## CryptoDB

### Kazuhiro Suzuki

#### Publications

Year
Venue
Title
2008
EUROCRYPT
2008
EPRINT
In the model of perfectly secure message transmission schemes (PSMTs), there are $n$ channels between a sender and a receiver. An infinitely powerful adversary $\A$ may corrupt (observe and forge)the messages sent through $t$ out of $n$ channels. The sender wishes to send a secret $s$ to the receiver perfectly privately and perfectly reliably without sharing any key with the receiver. In this paper, we show the first $2$-round PSMT for $n=2t+1$ such that not only the transmission rate is $O(n)$ but also the computational costs of the sender and the receiver are both polynomial in $n$. This means that we solve the open problem raised by Agarwal, Cramer and de Haan at CRYPTO 2006.
2007
EPRINT
It is known that perfectly secure ($1$-round, $n$-channel) message transmission (MT) schemes exist if and only if $n \geq 3t+1$, where $t$ is the number of channels that the adversary can corrupt. Then does there exist an {\it almost} secure MT scheme for $n=2t+1$ ? In this paper, we first sum up a number flaws of the previous {\it almost} secure MT scheme presented at Crypto 2004. (The authors already noted in thier presentation at Crypto'2004 that their scheme was flawed.) We next show an equivalence between almost secure MT schemes and secret sharing schemes with cheaters. By using our equivalence, we derive a lower bound on the communication complexity of almost secure MT schemes. Finally, we present a near optimum scheme which meets our bound approximately. This is the first construction of provably secure almost secure ($1$-round, $n$-channel) MT schemes for $n=2t+1$.
2007
EPRINT
The hash function HAVAL is an Australian extension of well known Merkle-Damg\r{a}rd hash functions such as MD4 and MD5. It has three variants, $3$-, $4$- and $5$-pass HAVAL. On $3$-pass HAVAL, the best known attack finds a collision pair with $2^{7}$ computations of the compression function. To find $k$ collision pairs, it requires $2^{7}k$ computations. In this paper, we present a better collision attack on $3$-pass HAVAL, which can find $k$ collision pairs with only $2k+33$ computations. Further, our message differential is different from the previous ones. (It is important to find collisions for different message differentials.)

#### Coauthors

Kaoru Kurosawa (4)