def encrypt(policy_str, pool, group=None): print('policy_str in ABEnc=',policy_str) if group is None: group = PairingGroup('SS512') util = SecretUtil(group, False) policy = util.createPolicy(policy_str) secret = pool.pop('s') print('policy in ABEnc=',policy) sshares = util.calculateSharesList(secret, policy) sshares = dict([(x[0].getAttributeAndIndex(), x[1]) for x in sshares]) print('sshares in ABEnc=',sshares) C0 = pool.pop('C0') C_x_1, C_x_2, C_x_3, C_x_4, C_x_5 = {},{},{},{},{} for attr, s_share in sshares.items(): component = pool['components'].pop() C_x_1[attr] = component['C_j_1'] C_x_2[attr] = component['C_j_2'] C_x_3[attr] = component['C_j_3'] C_x_4[attr] = s_share - component['lambda_prime_j'] C_x_5[attr] = component['t_j'] * (group.hash(unicode(attr),ZR) - component['x_j']) ct = {'policy':policy_str, 'C0':C0,'C_j_1':C_x_1, 'C_j_2':C_x_2, 'C_j_3':C_x_3, 'C_j_4':C_x_4, 'C_j_5':C_x_5} print('ct in ABEnc=',ct) return (pool, ct)
class MAABE(object): def __init__(self, groupObj): self.util = SecretUtil(groupObj, verbose=False) #Create Secret Sharing Scheme self.group = groupObj #:Prime order group def setup(self): '''Global Setup (executed by CA)''' #:In global setup, a bilinear group G of prime order p is chosen #:The global public parameters, GP and p, and a generator g of G. A random oracle H maps global identities GID to elements of G #:group contains #:the prime order p is contained somewhere within the group object g = self.group.random(G1) #: The oracle that maps global identities GID onto elements of G #:H = lambda str: g** group.hash(str) H = lambda x: self.group.hash(x, G1) a = self.group.random() b = self.group.random() g_a = g**a g_b = g**b GPP = {'g': g, 'g_a': g_a, 'g_b': g_b, 'H': H} GMK = {'a': a, 'b': b} return (GPP, GMK) def registerUser(self, GPP): '''Generate user keys (executed by the user).''' g = GPP['g'] ugsk1 = self.group.random() ugsk2 = self.group.random() ugpk1 = g**ugsk1 ugpk2 = g**ugsk2 return ((ugpk1, ugsk2), { 'pk': ugpk2, 'sk': ugsk1 }) # (private, public) def setupAuthority(self, GPP, authorityid, attributes, authorities): '''Generate attribute authority keys (executed by attribute authority)''' if authorityid not in authorities: alpha = self.group.random() beta = self.group.random() gamma = self.group.random() SK = {'alpha': alpha, 'beta': beta, 'gamma': gamma} PK = { 'e_alpha': pair(GPP['g'], GPP['g'])**alpha, 'g_beta': GPP['g']**beta, 'g_beta_inv': GPP['g']**~beta } authAttrs = {} authorities[authorityid] = (SK, PK, authAttrs) else: SK, PK, authAttrs = authorities[authorityid] for attrib in attributes: if attrib in authAttrs: continue versionKey = self.group.random() # random or really 'choose' ? h = GPP['H'](attrib) pk = h**versionKey authAttrs[attrib] = { 'VK': versionKey, #secret 'PK1': pk, #public 'PK2': pk**SK['gamma'] #public } return (SK, PK, authAttrs) def keygen(self, GPP, authority, attribute, userObj, USK=None): '''Generate user keys for a specific attribute (executed on attribute authority)''' if 't' not in userObj: userObj['t'] = self.group.random() #private to AA t = userObj['t'] ASK, APK, authAttrs = authority u = userObj if USK is None: USK = {} if 'K' not in USK or 'KS' not in USK or 'AK' not in USK: USK['K'] = \ (GPP['g'] ** ASK['alpha']) * \ (GPP['g_a'] ** u['sk']) * \ (GPP['g_b'] ** t) USK['KS'] = GPP['g']**t USK['AK'] = {} AK = (u['pk'] ** (t * ASK['beta'])) * \ ((authAttrs[attribute]['PK1'] ** ASK['beta']) ** (u['sk'] + ASK['gamma'])) USK['AK'][attribute] = AK return USK def encrypt(self, GPP, policy_str, k, authority): '''Generate