<s>
In	O
computing	O
,	O
the	O
SSH	B-Protocol
File	I-Protocol
Transfer	I-Protocol
Protocol	I-Protocol
(	O
also	O
known	O
as	O
Secure	O
File	B-Protocol
Transfer	I-Protocol
Protocol	I-Protocol
or	O
SFTP	O
)	O
is	O
a	O
network	O
protocol	O
that	O
provides	O
file	B-Application
access	I-Application
,	O
file	B-Protocol
transfer	I-Protocol
,	O
and	O
file	B-Application
management	I-Application
over	O
any	O
reliable	O
data	B-General_Concept
stream	I-General_Concept
.	O
</s>
<s>
It	O
was	O
designed	O
by	O
the	O
Internet	O
Engineering	O
Task	O
Force	O
(	O
IETF	O
)	O
as	O
an	O
extension	O
of	O
the	O
Secure	B-Protocol
Shell	I-Protocol
protocol	I-Protocol
(	O
SSH	B-Protocol
)	O
version	O
2.0	O
to	O
provide	O
secure	O
file	B-Protocol
transfer	I-Protocol
capabilities	O
.	O
</s>
<s>
The	O
IETF	O
Internet	O
Draft	O
states	O
that	O
,	O
even	O
though	O
this	O
protocol	O
is	O
described	O
in	O
the	O
context	O
of	O
the	O
SSH-2	O
protocol	O
,	O
it	O
could	O
be	O
used	O
in	O
a	O
number	O
of	O
different	O
applications	O
,	O
such	O
as	O
secure	O
file	B-Protocol
transfer	I-Protocol
over	O
Transport	B-Protocol
Layer	I-Protocol
Security	I-Protocol
(	O
TLS	O
)	O
and	O
transfer	O
of	O
management	O
information	O
in	O
VPN	B-Application
applications	O
.	O
</s>
<s>
This	O
protocol	O
assumes	O
that	O
it	O
is	O
run	O
over	O
a	O
secure	O
channel	O
,	O
such	O
as	O
SSH	B-Protocol
,	O
that	O
the	O
server	O
has	O
already	O
authenticated	O
the	O
client	B-Protocol
,	O
and	O
that	O
the	O
identity	O
of	O
the	O
client	B-Protocol
user	O
is	O
available	O
to	O
the	O
protocol	O
.	O
</s>
<s>
Compared	O
to	O
the	O
SCP	B-Protocol
protocol	O
,	O
which	O
only	O
allows	O
file	B-Protocol
transfers	I-Protocol
,	O
the	O
SFTP	O
protocol	O
allows	O
for	O
a	O
range	O
of	O
operations	O
on	O
remote	O
files	O
which	O
make	O
it	O
more	O
like	O
a	O
remote	O
file	B-Application
system	I-Application
protocol	O
.	O
</s>
<s>
An	O
SFTP	O
client	B-Protocol
's	O
extra	O
capabilities	O
include	O
resuming	O
interrupted	O
transfers	O
,	O
directory	O
listings	O
,	O
and	O
remote	O
file	O
removal	O
.	O
</s>
<s>
SFTP	O
attempts	O
to	O
be	O
more	O
platform-independent	O
than	O
SCP	B-Protocol
;	O
with	O
SCP	B-Protocol
,	O
for	O
instance	O
,	O
the	O
expansion	O
of	O
wildcards	B-Algorithm
specified	O
by	O
the	O
client	B-Protocol
is	O
up	O
to	O
the	O
server	O
,	O
whereas	O
SFTP	O
's	O
design	O
avoids	O
this	O
problem	O
.	O
</s>
<s>
While	O
SCP	B-Protocol
is	O
most	O
frequently	O
implemented	O
on	O
Unix	B-Application
platforms	O
,	O
SFTP	O
servers	O
are	O
commonly	O
available	O
on	O
most	O
platforms	O
.	O
</s>
<s>
The	O
file	B-Protocol
transfer	I-Protocol
is	O
fast	O
in	O
SCP	B-Protocol
when	O
compared	O
to	O
the	O
SFTP	O
protocol	O
due	O
to	O
the	O
back	O
and	O
forth	O
nature	O
of	O
the	O
SFTP	O
protocol	O
.	O
</s>
<s>
In	O
SFTP	O
,	O
the	O
file	B-Protocol
transfer	I-Protocol
can	O
be	O
