public static BFCText encrypt(BFUserPublicKey pk, byte[] m, Random rnd)
{
Pairing e = pk.Param.Pairing;
byte[] sigma = new byte[BFCipher.sigmaBitLength / 8];
rnd.NextBytes(sigma);
//sigma||m
byte[] toHash = new byte[sigma.Length + m.Length];
Array.Copy(sigma, 0, toHash, 0, sigma.Length);
Array.Copy(m, 0, toHash, sigma.Length, m.Length);
//hash(sigma||m) to biginteger r;
Field field = e.Curve2.Field;
BigInt r = BFUtil.HashToField(toHash, field);
//hash(ID) to point
byte[] bid = null;
String ID = pk.Key;
bid = Encoding.UTF8.GetBytes(ID);
Point Q = BFUtil.HashToPoint(bid, e.Curve, e.Cofactor);
//gID = e(Q, sP), sP is Ppub
FieldElement gID = e.Compute(Q, pk.Param.Ppub);
//U=rP
Point U = e.Curve2.Multiply(pk.Param.P, r);
//gID^r
FieldElement gIDr = e.Gt.Pow(gID, r);
//V=sigma xor hash(gID^r)
byte[] hash = BFUtil.HashToLength(gIDr.ToUByteArray(), sigma.Length); //This could fail
byte[] V = BFUtil.XorTwoByteArrays(sigma, hash);
//W =m xor hash(sigma)
hash = BFUtil.HashToLength(sigma, m.Length);
byte[] W = BFUtil.XorTwoByteArrays(m, hash);
return(new BFCText(U, V, W));
}
public static KeyPair Extract(KeyPair masterKey, String ID, Random rnd)
{
//user public key is ID+ public parameters
BFUserPublicKey pk = new BFUserPublicKey(ID, (BFMasterPublicKey)masterKey.Public);
Pairing e = ((BFMasterPublicKey)masterKey.Public).Pairing;
//user private key: hash(ID)->point Q
//sQ, s is the master private key
byte[] bid = null;
bid = Encoding.UTF8.GetBytes(ID);
Point Q = BFUtil.HashToPoint(bid, e.Curve, e.Cofactor);
BigInt s = ((BFMasterPrivateKey)masterKey.Private).Key;
Q = e.Curve.Multiply(Q, s);
BFUserPrivateKey sk = new BFUserPrivateKey(Q, (BFMasterPublicKey)masterKey.Public);
return(new KeyPair(pk, sk));
}
