JP3115350B2 - Encryption method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an encryption method for encrypting a sentence, and more particularly to an application method of a data encryption standard (DES) published by the US Department of Commerce. When the data encryption standard is used for an IC card or the like, it is required to reduce the memory capacity.

[0002]

2. Description of the Related Art Conventionally, when a data encryption standard DES is used, as shown in FIG. 3, the encryption / decryption processing unit 22 and the key schedule processing unit 21 are roughly divided into two parts. The key schedule processing unit 21 schedules the key every time the process is performed, and the encryption processing unit 22 encrypts the input plaintext based on the key after the scheduling, and outputs the encrypted text.

[0003]

For this reason, for example, an IC
Even in a portable system such as a card, it is necessary to repeat the key schedule for encryption by the key schedule processing unit 21 every time the encryption process is performed, and a program for performing this process is stored in the IC card. There is a problem that it is necessary to store the data, which increases the memory capacity and slows down the processing. For this reason, when the memory capacity is limited as in the case of an IC card, it is required to omit the processing (program) when encrypting data to reduce the memory capacity and to save the processing time. .

According to the present invention, a key schedule process is omitted, a key after a schedule is registered in advance, and an encryption process is performed using the key, thereby reducing the memory capacity and speeding up the process without deteriorating the reliability. The purpose is to plan.

[0005]

Means for solving the problem will be described with reference to FIG. In FIG. 1, an encryption processing unit 2 encrypts an input sentence based on a scheduled key extracted from a key buffer 3. The key buffer 3 is a buffer that stores in advance a key after a schedule generated using a unique key as an input.

[0006]

According to the present invention, as shown in FIG. 1, a portable medium (for example, an IC card) 1 is provided with a key buffer 3 and an encryption processing unit 2, and the encryption processing unit 2 transmits the key buffer 3 It encrypts based on the key after the schedule extracted from, and outputs the ciphertext.

Therefore, the key schedule processing is omitted,
By storing in the key buffer 3 a scheduled key generated by scheduling in advance based on the unique key of the portable medium 1 in the key buffer 3, the schedule processing in the portable medium (for example, an IC card) 1 is performed. This makes it possible to reduce the memory capacity and increase the processing speed while maintaining the reliability.

[0008]

Next, the structure and operation of an embodiment of the present invention will be sequentially described in detail with reference to FIGS. In FIG. 1, a medium 1 is a portable medium, for example, a portable medium such as an IC card. This medium 1 outputs a ciphertext encrypted by DES (data encryption standard published by the United States Department of Commerce) when outputting a text, or receives and decrypts a ciphertext to generate a plaintext. It is.

The encryption processing unit (decryption processing unit) 2 encrypts the plaintext using the key after scheduling from the key buffer 3 and decrypts the ciphertext (see the flowchart of FIG. 2). ). Key buffer 3
The key is pre-stored in the key issuance unit 6 of the card issuing machine 5 at the time of issuance of the card, which is scheduled after scheduling the unique key of the portable medium 1.

The IC card 4 is a portable card, holds an encryption processing unit (decryption processing unit) 2 and a key buffer 3 according to the present invention, encrypts plain text, and outputs (transmits) cipher text. ) Or decrypting the received ciphertext. The card issuing machine 5 is an IC card 4
And when the IC card 4 is issued,
A schedule is performed based on the input unique key, a key after the schedule is generated, and stored in the key buffer 3 of the IC card 4 in advance.

The key schedule processing unit 6 generates a key after scheduling required for encryption based on the input unique key. For example, as in DES,
A unique key of a 64-bit IC card is input, and a key required to perform 48-bit, 16-stage encryption (decryption) is generated. Next, the operation of the configuration of FIG. 1 will be described in detail according to the order shown in the flowchart of FIG.

In FIG. 2, S1 inputs a unique key (64 bits) possessed by the card. this is,
When issuing the IC card 4 of FIG. 1, the card issuing machine 5 inputs a unique key possessed by the card. In step S2, a key schedule process is performed. This is the unique unique key (64 bits) of the IC card entered in S1
, A 48-bit × 16-stage key is generated as a post-scheduling key required for encryption.

