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got dkim-validation working with oversigned headers and sha256 hashing algorithm
This commit is contained in:
Ralf Becker
parent
ed370717ad
commit
81376af3f3
@ -35,6 +35,9 @@ class ischedule_server extends groupdav
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*/
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const REQUIRED_DKIM_HEADERS = 'iSchedule-Version:iSchedule-Message-ID:Content-Type:Originator:Recipient';
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/**
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* Constructor
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*/
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public function __construct()
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{
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// install our own exception handler sending exceptions as http status
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@ -119,12 +122,16 @@ class ischedule_server extends groupdav
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}
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if (($missing = array_diff(explode(':', strtolower(self::REQUIRED_DKIM_HEADERS.':DKIM-Signature')), array_keys($headers))))
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{
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error_log(array2string(array_keys($headers)));
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//error_log('headers='.array2string(array_keys($headers)).', required='.self::REQUIRED_DKIM_HEADERS.', missing='.array($missing));
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throw new Exception ('Bad Request: missing required headers: '.implode(', ', $missing), 400);
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}
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// validate dkim signature
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if (!self::dkim_validate($headers, $this->request, $error))
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// for multivalued Recipient header: as PHP engine agregates them ", " separated,
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// we cant tell it apart from ", " separated recipients in one header, therefore we try to validate both.
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// It will fail if multiple recipients in a single header are also ", " separated (just comma works fine)
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if (!self::dkim_validate($headers, $this->request, $error, true) &&
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!self::dkim_validate($headers, $this->request, $error, false))
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{
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throw new Exception('Bad Request: DKIM signature invalid: '.$error, 400);
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}
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@ -312,15 +319,23 @@ error_log(array2string(array_keys($headers)));
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/**
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* Validate DKIM signature
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*
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* For multivalued Recipient header(s): as PHP engine agregates them ", " separated,
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* we can not tell these apart from ", " separated recipients in one header!
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*
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* Therefore we can only try to validate both situations.
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*
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* It will fail if multiple recipients in a single header are also ", " separated (just comma works fine).
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*
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* @param array $headers header-name in lowercase(!) as key
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* @param string $body
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* @param string &$error=null error if false returned
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* @param boolean $split_recipients=null true=split recpients in multiple headers, false dont, default null try both
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* @return boolean true if signature could be validated, false otherwise
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* @todo other dkim q= methods: http/well-known bzw private-exchange
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*/
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public static function dkim_validate(array $headers, $body, &$error=null, $required_headers=self::REQUIRED_DKIM_HEADERS)
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public static function dkim_validate(array $headers, $body, &$error=null, $split_recipients=null)
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{
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// parse dkim siginature
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// parse dkim signature
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if (!isset($headers['dkim-signature']) ||
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!preg_match_all('/[\t\s]*([a-z]+)=([^;]+);?/i', $headers['dkim-signature'], $matches))
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{
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@ -329,17 +344,26 @@ error_log(array2string(array_keys($headers)));
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}
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$dkim = array_combine($matches[1], $matches[2]);
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if (($missing=array_diff(explode(':', strtolower($required_headers)), explode(':', strtolower($dkim['h'])))))
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{
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$error = "Missing required headers: ".implode(', ', $missing);
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return false;
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}
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// create headers array
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$dkim_headers = array();
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$check = $headers;
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foreach(explode(':', strtolower($dkim['h'])) as $header)
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{
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$dkim_headers[] = $header.': '.$headers[$header];
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// dkim oversigning: ommit not existing headers in signing
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if (!isset($check[$header])) continue;
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$value = $check[$header];
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unset($check[$header]);
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// special handling of multivalued recipient header
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if ($header == 'recipient' && (!isset($split_recipients) || $split_recipients))
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{
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if (!is_array($value)) $value = explode(', ', $value);
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$v = array_pop($value); // dkim uses reverse order!
