Structure-independent meta-encryption scheme

Abstract

The ciphertext C generated by an existing encryption scheme is handled independently of the internal specifications of that scheme, and the ciphertext C is divided into variable-length segments according to boundary information b_i based on the outer layer key state S. By changing the outer layer key state S along with the generation of the ciphertext, the inverse operation of the reversible transformation makes it impossible for a third party to make assumptions about the partitioning position or the decryption process, thus increasing the difficulty of decryption. [Solution] The present invention is an outer layer cryptographic processing method that takes a ciphertext C generated by an existing cryptographic scheme as input, maintains an outer layer key state S without referring to the internal specifications of the scheme, derives boundary information b_i using only S as input, and divides the ciphertext C into variable-length segments. The ciphertext C is read as segments seg_i according to the boundary information b_i, and an outer layer code s_i is derived based on each seg_i and the outer layer key state S. The outer layer code s_i is used to update the outer layer key state S, and the updated S influences the derivation of the next boundary information b_{i+1}. S → b_i → seg_i → s_i → S update → b_{i+1} This creates an interdependent structure. The ciphertext C is not fixed, the state transitions in the outer layer processing increase, and it becomes difficult for a third party to make assumptions about the processing.

Description

Technical Field

[0001] The present invention relates to an outer layer cryptographic processing technology that receives a ciphertext generated by an existing encryption method as input, divides the ciphertext into variable lengths in an outer processing layer without referring to the internal specifications of the encryption method, and performs outer layer processing based on the division result.

[0002] More specifically, the present invention relates to an outer layer cryptographic processing technology that does not depend on structural attributes such as delimiter positions and lengths of ciphertexts, derives boundary information b_i using only an outer layer key state S as input, divides a ciphertext into variable lengths based on the boundary information b_i, updates the outer layer key state S using each segment seg_i and an outer layer code s_i derived based on the outer layer key state S, and has an interdependent (cyclic) structure in which the updated outer layer key state S affects the determination of the next division position.

[0003] As used herein, the term "meta-encryption method" is a general term for encryption methods that divide ciphertext into variable lengths in an outer processing layer and apply outer layer processing to the division units without depending on the internal specifications of an existing encryption method. The "outer layer cryptographic processing method" recited in the claims refers to a method for specifically implementing the meta-encryption method.

[0004] Meta-encryption adds an independent outer layer processing to the outside of an existing encryption method while maintaining the security of the existing encryption method, and forms an outer layer cryptographic layer in which the outer layer key state S and the division positions of the ciphertext change interdependently.

Background Art

[0005] Conventional encryption methods operate on the premise of certain internal specifications in the ciphertext generation process, and structural attributes such as block boundaries and bit lengths of ciphertext are fixed. While these attributes contribute to improving the efficiency of cryptographic processing, they can also be used as clues for inferring how to handle ciphertext in cryptographic analysis.

[0006] However, no outer layer cryptography had been proposed that, instead of treating ciphertexts at fixed boundaries, dynamically determines the partitioning position of the ciphertext using only the outer layer key state S as input, updates the outer layer key state S based on the outer layer code s_i derived from the segment seg_i and the outer layer key state S, and has an interdependent structure (circular structure) in which the updated outer layer key state S influences the determination of the next partitioning position.

[0007] Furthermore, no practical method was known for meta-encryption techniques that divide the ciphertext into variable-length segments, perform outer layer processing, and form an independent outer layer encryption layer in which the handling of the ciphertext changes over time due to changes in the outer layer key state S, without referring to the internal specifications of existing encryption methods. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Patent documents relating to block cipher schemes [Patent Document 2] Patent documents relating to stream cipher schemes [Patent Document 3] Patent documents relating to superencryption. [Patent Document 4] Patent documents relating to encryption usage modes (CFB, OFB, CTR, etc.) [Non-patent literature]

[0009] [Non-Patent Document 1] FIPS-197 (AES standard) [Non-Patent Document 2] RFC 3686 (AES-CTR mode) [Non-Patent Document 3] ISO / IEC 18033 (International standard for cryptographic methods) [Non-Patent Document 4] Bruce Schneier,"Applied Cryptography" [Non-Patent Document 5] General explanatory paper on self-synchronizing stream ciphers [Overview of the project] [Problems that the invention aims to solve]

[0010] In conventional encryption methods, the delimiter positions of the ciphertext are fixed, making it difficult to introduce an outer layer that treats the ciphertext as a meaningless sequence of information and dynamically changes its delimiter positions based on the key state. Furthermore, even in methods that utilize the local contents of the ciphertext to update the internal state, such as self-synchronizing stream ciphers, there was no cyclical structure in which the handling of the outer key state and the ciphertext mutually depend on each other, such as the partitioning position of the ciphertext depending on the key state update result, and the updated key state influencing the next partitioning position. The challenge is to realize an outer layer cryptographic processing method in which the handling of ciphertext and the outer layer key state change in an interdependent manner, and which is capable of encryption and decryption. [Means for solving the problem]

[0011] The structure-independent meta-encryption scheme of the present invention maintains an outer layer key state S dedicated to outer layer processing, derives boundary information b_i using only S as input, and divides the ciphertext C into variable-length segments. For each segment seg_i, a reversible transformation is performed using the outer layer processing information derived from the outer layer key state S to generate the outer layer ciphertext C'. Furthermore, based on the segment seg_i and the outer layer key state S, the outer layer code s_i is derived, the outer layer key state S is updated, and the next boundary information b_{i+1} is derived from the updated S. This results in a circulating structure characteristic of the present invention. S → b_i → seg_i → s_i → S update → b_{i+1} An outer layer cryptographic processing system equipped with this system is formed. Note that seg'_i, obtained through the reversible transformation, is the output for constructing the outer layer ciphertext C' and is not included in the above circular structure. Effects of the Invention

