Patent ID: 7224795
Filing Date: 2007-05-29
Classification: H04L

Abstract:
1. A variable-length key cryptosystem performing stream cryptographic processing in which, in an encryption of plain text, a plain text and a cryptographic key are added to each other by considering respective characters as numerical values, a string obtained by the addition is used as an encrypted text, and in a decryption, values of the cryptographic key obtained by considering respective characters as numerical values are subtracted from values of the encrypted text by considering respective characters thereof as numerical values, the cryptosystem comprising: a computer including a variable-length key generation processing part generating a cryptographic key having a first length; and a data string length detection part detecting a length of a character string, wherein the variable-length key generation processing part further comprises: wherein, upon a length of a generated converted character string reaching a length of a plain text that is a length that has already been used in generating a cryptographic key used in encryption, the generation processor: continues character conversion to generate a converted character string with a length that has not been used in generating a cryptographic key by: