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From: David Howells <dhowells-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
To: denkenz-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org,
	jarkko.sakkinen-VuQAYsv1563Yd54FQh9/CA@public.gmane.org,
	jejb-23VcF4HTsmIX0ybBhKVfKdBPR1lH4CV8@public.gmane.org
Cc: tpmdd-devel-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org,
	linux-integrity-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	keyrings-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	linux-security-module-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
Subject: [PATCH 18/23] TPMLIB: Encapsulate XOR-based encryption with authkey derivative
Date: Tue, 21 Aug 2018 16:58:51 +0100
Message-ID: <153486713189.13066.10919642243213217779.stgit@warthog.procyon.org.uk> (raw)
In-Reply-To: <153486700916.13066.12870860668352070081.stgit-S6HVgzuS8uM4Awkfq6JHfwNdhmdF6hFW@public.gmane.org>

Encapsulate XOR-based encryption with a symmetric key derived from the authkey
so that it can be used in multiple functions.

Signed-off-by: David Howells <dhowells-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
---

 drivers/char/tpm/tpm-library.c |   42 +++++++++++++++++++++++++++++++---------
 1 file changed, 33 insertions(+), 9 deletions(-)

diff --git a/drivers/char/tpm/tpm-library.c b/drivers/char/tpm/tpm-library.c
index 329b5c3f23a2..9234a2e7608f 100644
--- a/drivers/char/tpm/tpm-library.c
+++ b/drivers/char/tpm/tpm-library.c
@@ -489,6 +489,30 @@ struct tpm_digests {
 	struct tpm_odd_nonce ononce;
 };
 
+/*
+ * Calculate an XOR-based symmetric key that can be used to encrypt protected
+ * data.  The key is left in td->xorhash.
+ */
+static int tpm_calc_symmetric_authkey(struct tpm_digests *td,
+				      const u8 *secret,
+				      const struct tpm_even_nonce *enonce)
+{
+	memcpy(td->xorwork, secret, SHA1_DIGEST_SIZE);
+	memcpy(td->xorwork + SHA1_DIGEST_SIZE, enonce->data, SHA1_DIGEST_SIZE);
+	return TSS_sha1(td->xorwork, SHA1_DIGEST_SIZE * 2, td->xorhash);
+}
+
+/*
+ * Encrypt/decrypt data with a previously calculated XOR-based symmetric key.
+ */
+static void tpm_crypt_with_authkey(const struct tpm_digests *td,
+				   const u8 *data, u8 *buffer)
+{
+	int i;
+	for (i = 0; i < SHA1_DIGEST_SIZE; ++i)
+		buffer[i] = td->xorhash[i] ^ data[i];
+}
+
 /**
  * tpm_seal - Encrypt one key according to another plus PCR state
  * @chip: The chip to use
@@ -528,7 +552,6 @@ int tpm_seal(struct tpm_chip *chip,
 	int encdatasize;
 	int storedsize;
 	int ret;
-	int i;
 
 	/* alloc some work space for all the hashes */
 	td = kmalloc(sizeof *td, GFP_KERNEL);
@@ -541,13 +564,18 @@ int tpm_seal(struct tpm_chip *chip,
 		goto out;
 	dump_sess(&sess);
 
-	/* calculate encrypted authorization value */
-	memcpy(td->xorwork, sess.secret, SHA1_DIGEST_SIZE);
-	memcpy(td->xorwork + SHA1_DIGEST_SIZE, sess.enonce.data, SHA1_DIGEST_SIZE);
-	ret = TSS_sha1(td->xorwork, SHA1_DIGEST_SIZE * 2, td->xorhash);
+	/* We need to pass a 'password' to the TPM with which it will encrypt
+	 * the sealed data before returning it.  So that the password doesn't
+	 * travel to the TPM in the clear, we generate a symmetric key from the
+	 * negotiated and encrypted session data and encrypt the password with
+	 * that.
+	 */
+	ret = tpm_calc_symmetric_authkey(td, sess.secret, &sess.enonce);
 	if (ret < 0)
 		goto out;
+	tpm_crypt_with_authkey(td, encauth, td->encauth);
 
+	/* Set up the parameters we will be sending */
 	ret = tpm_gen_odd_nonce(chip, &td->ononce);
 	if (ret < 0)
 		goto out;
@@ -556,10 +584,6 @@ int tpm_seal(struct tpm_chip *chip,
 	pcrinfosize_be	= cpu_to_be32(pcrinfosize);
 	cont = 0;
 
-	/* encrypt data authorization key */
-	for (i = 0; i < SHA1_DIGEST_SIZE; ++i)
-		td->encauth[i] = td->xorhash[i] ^ encauth[i];
-
 	/* calculate authorization HMAC value */
 	BUG_ON(!pcrinfo);
 	ret = TSS_authhmac(td->pubauth, sess.secret, SHA1_DIGEST_SIZE,


