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An object is to enhance the difficulty in decrypting ciphertext. In order to do input into an encryption algorithm that receives plaintext to output ciphertext, a particular plaintext detector for detecting that the plaintext satisfying a predetermined condition is inputted, the particular plaintex

An object is to enhance the difficulty in decrypting ciphertext. In order to do input into an encryption algorithm that receives plaintext to output ciphertext, a particular plaintext detector for detecting that the plaintext satisfying a predetermined condition is inputted, the particular plaintext detector includes: a receiving part for receiving the plaintext; a counter part for separating a predetermined part from a bit string forming the plaintext into a fixed part and a remaining part into a variable part, counting the inputted plaintext having a value of the fixed part included in a set of values of the fixed parts at every set of the values of the fixed parts formed of 1 or a plurality of the values of the fixed parts, and storing it as a separate count; and a detecting part for outputting a detection signal when at least one of the separate counts exceeds a predetermined number. The particular plaintext detector is used to receive a detection signal for proper action, which allows the increased difficulty of decryption.

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What is claimed is: 1. A particular plaintext detector for detecting whether each of a plurality of plaintexts to be inputted into a predetermined encryption algorithm satisfies a predetermined condition, the particular plaintext detector comprising: a receiving part receiving the plurality of plai

What is claimed is: 1. A particular plaintext detector for detecting whether each of a plurality of plaintexts to be inputted into a predetermined encryption algorithm satisfies a predetermined condition, the particular plaintext detector comprising: a receiving part receiving the plurality of plaintexts sequentially; a counter part separating a predetermined part from a bit string forming each of the plaintexts into a fixed part and a remaining part into a variable part, counting the number of inputted plaintexts each of which has the same value of the fixed part, and storing the number as a separate count; and a detecting part outputting a detection signal that shows the encryption algorithm is susceptible to decryption attack when at least one of the separate counts exceeds a predetermined number. 2. A particular plaintext detector for detecting whether each of a plurality of plaintexts, to be inputted into a block encryption algorithm, satisfies a predetermined condition, the block encryption algorithm receiving and stirring each of the plurality of plaintexts with a key step by step to perform encryption and outputting ciphertext, the particular plaintext detector comprising: a receiving part receiving the plurality of plaintexts sequentially; a counter part separating a predetermined part from a bit string forming each of the plaintexts into a fixed part and a remaining part into a variable part, counting the number of inputted plaintexts each of which has the same value of the fixed part, and storing the number as a separate count; and a detecting part outputting a detection signal that shows the encryption algorithm is susceptible to decryption attack when at least one of the separate counts exceeds a predetermined number. 3. A particular plaintext detector for detecting whether each of a plurality of plaintexts to be inputted into a KASUMI type encryption algorithm having a stirring step satisfies a predetermined condition, the KASUMI type encryption algorithm equal to KASUMI which is a block encryption algorithm that receives the plurality of plaintexts sequentially, has a plurality of stirring steps for stirring with a key, and performs encryption step by step to output ciphertext, the particular plaintext detector comprising: a receiving part receiving the plurality of plaintexts sequentially; a counter part separating 17th to 32nd bits of each of the plurality of plaintexts into a fixed part and 1st to 16th bits and 33rd to 64th bith thereof into a variable part, counting the number of inputted plaintexts each of which has the same value of the fixed part, and storing it as a separate count; and a detecting part outputting a detection signal that shows the encryption algorithm is susceptible to decryption attack when at least one of the separate counts exceeds a predetermined number. 4. A filter apparatus for limiting an output of ciphertext from an encryption algorithm that receives a plurality of plaintexts and outputs ciphertext, the filter apparatus comprising: a receiving part receiving the plurality of plaintexts sequentially; a counter part separating a predetermined part from a bit string forming each of the plaintexts into a fixed part and a remaining part into a variable part, counting the number of inputted plaintexts each of which has the same value of the fixed part, and storing it as a separate count; and a detecting part outputting a detection signal when at least one of the separate counts exceeds a predetermined number; and a filter apparatus main body outputting each of the plaintext when a detection signal is not outputted from the detecting part, and for holding the further output of each of the plurality of plaintexts until it receives a process restart signal for instructing a restart of outputting each of the plurality of plaintext when the detection signal that shows the encryption algorithm is susceptible to a decryption attack is outputted. 