JP7250587B2 - Communication device, control method and program - Google Patents

Description

The present invention relates to a device for verifying digital certificates.

There is a communication system that authenticates a client and a server using a digital certificate and performs encrypted communication (Patent Document 1). Since a digital certificate has an extension area and can contain various extension data, the size of the digital certificate increases or decreases depending on the number and size of the extension data. The extension field can also include a domain name, which is one of the owner information of the digital certificate.

JP 2013-24845 A

A client that accepts a digital certificate that includes a domain name in the extension area checks whether the domain name of the destination server matches the domain name included in the digital certificate as a security measure against tampering and spoofing. It is necessary to confirm. In general, in a communication device with limited computational resources such as a digital camera, processing for the confirmation takes time. Therefore, when a digital certificate containing a large extension area is received from an unauthorized server or the like, it takes time to complete the confirmation process, and the server cannot be confirmed. There was a problem that the

In view of the above problems, it is an object of the present invention to reduce the possibility of taking a long time to check an extension area included in a digital certificate.

A communication device according to the present invention includes receiving means for receiving a digital certificate from an information processing device, size information of a predetermined extension area included in the digital certificate received by the receiving means, and the predetermined extension area. acquiring means for acquiring at least one of information relating to the number of data contained in the extension area; confirming means for confirming whether the domain name of the information processing apparatus is included in the domain name contained in the predetermined extension area; communication means for performing encrypted communication with the information processing device based on the result of confirmation by the means; and disconnection from the information processing device based on the information acquired by the acquisition means without confirmation by the confirmation means. and a control means for controlling such that

According to the present invention, it is possible to reduce the possibility of taking a long time to check the extension area included in the digital certificate.

The block diagram of a communication system. FIG. 2 is a hardware configuration diagram of a digital camera; A flow chart executed by a digital camera. A flow chart executed by a digital camera. A flow chart executed by a digital camera. A flow chart executed by a digital camera. FIG. 4 is a sequence diagram showing processing executed in a communication system; Configuration diagram of a digital certificate.

FIG. 1 shows the configuration of a communication system 100 according to this embodiment. The communication system 100 includes a communication device (eg, digital camera) and an information processing device (eg, server). A digital camera will be described below as an example of a communication device, but the present invention is not limited to this. That is, the communication device may be, for example, a PC, a tablet terminal, a portable game machine, a personal digital assistant (PDA), or the like. Also, the above configuration may be provided as a communication system comprising a plurality of devices instead of a single communication device.

In this embodiment, the digital camera 101 has a wireless communication function. Here, it is assumed that the wireless communication function is a wireless LAN function conforming to the IEEE802.11 series standard. However, other wireless communication functions such as Bluetooth (registered trademark), MBOA, UWB, ZigBee, and NFC (Near Field Communication) may be used. Also, wired communication such as a wired LAN may be performed in place of or in addition to wireless communication. Here, LAN is an abbreviation for Local Area Network. MBOA is an abbreviation for Multi Band OFDM Alliance. UWB is an abbreviation for Ultra Wide Band, and includes wireless USB, wireless 1394, WINET, and the like. Server 102 and wireless LAN AP 103 are connected to backbone network 105 . The backbone network 105 is, for example, the Internet, but may be a local network or the like. A digital camera 101 can connect to a wireless LAN network constructed by a wireless LAN AP 103 and communicate with a server 102 via wireless LAN communication 104 . Note that the digital camera 101 may use a wireless LAN network constructed by an external device other than the wireless LAN AP 103 . Here, the external device can be a smart phone, a PC, or the like.

FIG. 2A shows a hardware configuration diagram of the digital camera 101 according to this embodiment. A wireless LAN control unit 201 performs various types of wireless LAN communication control based on the IEEE 802.11 series standard and protocol processing related to wireless LAN communication. Antenna 202 is used for wireless LAN communication. A control unit 203 controls the entire digital camera 101 by executing a control program stored in the ROM 204 .

