WO1995034968A1

WO1995034968A1 - Device for decoding decoding algorithms and method of encrypting and decoding such algorithms using the device

Info

Publication number: WO1995034968A1
Application number: PCT/DE1995/000733
Authority: WO
Inventors: Jozsef Bugovics
Original assignee: Esd Vermögensverwaltungsgesellschaft Mbh
Priority date: 1994-06-16
Filing date: 1995-05-30
Publication date: 1995-12-21
Also published as: DE4420970A1; EP0765550A1; AU3862795A

Abstract

The aim of the invention is to develop a system and method which can work with variable encryption algorithms and which ensures the secure transfer of the algorithm without it being detected and prevents the algorithm without it being detected and prevents the algorithm being broken. This aim is achieved by virtue of the fact that the decoding device consists of an integrated circuit (1) associated with a central processing unit (2), an internal non-readable volatile random-access memory (3) used as working memory and an internal non-readable non-volatile read-only memory (4) plus an interface (5), each decoding device differing from every other by the content of the ROM (4) and being partly integrated in an integrated circuit (1) and that the interface (5) is located between the central processing unit (2) and the personal computer (6) and connected, together with central processing unit (2), to the personal computer (6) by a data path (a).

Description

Decryption device for decryption algorithms and method for performing the encryption and decryption thereof

The invention relates to a decryption device for decryption algorithms and the method for carrying out the encryption and decryption thereof, in that the decryption device grants access to authorized persons and excludes unauthorized persons from access.

Digital information is being sent on an increasingly larger scale via secure distribution channels. However, this information should only reach certain recipients and should not be read by unauthorized persons. The procedures for transmitting such information are already very much adapted to the needs of the industry.

However, the further development of computing technology shows problems with the security of the encryption / decryption algorithms currently used.

An encryption algorithm that is currently used primarily by industry is the "data-encryption algorithm" DEA, which has been developed by IBM since 1960 and was declared the norm by the U.S. National Bureau of Standards in 1977.

This encryption algorithm is currently being tested for German and international standards *. ^•

There have been repeated attempts to decrypt information encrypted with the DEA. These have so far not been successful according to the state of the art (since the computing power was not available).

However, special processors have recently been developed which are particularly suitable for decrypting encryption systems. So that it is z. B. possible to break the standard DEA (with hardware costs of about $ 80,000, As of 1992). Richard Zippel gives a good overview of the development in "Programming the Data structure accelerator" in Proceedings of Jerusalem Conference of Information, Technology, Jerusalem, Israel, October 1990.

The development and use of new encryption algorithms is therefore of great importance.

However, since it is not possible to develop a secure encryption algorithm, it is necessary to make the algorithms interchangeable.

The modern options for breaking an encryption algorithm are based on the presence of so-called plain texts (unencrypted

Information) and the associated ciphertexts (encrypted information). To block systems such. B. to break the DEA, the amount of these texts must be very large. This is e.g. B. necessary to perform such methods as differential cryptanalysis by Biham and Shamir. This method is the best attack currently available on trestle encryption systems such as the DEA

(described in Eli Biham and Adi Shamir "Differential Cryptoanalysis of DES-like Cryptosystems" in Journal of Cryptology vol. 4 pp 3-72, 1991).

It is therefore necessary to keep the amount of plain / ciphertexts available to third parties as small as possible. This is possible if the information is encrypted with frequently changing encryption algorithms. Third parties who want to decrypt the messages have to develop a new "cracking algorithm" each time the encryption method is changed.

It is therefore necessary to create a system that can work with variable encryption algorithms. It is also necessary to secure the transmission of the encryption algorithm against recognition and thus to make it more difficult to break the decryption algorithm. This is due to the simple fact that an encryption algorithm that is unknown is much more difficult to break than a known one. This is also necessary so that it is not known which encryption algorithm is used to encrypt which information.

There is therefore a need to find a method with which it is possible to distribute encryption algorithms and to protect the transmission of these against exploration.

Furthermore, it is necessary that the owner of a

Decryption device is not possible to pass on the decryption process and thus enable the exploration of the encryption algorithm.

There is a special processor as part of this process to create the

Distribution and protection of the decryption algorithms from transmission inexpensively and securely implemented.

According to the invention, this object is achieved by the features specified in patent claim 1 and patent claim 2.

The invention is illustrated below with reference to FIG. 1, which is the

Decryption device of decryption algorithms shows and the method for performing the encryption and decryption of digital information.

