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KyoohyungHan / FullRNS-HEAAN

This is code for homomorphic encryption scheme "a Full RNS variant of HEAAN"
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A question about Negative number multiplication #2

Open siaaron045 opened 5 years ago

siaaron045 commented 5 years ago

I am sorry to trouble you. When i use FullRNS-HEAAN to do a negative number multiplication, the answer is wrong. Can FullRNS-HEAAN do negative number multiplication?(negative number addition is right) Thanks a million.

KyoohyungHan commented 5 years ago

Hi siaaron045

I tested as the following command.

// Encrypt mvec
Ciphertext cipher = scheme.encrypt(mvec, slots, L);

// Multiple negative value (= -0.1)
Ciphertext cmultCipher = scheme.multByConst(cipher, -0.1);
scheme.reScaleByAndEqual(cmultCipher, 1);

I checked the decrypted result. And It seems correct. It would be better if you can attach some part of your code.

Best, Kyoohyung Han

siaaron045 commented 5 years ago

I test your code and the answer is right, but when ''cipher'' is a negative number's ciphertext or make multiplication of two negative ciphertext,the answer is wrong. like this: //Encrypt mvec=-5 Ciphertext cipher1 = scheme.encrypt(mvec, slots, L); Ciphertext cipher2=cipher1; Ciphertext cmultCipher = scheme.multByConst(cipher1, -1); //or Ciphertext cmultCipher = scheme.mult(cipher1, cipher2); scheme.reScaleByAndEqual(cmultCipher, 1); both of the answers are wrong. So the encrypted number can't be negative?

KyoohyungHan commented 5 years ago

Oh... when I put -1 instead of -5 it works.

This problem came from the negate function in Context.cpp. I will fix this problem soon.

Thanks for the report.

siaaron045 commented 5 years ago

Yes,but it works only when mvec=-1, i put -2,-3,-4 the answers are wrong. And the function scheme.mult(cipher1, cipher2) does not work when make multiplication of two negative ciphertext expect -1. Thanks.

siaaron045 commented 5 years ago

The error still exist. I hope you can take some time to fix it. Thank you.

pdroalves commented 4 years ago

@KyoohyungHan Looks like you found the error source. Can you be more specific where is it? I think I can submit a patch.

Cmiiii commented 1 year ago

The error still exist. I hope you can take some time to fix it. Thank you.

Hi~ is this problem solved? I found the same error too,but i have no idea how to fix it?Where exactly does this problem occur?

czh-rot commented 1 year ago

This problem is not because of the negate function, but because of a problem with encode, where for copying simply adding the modulus leads to an encoding error. You can fix it by referring to the encoding functions of OPENFHE or Lattigo.