The ROM 204 is a ROM that stores control programs executed by the control unit 203 . Various operations to be described later are performed by the control unit 203 executing a control program stored in the ROM 204 . The RAM 205 is used as a work memory for executing the control program and for temporary storage of data. A storage unit 206 stores various information such as parameters required for communication and compression-encoded image data. The storage unit 206 may be detachable from the digital camera 101 .

An operation unit 207 is used by the user to operate the digital camera 101 . A display unit 208 outputs visually recognizable information such as an LCD or LED, or outputs sound such as a speaker. A microphone 209 acquires voice and the like. The packet transmitting/receiving unit 210 transmits/receives packets related to various communications. The imaging unit 211 captures an optical image of a subject. An image processing unit 212 converts the captured image output from the imaging unit 211 into image data in a predetermined format, and performs various processing such as brightness and color correction of the image data. The encoding/decoding unit 213 performs predetermined high-efficiency encoding (for example, discrete cosine transform, variable length encoding after quantization) on the image data output from the image processing unit 212 . A reproduction unit 214 reproduces the compression-encoded image data. A power supply unit 215 supplies power to the digital camera 101 .

Next, FIG. 2B shows a software block configuration realized by the control unit 203 reading out the program stored in the ROM 204. As shown in FIG. The instruction determination unit 251 determines that the user has issued an instruction to start the communication function via a button or the like of the operation unit 207 . A storage control unit 252 controls the storage unit 206 to store data and read data to the RAM 205 . The display control unit 253 controls the display unit 208 to perform various displays. The transmitting unit 254 uses the packet transmitting/receiving unit 210, the wireless LAN control unit 201, and the like to make a request to the server 102, transmit data, and the like. The receiving unit 255 uses the packet transmitting/receiving unit 210, the wireless LAN control unit 201, and the like to receive a response from the server 102, data reception, and the like.

The extension area attribute acquisition unit 256 acquires attributes related to extension areas in the digital certificate received from the server 102 by the reception unit 255 . The digital certificate has the configuration (field) shown in FIG. 8(a). The details of the extension area included in the digital certificate have a configuration (field) as shown in FIG. 8(b). The extension area includes size information 801 indicating the size of the entire extension area, size information 802 indicating the size of the data portion of the extension area, and the like.

The domain name verification unit 257 verifies (confirms) the domain name included in the digital certificate received from the server 102 by the reception unit 255 and the domain name of the server 102 to which it is connected. The disconnect determination unit 258 determines whether or not to disconnect from the server 102 based on the verification result (confirmation result) of the domain name verification unit 257 .

All functional blocks shown in FIG. 2 are interrelated in terms of software or hardware. Also, the functional blocks described above are merely examples, and a plurality of functional blocks may constitute one functional block, or any one of the functional blocks may be further divided into blocks that perform a plurality of functions.

In the following, after explaining the processing executed by the digital camera 101, an example of the flow of processing executed within the communication system will be explained. In the following description, it is assumed that wireless LAN communication 104 between digital camera 101 and wireless LAN AP 103 has been established in advance. Also, the following description assumes that TCP (Transmission Control Protocol) and TLS (Transport Layer Security) protocol are used for encrypted communication between the digital camera 101 and the server 102 .

FIG. 3 is a flowchart showing the flow of processing executed when the digital camera 101 starts the cloud cooperation mode. This processing can be started when the user operates the operation unit 207 of the digital camera 101 to select start of the cloud cooperation mode, but is not limited to this. For example, it can be started when an image is captured by the digital camera 101 or when a request to start the cloud cooperation mode is received from an external device.

When the cloud cooperation mode is started, first, in S301, the digital camera 101 selects the server 102 as a connection destination, and advances the processing to S302. Here, the server 102 to be connected can be selected by displaying a list of connectable servers stored in the storage unit 206 on the display unit 208 and giving an instruction by the user via the operation unit 207 . However, it is not limited to this. For example, the digital camera 101 automatically selects according to the function scheduled to be executed in the cloud cooperation mode. Note that the functions scheduled to be executed may be uploading moving images, live streaming, or the like, but are not limited to these. In S302, the digital camera 101 starts secure connection processing. Note that the secure connection process refers to a process of establishing a TCP session for performing encrypted communication with the server 102, exchanging key information, and the like. Details of the secure connection process will be described later.

