Information processing device, communication system, information processing method, and program

Abstract

This information processing device comprises a secure region and a security chip. The secure region conceals target information, which is about a to-be-generated target of a blind signature, and requests a signature for concealment information obtained by the concealment from the security chip. The security chip generates a first message using the concealment information and a signature secret key generated by the security chip, and transmits the first message to the secure region. The secure region generates a second message using the target information and the first message, and transmits the second message to the security chip. The security chip generates a third message using the signature secret key and the second message, and transmits the third message to the secure region. The secure region generates the blind signature from the third message and a message generated from the first message.

Description

Information processing device, communication system, information processing method, and program

[0001] The present invention relates to a secret execution technology in the field of information and communications.

[0002] Recent machines include a Trusted Execution Environment (TEE), which is a function that enables safe execution of critical processes independently of the OS. Such machines include not only servers but also terminals such as smartphones.

[0003] WO2022 / 162797

[0004] However, in conventional technologies, when using a security chip (e.g., SecureElement) from a secure area (e.g., Secure World such as TrustZone (registered trademark), commonly referred to as TEE), it is necessary to pass through a non-secure area (referred to as Normal World) once due to a lack of libraries, etc., which poses issues with the confidentiality and tamper-resistance of messages. To solve this, a natural configuration in which a communication channel is encrypted by exchanging keys with the security chip and using a common key places a load of key exchange on the resource-saving security chip, and also requires a large memory size for a "key ring" for key management.

[0005] The present invention has been made in consideration of the above points, and aims to provide a technology that enables a secure area to generate a signature while keeping it secret from a non-secure area and efficiently cooperating with a resource-saving security chip environment.

[0006] According to the disclosed technology, there is provided an information processing device comprising: a secure area; and a security chip; wherein the secure area conceals target information, which is information for which a blind signature is to be generated, and requests the security chip to sign the concealed information obtained by the concealment; the security chip generates a first message using a signature private key generated by the security chip and the concealed information, and transmits the first message to the secure area; the secure area generates a second message using the target information and the first message, and transmits the second message to the security chip; the security chip generates a third message using the signature private key and the second message, and transmits the third message to the secure area; and the secure area generates the blind signature from a message generated from the first message and the third message.

[0007] According to the disclosed technology, the secure area can efficiently cooperate with the resource-saving security chip environment to generate a signature while keeping it secret from the non-secure area.

[0008] It is a diagram for explaining a blind signature.It is a diagram showing an EdDSA signature.It is a diagram showing an example of the configuration of a communication system in an embodiment of the present invention.It is a sequence diagram for explaining the operation of the communication system.It is a diagram showing an example of the hardware configuration of an apparatus.

[0009] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. The embodiment described below is merely an example, and the embodiment to which the present invention is applied is not limited to the following embodiment.

[0010] Below, the problem will be explained in more detail first, and then the technology according to the present embodiment will be explained.

[0011] (Regarding Technical Issues Relating to the Embodiments) As described above, in the conventional technology, when using a security chip (e.g., Secure Element) from a secure area (general TEE), it is necessary to pass through a non-secure area (called Normal World) once due to a lack of libraries or the like, which poses issues in the confidentiality and tamper-resistance of messages. To solve this, a natural configuration in which a communication channel is encrypted by exchanging keys with the security chip and using a common key places a load of key exchange on the resource-saving security chip, and also requires a large memory size for a "key ring" for key management.

[0012] Therefore, a technology is needed that enables the secure area to generate a signature in an efficient manner in cooperation with a resource-saving security chip environment while keeping it secret from the non-secure area.

[0013] A conventional technique related to solving the above-mentioned problems is disclosed in Patent Document 1. The technique disclosed in Patent Document 1 uses blind signatures to conceal communications passing through a non-secure area, and provides protection by creating a pseudo-secure area that includes a general TEE and a security chip.

[0014] However, the technology disclosed in Patent Document 1 is based on RSA blind signatures, and therefore cannot be used in combination with more advanced functions that are expected to be used in the future, such as EdDSA / batch verification. Batch verification (also called batch signature verification) is a technology that verifies multiple signatures simultaneously with less computational effort than verifying all signatures independently.