[0012] According to the present invention, the following effects are obtained. (1) A ciphertext is handled as a meaningless information string, and based on the outer layer key state S, the division position changes over time, making it difficult for a third party to infer the operation of the outer layer processing, thereby improving the difficulty of decryption as an outer cipher layer. (The mechanism by which decryption difficulty is improved will be described later) (2) The present method does not refer to the internal specifications of an existing encryption method, and performs reversible conversion on the outside thereof, so that an independent outer cipher layer can be added while maintaining the security of existing encryption methods (AES, DES, RSA, etc.). In addition, due to the structure that does not depend on internal specifications, the outer layer processing unit can be configured to be relatively lightweight (The lightweight nature of the outer layer processing will be described later). (3) Since the update of the outer layer key state S and the variable-length division form a cyclic structure, the handling method of the ciphertext changes over time, and uncertainty derived from the cyclic structure is added (The additional structure of uncertainty will be described later). Brief Description of Drawings

[0013] [Figure 1] Overall configuration including encryption and decryption of the outer layer encryption processing method of the present invention [Figure 2] Reference comparison: Differences between the conventional method (RSA) and the present invention Mode for Carrying Out the Invention

[0014] [Structure-independent meta-encryption method] Figure 1 is a diagram showing the conceptual configuration of the outer layer encryption processing method according to the present invention. The ciphertext C

[0100] generated by an existing encryption scheme is input to the outer layer processing unit

[0101] in the outer processing layer without referring to the internal specifications of the encryption scheme. The outer layer processing unit

[0101] divides the ciphertext C

[0100] into variable-length segments according to boundary information b_i derived based on the outer layer key state S

[0104] without referring to the contents of the ciphertext C

[0100] , applies a reversible transformation to each divided segment seg_i using outer layer processing information generated from the outer layer key state S

[0104] to obtain the outer layer encryption result seg'_i, and constructs the outer layer ciphertext C'

[0105] by concatenating these segments. Furthermore, outer layer processing is applied based on the outer layer key state S

[0104] and segment seg_i to derive the outer layer code s_i

[0102] . The boundary information b_i is determined solely from the outer layer key state S

[0104] and does not depend on the content of the ciphertext C

[0100] .

[0015] The correspondence with each component described in claim 9 is as follows. In other words, the "outer layer key state holding unit" of claim 9 corresponds to the outer layer key state S

[0104] of this embodiment, the "boundary derivation unit", the "splitting unit", and the "outer layer processing unit" (including reversible transformation and generation of outer layer code s_i) correspond to the functions included in the outer layer processing unit

[0101] of this embodiment, and the "key state update unit" corresponds to the key information management unit

[0103] of this embodiment.

[0016] The outer layer code s_i

[0102] is input to the key information management unit

[0103] as information indicating how the ciphertext C

[0100] is handled in the outer layer processing. The key information management unit

[0103] updates the outer layer key state S

[0104] based on the outer layer code s_i

[0102] and generates a new outer layer key state S

[0104] . The updated outer layer key state S

[0104] is used to derive the next boundary information b_{i+1}. This results in a circulating structure characteristic of the present invention. S → b_i → seg_i → s_i → S update → b_{i+1} This is formed in the outer processing layer. Note that seg'_i obtained by the reversible transformation is the output for constructing the outer layer ciphertext C'

[0105] and is not included in the above circular structure.

[0017] The outer layer key state S

[0104] is state information held exclusively for outer layer processing and is artificially constructed in the outer processing layer independently of the internal operation of the existing cryptographic scheme. In the decryption process, the same initial outer layer key state S0 as in the encryption process is maintained, boundary information b_i is derived from S0, the outer layer ciphertext C'

[0105] is divided into variable-length segments, and the same outer layer processing information as on the encryption side is regenerated. The inverse operation of the reversible transformation is then applied to restore the original seg_i. By re-deriving the outer layer code s_i

[0102] based on the recovered seg_i and outer layer key state S

[0104] , and updating the outer layer key state S

[0104] , the same circular structure as the encryption side can be reproduced on the decryption side.

[0018] With the configuration shown in Figure 1, the division position of the ciphertext C

[0100] changes over time depending on the outer layer key state S

[0104] , and outer layer processing that does not depend on the shape or regularity of the ciphertext C

[0100] is realized. The interdependence between the outer layer key state S

[0104] and the boundary information b_i makes it difficult for a third party to infer the operation of the outer layer processing from the ciphertext C

[0100] . Furthermore, since the same outer layer key state S

[0104] is reproduced in both the encryption and decryption processes, even with variable-length partitioning, the boundary information b_i and the outer layer processing information are synchronized, and the original ciphertext C

[0100] can be reliably restored from the outer layer ciphertext C'

[0105] . This invention provides a novel cryptographic processing system that adds uncertainty originating from the outer layer processing while maintaining the security of existing cryptographic schemes.

