<s>
Privacy-Enhanced	B-Protocol
Mail	I-Protocol
(	O
PEM	O
)	O
is	O
a	O
de	O
facto	O
file	O
format	O
for	O
storing	O
and	O
sending	O
cryptographic	O
keys	O
,	O
certificates	O
,	O
and	O
other	O
data	O
,	O
based	O
on	O
a	O
set	O
of	O
1993	O
IETF	O
standards	O
defining	O
"	O
privacy-enhanced	O
mail.	O
"	O
</s>
<s>
While	O
the	O
original	O
standards	O
were	O
never	O
broadly	O
adopted	O
and	O
were	O
supplanted	O
by	O
PGP	B-Application
and	O
S/MIME	B-Protocol
,	O
the	O
textual	O
encoding	O
they	O
defined	O
became	O
very	O
popular	O
.	O
</s>
<s>
Many	O
cryptography	O
standards	O
use	O
ASN.1	B-Protocol
to	O
define	O
their	O
data	O
structures	O
,	O
and	O
Distinguished	O
Encoding	O
Rules	O
(	O
DER	O
)	O
to	O
serialize	O
those	O
structures	O
.	O
</s>
<s>
The	O
PEM	O
format	O
solves	O
this	O
problem	O
by	O
encoding	O
the	O
binary	O
data	O
using	O
base64	B-Protocol
.	O
</s>
<s>
The	O
label	O
inside	O
a	O
PEM	B-Protocol
file	I-Protocol
represents	O
the	O
type	O
of	O
the	O
data	O
more	O
accurately	O
than	O
the	O
file	O
suffix	O
,	O
since	O
many	O
different	O
types	O
of	O
data	O
can	O
be	O
saved	O
in	O
a	O
"	O
.pem	O
"	O
file	O
.	O
</s>
<s>
In	O
particular	O
PEM	O
refers	O
to	O
the	O
header	O
and	O
base64	B-Protocol
wrapper	O
for	O
a	O
binary	O
format	O
contained	O
within	O
,	O
but	O
does	O
not	O
specify	O
any	O
type	O
or	O
format	O
for	O
the	O
binary	O
data	O
,	O
so	O
that	O
a	O
PEM	B-Protocol
file	I-Protocol
may	O
contain	O
"	O
almost	O
anything	O
base64	B-Protocol
encoded	O
and	O
wrapped	O
with	O
BEGIN	O
and	O
END	O
lines	O
"	O
.	O
</s>
<s>
A	O
PEM	B-Protocol
file	I-Protocol
may	O
contain	O
multiple	O
instances	O
.	O
</s>
<s>
For	O
instance	O
,	O
an	O
operating	O
system	O
might	O
provide	O
a	O
file	O
containing	O
a	O
list	O
of	O
trusted	O
CA	B-Architecture
certificates	I-Architecture
,	O
or	O
a	O
web	O
server	O
might	O
be	O
configured	O
with	O
a	O
"	O
chain	O
"	O
file	O
containing	O
an	O
end-entity	O
certificate	O
plus	O
a	O
list	O
of	O
intermediate	O
certificates	O
.	O
</s>
<s>
The	O
PEM	O
format	O
was	O
first	O
developed	O
in	O
the	O
privacy-enhanced	B-Protocol
mail	I-Protocol
series	O
of	O
RFCs	O
:	O
RFC	O
1421	O
,	O
RFC	O
1422	O
,	O
RFC	O
1423	O
,	O
and	O
RFC	O
1424	O
.	O
</s>
<s>
These	O
standards	O
assumed	O
prior	O
deployment	O
of	O
a	O
hierarchical	O
public	B-Architecture
key	I-Architecture
infrastructure	I-Architecture
(	O
PKI	O
)	O
with	O
a	O
single	O
root	O
.	O
</s>
<s>
These	O
standards	O
were	O
eventually	O
obsoleted	O
by	O
PGP	B-Application
and	O
S/MIME	B-Protocol
,	O
competing	O
e-mail	O
encryption	O
standards	O
.	O
</s>
<s>
The	O
initiative	O
to	O
develop	O
Privacy	B-Protocol
Enhanced	I-Protocol
Mail	I-Protocol
began	O
in	O
1985	O
on	O
behalf	O
of	O
the	O
PSRG	O
(	O
Privacy	O
and	O
Security	O
Research	O
Group	O
)	O
also	O
known	O
as	O
the	O
Internet	O
Research	O
Task	O
Force	O
.	O
</s>
