<s>
GNU	O
Privacy	O
Guard	O
(	O
GnuPG	O
or	O
GPG	O
)	O
is	O
a	O
free-software	B-Application
replacement	O
for	O
Symantec	O
's	O
PGP	B-Application
cryptographic	O
software	O
suite	O
.	O
</s>
<s>
Modern	O
versions	O
of	O
PGP	B-Application
are	O
interoperable	O
with	O
GnuPG	O
and	O
other	O
OpenPGP-compliant	O
systems	O
.	O
</s>
<s>
GnuPG	O
is	O
part	O
of	O
the	B-Application
GNU	I-Application
Project	I-Application
and	O
received	O
major	O
funding	O
from	O
the	O
German	O
government	O
in	O
1999	O
.	O
</s>
<s>
GnuPG	O
is	O
a	O
hybrid-encryption	O
software	O
program	O
because	O
it	O
uses	O
a	O
combination	O
of	O
conventional	O
symmetric-key	B-Algorithm
cryptography	I-Algorithm
for	O
speed	O
,	O
and	O
public-key	B-Application
cryptography	I-Application
for	O
ease	O
of	O
secure	O
key	O
exchange	O
,	O
typically	O
by	O
using	O
the	O
recipient	O
's	O
public	B-Application
key	I-Application
to	O
encrypt	O
a	O
session	O
key	O
which	O
is	O
used	O
only	O
once	O
.	O
</s>
<s>
This	O
mode	O
of	O
operation	O
is	O
part	O
of	O
the	O
OpenPGP	O
standard	O
and	O
has	O
been	O
part	O
of	O
PGP	B-Application
from	O
its	O
first	O
version	O
.	O
</s>
<s>
The	O
GnuPG1.x	O
series	O
uses	O
an	O
integrated	O
cryptographic	O
library	O
,	O
while	O
the	O
GnuPG2.x	O
series	O
replaces	O
this	O
with	O
Libgcrypt	B-Application
.	O
</s>
<s>
GnuPG	O
encrypts	O
messages	O
using	O
asymmetric	B-Application
key	I-Application
pairs	I-Application
individually	O
generated	O
by	O
GnuPG	O
users	O
.	O
</s>
<s>
The	O
resulting	O
public	B-Application
keys	I-Application
may	O
be	O
exchanged	O
with	O
other	O
users	O
in	O
a	O
variety	O
of	O
ways	O
,	O
such	O
as	O
Internet	O
key	O
servers	O
.	O
</s>
<s>
They	O
must	O
always	O
be	O
exchanged	O
carefully	O
to	O
prevent	O
identity	O
spoofing	O
by	O
corrupting	O
public	B-Application
key	I-Application
↔	O
"	O
owner	O
"	O
identity	O
correspondences	O
.	O
</s>
<s>
GnuPG	O
also	O
supports	O
symmetric	B-Algorithm
encryption	I-Algorithm
algorithms	O
.	O
</s>
<s>
By	O
default	O
,	O
GnuPG	O
uses	O
the	O
AES	B-Algorithm
symmetrical	O
algorithm	O
since	O
version	O
2.1	O
,	O
CAST5	B-Algorithm
was	O
used	O
in	O
earlier	O
versions	O
.	O
</s>
<s>
For	O
a	O
long	O
time	O
,	O
it	O
did	O
not	O
support	O
the	O
IDEA	B-Algorithm
encryption	I-Algorithm
algorithm	I-Algorithm
used	O
in	O
PGP	B-Application
.	O
</s>
<s>
It	O
was	O
in	O
fact	O
possible	O
to	O
use	O
IDEA	B-Algorithm
in	O
GnuPG	O
by	O
downloading	O
a	O
plugin	O
for	O
it	O
,	O
however	O
,	O
this	O
might	O
require	O
a	O
license	O
for	O
some	O
uses	O
in	O
