| CPC H04L 9/008 (2013.01) [H04L 9/0631 (2013.01)] | 15 Claims |

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1. A method of performing a homomorphic permutation by a server, the method comprising:
noise sampling and encoding the sampled noise, via a ciphertext generation portion;
generating, via the ciphertext generation portion, a first ciphertext by adding first noise to a basic ciphertext;
transmitting, via a transmission portion, the first ciphertext to a client;
performing, via an operation portion, a predetermined operation on the first noise;
receiving, via a reception portion, a second ciphertext from the client; and
extracting, via an extraction portion, the basic ciphertext on which the predetermined operation is performed, by removing, from the second ciphertext, second noise,
wherein the second ciphertext is a ciphertext that is re-encrypted by the client after decrypting the first ciphertext and performing the predetermined operation on the decrypted first ciphertext,
wherein the first noise indicates the encoded sampled noise, and the second noise indicates the first noise on which the predetermined operation is performed by the operation portion in the server, and
wherein the predetermined operation is previously agreed upon between the server and the client.
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