<s>
Digital	B-Protocol
credentials	I-Protocol
are	O
the	O
digital	O
equivalent	O
of	O
paper-based	O
credentials	O
.	O
</s>
<s>
Just	O
as	O
a	O
paper-based	O
credential	O
could	O
be	O
a	O
passport	B-Protocol
,	O
a	O
driver	O
's	O
license	O
,	O
a	O
membership	O
certificate	O
or	O
some	O
kind	O
of	O
ticket	O
to	O
obtain	O
some	O
service	O
,	O
such	O
as	O
a	O
cinema	O
ticket	O
or	O
a	O
public	O
transport	O
ticket	O
,	O
a	O
digital	B-Protocol
credential	I-Protocol
is	O
a	O
proof	O
of	O
qualification	O
,	O
competence	O
,	O
or	O
clearance	O
that	O
is	O
attached	O
to	O
a	O
person	O
.	O
</s>
<s>
Also	O
,	O
digital	B-Protocol
credentials	I-Protocol
prove	O
something	O
about	O
their	O
owner	O
.	O
</s>
<s>
Because	O
of	O
the	O
still	O
evolving	O
,	O
and	O
sometimes	O
conflicting	O
,	O
terminologies	O
used	O
in	O
the	O
fields	O
of	O
computer	O
science	O
,	O
computer	O
security	O
,	O
and	O
cryptography	O
,	O
the	O
term	O
"	O
digital	B-Protocol
credential	I-Protocol
"	O
is	O
used	O
quite	O
confusingly	O
in	O
these	O
fields	O
.	O
</s>
<s>
In	O
operating	B-General_Concept
system	I-General_Concept
design	O
,	O
credentials	O
are	O
the	O
properties	O
of	O
a	O
process	B-Operating_System
(	O
such	O
as	O
its	O
effective	O
UID	B-Application
)	O
that	O
is	O
used	O
for	O
determining	O
its	O
access	O
rights	O
.	O
</s>
<s>
Digital	O
badges	O
are	O
a	O
form	O
of	O
digital	B-Protocol
credential	I-Protocol
that	O
indicate	O
an	O
accomplishment	O
,	O
skill	O
,	O
quality	O
or	O
interest	O
.	O
</s>
<s>
Consequently	O
,	O
digital	O
cash	O
protocols	O
have	O
to	O
make	O
an	O
extra	O
effort	O
to	O
avoid	O
the	O
double	B-Operating_System
spending	I-Operating_System
of	O
coins	O
.	O
</s>
<s>
This	O
commonality	O
,	O
the	O
binding	O
to	O
an	O
individual	O
,	O
is	O
why	O
digital	O
cash	O
and	O
digital	B-Protocol
credentials	I-Protocol
share	O
many	O
commonalities	O
.	O
</s>
<s>
In	O
fact	O
most	O
implementations	O
of	O
anonymous	O
digital	B-Protocol
credential	I-Protocol
also	O
realize	O
digital	O
cash	O
.	O
</s>
<s>
The	O
main	O
idea	O
behind	O
anonymous	O
digital	B-Protocol
credentials	I-Protocol
is	O
that	O
users	O
are	O
given	O
cryptographic	O
tokens	O
which	O
allow	O
them	O
to	O
prove	O
statements	O
about	O
themselves	O
and	O
their	O
relationships	O
with	O
public	O
and	O
private	O
organizations	O
anonymously	O
.	O
</s>
<s>
Anonymous	O
digital	B-Protocol
credentials	I-Protocol
are	O
thus	O
related	O
to	O
privacy	O
and	O
anonymity	O
.	O
</s>
<s>
Paper	O
world	O
analogues	O
of	O
personalized	O
,	O
or	O
non-anonymous	O
credentials	O
are	O
:	O
passports	B-Protocol
,	O
driving	O
licenses	O
,	O
credit	O
cards	O
,	O
health	O
insurance	O
cards	O
,	O
club	O
membership	O