5. An encryption apparatus for executing an encryption algorithm that receives each of a plurality of plaintexts to output ciphertext in which the encryption algorithm is changeable, the encryption apparatus comprising: a receiving part receiving the plurality of the plaintexts sequentially; a counter part separating a predetermined part from a bit string forming each of the plaintexts into a fixed part and a remaining part into a variable part, counting the number of inputted plaintexts each of which has the same value of the fixed part, and storing the number as a separate count; and a detecting part outputting a detection signal that shows the encryption algorithm is susceptible to decryption attack when at least one of the separate counts exceeds a predetermined number; an encryption apparatus main body performing the encryption algorithm for encryption of those plurality of plaintexts subject to the detecting part and the detection signal is not outputted from the detecting part, and for holding output of any plurality of plaintexts when the detection signal is outputted; an indication signal receiving part receiving an indication signal for indicating a change in the encryption algorithm for subsequent encryption; and a setting part outputting cipher setting information required for setting the encryption algorithm executed by the encryption apparatus main body and counter part setting information required for setting information corresponding to the encryption algorithm for the fixed part and the set of the values of the fixed parts and used by the counter part based on the indication signal, wherein the encryption apparatus main body and the counter part perform the settings based on the cipher setting information and the counter part setting information. 6. An encryption apparatus for executing an encryption algorithm that receives a plurality of plaintexts to calculate ciphertext with a key, the encryption apparatus comprising: a receiving part receiving the plurality of the plaintexts sequentially; a counter part separating a predetermined part from a bit string forming each of the plaintexts into a fixed part and a remaining part into a variable part, counting the number of inputted plaintexts each of which has the same value of the fixed part, and storing the number as a separate count; and a detecting part outputting a detection signal that shows the encryption algorithm is susceptible to decryption attack when at least one of the separate counts exceeds a predetermined number; and an encryption apparatus main body updating the key used for encryption when a detection signal is outputted from the detecting part. 7. A ciphertext storing apparatus for executing an encryption algorithm that receives a plurality of plaintexts to calculate ciphertext with a key, and storing the ciphertext, the ciphertext storing apparatus comprising: a receiving part receiving the plurality of the plaintexts sequentially; a counter part separating a predetermined part from a bit string forming each of the plaintexts into a fixed part and a remaining part into a variable part, counting the number of inputted plaintexts each of which has the same value of the fixed part, and storing the number as a separate count; and a detecting part outputting a detection signal that shows the encryption algorithm is susceptible to decryption attack when at least one of the separate counts exceeds a predetermined number; and a ciphertext storing part allowed to store ciphertext; and a ciphertext storing apparatus main body updating the key used for encryption when a detection signal is outputted from the detecting part, and for storing partially each of the plaintexts, the ciphertext, and key reference information allowing reference of the key having been used for encryption in the ciphertext storing part. 8. A filter apparatus for limiting output of ciphertext from a block encryption algorithm that receives and stirs each of a plurality of plaintexts with a key step by step to perform encryption and outputs ciphertext, the filter apparatus comprising: a receiving part receiving the plurality of the plaintexts sequentially; a counter part separating a predetermined part from a bit string forming each of the plaintexts into a fixed part and a remaining part into a variable part, counting the number of inputted plaintexts each of which has the same value of the fixed part, and storing the number as a separate count; and a detecting part outputting a detection signal that shows the encryption algorithm is susceptible to decryption attack when at least one of the separate counts exceeds a predetermined number; and a filter apparatus main body outputting each of the plaintext when a detection signal is not outputted from the detecting part, and for holding an output of each of the plurality of plaintexts until it receives a process restart signal for instructing a restart of outputting each of the held plurality of plaintext when the detection signal is outputted. 