Verification method, verification apparatus, and storage medium including program stored therein

1. A verification method for verifying content data to be used in a vehicle, the verification method comprising:

acquiring the content data;

acquiring, from a first plurality of pieces of partial data obtained by dividing the content data, a respective plurality of first hash values;

acquiring a signature generated by using the plurality of first hash values and a key;

acquiring state information that indicates a state of the vehicle;

determining an integer N that is greater than or equal to one based on the acquired state information;

generating, from N pieces of partial data, included in the first plurality of pieces of partial data, respective second hash values;

verifying the content data by using each of (a) a subset of the plurality of first hash values which are those respectively generated from the first plurality of pieces of partial data other than the N pieces of partial data,

(b) the generated second hash values, and

(c) the acquired signature;

and outputting information that indicates a result of the verifying, wherein: the state information indicates whether the vehicle is running or not running, and

in the determining, when the vehicle is determined to be running, a value of the integer N is determined so as to be equal to a first value, and

when the vehicle is determined to be not running, the value of the integer N is determined so as to be equal to a second value that is greater than the first value.

2. The verification method according to claim 1 , wherein the generating includes:

randomly selecting the N pieces of partial data from the first plurality of pieces of partial data, and

generating a corresponding one of the respective second hash values from each of the selected N pieces of partial data.

3. The verification method according to claim 1 , wherein

the state information indicates, as the state of the vehicle, a processing load imposed on an apparatus that executes the verification method, and

in the determining,

a value of the integer N is determined such that the higher the processing load is, the smaller the value of the integer N is.

4. The verification method according to claim 1 , wherein

the state information indicates, as the state of the vehicle, an amount of communication data included in a communication performed by an apparatus that executes the verification method, and

in the determining,

a value of the integer N is determined such that the greater the amount of communication data is, the smaller the value of the integer N is.

5. The verification method according to claim 1 , wherein

in the determining,

a value of the integer N is determined based on a type or a size of the content data.

6. The verification method according to claim 1 , wherein

the determining includes determining, based on a type of the content data, which pieces of the first plurality of pieces of partial data are selected as the N pieces of partial data.

7. The verification method according to claim 5 , wherein

the type of the content data includes a measure that indicates an update interval of the content data.

8. A verification apparatus that verifies content data to be used in a vehicle, comprising: a processor; and a memory that includes at least one set of instructions that, when executed by the processor, causes the processor to execute operations including:

acquiring the content data; acquiring, from a first plurality of pieces of partial data obtained by dividing the content data, a respective plurality of first hash values;

acquiring a signature generated by using the plurality of first hash values and a key;

acquiring state information that indicates a state of the vehicle; determining an integer N that is greater than or equal to one based on the acquired state information;

generating, from N pieces of partial data included in the first plurality of pieces of partial data, respective second hash values; verifying the content data by using each of (a) a subset of the plurality of first hash values which are those respectively generated from the first plurality of pieces of partial data other than the N pieces of partial data,

(b) the generated second hash values, and (c) the signature;

and outputting information that indicates a result of the verifying,

wherein: the state information indicates whether the vehicle is running or not running, and in the determining, when the vehicle is determined to be running, a value of the integer N is determined so as to be equal to a first value, and

when the vehicle is determined to be not running, the value of the integer N is determined so as to be equal to a second value that is greater than the first value.

9. A non-transitory computer-readable recording medium storing a program for verifying content data to be used in a vehicle, the program causing, when executed by a computer, the computer to implement a method, the method comprising:

acquiring the content data; acquiring, from a fit plurality of pieces of partial data obtained by dividing the content data, a respective plurality of first hash values;

acquiring a signature generated by using the plurality of first hash values and a key;

acquiring state information that indicates a state of the vehicle; determining an integer N that is greater than or equal to one based on the acquired state information;

generating, from N pieces of partial data included in the first plurality of pieces of partial data, respective second hash values;

verifying the content data by using each of (a) a subset of the plurality of first hash values which are those respectively generated from the first plurality of pieces of partial data other than the N pieces of partial data,

(b) the generated second hash values, and

(c) the acquired signature; and

outputting information that indicates a result of the verifying,

wherein: the state information indicates whether the vehicle is running or not running, and in the determining, when the vehicle is determined to be running, a value of the integer N is determined so as to be equal to a first value, and

when the vehicle is determined to be not running, the value of the integer N is determined so as to be equal to a second value that is greater than the first value.

10. A verification method for verifying content data to be used in a mobility, comprising:

acquiring the content data; acquiring, from a first plurality of pieces of partial data obtained by dividing the content data, a respective plurality of first hash values;

acquiring a signature generated by using the plurality of first hash values and a key; acquiring state information that indicates a state of the mobility;

determining an integer N that is greater than or equal to one based on the acquired state information;

generating, from N pieces of partial data included in the first plurality of pieces of partial data, respective second hash values;

verifying the content data by using each of (a) a subset of the plurality of first hash values which are those respectively generated from the first plurality of pieces of partial data other than the N pieces of partial data,

(b) the generated second hash values, and

(c) the acquired signature;

and outputting information that indicates a result of the verifying,

wherein: the state information indicates whether the vehicle is running or not running, and in the determining, when the vehicle is determined to be running, a value of the integer N is determined so as to be equal to a first value, and

when the vehicle is determined to be not running, the value of the integer N is determined so as to be equal to a second value that is greater than the first value.

11. The verification method according to claim 1 , wherein the key is a secret key.