the cipher-text from the content(-key) and a policy (executed by the content owner)''' #GPP are global parameters #k is the content key (group element based on AES key) #policy_str is the policy string #authority is the authority tuple _, APK, authAttrs = authority policy = self.util.createPolicy(policy_str) secret = self.group.random() shares = self.util.calculateSharesList(secret, policy) shares = dict([(x[0].getAttributeAndIndex(), x[1]) for x in shares]) C1 = k * (APK['e_alpha']**secret) C2 = GPP['g']**secret C3 = GPP['g_b']**secret C = {} CS = {} D = {} DS = {} for attr, s_share in shares.items(): k_attr = self.util.strip_index(attr) r_i = self.group.random() attrPK = authAttrs[attr] C[attr] = (GPP['g_a']**s_share) * ~(attrPK['PK1']**r_i) CS[attr] = GPP['g']**r_i D[attr] = APK['g_beta_inv']**r_i DS[attr] = attrPK['PK2']**r_i return { 'C1': C1, 'C2': C2, 'C3': C3, 'C': C, 'CS': CS, 'D': D, 'DS': DS, 'policy': policy_str } def decrypt(self, GPP, CT, user): '''Decrypts the content(-key) from the cipher-text (executed by user/content consumer)''' UASK = user['authoritySecretKeys'] USK = user['keys'] usr_attribs = list(UASK['AK'].keys()) policy = self.util.createPolicy(CT['policy']) pruned = self.util.prune(policy, usr_attribs) if pruned == False: return False coeffs = self.util.getCoefficients(policy) first = pair(CT['C2'], UASK['K']) * ~pair(CT['C3'], UASK['KS']) n_a = 1 ugpk1, ugsk2 = USK e_gg_auns = 1 for attr in pruned: x = attr.getAttributeAndIndex() y = attr.getAttribute() temp = \ pair(CT['C'][y], ugpk1) * \ pair(CT['D'][y], UASK['AK'][y]) * \ pair(CT['CS'][y], ~(UASK['KS'] ** ugsk2)) * \ ~pair(GPP['g'], CT['DS'][y]) e_gg_auns *= temp**(coeffs[x] * n_a) return CT['C1'] / (first / e_gg_auns) def ukeygen(self, GPP, authority, attribute, userObj): '''Generate update keys for users and cloud provider (executed by attribute authority?)''' ASK, _, authAttrs = authority oldVersionKey = authAttrs[attribute]['VK'] newVersionKey = oldVersionKey while oldVersionKey == newVersionKey: newVersionKey = self.group.random() authAttrs[attribute]['VK'] = newVersionKey u_uid = userObj['sk'] UKs = GPP['H'](attribute)**(ASK['beta'] * (newVersionKey - oldVersionKey) * (u_uid + ASK['gamma'])) UKc = (newVersionKey / oldVersionKey, (oldVersionKey - newVersionKey) / (oldVersionKey * ASK['gamma'])) authAttrs[attribute]['PK1'] = authAttrs[attribute]['PK1']**UKc[0] authAttrs[attribute]['PK2'] = authAttrs[attribute]['PK2']**UKc[0] return {'UKs': UKs, 'UKc': UKc} def skupdate(self, USK, attribute, UKs): '''Updates the user attribute secret key for the specified attribute (executed by non-revoked user)''' USK['AK'][attribute] = USK['AK'][attribute] * UKs def ctupdate(self, GPP, CT, attribute, UKc): '''Updates the cipher-text using the update key, because of the revoked attribute (executed by cloud provider)''' CT['C'][attribute] = CT['C'][attribute] * (CT['DS'][attribute]**UKc[1]) CT['DS'][attribute] = CT['DS'][attribute]**UKc[0]
class DACMACS(object): def __init__(self, groupObj): self.util = SecretUtil(groupObj, verbose=False) #Create Secret Sharing Scheme self.group = groupObj #:Prime order group def setup(self): '''Global Setup (executed by CA)''' #:In global setup, a bilinear group G of prime order p is chosen #:The global public parameters, GP and p, and a generator g of G. A random oracle H maps global identities GID to elements of G #:group contains #:the prime order p is contained somewhere within the group object g = self.group.random(G1) #: The oracle that maps global identities