<s>
In	O
cryptography	O
,	O
Tiger	B-Algorithm
is	O
a	O
cryptographic	B-Algorithm
hash	I-Algorithm
function	I-Algorithm
designed	O
by	O
Ross	O
Anderson	O
and	O
Eli	O
Biham	O
in	O
1995	O
for	O
efficiency	O
on	O
64-bit	B-Device
platforms	O
.	O
</s>
<s>
The	O
size	O
of	O
a	O
Tiger	B-Algorithm
hash	I-Algorithm
value	O
is	O
192	O
bits	O
.	O
</s>
<s>
Truncated	O
versions	O
(	O
known	O
as	O
Tiger/128	O
and	O
Tiger/160	O
)	O
can	O
be	O
used	O
for	O
compatibility	O
with	O
protocols	O
assuming	O
a	O
particular	O
hash	B-Algorithm
size	O
.	O
</s>
<s>
Unlike	O
the	O
SHA-2	B-Algorithm
family	O
,	O
no	O
distinguishing	O
initialization	O
values	O
are	O
defined	O
;	O
they	O
are	O
simply	O
prefixes	O
of	O
the	O
full	O
Tiger/192	O
hash	B-Algorithm
value	O
.	O
</s>
<s>
Tiger2	O
is	O
a	O
variant	O
where	O
the	O
message	O
is	O
padded	O
by	O
first	O
appending	O
a	O
byte	O
with	O
the	O
hexadecimal	O
value	O
of	O
0x80	O
as	O
in	O
MD4	B-Algorithm
,	O
MD5	B-Algorithm
and	O
SHA	O
,	O
rather	O
than	O
with	O
the	O
hexadecimal	O
value	O
of	O
0x01	O
as	O
in	O
the	O
case	O
of	O
Tiger	B-Algorithm
.	O
</s>
<s>
Tiger	B-Algorithm
is	O
based	O
on	O
Merkle	B-Algorithm
–	I-Algorithm
Damgård	I-Algorithm
construction	I-Algorithm
.	O
</s>
<s>
The	O
one-way	B-Algorithm
compression	I-Algorithm
function	I-Algorithm
operates	O
on	O
64-bit	B-Device
words	O
,	O
maintaining	O
3	O
words	O
of	O
state	O
and	O
processing	O
8	O
words	O
of	O
data	O
.	O
</s>
<s>
There	O
are	O
24	O
rounds	O
,	O
using	O
a	O
combination	O
of	O
operation	O
mixing	O
with	O
XOR	O
and	O
addition/subtraction	O
,	O
rotates	O
,	O
and	O
S-box	B-Algorithm
lookups	O
,	O
and	O
a	O
fairly	O
intricate	O
key	O
scheduling	O
algorithm	O
for	O
deriving	O
24	O
round	O
keys	O
from	O
the	O
8	O
input	O
words	O
.	O
</s>
<s>
Although	O
fast	O
in	O
software	O
,	O
Tiger	B-Algorithm
's	O
large	O
S-boxes	B-Algorithm
(	O
four	O
S-boxes	B-Algorithm
,	O
each	O
with	O
256	O
64-bit	B-Device
entries	O
totaling	O
8	O
KiB	O
)	O
make	O
implementations	O
in	O
hardware	O
or	O
microcontrollers	B-Architecture
difficult	O
.	O
</s>
<s>
Tiger	B-Algorithm
is	O
frequently	O
used	O
in	O
Merkle	B-Algorithm
hash	I-Algorithm
tree	I-Algorithm
form	O
,	O
where	O
it	O
is	O
referred	O
to	O
as	O
TTH	O
(	O
Tiger	B-Algorithm
Tree	O
Hash	B-Algorithm
)	O
.	O
</s>
<s>
TTH	O
is	O
used	O
by	O
many	O
clients	O
on	O
the	O
Direct	O
Connect	O
and	O
Gnutella	B-Protocol
file	O
sharing	O
networks	O
,	O
and	O
can	O
optionally	O
be	O
included	O
in	O
the	O
BitTorrent	B-Protocol
metafile	O
for	O
better	O
content	O
availability	O
.	O
</s>
<s>
Tiger	B-Algorithm
was	O
considered	O
for	O
inclusion	O
in	O
the	O
