--- title: JSEncrypt layout: default ---

# JSEncrypt

### Introduction

When browsing the internet looking for a good solution to RSA Javascript encryption, there is a whole slew of libraries that basically take the fantastic work done by Tom Wu @ http://www-cs-students.stanford.edu/~tjw/jsbn/ and then modify that code to do what they want.

What I couldn't find, however, was a simple wrapper around this library that basically uses the library practically untouched, but adds a wrapper to provide parsing of actual Private and Public key-pairs generated with OpenSSL.

This library is the result of these efforts.

Download Github Project

### How to use this library.

This library should work hand-in-hand with openssl. With that said, here is how to use this library.

- Within your terminal (Unix based OS) type the following:

    openssl genrsa -out rsa_1024_priv.pem 1024

- This generates a private key, which you can see by doing the following...

    cat rsa_1024_priv.pem #if you are on mac you can | pbcopy to copy to the clipboard

- You can then copy and paste this in the Private Key section of the demo page.
- Next, you can then get the public key by executing the following command.

    openssl rsa -pubout -in rsa_1024_priv.pem -out rsa_1024_pub.pem

- You can see the public key by typing...

    cat rsa_1024_pub.pem

- Now you can compare with the one generated in the demo page..
- Now you can then convert to and from encrypted text by doing the following in code.

    // Create the encryption object and set the key.
    var crypt = new JSEncrypt();
    crypt.setKey(__YOUR_OPENSSL_PRIVATE_OR_PUBLIC_KEY__); //You can use also setPrivateKey and setPublicKey, they are both alias to setKey

    //Eventhough the methods are called setPublicKey and setPrivateKey, remember
    //that they are only alias to setKey, so you can pass them both a private or
    //a public openssl key, just remember that setting a public key allows you to only encrypt.

    var text = 'test';
    // Encrypt the data with the public key.
    var enc = crypt.encrypt(text);
    // Now decrypt the crypted text with the private key.
    var dec = crypt.decrypt(enc);

    // Now a simple check to see if the round-trip worked.
    if (dec === text){
        alert('It works!!!');
    } else {
        alert('Something went wrong....');
    }

- Look at the example page to view this example in action.

### Other Information

This library heavily utilizes the wonderful work of Tom Wu found at http://www-cs-students.stanford.edu/~tjw/jsbn/.

This jsbn library was written using the raw variables to perform encryption. This is great for encryption, but most private keys use a Private Key in the PEM format seen below.

#### 1024 bit RSA Private Key in Base64 Format

    -----BEGIN RSA PRIVATE KEY-----
    MIICXgIBAAKBgQDHikastc8+I81zCg/qWW8dMr8mqvXQ3qbPAmu0RjxoZVI47tvs
    kYlFAXOf0sPrhO2nUuooJngnHV0639iTTEYG1vckNaW2R6U5QTdQ5Rq5u+uV3pMk
    7w7Vs4n3urQ6jnqt2rTXbC1DNa/PFeAZatbf7ffBBy0IGO0zc128IshYcwIDAQAB
    AoGBALTNl2JxTvq4SDW/3VH0fZkQXWH1MM10oeMbB2qO5beWb11FGaOO77nGKfWc
    bYgfp5Ogrql4yhBvLAXnxH8bcqqwORtFhlyV68U1y4R+8WxDNh0aevxH8hRS/1X5
    031DJm1JlU0E+vStiktN0tC3ebH5hE+1OxbIHSZ+WOWLYX7JAkEA5uigRgKp8ScG
    auUijvdOLZIhHWq7y5Wz+nOHUuDw8P7wOTKU34QJAoWEe771p9Pf/GTA/kr0BQnP
    QvWUDxGzJwJBAN05C6krwPeryFKrKtjOGJIniIoY72wRnoNcdEEs3HDRhf48YWFo
    riRbZylzzzNFy/gmzT6XJQTfktGqq+FZD9UCQGIJaGrxHJgfmpDuAhMzGsUsYtTr
    iRox0D1Iqa7dhE693t5aBG010OF6MLqdZA1CXrn5SRtuVVaCSLZEL/2J5UcCQQDA
    d3MXucNnN4NPuS/L9HMYJWD7lPoosaORcgyK77bSSNgk+u9WSjbH1uYIAIPSffUZ
    bti+jc1dUg5wb+aeZlgJAkEAurrpmpqj5vg087ZngKfFGR5rozDiTsK5DceTV97K
    a3Y+Nzl+XWTxDBWk4YPh2ZlKv402hZEfWBYxUDn5ZkH/bw==
    -----END RSA PRIVATE KEY-----

This library simply takes keys in the preceding format, and translates it to those variables needed to perform the encryptions used in Tom Wu's library.

Here are some good resources to investigate further.

- http://etherhack.co.uk/asymmetric/docs/rsa_key_breakdown.html
- http://www.di-mgt.com.au/rsa_alg.html
- https://polarssl.org/kb/cryptography/asn1-key-structures-in-der-and-pem

With this information, we can translate a private key format to the variables required with the jsbn library from Tom Wu by using the following mappings.

    modulus => n
    public exponent => e
    private exponent => d
    prime1 => p
    prime2 => q
    exponent1 => dmp1
    exponent2 => dmq1
    coefficient => coeff