[0015] In addition, as a result of future cryptography transition, it is expected that the number of security chips (e.g., SecureElement) that support RSA (2048 bits) will decrease, while the number of security chips that support EdDSA (P-256 and later) will increase. However, EdDSA signatures cannot be used in combination with EdDSA / batch verification as is.

[0016] (Outline of the embodiment) In this embodiment, an EdDSA key is generated from an ECDSA key, and an EdDSA blind signature is performed. Note that ECDSA is an abbreviation for Elliptic Curve Digital Signature Algorithm, and EdDSA is an abbreviation for Edwards-curve Digital Signature Algorithm. An outline of this technology will be described in the following (1) and (2).

[0017] (1) An EdDSA signature key for signing (e.g., for currency signatures) is generated (KDF) from an ECDSA initial signature key built into the security chip. In this embodiment, it is assumed that key generation (KDF / PRF) alone imposes a smaller load than encrypted communication. This technology can achieve a lighter load for resource-saving security chips. Note that KDF is an abbreviation for Key Derivation Function, and PRF is an abbreviation for Pseudo-Random Function.

[0018] (2) The technology according to this embodiment makes it possible to generate an EdDSA signature while keeping the message confidential between the security chip (signer) and the secure area (general TEE, user). That is, essentially, an EdDSA blind signature is realized. In this case, the security chip performs the same process as standard EdDSA key generation for key generation. The verifier can also use the standard EdDSA verification algorithm. The signature generation algorithm is different from the standard EdDSA signature generation algorithm, but corresponds to a modified version of the standard algorithm that has been divided. Furthermore, the secure area (general TEE, user) does not need to have any unique secret information when executing this protocol. Below, (2) will be explained in more detail.

[0019] (Regarding Blind Signatures) As described above, in this embodiment, EdDSA blind signatures are performed. Here, blind signatures will be described with reference to FIG. 1. A blind signature is a delegated anonymous signature, and enables a user (recipient) who has a message to be signed to generate a signature while keeping the message confidential from the signer. Note that the user, signer, and verifier more specifically refer to the user's device (or a processing unit within the device), the signer's device (or a processing unit within the device), and the verifier's device (or a processing unit within the device).

[0020] In the example shown in FIG. 1, the recipient generates M by masking the message m to which the recipient wishes to sign (to prevent the signer from viewing the message) in S1 (step 1) and S2, and sends M to the signer.

[0021] At S3 and S4, the signer uses the private key sk to generate a presignature (psig in FIG. 1) for M and sends it to the user (recipient). At S5, the user (recipient) obtains the signature sig for m.

[0022] Also, as shown in FIG. 1, a verifier verifies (m, sig) using the signer's public key pk.

[0023] (Regarding EdDSA Signatures) EdDSA signatures themselves are conventional technology, and key generation (KGen), signature (Sign), and verification (Vrfy) are shown in Figure 2. More detailed information about EdDSA signatures is provided in the reference document (Survey and Evaluation of the Security of EdDSA Digital Signature Structures, CRYPTREC EX-3002-2020). Hereinafter, as described below, R, e, and z in Sign will be referred to as the first message, second message, and third message, respectively.

[0024] R: First message e: Second message z: Third message (Basic idea of ​​Schnorr blind signature) Here, the basic idea of ​​Schnorr blind signature will be explained. In the following explanation, subscripts of superscripts will be expressed using "_". ｚ＿１ " is one example.

[0025] The basic idea of ​​Schnorr-type blind signatures is to use homomorphism in verifying the Schnorr protocol.

[0026] One instance y(=g) of the Schnorr protocol ｘ ) two transcripts (a １ , c １ , z １ ), (a ２ , c ２ , z ２ ) for g ｚ＿１ g ｚ＿２ = a １ y ｃ＿１ ・a ２ y ｃ＿２ Meet the following.

[0027] The verifier generates a simulation for the valid protocol generated by the signer, and uses it as a mask. Intuitively, the blind signature output by the user is (a ３ , z ３ ) = (a １ a ２ , z １ +z ２ ) so that

[0028] The outline of the Schnorr blind signature is as follows.

