<s>
In	O
cryptography	O
,	O
the	O
ADFGVX	B-Algorithm
cipher	I-Algorithm
was	O
a	O
manually	O
applied	O
field	O
cipher	B-Application
used	O
by	O
the	O
Imperial	O
German	O
Army	O
during	O
World	O
War	O
I	O
.	O
</s>
<s>
ADFGVX	B-Algorithm
was	O
in	O
fact	O
an	O
extension	O
of	O
an	O
earlier	O
cipher	B-Application
called	O
ADFGX	B-Algorithm
which	O
was	O
first	O
used	O
on	O
1	O
March	O
1918	O
on	O
the	O
German	O
Western	O
Front	O
.	O
</s>
<s>
ADFGVX	B-Algorithm
was	O
applied	O
from	O
1	O
June	O
1918	O
on	O
both	O
the	O
Western	O
Front	O
and	O
Eastern	O
Front	O
.	O
</s>
<s>
Invented	O
by	O
the	O
Germans	O
signal	O
corps	O
officers	O
Lieutenant	O
(	O
1891	O
–	O
1977	O
)	O
and	O
introduced	O
in	O
March	O
1918	O
with	O
the	O
designation	O
"	O
Secret	O
Cipher	B-Application
of	O
the	O
Radio	O
Operators	O
1918	O
"	O
(	O
Geheimschrift	O
der	O
Funker	O
1918	O
,	O
in	O
short	O
GedeFu	O
18	O
)	O
,	O
the	O
cipher	B-Application
was	O
a	O
fractionating	O
transposition	B-Algorithm
cipher	I-Algorithm
which	O
combined	O
a	O
modified	O
Polybius	O
square	O
with	O
a	O
single	O
columnar	O
transposition	B-Algorithm
.	O
</s>
<s>
The	O
cipher	B-Application
is	O
named	O
after	O
the	O
six	O
possible	O
letters	O
used	O
in	O
the	O
ciphertext	O
:	O
,	O
,	O
,	O
,	O
and	O
.	O
</s>
<s>
Nebel	O
designed	O
the	O
cipher	B-Application
to	O
provide	O
an	O
army	O
on	O
the	O
move	O
with	O
encryption	O
that	O
was	O
more	O
convenient	O
than	O
trench	O
codes	O
but	O
was	O
still	O
secure	O
.	O
</s>
<s>
In	O
fact	O
,	O
the	O
Germans	O
believed	O
the	O
ADFGVX	B-Algorithm
cipher	I-Algorithm
was	O
unbreakable	O
.	O
</s>
<s>
Next	O
,	O
the	O
fractionated	O
message	O
is	O
subject	O
to	O
a	O
columnar	O
transposition	B-Algorithm
.	O
</s>
<s>
The	O
message	O
is	O
written	O
in	O
rows	O
under	O
a	O
transposition	B-Algorithm
key	O
(	O
here	O
"	O
CARGO	O
"	O
)	O
:	O
</s>
<s>
Next	O
,	O
the	O
letters	O
are	O
sorted	O
alphabetically	O
in	O
the	O
transposition	B-Algorithm
key	O
(	O
changing	O
CARGO	O
to	O
ACGOR	O
)	O
by	O
rearranging	O
the	O
columns	O
beneath	O
the	O
letters	O
along	O
with	O
the	O
letters	O
themselves	O
:	O
</s>
<s>
In	O
practice	O
,	O
the	O
transposition	B-Algorithm
keys	O
were	O
about	O
two	O
dozen	O
characters	O
long	O
.	O
</s>
<s>
Long	O
messages	O
sent	O
in	O
the	O
ADFGX	B-Algorithm
cipher	I-Algorithm
were	O
broken	O
into	O
sets	O
of	O
messages	O
of	O
different	O
and	O
irregular	O
lengths	O
to	O
make	O
it	O
invulnerable	O
to	O
multiple	O
anagramming	O
.	O
</s>
<s>
Both	O
the	O
transposition	B-Algorithm
keys	O
and	O
the	O
fractionation	O
keys	O
were	O
changed	O
daily	O
.	O
</s>
<s>
In	O
June	O
1918	O
,	O
an	O
additional	O
letter	O
,	O
,	O
was	O
added	O
to	O
the	O
cipher	B-Application
.	O
</s>
<s>
The	O
cipher	B-Application
is	O
based	O
on	O
the	O
6	O
letters	O
ADFGVX	B-Algorithm
.	O
</s>
<s>
This	O
creates	O
the	O
table	O
below	O
with	O
the	O
letters	O
ADFGVX	B-Algorithm
as	O
column	O
headings	O
and	O
row	O
identifiers	O
:	O
</s>
<s>
This	O
cipher	B-Application
might	O
be	O
modified	O
by	O
transposing	O
the	O
rows	O
as	O
well	O
as	O
the	O
columns	O
,	O
creating	O
a	O
harder	O
but	O
improved	O
cipher	B-Application
.	O
</s>
<s>
ADFGVX	B-Algorithm
