gnu-social/plugins/OStatus/lib/magicenvelope.php

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<?php
/**
* StatusNet - the distributed open-source microblogging tool
* Copyright (C) 2010, StatusNet, Inc.
*
* A sample module to show best practices for StatusNet plugins
*
* PHP version 5
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU Affero General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU Affero General Public License for more details.
*
* You should have received a copy of the GNU Affero General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*
* @package StatusNet
* @author James Walker <james@status.net>
* @copyright 2010 StatusNet, Inc.
* @license http://www.fsf.org/licensing/licenses/agpl-3.0.html AGPL 3.0
* @link http://status.net/
*/
class MagicEnvelope
{
const ENCODING = 'base64url';
const NS = 'http://salmon-protocol.org/ns/magic-env';
protected $data = null; // When stored here it is _always_ base64url encoded
protected $data_type = null;
protected $encoding = null;
protected $alg = null;
protected $sig = null;
/**
* Extract envelope data from an XML document containing an <me:env> or <me:provenance> element.
*
* @param string XML source
* @return mixed associative array of envelope data, or false on unrecognized input
*
* @fixme will spew errors to logs or output in case of XML parse errors
* @fixme may give fatal errors if some elements are missing or invalid XML
* @fixme calling DOMDocument::loadXML statically triggers warnings in strict mode
*/
public function __construct($xml=null) {
if (!empty($xml)) {
$dom = DOMDocument::loadXML($xml);
if (!$dom instanceof DOMDocument) {
throw new ServerException('Tried to load malformed XML as DOM');
} elseif (!$this->fromDom($dom)) {
throw new ServerException('Could not load MagicEnvelope from DOM');
}
}
}
/**
* Retrieve Salmon keypair first by checking local database, but
* if it's not found, attempt discovery if it has been requested.
*
* @param Profile $profile The profile we're looking up keys for.
* @param boolean $discovery Network discovery if no local cache?
*/
public function getKeyPair(Profile $profile, $discovery=false) {
$magicsig = Magicsig::getKV('user_id', $profile->id);
if ($discovery && !$magicsig instanceof Magicsig) {
$magicsig = $this->discoverKeyPair($profile);
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// discoverKeyPair should've thrown exception if it failed
assert($magicsig instanceof Magicsig);
} elseif (!$magicsig instanceof Magicsig) { // No discovery request, so we'll give up.
throw new ServerException(sprintf('No public key found for profile (id==%d)', $profile->id));
}
return $magicsig;
}
/**
* Get the Salmon keypair from a URI, uses XRD Discovery etc.
*
* @return Magicsig with loaded keypair
*/
public function discoverKeyPair(Profile $profile)
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{
$signer_uri = $profile->getUri();
if (empty($signer_uri)) {
throw new ServerException(sprintf('Profile missing URI (id==%d)', $profile->id));
}
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$disco = new Discovery();
// Throws exception on lookup problems
$xrd = $disco->lookup($signer_uri);
$link = $xrd->get(Magicsig::PUBLICKEYREL);
if (is_null($link)) {
// TRANS: Exception.
throw new Exception(_m('Unable to locate signer public key.'));
}
// We have a public key element, let's hope it has proper key data.
$keypair = false;
$parts = explode(',', $link->href);
if (count($parts) == 2) {
$keypair = $parts[1];
} else {
// Backwards compatibility check for separator bug in 0.9.0
$parts = explode(';', $link->href);
if (count($parts) == 2) {
$keypair = $parts[1];
}
}
if ($keypair === false) {
// For debugging clarity. Keypair did not pass count()-check above.
// TRANS: Exception when public key was not properly formatted.
throw new Exception(_m('Incorrectly formatted public key element.'));
}
$magicsig = Magicsig::fromString($keypair);
if (!$magicsig instanceof Magicsig) {
common_debug('Salmon error: unable to parse keypair: '.var_export($keypair,true));
// TRANS: Exception when public key was properly formatted but not parsable.
throw new ServerException(_m('Retrieved Salmon keypair could not be parsed.'));
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}
return $magicsig;
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}
/**
* The current MagicEnvelope spec as used in StatusNet 0.9.7 and later
* includes both the original data and some signing metadata fields as
* the input plaintext for the signature hash.
*
* @return string
*/
public function signingText() {
return implode('.', array($this->data, // this field is pre-base64'd
Magicsig::base64_url_encode($this->data_type),
Magicsig::base64_url_encode($this->encoding),
Magicsig::base64_url_encode($this->alg)));
}
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/**
*
* @param <type> $text
* @param <type> $mimetype
* @param Magicsig $magicsig Magicsig with private key available.
* @return MagicEnvelope object with all properties set
*/
public static function signMessage($text, $mimetype, Magicsig $magicsig)
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{
$magic_env = new MagicEnvelope();
// Prepare text and metadata for signing
$magic_env->data = Magicsig::base64_url_encode($text);
$magic_env->data_type = $mimetype;
$magic_env->encoding = self::ENCODING;
$magic_env->alg = $magicsig->getName();
// Get the actual signature
$magic_env->sig = $magicsig->sign($magic_env->signingText());
return $magic_env;
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}
/**
* Create an <me:env> XML representation of the envelope.
*
* @return string representation of XML document
*/
public function toXML() {
$xs = new XMLStringer();
$xs->startXML();
$xs->elementStart('me:env', array('xmlns:me' => self::NS));
$xs->element('me:data', array('type' => $this->data_type), $this->data);
$xs->element('me:encoding', null, $this->encoding);
$xs->element('me:alg', null, $this->alg);
$xs->element('me:sig', null, $this->sig);
$xs->elementEnd('me:env');
$string = $xs->getString();
common_debug('MagicEnvelope XML: ' . $string);
return $string;
}
/*
* Extract the contained XML payload, and insert a copy of the envelope
* signature data as an <me:provenance> section.