OpenPGP	O
standard	O
,	O
but	O
was	O
abandoned	O
in	O
favor	O
of	O
RIPEMD-160	B-Algorithm
.	O
</s>
<s>
refers	O
to	O
TIGER	B-Algorithm
as	O
having	O
no	O
OID	O
,	O
whereas	O
the	O
GNU	B-Operating_System
Coding	O
Standards	O
list	O
TIGER	B-Algorithm
as	O
having	O
OID	O
1.3.6.1.4.1.11591.12.2	O
.	O
</s>
<s>
In	O
the	O
IPSEC	B-Protocol
subtree	O
,	O
HMAC-TIGER	O
is	O
assigned	O
OID	O
1.3.6.1.5.5.8.1.3	O
.	O
</s>
<s>
The	O
specification	O
of	O
Tiger	B-Algorithm
does	O
not	O
define	O
the	O
way	O
its	O
output	O
should	O
be	O
printed	O
but	O
only	O
defines	O
the	O
result	O
to	O
be	O
three	O
ordered	O
64-bit	B-Device
integers	O
.	O
</s>
<s>
In	O
the	O
example	O
below	O
,	O
the	O
192-bit	O
(	O
24-byte	O
)	O
Tiger	B-Algorithm
hashes	I-Algorithm
are	O
represented	O
as	O
48	O
hexadecimal	O
digits	O
in	O
little-endian	O
byte	O
order	O
.	O
</s>
<s>
The	O
following	O
demonstrates	O
a	O
43-byte	O
ASCII	B-Protocol
input	O
and	O
the	O
corresponding	O
Tiger	B-Algorithm
hashes	I-Algorithm
:	O
</s>
<s>
Even	O
a	O
small	O
change	O
in	O
the	O
message	O
will	O
(	O
with	O
very	O
high	O
probability	O
)	O
result	O
in	O
a	O
completely	O
different	O
hash	B-Algorithm
,	O
e.g.	O
</s>
<s>
The	O
hash	B-Algorithm
of	O
the	O
zero-length	O
string	O
is	O
:	O
</s>
<s>
Unlike	O
MD5	B-Algorithm
or	O
SHA-0/1	O
,	O
there	O
are	O
no	O
known	O
effective	O
attacks	O
on	O
the	O
full	O
24-round	O
Tiger	B-Algorithm
except	O
for	O
pseudo-near	O
collision	O
.	O
</s>
<s>
While	O
MD5	B-Algorithm
processes	O
its	O
state	O
with	O
64	O
simple	O
32-bit	O
operations	O
per	O
512-bit	O
block	O
and	O
SHA-1	O
with	O
80	O
,	O
Tiger	B-Algorithm
updates	O
its	O
state	O
with	O
a	O
total	O
of	O
144	O
such	O
operations	O
per	O
512-bit	O
block	O
,	O
additionally	O
strengthened	O
by	O
large	O
S-box	B-Algorithm
look-ups	O
.	O
</s>
<s>
John	O
Kelsey	O
and	O
Stefan	O
Lucks	O
have	O
found	O
a	O
collision-finding	O
attack	O
on	O
16-round	O
Tiger	B-Algorithm
with	O
a	O
time	O
complexity	O
equivalent	O
to	O
about	O
244	O
compression	O
function	O
invocations	O
and	O
another	O
attack	O
that	O
finds	O
pseudo-near	O
collisions	O
in	O
20-round	O
Tiger	B-Algorithm
with	O
work	O
less	O
than	O
that	O
of	O
248	O
compression	O
function	O
invocations	O
.	O
</s>
<s>
have	O
improved	O
upon	O
these	O
attacks	O
by	O
describing	O
a	O
collision	O
attack	O
spanning	O
19	O
rounds	O
of	O
Tiger	B-Algorithm
,	O
and	O
a	O
22-round	O
pseudo-near-collision	O
attack	O
.	O
</s>
<s>
These	O
attacks	O
require	O
a	O
work	O
effort	O
equivalent	O
to	O
about	O
262	O
and	O
244	O
evaluations	O
of	O
the	O
Tiger	B-Algorithm
compression	O
function	O
,	O
respectively	O
.	O
</s>