In step S3, the key after scheduling (48 bits × 16 steps) is stored in the key buffer 3. this is,
As described on the right, the key buffer 3 of FIG.
(48 bits x 16)
Is stored as shown. With the above processing, when the card issuing machine 5 issues the IC card 4, the schedule processing in the card issuing machine 5 causes the IC card 4 to be issued.
A schedule is generated based on the unique unique key of the scheduler to generate a scheduled key (48 bits × 16 stages) required for encryption (decryption), and this is stored in the key buffer 3 in advance. Thereby, the key buffer 3 of the IC card 4
Since the key after the unique schedule necessary for the encryption (decryption) is stored in advance, the key scheduling process is not required when the plaintext is encrypted (when the ciphertext is decrypted).

Next, in FIG. 2, S4 is a plain text (64
Bit). In this case, plain text to be encrypted, for example, ASCII code data, to be output (transmitted) by the IC card 4 is input in units of 64 bits. S5 is
Perform initial transposition. That is, as described on the right side, the 64-bit plaintext data input in S4 is randomly transposed using a table created in advance and not shown.

In step S6, a 16-step repetition process using keys is performed. In this method, as described on the right side, 64 bits of the input plaintext are divided into two blocks of 32 bits, a process using a key is performed on one of the blocks, and a process of exchanging the two blocks is repeated. In step S7, reverse initial transposition is performed.
In this case, as described on the right side, 64-bit data is randomly transposed using a table created in advance, not shown.

In step S8, the cipher text (64 bits) is output. By the above processing, when the IC card 4 attempts to output plain text, the plain text is divided into 64-bit units (S
4), initial transposition (S5), processing is performed using a key previously stored in the key buffer 3 (S6), and reverse initial transposition (S5).
7) Then, a 64-bit ciphertext is generated and output.

When the ciphertext is received, the ciphertext is decrypted by using a key stored in the key buffer 3 in advance, contrary to the encryption.

[0018]

As described above, according to the present invention,
A key that has been scheduled and generated in advance based on a unique key of the portable medium 1 and stored in the key buffer 3 is stored, and plaintext is encrypted (decrypted) using the key. Therefore, the key schedule processing in the portable medium (for example, an IC card) 1 is omitted, and the program for the schedule processing is eliminated.
The memory capacity can be reduced and processing can be performed at high speed while maintaining reliability. This greatly contributes to optimization in the case where encryption (decryption) processing is performed in a short time with limited memory resources such as an IC card. For example, I in FIG.
In the case of the C card 4, the memory capacity can be reduced by about 40% and the processing time can be reduced by about 30% as compared with the case where the conventional key schedule processing unit 21 of FIG. 3 is provided.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of one embodiment of the present invention.

FIG. 2 is a flowchart illustrating the operation of the present invention.

FIG. 3 is an explanatory diagram of a conventional technique.

[Explanation of symbols]

 1: medium (DES) 2: encryption processing unit (decryption processing unit) 3: key buffer 4: IC card 5: card issuing machine 6: key schedule processing unit

Continuation of the front page (56) References JP-A-4-361289 (JP, A) JP-A-55-41422 (JP, A) JP-A-59-220777 (JP, A) (58) Fields investigated (Int .Cl. ⁷ , DB name) G09C 1/00-5/00 H04K 1/00-3/00 H04L 9/00 G06K 17/00 G06K 19/00

Claims (2)

(57) [Claims] In a cipher system for encrypting a sentence, a key buffer (3) for pre-storing a post-scheduled key generated by inputting a unique key, and a post-scheduled key extracted from the key buffer (3). Based on the key,
An encryption system comprising an encryption processing unit (2) for encrypting a sentence and a portable medium (1), and configured to encrypt and output the sentence. 2. The encryption method according to claim 1, wherein said portable medium is an IC card.