9. An encryption apparatus for executing a block encryption algorithm that receives and stirs each of the plurality of plaintexts with a key, step by step, to perform encryption and outputs ciphertext in which the encryption algorithm is changeable, the encryption apparatus comprising; a receiving part receiving the plurality of the plaintexts sequentially; a counter part separating a predetermined part from a bit string forming each of the plaintexts into a fixed part and a remaining part into a variable part, counting the number of inputted plaintexts each of which has the same value of the fixed part, and storing the number as a separate count; and a detecting part outputting a detection signal that shows the encryption algorithm is susceptible to decryption attack when at least one of the separate counts exceeds a predetermined number; and an encryption apparatus main body executing the encryption algorithm for encryption when a detection signal is not outputted from the detecting part, and for holding output of each of the plurality of plaintexts when the detection signal is outputted; an indication signal receiving part receiving an indication signal for indicating a change in the encryption algorithm for subsequent encryption; and a setting part outputting cipher setting information required for setting the encryption algorithm executed by the encryption apparatus main body and counter part setting information for setting information corresponding to the encryption algorithm for the fixed part and the set of values of thefixed parts and used by the counter based on the indication signal, wherein the encryption apparatus main body and the counter part perform the settings based on the ciphertext setting information and the counter part setting information. 10. An encryption apparatus for executing a block encryption algorithm the receives and stirs each of a plurality of plaintexts with a key, step by step, to perform encryption and outputs ciphertext, the encryption apparatus comprising: a receiving part receiving the plurality of the plaintexts sequentially; a counter part separating a predetermined part from a bit string forming each of the plaintexts into a fixed part and a remaining part into a variable part, counting the number of inputted plaintexts each of which has the same value of the fixed part, and storing the number as a separate count; and a detecting part outputting a detection signal that shows the encryption algorithm is susceptible to decryption attack when at least one of the separate counts exceeds a predetermined number; and an encryption apparatus main body updating the key used for encryption when a detection signal is outputted from the detecting part. 11. A ciphertext storing apparatus for executing a block encryption algorithm that receives and stirs each of a plurality of plaintexts with a key, step by step, to perform encryption and outputs ciphertext, and storing the ciphertext, the ciphertext storing apparatus comprising: a receiving part receiving the plurality of the plaintexts sequentially; a counter part separating a predetermined part from a bit string forming each of the plaintexts into a fixed part and a remaining part into a variable part, counting the number of inputted plaintexts each of which has the same value of the fixed part, and storing the number as a separate count; a detecting part outputting a detection signal that shows the encryption algorithm is susceptible to decryption attack when at least one of the separate counts exceeds a predetermined number; a ciphertext storing part storing ciphertext; and a ciphertext storing apparatus main body updating the key used for encryption when a detection signal is outputted from the detecting part, and for storing partially each of the plaintexts, the ciphertext, and key reference information allowing reference of the key having been used for encryption in the ciphertext storing part. 12. A filter apparatus for limiting an putput of ciphertext from a KASUMI type encryption algorithm having a stirring step, the KASUMI type encryption algorithm equal to KASUMI which is a block encryption algorithm that receives a plurality of plaintexts sequentially, has a plurality of stirring steps for stirring with a key, and performs encryption step by step to output ciphertext, the filter apparatus comprising: a receiving part receiving the plurality of the plaintexts sequentially; a counter part separating 17th to 32nd bits of each of the plurality of plaintexts into a fixed part and 1st to 16th bits and 33rd to 64th bith thereof into a variable part, counting the number of inputted plaintexts each of which has the same value of the fixed part, and storing it as a separate count; a detecting part outputting a detection signal that shows the encryption algorithm is susceptible to decryption attack when at least one of the separate counts exceeds a predetermined number; and a filter apparatus main body outputting each of the plaintext when a detection signal is not outputted from the detecting part, and for holding the further output of each of the plurality of plaintexts until it receives a process restart signal for instructing a restart of outputting each of the held plurality of plaintext when the detection signal is outputted. 