Adds the xml file for the draft RFC and builds text and html versions
if the xml2rfc program is found.
Signed-off-by: James Bottomley <James.Bottomley@xxxxxxxxxxxxxxxxxxxxx>
---
v2: Add missing sections plus minor updates
---
Makefile.am | 2 +-
configure.ac | 4 +-
doc/Makefile.am | 15 +
doc/draft-bottomley-tpm2-keys.xml | 465 ++++++++++++++++++++++++++++++
4 files changed, 484 insertions(+), 2 deletions(-)
create mode 100644 doc/Makefile.am
create mode 100644 doc/draft-bottomley-tpm2-keys.xml
diff --git a/Makefile.am b/Makefile.am
index 33de0d9..787ba29 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -41,4 +41,4 @@ $(builddir)/%.1: $(srcdir)/%.1.in $(top_builddir)/%
install-data-hook:
cd $(DESTDIR)$(openssl_enginedir) && $(LN_S) -f libtpm2@SHREXT@ tpm2@SHREXT@
-SUBDIRS = tests
+SUBDIRS = tests doc
diff --git a/configure.ac b/configure.ac
index 6efa7a5..e102dd2 100644
--- a/configure.ac
+++ b/configure.ac
@@ -128,6 +128,8 @@ fi
AC_PATH_PROG(TPMSERVER, tpm_server,,/bin:/usr/bin:/usr/lib/ibmtss:/usr/libexec/ibmtss)
AC_PATH_PROG(SWTPM, swtpm,,/bin:/usr/bin:/usr/lib/ibmtss:/usr/libexec/ibmtss)
AC_PATH_PROG(SWTPM_IOCTL, swtpm_ioctl,,/bin:/usr/bin:/usr/lib/ibmtss:/usr/libexec/ibmtss)
+AC_CHECK_PROG(XML2RFC, xml2rfc, xml2rfc)
+AM_CONDITIONAL(HAVE_XML2RFC, test -n "${XML2RFC}")
CFLAGS="$CFLAGS -Wall"
SHREXT=$shrext_cmds
AC_SUBST(CFLAGS)
@@ -147,7 +149,7 @@ fi
AC_SUBST(testtpm)
-AC_OUTPUT([Makefile tests/Makefile])
+AC_OUTPUT([Makefile tests/Makefile doc/Makefile])
cat <<EOF
diff --git a/doc/Makefile.am b/doc/Makefile.am
new file mode 100644
index 0000000..0c24ce0
--- /dev/null
+++ b/doc/Makefile.am
@@ -0,0 +1,15 @@
+XML2RFC_TARGETS = draft-bottomley-tpm2-keys.txt \
+ draft-bottomley-tpm2-keys.html
+
+if HAVE_XML2RFC
+all: $(XML2RFC_TARGETS)
+
+clean-local:
+ rm -fr $(XML2RFC_TARGETS)
+endif
+
+$(builddir)/%.txt: $(srcdir)/%.xml
+ $(XML2RFC) --text -o $@ $<
+
+$(builddir)/%.html: $(srcdir)/%.xml
+ $(XML2RFC) --html -o $@ $<
diff --git a/doc/draft-bottomley-tpm2-keys.xml b/doc/draft-bottomley-tpm2-keys.xml
new file mode 100644
index 0000000..d2e9235
--- /dev/null
+++ b/doc/draft-bottomley-tpm2-keys.xml
@@ -0,0 +1,465 @@
+<?xml version="1.0"?>
+<!DOCTYPE rfc SYSTEM "rfc2629.dtd" [
+<!-- One method to get references from the online citation libraries.
+There has to be one entity for each item to be referenced.
+An alternate method (rfc include) is described in the references.
+-->
+<!ENTITY RFC2119 SYSTEM "http://xml.resource.org/public/rfc/bibxml/reference.RFC.2119.xml";>
+<!ENTITY RFC8017 SYSTEM "http://xml.resource.org/public/rfc/bibxml/reference.RFC.8017.xml";>
+]>
+<?rfc toc="yes" ?>
+<rfc ipr="trust200902" category="info" docName="draft-bottomley-tpm-keys-00">
+ <front>
+ <title abbrev="TPM 2 Key Format">ASN.1 Specification for TPM 2.0 Key Files</title>
+ <author initials="J." surname="Bottomley" fullname="James E.J. Bottomley">
+ <organization>Linux Kernel</organization>
+ <address>
+ <postal>
+ <street/>
+ <city/>
+ <region/>
+ <country>USA</country>
+ </postal>
+ <email>James.Bottomley@xxxxxxxxxxxxxxxxxxxxx</email>
+ </address>
+ </author>
+ <date month="May" year="2021"/>
+ <area>Security</area>
+ <keyword>I-D</keyword>
+ <keyword>Internet-Draft</keyword>
+ <keyword>X.509</keyword>
+ <abstract>
+ <t>
+ This specification is designed to be an extension to the ASN.1
+ (defined in <xref target="X.680"/>) specification of PKCS #1
+ <xref target="RFC8017"/> to define the file format of private
+ keys that need to be loaded into a TPM 2 device to operate.