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  parent reply index

Thread overview: 42+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-08-21 15:56 tpm: Provide a TPM access library David Howells
     [not found] ` <153486700916.13066.12870860668352070081.stgit-S6HVgzuS8uM4Awkfq6JHfwNdhmdF6hFW@public.gmane.org>
2018-08-21 15:56   ` [PATCH 01/23] TPM: Add new TPMs to the tail of the list to prevent inadvertent change of dev David Howells
     [not found]     ` <153486701644.13066.13372706238885253812.stgit-S6HVgzuS8uM4Awkfq6JHfwNdhmdF6hFW@public.gmane.org>
2018-08-21 18:30       ` Jason Gunthorpe
     [not found]         ` <20180821183004.GB25543-uk2M96/98Pc@public.gmane.org>
2018-08-24  6:24           ` Jarkko Sakkinen
     [not found]             ` <20180824062434.GB3584-VuQAYsv1563Yd54FQh9/CA@public.gmane.org>
2018-08-24  6:25               ` Jarkko Sakkinen
     [not found]                 ` <20180824062557.GC3584-VuQAYsv1563Yd54FQh9/CA@public.gmane.org>
2018-08-24 11:22                   ` Mimi Zohar
2018-08-24  6:19       ` Jarkko Sakkinen
2018-08-21 15:57   ` [PATCH 02/23] TPM: Provide a facility for a userspace TPM emulator David Howells
     [not found]     ` <153486702302.13066.15889029286852815542.stgit-S6HVgzuS8uM4Awkfq6JHfwNdhmdF6hFW@public.gmane.org>
2018-08-21 18:31       ` Jason Gunthorpe
     [not found]         ` <20180821183140.GD25543-uk2M96/98Pc@public.gmane.org>
2018-08-24  6:29           ` Jarkko Sakkinen
2018-08-21 15:57   ` [PATCH 03/23] TPM: Provide a platform driver for the user emulator driver David Howells
     [not found]     ` <153486702979.13066.16900998092976336647.stgit-S6HVgzuS8uM4Awkfq6JHfwNdhmdF6hFW@public.gmane.org>
2018-08-24  6:30       ` Jarkko Sakkinen
2018-08-21 15:57   ` [PATCH 04/23] TPM: Expose struct tpm_chip and related find_get and put functions David Howells
     [not found]     ` <153486703636.13066.16209594327379341518.stgit-S6HVgzuS8uM4Awkfq6JHfwNdhmdF6hFW@public.gmane.org>
2018-08-21 18:31       ` Jason Gunthorpe
     [not found]     ` <20180821183108.GC25543-uk2M96/98Pc@public.gmane.org>
2018-08-21 18:35       ` David Howells
2018-08-21 15:57   ` [PATCH 05/23] TPM: Use struct tpm_chip rather than chip number as interface parameter David Howells
     [not found]     ` <153486704294.13066.8818198038331415342.stgit-S6HVgzuS8uM4Awkfq6JHfwNdhmdF6hFW@public.gmane.org>
2018-08-24  7:42       ` Jarkko Sakkinen
2018-08-21 15:57   ` [PATCH 06/23] TPM: Move ordinal values from interface file to header with other ordinals David Howells
2018-08-21 15:57   ` [PATCH 07/23] TPM: Consolidate tpm_send(), transmit_cmd() and tpm_transmit() David Howells
2018-08-21 15:57   ` [PATCH 08/23] TPMLIB: Break TPM bits out of security/keys/trusted.c David Howells
     [not found]     ` <153486706322.13066.3105842100625841410.stgit-S6HVgzuS8uM4Awkfq6JHfwNdhmdF6hFW@public.gmane.org>
2018-08-24  7:52       ` Jarkko Sakkinen
     [not found]         ` <20180824075227.GG3584-VuQAYsv1563Yd54FQh9/CA@public.gmane.org>
2018-08-24  8:49           ` Jarkko Sakkinen
     [not found]         ` <20180824084930.GA10266-VuQAYsv1563Yd54FQh9/CA@public.gmane.org>
2018-08-24  9:33           ` David Howells
     [not found]             ` <25340.1535103190-S6HVgzuS8uM4Awkfq6JHfwNdhmdF6hFW@public.gmane.org>
2018-08-27  8:25               ` Jarkko Sakkinen
2018-08-21 15:57   ` [PATCH 09/23] TPMLIB: Do some source cleanups David Howells
2018-08-21 15:57   ` [PATCH 10/23] TPMLIB: Better format calls to TSS_*hmac*() David Howells
2018-08-21 15:58   ` [PATCH 11/23] TPMLIB: Put banner comments on public TPM library functions David Howells
2018-08-21 15:58   ` [PATCH 12/23] TPMLIB: Create tpm_{even, odd}_nonce structs to represent nonces David Howells
2018-08-21 15:58   ` [PATCH 13/23] TPMLIB: Rename store8() and storebytes() David Howells
2018-08-21 15:58   ` [PATCH 14/23] TPMLIB: Make store_s() take a void* data argument, not unsigned char* David Howells
2018-08-21 15:58   ` [PATCH 15/23] TPMLIB: Use __be32 rather than int32_t and use cpu_to_beX() and co David Howells
2018-08-21 15:58   ` [PATCH 16/23] TPMLIB: Put more comments into the HMAC generation functions David Howells
2018-08-21 15:58   ` [PATCH 17/23] TPMLIB: Provide a wrapper to load bytes out of the reply David Howells
2018-08-21 15:58   ` David Howells [this message]
2018-08-21 15:58   ` [PATCH 19/23] TPMLIB: Add some debugging code David Howells
2018-08-21 15:59   ` [PATCH 20/23] TPMLIB: Implement call to TPM_CreateWrapKey David Howells
2018-08-21 15:59   ` [PATCH 21/23] TPMLIB: Implement call to TPM_LoadKey2 David Howells
2018-08-21 15:59   ` [PATCH 22/23] TPMLIB: Provide call for TPM_FlushSpecific David Howells
2018-08-21 15:59   ` [PATCH 23/23] TPM: Add an asymmetric key subtype for handling TPM-based keys David Howells
2018-08-22 14:19   ` tpm: Provide a TPM access library Jarkko Sakkinen
     [not found] ` <20180822141956.GA28110-VuQAYsv1563Yd54FQh9/CA@public.gmane.org>
2018-08-22 14:45   ` David Howells
     [not found]     ` <13611.1534949106-S6HVgzuS8uM4Awkfq6JHfwNdhmdF6hFW@public.gmane.org>
2018-08-23 22:49       ` Jarkko Sakkinen

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