<s>
X.690	B-Protocol
is	O
an	O
ITU-T	O
standard	O
specifying	O
several	O
ASN.1	B-Protocol
encoding	O
formats	O
:	O
</s>
<s>
The	O
Basic	O
Encoding	O
Rules	O
(	O
BER	O
)	O
were	O
the	O
original	O
rules	O
laid	O
out	O
by	O
the	O
ASN.1	B-Protocol
standard	O
for	O
encoding	O
data	O
into	O
a	O
binary	O
format	O
.	O
</s>
<s>
The	O
rules	O
,	O
collectively	O
referred	O
to	O
as	O
a	O
transfer	O
syntax	O
in	O
ASN.1	B-Protocol
parlance	O
,	O
specify	O
the	O
exact	O
octets	O
(	O
8-bit	O
bytes	O
)	O
used	O
to	O
encode	O
data	O
.	O
</s>
<s>
X.680	B-Protocol
defines	O
a	O
syntax	O
for	O
declaring	O
data	O
types	O
,	O
for	O
example	O
:	O
booleans	O
,	O
numbers	O
,	O
strings	O
,	O
and	O
compound	O
structures	O
.	O
</s>
<s>
X.680	B-Protocol
defines	O
several	O
primitive	O
data	O
types	O
,	O
for	O
example	O
:	O
BooleanType	O
,	O
IntegerType	O
,	O
OctetStringType	O
.	O
</s>
<s>
(	O
ASN.1	B-Protocol
also	O
provides	O
for	O
constructed	O
types	O
built	O
from	O
other	O
types	O
.	O
)	O
</s>
<s>
X.690	B-Protocol
includes	O
rules	O
for	O
encoding	O
those	O
tags	O
,	O
data	O
values	O
(	O
content	O
)	O
,	O
and	O
the	O
lengths	O
of	O
that	O
encoded	O
data	O
.	O
</s>
<s>
BER	O
,	O
along	O
with	O
two	O
subsets	O
of	O
BER	O
(	O
the	O
Canonical	O
Encoding	O
Rules	O
and	O
the	O
Distinguished	O
Encoding	O
Rules	O
)	O
,	O
are	O
defined	O
by	O
the	O
ITU-T	O
'	O
s	O
X.690	B-Protocol
standards	O
document	O
,	O
which	O
is	O
part	O
of	O
the	O
ASN.1	B-Protocol
document	O
series	O
.	O
</s>
<s>
Basic	O
Encoding	O
Rules	O
specifies	O
in	O
general	O
terms	O
,	O
a	O
partially	O
self-describing	O
and	O
self-delimiting	O
protocol	O
for	O
encoding	O
ASN.1	B-Protocol
data	O
structures	O
.	O
</s>
<s>
These	O
types	O
of	O
encodings	O
are	O
commonly	O
called	O
type	B-Protocol
–	I-Protocol
length	I-Protocol
–	I-Protocol
value	I-Protocol
(	O
TLV	O
)	O
encodings	O
.	O
</s>
<s>
This	O
type	O
of	O
format	O
would	O
allow	O
a	O
receiver	O
to	O
decode	O
the	O
ASN.1	B-Protocol
information	O
from	O
an	O
incomplete	O
stream	O
,	O
without	O
requiring	O
any	O
pre-knowledge	O
of	O
the	O
size	O
,	O
content	O
,	O
or	O
semantic	O
meaning	O
of	O
the	O
data	O
,	O
though	O
some	O
specifics	O
of	O
the	O
protocol	O
would	O
need	O
to	O
be	O
provided	O
or	O
reverse-engineered	O
from	O
representative	O
samples	O
of	O
traffic	O
or	O
software	O
.	O
</s>
<s>
The	O
BER	O
identifier	O
octets	O
encode	O
the	O
ASN.1	B-Protocol
tags	O
.	O
</s>
<s>
ITU-T	O
X.680	B-Protocol
,	O
clause	O
8	O
,	O
table	O
1	O
.	O
</s>
<s>
The	O
following	O
tags	O
are	O
native	O
to	O
ASN.1	B-Protocol
:	O
</s>
<s>
The	O
identifier	O
octets	O
encode	O
the	O
ASN.1	B-Protocol
