在密碼學中，許多由National Institute of Standards and Technology (NIST)所提出之Block Cipher Modes of Operation (BCMO)已被廣泛地用在明文之區塊加密，但今天若干對BCMOs的攻擊方式已被發現了。換言之，BCMOs已不再是安全的加解密模式了。因此在這篇論文中，我們提出一個植基於回授之安全方式，稱為整合內部回授與外部鏈結加密方法和區塊密文運作的模式(Integration of Feedback and Link Encryption (簡稱IFLE) 模式)。該模式引入了隨機亂數金鑰IV，每次加密時，系統金鑰與IV共同產生了動態系統加密金鑰。再以之與二維運算對明文進行初次加密及以動態子換位盒進行二次加密，其次，以內部回授方式，將產生之結果當作下個明文區塊加密之動態系統加密金鑰。如此，同一個明文區塊會因為前一個明文區塊的不同而產生不同的密文區塊。之後，使用外部金鑰鍵結機制，安全有效地區隔了輸出密文與區塊密文。這是一個以循序動態金鑰對後續明文區塊加密，而增進加密系統破解複雜度與安全性之系統，經我們分析，IFLE是一個高安全性的區塊密文運作模式。

In the cryptography, some Block Cipher Modes of Operation (BCMO) proposed by the National Institute of Standards and Technology (NIST) have been widely used to cipher plaintext blocks. But today, different types of attacks on these BCMOs have been found, meaning the BCMOs have their own security problems. To solve the problem, in this thesis, we propose a novel feedback based security scheme, named the Integration of Feedback and Link Encryption Method (IFLE for short), which employs an internal feedback and an external linking approach to encrypt a plaintext block into a ciphertext block. Generally, in the IFLE, the block-cipher-encryption unit (BCE unit for short) introduces a random number key IV to generate four dynamic encryption keys, which cooperates with a two-dimensional operation we define to first encrypt a plaintext block into a ciphertext block. The ciphertext block is then secondly encrypted by using a dynamic child-transition box. This is the internal feedback mechanism, with which the same plaintext block with different previous plaintext blocks will generate different ciphertext blocks. By using a key chaining mechanism external to the BCE unit, the IFLE effectively and safely isolates the output ciphertext block and the output block of the BCE unit. The IFLE uses sequential dynamic keys to encrypt subsequent plaintext blocks. This truly increases the decryption complexity and security level of the proposed system. According to our analysis, the IFLE is a block cipher scheme with a very high safety.

誌謝 i
中文摘要 ii
Abstract iii
List of Contents iv
List of Figures vi
List of Tables viii
Chapter 1 Introduction 1
Chapter 2 Background and Related Work 3
2.1 Data Encryption Standard (DES) 3
2.2 Advanced Encryption Standard (AES) 5
2.3 Block cipher modes of operation 8
2.3.1 Electronic CodeBook (ECB) 8
2.3.2 Cipher Block Chaining (CBC) 9
2.3.3 Propagating Cipher Block Chaining (PCBC) 10
2.3.4 Cipher feedback (CFB) 11
2.3.5 Output Feedback (OFB) 13
2.3.6 Counter (CTR) 15
Chapter 3 Integration of Feedback and Link Encryption 16
3.1 Binary Adder 16
3.2 Transition Box 20
3.3 Integration of Feedback and Link Encryption (IFLE) 22
3.3.1 Encryption 22
3.3.2 Decryption 25
Chapter 4 Security Analyses 27
4.1 Security of the ECB 27
4.2 Security of the CBC 27
4.3 Security of the CFB 28
4.4 Security of the PCBC 28
4.5 Security of the OFB 28
4.5.1 An attack on IV that can be chosen 28
4.5.2 Attack on IV that cannot be chosen 28
4.6 Security of the CTR 29
4.6.1 Attack on cr able to be chosen 29
4.6.2 Attack on cr unable to be chosen 29
4.7 Security of the IFLE features 30
4.7.1 Dynamic System Keys 31
4.7.2 Security of Two-Dimensional Operation 31
4.7.3 Security of Dynamic Child Transition Box 33
4.7.4 Security of Internal Feedback Mechanism and External Link 33
4.7.5 Analyses of security mechanisms 34
Chapter 5 Performance Analysis 37
5.1 Binary Adder Performance Analysis 37
5.2 System Simulation 37
Chapter 6 Conclusions and Future Work 39
References 40

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