The decryption device of decryption algorithms shown in FIG. 1 is used for the purpose of illustration in multiple personal computers, wherein digital information is sent to selected decryption owners.

The decryption device shown here consists of an integrated circuit 1, a central processor CPU-2, an internal non-readable volatile memory with random access RAM-3 as working memory and a

internal non-readable non-volatile random access memory ROM-4, in which an internal non-readable decryption algorithm (EI) is stored, and an interface 5 are assigned, which is arranged between the central processor CPU-2 and the personal computer 6 and with the personal computer 6 is connected to data path a, and is partially integrated in an integrated circuit.

The method for carrying out the transmission of the decryption algorithm is shown in FIG. 1 in that the decryption device is used in a number of personal computers, digital information being sent to selected owners of decryption devices.

The transmission of a decryption algorithm to a decryption device is as follows:

The distributor chooses an encryption algorithm VE. This is intended to encrypt the information transmitted later. This

Encryption algorithm should be kept secret and must still be secure enough to offer security when encrypting messages. For this, z. B. different types of DES (e.g. with different S-boxes) or other encryption methods.

Now the VE encryption algorithm will be used

Decryption algorithm EE encrypted to illegible algorithm EEV. Any user of a decryption device who wants to receive a decryption algorithm can now report to the distribution point. This can e.g. B. verbally (also over the phone), in writing or electronically. He must identify himself using the decoder's public serial number. Since this serial number was only assigned once, the decryption device can be clearly identified. The distribution point can now decide whether the recipient is authorized to receive the decryption algorithm. This can also depend on payment.

When this is resolved, the encrypted decryption algorithm becomes

Transmit users of the decryption device and there decrypted to the algorithm EE in the decryption device. It is then possible to decrypt messages that have been encrypted using the encryption algorithm VE.

This is now to be illustrated using an exemplary embodiment.

The receipt of a decryption algorithm by the owner of the decryption device with the serial number SN = 1 is explained as an example.

The encrypted decryption algorithm to be transmitted to the decryption device with the serial number SN = 1 is generated as follows:

The distributor of the messages chooses an encryption algorithm VE, which is then to be used to encrypt the message to be transmitted later. This encryption algorithm is never publicly accessible, but is only transmitted in encrypted form.

The manufacturer of the decryption device (the distributor of the

Decryption algorithms and messages) have internal Decryption algorithms EI and also the associated ones

Encryption algorithms EIU of all decryption devices. These are stored in a database at the manufacturer or at the distributor.

It is EIIA, the internal decryption algorithm EI of the decryption device with the internal serial number SN = 1, which is known only to the manufacturer of the decryption device. Furthermore, EI1UA, the encryption algorithm also known only to the manufacturer of the decryption device, is suitable for EI IX.

Now the decryption algorithm EE to be transmitted to the decryption device is encrypted. This is done in such a way that the

Decryption algorithm EE with that for internal

Decryption algorithm EI matching encryption algorithm EIU to the illegible algorithm EEV is encrypted according to the following formula:

EEV: = EI1U (EE).

This encrypted algorithm EEV is transmitted to the decryption device with the serial number SN = 1.

This can e.g. B. verbally (also over the phone), in writing or electronically.

■ The transmitted algorithm is relatively short. This makes it difficult to crack the internal decryption algorithm of the decryption device EI. As shown above, many piain and

Ciphertexts are available to use promising cracking algorithms. In this case, however, this is not possible due to the brevity of the transmitted encrypted decryption algorithm EEV.

Now the decryption device is made functional at the receiver. The procedure after switching on the supply voltage or after an interruption in processing is as follows.

The central processor CPU-2 introduces one with the internal non-readable non-volatile memory with random access ROM-4 and the internal non-readable volatile memory with random access RAM-3

Self test through. This could e.g. B. done by a checksum.

Now the encrypted decryption algorithm EEV is read into the decryption device via interface 5. The decryption algorithm was previously entered in encrypted form by the user of the decryption device or read in another form.

Next, ROM-4 is stored using the internal non-readable non-volatile random access memory

Decryption algorithm EI the present in encrypted form

Decryption algorithm EEV decrypted with the internal decryption process EI. This is done in such a way that the central processor CPU-2, the decryption device stored in the internal non-readable non-volatile memory with random access ROM-4, is entered into the personal computer 6, executes instructions of the decryption algorithm EI and decrypts the encrypted decryption algorithm EEV as follows:

EE: = EI1 (EEV).

