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2021

A Key Manipulation Attack on Some Recent Isogeny-Based Key Agreement Protocols

Gönen, M. E., Tutdere, S. ., & Uzunkol, O. . (2021). A Key Manipulation Attack on Some Recent Isogeny-Based Key Agreement Protocols. Bulletin of the Iranian Mathematical Society . http://doi.org/10.1007/s41980-021-00534-6

Abstract

Recently, Daghigh et al. proposed some isogeny-based key agreement protocols in Bull. Iran. Math. Soc. 43 (2017), no. 4, 77-88. They claimed that their key exchange protocols based on supersingular isogenies provide the same security level as the Jao et al.’s protocol SIDH. This paper addresses first a vulnerability of these protocols to a key manipulation attack. Hence, unlike the security claims of Daghigh et al., these protocols unfortunately do not provide the same security when compared with SIDH. Second, we show in particular that the secret dual isogenies of the protocols can easily be retrieved by applying our key manipulation attack. We also discuss lastly the countermeasures to this attack.
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Uzunkol, Osmanbey

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Fachbereich 3: Information und Kommunikation
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2021

Journal Article

Mehmet Gönen

Seher Tutdere

Osmanbey Uzunkol
Delegating Supersingular Isogenies over F_p^2 with Cryptographic Applications

Pedersen, R. ., & Uzunkol, O. . (2021). Delegating Supersingular Isogenies over F_p^2 with Cryptographic Applications. IACR Cryptol. EPrint Arch., 2021, 506. Abgerufen von https://eprint.iacr.org/2021/506
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Uzunkol, Osmanbey

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2021

Journal Article

Robi Pedersen

Osmanbey Uzunkol

2020

Construction of arithmetic secret sharing schemes by using torsion limits

Tutdere, S. ., & Uzunkol, O. . (2020). Construction of arithmetic secret sharing schemes by using torsion limits. Hacettepe Journal of Mathematics and Statistics, 49, 638–647. http://doi.org/10.15672/hujms.460348
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Uzunkol, Osmanbey

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2020

Journal Article

Seher Tutdere

Osmanbey Uzunkol

2019

Comments on “verifiable outsourced attribute-based signature scheme”

Uzunkol, O. . (2019). Comments on “verifiable outsourced attribute-based signature scheme”. Multimedia Tools and Applications , 78(9), 11735–11742. http://doi.org/10.1007/s11042-018-6725-7

Abstract

Ren and Jiang recently published a “verifiable outsourced attribute-based signature scheme” in Multimedia Tools and Applications. In this note, we first provide two attacks on the verifiability of the semi-signatures of this scheme by showing that a malicious signing-cloud service provider (S-CSP) can always cheat the signer unlike the authors’ claim. Moreover, one of these attacks also implies that an untrusted S-CSP can always forge signatures contrary to the claimed unforgeability against chosen message attacks. Therefore, this scheme unfortunately does not satisfy the main security properties for a delegated signature scheme.
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Uzunkol, Osmanbey

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2019

Journal Article

Osmanbey Uzunkol
Secure delegation of group exponentiations: Efficient and fully verifiable schemes with two servers

Moritz, S. ., & Uzunkol, O. . (2019). Secure delegation of group exponentiations: Efficient and fully verifiable schemes with two servers. Security and Privacy, n/a, e70. http://doi.org/https://doi.org/10.1002/spy2.70 (Original work published 2019)

Abstract

Abstract Recent interactions between cloud service providers and mobile resource-constrained devices have increased the interest on the delegation of expensive computations to powerful external server providers. At the same time, security and verifiability of the delegated computation are challenging though highly demanded requirements for various application scenarios. Many security solutions using advanced cryptographic technologies require a large number of highly expensive group exponentiations (GEs). In this paper, we address the problems regarding secure and verifiable delegation of GEs. We first analyze two delegation schemes for GEs both introduced recently in Cluster Computing by Fu et al with the claim that they both provide full verifiability. Particularly, we show that the first scheme is only verifiable with a probability at most 2/3, and the second scheme is totally unverifiable. Then, we propose a secure, efficient and fully verifiable delegation scheme InvDel for a GE using two servers, where one of which is malicious. With InvDel the delegator does not require computations of any group inversions (GIs) while providing full verifiability. Then, we extend InvDel to SimInvDel which is the first, efficient and secure delegation scheme for n-simultaneous GEs achieving full verifiability for n > 1. Secondly, we give implementation results of InvDel and SimInvDel using an Android application together with a comprehensive efficiency analysis of computation and communication with the previous schemes. For instance, when the required CPU costs for a single GE are compared with a 4092-bit modulus, InvDel is more than 220-times (resp. more than two times) more efficient than the local computation (resp. using a previous fully verifiable scheme proposed in the literature). Finally, we also utilize InvDel and SimInvDel to speed-up the verification of Schnorr s signature and Cramer-Shoup encryption schemes.
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Uzunkol, Osmanbey

