<s>
Generic	B-Protocol
Bootstrapping	I-Protocol
Architecture	I-Protocol
(	O
GBA	O
)	O
is	O
a	O
technology	O
that	O
enables	O
the	O
authentication	O
of	O
a	O
user	O
.	O
</s>
<s>
-	O
There	O
is	O
no	O
need	O
for	O
user	O
enrollment	O
phase	O
nor	O
secure	O
deployment	O
of	O
keys	O
,	O
making	O
this	O
solution	O
a	O
very	O
low	O
cost	O
one	O
when	O
compared	O
to	O
PKI	B-Architecture
.	O
</s>
<s>
-	O
Another	O
advantage	O
is	O
the	O
ease	O
with	O
which	O
the	O
authentication	O
method	O
may	O
be	O
integrated	O
into	O
terminals	O
and	O
service	O
providers	O
,	O
as	O
it	O
is	O
based	O
on	O
HTTP	B-Protocol
's	O
well	O
known	O
"	O
Digest	B-Protocol
access	I-Protocol
authentication	I-Protocol
"	O
.	O
</s>
<s>
Every	O
Web	O
server	O
already	O
implement	O
HTTP	B-Protocol
digest	I-Protocol
authentication	I-Protocol
and	O
the	O
effort	O
to	O
implement	O
GBA	O
on	O
top	O
of	O
digest	B-Protocol
authentication	I-Protocol
is	O
minimal	O
.	O
</s>
<s>
A	O
Web	O
browser	O
(	O
in	O
fact	O
an	O
HTTP	B-Protocol
client	O
)	O
implementing	O
digest	B-Protocol
authentication	I-Protocol
and	O
the	O
special	O
case	O
designed	O
by	O
a	O
"	O
3gpp	O
"	O
string	O
in	O
the	O
HTTP	B-Protocol
header	O
.	O
</s>
<s>
In	O
the	O
shared	O
secret	O
cases	O
,	O
the	O
customer	O
and	O
the	O
operator	O
are	O
first	O
mutually	O
authenticated	O
through	O
3G	O
and	O
Authentication	O
Key	O
(	O
AKA	B-Protocol
)	O
and	O
they	O
agree	O
on	O
session	O
keys	O
which	O
can	O
then	O
be	O
used	O
between	O
the	O
client	O
and	O
services	O
that	O
the	O
customer	O
wants	O
to	O
use	O
.	O
</s>
<s>
Bootstrapping	O
Server	O
Function	O
(	O
BSF	O
)	O
mutually	O
authenticate	O
themselves	O
during	O
the	O
Ub	O
(	O
number	O
 [ 2 ] 	O
above	O
)	O
interface	O
,	O
using	O
the	O
Digest	B-Protocol
access	I-Protocol
authentication	I-Protocol
AKA	B-Protocol
protocol	O
.	O
</s>
<s>
Diameter	B-Protocol
Base	O
Protocol	O
.	O
</s>
<s>
NAFs	O
recover	O
the	O
key	O
session	O
of	O
BSF	O
during	O
the	O
Zn	O
 [ 5 ] 	O
interface	O
,	O
which	O
also	O
uses	O
the	O
diameter	B-Protocol
at	O
the	O
base	O
Protocol	O
.	O
</s>