easily	O
terminated	O
without	O
terminating	O
a	O
session	O
like	O
other	O
mechanisms	O
do	O
.	O
</s>
<s>
SFTP	O
is	O
not	O
FTP	B-Protocol
run	O
over	O
SSH	B-Protocol
,	O
but	O
rather	O
a	O
new	O
protocol	O
designed	O
from	O
the	O
ground	O
up	O
by	O
the	O
IETF	O
SECSH	O
working	O
group	O
.	O
</s>
<s>
It	O
is	O
sometimes	O
confused	O
with	O
Simple	O
File	B-Protocol
Transfer	I-Protocol
Protocol	I-Protocol
.	O
</s>
<s>
SFTP	O
is	O
most	O
often	O
used	O
as	O
subsystem	O
of	O
SSH	B-Protocol
protocol	O
version	O
2	O
implementations	O
,	O
having	O
been	O
designed	O
by	O
the	O
same	O
working	O
group	O
.	O
</s>
<s>
It	O
is	O
possible	O
,	O
however	O
,	O
to	O
run	O
it	O
over	O
SSH-1	O
(	O
and	O
some	O
implementations	O
support	O
this	O
)	O
or	O
other	O
data	B-General_Concept
streams	I-General_Concept
.	O
</s>
<s>
Running	O
an	O
SFTP	O
server	O
over	O
SSH-1	O
is	O
not	O
platform-independent	O
as	O
SSH-1	O
does	O
not	O
support	O
the	O
concept	O
of	O
subsystems	O
.	O
</s>
<s>
An	O
SFTP	O
client	B-Protocol
willing	O
to	O
connect	O
to	O
an	O
SSH-1	O
server	O
needs	O
to	O
know	O
the	O
path	O
to	O
the	O
SFTP	O
server	O
binary	O
on	O
the	O
server	O
side	O
.	O
</s>
<s>
This	O
is	O
an	O
advantage	O
over	O
the	O
common	O
FTP	B-Protocol
protocol	I-Protocol
.	O
</s>
<s>
The	O
Internet	O
Engineering	O
Task	O
Force	O
(	O
IETF	O
)	O
working	O
group	O
"	O
Secsh	O
"	O
that	O
was	O
responsible	O
for	O
the	O
development	O
of	O
the	O
Secure	B-Protocol
Shell	I-Protocol
version	O
2	O
protocol	O
(	O
RFC	O
4251	O
)	O
also	O
attempted	O
to	O
draft	O
an	O
extension	O
of	O
that	O
standard	O
for	O
secure	O
file	B-Protocol
transfer	I-Protocol
functionality	O
.	O
</s>
<s>
As	O
development	O
work	O
progressed	O
,	O
the	O
scope	O
of	O
the	O
Secsh	O
File	B-Protocol
Transfer	I-Protocol
project	O
expanded	O
to	O
include	O
file	B-Application
access	I-Application
and	O
file	B-Application
management	I-Application
.	O
</s>
<s>
Eventually	O
,	O
development	O
stalled	O
as	O
some	O
committee	O
members	O
began	O
to	O
view	O
SFTP	O
as	O
a	O
file	B-Application
system	I-Application
protocol	O
,	O
not	O
just	O
a	O
file	B-Application
access	I-Application
or	O
file	B-Protocol
transfer	I-Protocol
protocol	I-Protocol
,	O
which	O
places	O
it	O
beyond	O
the	O
purview	O
of	O
the	O
working	O
group	O
.	O
</s>
<s>
Prior	O
to	O
the	O
IETF	O
's	O
involvement	O
,	O
SFTP	O
was	O
a	O
proprietary	O
protocol	O
of	O
SSH	B-Protocol
Communications	O
Security	O
,	O
designed	O
by	O
Tatu	O
Ylönen	O
with	O
assistance	O
from	O
Sami	O
Lehtinen	O
in	O
1997	O
.	O
</s>
<s>
At	O
the	O
outset	O
of	O
the	O
IETF	O
Secure	B-Protocol
Shell	I-Protocol
File	B-Protocol
Transfer	I-Protocol
project	O
,	O
the	O
Secsh	O
group	O
stated	O
that	O
its	O
objective	O
of	O
SSH	B-Protocol
File	I-Protocol
Transfer	I-Protocol
Protocol	I-Protocol
was	O
to	O
provide	O
a	O
secure	O
file	B-Protocol
transfer	I-Protocol