After that, in S303, the digital camera 101 determines whether or not the secure connection was normally completed in S302. If the secure connection has been completed normally (YES in S302), the process proceeds to S304, and if the secure connection has not been completed normally (NO in S302), the process proceeds to S310. In S304, the digital camera 101 determines whether the domain name of the server 102 selected in S301 is IP address notation. If it is the IP address notation (YES at S304), the process proceeds to S307, and if it is not the IP address notation (NO at S304), the process proceeds to S305. In S305, the digital camera 101 starts domain name verification processing. Note that the domain name verification processing refers to processing for verifying whether or not the domain name of the server 102 selected in S301 matches the domain name in the server certificate received from the server 102 . Here, the server certificate is X. 509 standard digital certificate, but is not limited to this, and any digital certificate may be used. That is, any digital certificate containing encryption keys, signatures, etc. can be substituted. Details of the domain name verification process will be described later. After that, in S306, the digital camera 101 determines whether or not the domain name verification process in S305 was successful. If the domain name verification process succeeds (YES in S306), the process proceeds to S307; otherwise (NO in S306), the process proceeds to S310. In S307, the digital camera 101 displays on the display unit 208 that the connection with the server 102 selected in S301 was successful, and proceeds to S308. In S308, the digital camera 101 performs encrypted data communication with the server 102 using the key information exchanged in S302, and proceeds to S309. Here, the encrypted data communication may be message transmission/reception of TLS Application Data protocol. In S309, the digital camera 101 determines whether or not to end the cloud cooperation mode. Here, whether or not to end the cloud cooperation mode can be determined based on whether or not there is an end instruction by the user operating the operation unit 207, but the present invention is not limited to this. For example, the digital camera 101 may be terminated when there is no encrypted data communication for a certain period of time, or when an instruction to terminate the cloud cooperation mode is received from an external device. If the cloud cooperation mode is to be terminated (YES in S309), the process proceeds to S310, and if the cloud cooperation mode is not to be terminated (NO in S309), the process returns to S308. In S310, the digital camera 101 starts secure disconnection processing. Note that the secure disconnection processing refers to processing for disconnecting the communication session for encrypted communication with the server 102 established in S302. Details of the secure disconnection process will be described later. After that, in S311, the digital camera 101 determines whether or not the secure disconnection processing of S310 is normal disconnection, that is, whether or not the secure connection processing of S302 and the domain name verification processing of S305 have succeeded. If the disconnection is normal (YES in S311), the process proceeds to S312, and if the disconnection is not normal (NO in S311), the process proceeds to S313. In S312, the digital camera 101 displays on the display unit 208 that the disconnection from the server 102 has been completed, and ends the cloud cooperation mode. On the other hand, in S313, the digital camera 101 displays on the display unit 208 that an error has occurred in the connection with the server 102, and ends the cloud cooperation mode.

Next, the flow of processing executed when secure connection processing is started in the digital camera 101 will be described with reference to FIG.

