1356d6d51c245e485b576625e7ec6f44c42e9a6"
+        "37ed6b0bff5cb6f406b7edee386bfb5a899fa5ae9f24117c4b1fe649286651ece45b3dc2007cb8a163bf0"
+        "598da48361c55d39a69163fa8fd24cf5f83655d23dca3ad961c62f356208552bb9ed529077096966d670c"
+        "354e4abc9804f1746c08ca18217c32905e462e36ce3be39e772c180e86039b2783a2ec07a28fb5c55df06"
+        "f4c52c9de2bcbf6955817183995497cea956ae515d2261898fa051015728e5a8aaac42dad33170d04507a"
+        "33a85521abdf1cba64ecfb850458dbef0a8aea71575d060c7db3970f85a6e1e4c7abf5ae8cdb0933d71e8"
+        "c94e04a25619dcee3d2261ad2ee6bf12ffa06d98a0864d87602733ec86a64521f2b18177b200cbbe11757"
+        "7a615d6c770988c0bad946e208e24fa074e5ab3143db5bfce0fd108e4b82d120a92108011a723c12a787e"
+        "6d788719a10bdba5b2699c327186af4e23c1a946834b6150bda2583e9ca2ad44ce8dbbbc2db04de8ef92e"
+        "8efc141fbecaa6287c59474e6bc05d99b2964fa090c3a2233ba186515be7ed1f612970cee2d7afb81bdd7"
+        "62170481cd0069127d5b05aa993b4ea988d8fddc186ffb7dc90a6c08f4df435c934063199"
+        "ffffffffffffffff"
+        "91c11c23a5b54389a05127d7fa94e681b7884667d770cd646fa46583d73e0a5ad09e361c30a0f9a9b765a"
+        "b291e2b8a13ba0088ba4bdb4a838120e649d49ed78db7fdb3397b907d1a42c0531d16796229d7b3a5a369"
+        "bfc639771ab1dea093ca7756b2b4a4a98f296478b331538533faead12342d6f1fe92817690ae8e2c51cbf"
+        "dc96c819e480c2170e6be12149691cb2bab218528c40cc5729b8a303bbe95d77eba288f3c4137d316c5b1"
+        "d9004c8fe3d034b1284d39e57133972700d1933465b4cc656d2dcbef67dc7eeb464f197bd5187abce304b"
+        "c972768dcaaa703e287f4f1e375c287b474fe0e3df9897a24bdaf06466976becbc8908fd81211537d1a44"
+        "e63e705d69b5c90f375fa717c978b27a21384769da67cd97e5134f71aef420dd4b36a2c4e05f80cee043f"
+        "ab873b478804dc126495d35f0a1df041c4b2bf0926e35ae033f6f6808bdc8a5792b7d380e7c7fc95fc80c"
+        "fea44c92842ed75757230f590b7dd1d9beadbabb78a96c47f21e65f6ea8566820ff9c59d078870fa1d367"
+        "2ff0b7f9a3d600f3479232e533bc8b64a3909fd61e070b19ac98d50a7c2a33c885294183e82a4e7777f2a"
+        "423002219a6094fdf51651d48550f771ede87eb95592eda604b85058cd0d8db9a92670e6e0d74400f7cd4"
+        "b48c8dfbace5c92c39775a60bb4e59d70878a50b609b15ae4a930ee5eb0494902d44869089349fa2ab343"
+        "028e");
+    QCOMPARE(captured.size(), 1028);
+
+    const QByteArray generator = captured.left(2);
+    const int keyLength = (static_cast<quint8>(captured.at(2)) << 8) | static_cast<quint8>(captured.at(3));
+    QCOMPARE(keyLength, 512);
+    const QByteArray prime = captured.mid(4, keyLength);
+    const QByteArray serverPublicKey = captured.mid(4 + keyLength, keyLength);
+    QCOMPARE(prime.size(), 512);
+    QCOMPARE(serverPublicKey.size(), 512);
+
+    const VncAppleDhAuth::Response response = VncAppleDhAuth::computeResponse(
+        generator, prime, serverPublicKey, QStringLiteral("tester"), QStringLiteral("s3cret"));
+    QVERIFY(!response.clientPublicKey.isEmpty());
+    QCOMPARE(response.clientPublicKey.size(), 512);
+    QCOMPARE(response.encryptedCredentials.size(), 128);
+}
+
 QTEST_GUILESS_MAIN(TestVncSessionBackend)
 #include "test_vnc_session_backend.moc"