How to encode data for use in Charm's attribute based encryption?

Question

I'm using Charm Crypto from Github. I'd like to use the attribute based encryption algorithms. The test code works fine, however, it uses a random message generated from PairingGroup. How do I use my own data for encryption?

>>> group = PairingGroup('SS512', secparam=512)
>>> msg = group.random(GT)

The PairingGroup has encode/decode methods, but they are not implemented. I just want to try this with "Hello world!".

Answer 1

Look at this class under charm/charm/test/toolbox/symcrypto_test.py

class SymmetricCryptoAbstractionTest(unittest.TestCase):

def testAESCBC(self):
    self.MsgtestAESCBC(b"hello world")

def testAESCBCLong(self):
    self.MsgtestAESCBC(b"Lots of people working in cryptography have no deep \
   concern with real application issues. They are trying to discover things \
    clever enough to write papers about -- Whitfield Diffie.")

def testAESCBC_Seperate(self):
    self.MsgTestAESCBCSeperate(b"Lots of people working in cryptography have no deep \
    concern with real application issues. They are trying to discover things \
    clever enough to write papers about -- Whitfield Diffie.")

def MsgtestAESCBC(self,msg):
    groupObj = PairingGroup('SS512')
    a =  SymmetricCryptoAbstraction(sha1(groupObj.random(GT)))
    ct = a.encrypt(msg)
    dmsg = a.decrypt(ct);
    assert msg == dmsg , 'o: =>%s\nm: =>%s' % (msg, dmsg)

def MsgTestAESCBCSeperate(self,msg):
    groupObj = PairingGroup('SS512')
    ran = groupObj.random(GT)
    a =  SymmetricCryptoAbstraction(sha1(ran))
    ct = a.encrypt(msg)        
    b =  SymmetricCryptoAbstraction(sha1(ran))
    dmsg = b.decrypt(ct);
    assert msg == dmsg , 'o: =>%s\nm: =>%s' % (msg, dmsg)

Answer 2

from charm.toolbox.pairinggroup import PairingGroup, GT
from ac17 import AC17CPABE


def main():
# instantiate a bilinear pairing map
pairing_group = PairingGroup('MNT224')

# AC17 CP-ABE under DLIN (2-linear)
cpabe = AC17CPABE(pairing_group, 2)

# run the set up
(pk, msk) = cpabe.setup()

# generate a key
attr_list = ['ONE', 'TWO', 'THREE']
key = cpabe.keygen(pk, msk, attr_list)

# choose a random message
msg = pairing_group.random(GT)

# generate a ciphertext
policy_str = '((ONE and THREE) and (TWO OR FOUR))'
ctxt = cpabe.encrypt(pk, msg, policy_str)

# decryption
rec_msg = cpabe.decrypt(pk, ctxt, key)
if debug:
    if rec_msg == msg:
        print ("Successful decryption.")
    else:
        print ("Decryption failed.")

if __name__ == "__main__":
    debug = False
    main()

I want to encrypt "hello world" too, how can I convert the msg whose type is str or bytes to pairing.Element?