Add TPM-backed X.509 host certificate support and fix TPM-build client auth

.github/workflows/tpm-ssh.yml

@@ -17,6 +17,10 @@ jobs:
       matrix:
         keytype: [ rsa, ecc ]
         sim: [ ibmswtpm2, fwtpm ]
+        # raw: plain TPM host key (verified with OpenSSH).
+        # x509: TPM host key presented as an X.509 certificate, verified by the
+        #       tpmcertserver/tpmcertclient example.
+        hostkey: [ raw, x509 ]
 
     steps:
     - uses: actions/checkout@v6
@@ -47,8 +51,17 @@ jobs:
       run: |
         cd wolfssl
         ./autogen.sh
+        # certgen/certreq/certext/cryptocb: generate the X.509 host certificate
+        # from the TPM key via the crypto callback.
+        EXTRA_CFLAGS="-DWC_RSA_NO_PADDING"
+        # The RSA x509v3-ssh-rsa host cert is SHA-1; modern wolfSSL otherwise
+        # rejects SHA-1 RSA signatures. Only needed for the RSA cells.
+        if [ "${{ matrix.keytype }}" = "rsa" ]; then
+            EXTRA_CFLAGS="$EXTRA_CFLAGS -DWC_SIG_MIN_HASH_TYPE=WC_HASH_TYPE_SHA"
+        fi
         ./configure --enable-wolftpm --enable-wolfssh --enable-keygen \
-            CFLAGS="-DWC_RSA_NO_PADDING"
+            --enable-certgen --enable-certreq --enable-certext --enable-cryptocb \
+            CFLAGS="$EXTRA_CFLAGS"
         make
         sudo make install
         sudo ldconfig
@@ -97,13 +110,14 @@ jobs:
       run: |
         cd wolfssh
         ./autogen.sh
-        ./configure --enable-tpm
+        ./configure --enable-tpm --enable-certs
         make
         sudo make install
         sudo ldconfig
 
     # Server host key resident in the TPM: the private key never enters RAM.
     - name: Test TPM host key (${{ matrix.keytype }})
+      if: matrix.hostkey == 'raw'
       run: |
         cd wolftpm
         ./examples/keygen/keygen hostkey.bin -${{ matrix.keytype }} -t -eh
@@ -129,9 +143,55 @@ jobs:
         cat ssh_out.txt
         grep -q "Authenticated to localhost" ssh_out.txt
 
+    # Server presents an X.509 host certificate whose private key lives in the
+    # TPM. The client verifies the certificate against it as the trusted CA and
+    # rejects a mismatched CA; the exchange hash is signed inside the TPM.
+    - name: Test TPM X.509 host certificate (${{ matrix.keytype }})
+      if: matrix.hostkey == 'x509'
+      run: |
+        cd wolfssh
+        ./examples/tpmcertserver/tpmcertserver -k ${{ matrix.keytype }} \
+            -p 22223 > tpmcert_server.txt 2>&1 &
+        echo "tpmcertserver (X.509 ${{ matrix.keytype }}) PID: $!"
+        # RSA key generation inside the TPM can take longer than ECC.
+        for i in $(seq 1 40); do
+            if ss -ltn 2>/dev/null | grep -q ':22223'; then break; fi
+            sleep 1
+        done
+        ./examples/tpmcertserver/tpmcertclient -A tpm-server-cert.der \
+            -p 22223 -h 127.0.0.1 > tpmcert_client.txt 2>&1
+        echo "----- server -----"; cat tpmcert_server.txt
+        echo "----- client -----"; cat tpmcert_client.txt
+        grep -q "verified server X.509 host certificate" tpmcert_client.txt
+        grep -q "Client connected and verified the TPM-backed host certificate" \
+            tpmcert_server.txt
+
+    # Negative test: a client that trusts an unrelated CA must reject the server.
+    - name: Test TPM X.509 host certificate rejects wrong CA (${{ matrix.keytype }})
+      if: matrix.hostkey == 'x509'
+      run: |
+        cd wolfssh
+        ./examples/tpmcertserver/tpmcertserver -k ${{ matrix.keytype }} \
+            -p 22224 > tpmcert_server_neg.txt 2>&1 &
+        echo "tpmcertserver (X.509 neg ${{ matrix.keytype }}) PID: $!"
+        for i in $(seq 1 40); do
+            if ss -ltn 2>/dev/null | grep -q ':22224'; then break; fi
+            sleep 1
+        done
+        # keys/ca-cert-ecc.der is an unrelated CA; the self-signed host cert
+        # does not chain to it, so the client must refuse to connect.
+        if ./examples/tpmcertserver/tpmcertclient -A keys/ca-cert-ecc.der \
+            -p 22224 -h 127.0.0.1 > tpmcert_client_neg.txt 2>&1; then
+            echo "ERROR: client accepted a server with an untrusted CA"
+            cat tpmcert_client_neg.txt
+            exit 1
+        fi
+        echo "client correctly rejected the untrusted server:"
+        cat tpmcert_client_neg.txt
+
     # Client public-key authentication with a TPM-resident key (RSA only).
     - name: Test TPM client public-key auth
-      if: matrix.keytype == 'rsa'
+      if: matrix.keytype == 'rsa' && matrix.hostkey == 'raw'
       run: |
         cd wolftpm
         ./examples/keygen/keygen keyblob.bin -rsa -t -pem -eh
@@ -147,7 +207,12 @@ jobs:
       if: always()
       uses: actions/upload-artifact@v7
       with:
-        name: test-artifacts-${{ matrix.keytype }}-${{ matrix.sim }}
+        name: test-artifacts-${{ matrix.keytype }}-${{ matrix.sim }}-${{ matrix.hostkey }}
+        if-no-files-found: ignore
         path: |
           wolftpm/hostkey.bin
           wolfssh/ssh_out.txt
+          wolfssh/tpmcert_server.txt
+          wolfssh/tpmcert_client.txt
+          wolfssh/tpmcert_server_neg.txt
+          wolfssh/tpmcert_client_neg.txt

README.md

@@ -622,6 +622,66 @@ Note: RSA host keys are signed with `rsa-sha2-256`. The default echoserver key
 auth produced by keygen is `ThisIsMyKeyAuth` (override with the `-G` example's
 `ECHOSERVER_TPM_KEY_AUTH`).
 