[0019] The outer layer processing in this invention is defined based on a structure in which the derivation of boundary information, outer layer encryption, generation of outer layer codes, and updating of outer layer key states operate in an interdependent manner, and does not depend on the content of specific mappings or mathematical formulas used in these processes. In other words, the present invention is S → b_i → seg_i → s_i → S update → b_{i+1} The invention is characterized by the cyclical structure of the outer layer processing itself, and the specific forms of the boundary information calculation method, the outer layer processing information generation method, the outer layer code generation method, and the outer layer key state update method are not essential components of the present invention. Therefore, the present invention can be implemented based on the structural relationship of the outer layer treatment without specifying the specific formula of the internal specifications. The specific forms shown in the embodiments described later are merely examples to aid in understanding the present invention and do not limit the technical scope of the present invention.

[0020] [Operation of structure-independent metacryptography] The basic operation of this system is as follows: (1) Maintain the outer layer key state S

[0104] . (2) Using only the outer layer key state S

[0104] as input, derive boundary information b_i. The ciphertext C

[0100] is divided into variable-length segments to obtain segment seg_i. (3) Based on the outer layer key state S

[0104] , outer layer processing information is generated. Applying a reversible transformation to seg_i, we obtain the outer layer encrypted segment seg'_i. These are sequentially concatenated to form the outer layer ciphertext C'

[0105] . (4) Apply outer layer processing to seg_i to derive the outer layer code s_i

[0102] , Based on the outer layer code s_i

[0102] , by a one-way function Update the outer layer key state S

[0104] . (5) Based on the updated outer layer key state S

[0104] , the following boundary information b_{i+1} The same partition position occurs in both the derivation, encryption, and decryption processes. It will be reproduced.

[0021] [Basic Operational Structure of Outer Layer Processing] The outer layer cryptographic processing method according to the present invention has a configuration that artificially defines how to handle ciphertext in the outer processing layer without referring to the internal specifications of existing cryptographic methods. The basic operation of this method is realized based on the following outer layer key states and outer layer processing units. In the following, in order to explain in more detail the steps (1) to (5) shown in [Operation of Structure-Independent Meta-Encryption], each step will be subdivided and described as seven processing units, each consisting of outer layer encryption, outer layer code derivation, and outer layer key state update, bundled at different levels of granularity.

[0022] In this embodiment, the outer layer encryption process and the derivation process of the outer layer code s_i are performed consecutively within a single step, but in claim 1, they are described as separate steps. Furthermore, in the above [Operation of Structure-Independent Meta-Encryption Method] (5 steps), the derivation of the outer layer code s_i is described together with the update of the outer layer key state S

[0104] in the same step, and in this section (7 steps), the derivation of the outer layer code s_i is described together with the outer layer encryption in the same step. However, in both cases, the outer layer encryption, outer layer code derivation, and outer layer key state update are bundled at different levels of granularity, but the processing order is the same.

[0023] Furthermore, the processing units (1) to (7) in this section correspond to the steps (1) to (8) of claim 1. That is, section (1) corresponds to step (1), section (2) corresponds to step (2), section (3) corresponds to step (3), section (4) corresponds to steps (4) (outer layer encryption) and (5) (outer layer code derivation) of claim 1, section (5) corresponds to step (6), section (6) corresponds to step (7), and section (7) corresponds to step (8) (decryption synchronization).

[0024] (1) A process of maintaining the outer layer key state S

[0104] The outer layer key state S

[0104] is state information specific to the outer layer, which is maintained independently of the encryption key of the existing encryption scheme.

[0025] (2) Step of deriving boundary information b_i from the outer layer key state S

[0104] Without referring to the contents of the ciphertext C

[0100] , boundary information b_i for variable-length partitioning is determined based on a predetermined portion of the outer layer key state S

[0104] . The boundary information b_i is determined solely from the outer layer key state S

[0104] and is kept confidential from third parties.

[0026] (3) A step of dividing the ciphertext C

[0100] into variable-length segments according to the boundary information b_i. The ciphertext C

[0100] is not dependent on the internal specifications of existing encryption schemes and is divided into multiple segments seg_i of variable length according to boundary information b_i.

[0027] (4) The process of encrypting each segment seg_i with an outer layer Based on the outer layer key state S

[0104] , outer layer processing information is generated, a reversible transformation is applied to seg_i to obtain the outer layer encrypted segment seg'_i, and these are sequentially concatenated to construct the outer layer ciphertext C'

[0105] . Furthermore, outer layer processing is applied based on the outer layer key state S

[0104] and seg_i to derive the outer layer code s_i

[0102] . Furthermore, since the reversible transformation is applied independently to each segment seg_i and does not cross between partition units, the boundary of the outer layer encrypted segment seg'_i obtained by encryption coincides with the boundary of the original seg_i. Therefore, the decryption process is synchronized based on the boundary information b_i, ensuring that seg_i can be reliably restored from seg'_i.

[0028] (5) Step of updating the outer layer key state S

[0104] based on the outer layer code s_i

[0102] . The outer layer code s_i

[0102] is used to update the outer layer key state S

[0104] , and the outer layer key state S

[0104] is updated by a one-way function. The updated outer layer key status S

[0104] will be reflected in the next outer layer processing.

[0029] (6) Steps to re-derive the next boundary information b_{i+1} based on the updated outer layer key state S

[0104] . The update result of the outer layer key state S

[0104] affects the next boundary determination, and the partition position of the ciphertext C

[0100] changes over time.

[0030] (7) Synchronization process in the decryption process On the decryption side, the same initial outer layer key state S0 as the encryption side is maintained, boundary information b_i is derived from S0, the outer layer ciphertext C'

[0105] is divided into variable-length segments, outer layer processing information is generated based on the outer layer key state S

[0104] , and the original seg_i is restored by applying the inverse operation of the reversible transformation. By re-deriving the outer layer code s_i

[0102] based on the recovered seg_i and outer layer key state S

[0104] , and updating the outer layer key state S

[0104] using a one-way function, the same circular structure as the encryption side can be reproduced on the decryption side.

