Conditional Digital Signatures

  • Marek Klonowski
  • Mirosław Kutyłowski
  • Anna Lauks
  • Filip Zagórski
Part of the Lecture Notes in Computer Science book series (LNCS, volume 3592)


We consider conditional digital signatures (CDS for short). According to this scheme a creator of a CDS signature, say Alice, signs a message M 1 conditioned by a Bob’s signature of M 2. The string created by Alice can be transformed into an Alice’s digital signature of M 1, once we are given a signature of M 2 generated by Bob. Until the moment of creating a Bob’s signature of M 2, Alice’s signature of M 1 does not exist in a technical sense. This differs from the previous solutions where merely a condition about M 2 has been included into a message signed by Alice. The key feature of our scheme is that Alice prepares the CDS signature before Bob actually signs M 2.

We propose two CDS schemes – the first one prohibits checking that a signature of M 1 has been prepared by Alice until Bob signs M 2. In the second case, Alice can prove interactively that the string created hides a CDS signature of some form, but the proof is useless for a third party.

We present applications of CDS signatures in business and European legal frameworks. In particular, CDS schemes can be used to build a system in which a signature can be retrieved at a given future date. This feature requires only an institution signing periodically the current time. The scheme is also quite useful for wireless mobile networks, where unreliability of communication may cause many problems. CDS scheme may be used there for signing in advance even if a protocol requires a fixed sequential schedule.


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  1. 1.
    Directive 1999/93/EC of the European Parliament and of the Council of 13 December 1999 on a Community framework for electronic signatures. Official Journal of the European Communities L13/12-19 19. 1 (2000)Google Scholar
  2. 2.
    Berta, I., Buttyán, Z., Vajda, I.: Migrating the Untrusted Terminal Problem Using Conditional Signatures. In: International Conference on Information Technology: Coding and Computing (ITCC), pp. 12–16. IEEE, Los Alamitos (2004)CrossRefGoogle Scholar
  3. 3.
    Chaum, D., van Antwerpen, H.: Undeniable signatures. In: Brassard, G. (ed.) CRYPTO 1989. LNCS, vol. 435, pp. 212–216. Springer, Heidelberg (1990)Google Scholar
  4. 4.
    Chaum, D., Pedersen, T.P.: Wallet databases with observers. In: Brickell, E.F. (ed.) CRYPTO 1992. LNCS, vol. 740, pp. 89–105. Springer, Heidelberg (1993)Google Scholar
  5. 5.
    ElGamal, T.: A Public Key Cryptosystem and a Signature Scheme Based on Discrete Logarithms. IEEE Transactions on Information Theory 31(4), 469–472 (1985)zbMATHCrossRefMathSciNetGoogle Scholar
  6. 6.
    Feige, U., Lapidot, D., Shamir, A.: Multiple Noninteractive Zero Knowledge Proofs Under General Assumptions. SICOMP 29(1), 1–28 (1999)zbMATHMathSciNetGoogle Scholar
  7. 7.
    Lee, B., Kim, K.: Fair Exchange of Digital Signatures using Conditional Signature. Symposium on Cryptography and Information Security 2002 (SCIS), vol. 1/2, Shirahama, Japan, 179–184 (2002)Google Scholar
  8. 8.
    De Santis, A., Persiano, G.: Zero-Knowledge Proofs of Knowledge Without Interaction. FOCS 33, 427–436 (1992)Google Scholar
  9. 9.
    Schnorr, C.P.: Efficient Signature Generation for Smart Cards. In: Brassard, G. (ed.) CRYPTO 1989. LNCS, vol. 435, pp. 239–252. Springer, Heidelberg (1990)Google Scholar
  10. 10.
    Shamir, A.: How to Share a Secret. CACM 22(11), 612–613 (1979)zbMATHMathSciNetGoogle Scholar

Copyright information

© Springer-Verlag Berlin Heidelberg 2005

Authors and Affiliations

  • Marek Klonowski
    • 1
  • Mirosław Kutyłowski
    • 1
  • Anna Lauks
    • 1
  • Filip Zagórski
    • 1
  1. 1.Institute of Mathematics and Computer ScienceWrocław University of Technology 

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