<s>
Intel	O
Trusted	B-Device
Execution	I-Device
Technology	I-Device
(	O
Intel	B-Device
TXT	I-Device
,	O
formerly	O
known	O
as	O
LaGrande	B-Device
Technology	I-Device
)	O
is	O
a	O
computer	O
hardware	O
technology	O
of	O
which	O
the	O
primary	O
goals	O
are	O
:	O
</s>
<s>
Attestation	O
of	O
the	O
authenticity	O
of	O
a	O
platform	O
and	O
its	O
operating	B-General_Concept
system	I-General_Concept
.	O
</s>
<s>
Assuring	O
that	O
an	O
authentic	O
operating	B-General_Concept
system	I-General_Concept
starts	O
in	O
a	O
trusted	O
environment	O
,	O
which	O
can	O
then	O
be	O
considered	O
trusted	O
.	O
</s>
<s>
Provision	O
of	O
a	O
trusted	O
operating	B-General_Concept
system	I-General_Concept
with	O
additional	O
security	O
capabilities	O
not	O
available	O
to	O
an	O
unproven	O
one	O
.	O
</s>
<s>
Intel	B-Device
TXT	I-Device
uses	O
a	O
Trusted	O
Platform	O
Module	O
(	O
TPM	O
)	O
and	O
cryptographic	O
techniques	O
to	O
provide	O
measurements	O
of	O
software	O
and	O
platform	O
components	O
so	O
that	O
system	O
software	O
as	O
well	O
as	O
local	O
and	O
remote	O
management	O
applications	O
may	O
use	O
those	O
measurements	O
to	O
make	O
trust	O
decisions	O
.	O
</s>
<s>
It	O
complements	O
Intel	B-Device
Management	I-Device
Engine	I-Device
.	O
</s>
<s>
It	O
defends	O
against	O
software-based	O
attacks	O
aimed	O
at	O
stealing	O
sensitive	O
information	O
by	O
corrupting	O
system	O
or	O
BIOS	B-Operating_System
code	O
,	O
or	O
modifying	O
the	O
platform	O
's	O
configuration	O
.	O
</s>
<s>
Measurements	O
consist	O
of	O
a	O
cryptographic	O
hash	O
using	O
a	O
Secure	O
Hashing	O
Algorithm	O
(	O
SHA	O
)	O
;	O
the	O
TPM	O
v1.0	O
specification	O
uses	O
the	O
SHA-1	B-Algorithm
hashing	O
algorithm	O
.	O
</s>
<s>
More	O
recent	O
TPM	O
versions	O
(	O
v2.0	O
+	O
)	O
call	O
for	O
SHA-2	B-Algorithm
.	O
</s>
<s>
For	O
server	O
platforms	O
,	O
the	O
first	O
measurement	O
is	O
made	O
by	O
hardware	O
(	O
i.e.	O
,	O
the	O
processor	O
)	O
to	O
measure	O
a	O
digitally	O
signed	O
module	O
(	O
called	O
an	O
Authenticated	O
Code	O
Module	O
or	O
ACM	O
)	O
provided	O
by	O
the	O
chipset	B-Device
manufacturer	O
.	O
</s>
<s>
The	O
ACM	O
then	O
measures	O
the	O
first	O
BIOS	B-Operating_System
code	O
module	O
,	O
which	O
can	O
make	O
additional	O
measurements	O
.	O
</s>
<s>
The	O
measurements	O
of	O
the	O
ACM	O
and	O
BIOS	B-Operating_System
code	O
modules	O
are	O
extended	O
to	O
PCR0	O
,	O
which	O
is	O
said	O
to	O
hold	O
the	O
static	O
core	O
root	O
of	O
trust	O
measurement	O
(	O
CRTM	O
)	O
as	O
well	O
as	O
the	O
measurement	O
of	O
the	O
BIOS	B-Operating_System
Trusted	O
Computing	O
Base	O
(	O
TCB	O
)	O
.	O
</s>
<s>
The	O
BIOS	B-Operating_System
measures	O
additional	O
components	O
into	O
PCRs	O
as	O
follows	O
:	O
</s>
<s>
The	O
dynamic	O
chain	O
of	O
trust	O
starts	O
when	O
the	O
operating	B-General_Concept
system	I-General_Concept
invokes	O
a	O
special	O
security	O
instruction	O
,	O
which	O
resets	O
dynamic	O
PCRs	O
(	O
PCR17	O
–	O
22	O
)	O
to	O
their	O
default	O
value	O
and	O
starts	O
the	O
measured	O
launch	O
.	O
</s>
<s>
The	O
first	O
dynamic	O
measurement	O
is	O
made	O
by	O
hardware	O
(	O
i.e.	O
,	O
the	O
processor	O
)	O
to	O
measure	O
another	O
digitally	O
signed	O
module	O
(	O
referred	O
to	O
as	O
the	O
SINIT	O
ACM	O
)	O
which	O
is	O
also	O
provided	O
by	O
the	O
chipset	B-Device
manufacturer	O
and	O
whose	O
signature	O
and	O
integrity	O
are	O
verified	O
by	O
the	O
processor	O
.	O
</s>
<s>
The	O
SINIT	O
ACM	O
then	O
measures	O
the	O
first	O
operating	B-General_Concept
system	I-General_Concept
code	O
module	O
(	O
referred	O
to	O
as	O
the	O
measured	O
launch	O
environment	O
–	O
MLE	O
)	O
.	O
</s>
<s>
The	O
technology	O
also	O
provides	O
a	O
more	O
secure	O
way	O
for	O
the	O
operating	B-General_Concept
system	I-General_Concept
to	O
initialize	O
the	O
platform	O
.	O
</s>
<s>
In	O
contrast	O
to	O
the	O
normal	O
processor	O
initialization	O
[	O
which	O
involved	O
the	O
boot-strap-processor	O
(	O
BSP	O
)	O
sending	O
a	O
Start-up	O
Inter-Processor	O
Interrupt	O
(	O
SIPI	O
)	O
to	O
each	O
Application	O
Processor	O
,	O
thus	O
starting	O
each	O
processor	O
in	O
"	O
real	O
mode	O
"	O
and	O
then	O
transitioning	O
to	O
"	O
virtual	O
mode	O
"	O
and	O
finally	O
to	O
"	O
protected	O
mode	O
"	O
]	O
,	O
the	O
operating	B-General_Concept
system	I-General_Concept
avoids	O
that	O
vulnerability	O
by	O
performing	O
a	O
secure	O
launch	O
(	O
a.k.a.	O
</s>
<s>
Additionally	O
,	O
those	O
values	O
can	O
be	O
used	O
to	O
identify	O
the	O
execution	O
environment	O
(	O
the	O
particular	O
BIOS	B-Operating_System
version	O
,	O
OS	O
level	O
,	O
configuration	O
,	O
etc	O
.	O
)	O
</s>
<s>
Numerous	O
server	O
platforms	O
include	O
Intel	B-Device
TXT	I-Device
,	O
and	O
TXT	O
functionality	O
is	O
leveraged	O
by	O
software	O
vendors	O
including	O
HyTrust	O
,	O
PrivateCore	O
,	O
Citrix	B-Application
,	O
and	O
VMware	O
.	O
</s>
<s>
Open-source	B-License
projects	O
also	O
utilize	O
the	O
TXT	O
functionality	O
;	O
for	O
example	O
,	O
tboot	O
provides	O
a	O
TXT-based	O
integrity	O
system	O
for	O
the	O
Linux	B-Operating_System
kernel	I-Operating_System
and	O
Xen	B-Operating_System
hypervisor	I-Operating_System
.	O
</s>
