gl/gc.h

   1 /* gc.h --- Header file for implementation agnostic crypto wrapper API.
   2  * Copyright (C) 2002, 2003, 2004, 2005, 2007  Simon Josefsson
   3  *
   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.
   8  *
   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.
  13  *
  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
  17  * 02110-1301, USA.
  18  *
  19  */
  20
  21 #ifndef GC_H
  22 # define GC_H
  23
  24 /* Get size_t. */
  25 # include <stddef.h>
  26
  27 enum Gc_rc
  28 {
  29   GC_OK = 0,
  30   GC_MALLOC_ERROR,
  31   GC_INIT_ERROR,
  32   GC_RANDOM_ERROR,
  33   GC_INVALID_CIPHER,
  34   GC_INVALID_HASH,
  35   GC_PKCS5_INVALID_ITERATION_COUNT,
  36   GC_PKCS5_INVALID_DERIVED_KEY_LENGTH,
  37   GC_PKCS5_DERIVED_KEY_TOO_LONG
  38 };
  39 typedef enum Gc_rc Gc_rc;
  40
  41 /* Hash types. */
  42 enum Gc_hash
  43 {
  44   GC_MD4,
  45   GC_MD5,
  46   GC_SHA1,
  47   GC_MD2,
  48   GC_RMD160,
  49   GC_SHA256,
  50   GC_SHA384,
  51   GC_SHA512
  52 };
  53 typedef enum Gc_hash Gc_hash;
  54
  55 enum Gc_hash_mode
  56 {
  57   GC_HMAC = 1
  58 };
  59 typedef enum Gc_hash_mode Gc_hash_mode;
  60
  61 typedef void *gc_hash_handle;
  62
  63 #define GC_MD2_DIGEST_SIZE 16
  64 #define GC_MD4_DIGEST_SIZE 16
  65 #define GC_MD5_DIGEST_SIZE 16
  66 #define GC_RMD160_DIGEST_SIZE 20
  67 #define GC_SHA1_DIGEST_SIZE 20
  68 #define GC_SHA256_DIGEST_SIZE 32
  69 #define GC_SHA384_DIGEST_SIZE 48
  70 #define GC_SHA512_DIGEST_SIZE 64
  71
  72 /* Cipher types. */
  73 enum Gc_cipher
  74 {
  75   GC_AES128,
  76   GC_AES192,
  77   GC_AES256,
  78   GC_3DES,
  79   GC_DES,
  80   GC_ARCFOUR128,
  81   GC_ARCFOUR40,
  82   GC_ARCTWO40
  83 };
  84 typedef enum Gc_cipher Gc_cipher;
  85
  86 enum Gc_cipher_mode
  87 {
  88   GC_ECB,
  89   GC_CBC,
  90   GC_STREAM
  91 };
  92 typedef enum Gc_cipher_mode Gc_cipher_mode;
  93
  94 typedef void *gc_cipher_handle;
  95
  96 /* Call before respectively after any other functions. */
  97 extern Gc_rc gc_init (void);
  98 extern void gc_done (void);
  99
 100 /* Memory allocation (avoid). */
 101 typedef void *(*gc_malloc_t) (size_t n);
 102 typedef int (*gc_secure_check_t) (const void *);
 103 typedef void *(*gc_realloc_t) (void *p, size_t n);
 104 typedef void (*gc_free_t) (void *);
 105 extern void gc_set_allocators (gc_malloc_t func_malloc,
 106                                gc_malloc_t secure_malloc,
 107                                gc_secure_check_t secure_check,
 108                                gc_realloc_t func_realloc,
 109                                gc_free_t func_free);
 110
 111 /* Randomness. */
 112 extern Gc_rc gc_nonce (char *data, size_t datalen);
 113 extern Gc_rc gc_pseudo_random (char *data, size_t datalen);
 114 extern Gc_rc gc_random (char *data, size_t datalen);
 115
 116 /* Ciphers. */
 117 extern Gc_rc gc_cipher_open (Gc_cipher cipher, Gc_cipher_mode mode,
 118                              gc_cipher_handle *outhandle);
 119 extern Gc_rc gc_cipher_setkey (gc_cipher_handle handle,
 120                                size_t keylen, const char *key);
 121 extern Gc_rc gc_cipher_setiv (gc_cipher_handle handle,
 122                               size_t ivlen, const char *iv);
 123 extern Gc_rc gc_cipher_encrypt_inline (gc_cipher_handle handle,
 124                                        size_t len, char *data);
 125 extern Gc_rc gc_cipher_decrypt_inline (gc_cipher_handle handle,
 126                                        size_t len, char *data);
 127 extern Gc_rc gc_cipher_close (gc_cipher_handle handle);
 128
 129 /* Hashes. */
 130
 131 extern Gc_rc gc_hash_open (Gc_hash hash, Gc_hash_mode mode,
 132                            gc_hash_handle *outhandle);
 133 extern Gc_rc gc_hash_clone (gc_hash_handle handle, gc_hash_handle *outhandle);
 134 extern size_t gc_hash_digest_length (Gc_hash hash);
 135 extern void gc_hash_hmac_setkey (gc_hash_handle handle,
 136                                  size_t len, const char *key);
 137 extern void gc_hash_write (gc_hash_handle handle,
 138                            size_t len, const char *data);
 139 extern const char *gc_hash_read (gc_hash_handle handle);
 140 extern void gc_hash_close (gc_hash_handle handle);
 141
 142 /* Compute a hash value over buffer IN of INLEN bytes size using the
 143    algorithm HASH, placing the result in the pre-allocated buffer OUT.