[0031] With the above configuration, the handling of the ciphertext C

[0100] and the outer layer key state S

[0104] change mutually in the outer layer processing system, adding uncertainty originating from the outer layer processing regardless of the internal specifications of the existing encryption scheme, and realizing an outer layer encryption layer that can decrypt even with variable-length partitions.

[0032] [The relationship between keys and cryptography (relationship in the outer layer)] In this invention, the relationship between key and cryptography refers to the relationship between an outer layer key state S

[0104] artificially constructed in the outer processing layer and a ciphertext C

[0100] , independent of the internal specifications of existing cryptographic schemes. The ciphertext C

[0100] is divided into variable-length segments based on the outer layer key state S

[0104] , and an outer layer code s_i

[0102] is derived from each segment seg_i. Furthermore, an outer layer encrypted segment seg'_i is obtained by applying a reversible transformation to seg_i using the outer layer processing information generated based on the outer layer key state S

[0104] , and the outer layer ciphertext C'

[0105] is constructed by sequentially concatenating these. On the other hand, the outer layer key state S

[0104] is updated based on the outer layer code s_i

[0102] . These change interdependently within the outer layer processing system, but the internal workings of existing cryptographic schemes and It is unrelated to the internal key structure.

[0033] [Treat ciphertext as meaningless sequences of information] Assuming that the ciphertext has its own unique block boundaries and regularities, the outer layer processing will behave in a specific direction. This can lead to a third party inferring the assumptions behind the outer layer processing. This method treats ciphertext as "meaningless continuous information" and divides it into variable-length segments according to boundary information b_i based on the outer layer key state S

[0104] , thereby achieving outer layer processing that is independent of the shape of the ciphertext and eliminating any room for third parties to make assumptions.

[0034] [The handling of ciphertext is not consistent due to the outer layer processing.] The outer layer processing divides the ciphertext C

[0100] into variable-length segments based on boundary information b_i derived from the outer layer key state S

[0104] . Since the boundary information b_i changes in accordance with the update of the outer layer key state S

[0104] , the handling of the ciphertext is not fixed, and the segment seg_i, the outer layer encryption result seg'_i, and the outer layer code s_i

[0102] may change over time. This ensures that the operation of the outer layer processing does not depend on the shape of the ciphertext, and that diversity in outer layer processing is maintained.

[0035] [It is difficult for a third party to identify the operation of the outer layer processing.] Because the derivation of boundary information b_i, the generation of outer layer encryption seg'_i, the generation of outer layer code s_i

[0102] , and the updating of outer layer key state S

[0104] in outer layer processing are interdependent and change accordingly, a third party cannot determine "where the ciphertext was delimited," "what kind of outer layer code was generated," or "which outer layer processing information was applied." Since the shape of the ciphertext cannot be used as a clue, and there is no basis for inferring the operation of the outer layer processing, The overall decryption difficulty of the outer layer cryptography increases.

[0036] [Mechanism that improves decryption difficulty] In the outer layer processing, the ciphertext C

[0100] is divided into variable-length segments based on boundary information b_i derived from the outer layer key state S

[0104] . A reversible transformation is applied to each segment using outer layer processing information generated from the outer layer key state S

[0104] to obtain the outer layer encryption result seg'_i. The outer layer key state S

[0104] is updated based on the outer layer code s_i

[0102] , and the updated outer layer key state S

[0104] affects the derivation of the next boundary information b_{i+1}. Therefore, the handling of the ciphertext and the outer layer key state change interdependently over time. A third party would need to consider a wide range of combinations of partitioning location, outer layer processing information, outer layer code, and key state update, which increases the overall difficulty of decrypting the outer layer processing.

[0037] [Do not refer to the internal specifications of the encryption method] This method does not utilize the internal workings or internal key structure of existing encryption methods, and treats the ciphertext C

[0100] solely as input for the outer layer processing. This allows for the addition of an outer layer of processing while maintaining the security of existing encryption methods.

[0038] [Structure that operates in the outer processing layer] An external processing layer is provided that operates independently of the layer in which the existing encryption scheme operates. This layer divides the ciphertext C

[0100] into variable-length segments, generates an outer layer encrypted seg'_i, derives an outer layer code s_i

[0102] , and updates the outer layer key state S

[0104] . This outer processing layer operates independently of existing cryptographic schemes and forms an independent cryptographic layer.

[0039] [Adding a new cryptographic layer while maintaining the security of existing encryption] This refers to a structure in which the security of the existing encryption method is enhanced by adding uncertainty inherent to the outer layer processing, while still utilizing the ciphertext C

[0100] generated by the existing encryption method, by performing variable-length partitioning, outer layer encryption, outer layer code generation, and outer layer key state updates through outer layer processing.

[0040] [Configuration for outer layer processing and key information updates] The system includes a configuration that uses the outer layer code s_i

[0102] obtained by outer layer processing to update the outer layer key state S

[0104] . This creates an interdependent structure in which the content of segment seg_i of the ciphertext C

[0100] affects the outer layer key state S

[0104] , and the updated outer layer key state S

[0104] affects the determination of the next partition position.

[0041] [Implemented as an independent processing layer located outside of existing encryption methods] The outer layer processing is configured independently of the operation of the existing encryption scheme, and takes the ciphertext C

[0100] as input. Variable-length partitioning, outer-layer encryption, and outer-layer code generation are performed based on the outer-layer key state S

[0104] . This allows for the creation of an additional cryptographic layer while maintaining the security of existing encryption methods.

