An information processing apparatus having an encryption part that encrypts by block encryption, and is embeddable in an electronic apparatus, the information processing apparatus comprising: segmenting means for 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; hash computing means for successively computing each of the one or more blocks segmented by the segmenting means by a GHASH function including a predetermined algorithm; authentication tag generating means for generating second encryption information that is obtained by encrypting a computed result of the hash computing means by the encryption part, and generating an authentication tag for authenticating a completeness of the first encryption information and an identity that decrypts the first encryption information, from the second 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 storage means for 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, and 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. segmenting means for 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; hash computing means for successively computing each of the one or more blocks segmented by the segmenting means by a GHASH function including a predetermined algorithm; authentication tag generating means for generating second encryption information that is obtained by encrypting a computed result of the hash computing means by the encryption part, and generating an authentication tag for authenticating a completeness of the first encryption information and an identity that decrypts the first encryption information, from the second 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 storage means for 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, and 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.