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2019

Journal Article

Stephan Moritz

Osmanbey Uzunkol

cloud security

lightweight cryptography for mobile security

secure delegation

verifiable computation
Secure Delegation of Isogeny Computations and Cryptographic Applications

Pedersen, R. ., & Uzunkol, O. . (2019). Secure Delegation of Isogeny Computations and Cryptographic Applications. In Proceedings of the 2019 ACM SIGSAC Conference on Cloud Computing Security Workshop (S. 29–42). New York, NY, USA: Association for Computing Machinery. http://doi.org/10.1145/3338466.3358913

Abstract

We address the problem of speeding up isogeny computation for supersingular elliptic curves over finite fields using untrusted computational resources like third party servers or cloud service providers (CSPs). We first propose new, efficient and secure delegation schemes. This especially enables resource-constrained devices (e.g. smart cards, RFID tags, tiny sensor nodes) to effectively deploy post-quantum isogeny-based cryptographic protocols. To the best of our knowledge, these new schemes are the first attempt to generalize the classical secure delegation schemes for group exponentiations and pairing computation to an isogeny-based post-quantum setting. Then, we apply these secure delegation subroutines to improve the performance of supersingular isogeny-based zero-knowledge proofs of identity. Our experimental results show that, at the 128-bit quantum-security level, the proving party only needs about 3% of the original protocol cost, while the verifying party s effort is fully reduced to comparison operations. Lastly, we also apply our delegation schemes to decrease the computational cost of the decryption step for the NIST postquantum standardization candidate SIKE.
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2019

Conference Paper

Robi Pedersen

Osmanbey Uzunkol

supersingular isogeny cryptography

lightweight cryptography

post-quantum cryptographic protocols

secure computation outsourcing

2018

Still wrong use of pairings in cryptography

Uzunkol, O. ., & Kiraz, M. S. (2018). Still wrong use of pairings in cryptography. Applied Mathematics and Computation, 333, 467–479. http://doi.org/10.1016/j.amc.2018.03.062 (Original work published 2025)
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2018

Journal Article

Osmanbey Uzunkol

Mehmet Kiraz
Hide the Modulus: A Secure Non-Interactive Fully Verifiable Delegation Scheme for Modular Exponentiations via CRT

Uzunkol, O. ., Rangasamy, J. ., & Kuppusamy, L. . (2018). Hide the Modulus: A Secure Non-Interactive Fully Verifiable Delegation Scheme for Modular Exponentiations via CRT. In Developments in Language Theory (S. 250–267). Springer International Publishing. http://doi.org/10.1007/978-3-319-99136-8_14
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2018

Conference Paper

Osmanbey Uzunkol

Jothi Rangasamy

Lakshmi Kuppusamy
A More Efficient Secure Fully Verifiable Delegation Scheme for Simultaneous Group Exponentiations

Moritz, S. ., & Uzunkol, O. . (2018). A More Efficient Secure Fully Verifiable Delegation Scheme for Simultaneous Group Exponentiations. In Lecture Notes in Computer Science (S. 74–93). Springer International Publishing. http://doi.org/10.1007/978-3-030-03712-3_7
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2018

Conference Paper

Stephan Moritz

Osmanbey Uzunkol

2017

A More Efficient 1-Checkable Secure Outsourcing Algorithm for Bilinear Maps.

Kalkar, Öznur ., Kiraz, M. S., Sertkaya, I. ., & Uzunkol, O. . (2017). A More Efficient 1-Checkable Secure Outsourcing Algorithm for Bilinear Maps. In Information Security Theory and Practice - 11th IFIP WG 11.2 International Conference, WISTP 2017, Heraklion, Crete, Greece, September 28-29, 2017, Proceedings (S. 155–164). http://doi.org/10.1007/978-3-319-93524-9_10
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2017

Conference Paper

Öznur Kalkar

Mehmet Kiraz

Isa Sertkaya

Osmanbey Uzunkol

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