+ </t>
+ </abstract>
+ </front>
+ <middle>
+ <section anchor="intro" title="Introduction">
+ <t>
+ The Security of private keys has long been a concern and the
+ ability of ubiquitous devices like TPMs has made it useful to
+ use them for secure private key storage. With the advent of
+ TPM 2.0, private key storage inside the TPM (acting as a token
+ which could be referred to by PKCS #11) has been discouraged,
+ and instead key files which are loaded and evicted as
+ necessary is the encouraged format. This standard defines an
+ interoperable ASN.1 representation for such key files, so that
+ a key created by one tool should be loadable by a different
+ one.
+ </t>
+ </section>
+ <section anchor="terms" title="Terminology">
+ <t>
+ The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL
+ NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and
+ "OPTIONAL" in this document are to be interpreted as described in
+ <xref target="RFC2119"/>.
+ </t>
+ <section title="Notation">
+ <dl>
+ <dt>ASN.1</dt>
+ <dd>Abstract Syntax Notation defined in
+ <xref target="X.680"/></dd>
+ <dt>DER</dt>
+ <dd>Distinguished Encoding Rules. Basically a defined binary
+ representation for ASN.1</dd>
+ <dt>MSO</dt>
+ <dd>Most Significant Octet (the highest order
+ byte of an integer)</dd>
+ <dt>PEM</dt>
+ <dd>Privacy enhanced Electronic Mail. An ASCII compatible
+ representation of DER</dd>
+ <dt>TCG</dt>
+ <dd>Trusted Computing Group</dd>
+ <dt>TPM</dt>
+ <dd>Trusted Platform Module</dd>
+ </dl>
+ </section>
+ </section>
+ <section anchor="keyrep" title="Key Representation">
+ <t>
+ All TPM 2.0 keys consist of two binary pieces, a public part,
+ which can be parsed according to the TPM specification for
+ TPM2B_PUBLIC <xref target="TPM2.0"/> and a private part, which
+ is cryptographically sealed in such a way as to be only
+ readable on the TPM that created it. The purpose of this
+ specification is to specify a format by which the public and
+ private pieces of a TPM key can be loaded.
+ </t>
+ <t>
+ The design of the TPMkey ASN.1 format is that it should have a
+ distinguishing OID at the beginning so the DER form of the
+ key can be easily recognized. In PEM form, the key MUST have
+ "-----BEGIN TSS2 PRIVATE KEY-----" and "-----END TSS2 PRIVATE
+ KEY-----" as the PEM guards. All additional information that
+ may be needed to load the key is specified as optional
+ explicit elements, which can be extended by later
+ specifications, which is why the TPMkey is not versioned.
