<s>
DNS-based	B-Protocol
Authentication	I-Protocol
of	I-Protocol
Named	I-Protocol
Entities	I-Protocol
(	O
DANE	O
)	O
is	O
an	O
Internet	B-Application
security	I-Application
protocol	O
to	O
allow	O
X.509	O
digital	O
certificates	O
,	O
commonly	O
used	O
for	O
Transport	B-Protocol
Layer	I-Protocol
Security	I-Protocol
(	O
TLS	O
)	O
,	O
to	O
be	O
bound	O
to	O
domain	O
names	O
using	O
Domain	B-Protocol
Name	I-Protocol
System	I-Protocol
Security	I-Protocol
Extensions	I-Protocol
(	O
DNSSEC	B-Protocol
)	O
.	O
</s>
<s>
It	O
is	O
proposed	O
in	O
as	O
a	O
way	O
to	O
authenticate	O
TLS	O
client	O
and	O
server	O
entities	O
without	O
a	O
certificate	B-Architecture
authority	I-Architecture
(	O
CA	B-Architecture
)	O
.	O
</s>
<s>
TLS/SSL	B-Protocol
encryption	O
is	O
currently	O
based	O
on	O
certificates	O
issued	O
by	O
certificate	B-Architecture
authorities	I-Architecture
(	O
CAs	O
)	O
.	O
</s>
<s>
Within	O
the	O
last	O
few	O
years	O
,	O
a	O
number	O
of	O
CA	B-Architecture
providers	O
suffered	O
serious	O
security	O
breaches	O
,	O
allowing	O
the	O
issuance	O
of	O
certificates	O
for	O
well-known	O
domains	O
to	O
those	O
who	O
do	O
n't	O
own	O
those	O
domains	O
.	O
</s>
<s>
Trusting	O
a	O
large	O
number	O
of	O
CAs	O
might	O
be	O
a	O
problem	O
because	O
any	O
breached	O
CA	B-Architecture
could	O
issue	O
a	O
certificate	O
for	O
any	O
domain	O
name	O
.	O
</s>
<s>
DANE	O
needs	O
the	O
DNS	O
records	O
to	O
be	O
signed	O
with	O
DNSSEC	B-Protocol
for	O
its	O
security	O
model	O
to	O
work	O
.	O
</s>
<s>
Additionally	O
DANE	O
allows	O
a	O
domain	O
owner	O
to	O
specify	O
which	O
CA	B-Architecture
is	O
allowed	O
to	O
issue	O
certificates	O
for	O
a	O
particular	O
resource	O
,	O
which	O
solves	O
the	O
problem	O
of	O
any	O
CA	B-Architecture
being	O
able	O
to	O
issue	O
certificates	O
for	O
any	O
domain	O
.	O
</s>
<s>
Until	O
recently	O
,	O
there	O
has	O
been	O
no	O
widely	O
implemented	O
standard	O
for	O
encrypted	B-Protocol
email	I-Protocol
transfer	O
.	O
</s>
<s>
Sending	O
an	O
email	O
is	O
security	O
agnostic	O
;	O
there	O
is	O
no	O
URI	B-Protocol
scheme	O
to	O
designate	O
secure	O
SMTP	O
.	O
</s>
<s>
Consequently	O
,	O
most	O
email	O
that	O
is	O
delivered	O
over	O
TLS	O
uses	O
only	O
opportunistic	B-Protocol
encryption	I-Protocol
.	O
</s>
<s>
Since	O
DNSSEC	B-Protocol
provides	O
authenticated	O
denial	O
of	O
existence	O
(	O
allows	O
a	O
resolver	O
to	O
validate	O
that	O
a	O
certain	O
domain	O
name	O
does	O
not	O
exist	O
)	O
,	O
DANE	O
enables	O
an	O
incremental	O
transition	O
to	O
verified	O
,	O
encrypted	O
SMTP	O
without	O
any	O
other	O
external	O
mechanisms	O
,	O
as	O
described	O
by	O
.	O
</s>
<s>
Additionally	O
,	O
exists	O
for	O
applying	O
DANE	O
to	O
S/MIME	B-Protocol
,	O
and	O
standardises	O
bindings	O
for	O
OpenPGP	B-Application
.	O
</s>
<s>
Google	B-Application
Chrome	I-Application
does	O
not	O
support	O
DANE	O
,	O
since	O
Google	B-Application
Chrome	I-Application
wishes	O
to	O
eliminate	O
the	O
use	O
of	O
1024-bit	O
RSA	O
within	O
the	O
browser	O
(	O
DNSSEC	B-Protocol
previously	O
used	O
a	O
1024-bit	O
RSA	O
signed	O
root	O
,	O
and	O
many	O
zones	O
are	O
still	O
signed	O
with	O
1024-bit	O
RSA	O
