1 /* gc.h --- Header file for implementation agnostic crypto wrapper API.
2 * Copyright (C) 2002, 2003, 2004, 2005 Simon Josefsson
4 * This file is free software; you can redistribute it and/or modify
5 * it under the terms of the GNU General Public License as published
6 * by the Free Software Foundation; either version 2, or (at your
7 * option) any later version.
9 * This file is distributed in the hope that it will be useful, but
10 * WITHOUT ANY WARRANTY; without even the implied warranty of
11 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
12 * General Public License for more details.
14 * You should have received a copy of the GNU General Public License
15 * along with this file; if not, write to the Free Software
16 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
35 GC_PKCS5_INVALID_ITERATION_COUNT,
36 GC_PKCS5_INVALID_DERIVED_KEY_LENGTH,
37 GC_PKCS5_DERIVED_KEY_TOO_LONG
39 typedef enum Gc_rc Gc_rc;
47 typedef enum Gc_hash Gc_hash;
49 #define GC_MD5_DIGEST_SIZE 16
50 #define GC_SHA1_DIGEST_SIZE 20
64 typedef enum Gc_cipher Gc_cipher;
71 typedef enum Gc_cipher_mode Gc_cipher_mode;
73 typedef void *gc_cipher_handle;
75 /* Call before respectively after any other functions. */
76 extern Gc_rc gc_init (void);
77 extern void gc_done (void);
79 /* Memory allocation (avoid). */
80 typedef void *(*gc_malloc_t) (size_t n);
81 typedef int (*gc_secure_check_t) (const void *);
82 typedef void *(*gc_realloc_t) (void *p, size_t n);
83 typedef void (*gc_free_t) (void *);
84 extern void gc_set_allocators (gc_malloc_t func_malloc,
85 gc_malloc_t secure_malloc,
86 gc_secure_check_t secure_check,
87 gc_realloc_t func_realloc,
91 extern Gc_rc gc_cipher_open (Gc_cipher cipher, Gc_cipher_mode mode,
92 gc_cipher_handle * outhandle);
93 extern Gc_rc gc_cipher_setkey (gc_cipher_handle handle,
94 size_t keylen, const char *key);
95 extern Gc_rc gc_cipher_setiv (gc_cipher_handle handle,
96 size_t ivlen, const char *iv);
97 extern Gc_rc gc_cipher_encrypt_inline (gc_cipher_handle handle,
98 size_t len, char *data);
99 extern Gc_rc gc_cipher_decrypt_inline (gc_cipher_handle handle,
100 size_t len, char *data);
101 extern Gc_rc gc_cipher_close (gc_cipher_handle handle);
105 /* Compute a hash value over buffer IN of INLEN bytes size using the
106 algorithm HASH, placing the result in the pre-allocated buffer OUT.
107 The required size of OUT depends on HASH, and is generally
108 GC_<HASH>_DIGEST_SIZE. For example, for GC_MD5 the output buffer
109 must be 16 bytes. The return value is 0 (GC_OK) on success, or
110 another Gc_rc error code. */
112 gc_hash_buffer (Gc_hash hash, const void *in, size_t inlen, char *out);
114 /* One-call interface. */
115 extern Gc_rc gc_md5 (const void *in, size_t inlen, void *resbuf);
116 extern Gc_rc gc_sha1 (const void *in, size_t inlen, void *resbuf);
117 extern Gc_rc gc_hmac_md5 (const void *key, size_t keylen,
118 const void *in, size_t inlen,
120 extern Gc_rc gc_hmac_sha1 (const void *key, size_t keylen,
121 const void *in, size_t inlen,
124 /* Derive cryptographic keys from a password P of length PLEN, with
125 salt S of length SLEN, placing the result in pre-allocated buffer
126 DK of length DKLEN. An iteration count is specified in C, where a
127 larger value means this function take more time (typical iteration
128 counts are 1000-20000). This function "stretches" the key to be
129 exactly dkLen bytes long. GC_OK is returned on success, otherwise
130 an Gc_rc error code is returned. */
132 gc_pbkdf2_sha1 (const char *P, size_t Plen,
133 const char *S, size_t Slen,
135 char *DK, size_t dkLen);
140 From: Simon Josefsson <jas@extundo.com>
141 Subject: Re: generic crypto
142 Newsgroups: gmane.comp.lib.gnulib.bugs
143 Cc: bug-gnulib@gnu.org
144 Date: Fri, 07 Oct 2005 12:50:57 +0200
145 Mail-Copies-To: nobody
147 Paul Eggert <eggert@CS.UCLA.EDU> writes:
149 > Simon Josefsson <jas@extundo.com> writes:
151 >> * Perhaps the /dev/*random reading should be separated into a separate
152 >> module? It might be useful outside of the gc layer too.
154 > Absolutely. I've been meaning to do that for months (for a "shuffle"
155 > program I want to add to coreutils), but hadn't gotten around to it.
