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```							Two Stories of Ring Signatures

Yoshikazu Hanatani *
Kazuo Ohta *

*The University of Electro-Communications1
Ring Signature : Present
• In 2001, a ring signature scheme was
proposed by Rivest, Shamir, Tauman.

• The signature scheme convinces a verifier
that a document has been signed by one
of n independent signers.

2
Ring Signature : Present
• A signer can connect the head and
tail of the series of values by using
own secret key.
• A verifier computes series of
values from the message and
members’ public keys, and checks
that a signature has a ring
structure.

Anyone cannot distinguish a part of the
signature which is used secret key.
Anyone cannot distinguish
the actual signer.             3
Ring Signature : Old
• Once upon a time, there was a signature scheme
like a ring signature scheme in Japan.

4
http://www.nihonkoenmura.jp/theme3/takarabito07.htm
Background
• In 1756 (in the middle of
Edo period), a signature was
generated as a proof of
solidarity when farmers in a
certain village resisted
their ruler.
• A purpose of the shape of
this signature is to hide

5
Reason for a shape of ring
• If members simply signed,
the first signer would be

• Members sequentially signed
like a ring, try to hide the
order of signers.
• The members who
participate in the signature
take equal responsibility.
6
Derivation
• The signature scheme is called
“KARAKASARENPAN”.
KARAKASARENPAN

An umbrella      Joint signatures

•Because the shape of the signature looks like

7
Various “KARAKASARENPAN”

http://www.archives.pref.fukui.jp/fukui/07/zusetsu/C26/C261.htm       http://asao20.hp.infoseek.co.jp/karakasa.htm

http://www.pref.iwate.jp/~hp0910/korenaani/h/032.html                       8
Comparison
Ring signature   “KARAKASARENPAN”

Shape              Ring                Ring
The number
of signers             1                  n
Other’s
cooperation         Unnecessary        Necessary
A signer to
shift the blame     Possible           Impossible
to members

Purpose          Hide an actual    Hide a members’
9
Ring Signature : Future
• Ring Signature schemes which have an
involved members of the ring can deny
the signature, are proposed.
CRYPTO2002
Deniable ring authentication.
M. Naor
In preparing
Toward the Fair Anonymous Signatures:
Deniable Ring Signatures
Yuichi Komano, Kazuo Ohta,
Atsushi Shimbo, Shinichi Kawamura 10

```
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