389 lines
13 KiB
PHP
389 lines
13 KiB
PHP
<?php /*
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LibreSSL - CAcert web application
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Copyright (C) 2004-2011 CAcert Inc.
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This program is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; version 2 of the License.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program; if not, write to the Free Software
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Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
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*/
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// failWithId()
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require_once 'general.php';
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/**
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* Checks whether the given CSR contains a vulnerable key
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*
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* @param $csr string
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* The CSR to be checked
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* @param $encoding string [optional]
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* The encoding the CSR is in (for the "-inform" parameter of OpenSSL,
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* currently only "PEM" (default) or "DER" allowed)
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* @return string containing the reason if the key is considered weak,
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* empty string otherwise
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*/
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function checkWeakKeyCSR($csr, $encoding = "PEM")
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{
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$encoding = escapeshellarg($encoding);
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$status = runCommand("openssl req -inform $encoding -text -noout",
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$csr, $csrText);
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if ($status === true) {
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return failWithId("checkWeakKeyCSR(): Failed to start OpenSSL");
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}
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if ($status !== 0 || $csrText === "") {
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return _("I didn't receive a valid Certificate Request. Hit ".
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"the back button and try again.");
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}
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return checkWeakKeyText($csrText);
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}
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/**
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* Checks whether the given X509 certificate contains a vulnerable key
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*
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* @param $cert string
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* The X509 certificate to be checked
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* @param $encoding string [optional]
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* The encoding the certificate is in (for the "-inform" parameter of
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* OpenSSL, currently only "PEM" (default), "DER" or "NET" allowed)
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* @return string containing the reason if the key is considered weak,
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* empty string otherwise
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*/
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function checkWeakKeyX509($cert, $encoding = "PEM")
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{
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$encoding = escapeshellarg($encoding);
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$status = runCommand("openssl x509 -inform $encoding -text -noout",
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$cert, $certText);
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if ($status === true) {
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return failWithId("checkWeakKeyX509(): Failed to start OpenSSL");
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}
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if ($status !== 0 || $certText === "") {
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return _("I didn't receive a valid Certificate Request. Hit ".
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"the back button and try again.");
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}
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return checkWeakKeyText($certText);
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}
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/**
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* Checks whether the given SPKAC contains a vulnerable key
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*
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* @param $spkac string
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* The SPKAC to be checked
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* @param $spkacname string [optional]
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* The name of the variable that contains the SPKAC. The default is
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* "SPKAC"
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* @return string containing the reason if the key is considered weak,
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* empty string otherwise
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*/
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function checkWeakKeySPKAC($spkac, $spkacname = "SPKAC")
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{
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$spkacname = escapeshellarg($spkacname);
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$status = runCommand("openssl spkac -spkac $spkacname", $spkac, $spkacText);
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if ($status === true) {
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return failWithId("checkWeakKeySPKAC(): Failed to start OpenSSL");
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}
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if ($status !== 0 || $spkacText === "") {
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return _("I didn't receive a valid Certificate Request. Hit the ".
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"back button and try again.");
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}
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return checkWeakKeyText($spkacText);
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}
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/**
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* Checks whether the given text representation of a CSR or a SPKAC contains
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* a weak key
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*
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* @param $text string
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* The text representation of a key as output by the
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* "openssl <foo> -text -noout" commands
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* @return string containing the reason if the key is considered weak,
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* empty string otherwise
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*/
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function checkWeakKeyText($text)
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{
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/* Which public key algorithm? */
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if (!preg_match('/^\s*Public Key Algorithm: ([^\s]+)$/m', $text,
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$algorithm))
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{
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return failWithId("checkWeakKeyText(): Couldn't extract the ".
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"public key algorithm used.\nData:\n$text");
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} else {
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$algorithm = $algorithm[1];
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}
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if ($algorithm === "rsaEncryption")
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{
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if (!preg_match('/^\s*RSA Public Key: \((\d+) bit\)$/m', $text, $keysize))
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{
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return failWithId("checkWeakKeyText(): Couldn't parse the RSA ".
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"key size.\nData:\n$text");
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} else {
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$keysize = intval($keysize[1]);
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}
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if ($keysize < 2048)
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{
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return sprintf(_("The keys that you use are very small ".
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"and therefore insecure. Please generate stronger ".
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"keys. More information about this issue can be ".
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"found in %sthe wiki%s"),
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"<a href='//wiki.cacert.org/WeakKeys#SmallKey'>",
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"</a>");
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}
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$debianVuln = checkDebianVulnerability($text, $keysize);
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if ($debianVuln === true)
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{
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return sprintf(_("The keys you use have very likely been ".
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"generated with a vulnerable version of OpenSSL which ".
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"was distributed by debian. Please generate new keys. ".