[0029] The signer generates the key and signature for the normal Schnorr signature. Here, the key pair is (vk, sk) = (x, y = g ｘ )

[0030] The user provides a simulated transcript of the Schnorr protocol. ２ :=g ｚ＿２y －ｃ＿１ , c ２ , z ２ ) (c ２ , z ２ is generated randomly.

[0031] Signer's first message a １ In response to ３ :=a １ ・a ２ , c ３ ←H(M, a ３ ) as c １ :=c ３ -c ２ (c ３ = c １ +c ２ In response, the signer generates z １ For z ３ :=z １ +z ２ and a ３ Let be the signature for the message M that the user finally outputs.

[0032] (Assumptions) The system configuration and operation according to this embodiment will be described below, but the assumptions in the description are as follows.

[0033] P is a secure hash function. b is a prime number and the length of the public key. H: {0, 1} ＊ →{0, 1} ２ｂ is a hash function modeled as a random oracle, with c=2 or 3.

[0034] E （ｐ，ａ，ｄ） is a twisted Edwards curve, and #E （ｐ，ａ，ｄ） =2 ｃ l, where l is a prime number.

[0035] n is an integer and satisfies c≦n<b (e.g., b=256, n=254). B is E （ｐ，ａ，ｄ） is the base point above, and #=l.

[0036] For other details about EdDSA, please refer to the values ​​listed in the reference document (Survey and Evaluation of the Security of the EdDSA Digital Signature Structure, CRYPTREC EX-3002-2020).

[0037] (System Configuration Example) Fig. 3 shows a configuration example of a communication system according to an embodiment of the present invention. As shown in Fig. 3, the communication system according to this embodiment includes information processing device 100, terminal 200, and bank device 300. These devices are connected to a communication network and are capable of communicating with each other.

[0038] In this embodiment, it is assumed that electronic currency (hereinafter referred to as currency) is circulated in the communication system, and therefore bank device 300 (e.g., issuing bank, commercial bank number) is shown. Note that circulation of currency is merely one example of an application of the technology according to this embodiment, and the technology according to this embodiment can be applied to any field.

[0039] In the above-described circulation of currency, it is assumed that secure area 110 is the sender of currency and terminal 200 is the receiver of currency.

[0040] In this embodiment, the information processing device 100 includes a security chip 120 and a secure area 110. The security chip 120 has a tamper-resistant area that securely stores a signature key (private key) including measures against physical attacks by the machine owner. The security chip 120 is, for example, a TPM (Trusted Platform Module) or an SE (Secure Element). The secure area 110 is a general TEE.

[0041] The area between the secure area 110 and the security chip 120 in the information processing device 100 is a non-secure area (REE: Rich Execution Environment).

[0042] It is also assumed that both the secure area 110 and the security chip 120 are trusted, and that the resources of the security chip 120 are poor.

[0043] In the above configuration, the security chip 120 corresponds to the signer, the secure area 110 corresponds to the user, and the terminal 200 corresponds to the verifier.

[0044] (Protocol in this embodiment) Hereinafter, the process contents (protocol) executed by the signer, user, and verifier in this embodiment will be described.

