| 2011 | IWSEC | Unforgeability of Re-Encryption Keys against Collusion Attack in Proxy Re-Encryption. | Ryotaro Hayashi, Tatsuyuki Matsushita, Takuya Yoshida, Yoshihiro Fujii, Koji Okada |
| 2008 | IWSEC | Simple and Efficient Group Signature Scheme Assuming Tamperproof Devices. | Takuya Yoshida, Koji Okada |
| 1994 | ASIACRYPT | Combinatorial Interpretation of Secret Sharing Schemes. | Kaoru Kurosawa, Koji Okada |
| 1994 | ASIACRYPT | Security of the Center in Key Distribution Schemes. | Kaoru Kurosawa, Koji Okada, Keiichi Sakano |
| 1994 | ASIACRYPT | Low Exponent Attack against Elliptic Curve RSA. | Kaoru Kurosawa, Koji Okada, Shigeo Tsujii |
| 1994 | ASIACRYPT | Lower Bound on the Size of Shares of Nonperfect Secret Sharing Schemes. | Koji Okada, Kaoru Kurosawa |
| 1993 | EuroCrypt | Nonperfect Secret Sharing Schemes and Matroids. | Kaoru Kurosawa, Koji Okada, Keiichi Sakano, Wakaha Ogata, Shigeo Tsujii |
| 1987 | ICSE | Parameterized Programming in OBJ2. | Kokichi Futatsugi, Joseph A. Goguen, Jos Meseguer, Koji Okada |
| 1982 | ICSE | A Hierarchical Structuring Method for Functional Software Systems. | Kokichi Futatsugi, Koji Okada |