CODEWITHSUNDEEP
java
Hsu Amanda
Hsu Amanda

Reputation: 31

How to decrypt a string use the JPBC

I need to multiply between a string and a GT( e(g,g)^n ) type element in the group. I convert the string to element first and then I have a problem when I want to decrypt a message.

Here is the code in simple version:

    TypeACurveGenerator pg = new TypeACurveGenerator(160,512);
    //generate the parameters of the elliptic curve
    PairingParameters typeAParams = pg.generate();
    //initialize the pairing
    PairingFactory.getInstance().setUsePBCWhenPossible(true);
    Pairing p= PairingFactory.getPairing(typeAParams);

    String s="hahaha test";
    Element g = p.getGT().newElementFromBytes(Base64.encodeBytes(s.getBytes()).getBytes());
    byte[] s3 = Base64.decode(g.toString());
    System.out.println(s);
    System.out.println(g);
    System.out.println(s3);

then the compile displays:

Bad Base64 input character decimal 123 in array position 0 (error line: byte[] s3 = Base64.decode(g.toString()); )

I'm confused about this result and I don't have the ability to resolve it.

I then tried another method, but it is always different after decode(compare with original string)

here is a simple version of my code:

    TypeACurveGenerator pg = new TypeACurveGenerator(160,512);
    //generate the parameters of the elliptic curve
    PairingParameters typeAParams = pg.generate();
    //initialize the pairing
    PairingFactory.getInstance().setUsePBCWhenPossible(true);
    Pairing p= PairingFactory.getPairing(typeAParams);
    String s="hahaha test";
    Element g = p.getGT().newElementFromBytes(Base64.decode(s));
    String s3 = Base64.encodeBytes(g.toBytes());
    System.out.println(s);
    System.out.println(g);
    System.out.println(s3);

and the compile display

hahaha test
{x=146958119709534,y=0}
AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAACFqFqFq14AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA==

I have no idea about why it is different between original string and after decode...

can anyone know the problem or give me some advice?

Upvotes: 0

Views: 208

Answers (1)

Andrew Charneski
Andrew Charneski

Reputation: 488

You may be confusing the Base64 encoding method for the encryption primitive you seem to be trying to use. In the first code sample, you attempt to Base64-decode the string produced by Element.toString, and in the second you attempt to Base64-decode your test string. Neither string is base64-encoded to begin with, so this will most likely fail.

If you are trying to encrypt data, I think you should be looking for a much higher-level API than the one you are working with. Low-level cryptographic primitives are extremely easy to use in an insecure manner, even if you do get valid decryption and it appears to work.

Upvotes: 1

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