countries	O
in	O
which	O
IDEA	B-Algorithm
was	O
patented	O
.	O
</s>
<s>
Starting	O
with	O
versions	O
1.4.13	O
and	O
2.0.20	O
,	O
GnuPG	O
supports	O
IDEA	B-Algorithm
because	O
the	O
last	O
patent	O
of	O
IDEA	B-Algorithm
expired	O
in	O
2012	O
.	O
</s>
<s>
Support	O
of	O
IDEA	B-Algorithm
is	O
intended	O
"	O
to	O
get	O
rid	O
of	O
all	O
the	O
questions	O
from	O
folks	O
either	O
trying	O
to	O
decrypt	O
old	O
data	O
or	O
migrating	O
keys	O
from	O
PGP	B-Application
to	O
GnuPG	O
"	O
,	O
and	O
hence	O
is	O
not	O
recommended	O
for	O
regular	O
use	O
.	O
</s>
<s>
More	O
recent	O
releases	O
of	O
GnuPG2.x	O
(	O
"	O
modern	O
"	O
and	O
the	O
now	O
deprecated	O
"	O
stable	O
"	O
series	O
)	O
expose	O
most	O
cryptographic	O
functions	O
and	O
algorithms	O
Libgcrypt	B-Application
(	O
its	O
cryptography	O
library	O
)	O
provides	O
,	O
including	O
support	O
for	O
elliptic	O
curve	O
cryptography	O
(	O
ECDH	B-Protocol
,	O
ECDSA	O
and	O
EdDSA	B-Algorithm
)	O
in	O
the	O
"	O
modern	O
"	O
series	O
(	O
i.e.	O
</s>
<s>
The	O
German	O
Federal	O
Ministry	O
of	O
Economics	O
and	O
Technology	O
funded	O
the	O
documentation	O
and	O
the	O
port	O
to	O
Microsoft	B-Application
Windows	I-Application
in	O
2000	O
.	O
</s>
<s>
GnuPG	O
is	O
a	O
system	O
compliant	O
to	O
the	O
OpenPGP	O
standard	O
,	O
thus	O
the	O
history	O
of	O
OpenPGP	O
is	O
of	O
importance	O
;	O
it	O
was	O
designed	O
to	O
interoperate	O
with	O
PGP	B-Application
,	O
an	O
email	O
encryption	O
program	O
initially	O
designed	O
and	O
developed	O
by	O
Phil	O
Zimmermann	O
.	O
</s>
<s>
Although	O
the	O
basic	O
GnuPG	O
program	O
has	O
a	O
command-line	B-Application
interface	I-Application
,	O
there	O
exists	O
various	O
front-ends	B-Architecture
that	O
provide	O
it	O
with	O
a	O
graphical	B-Application
user	I-Application
interface	I-Application
.	O
</s>
<s>
For	O
example	O
,	O
GnuPG	O
encryption	O
support	O
has	O
been	O
integrated	O
into	O
KMail	O
and	O
Evolution	B-Language
,	O
the	O
graphical	O
email	B-Protocol
clients	I-Protocol
found	O
in	O
KDE	B-Application
and	O
GNOME	B-Application
,	O
the	O
most	O
popular	O
Linux	B-Application
desktops	O
.	O
</s>
<s>
There	O
are	O
also	O
graphical	O
GnuPG	O
front-ends	B-Architecture
,	O
for	O
example	O
Seahorse	B-Application
for	O
GNOME	B-Application
and	O
KGPG	B-Language
and	O
Kleopatra	O
for	O
KDE	B-Application
.	O
</s>
<s>
GPGTools	O
provides	O
a	O
number	O
of	O
front-ends	B-Architecture
for	O
OS	O
integration	O
of	O
encryption	O
and	O
key	O
management	O
as	O
well	O
as	O
GnuPG	O
installations	O
via	O
Installer	O
packages	B-Application
