<s>
In	O
cryptography	O
,	O
security	O
(	O
engineering	O
)	O
protocol	B-Protocol
notation	O
,	O
also	O
known	O
as	O
protocol	B-Protocol
narrations	O
and	O
Alice	O
&	O
Bob	O
notation	O
,	O
is	O
a	O
way	O
of	O
expressing	O
a	O
protocol	B-Protocol
of	O
correspondence	O
between	O
entities	O
of	O
a	O
dynamic	O
system	O
,	O
such	O
as	O
a	O
computer	B-Architecture
network	I-Architecture
.	O
</s>
<s>
They	O
may	O
have	O
access	O
to	O
a	O
server	O
S	O
,	O
shared	B-Algorithm
keys	I-Algorithm
K	O
,	O
timestamps	O
T	O
,	O
and	O
can	O
generate	O
nonces	O
N	O
for	O
authentication	O
purposes	O
.	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
plaintext	O
X	O
encrypted	O
under	O
shared	B-Algorithm
key	I-Algorithm
KA	O
,	O
B	O
.	O
</s>
<s>
A	O
key	O
with	O
two	O
subscripts	O
,	O
KA	O
,	O
B	O
,	O
is	O
a	O
symmetric	B-Algorithm
key	I-Algorithm
shared	O
by	O
the	O
two	O
corresponding	O
individuals	O
.	O
</s>
<s>
See	O
Kerberos	B-Protocol
as	O
an	O
example	O
.	O
</s>
<s>
Some	O
sources	O
refer	O
to	O
this	O
notation	O
as	O
Kerberos	B-Protocol
Notation	O
.	O
</s>
<s>
Several	O
models	O
exist	O
to	O
reason	O
about	O
security	B-Protocol
protocols	I-Protocol
in	O
this	O
way	O
,	O
one	O
of	O
which	O
is	O
BAN	O
logic	O
.	O
</s>
<s>
Security	B-General_Concept
protocol	I-General_Concept
notation	I-General_Concept
inspired	O
many	O
of	O
the	O
programming	O
languages	O
used	O
in	O
choreographic	B-Application
programming	I-Application
.	O
</s>
