Cryptographic method modifiable during run time

The invention relates to a cryptographic method that at the beginning of their term on a Computer or microcontroller is undetermined. The compilation process of Key is a program piece generated in machine language, which the cryptographic specifies method during the term of a cryptographic program. By changing the key and recompile the program piece can in modified machine language during the term of a cryptographic program will.

Cryptographic methods are known since ancient times and are widely used before particularly in computer networks, in smart card and communications systems, messages a group of receivers make available, information on their to protect transmission and to authenticate data. International Banking and telecommunications industries require fast and secure data encryption methods, to which are imposed secrecy comply.

Known are methods that make use of the simple substitution of letters, and block ciphers with permutations, additions and substitutions of Bit groups of a linked with a key message. Furthermore, methods that perform arithmetic operations with large numbers, however, in which the reversal of Arithmetic operation for lack of suitable mathematical methods involve high Time is determined, known, and are widely used. Besides exist Methods that perform a large number of shift operations long key or use random number generators to the above bitwise EXOR operation resulting key to perform a message whose encryption and decryption. Virtually any known method for calculation of a bit pattern, which is the Bit pattern is different of the original message, is used in cryptography. For this reason, today there is a flood of algorithms that a more or less large cryptographic security offer.

With mixing of messages to be encrypted and a staggered implementation of various cryptographic methods is attempted usually single known to conceal weaknesses of the known cryptographic methods. An acquaintance Weakness of a cryptographic method, for example, the transparency of the be key in the encrypted data or too short a key, so that by Try a number of possible keys, the encrypted data is decrypted can.

Many well-known cryptographic methods have in common that at the beginning of the execution of the Methods on a computer system, the arrangement of the machine instructions in the program memory the computer system is determined. When trying a known cryptographic breaking method for the purpose of decrypting data, sampling a will large number of possible key in on one or more specialized computers finite time lead to success. Thus, by the extension of the key used higher security can be achieved as a rule, does not render the data encryption time required in the best case linear, however, usually quadratically with the number Key bits grows. For the case that a method is found in the future, with the the number of required to break the cryptographic method attempts substantially is reduced, there is a significant security risk for all already with the procedure encrypted data. however Läge the sequence of interdependent cryptographic processes not in advance firmly, so would the Try different key every possible combination apart nonlinear cryptographic processes are additionally tested. at the same key length and execution time would therefore be the tasting of a factor possible combinations of cryptographic processes larger numtrials required.

"Sequential Test Generator: Past, Present and Future" (Integration, The VLSI Joumal, Dec. 1998) by Yong Chang Kim and Kewal K. Saluja describes a method for Generating random numbers for use as a test pattern by algorithms in turn are generated pseudo-randomly.

US5222139 describes a method for encrypting that of the features The preamble of claim 1 comprises.

The rates in the characterizing part of patent claim 1 solve the Task, an alternative method for generating pseudo-random numbers for cryptographic purposes to create.

Through a compilation process of a key is a piece of program generated in machine language, which the cryptographic method during the term or part of the term of a cryptographic program specifies. By changing the key and recompilation of the cryptographic method, the program fragment in machine language during the term of a cryptographic program be changed, whereby the disadvantages described above do not occur.

This problem is solved by the features listed in claim 1st

An inventive cryptographic method consists of a limited number of cryptographic Program fragments that are executed sequentially in any order can and the contents of a data memory by permutations, remainder calculations, Bit shifts permutations of bit groups and other non-linear change operations often. The order in which the cryptographic Program fragments can be selected, in an advantageous embodiment, a with a password initialized pseudo-random number generator, which controls a compiler, with the cryptographic program fragments finally translated into machine code will. During execution of the machine code of the contents of the data memory is quasi randomly scrambled. carried out the transfer of the data to be encrypted in the encrypted data for example, by logical EXOR operation on the data to be encrypted with the content of the data memory.

The big advantage of a cryptographic method of the invention is to increase the breaking of a comparable known cryptographic method whose Machine code is already set at the beginning of the term, the effort required. The Number of contributory attempts grows exponentially with the number of aligned cryptographic program fragments from which the machine code is constructed. The cryptographic program fragments must be interchangeable, non-linear and have a comparable cryptographic security. Moreover, can in an advantageous embodiment of cryptographic program fragments from where the machine code is constructed on almost any known microprocessor be performed within a few instruction cycles. It can thus in smart card applications, to the use of a special circuit block for encryption operations be waived. The program executed by the processor core of the fragments Machine code offer exponentially by using the code length of the machine code growing number of possible combinations a well expontentiell growing Attack security. The processing time of the machine code, however only increases linearly with the code length to.

