<s>
In	O
computer	B-General_Concept
science	I-General_Concept
,	O
a	O
session	B-Protocol
identifier	I-Protocol
,	O
session	B-Protocol
ID	I-Protocol
or	O
session	B-Protocol
token	I-Protocol
is	O
a	O
piece	O
of	O
data	O
that	O
is	O
used	O
in	O
network	O
communications	O
(	O
often	O
over	O
HTTPS	B-Protocol
)	O
to	O
identify	O
a	O
session	B-Protocol
,	O
a	O
series	O
of	O
related	O
message	O
exchanges	O
.	O
</s>
<s>
Session	B-Protocol
identifiers	I-Protocol
become	O
necessary	O
in	O
cases	O
where	O
the	O
communications	O
infrastructure	O
uses	O
a	O
stateless	B-Protocol
protocol	I-Protocol
such	O
as	O
HTTP	B-Protocol
.	I-Protocol
</s>
<s>
In	O
such	O
a	O
situation	O
,	O
it	O
is	O
vital	O
to	O
keep	O
track	O
of	O
the	O
current	O
state	O
of	O
the	O
shopper	O
's	O
cart	O
,	O
and	O
a	O
session	B-Protocol
ID	I-Protocol
is	O
one	O
way	O
to	O
achieve	O
that	O
goal	O
.	O
</s>
<s>
A	O
session	B-Protocol
ID	I-Protocol
is	O
typically	O
granted	O
to	O
a	O
visitor	O
on	O
their	O
first	O
visit	O
to	O
a	O
site	O
.	O
</s>
<s>
It	O
is	O
different	O
from	O
a	O
user	O
ID	O
in	O
that	O
sessions	O
are	O
typically	O
short-lived	O
(	O
they	O
expire	O
after	O
a	O
preset	O
time	O
of	O
inactivity	O
which	O
may	O
be	O
minutes	O
or	O
hours	O
)	O
and	O
may	O
become	O
invalid	O
after	O
a	O
certain	O
goal	O
has	O
been	O
met	O
(	O
for	O
example	O
,	O
once	O
the	O
buyer	O
has	O
finalized	O
their	O
order	O
,	O
they	O
cannot	O
use	O
the	O
same	O
session	B-Protocol
ID	I-Protocol
to	O
add	O
more	O
items	O
)	O
.	O
</s>
<s>
As	O
session	B-Protocol
IDs	I-Protocol
are	O
often	O
used	O
to	O
identify	O
a	O
user	O
that	O
has	O
logged	O
into	O
a	O
website	O
,	O
they	O
can	O
be	O
used	O
by	O
an	O
attacker	O
to	O
hijack	B-Protocol
the	I-Protocol
session	I-Protocol
and	O
obtain	O
potential	O
privileges	O
.	O
</s>
<s>
A	O
session	B-Protocol
ID	I-Protocol
is	O
usually	O
a	O
randomly	O
generated	O
string	O
to	O
decrease	O
the	O
probability	O
of	O
obtaining	O
a	O
valid	O
one	O
by	O
means	O
of	O
a	O
brute-force	B-Algorithm
search	I-Algorithm
.	O
</s>
<s>
Many	O
servers	O
perform	O
additional	O
verification	O
of	O
the	O
client	O
,	O
in	O
case	O
the	O
attacker	O
has	O
obtained	O
the	O
session	B-Protocol
ID	I-Protocol
.	O
</s>
<s>
Locking	O
a	O
session	B-Protocol
ID	I-Protocol
to	O
the	O
client	O
's	O
IP	B-Protocol
address	I-Protocol
is	O
a	O
simple	O
and	O
effective	O
measure	O
as	O
long	O
as	O
the	O
attacker	O
cannot	O
connect	O
to	O
the	O
server	O
from	O
the	O
same	O
address	O
,	O
but	O
can	O
conversely	O
cause	O
problems	O
for	O
a	O
client	O
if	O
the	O
client	O
has	O
multiple	O
routes	O
to	O
the	O
server	O
(	O
e.g.	O
</s>
<s>
redundant	O
internet	O
connections	O
)	O
and	O
the	O
client	O
's	O
IP	B-Protocol
address	I-Protocol
undergoes	O
Network	B-Protocol
Address	I-Protocol
Translation	I-Protocol
.	O
</s>
<s>
Examples	O
of	O
the	O
names	O
that	O
some	O
programming	O
languages	O
use	O
when	O
naming	O
their	O
cookie	O
include	O
JSESSIONID	B-Protocol
(	O
Java	B-Language
EE	I-Language
)	O
,	O
PHPSESSID	B-Protocol
(	O
PHP	B-Application
)	O
,	O
and	O
ASPSESSIONID	O
(	O
Microsoft	O
ASP	B-General_Concept
)	O
.	O
</s>