First, in S401, the digital camera 101 establishes a TCP connection, and advances the processing to S402. In S402, the digital camera 101 transmits a secure connection start request, and advances the process to S403. Here, the secure connection initiation request can be a Client Hello message of the TLS Handshake protocol. The Client Hello message can include the TLS protocol version supported by the digital camera 101, an encryption algorithm, a session ID, and the like. In S403, the digital camera 101 receives the server certificate and advances the process to S404. Here, the reception of the server certificate can be received by a Certificate message of the TLS Handshake protocol. Before and after receiving the Certificate message, a Server Hello message, a Server Hello Done message, and a Server Key Exchange message can be received. In S404, the digital camera 101 determines whether or not the server certificate was successfully received in S403. Here, whether or not the server certificate has been successfully received can be determined based on whether or not the size of the server certificate is equal to or smaller than a threshold value, but the present invention is not limited to this. For example, if the format of the received server certificate is other than a predetermined format, it may be determined that reception has failed. If the server certificate has been successfully received (YES in S404), the process proceeds to S405, and if the server certificate has failed to be received (NO in S404), the process proceeds to S411. In S405, the digital camera 101 verifies the validity of the server certificate received in S403, and advances the process to S406. The validity of the server certificate is verified by determining whether or not the signature included in the server certificate has been tampered with using a root (CA) certificate stored in advance in the storage unit 206. can be verified. In S406, the digital camera 101 determines whether the server certificate received in S405 is valid. If the server certificate is determined to be valid (YES in S406), the process proceeds to S407, and if the server certificate is determined to be invalid (NO in S406), the process proceeds to S411. In S407, the digital camera 101 transmits the key information and advances the processing to S408. Here, the key information can be transmitted by a Client Key Exchange message of the TLS Handshake protocol. Also, the key information can be information obtained by encrypting a self-generated pre-master secret using the public key included in the received server certificate. In S408, the digital camera 101 transmits a secure connection completion notification, and advances the process to S409. Here, the secure connection completion notification can be a Finished message of the TLS Handshake protocol. Before sending the Finished message, a Change Cipher Spec message of the Change Cipher Spec protocol can be sent. In S409, the digital camera 101 receives the secure connection completion notification, and advances the process to S410. Note that a Change Cipher Spec message of the Change Cipher Spec protocol can be received before receiving the secure connection completion notification. In S410, the digital camera 101 determines that the secure connection process has succeeded, and terminates this process. On the other hand, in S411, the digital camera 101 determines that the secure connection process has resulted in an error, and terminates this process.

Next, the flow of processing executed when domain name verification processing is started in the digital camera 101 will be described with reference to FIG.

First, in S501, the digital camera 101 acquires the size 801 of the entire predetermined extension area of the received server certificate, and advances the process to S502. Here, the predetermined extension area may be a SAN (Subject Alternative Name), but is not limited to this. That is, it can be replaced with any field that contains a domain name.

Subsequently, in S502, the digital camera 101 determines whether or not the received server certificate has a predetermined extension area. Here, whether or not the predetermined extension area exists can be determined by determining whether the size of the entire predetermined extension area acquired in S501 is 0 or not. If the predetermined extension area exists (YES in S502), the process proceeds to S503, and if the predetermined extension area does not exist (NO in S502), the process proceeds to S512. In S503, the digital camera 101 confirms the size 801 of the entire predetermined extension area acquired in S501, and determines whether or not the size of the extension area is equal to or less than a threshold. If the size of the extension area is equal to or less than the threshold (YES in S503), the process proceeds to S504, and if the size of the extension area is greater than the threshold (NO in S503), the process proceeds to S515. Here, whether or not the size of the extension area is equal to or less than the threshold is determined using the size 801 of the entire predetermined extension area of the received server certificate, but the present invention is not limited to this. For example, it can be determined using the data size 802 of the predetermined extension area. In S504, the digital camera 101 sets the head data of the extension area as data to be verified, and advances the process to S505. The extension area and the data in the extension area are ASN. 1 (Abstract Syntax Notation One) DER (Distinguished Encoding Rules) format, but is not limited to this. For example, ASN. 1, or XML (Extensible Markup Language) or the like. In S505, the digital camera 101 acquires the data type of the target data, and advances the processing to S506. Here, the data type can be a domain name, IP address, email address, URI (Uniform Resource Identifier), or the like. In S506, the digital camera 101 determines whether the data type is a domain name. If the data type is a domain name (YES at S506), the process proceeds to S507, and if the data type is not a domain name (NO at S506), the process proceeds to S510. In S507, the digital camera 101 acquires the data size, that is, the length of the domain name, and advances the processing to S508. In S508, the digital camera 101 acquires data, that is, the domain name, and advances the processing to S509. In S509, the digital camera 101 determines whether or not the domain name of the server 102, which is the connection destination selected in S301, matches the domain name acquired in S508. Here, whether or not the domain names match can be determined by comparison without distinguishing between uppercase and lowercase letters. Also, if the domain name acquired in S508 contains a wildcard notation, the part can be interpreted as an arbitrary character string and compared, but the character string is not limited to this. For example, it is possible to compare by interpreting a wild card notation as a character and comparing by exact match. If the domain names match (YES in S509), the process proceeds to S514, and if the domain names do not match (NO in S509), the process proceeds to S510. In S510, the digital camera 101 determines whether or not the next data exists in the extension area. Here, whether or not there is next data in the extension area can be determined by determining whether or not the total size of the verified data is larger than the size of the extension area acquired in S501. If the next data exists in the extension area (YES at S510), the process proceeds to S511, and if the next data does not exist in the extension area (NO at S510), the process proceeds to S515. In S511, the digital camera 101 sets the next data in the extension area as verification target data, and returns the process to S505. On the other hand, in S512, the digital camera 101 acquires the domain name in the server certificate, and advances the process to S513. Here, the domain name in the server certificate can be CN (Common Name). In S513, the digital camera 101 determines whether the domain name of the server 102, which is the connection destination selected in S301, matches the domain name acquired in S512. Note that the determination of whether the domain names match is the same as in S509, so the description is omitted. If the domain names match (YES at S513), the process proceeds to S514, and if the domain names do not match (NO at S513), the process proceeds to S515. In S514, the digital camera 101 determines that the verification of the domain name has succeeded, and terminates this processing. On the other hand, in S515, the digital camera 101 determines that verification of the domain name has failed, and terminates this processing.

