<s>
Secure	B-Protocol
Hypertext	I-Protocol
Transfer	I-Protocol
Protocol	I-Protocol
(	O
S-HTTP	B-Protocol
)	O
is	O
an	O
obsolete	O
alternative	O
to	O
the	O
HTTPS	B-Protocol
protocol	O
for	O
encrypting	O
web	O
communications	O
carried	O
over	O
the	O
Internet	O
.	O
</s>
<s>
Even	O
though	O
S-HTTP	B-Protocol
was	O
first	O
to	O
market	O
,	O
Netscape	O
's	O
dominance	O
of	O
the	O
browser	O
market	O
led	O
to	O
HTTPS	B-Protocol
becoming	O
the	O
de	O
facto	O
method	O
for	O
securing	O
web	O
communications	O
.	O
</s>
<s>
S-HTTP	B-Protocol
encrypts	O
only	O
the	O
served	O
page	O
data	O
and	O
submitted	O
data	O
like	O
POST	O
fields	O
,	O
leaving	O
the	O
initiation	O
of	O
the	O
protocol	O
unchanged	O
.	O
</s>
<s>
Because	O
of	O
this	O
,	O
S-HTTP	B-Protocol
could	O
be	O
used	O
concurrently	O
with	O
HTTP	B-Protocol
(	O
unsecured	O
)	O
on	O
the	O
same	O
port	O
,	O
as	O
the	O
unencrypted	O
header	O
would	O
determine	O
whether	O
the	O
rest	O
of	O
the	O
transmission	O
is	O
encrypted	O
.	O
</s>
<s>
In	O
contrast	O
,	O
HTTP	B-Protocol
over	O
TLS	O
wraps	O
the	O
entire	O
communication	O
within	O
Transport	B-Protocol
Layer	I-Protocol
Security	I-Protocol
(	O
TLS	O
;	O
formerly	O
SSL	O
)	O
,	O
so	O
the	O
encryption	O
starts	O
before	O
any	O
protocol	O
data	O
is	O
sent	O
.	O
</s>
<s>
This	O
creates	O
a	O
name-based	O
virtual	O
hosting	O
"	O
chicken	O
and	O
egg	O
"	O
issue	O
with	O
determining	O
which	O
DNS	B-Protocol
name	I-Protocol
was	O
intended	O
for	O
the	O
request	O
.	O
</s>
<s>
This	O
means	O
that	O
HTTPS	B-Protocol
implementations	O
without	O
Server	B-Protocol
Name	I-Protocol
Indication	I-Protocol
(	O
SNI	O
)	O
support	O
require	O
a	O
separate	O
IP	B-Protocol
address	I-Protocol
per	O
DNS	B-Protocol
name	I-Protocol
,	O
and	O
all	O
HTTPS	B-Protocol
implementations	O
require	O
a	O
separate	O
port	O
(	O
usually	O
443	O
vs.	O
HTTP	B-Protocol
's	O
standard	O
80	O
)	O
for	O
unambiguous	O
use	O
of	O
encryption	O
(	O
treated	O
in	O
most	O
browsers	O
as	O
a	O
separate	O
URI	O
scheme	O
,	O
https://	O
)	O
.	O
</s>
<s>
As	O
documented	O
in	O
RFC	O
2817	O
,	O
HTTP	B-Protocol
can	O
also	O
be	O
secured	O
by	O
implementing	O
HTTP/1.1	B-Protocol
Upgrade	I-Protocol
headers	I-Protocol
and	O
upgrading	O
to	O
TLS	O
.	O
</s>
<s>
Running	O
HTTP	B-Protocol
over	O
TLS	O
negotiated	O
in	O
this	O
way	O
does	O
not	O
have	O
the	O
implications	O
of	O
HTTPS	B-Protocol
with	O
regards	O
to	O
name-based	O
virtual	O
hosting	O
(	O
no	O
extra	O
IP	B-Protocol
addresses	I-Protocol
,	O
ports	O
,	O
or	O
URI	O
space	O
)	O
.	O
</s>
<s>
In	O
S-HTTP	B-Protocol
,	O
the	O
desired	O
URL	O
is	O
not	O
transmitted	O
in	O
the	O
cleartext	O
headers	O
,	O
but	O
left	O
blank	O
;	O
another	O
set	O
of	O
headers	O
is	O
present	O
inside	O
the	O
encrypted	O
payload	O
.	O
</s>
<s>
In	O
HTTP	B-Protocol
over	O
TLS	O
,	O
all	O
headers	O
are	O
inside	O
the	O
encrypted	O
payload	O
and	O
the	O
server	O
application	O
does	O
not	O
generally	O
have	O
the	O
opportunity	O
to	O
gracefully	O
recover	O
from	O
TLS	O
fatal	O
errors	O
(	O
including	O
'	O
client	O
certificate	O
is	O
untrusted	O
 '	O
and	O
'	O
client	O
certificate	O
is	O
expired	O
 '	O
)	O
.	O
</s>
