secure_comparison.keyholder module

Party that holds the secret keys. Bob; B in the paper.

class secure_comparison.keyholder.KeyHolder(l_maximum_bit_length, communicator=None, other_party='', scheme_paillier=None, scheme_dgk=None, session_id=0)

Bases: object

Player Bob in the secure comparison protocol, holds the keys.

__init__(l_maximum_bit_length, communicator=None, other_party='', scheme_paillier=None, scheme_dgk=None, session_id=0)

Parameters:

• l_maximum_bit_length (int) – maximum bit length used to constrain variables (\(l\)).

• communicator (Optional[Communicator]) – object for handling communication with the Initiator during the protocol.

• other_party (str) – identifier of the other party

• scheme_paillier (Optional[Paillier]) – Paillier encryption scheme (including secret key) used to produce \([[x]]\) and \([[y]]\), Alice’s input.

• scheme_dgk (Optional[DGK]) – DGK encryption scheme (including secret key).

• session_id (int) – keeps track of the session.

async make_and_send_encryption_schemes(session_id=1, key_length_paillier=2048, v_bits_dgk=160, n_bits_dgk=2048)

Initialize Paillier and DGK encryption schemes if they don’t already exist and sends public keys to Alice.

Parameters:

• session_id (int) – integer to distinguish between session

• key_length_paillier (int) – key length paillier

• v_bits_dgk (int) – number of bits DGK private keys \(v_p\) and \(v_q\)

• n_bits_dgk (int) – number of bits DGK public key \(n\)

Raises:

ValueError – raised when communicator is not propertly configured.

Return type:

None

async perform_secure_comparison()

Performs the secure comparison secure comparison for Bob. Including required communication with Alice.

Raises:

ValueError – raised when communicator is not properly configured.

Return type:

None

static step_2(z_enc, l, scheme_paillier)

\(B\) decrypts \([[z]]\), and computes \(\beta = z \mod 2^l\).

Parameters:

• z_enc (PaillierCiphertext) – Encrypted value of \(z\): \([[z]]\).

• l (int) – Fixed value, such that \(0 \leq x,y < 2^l\), for any \(x, y\) that will be given as input to this method.

• scheme_paillier (Paillier) – Paillier encryption scheme.

Return type:

Tuple[int, int]

Returns:

Tuple containing as first entry the plaintext value of \(z\). The second entry is the value \(\beta = z \mod 2^l\).

static step_4a(z, scheme_dgk, scheme_paillier, l)

\(B\) computes the encrypted bit \([d]\) where \(d = (z < (N - 1)/2)\) is the bit informing \(A\) whether a carryover has occurred.

Parameters:

• z (int) – Plaintext value of \(z\).

• scheme_dgk (DGK) – DGK encryption scheme.

• scheme_paillier (Paillier) – Paillier encryption scheme.

Return type:

DGKCiphertext

Returns:

Encrypted value of the bit \(d = (z < (N - 1)/2)\): \([d]\).

static step_4b(beta, l, scheme_dgk)

\(B\) computes the encrypted bits \([\beta_i], 0 \leq i < l\) to \(A\).

Parameters:

• beta (int) – The value \(\beta\) from step 2.

• l (int) – Fixed value, such that \(0 \leq x,y < 2^l\), for any \(x, y\) that will be given as input to this method.

• scheme_dgk (DGK) – DGK encryption scheme.

Return type:

List[DGKCiphertext]

Returns:

List containing the encrypted values of the bits \(\beta_i\): \([\beta_i], 0 \leq i < l\) to \(A\).

static step_4j(c_is_enc, scheme_dgk)

\(B\) checks whether one of the numbers \(c_i\) is decrypted to zero. If he finds one, \(\delta_B \leftarrow 1\), else \(\delta_B \leftarrow 0\).

Parameters:

• c_is_enc (List[DGKCiphertext]) – List containing the encrypted values of the bits \(c_i\): \([c_i], 0 \leq i < l\).

• scheme_dgk (DGK) – DGK encryption scheme.

Return type:

int

Returns:

Value \(\delta_B\).

static step_5(z, l, delta_b, scheme_paillier)

\(B\) computes \(\zeta_1 = z \div 2^l\) and encrypts it to \([[\zeta_1]]\) and computes \(\zeta_2 = (z + N) \div 2^l\) and encrypts it to \([[\zeta_2]]\). \(B\) also encrypts \(\delta_B\) to \([[\delta_B]]\).

Parameters:

• z (int) – Plaintext value of \(z\).

• l (int) – Fixed value, such that \(0 \leq x,y < 2^l\), for any \(x, y\) that will be given as input to this method.

• delta_b (int) – The value \(\delta_B\) from step 4j.

• scheme_paillier (Paillier) – Paillier encryption scheme.

Return type:

Tuple[PaillierCiphertext, PaillierCiphertext, PaillierCiphertext]

Returns:

A tuple with the first entry being the encrypted value of \(\zeta_1\): \([[\zeta_1]]\). The second entry is the encrypted value of \(\zeta_2\): \([[\zeta_2]]\). The third entry is the encrypted value of \(\delta_B\): \([[\delta_B]]\).