tag	O
's	O
class	O
number	O
and	O
type	O
number	O
.	O
</s>
<s>
Note	O
that	O
there	O
may	O
be	O
no	O
contents	O
octets	O
(	O
hence	O
,	O
the	O
element	O
has	O
a	O
length	O
of	O
0	O
)	O
if	O
only	O
the	O
existence	O
of	O
the	O
ASN.1	B-Protocol
object	O
,	O
or	O
its	O
emptiness	O
,	O
is	O
to	O
be	O
noted	O
.	O
</s>
<s>
For	O
example	O
,	O
this	O
is	O
the	O
case	O
for	O
an	O
ASN.1	B-Protocol
NULL	O
value	O
.	O
</s>
<s>
CER	O
(	O
Canonical	O
Encoding	O
Rules	O
)	O
is	O
a	O
restricted	O
variant	O
of	O
BER	O
for	O
producing	O
unequivocal	O
transfer	O
syntax	O
for	O
data	O
structures	O
described	O
by	O
ASN.1	B-Protocol
.	O
</s>
<s>
DER	O
(	O
Distinguished	O
Encoding	O
Rules	O
)	O
is	O
a	O
restricted	O
variant	O
of	O
BER	O
for	O
producing	O
unequivocal	O
transfer	O
syntax	O
for	O
data	O
structures	O
described	O
by	O
ASN.1	B-Protocol
.	O
</s>
<s>
DER	O
is	O
a	O
subset	O
of	O
BER	O
providing	O
for	O
exactly	O
one	O
way	O
to	O
encode	O
an	O
ASN.1	B-Protocol
value	O
.	O
</s>
<s>
BER	O
,	O
as	O
explained	O
above	O
,	O
is	O
the	O
basic	O
set	O
of	O
encoding	O
rules	O
given	O
by	O
ITU-T	O
X.690	B-Protocol
for	O
the	O
transfer	O
of	O
ASN.1	B-Protocol
data	O
structures	O
.	O
</s>
<s>
As	O
stated	O
in	O
the	O
X.690	B-Protocol
standard	O
,	O
"	O
Alternative	O
encodings	O
are	O
permitted	O
by	O
the	O
basic	O
encoding	O
rules	O
as	O
a	O
sender	O
's	O
option	O
.	O
</s>
<s>
In	O
order	O
to	O
facilitate	O
a	O
choice	O
between	O
encoding	O
rules	O
,	O
the	O
X.690	B-Protocol
standards	O
document	O
provides	O
the	O
following	O
guidance	O
:	O
</s>
<s>
The	O
most	O
popular	O
of	O
these	O
are	O
XML-based	O
alternatives	O
,	O
such	O
as	O
the	O
XML	B-Protocol
Encoding	I-Protocol
Rules	I-Protocol
and	O
ASN.1	B-Protocol
SOAP	B-Application
.	O
</s>
<s>
In	O
addition	O
,	O
there	O
is	O
a	O
standard	O
mapping	O
to	O
convert	O
an	O
XML	O
Schema	O
to	O
an	O
ASN.1	B-Protocol
schema	O
,	O
which	O
can	O
then	O
be	O
encoded	O
using	O
BER	O
.	O
</s>
<s>
The	O
SNMP	B-Protocol
and	O
LDAP	B-Protocol
protocols	O
specify	O
ASN.1	B-Protocol
with	O
BER	O
as	O
their	O
required	O
encoding	O
scheme	O
.	O
</s>
<s>
The	O
digital	O
signature	O
standard	O
PKCS	O
#7	O
also	O
specifies	O
ASN.1	B-Protocol
with	O
BER	O
to	O
encode	O
encrypted	O
messages	O
and	O
their	O
digital	O
signature	O
or	O
digital	B-Algorithm
envelope	I-Algorithm
.	O
</s>
<s>
Many	O
telecommunication	O
systems	O
,	O
such	O
as	O
ISDN	B-Protocol
,	O
toll-free	O
call	O
routing	O
,	O
and	O
most	O
cellular	O
phone	O
services	O
use	O
ASN.1	B-Protocol
with	O
BER	O
to	O
some	O
degree	O
for	O
transmitting	O
control	O
messages	O
over	O
the	O
network	O
.	O
</s>