+ </t>
+ <section anchor="tpmkey" title="TPMkey Syntax">
+ <figure><artwork>
+ TPMKey ::= SEQUENCE {
+ type OBJECT IDENTIFIER
+ emptyAuth [0] EXPLICIT BOOLEAN OPTIONAL
+ policy [1] EXPLICIT SEQUENCE OF TPMPolicy OPTIONAL
+ secret [2] EXPLICIT OCTET STRING OPTIONAL
+ parent INTEGER
+ pubkey OCTET STRING
+ privkey OCTET STRING
+ }
+ </artwork></figure>
+ <t>
+ The fields of type TPMKey have the following meanings:
+ </t>
+ <section title="type">
+ <t>
+ A unique OID specifying the key type. This standard
+ currently defines three types of keys: a loadable key,
+ specified by id-loadablekey, (to be loaded with
+ TPM2_Load), an importable key, specified by
+ id-importablekey, (to be loaded with TPM2_Import) and a
+ sealed data key, specified by id-sealedkey, (to be
+ extracted with TPM2_Unseal). The TCG has reserved the
+ following OID prefix for this:
+ </t>
+ <figure><artwork>
+ id-tpmkey OBJECT IDENTIFIER ::=
+ {joint-iso-itu-t(2) international-organizations(23) 133 10}
+ </artwork></figure>
+ <t>
+ And the three key types are:
+ </t>
+ <figure><artwork>
+ id-loadablekey OBJECT IDENTIFIER ::=
+ {id-tpmkey 3}
+ </artwork></figure>
+ <figure><artwork>
+ id-importablekey OBJECT IDENTIFIER ::=
+ {id-tpmkey 4}
+ </artwork></figure>
+ <figure><artwork>
+ id-sealedkey OBJECT IDENTIFIER ::=
+ {id-tpmkey 5}
+ </artwork></figure>
+ </section>
+ <section title="emptyAuth">
+ <t>
+ An implementation needs to know as it formulates the
+ TPM2_Load/Import/Unseal command whether it must also send
+ down an authorization, so this parameter gives that
+ indication. emptyAuth MUST be true if authorization is
+ NOT required and MUST BE either false or absent if
+ authorization is required. Since this element has
+ three states (one representing true and two representing
+ false) it is RECOMMENDED that implementations emitting
+ TPMkey representations use absence of the tag to represent
+ false. However, implementations reading TPMKey MUST
+ be able to process all three possible states.
+ </t>
+ </section>
+ <section title="policy">
+ <t>
+ This MUST be present if the TPM key has a policy hash
+ because it describes to the implementation how to
+ construct the policy. The forms of the policy statement
+ are described in section <xref target="policy"/>.
+ </t>
+ </section>
+ <section title="secret">
+ <t>
+ This section describes the additional cryptographic
+ secret used to specify the outer wrapping of an
+ importable key. It MUST be present for key type
+ id-importablekey and MUST NOT be present for any other
+ key type.
+ </t>
+ <t>
+ Importable keys (designed to be processed by TPM2_Import)
+ MUST have an unencrypted inner wrapper (symmetricAlg MUST
+ be TPM_ALG_NULL and encryptionKey MUST be empty) and an
+ outer wrapper encrypted to the parent key using
+ inSymSeed. The secret parameter is the fully marshalled
+ TPM2B_ENCRYPTED_SECRET form of inSymSeed.
+ </t>
+ </section>
+ <section title="parent">
+ <t>
+ This MUST be present for all keys and specifies the handle
+ of the parent key. The parent key SHOULD be either a
+ persistent handle (MSO 0x81) or a permanent handle (MSO
+ 0x40). Since volatile handle numbering can change
+ unexpectedly depending on key load order, the parent
+ SHOULD NOT be a volatile handle (MSO 0x80). The parent MUST
+ NOT have any other MSO.
+ </t>
+ <t>
+ If a permanent handle (MSO 0x40) is specified then the
+ implementation MUST run TPM2_CreatePrimary on the handle
+ using the TCG specified Elliptic Curve template for the
+ NIST P-256 curve and use the primary key so generated as
+ the parent.
+ </t>
+ </section>
+ <section title="pubkey">
+ <t>
+ This MUST be present and MUST correspond to the fully
+ marshalled TPM2B_PUBLIC structure of the TPM Key.
+ </t>
+ </section>
+ <section title="privkey">
+ <t>
+ This MUST be present and MUST correspond to the fully
+ marshalled TPM2B_PRIVATE structure of the TPM Key. For
+ importable keys, this must be the duplicate parameter that
+ would be input to TPM2_Import.
+ </t>
+ </section>
+ </section>
+ </section>
+ <section anchor="policy" title="Key Policy Specification">
+ <t>
+ Policy is constructed on a TPM by executing a sequence of
+ policy statements. This specification currently only defines
+ a limited subset of the allowed policy statements. The policy
+ is specified by a hash, which the execution of the policy
+ statements must reach in order for the policy to be validated
+ (See <xref target="TPM2.0"/> Part 1 for a detailed description.
+ </t>
+ <t>
+ The TPMPolicy ASN.1 MUST be a sequence of policy statements
+ which correspond exactly to TPM policy instructions in the
+ order they should be executed and additionally from which the
+ ultimate policy hash can be constructed.
+ </t>
+ <t>
+ The current policy specification is strictly for AND based
+ policy only and may be extended at a later date with OR
+ policy. However, the ASN.1 for policy is formulated as CONS
+ elements, leaving the possibility of adding additional but
+ optional elements for policy statements which are not
+ supported by this standard (such as TPM2_PolicyAuthorize).