,	O
although	O
the	O
modern	O
default	O
is	O
256-bit	O
ECDSA	O
)	O
.	O
</s>
<s>
According	O
to	O
Adam	O
Langley	O
the	O
code	O
was	O
written	O
and	O
,	O
although	O
it	O
is	O
not	O
in	O
Chrome	B-Application
today	O
,	O
it	O
remains	O
available	O
in	O
add-on	O
form	O
.	O
</s>
<s>
Mozilla	B-Application
Firefox	I-Application
(	O
before	O
version	O
57	O
)	O
had	O
support	O
via	O
an	O
add-on	O
.	O
</s>
<s>
GNU	B-Application
Privacy	I-Application
Guard	I-Application
Allows	O
fetching	O
keys	O
via	O
OpenPGP	B-Application
DANE	O
(	O
--auto-key-locate	O
)	O
.	O
</s>
<s>
The	O
TLSA	B-Protocol
RR	O
(	O
Resource	O
Record	O
)	O
for	O
a	O
service	O
is	O
located	O
at	O
a	O
DNS	O
name	O
that	O
specifies	O
certificate	O
constraints	O
should	O
be	O
applied	O
for	O
the	O
services	O
at	O
a	O
certain	O
TCP	O
or	O
UDP	O
port	O
.	O
</s>
<s>
At	O
least	O
one	O
of	O
the	O
TLSA	B-Protocol
RRs	O
must	O
provide	O
a	O
validation	O
(	O
path	O
)	O
for	O
the	O
certificate	O
offered	O
by	O
the	O
service	O
at	O
the	O
specified	O
address	O
.	O
</s>
<s>
HTTP	O
requires	O
that	O
the	O
Common	O
Name	O
in	O
the	O
X.509	O
certificate	O
provided	O
by	O
the	O
service	O
matches	O
regardless	O
of	O
the	O
TLSA	B-Protocol
asserting	O
its	O
validity	O
.	O
</s>
<s>
The	O
first	O
field	O
after	O
the	O
TLSA	B-Protocol
text	O
in	O
the	O
DNS	O
RR	O
,	O
specifies	O
how	O
to	O
verify	O
the	O
certificate	O
.	O
</s>
<s>
A	O
value	O
of	O
0	O
is	O
for	O
what	O
is	O
commonly	O
called	O
CA	B-Architecture
constraint	O
(	O
and	O
PKIX-TA	O
)	O
.	O
</s>
<s>
The	O
certificate	O
provided	O
when	O
establishing	O
TLS	O
must	O
be	O
issued	O
by	O
the	O
listed	O
root-CA	O
or	O
one	O
of	O
its	O
intermediate	O
CAs	O
,	O
with	O
a	O
valid	O
certification	O
path	O
to	O
a	O
root-CA	O
already	O
trusted	O
by	O
the	O
application	O
doing	O
the	O
verification	O
.	O
</s>
<s>
The	O
record	O
may	O
just	O
point	O
to	O
an	O
intermediate	O
CA	B-Architecture
,	O
in	O
which	O
case	O
the	O
certificate	O
for	O
this	O
service	O
must	O
come	O
via	O
this	O
CA	B-Architecture
,	O
but	O
the	O
entire	O
chain	O
to	O
a	O
trusted	O
root-CA	O
must	O
still	O
be	O
valid	O
.	O
</s>
<s>
The	O
certificate	O
used	O
must	O
match	O
the	O
TLSA	B-Protocol
record	O
,	O
and	O
it	O
must	O
also	O
pass	O
PKIX	O
certification	B-Protocol
path	I-Protocol
validation	I-Protocol
to	O
a	O
trusted	O
root-CA	O
.	O
</s>
<s>
The	O
TLSA	B-Protocol
record	O
matches	O
the	O
certificate	O
of	O
the	O
root	O
CA	B-Architecture
,	O
or	O
one	O
of	O
the	O
intermediate	O
CAs	O
,	O
of	O
the	O
certificate	O
in	O
use	O
by	O
the	O
service	O
.	O
</s>
<s>
The	O
certification	O
path	O
must	O
be	O
valid	O
up	O
to	O
the	O
matching	O
certificate	O
,	O
but	O
there	O
is	O
no	O
need	O
for	O
a	O
trusted	O
root-CA	O
.	O
</s>
<s>
The	O
TLSA	B-Protocol
record	O
matches	O
the	O
used	O
certificate	O
itself	O
.	O
</s>
<s>
The	O
TLSA	B-Protocol
record	O
for	O
www.ietf.org	O
specifies	O
to	O
check	O
the	O
SHA-256	O
hash	O
of	O
the	O
public	O
key	O
of	O
the	O
certificate	O
provided	O
,	O
ignoring	O
any	O
CA	B-Architecture
.	O
</s>
<s>
Their	O
mail	O
service	O
has	O
the	O
same	O
exact	O
certificate	O
and	O
TLSA	B-Protocol
.	O
</s>
