Information processing apparatus, program, and storage medium
An information processing apparatus has an encryption part that encrypts by block encryption, and is embeddable in an electronic apparatus, and achieves the above object by segmenting an authentication target message into one or more blocks for every 128 bits, the authentication target message including at least a predetermined authentication parameter and first encryption information that is obtained by encrypting plaintext information by the encryption part, successively computing each of the one or more segmented blocks by a GHASH function including a predetermined algorithm, using a plurality of 8-bit arrays including 16 elements, and generating second encryption information that is obtained by encrypting a computed result by the encryption part, to generate an authentication tag.
1. An information processing apparatus embedded in an electronic apparatus, comprising:
a storage that stores a program; and
a processor that executes the program to perform a process including
segmenting an authentication target message into one or more blocks for every 128 bits, the authentication target message including at least a predetermined authentication parameter, and first encryption information that is obtained by encrypting plaintext information by block encryption;
successively computing each of the one or more blocks by a GHASH function including a predetermined algorithm;
generating second encryption information by encrypting for each block, using the block encryption, a computed result of the GHASH function, and generating, from the second encryption information, an authentication tag for authenticating a completeness of the first encryption information and an identity that decrypts the first encryption information, wherein the GHASH function uses a predetermined array of 128 bits and computes a number of times a shift operation to shift information stored in the predetermined array by 1 bit to the right is required, to perform, in one operation, the shift operation amounting to the computed number of times the shift operation to shift the information by 1 bit to the right is required; and
storing a conversion table in which a bit string corresponding to an irreducible polynomial of a Galois field represented by GF(2 128 ) is converted according to the number of times the shift operation to shift the information stored in the predetermined array of the predetermined algorithm by 1 bit to the right is required,
wherein the GHASH function computes an exclusive-OR of the information stored in the predetermined array and a bit string after conversion, using the bit string after conversion in the conversion table, according to the number of times the shift operation is required, with respect to an exclusive-OR of the information stored in the predetermined array of the predetermined algorithm and the bit string.
2. The information processing apparatus as claimed in claim 1 , wherein the predetermined array is an array including 8 16-bit elements.
3. The information processing apparatus as claimed in claim 1 , wherein the predetermined array is an array including 4 32-bit elements.
4. The information processing apparatus as claimed in claim 1 , wherein the predetermined array is an array including 16 8-bit elements.
5. A method of encrypting information by a processor embedded in an electronic apparatus, comprising:
segmenting, by the processor, an authentication target message into one or more blocks for every 128 bits, the authentication target message including at least a predetermined authentication parameter, and first encryption information that is obtained by encrypting plaintext information by block encryption;
successively computing, by the processor, each of the one or more blocks by a GHASH function including a predetermined algorithm;
generating, by the processor, second encryption information by encrypting for each block, using the block encryption, a computed result of the GHASH function, and generating, from the second encryption information, an authentication tag for authenticating a completeness of the first encryption information and an identity that decrypts the first encryption information, wherein the GHASH function uses a predetermined array of 128 bits and computes a number of times a shift operation to shift information stored in the predetermined array by 1 bit to the right is required, to perform, in one operation, the shift operation amounting to the computed number of times the shift operation to shift the information by 1 bit to the right is required; and
storing, by the processor, a conversion table in which a bit string corresponding to an irreducible polynomial of a Galois field represented by GF(2 128 ) is converted according to the number of times the shift operation to shift the information stored in the predetermined array of the predetermined algorithm by 1 bit to the right is required,
wherein the GHASH function computes an exclusive-OR of the information stored in the predetermined array and a bit string after conversion, using the bit string after conversion in the conversion table, according to the number of times the shift operation is required, with respect to an exclusive-OR of the information stored in the predetermined array of the predetermined algorithm and the bit string.
6. A non-transitory computer-readable storage medium that stores a program which, when executed by a computer embedded in an electronic apparatus, performs a process comprising:
segmenting an authentication target message into one or more blocks for every 128 bits, the authentication target message including at least a predetermined authentication parameter, and first encryption information that is obtained by encrypting plaintext information by block encryption;
successively computing each of the one or more blocks by a GHASH function including a predetermined algorithm;
generating second encryption information by encrypting for each block, using the block encryption, a computed result of the GHASH function, and generating, from the second encryption information, an authentication tag for authenticating a completeness of the first encryption information and an identity that decrypts the first encryption information, wherein the GHASH function uses a predetermined array of 128 bits and computes a number of times a shift operation to shift information stored in the predetermined array by 1 bit to the right is required, to perform, in one operation, the shift operation amounting to the computed number of times the shift operation to shift the information by 1 bit to the right is required; and
storing a conversion table in which a bit string corresponding to an irreducible polynomial of a Galois field represented by GF(2 128 ) is converted according to the number of times the shift operation to shift the information stored in the predetermined array of the predetermined algorithm by 1 bit to the right is required,
wherein the GHASH function computes an exclusive-OR of the information stored in the predetermined array and a bit string after conversion, using the bit string after conversion in the conversion table, according to the number of times the shift operation is required, with respect to an exclusive-OR of the information stored in the predetermined array of the predetermined algorithm and the bit string.