<s>
A	O
security	B-Protocol
protocol	I-Protocol
(	O
cryptographic	B-Protocol
protocol	I-Protocol
or	O
encryption	B-Protocol
protocol	I-Protocol
)	O
is	O
an	O
abstract	O
or	O
concrete	O
protocol	O
that	O
performs	O
a	O
security-related	O
function	O
and	O
applies	O
cryptographic	O
methods	O
,	O
often	O
as	O
sequences	O
of	O
cryptographic	O
primitives	O
.	O
</s>
<s>
Cryptographic	B-Protocol
protocols	I-Protocol
are	O
widely	O
used	O
for	O
secure	O
application-level	O
data	O
transport	O
.	O
</s>
<s>
A	O
cryptographic	B-Protocol
protocol	I-Protocol
usually	O
incorporates	O
at	O
least	O
some	O
of	O
these	O
aspects	O
:	O
</s>
<s>
For	O
example	O
,	O
Transport	B-Protocol
Layer	I-Protocol
Security	I-Protocol
(	O
TLS	O
)	O
is	O
a	O
cryptographic	B-Protocol
protocol	I-Protocol
that	O
is	O
used	O
to	O
secure	O
web	O
(	O
HTTPS	B-Protocol
)	O
connections	O
.	O
</s>
<s>
It	O
has	O
an	O
entity	O
authentication	O
mechanism	O
,	O
based	O
on	O
the	O
X.509	O
system	O
;	O
a	O
key	O
setup	O
phase	O
,	O
where	O
a	O
symmetric	B-Algorithm
encryption	I-Algorithm
key	O
is	O
formed	O
by	O
employing	O
public-key	O
cryptography	O
;	O
and	O
an	O
application-level	O
data	O
transport	O
function	O
.	O
</s>
<s>
There	O
are	O
other	O
types	O
of	O
cryptographic	B-Protocol
protocols	I-Protocol
as	O
well	O
,	O
and	O
even	O
the	O
term	O
itself	O
has	O
various	O
readings	O
;	O
Cryptographic	O
application	O
protocols	O
often	O
use	O
one	O
or	O
more	O
underlying	O
key	B-Protocol
agreement	I-Protocol
methods	O
,	O
which	O
are	O
also	O
sometimes	O
themselves	O
referred	O
to	O
as	O
"	O
cryptographic	B-Protocol
protocols	I-Protocol
"	O
.	O
</s>
<s>
For	O
instance	O
,	O
TLS	O
employs	O
what	O
is	O
known	O
as	O
the	O
Diffie	B-Protocol
–	I-Protocol
Hellman	I-Protocol
key	I-Protocol
exchange	I-Protocol
,	O
which	O
although	O
it	O
is	O
only	O
a	O
part	O
of	O
TLS	O
per	O
se	O
,	O
Diffie	B-Protocol
–	I-Protocol
Hellman	I-Protocol
may	O
be	O
seen	O
as	O
a	O
complete	O
cryptographic	B-Protocol
protocol	I-Protocol
in	O
itself	O
for	O
other	O
applications	O
.	O
</s>
<s>
A	O
wide	O
variety	O
of	O
cryptographic	B-Protocol
protocols	I-Protocol
go	O
beyond	O
the	O
traditional	O
goals	O
of	O
data	O
confidentiality	O
,	O
integrity	O
,	O
and	O
authentication	O
to	O
also	O
secure	O
a	O
variety	O
of	O
other	O
desired	O
characteristics	O
of	O
computer-mediated	O
collaboration	O
.	O
</s>
<s>
Blind	O
signatures	O
can	O
be	O
used	O
for	O
digital	O
cash	O
and	O
digital	B-Protocol
credentials	I-Protocol
to	O
prove	O
that	O
a	O
person	O
holds	O
an	O
attribute	O
or	O
right	O
without	O
revealing	O
that	O
person	O
's	O
identity	O
or	O
the	O
identities	O
of	O
parties	O
that	O
person	O
transacted	O
with	O
.	O
</s>
<s>
Secure	B-Protocol
multiparty	I-Protocol
computation	I-Protocol
can	O
be	O
used	O
to	O
compute	O
answers	O
(	O
such	O
as	O
determining	O
the	O
highest	O
bid	O
in	O
an	O
auction	O
)	O
based	O
on	O
confidential	O
data	O
(	O
such	O
as	O
private	O
bids	O
)	O
,	O
so	O
that	O
when	O
the	O
protocol	O
is	O
complete	O
the	O
participants	O
know	O
only	O
their	O
own	O
input	O
and	O
the	O
answer	O
.	O
</s>
<s>
Undeniable	B-Algorithm
signatures	I-Algorithm
include	O
interactive	O
protocols	O
that	O
allow	O
the	O
signer	O
to	O
prove	O
a	O
forgery	O
and	O
limit	O
who	O
can	O
verify	O
the	O
signature	O
.	O
</s>
<s>
Cryptographic	B-Protocol
protocols	I-Protocol
can	O
sometimes	O
be	O
verified	O
formally	O
on	O
an	O
abstract	O
level	O
.	O
</s>
<s>
Logics	O
,	O
concepts	O
and	O
calculi	O
used	O
for	O
formal	O
reasoning	O
of	O
security	B-Protocol
protocols	I-Protocol
:	O
</s>
<s>
Research	O
projects	O
and	O
tools	O
used	O
for	O
formal	O
verification	O
of	O
security	B-Protocol
protocols	I-Protocol
:	O
</s>
<s>
To	O
formally	O
verify	O
a	O
protocol	O
it	O
is	O
often	O
abstracted	O
and	O
modelled	O
using	O
Alice	B-General_Concept
&	I-General_Concept
Bob	I-General_Concept
notation	I-General_Concept
.	O
</s>
<s>
This	O
states	O
that	O
Alice	O
intends	O
a	O
message	O
for	O
Bob	O
consisting	O
of	O
a	O
message	O
encrypted	O
under	O
shared	B-Algorithm
key	I-Algorithm
.	O
</s>