13. An encryption apparatus for executing a KASUMI type encryption algorithm having a stirring step, the KASUMI type encryption algorithm equal to KASUMI which is a block encryption algorithm that receives a plurality of plaintexts sequentially, has a plurality of stirring steps for stirring with a key, and performs encryption step by step to output ciphertext in which the encryption algorithm is changeable, the encryption apparatus comprising: a receiving part receiving the plurality of the plaintexts sequentially; a counter part separating 17th to 32nd bits of each of the plurality of plaintexts into a fixed part and 1st to 16th bits and 33rd to 64th bith thereof into a variable part, counting the number of inputted plaintexts each of which has the same value of the fixed part, and storing it as a separate count; a detecting part outputting a detection signal that shows the encryption algorithm is susceptible to decryption attack when at least one of the separate counts exceeds a predetermined number; an encryption apparatus main body executing the encryption algorithm for encryption of those plurality of plaintexts subject to the detecting part and the detection signal is not outputted from the detecting part, and for holding an output of each of the plurality of plaintexts when the detection signal is outputted, an indication signal receiving part receiving an indication signal for indicating a change in the encryption algorithm for subsequent encryption; and a setting part outputting cipher setting information required for setting the encryption algorithm executed by the encryption apparatus main body and counter part setting information corresponding to the encryption algorithm for the fixed part and used by the counter part based on the indication signal, wherein the encryption apparatus main body and the counter part perform the settings based on the ciphertext setting information and the counter part setting information. 14. An encryption apparatus for executing a KASUMI type encryption algorithm having a stirring step, the KASUMI type encryption algorithm equal to KASUMI which is a block encryption algorithm that receives a plurality of plaintexts sequentially, has a plurality of stirring steps for stirring with a key, and performs encryption step by step to output ciphertext, the encryption apparatus comprising: a receiving part receiving the plurality of the plaintexts sequentially; a counter part separating 17th to 32nd bits of each of the plurality of plaintexts into a fixed part and 1st to 16th bits and 33rd to 64th bith thereof into a variable part, counting the number of inputted plaintexts each of which has the same value of the fixed part, and storing it as a separate count; a detecting part outputting a detection signal that shows the encryption algorithm is susceptible to decryption attack when at least one of the separate counts exceeds a predetermined number; an encryption apparatus main body updating the key used for encryption when a detection signal is outputted from the detecting part. 15. A ciphertext storing apparatus for executing a KASUMI type encryption algorithm having a stirring step, the KASUMI type encryption algorithm equal to KASUMI which is a block encryption algorithm that receives a plurality of plaintexts sequentially, has a plurality of stirring steps for stirring with a key, and performs encryption step by step to output ciphertext, and storing the ciphertext, the ciphertext storing apparatus comprising: a receiving part receiving the plurality of the plaintexts sequentially; a counter part separating 17th to 32nd bits of each of the plurality of plaintexts into a fixed part and 1st to 16th bits and 33rd to 64th bith thereof into a variable part, counting the number of inputted plaintexts each of which has the same value of the fixed part, and storing it as a separate count; a detecting part outputting a detection signal that shows the encryption algorithm is susceptible to decryption attack when at least one of the separate counts exceeds a predetermined number; a ciphertext storing part allowed to store ciphertext; and a ciphertext storing apparatus main body updating the key used for encryption when a detection signal is outputted from the detecting part, and for storing partially each of the plaintexts, the ciphertext, and key reference information allowing reference of the key having been used for encryption in the ciphertext storing part. 16. A plaintext detector system for analyzing potential susceptibility for blocks of plaintext, to be encrypted by an encryption algorithm, of being decrypted by an unauthorized party and increasing the security of the encryption of such plaintext, comprising: a receiving unit receiving a block of plaintext to be encrypted; a counter unit connected to the receiving unit to separate, from the block of plaintext, a predetermined bit string, and to compute a value based on counting the predetermined bit string as virtually continuing bits to represent a susceptibility standard of unauthorized decryption; and a detecting unit comparing the computed value with a predetermined stored value wherein the block of plaintext is less than the susceptibility standard predetermined stored value is provided a first signal that will permit encryption and the block of plaintext that is equal or greater than the susceptibility standard predetermined stored value is provided a second signal to change a manner of execution of the encryption algorithm of the block of plaintext to increase security. 17. The plaintext detector system of claim 16 where the second signal enables a change of a key used by the encryption algorithm.