156 > It would have to be generalized a bit. I'd like to have the file
157 > descriptor cached, for example.
159 I'll write a separate module for that part.
161 I think we should even add a good PRNG that is re-seeded from
162 /dev/*random frequently. GnuTLS can need a lot of random data on a
163 big server, more than /dev/random can supply. And /dev/urandom might
164 not be strong enough. Further, the security of /dev/*random can also
167 >> I'm also not sure about the names of those functions, they suggest
168 >> a more higher-level API than what is really offered (i.e., the
169 >> names "nonce" and "pseudo_random" and "random" imply certain
170 >> cryptographic properties).
172 > Could you expand a bit more on that? What is the relationship between
173 > nonce/pseudorandom/random and the /dev/ values you are using?
175 There is none, that is the problem.
177 Applications generally need different kind of "random" numbers.
178 Sometimes they just need some random data and doesn't care whether it
179 is possible for an attacker to compute the string (aka a "nonce").
180 Sometimes they need data that is very difficult to compute (i.e.,
181 computing it require inverting SHA1 or similar). Sometimes they need
182 data that is not possible to compute, i.e., it wants real entropy
183 collected over time on the system. Collecting the last kind of random
184 data is very expensive, so it must not be used too often. The second
185 kind of random data ("pseudo random") is typically generated by
186 seeding a good PRNG with a couple of hundred bytes of real entropy
187 from the "real random" data pool. The "nonce" is usually computed
188 using the PRNG as well, because PRNGs are usually fast.
190 Pseudo-random data is typically used for session keys. Strong random
191 data is often used to generate long-term keys (e.g., private RSA
194 Of course, there are many subtleties. There are several different
195 kind of nonce:s. Sometimes a nonce is just an ever-increasing
196 integer, starting from 0. Sometimes it is assumed to be unlikely to
197 be the same as previous nonces, but without a requirement that the
198 nonce is possible to guess. MD5(system clock) would thus suffice, if
199 it isn't called too often. You can guess what the next value will be,
200 but it will always be different.
202 The problem is that /dev/*random doesn't offer any kind of semantic
203 guarantees. But applications need an API that make that promise.
205 I think we should do this in several steps:
207 1) Write a module that can read from /dev/*random.
209 2) Add a module for a known-good PRNG suitable for random number
210 generation, that can be continuously re-seeded.
212 3) Add a high-level module that provide various different randomness
213 functions. One for nonces, perhaps even different kind of nonces,
214 one for pseudo random data, and one for strong random data. It is
215 not clear whether we can hope to achieve the last one in a portable
218 Further, it would be useful to allow users to provide their own
219 entropy source as a file, used to seed the PRNG or initialize the
220 strong randomness pool. This is used on embedded platforms that
221 doesn't have enough interrupts to hope to generate good random data.
223 > For example, why not use OpenBSD's /dev/arandom?
225 I don't trust ARC4. For example, recent cryptographic efforts
226 indicate that you must throw away the first 512 bytes generated from
227 the PRNG for it to be secure. I don't know whether OpenBSD do this.
228 Further, I recall some eprint paper on RC4 security that didn't
231 While I trust the random devices in OpenBSD more than
232 Solaris/AIX/HPUX/etc, I think that since we need something better on
233 Solaris/AIX/HPUX we'd might as well use it on OpenBSD or even Linux
236 > Here is one thought. The user could specify a desired quality level
237 > range, and the implementation then would supply random data that is at
238 > least as good as the lower bound of the range. I.e., ihe
239 > implementation refuses to produce any random data if it can't generate
240 > data that is at least as good as the lower end of the range. The
241 > upper bound of the range is advice from the user not to be any more
242 > expensive than that, but the implementation can ignore the advice if
243 > it doesn't have anything cheaper.
245 I'm not sure this is a good idea. Users can't really be expected to
246 understand this. Further, applications need many different kind of
247 random data. Selecting the randomness level for each by the user will
250 I think it is better if the application decide, from its cryptographic
251 requirement, what entropy quality it require, and call the proper API.
252 Meeting the implied semantic properties should be the job for gnulib.
254 >> Perhaps gc_dev_random and gc_dev_urandom?
256 > To some extent. I'd rather insulate the user from the details of
257 > where the random numbers come from. On the other hand we need to
258 > provide a way for applications to specify a file that contains
259 > random bits, so that people can override the defaults.
263 This may require some thinking before it is finalized. Is it ok to
264 install the GC module as-is meanwhile? Then I can continue to add the
265 stuff that GnuTLS need, and then come back to re-working the
266 randomness module. That way, we have two different projects that use
267 the code. GnuTLS includes the same randomness code that was in GNU
268 SASL and that is in the current gc module. I feel much more
269 comfortable working in small steps at a time, rather then working on
270 this for a long time in gnulib and only later integrate the stuff in