[0042] [Does not require complex internal specifications] The outer layer processing treats the ciphertext C

[0100] as a simple sequence of information and divides it using boundary information b_i based on the outer layer key state S

[0104] , thus eliminating the need to refer to the internal specifications of existing encryption schemes.

[0043] [Composed of relatively lightweight processing] The outer layer processing consists of a combination of variable-length partitioning, outer layer encryption, outer layer code generation, and outer layer key state updates, and does not require large-scale internal state management.

[0044] [External processing diversifies how ciphertexts are handled.] Because there are multiple options for the method of deriving boundary information b_i based on the outer layer key state S

[0104] , the method of generating outer layer processing information used for outer layer encryption, the method of generating the outer layer code s_i

[0102] , and the method of updating the outer layer key state S

[0104] , the handling of the ciphertext C

[0100] is diverse, and a third party cannot determine which handling method was adopted.

[0045] [The overall difficulty of decryption increases with the outer layer of cryptography.] Because the handling of the ciphertext C

[0100] and the updating of the outer layer key state S

[0104] are mutually dependent and change accordingly, the state space that a third party must consider increases, and the overall difficulty of decryption in the outer layer processing increases.

[0046] [The method for handling ciphertext is not fixed.] Because the update result of the outer layer key state S

[0104] based on the outer layer code s_i

[0102] affects the derivation of the next boundary information b_{i+1}, the partition position of the ciphertext C

[0100] is not fixed but changes over time.

[0047] [The key information affects how the next ciphertext is handled.] The update result of the outer layer key state S

[0104] based on the outer layer code s_i

[0102] affects the derivation of boundary information b_{i+1} in subsequent outer layer processing and changes how the ciphertext C

[0100] is handled.

[0048] [Structurally independent and cannot be assumed by third parties] The outer layer processing does not assume that the ciphertext C

[0100] is handled according to a specific format or rule, but rather artificially divides it into variable lengths according to boundary information b_i based on the outer layer key state S

[0104] .

[0049] [A structure that adds "uncertainty" to the security of existing cryptography] In addition to the security of existing encryption methods, uncertainty arising from variable-length partitioning based on the outer layer key state S

[0104] , the outer layer encryption result seg'_i, and state updates based on the outer layer code s_i

[0102] is added, improving the overall difficulty of decryption. This structure corresponds to the addition of uncertainty arising from the cyclic structure shown in effect (3).

[0050] [Definition of Terms] [Meta-cipher] This refers to an external processing system that takes a ciphertext C

[0100] generated by an existing encryption scheme as input, divides the ciphertext C

[0100] into variable-length segments according to boundary information b_i based on the outer layer key state S

[0104] without referring to the internal specifications of the said encryption scheme, and applies outer layer encryption and outer layer processing to each segment seg_i. It features a structure that adds an independent outer layer of encryption while maintaining the security of existing encryption. Furthermore, the term "meta-encryption scheme," which will be discussed later, is a general term for cryptographic schemes that systematize the outer layer processing structure of the meta-encryption defined here as a scheme.

[0051] [Meta-encryption scheme] This refers to a general term for an encryption scheme that includes a series of outer layer processes, in which the ciphertext C

[0100] is divided into variable-length segments based on the outer layer key state S

[0104] , a reversible transformation is applied to each segment seg_i using outer layer processing information generated based on the outer layer key state S

[0104] to obtain an outer layer encrypted segment seg'_i, outer layer processing is applied to seg_i to derive an outer layer code s_i

[0102] , and the outer layer key state S

[0104] is updated based on the outer layer code s_i

[0102] . In the decryption process, a reversible transformation is achieved by reproducing the same outer layer key state S

[0104] .

[0052] [Boundary information b] Boundary information b refers to information indicating the division length for dividing the ciphertext C

[0100] into variable-length segments, which is derived based on a predetermined portion of the outer layer key state S

[0104] . The boundary information b_i is determined solely from the outer layer key state S

[0104] without referring to the contents of the ciphertext C

[0100] , and the same partition position is reproduced by using the same outer layer key state S

[0104] in both the encryption and decryption processes. Note that the specific method for calculating boundary information b_i is not limited to the present invention, and an example is shown to aid understanding in the embodiments described later. The boundary information b_i indicates the division length, and its cumulative value uniquely determines the division position (delimiter) in the ciphertext.

[0053] [External treatment] This refers to the process of deriving boundary information b_i from the outer layer key state S

[0104] , dividing the ciphertext C

[0100] into variable-length segments, and performing outer layer encryption and outer layer code generation for each segment seg_i. The ciphertext C

[0100] is treated as a meaningless sequence of information, and the internal specifications of existing encryption schemes are not utilized.

[0054] [Outer layer cryptography] This refers to a processing system that uses the outer layer code s_i

[0102] obtained by outer layer processing to update the outer layer key state S

[0104] , and has an interdependent structure in which the updated outer layer key state S

[0104] influences the derivation of the next boundary information b_{i+1}. Both the outer layer encryption seg'_i and the outer layer code s_i

[0102] affect the outer layer key state S

[0104] .

[0055] [Outer layer processing unit] This refers to a variable-length segment seg_i determined based on boundary information b_i derived from the outer layer key state S

[0104] . It is artificially defined, independently of the block structure of existing cryptographic schemes.

