<s>
A	O
Lucky	B-Protocol
Thirteen	I-Protocol
attack	I-Protocol
is	O
a	O
cryptographic	O
timing	O
attack	O
against	O
implementations	O
of	O
the	O
Transport	B-Protocol
Layer	I-Protocol
Security	I-Protocol
(	O
TLS	O
)	O
protocol	O
that	O
use	O
the	O
CBC	O
mode	O
of	O
operation	O
,	O
first	O
reported	O
in	O
February	O
2013	O
by	O
its	O
developers	O
Nadhem	O
J	O
.	O
AlFardan	O
and	O
Kenny	O
Paterson	O
of	O
the	O
Information	O
Security	O
Group	O
at	O
Royal	O
Holloway	O
,	O
University	O
of	O
London	O
.	O
</s>
<s>
It	O
is	O
a	O
new	O
variant	O
of	O
Serge	O
Vaudenay	O
's	O
padding	B-Application
oracle	I-Application
attack	I-Application
that	O
was	O
previously	O
thought	O
to	O
have	O
been	O
fixed	O
,	O
that	O
uses	O
a	O
timing	O
side-channel	O
attack	O
against	O
the	O
message	B-Algorithm
authentication	I-Algorithm
code	I-Algorithm
(	O
MAC	O
)	O
check	O
stage	O
in	O
the	O
TLS	O
algorithm	O
to	O
break	O
the	O
algorithm	O
in	O
a	O
way	O
that	O
was	O
not	O
fixed	O
by	O
previous	O
attempts	O
to	O
mitigate	O
Vaudenay	O
's	O
attack	O
.	O
</s>
<s>
Martin	O
R	O
.	O
Albrecht	O
and	O
Paterson	O
have	O
since	O
demonstrated	O
a	O
variant	O
Lucky	B-Protocol
Thirteen	I-Protocol
attack	I-Protocol
against	O
Amazon	O
's	O
s2n	B-Protocol
TLS	O
implementation	O
,	O
even	O
though	O
s2n	B-Protocol
includes	O
countermeasures	O
intended	O
to	O
prevent	O
timing	O
attacks	O
.	O
</s>
