Written by Jamie Tanna
on January 10, 2019
CC-BY-NC-SA-4.0 Apache-2.0
2 mins

Converting X.509 and PKCS#8 `.pem` file to a JWKS (in Node.JS)

When working with public/private keypairs, it's most likely you'll be dealing with files most commonly ending in .pem (X.509 certificates). However, there are cases where you'll want to convert your traditionally formatted file to a JWKS format.

Note that I know this is hacky but it works, so y'know, I'm okay with that. If I just wanted to convert an X.509 key, rsa-pem-to-jwk would be up to scratch, but unfortunately doesn't support PKCS#8 at this time.

The Keys

We have two files, x509.pem:

And pkcs8.key:

These are both the same private key, just in different formats.

The Code

The core of the code is below which is a command-line tool which takes two arguments - the path to the file we want to convert, and whether we want to dump the private key, too. This defaults to false as it can be dangerous to leak a private key - I've triple checked that the files above have been freshly generated!

const jose = require('node-jose');
const fs = require('fs');

const args = process.argv.slice(2);

const key = fs.readFileSync(args[0]);
const keystore = jose.JWK.createKeyStore();

var DUMP_PRIVATE_KEY = ('true' == args[1]);

keystore
  .add(key, 'pem')
  .then(function(_) {
    const jwks = keystore.toJSON(DUMP_PRIVATE_KEY);
    console.log(JSON.stringify(jwks, null, 4));
  });

The Result

This gives us a nice, pretty-printed JWKS that we can then use with other tooling - yay!

