International Association for Cryptologic Research

International Association
for Cryptologic Research

CryptoDB

Jorge Nakahara Jr.

Publications

Year
Venue
Title
2010
CHES
2009
FSE
2002
EPRINT
Square Attacks on Reduced-Round Variants of the Skipjack Block Cipher
Jorge Nakahara Jr Bart Preneel Joos Vandewalle
This report surveys on a series of Square attacks on reduced-round versions of the Skipjack block cipher. {\bf Skipjack} is an iterated block cipher encrypting 64-bit plaintext blocks into 64-bit ciphertext blocks, using an 80-bit key. Its design is based on a generalized Feistel Network making up 32 rounds of two different types. This cipher was developed by the National Security Agency for the Clipper chip and Fortezza PC card.
2002
EPRINT
A note on Weak Keys of PES, IDEA and some Extended Variants
Jorge Nakahara Jr Bart Preneel Joos Vandewalle
This paper presents an analysis of the PES cipher in a similar setting as done by Daemen et al. at Crypto'93 for IDEA. The following results were obtained for 8.5 round PES: a linear weak-key class of size $2^{48}$; two distinct differential weak-key classes of size $2^{41}$; two differential-linear weak-key classes of size $2^{62}$. For 17-round PES (double-PES): a linear weak-key class of size $2^7$, and a differential weak-key class of size $2^7$ were found. Daemen suggested a modified key schedule for IDEA in order to avoid weak keys. We found a differential weak-key class of size $2^{83}$ for 2.5-round IDEA under his redesigned key schedule, and differential-linear relations for 3.5-round IDEA.
2001
FSE
2001
EPRINT
SQUARE Attacks on Reduced-Round PES and IDEA Block Ciphers
This paper reports on variants of the Square attack applied to reduced-round versions of the PES and IDEA block ciphers. Attacks on 2.5 rounds of IDEA require $3\cdot 2^{16}$ chosen-plaintexts and recover 78 key bits. A new kind of attack, the Square related-key attack, is applied on 2.5 rounds of IDEA and recovers 32 key bits, with 2 chosen-plaintexts and $2^{17}$ related keys. Similar results hold for 2.5 rounds of PES. Implementations of the attacks on 32-bit block mini-versions of both ciphers confirmed the expected computational complexity. Although our attacks do not improve on previous approaches, this report shows new variants of the Square attack on word-oriented block ciphers like IDEA and PES.
2000
FSE