[RFC v2 0/5] TPM support for gpg

James Bottomley James.Bottomley at HansenPartnership.com
Sat Mar 10 23:50:00 CET 2018

On Sat, 2018-03-10 at 13:03 +0100, Werner Koch wrote:
> On Mon,  5 Mar 2018 20:12, James.Bottomley at HansenPartnership.com
> said:
> > 
> > Since the last posting, I've tidied up a few things and added
> > support for Elliptic Curve keys (as a separate patch, currently,
> > but it could be rolled into the base).
> Thanks for the patches.  I pushed them to a new tpm-work branch.

Great, thanks!

> As of now it is required that libtss0-dev is installed.  Debian
> Stetch does not have it but it is easy to install from Sid.

Actually, libtss-dev, but yes.  However, there's a problem with that
package (which is why it hasn't migrated from unstable) and it turns
out the person who maintains it has left IBM, so I can't get it fixed.

I think what's going to happen is that IBM will submit a new one with
the ibm prefix, largely because Intel is trying to submit a tss package
as well.  I was hoping to get these two merged (the Intel one lacks the
crypto pieces which are necessary for gpg key handling, so simply
adding the IBM one seemed like a good solution) but it looks
increasingly less likely that will happen, so separate namespaces seems
a better approach.

>   There are no real configure checks right now but I added an #error
> to explain what is going wrong if you try to build without this
> dependency.  I have not tested the new code myself.

How about the below for a stab at gating the configure on the presence
of the TPM library.

> Before this goes into master or a 2.3 release, I would like to move
> the entire TPM access code out to a separate daemon much like
> scdaemon works.  Maybe it is even possible to get rid of the
> dlopening, but the major thing is that this code and its dependency
> on OpenSSL gets out of gpg-agent.

I should have removed the direct openssl dependency with the shift to
gcrypt AES handling.  However, I'll look at doing a separate daemon.
 It certainly should be simple enough.

> James: The 3 new files are missing the copyright blurbs, can you
> please send a patch to add them?  I would not mind if you can
> directly add an   SPDX-License-Identifier: GPL-3.0+
> line (GPL-2.0+ if you prefer).

Sure thing.  SPX should work.  I'll keep them at GPL-2.0+ just in case
I (or anyone else) need to cut and paste into a GPL-2.0 project.


From cc7a25e6b41b7da07970e7ca5f57129244a8214b Mon Sep 17 00:00:00 2001
From: James Bottomley <James.Bottomley at HansenPartnership.com>
Date: Tue, 6 Mar 2018 15:02:43 -0800
Subject: [PATCH] configure: Make TPM2 support conditional

This adds a configure stanza to check for the necessary libtss to
support TPM functions.  If found, the library functions will be
dynamically loaded, meaning that a system built with TPM2 support will
still execute correctly (obviously minus TPM2 support) if installed
without libtss being present.

Signed-off-by: James Bottomley <James.Bottomley at HansenPartnership.com>
 agent/Makefile.am |  7 +++++--
 agent/agent.h     | 26 ++++++++++++++++++++++++++
 configure.ac      | 11 +++++++++++
 3 files changed, 42 insertions(+), 2 deletions(-)

diff --git a/agent/Makefile.am b/agent/Makefile.am
index 1b8ac508f..c92c0ad06 100644
--- a/agent/Makefile.am
+++ b/agent/Makefile.am
@@ -51,12 +51,15 @@ gpg_agent_SOURCES = \
 	protect.c \
 	trustlist.c \
 	divert-scd.c \
-	divert-tpm2.c \
-	tpm2.c \
 	cvt-openpgp.c cvt-openpgp.h \
 	call-scd.c \
+gpg_agent_SOURCES += tpm2.c \
+	divert-tpm2.c
 common_libs = $(libcommon)
 commonpth_libs = $(libcommonpth)
diff --git a/agent/agent.h b/agent/agent.h
index 0ff487a59..dd6d6cb24 100644
--- a/agent/agent.h
+++ b/agent/agent.h
@@ -534,6 +534,7 @@ gpg_error_t agent_marktrusted (ctrl_t ctrl, const char *name,
 void agent_reload_trustlist (void);
 /*-- divert-tpm2.c --*/
 int divert_tpm2_pksign (ctrl_t ctrl, const char *desc_text,
                         const unsigned char *digest, size_t digestlen, int algo,
                         const unsigned char *shadow_info, unsigned char **r_sig,
@@ -544,6 +545,31 @@ int divert_tpm2_pkdecrypt (ctrl_t ctrl, const char *desc_text,
                            char **r_buf, size_t *r_len, int *r_padding);
 int divert_tpm2_writekey (ctrl_t ctrl, const unsigned char *grip,
                           gcry_sexp_t s_skey);
+static inline int divert_tpm2_pksign (ctrl_t ctrl, const char *desc_text,
+				      const unsigned char *digest,
+				      size_t digestlen, int algo,
+				      const unsigned char *shadow_info,
+				      unsigned char **r_sig,
+				      size_t *r_siglen)
+  return -EINVAL;
+static inline int divert_tpm2_pkdecrypt (ctrl_t ctrl, const char *desc_text,
+					 const unsigned char *cipher,
+					 const unsigned char *shadow_info,
+					 char **r_buf, size_t *r_len,
+					 int *r_padding)
+  return -EINVAL;
+static inline int divert_tpm2_writekey (ctrl_t ctrl, const unsigned char *grip,
+					gcry_sexp_t s_skey)
+  return -EINVAL;
 /*-- divert-scd.c --*/
diff --git a/configure.ac b/configure.ac
index 7522b6922..6df4d0a57 100644
--- a/configure.ac
+++ b/configure.ac
@@ -100,6 +100,7 @@ have_gnutls=no
@@ -1590,6 +1591,15 @@ AC_SUBST(NETLIBS)
+# TPM libtss library .. don't compile TPM support if we don't have it
+AC_CHECK_LIB(tss, TSS_Create, [have_libtss=yes])
+if test "$have_libtss" = yes; then
+   AC_DEFINE(HAVE_LIBTSS, 1, [Defined if we have TPM2 support library])
+AM_CONDITIONAL(HAVE_LIBTSS, test "$have_libtss" = yes)
 # Setup gcc specific options
@@ -2072,6 +2082,7 @@ echo "
         TLS support:         $use_tls_library
         TOFU support:        $use_tofu
         Tor support:         $show_tor_support
+        TPM support:         $have_libtss
 if test x"$use_regex" != xyes ; then
 echo "
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