functionality	O
over	O
any	O
reliable	O
data	B-General_Concept
stream	I-General_Concept
,	O
and	O
to	O
be	O
the	O
standard	O
file	B-Protocol
transfer	I-Protocol
protocol	I-Protocol
for	O
use	O
with	O
the	O
SSH-2	O
protocol	O
.	O
</s>
<s>
The	O
term	O
SFTP	O
can	O
also	O
refer	O
to	O
Secure	B-Protocol
file	I-Protocol
transfer	I-Protocol
program	I-Protocol
,	O
a	O
command-line	B-Application
program	I-Application
that	O
implements	O
the	O
client	B-Protocol
part	O
of	O
this	O
protocol	O
.	O
</s>
<s>
As	O
an	O
example	O
,	O
the	O
sftp	O
program	B-Application
supplied	O
with	O
OpenSSH	B-Language
implements	O
this	O
.	O
</s>
<s>
Some	O
implementations	O
of	O
the	O
scp	B-Protocol
program	B-Application
support	O
both	O
the	O
SFTP	O
and	O
SCP	B-Protocol
protocols	O
to	O
perform	O
file	B-Protocol
transfers	I-Protocol
,	O
depending	O
on	O
what	O
the	O
server	O
supports	O
.	O
</s>
<s>
Some	O
FTP	B-Protocol
server	I-Protocol
implementations	I-Protocol
implement	O
the	O
SFTP	O
protocol	O
;	O
however	O
,	O
outside	O
of	O
dedicated	O
file	O
servers	O
,	O
SFTP	O
protocol	O
support	O
is	O
usually	O
provided	O
by	O
an	O
SSH	B-Protocol
server	I-Protocol
implementation	I-Protocol
,	O
as	O
it	O
shares	O
the	O
default	O
port	O
of	O
22	O
with	O
other	O
SSH	B-Protocol
services	O
.	O
</s>
<s>
SFTP	O
implementations	O
may	O
include	O
an	O
SSH	B-Protocol
protocol	O
implementation	O
to	O
leverage	O
integration	O
of	O
SSH	B-Protocol
connection	O
details	O
with	O
preexisting	O
FTP	B-Protocol
server	I-Protocol
access	O
controls	O
,	O
where	O
an	O
alternative	O
SSH	B-Protocol
server	I-Protocol
is	O
tolerable	O
or	O
where	O
alternative	O
ports	O
may	O
be	O
used	O
.	O
</s>
<s>
An	O
SSH-2	O
server	O
which	O
supports	O
subsystems	O
may	O
be	O
leveraged	O
to	O
keep	O
a	O
uniform	O
SSH	B-Protocol
implementation	O
while	O
enhancing	O
access	O
controls	O
with	O
third	O
party	O
software	O
,	O
at	O
the	O
cost	O
of	O
fine-grained	O
integration	O
with	O
connection	O
details	O
,	O
and	O
SSH-1	O
compatibility	O
.	O
</s>
<s>
There	O
are	O
standard	O
tools	O
for	O
logging	O
FTP	B-Protocol
transactions	O
,	O
like	O
TIS	O
gdev	O
or	O
SUSE	O
FTP	B-Protocol
proxy	O
,	O
but	O
SFTP	O
is	O
encrypted	O
,	O
rendering	O
traditional	O
proxies	O
ineffective	O
for	O
controlling	O
SFTP	O
traffic	O
.	O
</s>
<s>
There	O
are	O
some	O
tools	O
that	O
implement	O
man-in-the-middle	O
for	O
SSH	B-Protocol
which	O
also	O
feature	O
SFTP	O
control	O
.	O
</s>
<s>
Examples	O
of	O
such	O
a	O
tool	O
are	O
Shell	O
Control	O
Box	O
from	O
Balabit	O
and	O
CryptoAuditor	O
from	O
SSH	B-Protocol
Communications	O
Security	O
(	O
the	O
original	O
developer	O
of	O
the	O
Secure	B-Protocol
Shell	I-Protocol
protocol	I-Protocol
)	O
which	O
provides	O
functions	O
such	O
as	O
SFTP	O
transaction	O
logging	O
and	O
logging	O
of	O
the	O
actual	O
data	O
transmitted	O
on	O
the	O
wire	O
.	O
</s>