GID onto elements of G #:H = lambda str: g** group.hash(str) H = lambda x: self.group.hash(x, G1) a = self.group.random() g_a = g**a GPP = {'g': g, 'g_a': g_a, 'H': H} GMK = {'a': a} return (GPP, GMK) def registerUser(self, GPP): '''Generate user keys (executed by the user).''' g = GPP['g'] u = self.group.random() z = self.group.random() g_u = g**u g_z = g**(1 / z) return ((g_u, z), {'g_z': g_z, 'u': u}) # (private, public) def setupAuthority(self, GPP, authorityid, attributes, authorities): '''Generate attribute authority keys (executed by attribute authority)''' if authorityid not in authorities: alpha = self.group.random() beta = self.group.random() gamma = self.group.random() SK = {'alpha': alpha, 'beta': beta, 'gamma': gamma} PK = { 'e_alpha': pair(GPP['g'], GPP['g'])**alpha, 'g_beta_inv': GPP['g']**(1 / beta), 'g_beta_gamma': GPP['g']**(gamma / beta) } authAttrs = {} authorities[authorityid] = (SK, PK, authAttrs) else: SK, PK, authAttrs = authorities[authorityid] for attrib in attributes: if attrib in authAttrs: continue versionKey = self.group.random() # random or really 'choose' ? h = GPP['H'](attrib) pk = ((GPP['g']**versionKey) * h)**SK['gamma'] authAttrs[attrib] = { 'VK': versionKey, #secret 'PK': pk, #public } return (SK, PK, authAttrs) def keygen(self, GPP, authority, attribute, userObj, USK=None): '''Generate user keys for a specific attribute (executed on attribute authority)''' if 't' not in userObj: userObj['t'] = self.group.random() #private to AA t = userObj['t'] ASK, APK, authAttrs = authority u = userObj if USK is None: USK = {} if 'K' not in USK or 'L' not in USK or 'R' not in USK or 'AK' not in USK: USK['K'] = \ (u['g_z'] ** ASK['alpha']) * \ (GPP['g_a'] ** u['u']) * \ (GPP['g_a'] ** (t / ASK['beta'])) USK['L'] = u['g_z']**(ASK['beta'] * t) USK['R'] = GPP['g_a']**t USK['AK'] = {} AK = (u['g_z'] ** (ASK['beta'] * ASK['gamma'] * t)) * \ (authAttrs[attribute]['PK'] ** (ASK['beta'] * u['u'])) USK['AK'][attribute] = AK return USK def encrypt(self, GPP, policy_str, k, authority): '''Generate the cipher-text from the content(-key) and a policy (executed by the content owner)''' #GPP are global parameters #k is the content key (group element based on AES key) #policy_str is the policy string #authority is the authority tuple _, APK, authAttrs = authority policy = self.util.createPolicy(policy_str) secret = self.group.random() shares = self.util.calculateSharesList(secret, policy) shares = dict([(x[0].getAttributeAndIndex(), x[1]) for x in shares]) C1 = k * (APK['e_alpha']**secret) C2 = GPP['g']**secret C3 = APK['g_beta_inv']**secret C = {} D = {} DS = {} for attr, s_share in shares.items(): k_attr = self.util.strip_index(attr) r_i = self.group.random() attrPK = authAttrs[attr] C[attr] = (GPP['g_a']**s_share) * ~(attrPK['PK']**r_i) D[attr] = APK['g_beta_inv']**r_i DS[attr] = ~(APK['g_beta_gamma']**r_i) return { 'C1': C1, 'C2': C2, 'C3': C3, 'C': C, 'D': D, 'DS': DS, 'policy': policy_str } def generateTK(self, GPP, CT, UASK, g_u): '''Generates a token using the user's attribute secret keys to offload the decryption process (executed by cloud provider)''' usr_attribs = list(UASK['AK'].keys()) policy = self.util.createPolicy(CT['policy']) pruned = self.util.prune(policy, usr_attribs) if pruned == False: return False coeffs = self.util.getCoefficients(policy) dividend = pair(CT['C2'], UASK['K']) * ~pair(UASK['R'], CT['C3']) n_a = 1 divisor = 1 for attr in pruned: x = attr.getAttributeAndIndex() y = attr.getAttribute() temp = \ pair(CT['C'][y], g_u) * \ pair(CT['D'][y], UASK['AK'][y]) * \ pair(CT['DS'][y], UASK['L']) divisor *= temp**(coeffs[x] * n_a) return dividend / divisor def decrypt(self, CT, TK, z): '''Decrypts the content(-key) from the cipher-text using the token and the user secret key (executed by user/content consumer)''' return CT['C1'] / (TK**z) def ukeygen(self, GPP, authority, attribute, userObj): '''Generate update keys for users and cloud provider (executed by attribute authority?)''' ASK, _, authAttrs = authority oldVersionKey = authAttrs[attribute]['VK'] newVersionKey = oldVersionKey while oldVersionKey == newVersionKey: newVersionKey = self.group.random() authAttrs[attribute]['VK'] = newVersionKey u = userObj['u'] AUK = ASK['gamma'] * (newVersionKey - oldVersionKey) KUK = GPP['g']**(u * ASK['beta'] * AUK) CUK = ASK['beta'] * AUK / ASK['gamma'] authAttrs[attribute]['PK'] = authAttrs[attribute]['PK'] * (GPP['g']** AUK) return {'KUK': KUK, 'CUK': CUK} def skupdate(self, USK, attribute, KUK): '''Updates the user attribute secret key for the specified attribute (executed by non-revoked user)''' USK['AK'][attribute] = USK['AK'][attribute] * KUK def ctupdate(self, GPP, CT, attribute, CUK): '''Updates the cipher-text using the update key, because of the revoked attribute (executed by cloud provider)''' CT['C'][attribute] = CT['C'][attribute] * (CT['DS'][attribute]**CUK)
class OMACPABE(object): def __init__(self, group_object): # initialize class object with secret sharing utility # and appropriate group object self.util = SecretUtil(group_object, verbose=False) self.group = group_object # certificate authority (CA) setup function def abenc_casetup(self): """ Global setup function run by the CA to generate the Global Master Key (GMK) and the Global Public Parameters (GPP) :return: GMK, GPP """ # initialize bilinear group G of prime p with generator g g = self.group.random(G1) # initialize hash function that maps to an element of G H = lambda x: self.group.hash(x, G1) # select random elements from Z_p a = self.group.random(ZR) b = self.group.random(ZR) g_a = g**a g_b = g**b # Global Public Parameters (GPP) = g, g_a, g_b, H GPP = { 'g': g, 'g_a': g_a, 'g_b': g_b, 'H': H, } # Global Master Key (GMK) = a, b GMK = { 'a': a, 'b': b, } # return (GPP, GMK) def abenc_userreg(self, GPP, entity='user'): """ User registration by Certificate Authority (CA) to generate corresponding key pairs (i.e. Public and Private keys) :param GPP: Global Public Parameters (GPP) :param entity: the entity executing algorithm # :param registered_users: Dictionary of already registered users :return: User Global Secret and Public Keys (GSK_uid, GSK_uid_prime, GPK_uid, GPK_uid_prime) """ # group generator from GPP g = GPP['g'] # random numbers as user global secret keys u_uid = self.group.random(ZR) u_uid_prime = self.group.random(ZR) # user global public keys g_u_uid = g**u_uid g_u_uid_prime = g**(1 / u_uid_prime) # secret public key pair sent to user GSK_uid_prime = u_uid_prime GPK_uid = g_u_uid # secret public key pair to be sent to registered Attribute Authorities (AAs) GSK_uid = u_uid GPK_uid_prime = g_u_uid_prime return (GPK_uid, GSK_uid_prime), { 'GSK_uid': GSK_uid, 'GPK_uid_prime': GPK_uid_prime, 'u_uid': u_uid, } def abenc_aareg(self, GPP, authority_id, attributes, registered_authorities): """ Registration of Attribute Authorities (AA) by the Certificate Authority (CA) :param GPP: Global Public Parameters (GPP) :param authority_id: Unique ID for Attribute Authority :param attributes: Attributes managed by the authority :param registered_authorities: Dictionary