RSA signature in JavaScript

Question

I am new to encryption. I would like to sign a piece of data using a JavaScript RSA library before sending it to the server.

I am trying to use the JavaScript library jsrsasign: http://kjur.github.io/jsrsasign/ to sign the data.

I have generated a modulus (n), public exponent (e) and a private exponent (d) and trying to them to sign the data.

var privateExponent = "4B48F60D02460811DABF74D79770E8DD72B5EEFF1324F651D4543D98B8C9F0F7ED3E245C49D967A30B279564AFF4FE53E2D92704FB4D6E923732F4AF8CFDA2114A49B6E425FD44AEACB80F00125AF6468F1A666EDDD5CFD6BFAB27950EF3DFB78671734BF1BB782CBB654A7FBB9BFB897E37F0324710360E1515B1FF0EE7FAF1";

var modulus = "00A68A945DE1175E4EBA23C53B8A1237CE9AA292020ECB373D90837FBD8DB8164687B7913543EA838E2B669BD1626FA9872397C5398485D951CFC229E102A78654B61E9EB2BC3B36BD2624ACF5C8B82ABD33A5AF4144C55034A3E5BF8282F3D5CB0CF9F550844E68A58DADC3BCC7CF726F227F8EC5FAC2494F1FBDEEF39212B5FF";

var publicExponent = "10001";

I have been trying to use them to sign a piece of the data as follows:

var signature = "Hello world";
var rsa = new RSAKey();
rsa.setPrivate(modulus, publicExponent, privateExponent);

var result = rsa.signString(signature, 'sha256');
rsa.setPublic(modulus, publicExponent);

console.log(result);
console.log(rsa.verifyString(result, 'sha256'));

However the verify function keeps returning false. I have no idea what I am doing wrong.

The functions setPublic and setPrivate are part rsa2.js

Answer 1

There is an error in the verifyString call. The API says:

verifyString(sMsg, hSig)
  verifies a sigature for a message string with RSA public key.
  Parameters:
    {String} sMsg
        message string to be verified.
    {String} hSig
        hexadecimal string of siganture.
        non-hexadecimal charactors including new lines will be ignored.

    Returns:
        returns 1 if valid, otherwise 0

It means that the code you need to call is:

rsa.verifyString(signature, result)

However the variable names are confusing. The result var is actually the signature.

signString function is using PCSK#1 v1.5 padding therefore you do not need to pass the digest algorithm to the verify function. This information is already present in the signature.