Tweak-Length Extension for Tweakable Blockciphers

Modular design via a tweakable blockcipher (TBC) offers efficient authenticated encryption (AE) schemes (with associated data) that call a blockcipher once for each data block (of associated data or a plaintext). However, the existing efficient blockcipher-based TBCs are secure up to the birthday bound, where the underlying keyed blockcipher is a secure strong pseudorandom permutation. Existing blockcipher-based AE schemes with beyond-birthday-bound (BBB) security are not efficient, that is, a blockcipher is called twice or more for each data block. In this paper, we present a TBC, XKX, that offers efficient blockcipher-based AE schemes with BBB security, by combining with efficient TBC-based AE schemes such as ΘCB3 and

Download Full-text

Format-Preserving Encryption Algorithms Using Families of Tweakable Blockciphers

Information Security and Cryptology - ICISC 2014 - Lecture Notes in Computer Science ◽

10.1007/978-3-319-15943-0_9 ◽

2015 ◽

pp. 132-159 ◽

Cited By ~ 2

Author(s):

Jung-Keun Lee ◽

Bonwook Koo ◽

Dongyoung Roh ◽

Woo-Hwan Kim ◽

Daesung Kwon

Keyword(s):

Encryption Algorithms ◽

Tweakable Blockciphers

Download Full-text

Improved Security Bounds for Generalized Feistel Networks

IACR Transactions on Symmetric Cryptology ◽

10.46586/tosc.v2020.i1.425-457 ◽

2020 ◽

pp. 425-457

Author(s):

Yaobin Shen ◽

Chun Guo ◽

Lei Wang

Keyword(s):

Coupling Analysis ◽

Random Functions ◽

Feistel Networks ◽

Type 3 ◽

Tweakable Blockciphers ◽

First Time

We revisit the security of various generalized Feistel networks. Concretely, for unbalanced, alternating, type-1, type-2, and type-3 Feistel networks built from random functions, we substantially improve the coupling analyzes of Hoang and Rogaway (CRYPTO 2010). For a tweakable blockcipher-based generalized Feistelnetwork proposed by Coron et al. (TCC 2010), we present a coupling analysis and for the first time show that with enough rounds, it achieves 2n-bit security, and this provides highly secure, double-length tweakable blockciphers.

Download Full-text

Turning Online Ciphers Off

IACR Transactions on Symmetric Cryptology ◽

10.46586/tosc.v2017.i2.105-142 ◽

2017 ◽

pp. 105-142

Author(s):

Elena Andreeva ◽

Guy Barwell ◽

Ritam Bhaumik ◽

Mridul Nandi ◽

Dan Page ◽

...

Keyword(s):

Variable Length ◽

Close Relationship ◽

Beyond Birthday Bound ◽

Tweakable Blockciphers ◽

Full Proof ◽

Provably Secure

CAESAR has caused a heated discussion regarding the merits of one-pass encryption and online ciphers. The latter is a keyed, length preserving function which outputs ciphertext blocks as soon as the respective plaintext block is available as input. The immediacy of an online cipher affords a clear performance advantage, but it comes at a price: ciphertext blocks cannot depend on later plaintext blocks, limiting diffusion and hence security. We show how one can attain the best of both worlds by providing provably secure constructions, achieving full cipher security, based on applications of an online cipher around blockwise reordering layers. Explicitly, we show that with just two calls to the online cipher, prp security up to the birthday bound is both attainable and maximal. Moreover, we demonstrate that three calls to the online cipher suffice to obtain beyond birthday bound security. We provide a full proof of this for a prp construction, and, in the ±prp setting, security against adversaries who make queries of any single length. As part of our investigation, we extend an observation by Rogaway and Zhang by further highlighting the close relationship between online ciphers and tweakable blockciphers with variable-length tweaks.

Download Full-text