A
Glossary of Terms
186
Certificate
A
certificate
is
a
digital
proof
of
identity.
CHAP
Challenge
Handshake
Authentication
Protocol.
Cipher
Cipher
is
a
method
of
encrypting
text
(to
produce
cipher
text)
in
which
a
cryptographic
key
and
algorithm
are
applied
to
a
block
of
data
(for
example,
64
contiguous
bits)
at
once
as
a
group
rather
than
to
one
bit
at
a
time.
CRL
Certificate
Revocation
Lists.
A
certificate
revocation
list
(CRL)
contains
a
list
of
all
certificates
that
has
been
cancelled
before
their
expiration
date.
DES
Data
Encryption
Standard.
DES
is
a
US
Federal
Information
Processing
Standard
(FIPS)
that
defines
the
Data
Encryption
Algorithm
(DEA).
The
term
DES
is
also
commonly
used
when
referring
to
the
algorithm.
The
algorithm
itself
is
a
symmetric
block
cipher
with
a
block
size
of
64
bits
and
a
key
length
of
64
bits
(of
which
8
are
parity
bits).
Diffie
‐
Hellman
key
exchange
A
method
for
key
exchange
between
two
parties.
This
method
can
be
used
to
generate
an
unbiased
secret
key
over
an
insecure
medium.
The
method
has
many
variants.
A
well
known
attack
called
the
man
‐
in
‐
the
‐
middle
attack
forces
the
use
of
digital
signatures
or
other
means
of
authentication
with
the
Diffie
‐
Hellman
protocol.
Dictionary
attack
A
dictionary
attack
is
a
method
of
breaking
into
a
password
‐
protected
computer
or
server
by
systematically
entering
every
word
in
a
dictionary
as
a
password.
A
dictionary
attack
can
also
be
used
in
an
attempt
to
find
the
key
necessary
to
decrypt
an
encrypted
message
or
document.
Diff
‐
Serv
Differentiated
Services.
Differentiated
Services
(DiffServ,
or
DS)
is
a
protocol
for
specifying
and
controlling
network
traffic
by
class
so
that
certain
types
of
traffic
get
precedence
‐
for
example,
voice
traffic,
which
requires
a
relatively
uninterrupted
flow
of
data,
might
get
precedence
over
other
kinds
of
traffic.
Denial
of
service
(DoS)
Denotes
attacks
that
do
not
cause
a
security
violation
per
se,
but
harm
the
availability
of
a
service.
For
example,
if
an
attacker
sends
lots
of
forged
packets
to
an
IPsec
VPN
host,
they
may
degrade
the
performance
of
the
host.
One
of
the
design
goals
in
the
architecture
has
been
to
minimize
the
consequences
of
denial
‐
of
‐
service
attacks.