[0056] [Outer layer processing] This refers to a configuration belonging to an outer processing layer that derives boundary information b_i from the outer layer key state S

[0104] , divides the ciphertext C

[0100] into variable-length segments, and performs outer layer encryption and outer layer code generation on the segments seg_i.

[0057] [Outer layer code] This refers to the code s_i derived by applying outer layer processing based on the outer layer key state S

[0104] and segment seg_i. The outer layer code s_i is used to update the outer layer key state S

[0104] .

[0058] [key] This refers to conceptual information regarding the outer layer key state S

[0104] used in outer layer processing.

[0059] [Key Information] This refers to information regarding the outer layer key status S

[0104] and its updates.

[0060] [Key information management department] This refers to a configuration in which the outer layer key state S

[0104] is updated based on the outer layer code s_i

[0102] , and the updated outer layer key state S

[0104] is used to derive the next boundary information b_{i+1}. In this specification, "key" and "key information" are comprehensive concepts that refer to information associated with the outer layer key state S, and the outer layer key state S constitutes the core of the key-related information in this system.

[0061] [Ciphertext C] This refers to the ciphertext C

[0100] generated by an existing encryption method, which is a sequence of information input to the outer layer processing.

[0062] [Outer layer ciphertext C'] This refers to the output of the outer layer processing, which is constructed by sequentially concatenating the outer layer encryption results seg'_i obtained by dividing the ciphertext C

[0100] into variable-length segments according to the boundary information b_i derived based on the outer layer key state S

[0104] , and applying a reversible transformation using outer layer processing information to each segment seg_i. Note that seg'_i is used as the output of the outer layer processing and is not included in the circular structure involved in updating the outer layer key state S

[0104] .

[0063] [Structure independent] This refers to the property of treating ciphertext C

[0100] as a black box and executing outer layer processing without referring to the internal specifications of the existing encryption scheme used to generate ciphertext C

[0100] .

[0064] [Cryptographic layer] This refers to the processing layer where cryptographic processing takes place. It includes an inner layer where existing encryption methods operate and an outer layer where outer layer cryptographic processing operates.

[0065] [New cryptographic layer] This refers to an outer layer of cryptographic processing that is added on top of existing encryption schemes.

[0066] [Difficulty in decryption] This refers to a property where the partition positions of the outer layer key state S

[0104] and the ciphertext C

[0100] change in an interdependent manner, making it difficult for a third party to predict the operation of the outer layer processing. The decryption side can perform synchronous decryption by sharing the outer layer key state S0.

[0067] [First Embodiment: Specific Example of Outer Layer Processing Operation] This embodiment is an example intended to aid in understanding the present invention and does not limit the technical scope of the present invention. The outer layer processing is performed using the outer layer key state S

[0104] and the ciphertext C

[0100] as inputs, through the following steps.

[0068] (1) Maintaining the outer layer key state S

[0104] The outer layer key state S

[0104] is state information dedicated to outer layer processing and is maintained independently of the encryption key of the existing encryption scheme.

[0069] (2) Derivation of boundary information b_i (an example of this embodiment) Boundary information b_i is calculated by interpreting a predetermined portion of the outer layer key state S

[0104] as an integer value without referring to the contents of the ciphertext C

[0100] , and adding the minimum length L_min to the remainder obtained by dividing it by the variable width R. For example, it can be derived from the following formula: b_i = L_min + ( int(S[0:4]) mod R ) Furthermore, this calculation formula does not limit the present invention, and the method for deriving boundary information b_i can be arbitrarily set.

[0070] (3) Variable-length partitioning of ciphertext C

[0100] According to the derived boundary information b_i, the ciphertext C

[0100] is divided into multiple variable-length segments seg_i in order from the beginning. The division position changes over time depending on the outer layer key state S

[0104] and is not fixed.

[0071] (4) Outer layer encryption and derivation of outer layer code s_i

[0102] (an example of this embodiment) For each segment seg_i, a key stream ks_i is generated from the outer layer key state S

[0104] , and a reversible transformation is applied to obtain the outer layer encryption result seg'_i. For example, the following reversible transformation using XOR can be used: seg'_i = seg_i XOR ks_i Furthermore, by applying a collision-resistant hash function H to the outer layer key state S

[0104] and seg_i as input, the outer layer code s_i

[0102] is derived, for example, by the following equation: s_i = H(S || seg_i) These specific formulas do not limit the present invention.

[0072] (5) Updating the outer layer key state S

[0104] (an example of this embodiment) The update of the outer layer key state S

[0104] based on the outer layer code s_i

[0102] is performed using a one-way function F, for example, by the following equation: S ← F(S, s_i) The updated outer layer key state S

[0104] is used to derive the next boundary information b_{i+1}.

[0073] (6) Re-derivation of the next boundary information b_{i+1} Based on the updated outer layer key state S

[0104] , the new boundary information b_{i+1} is re-derived, and the division position of the next segment is determined.

[0074] (7) Synchronization operation in the decoding process On the decryption side, the same initial outer layer key state S0 as the encryption side is maintained, boundary information b_i is derived from S0, the outer layer ciphertext C'

[0105] is divided into variable lengths, and the same key stream ks_i as the encryption side is regenerated. seg_i = the inverse operation of the reversible transformation (seg'_i) Restore the original seg_i. Based on the recovered seg_i and outer layer key state S

[0104] , the outer layer code s_i

[0102] is re-derived, and the outer layer key state S

[0104] is updated, thereby creating the same circular structure as the encryption side. S → b_i → seg_i → s_i → S update → b_{i+1} This can be reproduced on the decoding side, enabling synchronous decoding even with variable-length partitioning.