for	O
macOS	B-Application
.	O
</s>
<s>
GPG	O
Suite	O
installs	O
all	O
related	O
OpenPGP	O
applications	O
(	O
GPG	O
Keychain	O
)	O
,	O
plugins	O
(	O
GPG	O
Mail	O
)	O
and	O
dependencies	O
(	O
MacGPG	B-Operating_System
)	O
,	O
along	O
with	O
GPG	O
Services	O
(	O
integration	O
into	O
macOS	B-Application
Services	O
menu	O
)	O
to	O
use	O
GnuPG	O
based	O
encryption	O
.	O
</s>
<s>
Instant	B-Application
messaging	I-Application
applications	O
such	O
as	O
Psi	B-Language
and	O
Fire	B-Protocol
can	O
automatically	O
secure	O
messages	O
when	O
GnuPG	O
is	O
installed	O
and	O
configured	O
.	O
</s>
<s>
Web-based	O
software	O
such	O
as	O
Horde	B-Language
also	O
makes	O
use	O
of	O
it	O
.	O
</s>
<s>
The	O
cross-platform	O
extension	B-Operating_System
Enigmail	B-Operating_System
provides	O
GnuPG	O
support	O
for	O
Mozilla	B-Application
Thunderbird	I-Application
and	O
SeaMonkey	B-Language
.	O
</s>
<s>
Similarly	O
,	O
Enigform	O
provides	O
GnuPG	O
support	O
for	O
Mozilla	B-Application
Firefox	I-Application
.	O
</s>
<s>
In	O
2005	O
,	O
g10	O
Code	O
GmbH	O
and	O
Intevation	O
GmbH	O
released	O
Gpg4win	B-Application
,	O
a	O
software	O
suite	O
that	O
includes	O
GnuPG	O
for	O
Windows	O
,	O
GNU	O
Privacy	O
Assistant	O
,	O
and	O
GnuPG	O
plug-ins	O
for	O
Windows	B-Protocol
Explorer	I-Protocol
and	O
Outlook	B-Application
.	O
</s>
<s>
In	O
June	O
2017	O
,	O
a	O
vulnerability	O
(	O
CVE-2017-7526	O
)	O
was	O
discovered	O
within	O
Libgcrypt	B-Application
by	O
Bernstein	O
,	O
Breitner	O
and	O
others	O
:	O
a	O
library	O
used	O
by	O
GnuPG	O
,	O
which	O
enabled	O
a	O
full	O
key	O
recovery	O
for	O
RSA-1024	O
and	O
about	O
more	O
than	O
1/8th	O
of	O
RSA-2048	O
keys	O
.	O
</s>
<s>
This	O
side-channel	O
attack	O
exploits	O
the	O
fact	O
that	O
Libgcrypt	B-Application
used	O
a	O
sliding	O
windows	O
method	O
for	O
exponentiation	O
which	O
leads	O
to	O
the	O
leakage	O
of	O
exponent	O
bits	O
and	O
to	O
full	O
key	O
recovery	O
.	O
</s>
<s>
In	O
October	O
2017	O
,	O
the	O
ROCA	O
vulnerability	O
was	O
announced	O
that	O
affects	O
RSA	B-Architecture
keys	O
generated	O
by	O
YubiKey	O
4	O
tokens	O
,	O
which	O
often	O
are	O
used	O
with	O
PGP/GPG	O
.	O
</s>
<s>
Many	O
published	O
PGP	B-Application
keys	O
were	O
found	O
to	O
be	O
susceptible	O
.	O
</s>
<s>
In	O
January	O
2021	O
,	O
Libgcrypt	B-Application
1.9.0	O
was	O
released	O
,	O
which	O
was	O
found	O
to	O
contain	O
a	O
severe	O
bug	O
that	O
was	O
simple	O
to	O
exploit	O
.	O
</s>
<s>
A	O
fix	O
was	O
released	O
10	O
days	O
later	O
in	O
Libgcrypt	B-Application
1.9.1	O
.	O
</s>
