| 摘要 |
PROBLEM TO BE SOLVED: To provide a public key encryption technology that uses a trapdoor one-way replacement function that is more efficient than the conventional art and secure against CCA (adaptive chosen-ciphertext attacks). SOLUTION: An encryption device divides an n-z bit (n>z≥k) plaintext m into a v-z bit (n>v-z≥2k) first plaintext m<SB>1</SB>and an n-v bit second plaintext m<SB>2</SB>, determines the bit coupling value of a z bit random number r and the first plaintext m<SB>1</SB>as a bit string t<SB>(0)</SB>, and determines the second plaintext m<SB>2</SB>as a bit string s<SB>(0)</SB>. When a round number R (R≥4) is an even number, the encryption device sequentially calculates, starting from i=0 to i=(R/2)-1, h<SB>(2×i+1)</SB>=H<SB>(2×i+1)</SB>(t<SB>(i)</SB>), s<SB>(i+1)</SB>=s<SB>(i)</SB>(+)h<SB>(2×i+1)</SB>, h<SB>(2×i+2)</SB>=H(<SB>2×i+2)</SB>(s<SB>(i+1)</SB>), t<SB>(i+1)</SB>=t<SB>(i)</SB>¾h<SB>(2×i+2)</SB>to create bit strings t<SB>(R/2)</SB>and s<SB>(R/2)</SB>, and creates a ciphertext u=f(y) wherein a trapdoor one-way replacement function is applied to their bit coupling value y. COPYRIGHT: (C)2009,JPO&INPIT
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