[0045] <Key Generation SGen> The signer generates a key using the same process as for a normal EdDSA signature. The specific procedure is as follows. To indicate the order of the process, line numbers (step numbers) are added to the left. The same applies to the subsequent processes. Note that sk may be called the signature private key, and vk may be called the signature verification key. SGen(1 κ ): 1:s ε ←{0, 1} ｂ ; 2: (h ０ , ...h ２ｂ－１ ) ← H(s ε );#∀i,h ｉ ∈{0, 1} 3: s←2 ｎ +Σ ｉ＝ｃ ｎ－１ h ｉ 2 ｉ ; 4: s'←(h ｂ , ...h ２ｂ－１ ); 5: A←sB; 6: vk←A; 7: sk←(s,s'); 8: return (vk,sk); <User's message specification> A major feature of EdDSA signatures is that the signature generation algorithm is deterministic. That is, while the first message in the Schnorr protocol must be message-dependent, in blind signatures the signer cannot know the message to be signed, so the user must first share information about the message with the signer (without leaking the message itself from the communication). The message specification process is as follows: U １ (m, P): 1: P ｍ ←P(m); 2:return P ｍ <Signature Generation (1): Signature Generation by Signer> The signer generates a signature by the following procedure: ｍ Generate a dependent EdDSA signature for the first message. ｍThis corresponds to the process of generating a normal EdDSA signature for S １ (sk, P ｍ ): 1:(s, s')←sk; 2:r←H(s', P ｍ ) ; 3: R←rB; 4: return R; <Signature Generation (2): Signature Generation by User> For the first message R from the signer, the user generates a second message R' by the following procedure. ２ (m, R): 1:α,β←{0,1} ２ｂ 2: R'←R+αB-βA; 3: e'←H(R', A, m); 4: e←e'-β(mod l); 5: return(e, R') (only e is passed to the signer); <Signature Generation (3): Signing by Signer> For the second message R' from the user, the signer generates a third message (similar to EdDSA signature generation) using the following procedure. S ２ (sk, vk, e): 1: (s, s')←sk; 2: z←r+es(mod l) 3: return z; <Signature Generation (4): Signature Generation by User> For the third message z from the signer, the user generates the final blind signature σ by the following procedure. U ３ (α, R', z): 1: z'←z+α(mod l); 2: σ←(R', z'); 3: return σ; <Verification algorithm> The verifier performs verification using the same verification algorithm as for normal EdDSA signatures shown below. Ver(vk, m, σ): 1: (R', z')←σ; A←vk; 2: (A, R') is E （ｐ，ａ，ｄ） If not, Return τ:=0; 3: Else e'←H(R',m); 4: If(2 ｃ z') B = 2 ｃ R'+(2 ｃe') A ·τ←1; 5: Else τ←0; 6: Return τ; (Processing Sequence) With reference to Figure 4, an example of a processing sequence executed using the above-mentioned protocol in the communication system of this embodiment will be described. As mentioned above, the security chip 120 corresponds to the signer, the secure area 110 corresponds to the user, and the terminal 200 corresponds to the verifier. Furthermore, from the perspective of currency circulation, the secure area 110 corresponds to the sender, and the terminal 200 corresponds to the receiver.

[0046] In S101, the security chip 120 performs the following: (sk, vk)←SGen(1 κ ) to generate the key.

[0047] In S102, the secure area 110 １ A user message is specified by (m, P).

[0048] In S103, the secure area 110 requests the security chip 120 to sign by sending P(m).

[0049] In S104, the security chip 120 １ (sk, P ｍ ) to generate a signature (1).

[0050] In S105, the security chip 120 sets R=S for the secure area 110. １ (sk, P ｍ ) is sent as a Commit.

[0051] In S106, the secure area 110 ２ A signature is generated (2) using (m, R).

[0052] In S107, the secure area 110 transmits e=U to the security chip 120. ２ Send (m, R) as a Challenge.

[0053] In S108, the security chip 120 ２ A signature is generated (3) using (sk, vk, e).

[0054] In S109, the security chip 120 performs z=S ２ Sending (sk, vk, e) commands signature generation.

[0055] In S110, the security chip 120 ３ A signature is generated (4) using (α, R′, z).

[0056] Meanwhile, in S100 , bank device 300 sends its public key certificate to terminal 200 .

[0057] In S111, the secure area 110 transmits the signed token (including m, σ) and the public key certificate (sender, vk) to the terminal 200.

[0058] In S112, the terminal 200 executes the verification algorithm Ver(vk, m, σ) to perform signature verification, and if the signature verification is successful, receives the currency token.

[0059] This concludes the description of the sequence.

[0060] In the above process, it is not necessary to keep the security chip 120 secret, but it is assumed that the communication path between the security chip 120 and the secure area 110 is kept secret. In addition, in the above process, it is assumed that the security chip 120 is not rich enough to terminate encrypted communication. If the security chip 120 does not need to know the message to be signed (in other words, if it is sufficient to authenticate the signature request application), a blind signature will suffice.

[0061] From the viewpoint of feasibility, the signature processing executed by the security chip 120 (TPM, SE, etc.) is generally the same as the normal EdDSA signature processing. In other words, it is like dividing the normal EdDSA signature processing. Furthermore, the key generation processing is the same as the normal EdDSA signature processing. Therefore, it is expected that the processing according to this embodiment can be implemented by, for example, a Java applet.