[0075] It should be noted that the specific forms of each process shown in this embodiment (such as the boundary information calculation formula, the outer layer encryption method, the method for deriving the outer layer code, and the method for updating the outer layer key state) are merely examples to aid in understanding the present invention and do not limit the technical scope of the present invention.

[0076] [Second Embodiment: Basic Configuration Based on Outer Layer Treatment] This embodiment relates to a basic configuration in which the ciphertext C

[0100] is divided into variable-length segments based on boundary information b_i derived from the outer layer key state S

[0104] , and outer layer encryption and outer layer code generation are performed for each segment seg_i. Segment seg_i is artificially defined by boundary information b_i, which is determined solely from the outer layer key state S

[0104] , independently of the block structure of existing cryptographic schemes.

[0077] As a result, the partition position of the ciphertext C

[0100] changes over time depending on the outer layer key state S

[0104] , and the outer layer encryption result seg'_i and outer layer code s_i

[0102] also change over time. The derived outer layer code s_i

[0102] is used to update the outer layer key state S

[0104] , and the updated outer layer key state S

[0104] influences the derivation of the next boundary information b_{i+1}. This interdependent structure is composed of an outer processing layer, independent of the internal specifications of existing cryptographic schemes.

[0078] The outer layer processing in this embodiment involves treating the ciphertext C

[0100] as a meaningless sequence of information, dividing it into variable-length segments according to boundary information b_i based on the outer layer key state S

[0104] , applying a reversible transformation to each segment seg_i using outer layer processing information generated based on the outer layer key state S

[0104] to obtain an outer layer encrypted segment seg'_i, and then applying outer layer processing to seg_i to derive the outer layer code s_i

[0102] . As a result, third parties cannot use the shape or regularity of the ciphertext C

[0100] as a clue, making it difficult to determine the operation of the outer layer processing.

[0079] [Third Embodiment: Configuration Based on Alternative Handling of Outer Layer Codes] This embodiment relates to a configuration that, in addition to the configuration of the first embodiment, includes multiple options regarding which part of the outer layer code s_i

[0102] is used to update the outer layer key state S

[0104] . The entire outer layer code s_i

[0102] may be used, or only a portion of the bit sequence may be extracted and used, or a value combining multiple outer layer codes may be used for the update.

[0080] This results in diversity not only in the partitioning position of the ciphertext C

[0100] , but also in the way the outer layer code s_i

[0102] is used. The existence of multiple methods for updating the outer layer key state S

[0104] leads to greater diversity in the derivation of the next boundary information b_{i+1}, increasing the number of state transition combinations in the outer layer processing. This structure consists of an outer processing layer independent of the internal specifications of existing cryptographic schemes, making it even more difficult for third parties to determine the operation of the outer layer processing.

[0081] [Fourth Embodiment: Application of Outer Layer Cryptography in Industrial Fields] This embodiment demonstrates how the outer layer cryptographic processing method of the present invention can be used in industrial fields. This method operates in an outer layer processing layer that does not refer to the internal specifications of existing encryption methods, divides the ciphertext C

[0100] into variable-length segments according to boundary information b_i based on the outer layer key state S

[0104] , and derives the outer layer encryption seg'_i and outer layer code s_i

[0102] . Therefore, it can be applied to existing communication devices, recording devices, and information processing devices without requiring any additional modifications.

[0082] In a communication device, the ciphertext C

[0100] generated by an existing encryption scheme is used directly as input for the outer layer processing. By dividing it into variable-length segments according to boundary information b_i based on the outer layer key state S

[0104] and deriving the outer layer encryption seg'_i and outer layer code s_i

[0102] , uncertainty originating from the outer layer processing can be added to how the ciphertext is handled in the communication path. Since the boundary information b_i is determined solely from the outer layer key state S

[0104] without referring to the contents of the ciphertext C

[0100] , there is no need to change the processing system on the communication device side.

[0083] In a recording device, the ciphertext C

[0100] stored on the recording medium is reinterpreted to a variable length according to boundary information b_i based on the outer layer key state S

[0104] , and the outer layer encrypted seg'_i and outer layer code s_i

[0102] are derived for each segment seg_i, thereby adding an additional difficulty derived from the outer layer processing against unauthorized reading of the recording medium. This method treats the ciphertext C

[0100] as a black box, thus eliminating the need to modify the internal specifications of the recording device.

[0084] In an information processing device, the updated outer layer key state S

[0104] can be combined with the existing processing system by reflecting the outer layer encryption seg'_i and outer layer code s_i

[0102] obtained by outer layer processing into the processing inside the device. The update of the outer layer key state S

[0104] is performed based on the outer layer code s_i

[0102] , and the updated outer layer key state S

[0104] affects the derivation of the next boundary information b_{i+1}, making it possible to incorporate an outer layer processing system into the device in which the handling of the ciphertext C

[0100] changes over time.

[0085] In this embodiment, the outer layer cryptographic processing method of the present invention can be used in industrial fields such as communications, recording, and information processing by adding uncertainty based on the interdependent structure of the outer layer key state S

[0104] and boundary information b_i as an outer processing layer, in addition to the security of existing cryptographic methods.

[0086] [Detailed explanation of Figure 1] Figure 1 shows the overall configuration of the encryption and decryption processes in the outer layer cryptographic processing method of the present invention.