The limited number of cryptographic program fragments strung together by the compiler are, other cryptographic operations than permutations, Remainder calculations, bit shifts and / or permutations of bit groups in Data storage perform. In particular, CRC Kodeberechnungen, the calculation of non-linear mathematical formulas and linear congruent random number calculations conceivable. The the compiler available cryptographic program fragments are limited by controlled by the input assignment of constants and by adjusting the operation of variable in your function.

It is also conceivable that the execution of the machine code for better portability the cryptographic method on computer different internal structure with is accomplished an interpreter. The execution speed of machine code is thereby reduced, but can in an advantageous embodiment of a according to the invention cryptographic method from the differences in the Central units of different computer independent interpretation of the machine code be considered.

It is further contemplated that the cryptographic method in a cryptographic Program can also be used as a generator for pseudo-random numbers. The overpass the data to be encrypted in the encrypted data by logical EXOR operation on the data to be encrypted with the content of the data memory on the other hand does not take place here, the contents of the data memory as a quasi random number in a cryptographic program used.

Further features, details and advantages of the invention will be apparent from the accompanying drawing and the following description of an invention cryptographic method. In the drawings:<dl tsize="7" compact="compact"><dt>figure 1</dt><dd>a schematic representation of an embodiment of an inventive cryptographic method</dd></dl>

In the schematic diagram of Figure 1 is designated by the numeral 20 cryptographic Method shown. It consists of a source code by entering the password- 1 controlled source code pseudo-random number generator 2, which has a generated pseudorandom number sequence, which is latched in Quellkodespeicher 3 and is converted by the compiler 4 in machine code fifth The machine code 5 accesses during the execution of the data memory indicated by the reference numeral 6 by frequent read / write operations to. The data memory 6 is a by the password 11 influenced and generated in the pseudo-random number generator 10 Pseudorandom number sequence initialized. Repeated execution of the machine code 5, when executed in a central processing unit of a computer, a large number of bits in Data storage 6 reversed, permuted and data words in the data memory 6 by Division remainder calculations other data words is replaced from the data memory 6, the full contents of the data memory 6 scrambled quasi random. With the aid of EXOR function 8, the data to be encrypted 7 by linking with the Content of the data memory 6 transferred in the encrypted data. 9 The logical EXOR function 8 can both blocks, as well as in smaller data packets as bytes, words, or double words are applied to the data to be encrypted. 7

When decrypting the encrypted data, the encrypted data 9 9 are in reverse direction with the contents of the data memory 6 by the EXOR function 8 logically linked to the data store for data to be encrypted the decrypted 7 to obtain data. The source code password 1, and the password 11 have both the Encryption process and the decryption be identical. Otherwise results upon execution of the machine code 5 in a central processing unit of a computer with high Security is not the same content data in the data memory 6, and there is a faulty transfer of the encrypted data 9 on the reverse applied EXOR function 8 in the decrypted data in the data store for to be encrypted Data. 7

Due to the fact that only after recognition of the password 1 conclusions about the cryptographic algorithm can be drawn, the security of increased order encrypted data by a factor by the number of non-linear combinations cryptographic program fragments 12 which are strung together by the compiler 4, is determined. Forming in an advantageous embodiment, permutations, remainder calculations, Bit shifts and permutations of bit groups the set of possible Program fragments 12, as each of the four program fragments 12 each of the four Program fragments follow 12th The number of possible combinations is calculated accordingly potential from the supply of program fragments 12 to the number of joined Program fragments 12. For example, if n = 16 program fragments 12 from a compiled set of four possible code fragments 12 with the compiler and 4 in the converted machine code 5, a 4ⁿ = 4¹⁶ = 2³² = 4294967296 possibilities determined without the running time of the machine code 5 when executed in a central processing unit a computer influence. It is demanding, however, that a minimum number program fragments 12 joined to the bits in Datenspei cher 7 sufficient to scramble. In an advantageous embodiment, more than 512 fragments of a program 12 joined. There are obtained in this case 4⁵¹² = 2¹⁰²⁴ = 1.7977 * 10³⁰⁸ possible Combinations for the machine code. 5