[0062] 4 is executed by running a program (e.g., a Java applet) in each of the secure area 110 and the security chip 120. As will be described later, the program may be provided by a recording medium 1001 such as a memory card, or may be downloaded from a network.

[0063] (Hardware Configuration Example) Any of the devices (information processing device 100, terminal 200, etc.) in this embodiment can be realized by, for example, causing a computer to execute a program. This computer may be a physical computer or a virtual machine on the cloud.

[0064] That is, the device can be realized by executing a program corresponding to the processing performed by the device using hardware resources such as a CPU and memory built into a computer. The program can be recorded on a computer-readable recording medium (such as a portable memory) and stored or distributed. The program can also be provided via a network such as the Internet or email.

[0065] FIG. 5 is a diagram showing an example of the hardware configuration of the computer. The computer in FIG. 5 includes a drive device 1000, an auxiliary storage device 1002, a memory device 1003, a CPU 1004, an interface device 1005, a display device 1006, an input device 1007, and an output device 1008, all of which are interconnected by a bus BS. Note that some of these devices may be omitted. For example, if no display is required, the display device 1006 may be omitted. The information processing device 100 also includes a security chip 1009 (corresponding to the security chip 120 described above). The secure area 110 may be realized by the memory device 1003 and the CPU 1004 (and software that realizes the general TEE), or hardware for the secure area 110 may be provided separately from the CPU 1004.

[0066] The program that realizes the processing on the computer is provided by a recording medium 1001, such as a CD-ROM or a memory card. When the recording medium 1001 storing the program is set in the drive device 1000, the program is installed from the recording medium 1001 to the auxiliary storage device 1002 via the drive device 1000. However, the program does not necessarily have to be installed from the recording medium 1001, but may be downloaded from another computer via a network. The auxiliary storage device 1002 stores the installed program as well as necessary files, data, etc.

[0067] The memory device 1003 reads and stores a program from the auxiliary storage device 1002 when an instruction to start the program is received. The CPU 1004 realizes functions related to the device in accordance with the program stored in the memory device 1003. The interface device 1005 is used as an interface for connecting to a network, and functions as a transmitter and receiver. The display device 1006 displays a GUI (Graphical User Interface) or the like according to the program. The input device 1007 is composed of a keyboard, mouse, buttons, a touch panel, or the like, and is used to input various operation instructions. The output device 1008 outputs the results of calculations.

[0068] (Summary of the embodiment, effects, etc.) The technology described in this embodiment allows a secure area where a signature for a message is to be obtained (for example, a secure area where a currency payment is to be made) to generate a signature while keeping it secret from non-secure areas and efficiently cooperating with a resource-saving security chip environment.

[0069] The following additional notes are provided regarding the above-described embodiments.

[0070] <Additional Notes> (Additional Item 1) An information processing device comprising: a secure area and a security chip, wherein the secure area conceals target information that is information for which a blind signature is to be generated, and requests the security chip to sign the concealed information obtained by the concealment, the security chip generates a first message using a signature private key generated by the security chip and the concealed information, and transmits the first message to the secure area, the secure area generates a second message using the target information and the first message, and transmits the second message to the security chip, the security chip generates a third message using the signature private key and the second message, and transmits the third message to the secure area, and the secure area generates the blind signature from a message generated from the first message and the third message. (Additional Item 2) The information processing device according to Additional Item 1, wherein the security chip generates the first message using a hash value of the concealed information and secret information constituting the signature private key. (Supplementary Item 3) The information processing device according to Supplementary Item 1, wherein the secure area generates the second message using hash values ​​for a message generated from the first message, information generated from secret information constituting the signature private key, and the target information. (Supplementary Item 4) The information processing device according to Supplementary Item 1, wherein the security chip generates the third message using secret information constituting the signature private key, the second message, and hash values ​​for secret information constituting the signature private key and the anonymization information. (Supplementary Item 5) The information processing device according to Supplementary Item 1, wherein the security chip generates a signature verification key and the signature private key using a key generation method for EdDSA signatures. (Supplementary Item 6) A communication system comprising: the information processing device according to any one of Supplementary Items 1 to 5; and a terminal that verifies the blind signature generated by the information processing device using the signature verification key.(Supplementary Item 7) An information processing method in an information processing device comprising a secure area and a security chip, comprising: a step in which the secure area conceals target information, which is information for which a blind signature is to be generated, and requests the security chip to sign the concealed information obtained by the concealment; a step in which the security chip generates a first message using a signature private key generated by the security chip and the concealed information, and transmits the first message to the secure area; a step in which the secure area generates a second message using the target information and the first message, and transmits the second message to the security chip; a step in which the security chip generates a third message using the signature private key and the second message, and transmits the third message to the secure area; and a step in which the secure area generates the blind signature from a message generated from the first message and the third message. (Supplementary Item 8) A non-transitory storage medium storing a program that causes a computer including a secure area and a security chip to execute the following processes: a process in which the secure area conceals target information, which is information for which a blind signature is to be generated, and requests the security chip to sign the concealed information obtained by the concealment; a process in which the security chip generates a first message using the concealed information and a signature private key generated by the security chip, and transmits the first message to the secure area; a process in which the secure area generates a second message using the target information and the first message, and transmits the second message to the security chip; a process in which the security chip generates a third message using the signature private key and the second message, and transmits the third message to the secure area; and a process in which the secure area generates the blind signature from a message generated from the first message and the third message.

