| 摘要 |
PROBLEM TO BE SOLVED: To improve the safety of various kinds of data by recording ciphered transmission data in a recording medium unable for rewriting as time added data where time information is added by means of a time information adding means. SOLUTION: Time information for a time added data is added to transmission work data in a compressed state by a time information compressing means. When time information is recorded in the recording medium as time data unable for rewriting after ciphering, the state becomes the one where decoding or rewriting is not easily executed since ciphered time information is, moreover, added to ciphered transmission data in a certain plate of time added data even when the data is leaked. A cipher key is required in ciphering time information, a decoding key is required in decoding and the cipher key and the decoding key are provided by a receivern. Thus, a call originator safely trusts data to the receiver. |