+TPM SERVER HOST KEY WITH X.509 CERTIFICATE (ECDSA / RSA)
+=======================================================
+
+The server can present an X.509 certificate as its host key while the matching
+private key stays non-exportable inside the TPM. The client verifies the
+certificate against a trusted CA, so the server's identity is authenticated and
+a man-in-the-middle cannot impersonate it. The exchange hash is signed inside
+the TPM; the private key never enters RAM.
+
+This requires wolfSSH built with certificate support in addition to TPM support,
+and wolfSSL/wolfTPM built with certificate generation:
+
+    wolfSSL
+        $ ./configure --enable-wolfssh --enable-wolftpm --enable-keygen \
+              --enable-certgen --enable-certreq --enable-certext \
+              --enable-cryptocb \
+              CFLAGS="-DWC_RSA_NO_PADDING"
+    wolfTPM
+        $ ./configure --enable-fwtpm --enable-swtpm
+    wolfSSH
+        $ ./configure --enable-tpm --enable-certs
+
+The example under `examples/tpmcertserver` creates a signing key inside the TPM,
+generates a self-signed X.509 certificate from it with
+`wolfTPM2_CSR_Generate_ex()`, then serves with `wolfSSH_CTX_UseTpmHostKey()` and
+`wolfSSH_CTX_UseCert_buffer()`. Run a TPM simulator first (`fwtpm_server` or
+`ibmswtpm2`), then:
+
+    ECDSA:  $ ./examples/tpmcertserver/tpmcertserver -k ecc
+    RSA:    $ ./examples/tpmcertserver/tpmcertserver -k rsa
+
+The server writes its certificate to `tpm-server-cert.der`. The companion
+client verifies the server against that certificate used as the trusted root:
+
+    $ ./examples/tpmcertserver/tpmcertclient -A tpm-server-cert.der
+
+To integrate this into your own server, load the certificate and bind the TPM
+key. Call `wolfSSH_CTX_UseTpmHostKey()` before `wolfSSH_CTX_UseCert_buffer()` so
+the certificate is linked to the TPM key slot:
+
+    wolfSSH_CTX_UseTpmHostKey(ctx, &tpmDev, &tpmKey);
+    wolfSSH_CTX_UseCert_buffer(ctx, certDer, certDerSz, WOLFSSH_FORMAT_ASN1);
+
+On the client, restrict the accepted host key algorithms to the certificate
+algorithms so the connection cannot silently fall back to a plain host key and
+skip certificate (CA) verification:
+
+    wolfSSH_CTX_SetAlgoListKey(ctx,
+        "x509v3-ecdsa-sha2-nistp256,x509v3-ssh-rsa");
+    wolfSSH_CTX_AddRootCert_buffer(ctx, caDer, caDerSz, WOLFSSH_FORMAT_ASN1);
+
+Notes:
+
+- ECDSA is recommended. It uses SHA-256 and needs no extra build options.
+- RSA certificate host keys use the `x509v3-ssh-rsa` algorithm, which is defined
+  with SHA-1. Modern wolfSSL rejects SHA-1 RSA signatures by default, so RSA
+  additionally requires wolfSSL built with
+  `-DWC_SIG_MIN_HASH_TYPE=WC_HASH_TYPE_SHA`. This re-enables a deprecated hash;
+  prefer ECDSA unless RSA is mandated.
+
 WOLFSSH APPLICATIONS
 ====================
 

examples/include.am

@@ -4,6 +4,7 @@
 
 include examples/client/include.am
 include examples/echoserver/include.am
+include examples/tpmcertserver/include.am
 include examples/portfwd/include.am
 include examples/sftpclient/include.am
 include examples/scpclient/include.am

examples/tpmcertserver/.gitignore

@@ -0,0 +1,3 @@
+/tpmcertserver
+/tpmcertclient
+/tpm-server-cert.der

examples/tpmcertserver/include.am

@@ -0,0 +1,21 @@
+# vim:ft=automake
+# All paths should be given relative to the root
+
+if BUILD_TPM
+if BUILD_CERTS
+if BUILD_EXAMPLE_SERVERS
+noinst_PROGRAMS += examples/tpmcertserver/tpmcertserver
+examples_tpmcertserver_tpmcertserver_SOURCES      = \
+                                    examples/tpmcertserver/tpmcertserver.c
+examples_tpmcertserver_tpmcertserver_LDADD        = src/libwolfssh.la
+examples_tpmcertserver_tpmcertserver_DEPENDENCIES = src/libwolfssh.la
+endif
+if BUILD_EXAMPLE_CLIENTS
+noinst_PROGRAMS += examples/tpmcertserver/tpmcertclient
+examples_tpmcertserver_tpmcertclient_SOURCES      = \
+                                    examples/tpmcertserver/tpmcertclient.c
+examples_tpmcertserver_tpmcertclient_LDADD        = src/libwolfssh.la
+examples_tpmcertserver_tpmcertclient_DEPENDENCIES = src/libwolfssh.la
+endif
+endif
+endif