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if ($value) $check[$header] = $value;
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$value = $v;
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}
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$dkim_headers[] = $header.': '.$value;
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}
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list($dkim_unsigned) = explode('b='.$dkim['b'], 'DKIM-Signature: '.$headers['dkim-signature']);
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$dkim_unsigned .= 'b=';
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@ -364,8 +388,8 @@ error_log(array2string(array_keys($headers)));
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}
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// Hash of the canonicalized body [tag:bh]
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list(,$hash_algo) = explode('/', $dkim['a']);
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$_bh= base64_encode(hash($hash_algo, $_b, true));
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list(,$hash_algo) = explode('-', $dkim['a']);
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$_bh = base64_encode(hash($hash_algo, $_b, true));
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// check body hash
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if ($_bh != $dkim['bh'])
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@ -386,22 +410,40 @@ error_log(array2string(array_keys($headers)));
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$_unsigned = mailDomainSigner::headSimpleCanon(implode("\r\n", $dkim_headers). "\r\n".$dkim_unsigned);
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break;
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case 'http/well-known':
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// todo
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default:
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$error = "Unknown header canonicalization '$header_canon'";
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return false;
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}
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error_log(__METHOD__."() unsigned='$_unsigned'");
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// fetch public key q=dns/txt method
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// ToDo other $dkim[q] methods: http/well-known bzw private-exchange
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if (!($dns = self::fetch_dns($dkim['d'], $dkim['s'])))
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// fetch public key using method in dkim q
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foreach(explode(':', $dkim['q']) as $method)
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{
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$error = "No public key for d='$dkim[d]' and s='$dkim[s]'";
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switch($method)
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{
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case 'dns/txt':
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$public_key = self::dns_txt_pubkey($dkim['d'], $dkim['s']);
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break;
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case 'private-exchange':
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$public_key = self::private_exchange_pubkey($dkim['d'], $dkim['s']);
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break;
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default: // not understood q method
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$public_key = false;
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break;
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}
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if ($public_key) break;
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}
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if (!$public_key)
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{
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$error = "No public key for d='$dkim[d]' and s='$dkim[s]' using methods q='$dkim[q]'";
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return false;
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}
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$public_key = "-----BEGIN PUBLIC KEY-----\n".chunk_split($dns['p'], 64, "\n")."-----END PUBLIC KEY-----\n";
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$ok = openssl_verify($_unsigned, base64_decode($dkim['b']), $public_key);
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$ok = openssl_verify($_unsigned, base64_decode($dkim['b']), $public_key, $hash_algo);
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//error_log(__METHOD__."() openssl_verify('$_unsigned', ..., '$public_key', '$hash_algo') returned ".array2string($ok));
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switch($ok)
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{
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@ -411,13 +453,73 @@ error_log(__METHOD__."() unsigned='$_unsigned'");
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case 0:
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$error = 'DKIM signature does NOT verify';
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error_log(__METHOD__."() unsigned='$_unsigned' $error");
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// if dkim did not validate, try not splitting Recipient header
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if (!isset($split_recipients))
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{
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return $this->dkim_validate($headers, $body, $error, $required_headers, false);
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}
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return false;
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}
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return true;
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}
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/**
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* Provisional private-exchange public keys
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*
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* @var array domain => selector => public key
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*/
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static $private_exchange = array(
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'example.com' => array(
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'ischedule' => '-----BEGIN PUBLIC KEY-----
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MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQDtocSHvSS1Nn0uIL4Sg+0wp6Kc
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W31WRC4Fww8P+jvsVAazVOxvxkShNSd18EvApiNa55P8WgKVEu02OQePjnjKNqfg
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JPeajkWy/0CJn+d6rX/ncPMGX2EYzqXy/CyVqpcnVAosToymo6VHL6ufhzlyLJFD
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znLtV121CZLUZlAySQIDAQAB
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-----END PUBLIC KEY-----',
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),
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'bedework.org' => array(
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'selector' => '-----BEGIN PUBLIC KEY-----
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MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQCuv+6UtGUdPerJ3s0HCng2sv3c
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R3ttma0JB6rMFfOTi1oHgk+h328MfGzhZK+SA9tsRPBcrJE/3uxs4SS2XNG9qRCG
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0YMmNFOmubht4RhQhS9drSNyMZbhy2MPVbl9lHAJULFdaDdLj1hc3xTMWy8sDa8s
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M8r0gHvp/sPSe9CQQQIDAQAB
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-----END PUBLIC KEY-----',
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),
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);
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/**
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* Fetch public key from dns txt recored dkim q=dns/txt
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*
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* @param string $d domain
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* @param string $s selector
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* @return string|boolean string with (full) public key or false if not found or other error retrieving it
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*/
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public static function private_exchange_pubkey($d, $s)
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{
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if (!isset(self::$private_exchange[$d]) || !isset(self::$private_exchange[$d][$s]))
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{
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return false;
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}
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return self::$private_exchange[$d][$s];
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}
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/**
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* Fetch public key from dns txt recored dkim q=dns/txt
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*
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* @param string $d domain
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* @param string $s selector
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* @return string|boolean string with (full) public key or false if not found or other error retrieving it
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*/
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public function dns_txt_pubkey($d, $s)
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{
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if (!($dns = self::fetch_dns($d, $s)))
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{
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return false;
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}
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return "-----BEGIN PUBLIC KEY-----\n".chunk_split($dns['p'], 64, "\n")."-----END PUBLIC KEY-----\n";
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}
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/**
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* Fetch dns record and return parsed array
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*
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