Hi Michael, list,
Attached is a script that I threw together to recreate the contents of
the PCR values on a system I've been using, by looking at some of the
debug values. I hope that you find it useful.
-Jon
Michael Gissing wrote:
Hi!
Now I'm trying to calculate PCR 17 by hand. I'm making only little progress on that issue. Here's
what I'm doing, there are some Questions in there, what I haven't understood. The informations below
are based on "Measured Launched Environment Developer's Guide - June 2008".
1) Set PCR to all 0s
2) Extend ( SHA-1( SinitMleData.SinitHash | SinitMleData.EdxSenterFlags ) )
2a) concatenate SinitMleData.SinitHash and SinitMleData.EdxSenterFlags
*) EdxSenterFlags are reported to be 0x00000000 - is that right?
*) how can I calculate SinitHash on my own? tboot copies hole SINIT
image to memory, but
a hash over the image file isn't the same as SinitMleData.SinitHash
3) MLE Developer's Guide says that all other items are concatenated and extended at one single
extend. Is that right?
3a) MLE Dev Guid says "SHA-1 hash of BIOS ACM - SinitMleData.BiosAcmID"
*) SinitMleData.BiosAcmID is not a hash, must it be hashed or not before
concatenation?
*) Where can I get the BiosAcmID of a system?
3b) MsegValid is 8 byte data, but has only two possible values, 0x0 and 0x1,
right?
The only purpose is to indicate whether StmHash is a hash or 0s, right?
3c) How is determined whether OsSinitData.Capabilities is extended or not?
4) tboot seems to extend SinitMleData.PolicyControl |
SinitMleData.LcpPolicyHash after ML to PCR 17
too. Why extend a second time?
any help would be appreciated,
greetz Michael
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#!/usr/bin/perl
#From: http://www.xav.com/perl/site/lib/Digest/SHA1.html
use Digest::SHA1 qw(sha1 sha1_hex sha1_base64);
# The purpose of this script is to try to reconstruct the PCR values
# on wren (Dell Optiplex 755 -> Intel TXT-capable) following a Flicker
# session. Pasted below are a dump of the sinit_mle_data structure,
# and the PCR values following a Flicker session that did not perform
# any PCR Extends. Section 1.9 of the Intel MLE Developer's Guide
# explains the contents of the PCRs. This script is a sanity-check.
# PCR values following the Flicker session
# PCR-17: B6 E8 42 6F 6D 9D C1 17 0E 62 8B 07 1E 0E C1 A3 EF 3F BC 9A
# PCR-18: C0 E7 CE 56 75 57 20 E3 3A 5B 51 52 DC C4 3F CE F1 75 3B 03
# TBOOT: sinit_mle_data at 7cb1d090, size 144
# 06 00 00 00 80 00 00 00 20 07 09 10 ff ff ff ff
# ff ff ff ff ff ff ff ff 00 00 00 00 00 00 00 00
# 00 00 00 00 d7 c8 b6 ac 59 a5 35 7b e5 54 a8 24
# 0a c8 5a 70 be ca 66 87 25 25 ec fb 1f fb c3 e5
# 3f 82 2c da 71 23 33 df 4a 24 17 de 00 00 00 00
# 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
# 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
# 00 00 00 00 00 00 00 00 18 19 40 7d 00 00 00 00
# 07 00 00 00 98 00 00 00 f0 00 00 00 40 01 00 00
# Put the above data into an array for easier processing
my @sinit_mle_data = qw(06 00 00 00 80 00 00 00 20 07 09 10 ff ff ff ff ff ff
ff ff ff ff ff ff 00 00 00 00 00 00 00 00 00 00 00 00 d7 c8 b6 ac 59 a5 35 7b
e5 54 a8 24 0a c8 5a 70 be ca 66 87 25 25 ec fb 1f fb c3 e5 3f 82 2c da 71 23
33 df 4a 24 17 de 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 18 19
40 7d 00 00 00 00 07 00 00 00 98 00 00 00 f0 00 00 00 40 01 00 00);
# Turn the array into a byte string
my $sinit_mle_data_blob;
foreach(@sinit_mle_data) {
#print "This one: $_\n";
my $this_byte_as_text = $_;
$sinit_mle_data_blob .= pack("C", hex($this_byte_as_text));
}
#dump_bytes($sinit_mle_data_blob);
###
### Do PCR 18 first since it is less complex
###
my $pcr18;
# First populate PCR 18 with 20 zeros
my $pcr18;
for($i=0;$i<20;$i++) {
$pcr18.=pack("C", 0x00);
}
my $SinitMleData_MleHash = substr($sinit_mle_data_blob, 56, 20);
$pcr18 = sha1($pcr18.$SinitMleData_MleHash);
print "Calculated PCR 18:\n";
dump_bytes($pcr18);
###
### Now do PCR 17
###
# First populate PCR 17 with 20 zeros
my $pcr17;
for($i=0;$i<20;$i++) {
$pcr17.=pack("C", 0x00);
}
### Recreate the first Extend of PCR 17
my $SinitMleData_SinitHash = substr($sinit_mle_data_blob, 36, 20);
#dump_bytes($SinitMleData_SinitHash);
my $SinitMleData_EdxSenterFlags = substr($sinit_mle_data_blob, 24, 4);
#dump_bytes($SinitMleData_EdxSenterFlags);
my $firstPcr17ExtendPayload =
sha1($SinitMleData_SinitHash.$SinitMleData_EdxSenterFlags);
$pcr17 = sha1($pcr17.$firstPcr17ExtendPayload);
### Now recreate the second Extend of PCR 17
my $SinitMleData_BiosAcm_ID = substr($sinit_mle_data_blob, 4, 20);
my $SinitMleData_MsegValid = substr($sinit_mle_data_blob, 28, 8);
my $SinitMleData_StmHash = substr($sinit_mle_data_blob, 76, 20);
my $SinitMleData_PolicyControl = substr($sinit_mle_data_blob, 116, 4);
my $SinitMleData_LcpPolicyHash = substr($sinit_mle_data_blob, 96, 20);
### Just guessing that Capabilities is all zeros since we're not using
### a policy or any of the more sophisticated launch control features.
my $OsSinitData_Capabilities = pack("I", 0);
my $secondPcr17ExtendPayload =
sha1($SinitMleData_BiosAcm_ID.
$SinitMleData_MsegValid.
$SinitMleData_StmHash.
$SinitMleData_PolicyControl.
$SinitMleData_LcpPolicyHash.
$OsSinitData_Capabilities);
$pcr17 = sha1($pcr17.$secondPcr17ExtendPayload);
print "Calculated PCR 17:\n";
dump_bytes($pcr17);
exit;
sub dump_bytes {
my($bytes) = @_;
my @chars = unpack("C*", $bytes);
my $i;
for($i=0; $i<length($bytes); $i++) {
printf("%02X", $chars[$i]);
if(($i>0) && !(($i+1)%16)) {
print "\n";
} else {
print " ";
}
}
if(length($bytes)%16) {
print "\n";
}
}
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what you do best, core application coding. Discover what's new with
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