of already registered authorities :return: Attribute Authority Secret and Public Key pairs with Version and Public keys for the attributes """ # check if authority has already been registered if authority_id not in registered_authorities: # generate random values to serves as attribute authority secret key alpha_aid = self.group.random(ZR) beta_aid = self.group.random(ZR) gamma_aid = self.group.random(ZR) # attribute authority secret key values SK_aid = { 'alpha_aid': alpha_aid, 'beta_aid': beta_aid, 'gamma_aid': gamma_aid } # attribute authority public key values PK_aid = { 'e_alpha': pair(GPP['g'], GPP['g'])**alpha_aid, 'g_beta_aid': GPP['g']**beta_aid, 'g_beta_aid_inv': GPP['g']**(1 / beta_aid), } authority_attributes = {} registered_authorities[authority_id] = (SK_aid, PK_aid, authority_attributes) else: SK_aid, PK_aid, authority_attributes = registered_authorities[ authority_id] # generate version and public keys for attributes for attribute in attributes: # check if attributes already exist with public and version keys # if they do, skip generation process if attribute in authority_attributes: continue # generate random element as version key version_key = self.group.random(ZR) h = GPP['H'](attribute) PK_1_attribute = h**version_key PK_2_attribute = h**(version_key * SK_aid['gamma_aid']) PK_attribute_aid = [PK_1_attribute, PK_2_attribute] authority_attributes[attribute] = { 'VK': version_key, 'PK': PK_attribute_aid, } return (SK_aid, PK_aid, authority_attributes) def abenc_keygen(self, GPP, authority, attribute, user_object, USK=None): """ Generate attribute authority related secret keys for users (executed by the corresponding attribute authority) :param GPP: Global Public Parameters :param authority: Attribute Authority Parameters :param attribute: Attribute for which secret key is being generated :param user_object: User :param USK: Generated attribute authority related user secret key :return: User Secret Key (USK) """ # generate random integer to tie attribute secret key to user if 't' not in user_object: user_object['t'] = self.group.random(ZR) t = user_object['t'] # assign corresponding attribute authority parameters ASK, APK, authority_attrs = authority u = user_object # create USK data set if none exists already if USK is None: USK = {} if 'K_uid_aid' not in USK or 'K_uid_aid_prime' not in USK or 'AK_uid_aid' not in USK: USK['K_uid_aid'] = (u['GPK_uid_prime']**ASK['alpha_aid']) * ( GPP['g_a']**u['u_uid']) * (GPP['g_b']**t) USK['K_uid_aid_prime'] = GPP['g']**t USK['AK_uid_aid'] = {} # generate attribute specific secret key parameters AK_uid_aid = (GPP['g'] ** (t * ASK['beta_aid'])) * authority_attrs[attribute]['PK'][0] \ ** (ASK['beta_aid'] * (u['u_uid'] + ASK['gamma_aid'])) USK['AK_uid_aid'][attribute] = AK_uid_aid return USK def abenc_encrypt(self, GPP, policy_string, k, authority): """ Encryption algorithm which encrypts the message given, based on the policy :param GPP: Global Public Parameters :param policy_string: Policy :param k: Content Key (i.e group element based on AES key) :param authority: Attribute Authority Parameters :return: Ciphertext """ APK = {} authority_attributes = {} authority_g_beta_inv = {} # extract the APK for the different authorities for authority_temp in authority.keys(): APK[authority_temp] = authority[authority_temp][1] # extract the PK values of the attributes of the attribute authorities # extract the corresponding g_beta_inverse values for the attribute authorities for item in