The invention discloses a privacy information protection method based on K-means clustering, and the method comprises the steps: carrying out the data
encryption of a plurality of clients CUi, obtaining an encrypted
ciphertext, and uploading the encrypted
ciphertext to a
cloud server; the
client CUi, the
cloud server CSP and the auxiliary
cloud server ACSP performing data interaction calculation to obtain a re-
encryption key; the cloud
server receiving the encrypted
ciphertext, re-encrypting the encrypted ciphertext to obtain a re-encrypted ciphertext of the same public key, and converting there-encrypted ciphertext into a Pillier encrypted ciphertext; the cloud
server side obtaining the encrypted ciphertext of the Paillier and then calculating clustering; and the cloud
server firstly converting the ciphertext of the clustering result into the ciphertext re-encrypted by the bidirectional addition homomorphic agent, then converting the ciphertext into the ciphertext under the public key of the
client, and finally returning the ciphertext of the clustering result to the
client for decryption. According to the method, the ciphertext of different public keys is clustered, the clustering result under the same public key is converted into the clustering result under different public keys to be returned to the client, and meanwhile, the private data of the client and the privacy of the clustering center are protected.