[0071] Although the present embodiment has been described above, the present invention is not limited to such a specific embodiment, and various modifications and changes are possible within the scope of the gist of the present invention described in the claims.

[0072] REFERENCE SIGNS LIST 100 Information processing device 110 Secure area 120 Security chip 200 Terminal 300 Bank device 1000 Drive device 1001 Recording medium 1002 Auxiliary storage device 1003 Memory device 1004 CPU 1005 Interface device 1006 Display device 1007 Input device 1008 Output device 1009 Security chip

Claims

1. An information processing device comprising: a secure area; and a security chip; wherein the secure area conceals target information, which is information for which a blind signature is to be generated, and requests the security chip to sign the concealed information obtained by the concealment; the security chip generates a first message using a signature private key generated by the security chip and the concealed information, and transmits the first message to the secure area; the secure area generates a second message using the target information and the first message, and transmits the second message to the security chip; the security chip generates a third message using the signature private key and the second message, and transmits the third message to the secure area; and the secure area generates the blind signature from a message generated from the first message and the third message.

2. The information processing device according to claim 1, wherein the security chip generates the first message using a hash value of the secret information constituting the signature private key and the anonymization information.

3. The information processing device according to claim 1, wherein the secure area generates the second message using a hash value for a message generated from the first message, information generated from secret information constituting the signature private key, and the target information.

4. The information processing device according to claim 1, wherein the security chip generates the third message using secret information constituting the signature private key, the second message, and a hash value for the secret information constituting the signature private key and the anonymization information.

5. The information processing device according to claim 1, wherein the security chip generates a signature verification key and the signature private key using a key generation method in EdDSA signatures.

6. A communication system comprising: an information processing device according to any one of claims 1 to 5; and a terminal that verifies the blind signature generated by the information processing device using a signature verification key.

7. An information processing method in an information processing device comprising a secure area and a security chip, comprising: a step in which the secure area conceals target information, which is information for which a blind signature is to be generated, and requests the security chip to sign the concealed information obtained by the concealment; a step in which the security chip generates a first message using the concealed information and a signature private key generated by the security chip, and sends the first message to the secure area; a step in which the secure area generates a second message using the target information and the first message, and sends the second message to the security chip; a step in which the security chip generates a third message using the signature private key and the second message, and sends the third message to the secure area; and a step in which the secure area generates the blind signature from a message generated from the first message and the third message.

8. A program that causes a computer having a secure area and a security chip to execute the following processes: a process in which the secure area conceals target information, which is information for which a blind signature is to be generated, and requests the security chip to sign the concealed information obtained by the concealment; a process in which the security chip generates a first message using the concealed information and a signature private key generated by the security chip, and sends the first message to the secure area; a process in which the secure area generates a second message using the target information and the first message, and sends the second message to the security chip; a process in which the security chip generates a third message using the signature private key and the second message, and sends the third message to the secure area; and a process in which the secure area generates the blind signature from a message generated from the first message and the third message.

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