was	O
cryptanalysed	O
by	O
French	O
Army	O
Lieutenant	O
Georges	O
Painvin	O
,	O
and	O
the	O
cipher	B-Application
was	O
broken	O
in	O
early	O
June	O
1918	O
.	O
</s>
<s>
His	O
method	O
of	O
solution	O
relied	O
on	O
finding	O
messages	O
with	O
stereotyped	O
beginnings	O
,	O
which	O
would	O
fractionate	O
them	O
and	O
then	O
form	O
similar	O
patterns	O
in	O
the	O
positions	O
in	O
the	O
ciphertext	O
that	O
had	O
corresponded	O
to	O
column	O
headings	O
in	O
the	O
transposition	B-Algorithm
table	O
.	O
</s>
<s>
However	O
,	O
that	O
was	O
not	O
the	O
only	O
trick	O
that	O
Painvin	O
used	O
to	O
crack	O
the	O
ADFGX	B-Algorithm
cipher	I-Algorithm
.	O
</s>
<s>
Also	O
,	O
after	O
substitution	O
but	O
before	O
transposition	B-Algorithm
,	O
the	O
columns	O
would	O
alternately	O
consist	O
entirely	O
of	O
"	O
top	O
"	O
and	O
"	O
side	O
"	O
letters	O
.	O
</s>
<s>
With	O
the	O
ADFGX	B-Algorithm
cipher	I-Algorithm
,	O
each	O
"	O
side	O
"	O
letter	O
or	O
"	O
top	O
"	O
letter	O
is	O
associated	O
with	O
five	O
plaintext	O
letters	O
.	O
</s>
<s>
The	O
result	O
was	O
still	O
transposed	O
,	O
but	O
to	O
unscramble	O
a	O
simple	O
transposition	B-Algorithm
was	O
all	O
that	O
he	O
still	O
had	O
to	O
do	O
.	O
</s>
<s>
Once	O
he	O
determined	O
the	O
transposition	B-Algorithm
scheme	O
for	O
one	O
message	O
,	O
he	O
would	O
then	O
be	O
able	O
to	O
crack	O
any	O
other	O
message	O
that	O
was	O
enciphered	O
with	O
the	O
same	O
transposition	B-Algorithm
key	O
.	O
</s>
<s>
Painvin	O
broke	O
the	O
ADFGX	B-Algorithm
cipher	I-Algorithm
in	O
April	O
1918	O
,	O
a	O
few	O
weeks	O
after	O
the	O
Germans	O
launched	O
their	O
Spring	O
Offensive	O
.	O
</s>
<s>
However	O
,	O
the	O
claim	O
that	O
Painvin	O
's	O
breaking	O
of	O
the	O
ADFGX	B-Algorithm
cipher	I-Algorithm
stopped	O
the	O
German	O
spring	O
offensive	O
of	O
1918	O
,	O
while	O
frequently	O
made	O
,	O
is	O
disputed	O
by	O
some	O
.	O
</s>
<s>
Regrettably	O
,	O
Sophie	O
de	O
Lastours	O
subscribes	O
to	O
the	O
traditional	O
French	O
view	O
that	O
the	O
solving	O
of	O
a	O
German	O
ADFGVX-telegram	O
by	O
Painvin	O
at	O
the	O
beginning	O
of	O
June	O
1918	O
was	O
decisive	O
for	O
the	O
Allied	O
victory	O
in	O
the	O
First	O
World	O
War	O
because	O
it	O
gave	O
timely	O
warning	O
of	O
a	O
forthcoming	O
German	O
offensive	O
meant	O
to	O
reach	O
Paris	O
and	O
to	O
inflict	O
a	O
critical	O
defeat	O
on	O
the	O
Allies	O
.	O
</s>
<s>
Moreover	O
,	O
it	O
is	O
usually	O
overlooked	O
that	O
the	O
basic	O
version	O
of	O
the	O
ADFGVX	B-Algorithm
cipher	I-Algorithm
had	O
been	O
created	O
especially	O
for	O
the	O
German	O
Spring	O
Offensive	O
in	O
1918	O
,	O
meant	O
to	O
deal	O
the	O
Allies	O
a	O
devastating	O
blow	O
.	O
</s>
<s>
It	O
was	O
hoped	O
that	O
the	O
cipher	B-Application
ADFGX	B-Algorithm
would	O
protect	O
German	O
communications	O
against	O
Allied	O
cryptographers	O
during	O
the	O
assault	O
,	O
which	O
happened	O
.	O
</s>
<s>
Telegrams	O
in	O
ADFGX	B-Algorithm
appeared	O
for	O
the	O
first	O
time	O
on	O
5	O
March	O
,	O
and	O
the	O
German	O
attack	O
started	O
on	O
21	O
March	O
.	O
</s>
<s>
The	O
ADFGX	B-Algorithm
and	O
ADFGVX	B-Algorithm
ciphers	I-Algorithm
are	O
now	O
regarded	O
as	O
insecure	O
.	O
</s>
