090d66b5b2e04de193e78e8af8c0897017dc13e5
[cacert-devel.git] / includes / lib / check_weak_key.php
1 <?php /*
2 LibreSSL - CAcert web application
3 Copyright (C) 2004-2011 CAcert Inc.
4
5 This program is free software; you can redistribute it and/or modify
6 it under the terms of the GNU General Public License as published by
7 the Free Software Foundation; version 2 of the License.
8
9 This program is distributed in the hope that it will be useful,
10 but WITHOUT ANY WARRANTY; without even the implied warranty of
11 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
12 GNU General Public License for more details.
13
14 You should have received a copy of the GNU General Public License
15 along with this program; if not, write to the Free Software
16 Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
17 */
18
19 // failWithId()
20 require_once 'general.php';
21
22
23 /**
24 * Checks whether the given CSR contains a vulnerable key
25 *
26 * @param $csr string
27 * The CSR to be checked
28 * @param $encoding string [optional]
29 * The encoding the CSR is in (for the "-inform" parameter of OpenSSL,
30 * currently only "PEM" (default) or "DER" allowed)
31 * @return string containing the reason if the key is considered weak,
32 * empty string otherwise
33 */
34 function checkWeakKeyCSR($csr, $encoding = "PEM")
35 {
36 $encoding = escapeshellarg($encoding);
37 $status = runCommand("openssl req -inform $encoding -text -noout",
38 $csr, $csrText);
39 if ($status === true) {
40 return failWithId("checkWeakKeyCSR(): Failed to start OpenSSL");
41 }
42
43 if ($status !== 0 || $csrText === "") {
44 return _("I didn't receive a valid Certificate Request. Hit ".
45 "the back button and try again.");
46 }
47
48 return checkWeakKeyText($csrText);
49 }
50
51 /**
52 * Checks whether the given X509 certificate contains a vulnerable key
53 *
54 * @param $cert string
55 * The X509 certificate to be checked
56 * @param $encoding string [optional]
57 * The encoding the certificate is in (for the "-inform" parameter of
58 * OpenSSL, currently only "PEM" (default), "DER" or "NET" allowed)
59 * @return string containing the reason if the key is considered weak,
60 * empty string otherwise
61 */
62 function checkWeakKeyX509($cert, $encoding = "PEM")
63 {
64 $encoding = escapeshellarg($encoding);
65 $status = runCommand("openssl x509 -inform $encoding -text -noout",
66 $cert, $certText);
67 if ($status === true) {
68 return failWithId("checkWeakKeyX509(): Failed to start OpenSSL");
69 }
70
71 if ($status !== 0 || $certText === "") {
72 return _("I didn't receive a valid Certificate Request. Hit ".
73 "the back button and try again.");
74 }
75
76 return checkWeakKeyText($certText);
77 }
78
79 /**
80 * Checks whether the given SPKAC contains a vulnerable key
81 *
82 * @param $spkac string
83 * The SPKAC to be checked
84 * @param $spkacname string [optional]
85 * The name of the variable that contains the SPKAC. The default is
86 * "SPKAC"
87 * @return string containing the reason if the key is considered weak,
88 * empty string otherwise
89 */
90 function checkWeakKeySPKAC($spkac, $spkacname = "SPKAC")
91 {
92 $spkacname = escapeshellarg($spkacname);
93 $status = runCommand("openssl spkac -spkac $spkacname", $spkac, $spkacText);
94 if ($status === true) {
95 return failWithId("checkWeakKeySPKAC(): Failed to start OpenSSL");
96 }
97
98 if ($status !== 0 || $spkacText === "") {
99 return _("I didn't receive a valid Certificate Request. Hit the ".
100 "back button and try again.");
101 }
102
103 return checkWeakKeyText($spkacText);
104 }
105
106 /**
107 * Checks whether the given text representation of a CSR or a SPKAC contains
108 * a weak key
109 *
110 * @param $text string
111 * The text representation of a key as output by the
112 * "openssl <foo> -text -noout" commands
113 * @return string containing the reason if the key is considered weak,
114 * empty string otherwise
115 */
116 function checkWeakKeyText($text)
117 {
118 /* Which public key algorithm? */
119 if (!preg_match('/^\s*Public Key Algorithm: ([^\s]+)$/m', $text,
120 $algorithm))
121 {
122 return failWithId("checkWeakKeyText(): Couldn't extract the ".
123 "public key algorithm used.\nData:\n$text");
124 } else {
125 $algorithm = $algorithm[1];
126 }
127
128
129 switch ((string)$algorithm) {
130 case "rsaEncryption":
131 if (!preg_match('/^\s*RSA Public Key: \((\d+) bit\)$/m', $text, $keysize))
132 {
133 return failWithId("checkWeakKeyText(): Couldn't parse the RSA ".
134 "key size.\nData:\n$text");
135 } else {
136 $keysize = intval($keysize[1]);
137 }
138
139 if ($keysize < 2048)
140 {
141 return sprintf(_("The keys that you use are very small ".
142 "and therefore insecure. Please generate stronger ".
143 "keys. More information about this issue can be ".