With this method, since the internal decryption algorithm Eil matches the encryption algorithm EIU1 with which the decryption algorithm EE was encrypted, the original decryption algorithm EE is created. This is stored in the internal non-readable volatile memory with random access RAM-3 and is therefore not accessible from the outside. It is therefore not possible to pass on the decryption algorithm since it is worthless in encrypted form and is not available in unencrypted form.

The decryption device is now ready for use.

The decryption of an encrypted message NV, e.g. B. verbally (also over the phone), in writing or electronically, in the decryption device with the serial number SN = 1 is now as follows:

The CPU loads the key K and the message NV via the interface 5. This

Keys must be transmitted in a secure way that is not accessible to third parties; this can also be done by encryption.

The message is then decrypted by the central processor CPU-2 using the decryption algorithm EE using the key K:

NE: = EE (NV, K).

The decrypted information NE is then output by the central processor CPU-2 via the interface 5 and is available to the receiver.

It is thus possible to encrypt information with different encryption algorithms and to decrypt with different decryption devices without the

Decryption algorithm must be made known or already exists in the decryption device.

Furthermore, the transmitted decryption algorithm can neither be passed on nor investigated, since it encrypts individually for each decryption device is transmitted and stored there is not readable and is only available for internal use of the decryption device with the corresponding serial number.

Reference symbols used

1 -integrated circuit-

2 -Central processor CPU-

3 - Internal non-readable volatile memory with random access RAM

4 -internal non-readable non-volatile memory with random access ROM-

5 interface

6 personal computers

a data path

used abbreviations

CPU = central processor

DEA = data encryption standard

EI = internal decryption algorithm

Eil = decryption algorithm internally for the decryption device with the serial number SN = 1

EIU = suitable for the internal decryption algorithm EI

Encryption algorithm

EI1U = encryption algorithm for the internal decryption algorithm for the decryption device with the serial number SN = 1

EE = decryption algorithm for encrypting

news

EEV = encrypted decryption algorithm for transmission

NE = unencrypted or decrypted message

NV = encrypted message

Key K = key for decrypting messages

VE = encryption algorithm when distributing the information to encrypt the digital information suitable for EE

(: =) = results from

Claims

1. decryption devices of decryption algorithms, characterized in that the distributor of the decryption algorithm encrypts them with an encryption algorithm (EIU) which corresponds to the decryption algorithm (EI) that is received in the respective one

There is an internal decryption unit that the decryption algorithm (EI) is not accessible to the public and cannot be explored, the user of the decryption device enters the encrypted decryption algorithm in the decryption device and this is decrypted within the decryption device, the decryption device comprising an integrated circuit - (l), the central processor CPU- (2), an internal non-readable volatile memory with random access RAM- (3) as working memory and an internal non-readable non-volatile memory with random access ROM- (4) and an interface ( 5) are assigned in that each decryption device differs from each other by the content of the internal non-volatile memory with random access ROM- (4) and partly in an integrated circuit- (l) and that the interface (5) between de m -central processor CPU- (2) and the personal computer (6) is arranged and connected to the -central processor CPU- (2) with the data path (a).

2. Decryption device of decryption algorithms and methods for performing the encryption and decryption thereof, characterized in that in

Step 1

from the distributor of the decryption algorithms, these are encrypted with an encryption algorithm (EIU) known only to the manufacturer of the decryption device (which corresponds to the decryption algorithm (EI) in the decryption unit), as follows: EEV: = EIU (EE)

and this encrypted algorithm (EEV) is transmitted to the decryption device, after which the decryption device carries out a self-test with the central processor CPU- (2) with the internal non-readable non-volatile random access memory ROM- (4), and that

The encrypted decryption algorithm (EEV) is read into the decryption device via the interface (5) and now with the help of the decryption algorithm (EI) stored in the internal non-readable non-volatile memory with random access ROM- (4) the encrypted decryption algorithm (EEV) with the internal decryption process

(EI) decrypted

EE: = EI (EEV)

with this method, the original decryption algorithm (EE) is again created, which is stored in the internal non-readable volatile memory with random access RAM- (3) and is therefore not accessible from the outside, so that the decryption device with the decryption algorithm (EE) is ready for use is and the decryption of a message (NV) takes place as follows that the CPU via the interface (5) the key (K), which via a secure transmission path, for. B. encryption, must be transmitted, and the message (NV) loads and the

Message from the central processor CPU- (2) is decrypted using the decryption algorithm (EE) using the key (K)

NE: = EE (NV, K) and the decrypted information (NE) is output by the central processor CPU- (2) via the interface (5) and is available to the recipient.