Next, a flow of processing executed when secure disconnection processing is started in the digital camera 101 will be described with reference to FIG.

First, in S601, the digital camera 101 transmits a secure connection disconnection notification, and advances the processing to S602. Here, the secure connection disconnection notification can be a Close Notify message of the TLS Alert protocol, but is not limited to this. For example, other messages defined in the TLS Alert protocol may be sent depending on what triggered the secure disconnect process. It should be noted that factors for starting the secure disconnection process can be failure to receive the server certificate, failure to verify the validity of the server certificate, excess size of the extension area of the server certificate, domain name mismatch, and the like. In S602, the digital camera 101 receives the secure connection disconnection notification, and advances the process to S603. In S<b>603 , the digital camera 101 disconnects TCP, and ends this processing.

In this processing, the secure connection disconnection notification is transmitted and received before TCP disconnection, but TCP disconnection may be performed without transmitting and receiving the secure connection disconnection notification. As a result, the time required for the disconnection process can be shortened when the process is to be terminated immediately by turning off the power supply or the like.

Next, the flow of processing executed in the communication system will be described using FIG. In this processing example, the digital camera 101 starts domain name verification processing after performing secure connection processing with the unauthorized server 102 . Since the size of the extension area in the server certificate received from the server 102 is larger than the threshold, the digital camera 101 does not perform subsequent verification processing, performs secure disconnection processing, and ends the cloud cooperation mode. Note that in this processing example, the domain name of the server 102, which is the connection destination, is not described as an IP address.

