How to decrypt plaintext from bilinear mapping in JPBC? - encryption

Question

Suppose the plaintext is a string, and I map the plaintext to the group using setFromHash function before I can perform the encryption operation, and the final decryption is only the hash of the plaintext, not the plaintext, how can I decrypt the plaintext or perform the bilinear operation without mapping the plaintext to the group? (Can this be achieved without using symmetric encryption)
setup(pairingParametersFileName, pkFileName, mskFileName);
keygen(pairingParametersFileName, userAttList, pkFileName, mskFileName, skFileName);
String msg = "dasddwhqoiuhdaiosnioacjijdqwi0jdaposdjiasojcbndusivbuiweshfsaoindoai";
//byte[] sha1Result = sha1(msg);
//Element message = PairingFactory.getPairing(pairingParametersFileName).getGT().newRandomElement().getImmutable();
//Element message = PairingFactory.getPairing(pairingParametersFileName).getGT().newElement().setFromHash(sha1Result, 0, sha1Result.length).getImmutable();
Element message = PairingFactory.getPairing(pairingParametersFileName).getGT().newElement().setFromHash(msg, 0, msg.length).getImmutable();
System.out.println("plaintext:" + msg);
encrypt(pairingParametersFileName, message, accessTree, pkFileName, ctFileName);
Element res = decrypt(pairingParametersFileName, accessTree, ctFileName, skFileName);
System.out.println("decrypt:" + res);
if (message.isEqual(res)) {
System.out.println("successful！");
}
Pairing bp = PairingFactory.getPairing(pairingParametersFileName);
Properties pkProp = loadPropFromFile(pkFileName);
String gString = pkProp.getProperty("g");
Element g = bp.getG1().newElementFromBytes(Base64.getDecoder().decode(gString)).getImmutable();
String g_betaString = pkProp.getProperty("g_beta");
Element g_beta = bp.getG1().newElementFromBytes(Base64.getDecoder().decode(g_betaString)).getImmutable();
String egg_alphaString = pkProp.getProperty("egg_alpha");
Element egg_alpha = bp.getGT().newElementFromBytes(Base64.getDecoder().decode(egg_alphaString)).getImmutable();
Properties ctProp = new Properties();
//compute CT=M *e(g,g)^(alpha s)
Element s = bp.getZr().newRandomElement().getImmutable();
Element CT = message.duplicate().mul(egg_alpha.powZn(s)).getImmutable();
Element C = g_beta.powZn(s).getImmutable();

Answer 1

this is not achievable, pairing-based CP-ABE, if encrypted, requires plaintext in the G_T group, but there is no good way to encode a message to the G_T group