*
* @return DOMDocument of Atom entry
*
* @fixme in case of XML parsing errors, this will spew to the error log or output
*/
public function getPayload()
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{
$dom = new DOMDocument();
if (!$dom->loadXML(Magicsig::base64_url_decode($this->data))) {
throw new ServerException('Malformed XML in Salmon payload');
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}
switch ($this->data_type) {
case 'application/atom+xml':
if ($dom->documentElement->namespaceURI !== Activity::ATOM
|| $dom->documentElement->tagName !== 'entry') {
throw new ServerException(_m('Salmon post must be an Atom entry.'));
}
$prov = $dom->createElementNS(self::NS, 'me:provenance');
$prov->setAttribute('xmlns:me', self::NS);
$data = $dom->createElementNS(self::NS, 'me:data', $this->data);
$data->setAttribute('type', $this->data_type);
$prov->appendChild($data);
$enc = $dom->createElementNS(self::NS, 'me:encoding', $this->encoding);
$prov->appendChild($enc);
$alg = $dom->createElementNS(self::NS, 'me:alg', $this->alg);
$prov->appendChild($alg);
$sig = $dom->createElementNS(self::NS, 'me:sig', $this->sig);
$prov->appendChild($sig);
$dom->documentElement->appendChild($prov);
break;
default:
throw new ServerException('Unknown Salmon payload data type');
}
return $dom;
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}
/**
* Find the author URI referenced in the payload Atom entry.
*
* @return string URI for author
* @throws ServerException on failure
*/
public function getAuthorUri() {
$doc = $this->getPayload();
$authors = $doc->documentElement->getElementsByTagName('author');
foreach ($authors as $author) {
$uris = $author->getElementsByTagName('uri');
foreach ($uris as $uri) {
return $uri->nodeValue;
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}
}
throw new ServerException('No author URI found in Salmon payload data');
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}
/**
* Attempt to verify cryptographic signing for parsed envelope data.
* Requires network access to retrieve public key referenced by the envelope signer.
*
* Details of failure conditions are dumped to output log and not exposed to caller.
*
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* @param Profile $profile profile used to get locally cached public signature key
* or if necessary perform discovery on.
*
* @return boolean
*/
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public function verify(Profile $profile)
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{
if ($this->alg != 'RSA-SHA256') {
common_log(LOG_DEBUG, "Salmon error: bad algorithm");
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return false;
}
if ($this->encoding != self::ENCODING) {
common_log(LOG_DEBUG, "Salmon error: bad encoding");
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return false;
}
try {
$magicsig = $this->getKeyPair($profile, true); // Do discovery too if necessary
} catch (Exception $e) {
common_log(LOG_DEBUG, "Salmon error: ".$e->getMessage());
return false;
}
return $magicsig->verify($this->signingText(), $this->sig);
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}
/**
* Extract envelope data from an XML document containing an <me:env> or <me:provenance> element.
*
* @param DOMDocument $dom
* @return mixed associative array of envelope data, or false on unrecognized input
*
* @fixme may give fatal errors if some elements are missing
*/
protected function fromDom(DOMDocument $dom)
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{
$env_element = $dom->getElementsByTagNameNS(self::NS, 'env')->item(0);
if (!$env_element) {
$env_element = $dom->getElementsByTagNameNS(self::NS, 'provenance')->item(0);
}
if (!$env_element) {
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return false;
}
$data_element = $env_element->getElementsByTagNameNS(self::NS, 'data')->item(0);
$sig_element = $env_element->getElementsByTagNameNS(self::NS, 'sig')->item(0);
$this->data = preg_replace('/\s/', '', $data_element->nodeValue);
$this->data_type = $data_element->getAttribute('type');
$this->encoding = $env_element->getElementsByTagNameNS(self::NS, 'encoding')->item(0)->nodeValue;
$this->alg = $env_element->getElementsByTagNameNS(self::NS, 'alg')->item(0)->nodeValue;
$this->sig = preg_replace('/\s/', '', $sig_element->nodeValue);
return true;
}
/**
* Encode the given string as a signed MagicEnvelope XML document,
* using the keypair for the given local user profile. We can of
* course not sign a remote profile's slap, since we don't have the
* private key.
*
* Side effects: will create and store a keypair on-demand if one
* hasn't already been generated for this user. This can be very slow
* on some systems.
*
* @param string $text XML fragment to sign, assumed to be Atom
* @param Profile $actor Profile of a local user to use as signer
*
* @return string XML string representation of magic envelope
*
* @throws Exception on bad profile input or key generation problems
* @fixme if signing fails, this seems to return the original text without warning. Is there a reason for this?
*/
public static function signForProfile($text, Profile $actor)
{
// We only generate keys for our local users of course, so let
// getUser throw an exception if the profile is not local.
$user = $actor->getUser();
// Find already stored key
$magicsig = Magicsig::getKV('user_id', $user->id);
if (!$magicsig instanceof Magicsig) {
// No keypair yet, let's generate one.
$magicsig = new Magicsig();
$magicsig->generate($user->id);
}
$magic_env = self::signMessage($text, 'application/atom+xml', $magicsig);
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assert($magic_env instanceof MagicEnvelope);
return $magic_env;
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}
}