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;
46 typedef enum Gc_hash Gc_hash;
48 #define GC_MD5_DIGEST_SIZE 16
50 /* Call before respectively after any other functions. */
51 extern int gc_init (void);
52 extern void gc_done (void);
54 /* Memory allocation (avoid). */
55 typedef void *(*gc_malloc_t) (size_t n);
56 typedef int (*gc_secure_check_t) (const void *);
57 typedef void *(*gc_realloc_t) (void *p, size_t n);
58 typedef void (*gc_free_t) (void *);
59 extern void gc_set_allocators (gc_malloc_t func_malloc,
60 gc_malloc_t secure_malloc,
61 gc_secure_check_t secure_check,
62 gc_realloc_t func_realloc,
67 /* Compute a hash value over buffer IN of INLEN bytes size using the
68 algorithm HASH, placing the result in the pre-allocated buffer OUT.
69 The required size of OUT depends on HASH, and is generally
70 GC_<HASH>_DIGEST_SIZE. For example, for GC_MD5 the output buffer
73 gc_hash_buffer (int hash, const void *in, size_t inlen, char *out);
75 /* One-call interface. */
76 extern int gc_md5 (const void *in, size_t inlen, void *resbuf);
77 extern int gc_hmac_md5 (const void *key, size_t keylen,
78 const void *in, size_t inlen,
84 From: Simon Josefsson <jas@extundo.com>
85 Subject: Re: generic crypto
86 Newsgroups: gmane.comp.lib.gnulib.bugs
87 Cc: bug-gnulib@gnu.org
88 Date: Fri, 07 Oct 2005 12:50:57 +0200
89 Mail-Copies-To: nobody
91 Paul Eggert <eggert@CS.UCLA.EDU> writes:
93 > Simon Josefsson <jas@extundo.com> writes:
95 >> * Perhaps the /dev/*random reading should be separated into a separate
96 >> module? It might be useful outside of the gc layer too.
98 > Absolutely. I've been meaning to do that for months (for a "shuffle"
99 > program I want to add to coreutils), but hadn't gotten around to it.
100 > It would have to be generalized a bit. I'd like to have the file
101 > descriptor cached, for example.
103 I'll write a separate module for that part.
105 I think we should even add a good PRNG that is re-seeded from
106 /dev/*random frequently. GnuTLS can need a lot of random data on a
107 big server, more than /dev/random can supply. And /dev/urandom might
108 not be strong enough. Further, the security of /dev/*random can also
111 >> I'm also not sure about the names of those functions, they suggest
112 >> a more higher-level API than what is really offered (i.e., the
113 >> names "nonce" and "pseudo_random" and "random" imply certain
114 >> cryptographic properties).
116 > Could you expand a bit more on that? What is the relationship between
117 > nonce/pseudorandom/random and the /dev/ values you are using?
119 There is none, that is the problem.
121 Applications generally need different kind of "random" numbers.
122 Sometimes they just need some random data and doesn't care whether it
123 is possible for an attacker to compute the string (aka a "nonce").
124 Sometimes they need data that is very difficult to compute (i.e.,
125 computing it require inverting SHA1 or similar). Sometimes they need
126 data that is not possible to compute, i.e., it wants real entropy
127 collected over time on the system. Collecting the last kind of random
128 data is very expensive, so it must not be used too often. The second
129 kind of random data ("pseudo random") is typically generated by
130 seeding a good PRNG with a couple of hundred bytes of real entropy
131 from the "real random" data pool. The "nonce" is usually computed
132 using the PRNG as well, because PRNGs are usually fast.
134 Pseudo-random data is typically used for session keys. Strong random
135 data is often used to generate long-term keys (e.g., private RSA
138 Of course, there are many subtleties. There are several different
139 kind of nonce:s. Sometimes a nonce is just an ever-increasing
140 integer, starting from 0. Sometimes it is assumed to be unlikely to
141 be the same as previous nonces, but without a requirement that the
142 nonce is possible to guess. MD5(system clock) would thus suffice, if
143 it isn't called too often. You can guess what the next value will be,
144 but it will always be different.
146 The problem is that /dev/*random doesn't offer any kind of semantic
147 guarantees. But applications need an API that make that promise.
149 I think we should do this in several steps:
151 1) Write a module that can read from /dev/*random.
153 2) Add a module for a known-good PRNG suitable for random number
154 generation, that can be continuously re-seeded.
156 3) Add a high-level module that provide various different randomness
157 functions. One for nonces, perhaps even different kind of nonces,
158 one for pseudo random data, and one for strong random data. It is
159 not clear whether we can hope to achieve the last one in a portable
162 Further, it would be useful to allow users to provide their own
163 entropy source as a file, used to seed the PRNG or initialize the
164 strong randomness pool. This is used on embedded platforms that
165 doesn't have enough interrupts to hope to generate good random data.
167 > For example, why not use OpenBSD's /dev/arandom?
169 I don't trust ARC4. For example, recent cryptographic efforts
170 indicate that you must throw away the first 512 bytes generated from
171 the PRNG for it to be secure. I don't know whether OpenBSD do this.
172 Further, I recall some eprint paper on RC4 security that didn't
175 While I trust the random devices in OpenBSD more than
176 Solaris/AIX/HPUX/etc, I think that since we need something better on
177 Solaris/AIX/HPUX we'd might as well use it on OpenBSD or even Linux
180 > Here is one thought. The user could specify a desired quality level
181 > range, and the implementation then would supply random data that is at
182 > least as good as the lower bound of the range. I.e., ihe
183 > implementation refuses to produce any random data if it can't generate
184 > data that is at least as good as the lower end of the range. The
185 > upper bound of the range is advice from the user not to be any more
186 > expensive than that, but the implementation can ignore the advice if
187 > it doesn't have anything cheaper.
189 I'm not sure this is a good idea. Users can't really be expected to
190 understand this. Further, applications need many different kind of
191 random data. Selecting the randomness level for each by the user will
194 I think it is better if the application decide, from its cryptographic
195 requirement, what entropy quality it require, and call the proper API.
196 Meeting the implied semantic properties should be the job for gnulib.
198 >> Perhaps gc_dev_random and gc_dev_urandom?
200 > To some extent. I'd rather insulate the user from the details of
201 > where the random numbers come from. On the other hand we need to
202 > provide a way for applications to specify a file that contains
203 > random bits, so that people can override the defaults.
207 This may require some thinking before it is finalized. Is it ok to
208 install the GC module as-is meanwhile? Then I can continue to add the
209 stuff that GnuTLS need, and then come back to re-working the
210 randomness module. That way, we have two different projects that use
211 the code. GnuTLS includes the same randomness code that was in GNU
212 SASL and that is in the current gc module. I feel much more
213 comfortable working in small steps at a time, rather then working on
214 this for a long time in gnulib and only later integrate the stuff in