Two Stories of Ring Signatures

1
Two Stories of Ring Signatures

• Yoshikazu Hanatani
• Kazuo Ohta

The University of Electro-Communications
2
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.

3
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.
4
Ring Signature Old

• Once upon a time, there was a signature scheme
  like a ring signature scheme in Japan.

http//www.nihonkoenmura.jp/theme3/takarabito07.ht
m
5
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 their leader.

6
Reason for a shape of ring

• If members simply signed,the first signer would
  be suspected of the leader.

• Members sequentially signed like a ring, try to
  hide the order of signers.
• The members who participate in the signature take
  equal responsibility.

7
Derivation

• The signature scheme is called KARAKASARENPAN.

KARAKASA
RENPAN
Joint signatures
An umbrella

• Because the shape of the signature looks like
  Japanese traditional umbrella.

8
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.h
tml
9
Comparison
Ring signature
KARAKASARENPAN
Shape
Ring
Ring
The number of signers
n
1
Others cooperation
Necessary
Unnecessary
A signer to shift the blame to members
Possible
Impossible
Hide an actual signer
Hide a members leader.
Purpose
10
Ring Signature Future

• Ring Signature schemes which have an additional
  functionality, with which the 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