putty.js

// Copyright 2018 Joyent, Inc.

module.exports = {
	read: read,
	write: write
};

var assert = require('assert-plus');
var Buffer = require('safer-buffer').Buffer;
var rfc4253 = require('./rfc4253');
var Key = require('../key');
var SSHBuffer = require('../ssh-buffer');
var crypto = require('crypto');
var PrivateKey = require('../private-key');

var errors = require('../errors');

// https://tartarus.org/~simon/putty-prerel-snapshots/htmldoc/AppendixC.html
function read(buf, options) {
	var lines = buf.toString('ascii').split(/[\r\n]+/);
	var found = false;
	var parts;
	var si = 0;
	while (si < lines.length) {
		parts = splitHeader(lines[si++]);
		if (parts &&
		    parts[0].toLowerCase() === 'putty-user-key-file-2') {
			found = true;
			break;
		}
	}
	if (!found) {
		throw (new Error('No PuTTY format first line found'));
	}
	var alg = parts[1];

	parts = splitHeader(lines[si++]);
	assert.equal(parts[0].toLowerCase(), 'encryption');
	var encryption = parts[1];

	parts = splitHeader(lines[si++]);
	assert.equal(parts[0].toLowerCase(), 'comment');
	var comment = parts[1];

	parts = splitHeader(lines[si++]);
	assert.equal(parts[0].toLowerCase(), 'public-lines');
	var publicLines = parseInt(parts[1], 10);
	if (!isFinite(publicLines) || publicLines < 0 ||
	    publicLines > lines.length) {
		throw (new Error('Invalid public-lines count'));
	}

	var publicBuf = Buffer.from(
	    lines.slice(si, si + publicLines).join(''), 'base64');
	var keyType = rfc4253.algToKeyType(alg);
	var key = rfc4253.read(publicBuf);
	if (key.type !== keyType) {
		throw (new Error('Outer key algorithm mismatch'));
	}

	si += publicLines;
	if (lines[si]) {
		parts = splitHeader(lines[si++]);
		assert.equal(parts[0].toLowerCase(), 'private-lines');
		var privateLines = parseInt(parts[1], 10);
		if (!isFinite(privateLines) || privateLines < 0 ||
			privateLines > lines.length) {
			throw (new Error('Invalid private-lines count'));
		}

		var privateBuf = Buffer.from(
			lines.slice(si, si + privateLines).join(''), 'base64');

		if (encryption === 'aes256-cbc') {
			if (!options.passphrase) {
				throw (new errors.KeyEncryptedError(
					options.filename, 'PEM'));
			}

			var iv = Buffer.from(Array
				.from({length: 16})
				.map(function () { return 0; }));
			var decipher = crypto.createDecipheriv(
				'aes-256-cbc',
				derivePPK2EncryptionKey(options.passphrase),
				iv);
			decipher.setAutoPadding(false);
			privateBuf = Buffer.concat([
				decipher.update(privateBuf), decipher.final()]);
		}

		key = new PrivateKey(key);
		if (key.type !== keyType) {
			throw (new Error('Outer key algorithm mismatch'));
		}

		var sshbuf = new SSHBuffer({buffer: privateBuf});
		if (alg === 'ssh-dss') {
			key.addPart('x', sshbuf.readPart());
		} else if (alg === 'ssh-rsa') {
			key.addPart('d', sshbuf.readPart());
			key.addPart('p', sshbuf.readPart());
			key.addPart('q', sshbuf.readPart());
			key.addPart('iqmp', sshbuf.readPart());
		} else if (alg.startsWith('ecdsa-sha2-nistp')) {
			key.addPart('d', sshbuf.readPart());
		} else if (alg === 'ssh-ed25519') {
			key.addPart('k', sshbuf.readPart());
		} else {
			throw new Error('Unsupported PPK key type: ' + alg);
		}
	}

	key.comment = comment;
	return (key);
}

function derivePPK2EncryptionKey(passphrase) {
	var hash1 = crypto.createHash('sha1').update(Buffer.concat([
		Buffer.from([0, 0, 0, 0]),
		Buffer.from(passphrase)
	])).digest();
	var hash2 = crypto.createHash('sha1').update(Buffer.concat([
		Buffer.from([0, 0, 0, 1]),
		Buffer.from(passphrase)
	])).digest();
	return (Buffer.concat([hash1, hash2]).slice(0, 32));
}

function splitHeader(line) {
	var idx = line.indexOf(':');
	if (idx === -1)
		return (null);
	var header = line.slice(0, idx);
	++idx;
	while (line[idx] === ' ')
		++idx;
	var rest = line.slice(idx);
	return ([header, rest]);
}

function write(key, options) {
	assert.object(key);
	if (!Key.isKey(key))
		throw (new Error('Must be a public key'));

	var alg = rfc4253.keyTypeToAlg(key);
	var buf = rfc4253.write(key);
	var comment = key.comment || '';

	var b64 = buf.toString('base64');
	var lines = wrap(b64, 64);

	lines.unshift('Public-Lines: ' + lines.length);
	lines.unshift('Comment: ' + comment);
	lines.unshift('Encryption: none');
	lines.unshift('PuTTY-User-Key-File-2: ' + alg);

	return (Buffer.from(lines.join('\n') + '\n'));
}

function wrap(txt, len) {
	var lines = [];
	var pos = 0;
	while (pos < txt.length) {
		lines.push(txt.slice(pos, pos + 64));
		pos += 64;
	}
	return (lines);
}