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"More information about this issue can be found in ".
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"%sthe wiki%s"),
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"<a href='//wiki.cacert.org/WeakKeys#DebianVulnerability'>",
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"</a>");
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} elseif ($debianVuln === false) {
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// not vulnerable => do nothing
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} else {
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return failWithId("checkWeakKeyText(): Something went wrong in".
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"checkDebianVulnerability().\nKeysize: $keysize\n".
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"Data:\n$text");
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}
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if (!preg_match('/^\s*Exponent: (\d+) \(0x[0-9a-fA-F]+\)$/m', $text,
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$exponent))
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{
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return failWithId("checkWeakKeyText(): Couldn't parse the RSA ".
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"exponent.\nData:\n$text");
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} else {
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$exponent = $exponent[1]; // exponent might be very big =>
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//handle as string using bc*()
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if (bccomp($exponent, "65537") < 0)
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{
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return sprintf(_("The keys you use might be insecure. ".
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"Although there is currently no known attack for ".
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"reasonable encryption schemes, we're being ".
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"cautious and don't allow certificates for such ".
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"keys. Please generate stronger keys. More ".
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"information about this issue can be found in ".
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"%sthe wiki%s"),
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"<a href='//wiki.cacert.org/WeakKeys#SmallExponent'>",
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"</a>");
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} elseif (!(bccomp($exponent, "65537") >= 0 &&
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(bccomp($exponent, "100000") === -1 ||
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// speed things up if way smaller than 2^256
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bccomp($exponent, bcpow("2", "256")) === -1) )) {
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// 65537 <= exponent < 2^256 recommended by NIST
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// not critical but log so we have some statistics about
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// affected users
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trigger_error("checkWeakKeyText(): Certificate for ".
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"unsuitable exponent '$exponent' requested",
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E_USER_NOTICE);
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}
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}
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// No weakness found
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return "";
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} // End RSA
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/*
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//Fails to work due to outdated OpenSSL 0.9.8o
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//For this to work OpenSSL 1.0.1f or newer is required
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//which is currently unavailable on the systems
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//If DSA2048 or longer is used the CSR hangs pending on the signer.
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if ($algorithm === "dsaEncryption")
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{
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if (!preg_match('/^\s*Public Key Algorithm:\s+dsaEncryption\s+pub:\s+([0-9a-fA-F:\s]+)\s+P:\s+([0-9a-fA-F:\s]+)\s+Q:\s+([0-9a-fA-F:\s]+)\s+G:\s+([0-9a-fA-F:\s]+)\s+$/sm', $text, $keydetail))
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{
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return failWithId("checkWeakKeyText(): Couldn't parse the DSA ".
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"key size.\nData:\n$text");
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}
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$key_pub = strtr(preg_replace("/[^0-9a-fA-F]/", "", $keydetail[1]), "ABCDEF", "abcdef");
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$key_P = strtr(preg_replace("/[^0-9a-fA-F]/", "", $keydetail[2]), "ABCDEF", "abcdef");
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$key_Q = strtr(preg_replace("/[^0-9a-fA-F]/", "", $keydetail[3]), "ABCDEF", "abcdef");
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$key_G = strtr(preg_replace("/[^0-9a-fA-F]/", "", $keydetail[4]), "ABCDEF", "abcdef");
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//Verify the numbers provided by the client
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$num_pub = @gmp_init($key_pub, 16);
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$num_P = @gmp_init($key_P, 16);
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$num_Q = @gmp_init($key_Q, 16);
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$num_G = @gmp_init($key_G, 16);
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$bit_P = ltrim(gmp_strval($num_P, 2), "0");
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$keysize = strlen($bit_P);
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if ($keysize < 2048) {
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return sprintf(_("The keys that you use are very small ".
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"and therefore insecure. Please generate stronger ".
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"keys. More information about this issue can be ".
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"found in %sthe wiki%s"),
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"<a href='//wiki.cacert.org/WeakKeys#SmallKey'>",
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"</a>");
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}
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//Following checks based on description of key generation in Wikipedia
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//These checks do not ensure a strong key, but at least check for enough sanity in the key material
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// cf. https://en.wikipedia.org/wiki/Digital_Signature_Algorithm#Key_generation
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//Check that P is prime
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if(!gmp_testprime($num_P)) {
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return failWithId("checkWeakKeyText(): The supplied DSA ".
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"key does seem to have a non-prime public modulus.\nData:\n$text");
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}
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//Check that Q is prime
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if(!gmp_testprime($num_Q)) {
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return failWithId("checkWeakKeyText(): The supplied DSA ".
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"key does seem to have a non-prime Q-value.\nData:\n$text");
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}
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//Check if P-1 is diviseable by Q
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if(0 !== gmp_cmp("1", gmp_mod($num_P, $num_Q))) {
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return failWithId("checkWeakKeyText(): The supplied DSA ".
