Multi-operation data encryption mechanism using dynamic data blocking and randomized substitution

Existing cryptosystems deal with static design features such as fixed sized data blocks, static substitution and apply identical set of known encryption operations in each encryption round. Fixed sized blocks associate several issues such as ineffective permutations, padding issues, deterministic brute force strength and known-length of bits which support the cracker in formulating of modern cryptanalysis. Existing static substitution policies are either not optimally fit for dynamic sized data blocks or contain known S-box transformation and fixed lookup tables. Moreover, static substitution does not directly correlate with secret key due to which it has not been shown safer especially for Advanced Encryption Standard (AES) and Data Encryption Standard (DES). Presently, entire cryptosystems encrypt each data block with identical set of known operations in each iteration, thereby lacked to offer dynamic selection of encryption operation. These discussed, static design features are fully known to the cracker, therefore caused the practical cracking of DES and undesirable security pitfalls against AES as witnessed in earlier studies. Various studies have reported the mathematical cryptanalysis of AES up to full of its 14 rounds. Thus, this situation completely demands the proposal of dynamic design features in symmetric cryptosystems. Firstly, as a substitute to fixed sized data blocks, the Dynamic Data Blocking Mechanism (DDBM) has been proposed to provide the facility of dynamic sized data blocks. Secondly, as an alternative of static substitution approach, a Randomized Substitution Mechanism (RSM) has been proposed which can randomly modify session-keys and plaintext blocks. Finally, Multi-operation Data Encryption Mechanism (MoDEM) has been proposed to tackle the issue of static and identical set of known encryption operations on each data block in each round. With MoDEM, the encryption operation can dynamically be selected against the desired data block from the list of multiple operations bundled with several sub-operations. The methods or operations such as exclusive-OR, 8-bit permutation, random substitution, cyclic-shift and logical operations are used. Results show that DDBM can provide dynamic sized data blocks comparatively to existing approaches. Both RSM and MoDEM fulfill dynamicity and randomness properties as tested and validated under recommended statistical analysis with standard tool. The proposed method not only contains randomness and avalanche properties but it also has passed recommended statistical tests within five encryption rounds (significant than existing). Moreover, mathematical testing shows that common security attacks are not applicable on MoDEM and brute force attack is significantly resistive

Protection against overflow attacks

Buffer overflow happens when the runtime process loads more data into the buffer than its design capacity. Bad programming style and lack of security concern cause overflow vulnerabilities in almost all applications on all the platforms;Buffer overflow attack can target any data in stack or heap. The current solutions ignore the overflowed targets other than return address. Function pointer, for example, is a possible target of overflow attack. By overflowing the function pointer in stack or heap, the attacker could redirect the program control flow when the function pointer is dereferenced to make a function call. To address this problem we implemented protection against overflow attacks targeting function pointers. During compiling phase, our patch collects the set of the variables that might change the value of function pointers at runtime. During running phase, the set is protected by encryption before the value is saved in memory and decryption before the value is used. The function pointer protection will cover all the overflow attacks targeting function pointers;To further extend the protection to cover all possible overflowing targets, we implemented an anomaly detection which checks the program runtime behavior against control flow checking automata. The control flow checking automata are derived from the source codes of the application. A trust value is introduced to indicate how well the runtime program matches the automata. The attacks modifying the program behavior within the source codes could be detected;Both function pointer protection and control flow checking are compiler patches which require the access to source codes. To cover buffer overflow attack and enforce security policies regardless of source codes, we implemented a runtime monitor with stream automata. Stream automata extend the concept of security automata and edit automata. The monitor works on the interactions between two virtual entities: system and program. The security policies are expressed in stream automata which perform Truncation, Suppression, Insertion, Metamorphosis, Forcing, and Two-Way Forcing on the interactions. We implement a program/operating system monitor to detect overflow attack and a local network/Internet monitor to enforce honeywall policies

Safe Cryptography Algorithms

V této práci jsou popsány současné kryptografické algoritmy, porovnání jejich vlastností, silné a slabé stránky a vhodné případy použití jednotlivých algoritmů. Hlavními tématy jsou bezpečnost algoritmů, jejich chyby, vylepšení a odolnost proti průnikům. Jako doplněk k šifrám je věnována pozornost i hašovacím funkcím. Také jsou ukázány nejběžnější metody kryptoanalýzy. Jako použití popsaných algoritmů v praxi uvádím systémy pro zabezpečený přenost dat, kterými jsou SSH a SSL/TLS a je proveden také praktický útok na SSL spojení. V závěru se nachází shrnutí a doporučení vybraných bezpečných algoritmů pro další použití a bezpečné parametry spojení pro SSH a SSL/TLS.In this thesis there is description of cryptographic algorithms. Their properties are being compared, weak and strong points and right usage of particular algorithms. The main topics are safeness of algorithms, their bugs and improvements and difficulty of breaching. As a complement to ciphers there are also hash functions taken in consideration. There are also showed the most common methods of cryptanalysis. As a practical application of described algorithms I analyze systems for secure data transfer SSH and SSL/TLS and demonstrate an attack on SSL connection. In conclusion there is recommendation of safe algorithms for further usage and safe parameters of SSH and SSL/TLS connections.