インターネットの急速な進展により，ネットワークセキュリティの重要性が叫ばれるようになってきた．ネットワークセキュリティ対策はさまざまな面から施さねばならないが，その基盤をなすのは，技術的対策である．なかでも暗号技術は，守秘と認証という基本機能をもち，情報を直接守るとともに，他のセキュリティ技術の要素技術としても用いられる．本稿では，この暗号技術の現状と動向を中心に，ネットワークセキュリティ対策について概観する．

本稿では，ブロック単位のスクランブル処理に基づく画像暗号化方式について解説する．一般に，暗号化された画像は周波数が高く，原画像と比較して，その圧縮効率が低下する．一方，この画像暗号化方式では，暗号化領域での圧縮効率が考慮されており，原画像と暗号化画像とで，圧縮効率が著しい差異を生じることなく保持される．また，総当たり攻撃や暗号文単独攻撃など既存の攻撃に対しても強固な耐性をもち，安全性の面からも評価されている．ここでは，著者らが行ってきた研究を中心にその概要と特徴について述べる．

Digital packet communication usually has structure of multiple layers and can be used by flexible operation. Nowadays, this type of communication is used for various networks such as Internet or aviation radio communication.

Wiretapping is a threat to general communication users in such type of networks. For example, very important information may be stolen by CRACKER or be rewritten while we havn't known yet. To protect users from these accidents, technologies of network data encryption or user authentication are very useful.

This report describes a new implementation method of cryptography and authentication and the result of the communication test using remote login command as a typical application on Internet. I installed stream-type data encryption routine to avoid wiretapping and new user authentication routine with advantage of “password” type method into the remote login command contained server and client programs. Moreover, I made communication experiment with the modified remote login program and evaluated the performance. The remote login program has enough performance about securing transmitted data or valid user authentication.

Lightweight block ciphers, which can be implemented with low cost, are suitable for improving the safety of small devices. PRINCE is a typical lightweight block cipher and suitable for unrolled architecture implementation. In addition, PRINCE can be achieved low latency and embedded in a small area. However, it has been reported that PRINCE with unrolled architecture implementation is vulnerable to power analysis. Regarding countermeasure against power analysis, the threshold implementation and rotating sboxes masking are popular countermeasures, these require large implementation overhead though. Therefore, this study proposes a low-overhead power analysis countermeasure method for PRINCE with unrolled architecture. Moreover, evaluation experiments using a field-programmable gate array verify the effectiveness of the proposed method. In experiments, the proposed method improved tamper resistance and reduced implementation overhead in comparison with the conventional method.