RSA and ECC in JavaScript

The jsbn library is a fast, portable implementation of large-number math in pure JavaScript, enabling public-key crypto and other applications on desktop and mobile browsers.


Source Code

The API for the jsbn library closely resembles that of the java.math.BigInteger class in Java. For example:
  x = new BigInteger("abcd1234", 16);
  y = new BigInteger("beef", 16);
  z = x.mod(y);
will print b60c.

Core Library





The demo encrypts strings directly using PKCS#1 encryption-style padding (type 2), which is currently the only supported format. To show interoperability with a potential OpenSSL-based backend that decrypts strings, try the following on any system with the OpenSSL command line tool installed:
  1. Generate a new public/private keypair:
    $ openssl genrsa -out key.pem
    Generating RSA private key, 512 bit long modulus
    e is 65537 (0x10001)
  2. Extract the modulus from your key:
    $ openssl rsa -in key.pem -noout -modulus
  3. Go to the RSA Encryption demo and paste the modulus value into the "Modulus (hex)" field at the bottom.
  4. Make sure the value in the "Public exponent" field is "10001", or whatever value your public key uses.
  5. Type in a short string (e.g. testing) into the "Plaintext (string)" field and click on "encrypt". The result should appear in the "Ciphertext" fields.
  6. Copy the base64 version of the ciphertext and paste it as the input of the following command:
    $ openssl base64 -d | openssl rsautl -inkey key.pem -decrypt
    Hit ctrl-D or whatever your OS uses for end-of-file. Your original plaintext should appear:


The speed tables contain detailed timing information for jsbn performing public-key operations such as RSA, ECC, and IBE.

Projects that use jsbn


Version 1.4 (7/1/2013):
Fixed variable name collision between sha1.js and base64.js.
Obtain entropy from window.crypto.getRandomValues where available.
Added ECCurveFp.encodePointHex.
Fixed inconsistent use of DV in jsbn.js.
Version 1.3 (7/3/2012):
Fixed bug when comparing negative integers of different word lengths.
Version 1.2 (3/29/2011):
Added square method to improve ECC performance.
Use randomized bases in isProbablePrime
Version 1.1 (9/15/2009):
Added support for utf-8 encoding of non-ASCII characters when PKCS1 encoding and decoding JavaScript strings.
Fixed bug when creating a new BigInteger("0") in a non power-of-2 radix.


jsbn is released under a BSD license. See LICENSE for details.
Tom Wu
Last modified: Tue Sep 15 23:30:00 PST 2009