<s>
Direct	B-Application
Anonymous	I-Application
Attestation	I-Application
(	O
DAA	O
)	O
is	O
a	O
cryptographic	O
primitive	O
which	O
enables	O
remote	O
authentication	O
of	O
a	O
trusted	O
computer	O
whilst	O
preserving	O
privacy	O
of	O
the	O
platform	O
's	O
user	O
.	O
</s>
<s>
ISO/IEC	O
20008	O
specifies	O
DAA	O
,	O
as	O
well	O
,	O
and	O
Intel	O
's	O
Enhanced	B-Application
Privacy	I-Application
ID	I-Application
(	O
EPID	O
)	O
2.0	O
implementation	O
for	O
microprocessors	B-Architecture
is	O
available	O
for	O
licensing	O
RAND-Z	O
along	O
with	O
an	O
open	O
source	O
SDK	O
.	O
</s>
<s>
In	O
principle	O
the	O
privacy	O
issue	O
could	O
be	O
resolved	O
using	O
any	O
standard	O
signature	O
scheme	O
(	O
or	O
public	B-Application
key	I-Application
encryption	I-Application
)	O
and	O
a	O
single	O
key	B-Application
pair	I-Application
.	O
</s>
<s>
Manufacturers	O
would	O
embed	O
the	O
private	B-Application
key	I-Application
into	O
every	O
TPM	O
produced	O
and	O
the	O
public	B-Application
key	I-Application
would	O
be	O
published	O
as	O
a	O
certificate	O
.	O
</s>
<s>
Signatures	O
produced	O
by	O
the	O
TPM	O
must	O
have	O
originated	O
from	O
the	O
private	B-Application
key	I-Application
,	O
by	O
the	O
nature	O
of	O
the	O
technology	O
,	O
and	O
since	O
all	O
TPMs	O
use	O
the	O
same	O
private	B-Application
key	I-Application
they	O
are	O
indistinguishable	O
ensuring	O
the	O
user	O
's	O
privacy	O
.	O
</s>
<s>
One	O
only	O
needs	O
to	O
look	O
at	O
the	O
precedent	O
of	O
Content	B-Algorithm
Scramble	I-Algorithm
System	I-Algorithm
(	O
CSS	O
)	O
,	O
an	O
encryption	O
system	O
for	O
DVDs	O
,	O
to	O
see	O
that	O
this	O
assumption	O
is	O
fundamentally	O
flawed	O
.	O
</s>
<s>
Each	O
TPM	O
has	O
an	O
embedded	O
RSA	B-Architecture
key	B-Application
pair	I-Application
called	O
an	O
Endorsement	O
Key	O
(	O
EK	O
)	O
which	O
the	O
privacy	O
CA	O
is	O
assumed	O
to	O
know	O
.	O
</s>
<s>
In	O
order	O
to	O
attest	O
the	O
TPM	O
generates	O
a	O
second	O
RSA	B-Architecture
key	B-Application
pair	I-Application
called	O
an	O
Attestation	O
Identity	O
Key	O
(	O
AIK	O
)	O
.	O
</s>
<s>
The	O
EPID	O
2.0	O
solution	O
embeds	O
the	O
private	B-Application
key	I-Application
in	O
the	O
microprocessor	B-Architecture
when	O
it	O
is	O
manufactured	O
,	O
inherently	O
distributes	O
the	O
key	O
with	O
the	O
physical	O
device	O
shipment	O
,	O
and	O
has	O
the	O
key	O
provisioned	O
and	O
ready	O
for	O
use	O
with	O
1st	O
power-on	O
.	O
</s>
<s>
The	O
entities	O
are	O
the	O
DAA	O
Member	O
(	O
TPM	O
platform	O
or	O
EPID-enabled	O
microprocessor	B-Architecture
)	O
,	O
the	O
DAA	O
Issuer	O
and	O
the	O
DAA	O
Verifier	O
.	O
</s>
<s>
Through	O
a	O
zero-knowledge	B-Protocol
proof	I-Protocol
the	O
Verifier	O
can	O
verify	O
the	O
credential	O
without	O
attempting	O
to	O
violate	O
the	O
platform	O
's	O
privacy	O
.	O
</s>
<s>
The	O
first	O
Direct	B-Application
Anonymous	I-Application
Attestation	I-Application
scheme	O
was	O
due	O
to	O
Brickell	O
,	O
Camenisch	O
,	O
and	O
Chen	O
;	O
that	O
scheme	O
proved	O
insecure	O
and	O
required	O
a	O
fix	O
.	O
</s>
<s>
Brickell	O
,	O
Chen	O
,	O
and	O
Li	O
improved	O
efficiency	O
of	O
that	O
first	O
scheme	O
using	O
symmetric	O
pairings	O
,	O
rather	O
than	O
RSA	B-Architecture
.	O
</s>