authority[authority_temp][2].keys(): authority_attributes[item] = authority[authority_temp][2][item] authority_g_beta_inv[item] = APK[authority_temp][ 'g_beta_aid_inv'] # extract policy and use policy elements to slit the secret # into their corresponding shares for encryption policy = self.util.createPolicy(policy_string) # generate secret through random element secret = self.group.random(ZR) # split secret into shares (this returns a list) shares = self.util.calculateSharesList(secret, policy) # process shares list to create a dict with attribute as key # and corresponding shares as value shares = dict([(x[0].getAttributeAndIndex(), x[1]) for x in shares]) # initialize blinding factor to hide key blinding_factor = 1 for authority_temp in authority.keys(): blinding_factor *= APK[authority_temp]['e_alpha'] # create C elements of encrypted file C = k * (blinding_factor**secret) C_prime = GPP['g']**secret C_prime_prime = GPP['g_b']**secret # create structure (dict) to hold the C_i and D_i elements of the encrypted file # these are the components related to the attributes C_i = {} C_i_prime = {} D_i = {} D_i_prime = {} # generate C_i and D_i elements for attribute, secret_share in shares.items(): # attribute_temp = self.util.strip_index(attribute) # generate random r_i element k_attr = self.util.strip_index(attribute) r_i = self.group.random(ZR) attribute_PK = authority_attributes[attribute] C_i[attribute] = (GPP['g_a']** secret_share) * ~(attribute_PK['PK'][0]**r_i) C_i_prime[attribute] = GPP['g']**r_i D_i[attribute] = authority_g_beta_inv[attribute]**r_i D_i_prime[attribute] = attribute_PK['PK'][1]**r_i return { 'C': C, 'C_prime': C_prime, 'C_prime_prime': C_prime_prime, 'C_i': C_i, 'C_i_prime': C_i_prime, 'D_i': D_i, 'D_i_prime': D_i_prime, 'policy': policy_string, } def abenc_generatetoken(self, GPP, CT, UASK, user_keys): """ Partial decryption of the ciphertext :param GPP: Global Public Parameters :param CT: Ciphertext elements :param UASK: Secret Keys for user gotten from Attribute Authorities :param user_keys: User global keys :return: Partially decrypted ciphertext """ # list to hold corresponding attributes possessed by the user user_attributes = [] for authority in UASK.keys(): user_attributes.extend(UASK[authority]['AK_uid_aid'].keys()) # access ciphertext policy encryption_policy = self.util.createPolicy(CT['policy']) # generate list of minimum policy elements needed for encryption # returns False if user fails policy assessment minimal_policy_list = self.util.prune(encryption_policy, user_attributes) # print(minimal_policy_list) # this is an error handling implementation that should be fixed later if not minimal_policy_list: return False # get attribute coefficients to be able to access their share of the secret coefficients = self.util.getCoefficients(encryption_policy) # initialize the dividend value for the token generation computation dividend = 1 for authority in UASK.keys(): dividend *= ( pair(CT['C_prime'], UASK[authority]['K_uid_aid']) * ~pair(CT['C_prime_prime'], UASK[authority]['K_uid_aid_prime'])) # attribute authority index? n_a = 1 # initialize divisor value for token generation computation divisor = 1 # create dict to hold attributes for the authorities and their corresponding secret keys attribute_keys = {} # create dict to hold attributes contained in the pruned list and their corresponding secret keys pruned_attribute_keys = {} # populate attribute with with corresponding key value pairs for authority in UASK.keys(): attribute_keys.update(UASK[authority]['AK_uid_aid']) # populate pruned attribute with corresponding