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]