+ </t>
+ <section title="TPMPolicy Syntax">
+ <figure><artwork>
+ TPMPolicy ::= SEQUENCE {
+ CommandCode [0] EXPLICIT INTEGER
+ CommandPolicy [1] EXPLICIT OCTET STRING
+ }
+ </artwork></figure>
+ <t>
+ The Fields of type TPMPolicy have the following meanings:
+ </t>
+ <section title="CommandCode">
+ <t>
+ This is the integer representation of the TPM command code
+ for the policy statement.
+ </t>
+ </section>
+ <section title="CommandPolicy">
+ <t>
+ This is a binary string representing a fully marshalled,
+ TPM ordered, command body for the TPM policy command.
+ Therefore to send the command, the implementation simply
+ marshalls the command code and appends this octet string
+ as the body.
+ </t>
+ <t>
+ Commands which have no body, such as TPM2_AuthVal, MUST be
+ specified as a zero length OCTET STRING
+ </t>
+ </section>
+ </section>
+ <section title="Policy Implementation Considerations">
+ <t>
+ The policy hash for AND based policies is constructed by extension of the prior policy hash
+ </t>
+ <figure><artwork>
+ newHash = HASH ( oldHash || policyHash )
+ </artwork></figure>
+ <t>
+ where policyHash is usually simply the hash of the fully
+ marshalled policy command (including the CommandCode).
+ However, this isn't true for TPM2_PolicyCounterTimer() so
+ always consult the <xref target="TPM2.0"/> specifications
+ for how to construct the policyHash.
+ </t>
+ <t>
+ The implementation should fail fast for policy problems, so
+ if an individual policy command returns a failure (which
+ usually indicates a particular policy requirement cannot be
+ met), that failure should be reported in as much detail as
+ possible and processing of the key should fail at that
+ point.
+ </t>
+ <section title="Authorization Policy">
+ <t>
+ When Authorization (Passing in a password) is required,
+ the emptyAuth parameter MUST be absent or set to false
+ and additionally the TPM_CC_PolicyAuthValue MUST be
+ specified as the command code for one entry in the
+ TPMPolicy sequence. However, the implementation MAY
+ choose to execute either TPM2_PolicyPassword for TPM_RS_PW
+ or TPM2_PolicyAuthValue for HMAC based authorization
+ depending on whether the command being authorized is using
+ sessions or not. If the policy does not require an
+ authorization then the emptyAuth parameter MUST be set to
+ true.
+ </t>
+ </section>
+ </section>
+ </section>
+ <section anchor="implementation" title="Implementation Considerations">
+ <t>
+ Implementations SHOULD support all TCG mandated algorithms,
+ but MAY omit those deemed insecure, such as the SHA1 hash.
+ </t>
+ <t>
+ TPM2_Import transforms the privKey into a TPM2B_PRIVATE which
+ can then be used as a source to TPM2_Load, making the loading
+ of importable keys is necessarily a two stage process, which
+ can be time consuming on some TPMs. Since the TPM2B_PRIVATE
+ structure emitted by TPM2_Import is fully secure,
+ Implementations SHOULD minimize the number of TPM2_Import
+ operations by caching the emitted TPM2B_PRIVATE.
+ </t>
+ </section>
+ <section anchor="security" title="Security Considerations">
+ <t>
+ The TPM 2.0 supports a variety of algorithms, the most common
+ being SHA1 and SHA256 for hashing and RSA2048 and NIST P-256
+ for asymmetric keys. Implementors SHOULD NOT use deprecated
+ algorithms, such as SHA1, for any TPM operation. In
+ particular, the algorithm used for the policy hash SHOULD NOT
+ be SHA1 and this means that SHA1 SHOULD NOT be used as the
+ name algorithm hash for any TPM key.
+ </t>
+ <t>
+ TPM 2.0 supports a session mode (TPM_RS_PW) where
+ authorizations are passed to the TPM in clear text over the
+ TPM connection. Implementations SHOULD consider the
+ possibility of snooping on the wire between the implementation
+ and the TPM, such as <xref target="TPM GENIE"/>, and SHOULD
+ use HMAC session authorizations as best practice for all TPM
+ keys.
+ </t>
+ <t>
+ In addition to snooping authorizations, snooping may also
+ occur when key material is being exchanged between the TPM and
+ the implementation, such as wrapping of private keys and the
+ sealing and unsealing operations for sealed keys.
+ Implementations SHOULD always use HMAC sessions with
+ TPMA_SESSION_DECRYPT when sensitive information is passed in
+ to the TPM and HMAC sessions with TPMA_SESSION_ENCRYPT when
+ sensitive information is received from the TPM.