144 "found in %sthe wiki%s"),
145 "<a href='//wiki.cacert.org/WeakKeys#SmallKey'>",
146 "</a>");
147 }
148
149 $debianVuln = checkDebianVulnerability($text, $keysize);
150 if ($debianVuln === true)
151 {
152 return sprintf(_("The keys you use have very likely been ".
153 "generated with a vulnerable version of OpenSSL which ".
154 "was distributed by debian. Please generate new keys. ".
155 "More information about this issue can be found in ".
156 "%sthe wiki%s"),
157 "<a href='//wiki.cacert.org/WeakKeys#DebianVulnerability'>",
158 "</a>");
159 } elseif ($debianVuln === false) {
160 // not vulnerable => do nothing
161 } else {
162 return failWithId("checkWeakKeyText(): Something went wrong in".
163 "checkDebianVulnerability().\nKeysize: $keysize\n".
164 "Data:\n$text");
165 }
166
167 if (!preg_match('/^\s*Exponent: (\d+) \(0x[0-9a-fA-F]+\)$/m', $text,
168 $exponent))
169 {
170 return failWithId("checkWeakKeyText(): Couldn't parse the RSA ".
171 "exponent.\nData:\n$text");
172 } else {
173 $exponent = $exponent[1]; // exponent might be very big =>
174 //handle as string using bc*()
175
176 if (bccomp($exponent, "3") === 0)
177 {
178 return sprintf(_("The keys you use might be insecure. ".
179 "Although there is currently no known attack for ".
180 "reasonable encryption schemes, we're being ".
181 "cautious and don't allow certificates for such ".
182 "keys. Please generate stronger keys. More ".
183 "information about this issue can be found in ".
184 "%sthe wiki%s"),
185 "<a href='//wiki.cacert.org/WeakKeys#SmallExponent'>",
186 "</a>");
187 } elseif (!(bccomp($exponent, "65537") >= 0 &&
188 (bccomp($exponent, "100000") === -1 ||
189 // speed things up if way smaller than 2^256
190 bccomp($exponent, bcpow("2", "256")) === -1) )) {
191 // 65537 <= exponent < 2^256 recommended by NIST
192 // not critical but log so we have some statistics about
193 // affected users
194 trigger_error("checkWeakKeyText(): Certificate for ".
195 "unsuitable exponent '$exponent' requested",
196 E_USER_NOTICE);
197 }
198 }
199
200 break;
201
202 /*
203 //Fails to work due to outdated OpenSSL 0.9.8o
204 //For this to work OpenSSL 1.0.1f or newer is required
205 //which is currently unavailable on the systems
206 //If DSA2048 or longer is used the CSR hangs pending on the signer.
207 case "dsaEncryption":
208 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, $keydetail))
209 {
210 return failWithId("checkWeakKeyText(): Couldn't parse the DSA ".
211 "key size.\nData:\n$text");
212 }
213
214 $key_pub = strtr(preg_replace("/[^0-9a-fA-F]/", "", $keydetail[1]), "ABCDEF", "abcdef");
215 $key_P = strtr(preg_replace("/[^0-9a-fA-F]/", "", $keydetail[2]), "ABCDEF", "abcdef");
216 $key_Q = strtr(preg_replace("/[^0-9a-fA-F]/", "", $keydetail[3]), "ABCDEF", "abcdef");
217 $key_G = strtr(preg_replace("/[^0-9a-fA-F]/", "", $keydetail[4]), "ABCDEF", "abcdef");
218
219 //Verify the numbers provided by the client
220 $num_pub = @gmp_init($key_pub, 16);
221 $num_P = @gmp_init($key_P, 16);
222 $num_Q = @gmp_init($key_Q, 16);
223 $num_G = @gmp_init($key_G, 16);
224
225 $bit_P = ltrim(gmp_strval($num_P, 2), "0");
226 $keysize = strlen($bit_P);
227
228 if ($keysize < 2048) {
229 return sprintf(_("The keys that you use are very small ".
230 "and therefore insecure. Please generate stronger ".
231 "keys. More information about this issue can be ".
232 "found in %sthe wiki%s"),
233 "<a href='//wiki.cacert.org/WeakKeys#SmallKey'>",
234 "</a>");
235 }
236
237 //Following checks based on description of key generation in Wikipedia
238 //These checks do not ensure a strong key, but at least check for enough sanity in the key material
239 // cf. https://en.wikipedia.org/wiki/Digital_Signature_Algorithm#Key_generation
240
241 //Check that P is prime
242 if(!gmp_testprime($num_P)) {
243 return failWithId("checkWeakKeyText(): The supplied DSA ".
244 "key does seem to have a non-prime public modulus.\nData:\n$text");
245 }
246
247 //Check that Q is prime
248 if(!gmp_testprime($num_Q)) {
249 return failWithId("checkWeakKeyText(): The supplied DSA ".
250 "key does seem to have a non-prime Q-value.\nData:\n$text");
251 }
252
253 //Check if P-1 is diviseable by Q
254 if(0 !== gmp_cmp("1", gmp_mod($num_P, $num_Q))) {
255 return failWithId("checkWeakKeyText(): The supplied DSA ".
