The basic model of the quantum stream cipher by Y-00 protocol is classified by its modulation format.
So far, PSK, IM, QAM formats as well as a modified QAM format were proposed in the literature.
However, there still exists some room for improvement.
The endpoints or vertex points in the IM and QAM formats have larger decision regions compared to those of other points.
In addition, to make further use of the intrinsic quantum noise appearing in all directions, QAM again becomes a good choice.
Thus another modified QAM format is proposed for the quantum stream cipher by Y-00 protocol and its error performance under the ciphertext only attacks is analyzed.

應用Y-00協定的量子串流密碼的基本模型可以用其調變方式來分類。截至目前為止，基於相位調變、強度調變、正交調幅式調變，與調整型正交調幅式調變的量子串流密碼已由美國西北大學團隊與日本玉川大學團隊陸續提出。但仔細觀察基於上述這些調變格式的量子密碼，可發現依然有些可以加強的地方。
在強度調變與正交調幅格式的星座圖上，位在端點或頂點的訊號，其決定區域比在其他位置的訊號大得多，也更容易成為竊聽者破解密碼系統的目標；此外，在基於相位調變或是強度調變的量子串流密碼裡，只有一個特定方向的量子雜訊能對竊聽者產生實質的干擾效果。因此，為了能進一步利用固有的全向量子雜訊，我們相信基於正交調幅式調變的量子密碼會是不錯的選擇。
本研究提出一個基於調整型同心圓正交調幅式調變、應用Y-00協定的量子密碼系統，經由移除正交調幅式調變在星座圖上具有較大決定區域的訊號而將訊號配置設計成同心圓型。再接著分析此密碼系統在合法接收端的錯誤率、常見的通訊距離下傳送訊號所需的最小平均功率，並分析模擬竊聽者端在四種針對不同標的密文攻擊下的最佳錯誤率表現。再將此模擬結果與基於相位調變的量子密碼系統的錯誤率作比較，討論、分析這二種量子串流密碼的錯誤率表現。

[1] H. P. Yuen, “A new approach to quantum cryptography I: General principles," quant-ph/0311061v6.
[2] O. Hirota, M. Sohma, M. Fuse, and K. Kato, “Quantum stream cipher by the Yuen 2000 protocol: Design and experiment by an intensity-modulation," Phys. Rev. A., vol.72, 022335, 2005.
[3] K. Ohhata, O. Hirota, M. Honda, S. Akutsu, Y. Doi, K. Harasawa, and K. Yamashita, “10-Gb/s optical transceiver using the Yuen 2000 encryption protocol," IEEE J. Light-wave Tech., vol.28, no.18, p.2714, 2010.
[4] O. Hirota, K. Kato, M. Sohma, and T. S. Usuda, “Quantum key disribution with unconditional security for all-optical fiber network," Proc.SPIE, vol.5161, p.320, 2004.
[5] O. Hirota, K. Kato, M. Sohma, T. S. Usuda, and K. Harasawa, “Quantum stream cipher based on optical communications," Proc.SPIE, vol.5551, p.206, 2004.
[6] E. Corndorf, G. Barbosa, C. Liang, H. P. Yuen, and P. Kumar, “High-speed data encryption over 25 km of fiber by two-mode coherent-state quantum cryptography," Opt. Lett., vol.28, no.21, 2003.
[7] E. Corndorf, C. Liang, G. S. Kanter, P. Kumar, and H. P. Yuen, “Quantum-noise randomized data encryption for wavelength-division-multiplexed fiber-optic networks," Phys. Rev. A., vol.71, 062326, 2005.
[8] K. Kato and O. Hirota, “Quantum stream cipher part IV: Effects of the deliberate signal randomization and the deliberate error randomization," Proc. SPIE, vol.6305, 630508, 2006.
[9] O. Hirota and K. Kurosawa, “Immunity against correlation attack on quantum stream cipher by Yuen 2000 protocol," Quant. Inform. Process., vol.6, no.2, pp.81-91, 2007.
[10] K. Kato and O. Hirota, “Quantum quadrature amplitude modulation system and its applicability to coherent-state quantum cryptography," Proc. SPIE, vol.5893, 589303, 2005.
[11] K. Kato and O. Hirota, “10 Gbps quantum stream cipher by Y-00 for super HDTV transmission with provable security," Proc. SPIE, vol.6710, 67100T, 2007.
[12] T. Shimizu, O. Hirota, and Y. Nagasako, “Running key mapping in a quantum stream cipher by the Yuen 2000 protocol," Phys. Rev. A., vol.77, 034305, 2008.
[13] C. W. Helstrom, “Bayes-cost reduction algorithm in quantum hypothesis testing," IEEE Trans. Inform. Theory, vol. IT-28, pp. 359-366, Mar. 1982.
[14] R. Nair et al., “Quantum-noise randomized ciphers," Phys. Rev. A., vol.74, 052309, 2006.
[15] O. Hirota, K. Kato, M. Shoma, and T. S. Ususda, “Quantum key distribution with unconditional security for all optical ber network," quant-ph, 0308007v1.
[16] K. Kato and O. Hirota, “Quantum quadrature amplitude modulation system and its applicability to coherent-state quantum cryptography," Proc. SPIE 5893, 589303, 2005.
[17] C. Shannon, “Communication Theory of Secrecy Systems," Bell Syst. Tehc. J. 28, 656, 1949.