| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide a capability to re-encrypt ciphertext with another encryption key without providing a decryption key. <P>SOLUTION: A re-encryption device outputs first input information τ<SB POS="POST">1</SB>and second input information τ<SB POS="POST">2</SB>corresponding to first ciphertext C1. A capability providing device uses the first input information τ<SB POS="POST">1</SB>to accurately calculate f(τ<SB POS="POST">1</SB>) with a probability larger than a certain probability and determines an obtained calculation result as first output information z<SB POS="POST">1</SB>, and it uses the second input information τ<SB POS="POST">2</SB>to accurately calculate f(τ<SB POS="POST">2</SB>) with the probability larger than the certain probability and determines an obtained calculation result as second output information z<SB POS="POST">2</SB>. The re-encryption device generates a calculation result, u=f(C1)<SP POS="POST">b</SP>x<SB POS="POST">1</SB>, from the first output information z<SB POS="POST">1</SB>, and generates a calculation result, v=f(C1)<SP POS="POST">a</SP>x<SB POS="POST">2</SB>, from the second output information z<SB POS="POST">2</SB>. When a value u<SP POS="POST">a</SP>to the calculation result u and a value v<SP POS="POST">b</SP>to the calculation result v mutually belong to a category of ciphertext for identical plaintext, the re-encryption device outputs a value u<SP POS="POST">b'</SP>v<SP POS="POST">a'</SP>with respect to integers a' and b' that satisfy a'a+b'b=1. <P>COPYRIGHT: (C)2013,JPO&INPIT |