key value pairs # from attribute list for attribute in minimal_policy_list: pruned_attribute_keys[str(attribute)] = attribute_keys[str( attribute)] # compute divisor for authority in UASK.keys(): temp_divisor = 1 for attribute in minimal_policy_list: x = attribute.getAttributeAndIndex() y = attribute.getAttribute() temp_divisor *= ( (pair(CT['C_i'][y], user_keys) * pair(CT['D_i'][y], pruned_attribute_keys[y]) * ~pair(CT['C_i_prime'][y], UASK[authority]['K_uid_aid_prime']) * ~pair(GPP['g'], CT['D_i_prime'][y]))**(coefficients[x] * n_a)) divisor *= temp_divisor Token = dividend / divisor return (Token, CT['C']) def abenc_decrypt(self, CT, TK, user_keys): """ Final decryption algorithm to reveal original message. To be run by the user :param CT: Original component of ciphertext that contains the encrypted message :param TK: Token generated during partial decryption of ciphertext :param user_keys: User global keys :return: Decrypted message """ message = CT / (TK**user_keys[1]) return message def abenc_ukeygen(self, GPP, authority, attribute, user_object): """ Generate update keys used in the revocation process for users and the cloud service provider. This will be run by the Attribute Authority. :param GPP: Global Public Parameters :param authority: Attribute Authority :param attribute: Attribute to be updated :param user_object: User :return: User attribute update keys and ciphertext update keys """ ASK, _, authAttrs = authority # attribute version key to be updated old_version_key = authAttrs[attribute]['VK'] # set new version key to old value new_version_key = old_version_key # ensure that new version key is different from original version key while old_version_key == new_version_key: new_version_key = self.group.random() # update version key of the attribute in the dictionary authAttrs[attribute]['VK'] = new_version_key u_uid = user_object['u_uid'] # create update key for users i.e to update the attribute involved KUK = GPP['H'](attribute)**(ASK['beta_aid'] * (new_version_key - old_version_key) * (u_uid + ASK['gamma_aid'])) # create update key for ciphertexts encrypted with attribute involved CUK = (new_version_key / old_version_key, (old_version_key - new_version_key) / (old_version_key * ASK['gamma_aid'])) # update the public parameters of the attribute involvedauthAttrs[attribute]['PK'][0] = authAttrs[attribute]['PK'][0] ** CUK[0] authAttrs[attribute]['PK'][1] = authAttrs[attribute]['PK'][1]**CUK[0] return { 'KUK': KUK, 'CUK': CUK, } def abenc_skupdate(self, USK, attribute, KUK): """ Updates the attribute secret key for the specific attribute. This is executed by a non-revoked user. :param USK: User secret key :param attribute: Attribute whose secret key is to be updated :param KUK: Update key for users :return: NA """ # update the secret key component of the affected attribute # print(USK) USK['AK_uid_aid'][attribute] = USK['AK_uid_aid'][attribute] * KUK def abenc_ctupdate(self, GPP, CT, attribute, CUK): """ Updates the ciphertexts that contain the specific attribute (revoked attribute). This is executed by the cloud service provider. :param GPP: Global Public Parameters :param CT: The affected ciphertext :param attribute: Attribute that is affected by the revocation process :param CUK: The Ciphertext Update Key :return: NA """ # update the corresponding components of the ciphertext that are related to the affected attribute CT['C_i'][attribute] = CT['C_i'][attribute] * ( CT['D_i_prime'][attribute]**CUK[1]) CT['D_i_prime'][attribute] = CT['D_i_prime'][attribute]**CUK[0]