CN114640437A - Universal key expansion fast method - Google Patents

Abstract

The present invention provides a general fast method for key expansion. The fast method for key expansion is a general key expansion method with an encryption key length of 256 bits and a round key length of 128 bits. The input encryption key passes through a predetermined round of The expansion of the number generates the output key, that is, the round key; the input encryption key of the first round is divided into two consecutive left and right key segments with a length of 128 bits. Or after the first transformation, the output 128-bit data is then subjected to the second transformation to obtain the output round key of the first round. Starting from the second round, the output round key of the previous round is fed back to NK, and then after the first round After the transformation and the second transformation, the output round key of the current round is obtained. Through the present invention, the overall balance and randomness of the extended key are higher, the correlation between the keys is lower, and the speed of generating the extended key is faster.

Description

A Universal Key Expansion Fast Method

technical field

The invention relates to the technical field of cryptography, in particular to a general fast method for key expansion.

Background technique

The block cipher algorithm is the mainstream algorithm for encrypting long data, and the key expansion algorithm is an important part of supporting the block cipher. Depending on the speed at which computer computing power develops, 256 bits will be the preferred encryption key length for most block cipher algorithms for a long time.

SUMMARY OF THE INVENTION

The present invention provides a general fast method for key expansion, so as to solve the 256-bit encryption key existing in the prior art, the balance and randomness are low, and at the same time, the correlation between the keys is high, and the expansion key is generated. problem of slow speed.

In order to solve the above-mentioned technical problems, the present invention provides a general fast method for key expansion. The fast method for key expansion is a general key expansion method with an encryption key length of 256 bits and a round key length of 128 bits. The encryption key is expanded by a predetermined number of rounds to generate an output key, that is, the round key; the input encryption key of the first round is divided into two consecutive left and right key segments with a length of 128 bits. The key segment undergoes the first transformation after bit-by-bit XOR, and the output 128-bit data is then transformed into the first round of the output round key. Starting from the second round, the output round key of the previous round is fed back to NK. , and then the output round key of the current round is obtained after the first transformation and the second transformation.

The input encryption key for the first round is 256 bits.

The first transformation includes performing bit-by-bit XOR operation on data obtained by sequentially connecting the first 16 bytes of data in the AES standard S-box table with NK.

The data obtained by sequentially connecting the first 16 bytes of data in the AES standard S-box table is 128 bits.

The second transformation includes dividing the data obtained after the first transformation into left and right data segments with a length of 64 bits, and then performing bit-by-bit XOR, shift and concatenation operations on the two data segments in sequence.

The second transformation includes an Rcon[n] operation, where n is the number of bits of offset.

Beneficial effects brought by the present invention: the general key expansion fast method of the present invention obtains the expanded key by performing XOR, shift and S-box operation on the 128-bit key in each round, so that the expanded key is The overall balance and randomness are higher, while the correlation between keys is lower, and the speed of generating extended keys is faster.

Description of drawings

1 is a block diagram of iterative generation of round keys according to a general key expansion fast method according to an embodiment of the present invention;

Fig. 2 is the NK initialization block diagram of the general key expansion quick method according to an embodiment of the present invention;

Detailed ways

In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

The input of the key expansion fast method is a 256-bit cryptographic algorithm encryption key, and an iterative manner is used to output a predetermined number of rounds L and a round key with a length of 128 bits. Therefore, the total length of the round key is 128×L.

As shown in Figure 1-2, a general key expansion fast method, the specific implementation steps are as follows:

Step 1: NK initialization: As shown in Figure 2, the output key CK=0, the 256-bit encryption key is equally divided into left and right parts with a length of 128 bits, which may be expressed as LK and RK. Perform bit-by-bit XOR operation on LK and RK, and the result is expressed as NK, then

Step 2: As shown in Figure 1, the data (128 bits) obtained by sequentially connecting the first 16 bytes of data in the AES standard S-box table is performed bit-by-bit XOR operation with NK. The result of the operation is expressed as SK, then

Step 3: Divide the SK into two consecutive left and right parts with a length of 64 bits, denoted as LSK and RSK, and perform the following operations:

RSK>>>>Rcon[32];

Step 4: connect the left and right parts of the data after completing the operation in step 3 to obtain the current round output key CK _i of 128 bits, i≥0, i represents the number of rounds;

Step 5: Let NK=CK _i , that is, update NK to the output round key CK _i of the previous round, and i increment by 1 automatically. Repeat steps 2-4 until the value of i is equal to the preset number of rounds and then jump out of the loop.

为异或运算，运算符号‖为联接运算。Step 1 is NK initialization, as shown in Figure 2; Steps 2 to 5 are the operation steps of iteratively generating the round key by the method, as shown in Figure 1. As shown in the figure, the operation symbol

is an exclusive OR operation, and the operator symbol ‖ is a concatenation operation.

The present invention only realizes the expansion of the encryption key through operations such as XOR, shift and S-box transformation for the encryption key of 256 bits. The key expansion method not only has good randomness such as balance, but also satisfies the property of lower correlation between round keys, and the key expansion speed is faster. According to the needs of the encryption algorithm, the key expansion method can generate an arbitrarily long round key. Therefore, this method is a general key expansion method suitable for the encryption key length of 256 bits and the round key length of 128 bits. .

To sum up, the general key expansion fast method of the present invention obtains the expanded key by performing XOR, shift and S-box operation on the 128-bit key in each round, so that the overall balance of the expanded key is balanced. and randomness is higher, while the correlation between keys is lower, and the speed of generating extended keys is faster.

The above description is only an embodiment of the present invention, and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the scope of the claims of the present invention.

Claims (6)

1. A universal method for expanding keys quickly is characterized in that: the method for rapidly expanding the key is a general key expansion method with the encryption key length of 256 bits and the round key length of 128bits, and an input encryption key is expanded by a preset round number to generate an output key, namely a round key; the input encryption key of the first round is divided into a left key segment and a right key segment which are 128bits in length and continuous, the two key segments are subjected to bit-by-bit XOR and then subjected to first transformation, the output 128-bit data is subjected to second transformation to obtain an output round key of the first round, the output round key of the previous round is fed back to NK from the second round, and then the output round key of the current round is obtained after the first transformation and the second transformation.

2. The universal key expansion express method of claim 1, wherein the input encryption key of the first round is 256 bits.

3. The universal key expansion express method of claim 1, wherein the first transformation comprises a bit-by-bit exclusive-or operation of data obtained by concatenating first 16 bytes of data in an AES standard S-box table sequentially with NK.

4. The universal key expansion method according to claim 3, wherein the data obtained by concatenating the first 16 bytes of data in the AES Standard S-box table in sequence is 128 bits.

5. The method of claim 1, wherein the second transformation comprises dividing the data obtained from the first transformation equally into two left and right data segments with a length of 64 bits, and then performing bitwise exclusive-or, shift and join operations on the two data segments in sequence.

6. A universal key expansion speed method according to claim 5, characterized in that the second transformation comprises Rcon [ n ] operations, where n is the number of bits of the offset.

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