<s>
A	O
TLS	B-Protocol
termination	I-Protocol
proxy	I-Protocol
(	O
or	O
SSL	B-Protocol
termination	I-Protocol
proxy	I-Protocol
,	O
or	O
SSL	B-Protocol
offloading	I-Protocol
)	O
is	O
a	O
proxy	B-Application
server	I-Application
that	O
acts	O
as	O
an	O
intermediary	O
point	O
between	O
client	B-Protocol
and	O
server	B-Application
applications	I-Application
,	O
and	O
is	O
used	O
to	O
terminate	O
and/or	O
establish	O
TLS	B-Protocol
(	O
or	O
DTLS	B-Protocol
)	O
tunnels	B-Protocol
by	O
decrypting	O
and/or	O
encrypting	O
communications	O
.	O
</s>
<s>
This	O
is	O
different	O
to	O
TLS	B-Protocol
pass-through	O
proxies	O
that	O
forward	O
encrypted	O
(	O
D	O
)	O
TLS	B-Protocol
traffic	O
between	O
clients	O
and	O
servers	O
without	O
terminating	O
the	O
tunnel	O
.	O
</s>
<s>
TLS	B-Protocol
termination	I-Protocol
proxies	I-Protocol
can	O
be	O
used	O
to	O
:	O
</s>
<s>
secure	O
plaintext	O
communications	O
over	O
untrusted	O
networks	O
by	O
tunnelling	O
them	O
in	O
(	O
D	O
)	O
TLS	B-Protocol
,	O
</s>
<s>
enable	O
otherwise	O
unsupported	O
integration	O
with	O
other	O
applications	O
that	O
provide	O
additional	O
capabilities	O
such	O
as	O
content	B-Protocol
filtering	I-Protocol
or	O
Hardware	O
security	O
module	O
,	O
</s>
<s>
enable	O
(	O
D	O
)	O
TLS	B-Protocol
protocol	I-Protocol
versions	O
,	O
extensions	O
,	O
or	O
capabilities	O
(	O
e.g.	O
</s>
<s>
OCSP	B-Protocol
stapling	I-Protocol
,	O
ALPN	B-Protocol
,	O
DANE	B-Protocol
,	O
CT	B-Protocol
validation	O
,	O
etc	O
.	O
)	O
</s>
<s>
unsupported	O
by	O
client	B-Protocol
or	O
server	B-Application
applications	I-Application
to	O
enhance	O
their	O
compatibility	O
and/or	O
security	O
,	O
</s>
<s>
work	O
around	O
buggy/insecure	O
(	O
D	O
)	O
TLS	B-Protocol
implementations	O
in	O
client	B-Protocol
or	O
server	B-Application
applications	I-Application
to	O
improve	O
their	O
compatibility	O
and/or	O
security	O
,	O
</s>
<s>
provide	O
additional	O
certificate-based	O
authentication	O
unsupported	O
by	O
server	B-Application
and/or	O
client	B-Protocol
applications	I-Protocol
or	O
protocols	O
,	O
</s>
<s>
reduce	O
the	O
load	B-Operating_System
on	O
the	O
main	O
servers	O
by	O
offloading	O
the	O
cryptographic	O
processing	O
to	O
another	O
machine	O
.	O
</s>
<s>
TLS	B-Protocol
termination	I-Protocol
proxies	I-Protocol
can	O
provide	O
three	O
connectivity	O
patterns	O
:	O
</s>
<s>
TLS	B-Protocol
Offloading	O
of	O
inbound	O
encrypted	O
(	O
D	O
)	O
TLS	B-Protocol
connection	O
from	O
a	O
client	B-Protocol
and	O
forwarding	O
communications	O
over	O
a	O
plain	O
text	O
connection	O
to	O
the	O
server	B-Application
.	O
</s>
<s>
TLS	B-Protocol
Encryption	I-Protocol
of	O
inbound	O
plaintext	O
connection	O
from	O
a	O
client	B-Protocol
and	O
forwarding	O
communications	O
over	O
an	O
encrypted	O
(	O
D	O
)	O
TLS	B-Protocol
connection	O
to	O
the	O
server	B-Application
.	O
</s>
<s>
TLS	B-Protocol
Bridging	O
of	O
two	O
encrypted	O
(	O
D	O
)	O
TLS	B-Protocol
connections	O
to	O
allow	O
inspection	O
and	O
filtering	O
of	O
encrypted	O
traffic	O
by	O
decrypting	O
inbound	O
(	O
D	O
)	O
TLS	B-Protocol
connection	O
from	O
a	O
client	B-Protocol
and	O
re-encrypting	O
it	O
with	O
another	O
(	O
D	O
)	O
TLS	B-Protocol
connection	O
to	O
the	O
server	B-Application
.	O
</s>
<s>
Combining	O
a	O
TLS	B-Protocol
Encrypting	O
proxy	O
in	O
front	O
of	O
a	O
client	B-Protocol
with	O
a	O
TLS	B-Protocol
