Method and system for generating/decrypting ciphertext, and method and system for searching ciphertexts in a database
There is provided a method of generating a ciphertext. The method includes encrypting an input data to produce an encrypted data, and randomizing the encrypted data to produce the ciphertext. In particular, the randomizing process includes performing an exclusive-or (xor) operation on the encrypted data with a cipher pad, whereby the cipher pad is generated based on an xor-homomorphic function of a first key using a second key generated based on the encrypted data. There is also provided a corresponding system for generating a ciphertext, a corresponding method and system for decrypting a ciphertext, and a corresponding method and system for searching ciphertexts in a database, such as at an untrusted server.
1. A computer-implemented method of generating a ciphertext, the method comprising:
encrypting, by a first computer processing system, an input data to produce an encrypted data; and
randomizing the encrypted data to produce the ciphertext prior to providing the ciphertext to a second computer processing system,
wherein said randomizing comprises performing, by the first computer processing system, an exclusive-or (xor) operation on the encrypted data with a cipher pad, and wherein the cipher pad is generated by the first computer processing system based on an xor-homomorphic function of a first key using a second key generated based on the encrypted data,
wherein said performing the xor operation on the encrypted data with the cipher pad comprises performing a first xor operation on a first portion of the encrypted data with the first key to produce a first portion of the ciphertext, and performing a second xor operation on a second portion of the encrypted data with the output of the xor-homomorphic function of the first key to produce a second portion of the ciphertext,
wherein the second key for the xor-homomorphic function is generated based on the first portion of the ciphertext.
2. The method according to claim 1 , wherein the cipher pad comprises the first key and an output of the xor-homomorphic function of the first key.
3. The method according to claim 1 , wherein the first key is a session key for the input data, the session key being a pseudorandom number.
4. The method according to claim 1 , wherein the xor-homomorphic function is a pseudorandom bit-permutation function or a circular shift function.
5. The method according to claim 1 , wherein the second key for the xor-homomorphic function is generated based on a hash function or a circular shift function of the first portion of the ciphertext.
6. A system for generating a ciphertext, the system comprising:
a memory to store one or more processor executable instructions; and
a processor, coupled with the memory, configure to execute the one or more instructions to:
encrypt an input data to produce an encrypted data, and
randomize the encrypted data to produce the ciphertext prior to providing the ciphertext to a second computer processing system,
wherein randomizing the encrypted data comprises the processor performing an exclusive-or (xor) operation on the encrypted data with a cipher pad, and wherein the cipher pad is generated by the system based on an xor-homomorphic function of a first key using a second key generated based on the encrypted data,
wherein performing the xor operation on the encrypted data with the cipher pad comprises the processor performing a first xor operation on a first portion of the encrypted data with the first key to produce a first portion of the ciphertext, and performing a second xor operation on a second portion of the encrypted data with the output of the xor-homornorphic function of the first key to produce a second portion of the ciphertext, and wherein the second key for the xor-homomorphic function is generated based on the first portion of the ciphertext.
7. The system according to claim 6 , wherein the cipher pad comprises the first key and an output of the first xor-homomorphic function of the first key.
8. The system according to claim 6 , wherein the first key is a session key for the input data, the session key being a pseudorandom number.
9. The system according to claim 6 , wherein the xor-homomorphic function is a pseudorandom bit-permutation function or a circular shift function.
10. The system according to claim 6 , wherein the second key for the xor-homomorphic function is generated based on a hash function or a circular shift function of the first portion of the ciphertext.