+ </t>
+ <t>
+ The easiest way to get the TPM to wrap an external private key
+ is to use TPM2_Import. However, since TPMA_SESSION_DECRYPT
+ only protects the first parameter (which is encryptionKey),
+ the duplicate should use inner symmetric encryption with a
+ randomly generated ephemeral key, which is then presented to
+ the TPM via the protected encryptionKey parameter.
+ </t>
+ <t>
+ The TPM has a mode where it can generate private key material
+ internally (using TPM2_Create) such that the private part of
+ the key can never leave the TPM. Implementations SHOULD
+ support this mode but should be aware that while keys created
+ like this may be more secure than wrapped keys, they can also
+ be used only while access to the TPM that created them is
+ available, so implementations SHOULD also support wrapping for
+ keys that are expected to outlive the TPM that's using them.
+ Clients can then develop best practices around TPM wrapped
+ identity keys, possibly with TPM created sub keys, which can
+ only be used on the device they were wrapped for.
+ </t>
+ <t>
+ Since TPM keys can only be used by the specific TPM that
+ created them, which is usually embedded in a piece of
+ hardware, they are secure against exfiltration attacks.
+ However, consideration should be given to an attacker gaining
+ access to the system containing the TPM. TPM keys are most
+ secure when used as part of an operating system that has
+ guaranteed trust properties, such as secure and measured boot.
+ Implementations SHOULD assist users in constructing key
+ policies that ensure the key can be used only when the
+ operating system is within its trusted parameters to minimize
+ threats from co-located attackers.
+ </t>
+ </section>
+ <section anchor="IANA" title="IANA Considerations">
+ <t>
+ None.
+ </t>
+ </section>
+ <section anchor="comments" title="Comments on and Enhancements to this Document">
+ <t>
+ Comments on this document should be addressed to the author
+ (James.Bottomley@xxxxxxxxxxxxxxxxxxxxx) but should also CC the
+ email lists of the two projects implementing this
+ specification:
+ </t>
+ <t>
+ The OpenSSL engine: openssl_tpm2_engine@xxxxxxxxx
+ </t>
+ <t>
+ The Linux Kernel: linux-integrity@xxxxxxxxxxxxxxx
+ </t>
+ <t>
+ The OpenSSL TPM2 engine <xref target="OPENSSL TPM2 ENGINE"/>
+ is currently the only implementation of this full
+ specification, so enhancements should be proposed after
+ patches implementing the enhancement have been accepted by
+ openssl_tpm2_engine or another full specification
+ implementation.
+ </t>
+ </section>
+
+ </middle>
+ <back>
+ <references title="Normative References">
+ &RFC2119;
+ &RFC8017;
+ <reference anchor="TPM2.0" target="https://trustedcomputinggroup.org/resource/tpm-library-specification/";>
+ <front>
+ <title>TPM 2.0 Library Specification</title>
+ <author>
+ <organization>Trusted Computing Group</organization>
+ </author>
+ <date year="2013" month="March" day="15"/>
+ </front>
+ </reference>
+ <reference anchor="X.680" target="https://itu.int/rec/T-REC-X.680-201508-I/en";>
+ <front>
+ <title>ITU-T Recommendation X.680,
+ Information technology - Abstract Syntax Notation One
+ (ASN.1): Specification of basic notation.</title>
+ <author><organization>International Telecommunication Union</organization></author>
+ <date year="2015" month="August"/>
+ </front>
+ </reference>
+ </references>
+ <references title="Informative References">
+ <reference anchor="TPM GENIE" target="https://www.nccgroup.com/globalassets/about-us/us/documents/tpm-genie.pdf";>
+ <front>
+ <title>TPM Genie: Interposer Attacks Against the Trusted
+ Platform Module Serial Bus</title>
+ <author initials="J." surname="Boone" fullname="J. Boone">
+ <organization>NCC Group</organization>
+ </author>
+ <date year="2018" month="March" day="9"/>
+ </front>
+ </reference>
+ <reference anchor="OPENSSL TPM2 ENGINE" target="https://git.kernel.org/pub/scm/linux/kernel/git/jejb/openssl_tpm2_engine.git/";>
+ <front>
+ <title>OpenSSL TPM2 Engine</title>
+ <author><organization>Open Source Project</organization></author>
+ </front>
+ </reference>
+ </references>
+ </back>
+</rfc>
--
2.26.2