Offloading	O
proxy	O
in	O
front	O
of	O
a	O
server	B-Application
,	O
can	O
allow	O
(	O
D	O
)	O
TLS	B-Protocol
encryption	I-Protocol
and	O
authentication	O
for	O
protocols	O
and	O
applications	O
that	O
do	O
n't	O
otherwise	O
support	O
it	O
,	O
with	O
two	O
proxies	O
maintaining	O
a	O
secure	O
(	O
D	O
)	O
TLS	B-Protocol
tunnel	O
over	O
untrusted	O
network	O
segments	O
between	O
client	B-Protocol
and	O
server	B-Application
.	O
</s>
<s>
A	O
proxy	O
used	O
by	O
clients	O
as	O
an	O
intermediary	O
gateway	O
for	O
all	O
outbound	O
connections	O
is	O
typically	O
called	O
a	O
Forward	O
proxy	O
,	O
while	O
a	O
proxy	O
used	O
by	O
servers	O
as	O
an	O
intermediary	O
gateway	O
for	O
all	O
inbound	O
connections	O
is	O
typically	O
called	O
a	O
Reverse	B-General_Concept
proxy	I-General_Concept
.	O
</s>
<s>
Forward	O
TLS	B-Protocol
bridging	O
proxies	O
that	O
allow	O
intrusion	O
detection	O
system	O
to	O
analyse	O
all	O
client	B-Protocol
traffic	O
are	O
typically	O
marketed	O
as	O
"	O
SSL	O
Forward	O
Proxy	O
"	O
.	O
</s>
<s>
TLS	B-Protocol
Offloading	O
and	O
TLS	B-Protocol
Bridging	O
proxies	O
typically	O
need	O
to	O
authenticate	O
themselves	O
to	O
clients	O
with	O
a	O
digital	O
certificate	O
using	O
either	O
PKIX	O
or	O
DANE	B-Protocol
authentication	O
.	O
</s>
<s>
Usually	O
the	O
server	B-Application
operator	O
supplies	O
to	O
its	O
reverse	B-General_Concept
proxy	I-General_Concept
a	O
valid	O
certificate	O
for	O
use	O
during	O
(	O
D	O
)	O
TLS	B-Protocol
handshake	O
with	O
clients	O
.	O
</s>
<s>
A	O
forward	O
proxy	O
operator	O
,	O
however	O
would	O
need	O
to	O
create	O
their	O
own	O
private	O
CA	B-Architecture
,	O
install	O
it	O
into	O
the	O
trust	O
store	O
of	O
all	O
clients	O
and	O
have	O
the	O
proxy	O
generate	O
a	O
new	O
certificate	O
signed	O
by	O
the	O
private	O
CA	B-Architecture
in	O
real	O
time	O
for	O
each	O
server	B-Application
that	O
a	O
client	B-Protocol
tries	O
to	O
connect	O
to	O
.	O
</s>
<s>
When	O
network	O
traffic	O
between	O
client	B-Protocol
and	O
server	B-Application
is	O
routed	O
via	O
a	O
proxy	O
,	O
it	O
can	O
operate	O
in	O
transparent	O
mode	O
by	O
using	O
the	O
client	B-Protocol
's	O
IP	B-Protocol
address	I-Protocol
instead	O
of	O
its	O
own	O
when	O
connecting	O
to	O
the	O
server	B-Application
and	O
using	O
the	O
server	B-Application
's	O
IP	B-Protocol
address	I-Protocol
when	O
responding	O
to	O
the	O
client	B-Protocol
.	O
</s>
<s>
If	O
a	O
Transparent	O
TLS	B-Protocol
Bridging	O
Proxy	O
has	O
a	O
valid	O
server	B-Application
certificate	O
,	O
neither	O
client	B-Protocol
nor	O
server	B-Application
would	O
be	O
able	O
to	O
detect	O
the	O
proxy	O
presence	O
.	O
</s>
<s>
An	O
adversary	O
that	O
has	O
compromised	O
the	O
private	O
key	O
of	O
the	O
server	B-Application
's	O
digital	O
certificate	O
or	O
is	O
able	O
to	O
use	O
a	O
compromised/coerced	O
PKIX	O
CAs	O
to	O
issue	O
a	O
new	O
valid	O
certificate	O
for	O
the	O
server	B-Application
,	O
could	O
perform	O
a	O
man-in-the-middle	O
attack	O
by	O
routing	O
TLS	B-Protocol
traffic	O
between	O
client	B-Protocol
and	O
server	B-Application
through	O
a	O
Transparent	O
TLS	B-Protocol
Bridging	O
Proxy	O
and	O
would	O
have	O
the	O
ability	O
to	O
copy	O
decrypted	O
communications	O
,	O
including	O
logon	O
credentials	O
,	O
and	O
modify	O
content	O
of	O
communications	O
on	O
the	O
fly	O
without	O
being	O
detected	O
.	O
</s>