cards	O
etc	O
.	O
</s>
<s>
Such	O
an	O
ID	O
,	O
be	O
it	O
a	O
passport	B-Protocol
,	O
a	O
driver	O
's	O
license	O
,	O
or	O
some	O
other	O
type	O
of	O
card	O
usually	O
contains	O
essential	O
personal	O
information	O
.	O
</s>
<s>
The	O
blind	O
signature	O
scheme	O
introduced	O
by	O
Chaum	O
was	O
based	O
on	O
RSA	B-Architecture
signatures	O
and	O
based	O
on	O
the	O
discrete	O
logarithm	O
problem	O
can	O
be	O
used	O
for	O
constructing	O
anonymous	O
credential	O
systems	O
.	O
</s>
<s>
Stefan	O
Brands	O
generalized	O
digital	B-Protocol
credentials	I-Protocol
with	O
secret-key	O
certificate	O
based	O
credentials	O
,	O
improving	O
on	O
Chaum	O
's	O
basic	O
blind-signature	O
based	O
system	O
in	O
both	O
the	O
discrete	O
logarithm	O
and	O
strong	O
RSA	B-Architecture
assumption	O
settings	O
.	O
</s>
<s>
Proofs	O
of	O
knowledge	O
relying	O
on	O
the	O
discrete	O
logarithm	O
problem	O
for	O
groups	O
of	O
known	O
order	O
and	O
on	O
the	O
special	O
RSA	B-Architecture
problem	O
for	O
groups	O
of	O
hidden	O
order	O
form	O
the	O
basis	O
for	O
most	O
of	O
today	O
's	O
group	O
signature	O
and	O
anonymous	O
credential	O
systems	O
.	O
</s>
<s>
Moreover	O
,	O
direct	B-Application
anonymous	I-Application
attestation	I-Application
a	O
protocol	O
for	O
authenticating	O
trusted	O
platform	O
modules	O
is	O
based	O
on	O
the	O
same	O
techniques	O
.	O
</s>
<s>
Direct	B-Application
anonymous	I-Application
attestation	I-Application
can	O
be	O
seen	O
as	O
the	O
first	O
commercial	O
application	O
of	O
multi	O
show	O
anonymous	O
digital	B-Protocol
credentials	I-Protocol
,	O
even	O
though	O
in	O
this	O
case	O
credentials	O
are	O
not	O
attached	O
to	O
persons	O
,	O
but	O
to	O
chips	O
and	O
consequently	O
computer	O
platforms	O
.	O
</s>
<s>
This	O
mechanism	O
can	O
be	O
combined	O
with	O
a	O
privacy	O
preserving	O
certificate	O
refresh	O
process	B-Operating_System
(	O
which	O
gives	O
a	O
fresh	O
unlinkable	O
credential	O
with	O
the	O
same	O
attributes	O
as	O
a	O
previous	O
spent	O
credential	O
)	O
.	O
</s>
<s>
Online	O
credentials	O
for	O
learning	O
are	O
digital	B-Protocol
credentials	I-Protocol
that	O
are	O
offered	O
in	O
place	O
of	O
traditional	O
paper	O
credentials	O
for	O
a	O
skill	O
or	O
educational	O
achievement	O
.	O
</s>
<s>
Directly	O
linked	O
to	O
the	O
accelerated	O
development	O
of	O
internet	O
communication	O
technologies	O
,	O
the	O
development	O
of	O
digital	O
badges	O
,	O
electronic	O
passports	B-Protocol
and	O
massive	O
open	O
online	O
courses	O
(	O
MOOCs	O
)	O
have	O
a	O
very	O
direct	O
bearing	O
on	O
our	O
understanding	O
of	O
learning	O
,	O
recognition	O
and	O
levels	O
as	O
they	O
pose	O
a	O
direct	O
challenge	O
to	O
the	O
status	O
quo	O
.	O
</s>