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"key does seem to have P mod Q === 1 (i.e. P-1 is not diviseable by Q).\nData:\n$text");
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}
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//Check the numbers are all less than the public modulus P
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if(0 <= gmp_cmp($num_Q, $num_P) || 0 <= gmp_cmp($num_G, $num_P) || 0 <= gmp_cmp($num_pub, $num_P)) {
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return failWithId("checkWeakKeyText(): The supplied DSA ".
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"key does seem to be normalized to have Q < P, G < P and pub < P.\nData:\n$text");
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}
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// No weakness found
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return "";
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} // End DSA
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*/
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return _("The keys you supplied use an unrecognized algorithm. ".
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"For security reasons these keys can not be signed by CAcert.");
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}
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/**
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* Reimplement the functionality of the openssl-vulnkey tool
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*
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* @param $text string
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* The text representation of a key as output by the
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* "openssl <foo> -text -noout" commands
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* @param $keysize int [optional]
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* If the key size is already known it can be provided so it doesn't
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* have to be parsed again. This also skips the check whether the key
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* is an RSA key => use wisely
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* @return TRUE if key is vulnerable, FALSE otherwise, NULL in case of error
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*/
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function checkDebianVulnerability($text, $keysize = 0)
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{
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$keysize = intval($keysize);
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if ($keysize === 0)
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{
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/* Which public key algorithm? */
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if (!preg_match('/^\s*Public Key Algorithm: ([^\s]+)$/m', $text,
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$algorithm))
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{
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trigger_error("checkDebianVulnerability(): Couldn't extract ".
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"the public key algorithm used.\nData:\n$text",
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E_USER_WARNING);
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return null;
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} else {
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$algorithm = $algorithm[1];
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}
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if ($algorithm !== "rsaEncryption") return false;
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/* Extract public key size */
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if (!preg_match('/^\s*RSA Public Key: \((\d+) bit\)$/m', $text,
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$keysize))
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{
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trigger_error("checkDebianVulnerability(): Couldn't parse the ".
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"RSA key size.\nData:\n$text", E_USER_WARNING);
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return null;
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} else {
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$keysize = intval($keysize[1]);
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}
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}
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// $keysize has been made sure to contain an int
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$blacklist = "/usr/share/openssl-blacklist/blacklist.RSA-$keysize";
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if (!(is_file($blacklist) && is_readable($blacklist)))
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{
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if (in_array($keysize, array(512, 1024, 2048, 4096)))
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{
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trigger_error("checkDebianVulnerability(): Blacklist for ".
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"$keysize bit keys not accessible. Expected at ".
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"$blacklist", E_USER_ERROR);
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return null;
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}
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trigger_error("checkDebianVulnerability(): $blacklist is not ".
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"readable. Unsupported key size?", E_USER_WARNING);
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return false;
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}
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/* Extract RSA modulus */
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if (!preg_match('/^\s*Modulus \(\d+ bit\):\n'.
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'((?:\s*[0-9a-f][0-9a-f]:(?:\n)?)+[0-9a-f][0-9a-f])$/m',
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$text, $modulus))
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{
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trigger_error("checkDebianVulnerability(): Couldn't extract the ".
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"RSA modulus.\nData:\n$text", E_USER_WARNING);
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return null;
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} else {
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$modulus = $modulus[1];
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// strip whitespace and colon leftovers
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$modulus = str_replace(array(" ", "\t", "\n", ":"), "", $modulus);
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// when using "openssl xxx -text" first byte was 00 in all my test
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// cases but 00 not present in the "openssl xxx -modulus" output
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if ($modulus[0] === "0" && $modulus[1] === "0")
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{
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$modulus = substr($modulus, 2);
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} else {
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trigger_error("checkDebianVulnerability(): First byte is not ".
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"zero", E_USER_NOTICE);
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}
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$modulus = strtoupper($modulus);
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}
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/* calculate checksum and look it up in the blacklist */
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$checksum = substr(sha1("Modulus=$modulus\n"), 20);
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// $checksum and $blacklist should be safe, but just to make sure
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$checksum = escapeshellarg($checksum);
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$blacklist = escapeshellarg($blacklist);
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$debianVuln = runCommand("grep $checksum $blacklist");
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if ($debianVuln === 0) // grep returned something => it is on the list
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{
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return true;
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} elseif ($debianVuln === 1) {
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// grep returned nothing
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return false;
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} else {
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trigger_error("checkDebianVulnerability(): Something went wrong ".
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"when looking up the key with checksum $checksum in the ".
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"blacklist $blacklist", E_USER_ERROR);
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return null;
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}
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// Should not get here
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return null;
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}
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