[0087] On the encryption side, the ciphertext C

[0100] is input to the outer layer processing unit

[0101] , boundary information b_i is derived from the outer layer key state S

[0104] , and the ciphertext C

[0100] is divided into variable-length segments seg_i. Based on the outer layer key state S

[0104] , outer layer processing information is generated, a reversible transformation is applied to seg_i to obtain the outer layer encryption result seg'_i, and by concatenating these, the outer layer ciphertext C'

[0105] is constructed.

[0088] Furthermore, the outer layer code s_i

[0102] is derived based on the outer layer key state S

[0104] and seg_i, and the outer layer key state S

[0104] is updated by the key information management unit

[0103] . The updated S is used to derive the next boundary information b_{i+1}, forming a cyclic structure characteristic of the present invention. S → b_i → seg_i → s_i → S update → b_{i+1} A formation is created. Note that seg'_i is the output for constructing the outer layer ciphertext C'

[0105] and is not included in the circular structure that determines the next boundary information b_{i+1}.

[0089] On the decryption side, the outer layer ciphertext C'

[0105] is taken as input, and boundary information b_i is derived from the same initial outer layer key state S0 as on the encryption side, and C' is divided into variable-length segments seg'_i. Based on the outer layer key state S

[0104] , the outer layer processing information is regenerated, and seg_i is restored by the reverse operation of the reversible transformation. By re-deriving the outer layer code s_i

[0102] based on the recovered seg_i and outer layer key state S

[0104] , and updating the outer layer key state S

[0104] , the same circular structure as the encryption side can be reproduced on the decryption side, and the variable-length partitioning can be synchronized.

[0090] The specific forms of each process shown in Figure 1 (such as the reversible transformation method, the method for deriving the outer layer code, and the method for updating the outer layer key state) are merely examples to aid in understanding the present invention and do not limit the technical scope of the present invention. [Explanation of symbols]

[0091] 100: Ciphertext C 101: Outer layer processing section 102: Outer layer code s_i 103:Key information management department 104: Outer layer key state S 105: Outer layer ciphertext C' [Note: Contact information] For inquiries regarding this application, please contact us at the address below. Email: gan3sys@outlook.jp

Claims

1. The input is a ciphertext C generated by an existing encryption method. It operates in the outer processing layer without referring to the internal specifications of the encryption method. An outer layer cryptographic processing method, (1) A step of maintaining the outer layer key state S dedicated to outer layer processing, (2) Based on the outer layer key state S, boundary information b_i that does not depend on the content of the ciphertext C is obtained The derivation process, (3) The ciphertext C is divided into multiple variable-length segments seg_i according to the boundary information b_i. The process of dividing, (4) Generate outer layer processing information based on the outer layer key state S, Applying a reversible transformation to the aforementioned segment seg_i, the outer layer encrypted segment seg'_i The process of obtaining, (5) Based on the outer layer key state S and the segment seg_i, the outer layer code s_i The derivation process, (6) A step of updating the outer layer key state S based on the outer layer code s_i, (7) A step of deriving the next boundary information b_{i+1} based on the updated outer layer key state S, (8) In the decryption process, the same initial outer layer key state S0 as in the encryption process is maintained. Boundary information b_i is derived from S0, and the outer layer ciphertext C' is divided into variable-length segments seg'_i. By generating outer layer processing information based on the outer layer key state S and then applying the reversible transformation in reverse, The segment seg_i is restored, Based on the recovered seg_i and outer layer key state S, the outer layer code s_i is re-derived. The process of updating the outer layer key state S, Includes, The outer layer key state S is synchronized in both the encryption and decryption processes. Even with variable-length partitioning, the same boundary information b_i is reproduced, It is characterized by the ability to recover ciphertext C from outer layer ciphertext C'. Outer layer cryptographic processing method.

2. In the outer layer cryptographic processing method described in claim 1, The function used to derive the aforementioned outer layer code s_i is, It is a cryptographic function that is collision-hard. Outer layer cryptographic processing method.

3. In the outer layer cryptographic processing method according to claim 1 or 2, The function used to update the outer layer key state S is, It is characterized by being a one-way cryptographic function. Outer layer cryptographic processing method.

4. In the outer layer cryptographic processing method described in claim 1, The aforementioned outer layer processing information is It is characterized by being information for reversible transformations generated based on the outer layer key state S. Outer layer cryptographic processing method.

5. In the outer layer cryptographic processing method described in claim 1, By selectively using part or all of the aforementioned outer layer code s_i The feature is that the outer layer key state S is updated. Outer layer cryptographic processing method.

6. In the outer layer cryptographic processing method described in claim 1, The boundary information b_i is based on multiple partial information of the outer layer key state S Derived characteristics Outer layer cryptographic processing method.

7. In the outer layer cryptographic processing method described in claim 1, The outer layer key state S is held as a fixed-length or variable-length information sequence. It is characterized by being regenerated by a cryptographic function each time it is updated. Outer layer cryptographic processing method.

8. In the outer layer cryptographic processing method described in claim 1, The aforementioned reversible transformation uses information generated based on the outer layer key state S. It is characterized by being a reversible conversion process. Outer layer cryptographic processing method.

9. The outer layer cryptographic processing method described in claim 1 is executed. An outer layer cryptographic processing device, (1) Outer layer key state holding part that holds the outer layer key state S, (2) Boundary derivation unit that derives boundary information b_i from the outer layer key state S, (3) A division unit that divides the ciphertext C into variable-length segments, (4) Outer layer processing unit that performs reversible transformation and generates outer layer code s_i, (5) Key state update unit that updates the outer layer key state S, An outer layer cryptographic processing unit equipped with the following:

10. The outer layer cryptographic processing method according to claim 1 A program designed to be executed by a computer.

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