Cryptography – Particular algorithmic function encoding
Reexamination Certificate
1998-08-06
2001-08-07
Swann, Tod (Department: 2132)
Cryptography
Particular algorithmic function encoding
C380S029000
Reexamination Certificate
active
06272221
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an encryption apparatus capable of keeping data-confidentiality in data communication or data accumulation and relates also to a recording medium for recording a program for realizing the above encryption apparatus.
This application is based on Patent Application No. Hei 9-213274 filed in Japan, and the content of which is incorporated herein by reference.
2. Background Art
A representative example of common-key cryptosystems (one example is disclosed in Japanese Patent Application, First application No. 51-108701, “Encryption Apparatus”) is a cryptosystem called DES (Data Encryption Standard). The DES is characterized in that it realizes a complicated encryption by repeating comparatively simple conversion processing. A variety of improvements are proposed in order to secure higher confidentiality of ciphers.
An example of such systems is the CBC mode of DES (disclosed in, for example, “Modern Cryptography” edited by Shinichi Ikeno and Kenji Koyama, an explanation of which is described in “Electronic Communication Society” p.66 (1986)). The CBC mode of DES is developed so as to make it difficult to perform decryption of the cipher, due to the fact that encryption of a block of the plaintext is affected by a result of the preceding encryption, and, as a result, the statistical characteristics of the plaintext are altered.
However, this cryptosystem has unsolved drawbacks in that encryption of one block cannot start unless encryption of the previous block is completed, and, in that there is still remaining a danger that this system suggests clues to a cryptoanalyst who intend to decrypt a cipher, since this system uses the same key for encryption of a number of blocks, which results in lack of confidentiality.
One of measures for solving these drawbacks is proposed as the “cipher chaining system”, disclosed in Japanese Patent Application, First Publication No. Hei 6-266284. The cipher chaining is a system in which an intermediate-key for acting on a conversion means performing encryption is updated for every plaintext according to an initial-value and a parcel of update-information of the intermediate-key.
However, this system is provided with only one series of initial-values for the intermediate-key.
In the conventional cipher chaining system, when a chosen plaintext cryptanalysis is performed by inputting the same plaintext successively, since all of the intermediate-key update-information is identical, and since the initial-value of the intermediate-key is fixed, the intermediate-key will not be updated. Consequently, there is a remaining danger that one can identify a change whether or not the intermediate-key is updated by observing the cipher while inputting the same plaintext successively.
Therefore, it is the object of the present invention to provide an encryption apparatus, which does not give a large tract of ciphertext encrypted by the same key and which makes it difficult for a cryptoanalyst to presume the intermediate-key update information stored in the apparatus. The encryption apparatus of the present invention is capable of high speed encryption by a parallel encryption system, and is also capable of maintaining an encryption speed, because it is possible to adopt a multiple parallel encryption mode in the case when there is the number of steps for a repetitive conversion.
SUMMARY OF THE INVENTION
The first embodiment of the present invention provides an encryption apparatus for producing a ciphertext string corresponding to a plaintext string based on an encryption key, said apparatus comprising:
at least one conversion means for performing linear or non-linear conversion of the bit strings;
an intermediate-key generating means for generating an initial-value of the intermediate-key by performing linear or non-linear bit-string conversion for an inputted intermediate-key;
an intermediate-key memory means for updating and storing the intermediate-key using an intermediate-key update-information;
wherein at least one of said conversion means forms a pair with said intermediate-key memory means, at least one of said paired conversion means is subjected to control of an intermediate-key stored in said intermediate-key memory means and generates an intermediate-key update-information for updating the intermediate-key whenever the bit string conversion is performed and transmits said intermediate-key update-information to said intermediate-key memory means forming a pair with said conversion means; said intermediate-key memory means stores a predetermined number of at least one of initial-values which is delivered from said intermediate-key generating means; and said apparatus comprising a selecting means for selecting at least one initial-value among initial-values stored in said intermediate-key memory means whenever the conversion of a bit string is performed, controlling the conversion means in a pair and updating the intermediate-key based on said intermediate-key update-information.
The first embodiment is characterized in that a bit string (an intermediate-key) for controlling the encryption conversion is updated whenever the encryption is carried out. This brings a result that the intermediate-key is updated whenever the encryption of a block is completed; thereby, a cryptoanalyst cannot obtain a large tract of ciphertexts which use the same key. Particularly, since at least one intermediate-key is provided and since the intermediate-key is updated by use of different initial-values, it becomes more difficult to perform decryption when compared with the conventional example in which the initial value is limited to one.
The second embodiment of the present invention provides an encryption apparatus, which is modified from the first embodiment in that said intermediate-key memory means stores a predetermined number of at least one parcel of the intermediate-key update-information delivered in the past; deletes an oldest intermediate-key update-information whenever receiving new intermediate-key update-information, and generates an intermediate-key to transmit to the following conversion means from a set of parcels of the intermediate-key update-information and a set of the intermediate-key initial-values as an input.
The second embodiment is characterized in that both the intermediate-key initial-values and the intermediate-key update-information are stored in a plurality of buffers, so that it is possible to suppress during communication the passing of bit errors to following bits.
The third embodiment of the present invention is an encryption apparatus which is modified from the first embodiment in that the intermediate-key memory means provided with more than two conversion means and being coupled with another conversion means in addition to the conversion means which originally forms a pair comprises a selection means to select intermediate-key update-information and an initial-value of the intermediate-key from a set of parcels of intermediate-key update-information and a set of initial-values of the intermediate-key and generates an intermediate-key to be transmitted to the following conversion means by inputting at least one parcel of selected intermediate-key update-information or at least one of initial-values, or at least one parcel of selected intermediate-key update-information and at least one of initial-values.
The third embodiment of the present invention is characterized in that the initial-values and the update-information of the intermediate-key stored in the intermediate-key memory means are delivered not only to the conversion means paired with the memory means, but also to the other conversion means, so that the types of updated intermediate-key are increased and decryption is rendered difficult.
The fourth embodiment of the present invention provides an encryption apparatus which is modified from the first embodiment in that the intermediate-key memory means provided with more than two conversion means and being coupled with another conversion means in addi
Foley & Lardner
NEC Corporation
Sulpizio, Jr. Ronald F.
Swann Tod
LandOfFree
Encryption apparatus and computor-readable recording medium... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Encryption apparatus and computor-readable recording medium..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Encryption apparatus and computor-readable recording medium... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2472143