In the digital camera 101, the user performs an operation for starting the cloud cooperation mode (M701), and selects the server 102 as the connection destination (M702, S301). When the selection is made, the digital camera 101 establishes connection with the wireless LAN AP 103 (M703) and starts secure connection processing (S302). When starting secure connection processing, the digital camera 101 establishes a TCP connection with the server 102 (M704, S401). When the TCP connection with the server 102 is completed, the digital camera 101 transmits a secure connection start request to the server 102 (M705, S402). Upon receiving the secure connection start request, the server 102 transmits the server certificate to the digital camera 101 (M706, S403). When the digital camera 101 successfully receives the server certificate (YES in S404), it verifies the validity of the server certificate (M707, S405). When the digital camera 101 determines that the server certificate is valid as a result of validation of the server certificate (YES in S406), it transmits key information to the server 102 (M708, S407), and transmits a secure connection completion notice (M709). , S408). Upon receiving the secure connection completion notification, the server 102 transmits the secure connection completion notification to the digital camera 101 (M710, S409). Upon receiving the secure connection completion notification, the digital camera 101 determines that the connection has been completed normally (S410), and terminates the secure connection process. The digital camera 101 successfully completes the secure connection processing (YES in S303), and since the domain name of the server 102 to which it is connected is not in IP address notation (NO in S304), it starts domain name verification processing (S305). . When starting the domain name verification process, the digital camera 101 acquires the size of the extension area in the server certificate (M711, S501). Here, since the extension area exists in the server certificate (YES in S502) and the size is larger than the threshold (NO in S503), the digital camera 101 does not perform subsequent processing and fails domain name verification. (S515), and terminates the domain name verification process. Since the domain name verification process has failed (NO in S306), the digital camera 101 starts secure disconnection process (S310). When starting secure disconnection processing, the digital camera 101 transmits a secure connection disconnection notification to the server 102 (M712, S601). Upon receiving the secure connection disconnection notification, the server 102 transmits the secure connection disconnection notification to the digital camera 101 (M713, S602). Upon receiving the secure connection disconnection notification, the digital camera 101 performs TCP disconnection (M714, S603) and terminates the secure disconnection process. When the secure disconnection process is completed, the digital camera 101 determines that the disconnection is not normal because the cause for starting the secure disconnection process is the failure of the domain name verification process (NO in S311), and displays the connection error UI (M715). , S313). After that, the digital camera 101 terminates the cloud cooperation mode (M716).

As described above, in this processing example, when the size of the extension area in the server certificate is larger than the threshold, the digital camera 101 does not perform subsequent processing related to domain name verification, and determines that the verification has failed. I made it As a result, when a server certificate containing a large extension area is received from an unauthorized server that should not be connected, it is possible to avoid unnecessary domain name verification, thereby suppressing deterioration in user usability. can.

In this embodiment, when the size of the extension area in the server certificate is larger than the threshold value, the digital camera 101 does not perform subsequent domain name verification processing and determines that the verification has failed. However, it is not limited to this. For example, if the server 102 that is the connection destination is a server that has been stored as being trusted by the user in advance, or if the network being connected is a local network, or if a predetermined condition is satisfied, the process can continue. As a result, even if the threshold is set to a lower value, it is possible to reliably connect to the server that is the legitimate connection destination, and if the connection destination is an unauthorized server, unnecessary domain name verification can be avoided. can do.

In the present embodiment, the digital camera 101 determines whether or not to continue the domain name verification process based on whether the size of the extension area in the server certificate is equal to or less than the threshold. , but not limited to this. For example, it can be determined based on whether or not the number of data types included in the extension area and the number of data that are domain names in the data are equal to or less than a threshold. Also, the size of the extension area and the number of data included in the extension area can be used to estimate the processing time required for domain name verification, and determination can be made based on whether the estimated processing time is less than or equal to a threshold. Furthermore, after starting the processing related to domain name verification, processing is triggered when the size of processed data, the number of data, the cumulative processing time (elapsed time since the start of processing), etc. exceed the threshold. may be aborted and determined to have failed verification. As a result, even if the size of the extension area in the server certificate of the server that is the legitimate connection destination is large to some extent, it is possible to connect, and if the connection destination is an unauthorized server, unnecessary domain name verification is possible. can be avoided.

In the present embodiment, when the digital camera 101 fails to connect to the server 102, the display unit 208 displays a connection error, but the present invention is not limited to this. For example, error types such as server certificate reception failure, server certificate validity verification failure, server certificate extension area size excess, domain name mismatch, and the like can be displayed. As a result, the user can easily grasp the cause of the connection error, and usability for the user can be further improved. Also, the digital camera 101 may notify the server 102 of the error.

In the present embodiment, the digital camera 101 performs the domain name verification process after completing the secure connection process, but the present invention is not limited to this. For example, the domain name verification process can be performed after receiving the server certificate or after completing the validity verification. As a result, unnecessary domain name verification can be avoided in the case of an unauthorized server, and unnecessary transmission of key information can be suppressed, thereby improving security.