256 "key does seem to have P mod Q === 1 (i.e. P-1 is not diviseable by Q).\nData:\n$text");
257 }
258
259 //Check the numbers are all less than the public modulus P
260 if(0 <= gmp_cmp($num_Q, $num_P) || 0 <= gmp_cmp($num_G, $num_P) || 0 <= gmp_cmp($num_pub, $num_P)) {
261 return failWithId("checkWeakKeyText(): The supplied DSA ".
262 "key does seem to be normalized to have Q < P, G < P and pub < P.\nData:\n$text");
263 }
264
265 break;
266 */
267
268 default:
269 return _("The keys you supplied use an unrecognized algorithm. ".
270 "For security reasons these keys can not be signed by CAcert.");
271 }
272
273 /* No weakness found */
274 return "";
275 }
276
277 /**
278 * Reimplement the functionality of the openssl-vulnkey tool
279 *
280 * @param $text string
281 * The text representation of a key as output by the
282 * "openssl <foo> -text -noout" commands
283 * @param $keysize int [optional]
284 * If the key size is already known it can be provided so it doesn't
285 * have to be parsed again. This also skips the check whether the key
286 * is an RSA key => use wisely
287 * @return TRUE if key is vulnerable, FALSE otherwise, NULL in case of error
288 */
289 function checkDebianVulnerability($text, $keysize = 0)
290 {
291 $keysize = intval($keysize);
292
293 if ($keysize === 0)
294 {
295 /* Which public key algorithm? */
296 if (!preg_match('/^\s*Public Key Algorithm: ([^\s]+)$/m', $text,
297 $algorithm))
298 {
299 trigger_error("checkDebianVulnerability(): Couldn't extract ".
300 "the public key algorithm used.\nData:\n$text",
301 E_USER_WARNING);
302 return null;
303 } else {
304 $algorithm = $algorithm[1];
305 }
306
307 if ($algorithm !== "rsaEncryption") return false;
308
309 /* Extract public key size */
310 if (!preg_match('/^\s*RSA Public Key: \((\d+) bit\)$/m', $text,
311 $keysize))
312 {
313 trigger_error("checkDebianVulnerability(): Couldn't parse the ".
314 "RSA key size.\nData:\n$text", E_USER_WARNING);
315 return null;
316 } else {
317 $keysize = intval($keysize[1]);
318 }
319 }
320
321 // $keysize has been made sure to contain an int
322 $blacklist = "/usr/share/openssl-blacklist/blacklist.RSA-$keysize";
323 if (!(is_file($blacklist) && is_readable($blacklist)))
324 {
325 if (in_array($keysize, array(512, 1024, 2048, 4096)))
326 {
327 trigger_error("checkDebianVulnerability(): Blacklist for ".
328 "$keysize bit keys not accessible. Expected at ".
329 "$blacklist", E_USER_ERROR);
330 return null;
331 }
332
333 trigger_error("checkDebianVulnerability(): $blacklist is not ".
334 "readable. Unsupported key size?", E_USER_WARNING);
335 return false;
336 }
337
338
339 /* Extract RSA modulus */
340 if (!preg_match('/^\s*Modulus \(\d+ bit\):\n'.
341 '((?:\s*[0-9a-f][0-9a-f]:(?:\n)?)+[0-9a-f][0-9a-f])$/m',
342 $text, $modulus))
343 {
344 trigger_error("checkDebianVulnerability(): Couldn't extract the ".
345 "RSA modulus.\nData:\n$text", E_USER_WARNING);
346 return null;
347 } else {
348 $modulus = $modulus[1];
349 // strip whitespace and colon leftovers
350 $modulus = str_replace(array(" ", "\t", "\n", ":"), "", $modulus);
351
352 // when using "openssl xxx -text" first byte was 00 in all my test
353 // cases but 00 not present in the "openssl xxx -modulus" output
354 if ($modulus[0] === "0" && $modulus[1] === "0")
355 {
356 $modulus = substr($modulus, 2);
357 } else {
358 trigger_error("checkDebianVulnerability(): First byte is not ".
359 "zero", E_USER_NOTICE);
360 }
361
362 $modulus = strtoupper($modulus);
363 }
364
365
366 /* calculate checksum and look it up in the blacklist */
367 $checksum = substr(sha1("Modulus=$modulus\n"), 20);
368
369 // $checksum and $blacklist should be safe, but just to make sure
370 $checksum = escapeshellarg($checksum);
371 $blacklist = escapeshellarg($blacklist);
372 $debianVuln = runCommand("grep $checksum $blacklist");
373 if ($debianVuln === 0) // grep returned something => it is on the list
374 {
375 return true;
376 } elseif ($debianVuln === 1) {
377 // grep returned nothing
378 return false;
379 } else {
380 trigger_error("checkDebianVulnerability(): Something went wrong ".
381 "when looking up the key with checksum $checksum in the ".
382 "blacklist $blacklist", E_USER_ERROR);
383 return null;
384 }
385
386 // Should not get here
387 return null;
388 }