# get our public
$ node pem-to-jwks.js x509.pem
{
    "keys": [
        {
            "kty": "RSA",
            "kid": "288WlRQvku-zrHFmvcAW86jnTF3qsMoEUKEbteI2K4A",
            "n": "qV-fGqTo8r6L52sIJpt44bxLkODaF0_wvIL_eYYDL55H-Ap-b1q4pd4YyZb7pARor_1mob6sMRnnAr5htmO1XucmKBEiNY-12zza0q9smjLm3-eNqq-8PgsEqBz4lU1YIBeQzsCR0NTa3J3OHfr-bADVystQeonSPoRLqSoO78oAtonQWLX1MUfS9778-ECcxlM21-JaUjqMD0nQR6wl8L6oWGcR7PjcjPQAyuS_ASTy7MO0SqunpkGzj_H7uFbK9Np_dLIOr9ZqrkCSdioA_PgDyk36E8ayuMnN1HDy4ak_Q7yEX4R_C75T0JxuuYio06hugwyREgOQNID-DVUoLw",
            "e": "AQAB"
        }
    ]
}
# get our private
$ node pem-to-jwks.js x509.pem true
{
    "keys": [
        {
            "kty": "RSA",
            "kid": "288WlRQvku-zrHFmvcAW86jnTF3qsMoEUKEbteI2K4A",
            "n": "qV-fGqTo8r6L52sIJpt44bxLkODaF0_wvIL_eYYDL55H-Ap-b1q4pd4YyZb7pARor_1mob6sMRnnAr5htmO1XucmKBEiNY-12zza0q9smjLm3-eNqq-8PgsEqBz4lU1YIBeQzsCR0NTa3J3OHfr-bADVystQeonSPoRLqSoO78oAtonQWLX1MUfS9778-ECcxlM21-JaUjqMD0nQR6wl8L6oWGcR7PjcjPQAyuS_ASTy7MO0SqunpkGzj_H7uFbK9Np_dLIOr9ZqrkCSdioA_PgDyk36E8ayuMnN1HDy4ak_Q7yEX4R_C75T0JxuuYio06hugwyREgOQNID-DVUoLw",
            "e": "AQAB",
            "d": "hndR21ddUYqRi9JfkDcSSzSwUX8R5jwjBaaCqLoKQX3J6VR7eHBv889VooXplheh_UaSeorkLb9Atd7ruF-EmKmuk1S28gr79-hiWa3H7MvIm647vGz0Z9VbhxQpDm9vLVtILbyYh1DVyRzHjOm9n4UyNmQfqolMjzF81_p6DUfpkMcDBJSlsTmRKMWPG0u8mFm8aB9ZftbryPO36QOny7g4_M8SZG1yxGTbypjyDTP9WqMmHpaC-66gLszjyxwEbVh69m-HsDEs7Qg9oMVG2FiwtDSXIApwfLk2v2Yk4-TeAD49rZzw-QcJ0yqPeVdq8cgyFOhwX-cPtQIm8X7AgQ",
            "p": "0bNpJzzOOgzpqaWkb-5PuUgY9AedUsnze24AtukXaN9VY7e5BLYcbE11RGeyj8kkhpotvZQ6WrYEfvSkfxBvoVc1q86FXiqlpwmUL-_jO4BbgESOK9eaWP1iWmWNrZpqwdnIeF3VZHfCIoFxRV_Tb_Sp8UNSueFgCH6IVJlfwSE",
            "q": "zsTarRYo9lLE8XvzpGzpjtrOHsnLuk2n5GXP6M2X89BL8yc8_5Fp99m_Em9vGAOhZBK9ActZuZEGSVVhfV1ImGw17tLyQZSCAvSzQpZSYpT9EDeZgn_oSorfUgMKppm1X4rl5Yz7lMR1khljdKt_X6gFA6ADL2h_ARK1bBRjr08",
            "dp": "lOfqTmN-KXiL39xwdM7rq6zHk1lo3KXtEIOfXEMOTXjxQJrwdaj_a-Rg1g8wm6uAFVicDFeaTFmdvazothWsvwuXYAWJbMGp2YASyytz1wehcea8ceNqhbB_y6L7RQA2uKp2EQrIgcwMfcYe8d1G3eQFXP2qW7XvJHj9Q92ZQiE",
            "dq": "E7TDOpfQE5nT10f-8n7Gy6yi1GBbIEhiZewmIoPlpYEGnAfzUlAjj1GbWkBwkBNYgFcg2FjvFjZyKO8QOYh4cL5vbXGBUSq8MVfs9b2p4Gdervr9kGhsVR5jJkfP7gzcMlzkiDoliAopQmFVDzuBCjbTM4M-inglEo8b508SKRU",
            "qi": "aJsDBhxQFDbpQr20TjgxImwBslVP9xIauy3ncCmjHix6Fc1l51gL71V1OWGnXaStGfoWy0gKkUnJuU3_X_xA_QwzAXPJYa-juRlD8BxTf7rmR_HC-XiVdyNnkU3afHtK4nShS2EuN2EXOrYDrbQoA13_a6Itk_55vDpJ3jciwS8"
        }
    ]
}

And for our PKCS#8 key:

# get our public
$ node pem-to-jwks.js pkcs8.key
{
    "keys": [
        {
            "kty": "RSA",
            "kid": "288WlRQvku-zrHFmvcAW86jnTF3qsMoEUKEbteI2K4A",
            "n": "qV-fGqTo8r6L52sIJpt44bxLkODaF0_wvIL_eYYDL55H-Ap-b1q4pd4YyZb7pARor_1mob6sMRnnAr5htmO1XucmKBEiNY-12zza0q9smjLm3-eNqq-8PgsEqBz4lU1YIBeQzsCR0NTa3J3OHfr-bADVystQeonSPoRLqSoO78oAtonQWLX1MUfS9778-ECcxlM21-JaUjqMD0nQR6wl8L6oWGcR7PjcjPQAyuS_ASTy7MO0SqunpkGzj_H7uFbK9Np_dLIOr9ZqrkCSdioA_PgDyk36E8ayuMnN1HDy4ak_Q7yEX4R_C75T0JxuuYio06hugwyREgOQNID-DVUoLw",
            "e": "AQAB"
        }
    ]
}
# get our private
$ node pem-to-jwks.js pkcs8.key true
{
    "keys": [
        {
            "kty": "RSA",
            "kid": "288WlRQvku-zrHFmvcAW86jnTF3qsMoEUKEbteI2K4A",
            "n": "qV-fGqTo8r6L52sIJpt44bxLkODaF0_wvIL_eYYDL55H-Ap-b1q4pd4YyZb7pARor_1mob6sMRnnAr5htmO1XucmKBEiNY-12zza0q9smjLm3-eNqq-8PgsEqBz4lU1YIBeQzsCR0NTa3J3OHfr-bADVystQeonSPoRLqSoO78oAtonQWLX1MUfS9778-ECcxlM21-JaUjqMD0nQR6wl8L6oWGcR7PjcjPQAyuS_ASTy7MO0SqunpkGzj_H7uFbK9Np_dLIOr9ZqrkCSdioA_PgDyk36E8ayuMnN1HDy4ak_Q7yEX4R_C75T0JxuuYio06hugwyREgOQNID-DVUoLw",
            "e": "AQAB",
            "d": "hndR21ddUYqRi9JfkDcSSzSwUX8R5jwjBaaCqLoKQX3J6VR7eHBv889VooXplheh_UaSeorkLb9Atd7ruF-EmKmuk1S28gr79-hiWa3H7MvIm647vGz0Z9VbhxQpDm9vLVtILbyYh1DVyRzHjOm9n4UyNmQfqolMjzF81_p6DUfpkMcDBJSlsTmRKMWPG0u8mFm8aB9ZftbryPO36QOny7g4_M8SZG1yxGTbypjyDTP9WqMmHpaC-66gLszjyxwEbVh69m-HsDEs7Qg9oMVG2FiwtDSXIApwfLk2v2Yk4-TeAD49rZzw-QcJ0yqPeVdq8cgyFOhwX-cPtQIm8X7AgQ",
            "p": "0bNpJzzOOgzpqaWkb-5PuUgY9AedUsnze24AtukXaN9VY7e5BLYcbE11RGeyj8kkhpotvZQ6WrYEfvSkfxBvoVc1q86FXiqlpwmUL-_jO4BbgESOK9eaWP1iWmWNrZpqwdnIeF3VZHfCIoFxRV_Tb_Sp8UNSueFgCH6IVJlfwSE",
            "q": "zsTarRYo9lLE8XvzpGzpjtrOHsnLuk2n5GXP6M2X89BL8yc8_5Fp99m_Em9vGAOhZBK9ActZuZEGSVVhfV1ImGw17tLyQZSCAvSzQpZSYpT9EDeZgn_oSorfUgMKppm1X4rl5Yz7lMR1khljdKt_X6gFA6ADL2h_ARK1bBRjr08",
            "dp": "lOfqTmN-KXiL39xwdM7rq6zHk1lo3KXtEIOfXEMOTXjxQJrwdaj_a-Rg1g8wm6uAFVicDFeaTFmdvazothWsvwuXYAWJbMGp2YASyytz1wehcea8ceNqhbB_y6L7RQA2uKp2EQrIgcwMfcYe8d1G3eQFXP2qW7XvJHj9Q92ZQiE",
            "dq": "E7TDOpfQE5nT10f-8n7Gy6yi1GBbIEhiZewmIoPlpYEGnAfzUlAjj1GbWkBwkBNYgFcg2FjvFjZyKO8QOYh4cL5vbXGBUSq8MVfs9b2p4Gdervr9kGhsVR5jJkfP7gzcMlzkiDoliAopQmFVDzuBCjbTM4M-inglEo8b508SKRU",
            "qi": "aJsDBhxQFDbpQr20TjgxImwBslVP9xIauy3ncCmjHix6Fc1l51gL71V1OWGnXaStGfoWy0gKkUnJuU3_X_xA_QwzAXPJYa-juRlD8BxTf7rmR_HC-XiVdyNnkU3afHtK4nShS2EuN2EXOrYDrbQoA13_a6Itk_55vDpJ3jciwS8"
        }
    ]
}

Written by Jamie Tanna on Thu, 10 Jan 2019 18:33:20 UTC, and last updated on Tue, 10 Dec 2019 16:49:37 UTC.