In the present embodiment, when the digital camera 101 determines that the domain name verification process has failed, it immediately executes the secure disconnection process, but the present invention is not limited to this. For example, the user can be warned that the server certificate is invalid, and the encrypted data communication can be continued. Note that the warning to the effect that the server certificate is invalid can be a validation failure, an expiration date, a domain name mismatch, or the like. As a result, when it is determined that the server certificate is invalid due to inadequate settings, etc., even if the server is a valid connection destination, temporary communication with the server can be performed while the user understands the security risks. It can be performed.

In this way, in a device with limited computational resources, it is possible to avoid unnecessary processing related to domain name verification and to suppress deterioration in user usability.

The present invention supplies a program that implements one or more functions of the above-described embodiments to a system or device via a network or a storage medium, and one or more processors in the computer of the system or device reads and executes the program. It can also be realized by processing to It can also be implemented by a circuit (for example, ASIC) that implements one or more functions.

101 digital camera 102 server 103 wireless LAN AP
104 wireless LAN signal 105 Internet

Claims (14)

A communication device,
receiving means for receiving a digital certificate from an information processing device;
acquisition means for acquiring at least one of size information of a predetermined extension area included in the digital certificate received by the reception means and information on the number of data included in the predetermined extension area;
confirmation means for confirming whether the domain name included in the predetermined extension area includes the domain name of the information processing device;
communication means for performing cryptographic communication with the information processing device based on a result of confirmation by the confirmation means;
Control means for controlling to disconnect communication with the information processing device without confirmation by the confirmation means based on the information acquired by the acquisition means;
A communication device comprising: 2. The communication apparatus according to claim 1, wherein the predetermined extension area is a SAN (Subject Alternative Name) area. The digital certificate is X. 3. The communication device according to claim 1, wherein the digital certificate conforms to the V.509 standard. the predetermined extension area has a field indicating the size of the predetermined extension area;
4. The communication apparatus according to any one of claims 1 to 3, wherein said acquisition means acquires said size information from said field. 4. The information about the number of data is the number of data types included in the predetermined extension area or the number of domain names included in the predetermined extension area. The communication device according to item 1. The control means controls to disconnect the communication when it is determined that the acquired information is larger than the threshold based on the acquired information and the threshold, and disconnects the communication when it is not determined to be greater than the threshold. control not to
The control means further controls not to disconnect the communication regardless of the information acquired by the acquisition means when the information processing device from which the digital certificate is received is stored as a trusted device. death,
6. The communication apparatus according to any one of claims 1 to 5, wherein confirmation is performed by said confirmation means when said communication is controlled so as not to be disconnected . When a predetermined period of time has passed since the confirmation by the confirmation means was started, the control means stops the confirmation by the confirmation means and disconnects from the information processing device. 7. The communication device according to any one of claims 1 to 6 . 8. The communication apparatus according to any one of claims 1 to 7 , further comprising notification means for notifying a predetermined error when said control means controls to disconnect from said information processing apparatus. 9. The communication apparatus according to claim 8 , wherein said notification means notifies said predetermined error to the user. 10. The communication apparatus according to claim 8 , wherein said predetermined error indicates an error based on information obtained by said obtaining means. The communication device according to any one of claims 1 to 10 , wherein the encrypted communication is communication based on TLS (Transport Layer Security) protocol. The control means establishes a TLS (Transport Layer Security) or TCP (Transmission Control Protocol) session with the information processing device based on the information acquired by the acquisition means without confirmation by the confirmation means. 12. The communication device according to any one of claims 1 to 11 , wherein the communication device is controlled to disconnect. A control method comprising:
a receiving step of receiving a digital certificate from an information processing device;
an acquiring step of acquiring at least one of size information of a predetermined extension area included in the digital certificate received in the receiving step and information on the number of data included in the predetermined extension area;
a confirmation step of confirming whether the domain name included in the predetermined extension area includes the domain name of the information processing device;
a communication step of performing predetermined communication with the information processing device based on the result of confirmation in the confirmation step;
a control step of controlling to disconnect from the information processing device without performing confirmation in the confirmation step based on the information acquired in the acquisition step;
A control method characterized by having A program for operating a computer as the communication device according to any one of claims 1 to 12 .

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