Class LWEEncryptionScheme

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Class Documentation

class lbcrypto::LWEEncryptionScheme

Additive public-key LWE scheme.

Public Functions

LWEEncryptionScheme() = default
LWEPrivateKey KeyGen(usint size, const NativeInteger &modulus) const

Generates a secret key of dimension n using modulus q

Parameters

  • size – lattice parameter for the additive LWE scheme

  • modulus – the modulus for the secret key

Returns

a shared pointer to the secret key

LWEPrivateKey KeyGenGaussian(usint size, const NativeInteger &modulus) const

Generates a secret key of dimension n using modulus q

Parameters

  • size – lattice parameter for the additive LWE scheme

  • modulus – the modulus for the secret key

Returns

a shared pointer to the secret key

LWEKeyPair KeyGenPair(const std::shared_ptr<LWECryptoParams> &params) const

Generates a public key of dimension N and modulus Q, secret key of dimension n using modulus q pair

Parameters

params – a shared pointer to LWE scheme parameters

Returns

a shared pointer to the public key, secret key pair

LWEPublicKey PubKeyGen(const std::shared_ptr<LWECryptoParams> &params, ConstLWEPrivateKey &skN) const

Generates a public key corresponding to a secret key of dimension N using modulus Q

Parameters

  • params – a shared pointer to LWE scheme parameters

  • skN – a secret key of dimension N

Returns

a shared pointer to the public key

LWECiphertext Encrypt(const std::shared_ptr<LWECryptoParams> &params, ConstLWEPrivateKey &sk, LWEPlaintext m, LWEPlaintextModulus p = 4, NativeInteger mod = 0) const

Encrypts a bit using a secret key (symmetric key encryption)

Parameters

  • params – a shared pointer to LWE scheme parameters

  • sk – the secret key

  • m – the plaintext

  • p – the plaintext space

  • mod – the ciphertext modulus to encrypt with; by default m_q in params

Returns

a shared pointer to the ciphertext

LWECiphertext EncryptN(const std::shared_ptr<LWECryptoParams> &params, ConstLWEPublicKey &pk, LWEPlaintext m, LWEPlaintextModulus p = 4, NativeInteger mod = 0) const

Encrypts a bit using a public key (asymmetric key encryption)

Parameters

  • params – a shared pointer to LWE scheme parameters

  • pk – the public key

  • m – the plaintext

  • p – the plaintext space

  • mod – the ciphertext modulus to encrypt with; by default m_q in params

Returns

a shared pointer to the ciphertext

LWECiphertext SwitchCTtoqn(const std::shared_ptr<LWECryptoParams> &params, ConstLWESwitchingKey &ksk, ConstLWECiphertext &ct) const

Converts a ciphertext (public key encryption) with modulus Q and dimension N to ciphertext with q and n

Parameters

  • ksk – the key switching key from secret key of dimension N to secret key of dimension n

  • ct – the ciphertext to convert

Returns

a shared pointer to the ciphertext

void Decrypt(const std::shared_ptr<LWECryptoParams> &params, ConstLWEPrivateKey &sk, ConstLWECiphertext &ct, LWEPlaintext *result, LWEPlaintextModulus p = 4) const

Decrypts the ciphertext using secret key sk

Parameters

  • params – a shared pointer to LWE scheme parameters

  • sk – the secret key

  • ct – the ciphertext

  • result – plaintext result

  • p – the plaintext space

void EvalAddEq(LWECiphertext &ct1, ConstLWECiphertext &ct2) const

Adds the second ciphertext to the first ciphertext

Parameters

  • ct1 – the ciphertext which will hold the sum

  • ct2 – the ciphertext to add

void EvalAddConstEq(LWECiphertext &ct, NativeInteger cnst) const

Adds the a constant to the ciphertext

Parameters

  • ct – the ciphertext which will hold the sum

  • cnst – the constant to add

void EvalSubEq(LWECiphertext &ct1, ConstLWECiphertext &ct2) const

Subtracts the second ciphertext from the first ciphertext, the result is held in the first ciphertext

Parameters

  • ct1 – the ciphertext which will hold the difference

  • ct2 – the ciphertext to subtract

void EvalSubEq2(ConstLWECiphertext &ct1, LWECiphertext &ct2) const

Subtracts the second ciphertext from the first ciphertext, the result is held in the first ciphertext

Parameters

  • ct1 – the ciphertext from which to subtract

  • ct2 – the ciphertext to subtract, will hold the difference

void EvalSubConstEq(LWECiphertext &ct, NativeInteger cnst) const

Subtracts the constant from the ciphertext

Parameters

  • ct1 – the ciphertext which will hold the difference

  • ct2 – the constant to subtract

void EvalMultConstEq(LWECiphertext &ct, NativeInteger cnst) const

Multiplies a ciphertext by a constant

Parameters

  • ct1 – the ciphertext which will hold the product

  • ct2 – the constant to multiply by

LWECiphertext ModSwitch(NativeInteger q, ConstLWECiphertext &ctQ) const

Changes an LWE ciphertext modulo Q into an LWE ciphertext modulo q

Parameters

  • q – modulus to

  • ctQ – the input ciphertext

Returns

resulting ciphertext

LWESwitchingKey KeySwitchGen(const std::shared_ptr<LWECryptoParams> &params, ConstLWEPrivateKey &sk, ConstLWEPrivateKey &skN) const

Generates a switching key to go from a secret key with (Q,N) to a secret key with (q,n)

Parameters

  • params – a shared pointer to LWE scheme parameters

  • sk – new secret key

  • skN – old secret key

Returns

a shared pointer to the switching key

LWECiphertext KeySwitch(const std::shared_ptr<LWECryptoParams> &params, ConstLWESwitchingKey &K, ConstLWECiphertext &ctQN) const

Switches ciphertext from (Q,N) to (Q,n)

Parameters

  • params – a shared pointer to LWE scheme parameters

  • K – switching key

  • ctQN – input ciphertext

Returns

a shared pointer to the resulting ciphertext

LWECiphertext NoiselessEmbedding(const std::shared_ptr<LWECryptoParams> &params, LWEPlaintext m) const

Embeds a plaintext bit without noise or encryption

Parameters

  • params – a shared pointer to LWE scheme parameters

  • m – - the plaintext

Returns

a shared pointer to the ciphertext