convert from openSSH public key format to PEM
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Patrick Roumanoff
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2 changed files with 166 additions and 0 deletions
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convert.html
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63
convert.html
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<!doctype html>
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<html>
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<head>
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<title>js-keygen: convert openssh to PEM</title>
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<script>module = {};</script>
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<script src="publicSshToPem.js"></script>
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<link rel="stylesheet" href="js-keygen.css">
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<link rel="icon" type="image/png" href="key.png">
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</head>
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<body>
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<div id="content">
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<h1>Convert openSSH public key format to PEM</h1>
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<p>Form the command line you can run
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<br>
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<code>ssh-keygen -f ~/.ssh/id_rsa -m 'PEM' -e > public.pem</code>
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<br> in order to export your openssh public key to a PEM file, but doing in so in javascript is not too difficult and doesn't
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require the webcrypto API, only a bit of ASN.1 knowledge.</p>
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<p>Again
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<a href="http://blog.oddbit.com/2011/05/08/converting-openssh-public-keys/">Converting open ssh public key</a> proves to be invaluable to come up with the tight conversion</p>
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<p>Result can be check with openssl asn.1 decoder
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<br>
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<code>openssl asn1parse -i -in public.pem</code>
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</p>
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<br> No data is being sent to the server, everything happens within the context of this web page.
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<br>
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<a href="https://twitter.com/share" class="twitter-share-button" data-via="pkr2">Tweet</a>
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<script>!function (d, s, id) { var js, fjs = d.getElementsByTagName(s)[0], p = /^http:/.test(d.location) ? 'http' : 'https'; if (!d.getElementById(id)) { js = d.createElement(s); js.id = id; js.src = p + '://platform.twitter.com/widgets.js'; fjs.parentNode.insertBefore(js, fjs); } }(document, 'script', 'twitter-wjs');</script>
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<hr>
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<div>
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<label for="key">OpenSSH public Key:</label>
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<br>
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<textarea id="key" style="height: 75px;" spellcheck="false">ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQDCD2bpwgflG43XNQ1pID6cjHfBLDeAptIiOpzD8ujYJXMNyFB5+omBsM3WZh9wN+qkFFCFx2PAxHlmlMJEgCQVye7rJw5SPjLcoZvMniyrYQTNk/+PkSKNs/hNCPTeuvhDWrC08U1dZwKNYR6ZcI+w4vZUNj26Ma6CqJZMxcrNuENWOPnaiuAayzBwC0x6TqwKwzK8FxPfG7VT3RADoU9CwKLjdz63NRXF7Kq2Q20dycPZk7lxmqt8bFt+WTkVtK8fPmAu+NjATdqhNmkw7FG7cfOYvf3n1kChLx923MWrKAaNoObx/b8otiz9wWSh8cxavDwzdsi1MJMXOvHSpwQT patrick@Patricks-MacBook-Pro.local
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</textarea>
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</div>
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<button id="generate">Convert</button>
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<div>
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<label for="pem">PEM:</label>
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<br>
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<textarea id="pem" disabled style="height: 150px;" spellcheck="false"></textarea>
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</div>
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<br>
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<hr> Made with
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<span style="color:magenta;">♥</span> by
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<a href="http://blog.roumanoff.com">Patrick Roumanoff</a>
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<a href="https://github.com/PatrickRoumanoff/js-keygen">
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<img style="position: absolute; top: 0; right: 0; border: 0;" src="https://camo.githubusercontent.com/365986a132ccd6a44c23a9169022c0b5c890c387/68747470733a2f2f73332e616d617a6f6e6177732e636f6d2f6769746875622f726962626f6e732f666f726b6d655f72696768745f7265645f6161303030302e706e67"
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alt="Fork me on GitHub" data-canonical-src="https://s3.amazonaws.com/github/ribbons/forkme_right_red_aa0000.png">
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</a>
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</div>
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<script>
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document.addEventListener("DOMContentLoaded", () => {
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document.querySelector("#generate").addEventListener("click", () => {
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document.querySelector("#pem").value = publicSshToPem(document.querySelector("#key").value)
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});
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});
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</script>
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</body>
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</html>
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103
publicSshToPem.js
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publicSshToPem.js
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/* eslint no-bitwise: 0 */
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function wrap(text, len) {
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const length = len || 72;
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let result = "";
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for (let i = 0; i < text.length; i += length) {
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result += text.slice(i, i + length);
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result += "\n";
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}
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return result;
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}
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function pemPublicKey(key) {
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return `---- BEGIN RSA PUBLIC KEY ----\n${wrap(key, 65)}---- END RSA PUBLIC KEY ----`;
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}
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function integerToOctet(n) {
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const result = [];
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for (let i = n; i > 0; i >>= 8) {
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result.push(i & 0xff);
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}
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return result.reverse();
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}
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function asnEncodeLen(n) {
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let result = [];
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if (n >> 7) {
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result = integerToOctet(n);
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result.unshift(0x80 + result.length);
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} else {
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result.push(n);
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}
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return result;
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}
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function checkHighestBit(v) {
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if (v[0] >> 7 === 1) {
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v.unshift(0); // add leading zero if first bit is set
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}
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return v;
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}
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function asn1Int(int) {
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const v = checkHighestBit(int);
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const len = asnEncodeLen(v.length);
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return [0x02].concat(len, v); // int tag is 0x02
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}
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function asn1Seq(seq) {
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const len = asnEncodeLen(seq.length);
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return [0x30].concat(len, seq); // seq tag is 0x30
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}
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function arrayToPem(a) {
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return window.btoa(a.map(c => String.fromCharCode(c)).join(""));
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}
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function arrayToString(a) {
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return String.fromCharCode.apply(null, a);
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}
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function stringToArray(s) {
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return s.split("").map(c => c.charCodeAt());
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}
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function pemToArray(pem) {
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return stringToArray(window.atob(pem));
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}
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function arrayToLen(a) {
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let result = 0;
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for (let i = 0; i < a.length; i += 1) {
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result = result * 256 + a[i];
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}
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return result;
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}
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function decodePublicKey(s) {
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const split = s.split(" ");
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const prefix = split[0];
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if (prefix !== "ssh-rsa") {
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throw new Error(`Unknown prefix: ${prefix}`);
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}
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const buffer = pemToArray(split[1]);
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const nameLen = arrayToLen(buffer.splice(0, 4));
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const type = arrayToString(buffer.splice(0, nameLen));
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if (type !== "ssh-rsa") {
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throw new Error(`Unknown key type: ${type}`);
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}
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const exponentLen = arrayToLen(buffer.splice(0, 4));
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const exponent = buffer.splice(0, exponentLen);
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const keyLen = arrayToLen(buffer.splice(0, 4));
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const key = buffer.splice(0, keyLen);
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return { type, exponent, key, name: split[2] };
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}
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function publicSshToPem(publicKey) {
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const { key, exponent } = decodePublicKey(publicKey);
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const seq = [key, exponent].map(asn1Int).reduce((acc, a) => acc.concat(a));
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return pemPublicKey(arrayToPem(asn1Seq(seq)));
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}
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module.exports = { publicSshToPem };
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