Virtual function to define the generation of all keys for scheme switching between CKKS and FHEW: the rotation keys for the baby-step/giant-step strategy, conjugation keys, switching key from CKKS to FHEW
Performs precomputations for the homomorphic decoding in CKKS. Given as a separate method than EvalCKKStoFHEWSetup to allow the user to specify a scale that depends on the CKKS and FHEW cryptocontexts
Parameters
cc – the CKKS cryptocontext from which to switch
scale – factor with which to scale the matrix in the linear transform
dim1 – baby-step for the linear transform
L – level on which the hom. decoding matrix should be. We want the hom. decoded ciphertext to be on the last level
Generates all keys for scheme switching: the rotation keys for the baby-step/giant-step strategy in the linear transform for the partial decryption, the switching key from FHEW to CKKS
Parameters
keypair – CKKS key pair
lwesk – FHEW secret key
numSlots – number of slots for the CKKS encryption of the FHEW secret key
numCtxts – number of values to encrypt from the LWE ciphertexts in the new CKKS ciphertext
dim1 – baby-step for the linear transform
L – level on which the hom. decoding matrix should be. We want the hom. decoded ciphertext to be on the last level
Performs the scheme switching on a vector of FHEW ciphertexts
Parameters
LWECiphertexts – FHEW/LWE ciphertexts to switch
numCtxts – number of values to encrypt from the LWE ciphertexts in the new CKKS ciphertext
numSlots – number of slots to encode in the new CKKS/RLWE ciphertext
p – plaintext modulus to use to decide postscaling, by default p = 4
pmin, pmax – plaintext space of the resulting messages (by default [0,2] assuming the LWE ciphertext had plaintext modulus p = 4 and only bits were encrypted)
dim1 – baby-step for the linear transform, necessary only for argmin
Returns
a CKKS ciphertext encrypting in its slots the messages in the LWE ciphertexts
Generates all keys for scheme switching: the rotation keys for the baby-step/giant-step strategy in the linear transform for the homomorphic encoding and partial decryption, the switching key from FHEW to CKKS
Performs precomputations for the homomorphic decoding in CKKS. Given as a separate method than EvalSchemeSwitchingSetup to allow the user to specify a scale that depends on the CKKS and FHEW cryptocontexts
Parameters
cc – the CKKS cryptocontext from which to switch
pLWE – the desired plaintext modulus for the new FHEW ciphertexts
scaleSign – factor to multiply the CKKS ciphertext when switching to FHEW in case the messages are too small; the resulting FHEW ciphertexts will encrypt values modulo pLWE, so scaleSign should account for this
unit – whether the input messages are normalized to the unit circle
Performs the scheme switching on the difference of two CKKS ciphertexts to compare, evaluates the sign function over the resulting FHEW ciphertexts, then performs the scheme switching back to a CKKS ciphertext
Parameters
ciphertext1, ciphertext2 – CKKS ciphertexts of messages that need to be compared
numCtxts – number of coefficients to extract from the CKKS ciphertext. If it is zero, it defaults to number of slots
numSlots – number of slots to encode the new CKKS ciphertext with
pLWE – the desired plaintext modulus for the new FHEW ciphertexts. If it is zero, it defaults to the large precision plaintext modulus Q/2beta
scaleSign – factor to multiply the CKKS ciphertext when switching to FHEW in case the messages are too small; the resulting FHEW ciphertexts will encrypt values modulo pLWE, so scaleSign should account for this
unit – whether the input messages are normalized to the unit circle
Returns
a CKKS ciphertext encrypting in its slots the sign of messages in the LWE ciphertexts
Computes the minimum and argument of the first numValues packed in a CKKS ciphertext via repeated scheme switchings to FHEW and back.
Parameters
ciphertext – CKKS ciphertexts of values that need to be compared
publicKey – public key of the CKKS cryptocontext
numValues – number of values to extract from the CKKS ciphertext. We always assume for the moment numValues is a power of two
numSlots – number of slots to encode the new CKKS ciphertext with
pLWE – the desired plaintext modulus for the new FHEW ciphertexts
scaleSign – factor to multiply the CKKS ciphertext when switching to FHEW in case the messages are too small; the resulting FHEW ciphertexts will encrypt values modulo pLWE, so scaleSign should account for this pLWE and scaleSign are given here only if the homomorphic decoding matrix is not scaled with the desired values
Returns
a vector of two CKKS ciphertexts where the first encrypts the minimum value and the second encrypts the index (in the representation specified by oneHot). The ciphertexts have junk after the first slot in the first ciphertext and after numValues in the second ciphertext if oneHot=true and after the first slot if oneHot=false.
Computes the maximum and argument of the first numValues packed in a CKKS ciphertext via repeated scheme switchings to FHEW and back.
Parameters
ciphertext – CKKS ciphertexts of values that need to be compared
publicKey – public key of the CKKS cryptocontext
numValues – number of values to extract from the CKKS ciphertext. We always assume for the moment numValues is a power of two
numSlots – number of slots to encode the new CKKS ciphertext with
pLWE – the desired plaintext modulus for the new FHEW ciphertexts
scaleSign – factor to multiply the CKKS ciphertext when switching to FHEW in case the messages are too small; the resulting FHEW ciphertexts will encrypt values modulo pLWE, so scaleSign should account for this pLWE and scaleSign are given here only if the homomorphic decoding matrix is not scaled with the desired values
Returns
a vector of two CKKS ciphertexts where the first encrypts the maximum value and the second encrypts the index (in the representation specified by oneHot). The ciphertexts have junk after the first slot in the first ciphertext and after numValues in the second ciphertext if oneHot=true and after the first slot if oneHot=false.