<s>
The	O
ANSI	O
X9.95	O
standard	O
for	O
trusted	O
timestamps	O
expands	O
on	O
the	O
widely	O
used	O
-	O
Internet	O
X.509	O
Public	B-Application
Key	I-Application
Infrastructure	O
Time-Stamp	O
Protocol	O
by	O
adding	O
data-level	O
security	O
requirements	O
that	O
can	O
ensure	O
data	O
integrity	O
against	O
a	O
reliable	O
time	O
source	O
that	O
is	O
provable	O
to	O
any	O
third	O
party	O
.	O
</s>
<s>
A	O
superset	O
of	O
the	O
IETF	O
's	O
RFC	O
3161	O
protocol	O
,	O
the	O
X9.95	O
standard	O
includes	O
definitions	O
for	O
specific	O
data	O
objects	O
,	O
message	O
protocols	O
,	O
and	O
trusted	O
timestamp	O
methods	O
,	O
such	O
as	O
digital	O
signature	O
,	O
MAC	B-Algorithm
,	O
linked	O
token	O
,	O
linked-and-signature	O
and	O
transient-key	O
methods	O
.	O
</s>
<s>
Other	O
regulatory	O
frameworks	O
also	O
require	O
that	O
time	O
that	O
is	O
moved	O
through	O
the	O
Network	B-Protocol
Time	I-Protocol
Protocol	I-Protocol
ntp	B-Protocol
is	O
properly	O
certified	O
and	O
authenticated	O
meaning	O
unauthenticated	O
use	O
of	O
time	O
from	O
any	O
provider	O
will	O
fail	O
X9.95	O
requirements	O
for	O
obtaining	O
time	O
in	O
a	O
provable	O
manner	O
.	O
</s>
<s>
When	O
a	O
requestor	O
requires	O
a	O
trusted	O
timestamp	O
for	O
a	O
piece	O
of	O
data	O
,	O
it	O
creates	O
a	O
hash	B-Algorithm
of	O
the	O
data	O
using	O
a	O
cryptographic	B-Algorithm
hash	I-Algorithm
function	I-Algorithm
and	O
sends	O
it	O
to	O
the	O
TSA	O
(	O
through	O
a	O
network	O
connection	O
)	O
.	O
</s>
<s>
The	O
TSA	O
then	O
signs	O
the	O
hash	B-Algorithm
and	O
the	O
time	O
of	O
signature	O
to	O
create	O
a	O
trusted	O
timestamp	O
.	O
</s>
<s>
For	O
applications	O
using	O
digitally	O
signed	O
data	O
,	O
the	O
requestor	O
signs	O
the	O
digital	O
hash	B-Algorithm
with	O
its	O
private	B-Application
key	I-Application
and	O
submits	O
the	O
digital	O
signature	O
to	O
the	O
TSA	O
,	O
which	O
performs	O
the	O
same	O
operations	O
as	O
in	O
the	O
previous	O
example	O
:	O
bind	O
the	O
submitted	O
data	O
with	O
a	O
timestamp	O
using	O
its	O
cryptographic	O
binding	O
and	O
return	O
the	O
results	O
to	O
the	O
requestor	O
.	O
</s>
<s>
When	O
the	O
requestor	O
receives	O
the	O
timestamp	O
token	O
from	O
the	O
TSA	O
,	O
it	O
also	O
optionally	O
signs	O
the	O
token	O
with	O
its	O
private	B-Application
key	I-Application
.	O
</s>
<s>
When	O
verification	O
is	O
needed	O
,	O
the	O
verifier	O
uses	O
the	O
RSA	B-Architecture
public	I-Architecture
key	I-Architecture
for	O
the	O
purported	O
interval	O
to	O
decrypt	O
the	O
timestamp	O
token	O
.	O
</s>
<s>
If	O
the	O
original	O
digital	O
hash	B-Algorithm
inside	O
the	O
token	O
matches	O
a	O
hash	B-Algorithm
generated	O
on	O
the	O
spot	O
,	O
then	O
the	O
verifier	O
has	O
verified	O
:	O
</s>
<s>
Since	O
public	B-Application
keys	I-Application
are	O
used	O
to	O
decrypt	O
the	O
tokens	O
,	O
this	O
evidence	O
can	O
be	O
provided	O
to	O
any	O
third	O
party	O
.	O
</s>