 144    The required size of OUT depends on HASH, and is generally
 145    GC_<HASH>_DIGEST_SIZE.  For example, for GC_MD5 the output buffer
 146    must be 16 bytes.  The return value is 0 (GC_OK) on success, or
 147    another Gc_rc error code. */
 148 extern Gc_rc
 149 gc_hash_buffer (Gc_hash hash, const void *in, size_t inlen, char *out);
 150
 151 /* One-call interface. */
 152 extern Gc_rc gc_md2 (const void *in, size_t inlen, void *resbuf);
 153 extern Gc_rc gc_md4 (const void *in, size_t inlen, void *resbuf);
 154 extern Gc_rc gc_md5 (const void *in, size_t inlen, void *resbuf);
 155 extern Gc_rc gc_sha1 (const void *in, size_t inlen, void *resbuf);
 156 extern Gc_rc gc_hmac_md5 (const void *key, size_t keylen,
 157                           const void *in, size_t inlen, char *resbuf);
 158 extern Gc_rc gc_hmac_sha1 (const void *key, size_t keylen,
 159                            const void *in, size_t inlen, char *resbuf);
 160
 161 /* Derive cryptographic keys from a password P of length PLEN, with
 162    salt S of length SLEN, placing the result in pre-allocated buffer
 163    DK of length DKLEN.  An iteration count is specified in C, where a
 164    larger value means this function take more time (typical iteration
 165    counts are 1000-20000).  This function "stretches" the key to be
 166    exactly dkLen bytes long.  GC_OK is returned on success, otherwise
 167    an Gc_rc error code is returned.  */
 168 extern Gc_rc
 169 gc_pbkdf2_sha1 (const char *P, size_t Plen,
 170                 const char *S, size_t Slen,
 171                 unsigned int c, char *DK, size_t dkLen);
 172
 173 /*
 174   TODO:
 175
 176   From: Simon Josefsson <jas@extundo.com>
 177   Subject: Re: generic crypto
 178   Newsgroups: gmane.comp.lib.gnulib.bugs
 179   Cc: bug-gnulib@gnu.org
 180   Date: Fri, 07 Oct 2005 12:50:57 +0200
 181   Mail-Copies-To: nobody
 182
 183   Paul Eggert <eggert@CS.UCLA.EDU> writes:
 184
 185   > Simon Josefsson <jas@extundo.com> writes:
 186   >
 187   >> * Perhaps the /dev/?random reading should be separated into a separate
 188   >>   module?  It might be useful outside of the gc layer too.
 189   >
 190   > Absolutely.  I've been meaning to do that for months (for a "shuffle"
 191   > program I want to add to coreutils), but hadn't gotten around to it.
 192   > It would have to be generalized a bit.  I'd like to have the file
 193   > descriptor cached, for example.
 194
 195   I'll write a separate module for that part.
 196
 197   I think we should even add a good PRNG that is re-seeded from
 198   /dev/?random frequently.  GnuTLS can need a lot of random data on a
 199   big server, more than /dev/random can supply.  And /dev/urandom might
 200   not be strong enough.  Further, the security of /dev/?random can also
 201   be questionable.
 202
 203   >>   I'm also not sure about the names of those functions, they suggest
 204   >>   a more higher-level API than what is really offered (i.e., the
 205   >>   names "nonce" and "pseudo_random" and "random" imply certain
 206   >>   cryptographic properties).
 207   >
 208   > Could you expand a bit more on that?  What is the relationship between
 209   > nonce/pseudorandom/random and the /dev/ values you are using?
 210
 211   There is none, that is the problem.
 212
 213   Applications generally need different kind of "random" numbers.
 214   Sometimes they just need some random data and doesn't care whether it
 215   is possible for an attacker to compute the string (aka a "nonce").
 216   Sometimes they need data that is very difficult to compute (i.e.,
 217   computing it require inverting SHA1 or similar).  Sometimes they need
 218   data that is not possible to compute, i.e., it wants real entropy
 219   collected over time on the system.  Collecting the last kind of random
 220   data is very expensive, so it must not be used too often.  The second
 221   kind of random data ("pseudo random") is typically generated by
 222   seeding a good PRNG with a couple of hundred bytes of real entropy
 223   from the "real random" data pool.  The "nonce" is usually computed
 224   using the PRNG as well, because PRNGs are usually fast.
 225
 226   Pseudo-random data is typically used for session keys.  Strong random
 227   data is often used to generate long-term keys (e.g., private RSA
 228   keys).
 229
 230   Of course, there are many subtleties.  There are several different
 231   kind of nonce:s.  Sometimes a nonce is just an ever-increasing
 232   integer, starting from 0.  Sometimes it is assumed to be unlikely to
 233   be the same as previous nonces, but without a requirement that the
 234   nonce is possible to guess.  MD5(system clock) would thus suffice, if
 235   it isn't called too often.  You can guess what the next value will be,
 236   but it will always be different.
 237
 238   The problem is that /dev/?random doesn't offer any kind of semantic
 239   guarantees.  But applications need an API that make that promise.
 240
 241   I think we should do this in several steps:
 242
 243   1) Write a module that can read from /dev/?random.
 244
 245   2) Add a module for a known-good PRNG suitable for random number
 246   generation, that can be continuously re-seeded.
 247
 248   3) Add a high-level module that provide various different randomness
 249   functions.  One for nonces, perhaps even different kind of nonces,
 250   one for pseudo random data, and one for strong random data.  It is
 251   not clear whether we can hope to achieve the last one in a portable
 252   way.
 253
 254   Further, it would be useful to allow users to provide their own
 255   entropy source as a file, used to seed the PRNG or initialize the
 256   strong randomness pool.  This is used on embedded platforms that
 257   doesn't have enough interrupts to hope to generate good random data.
 258
 259   > For example, why not use OpenBSD's /dev/arandom?
 260
 261   I don't trust ARC4.  For example, recent cryptographic efforts
 262   indicate that you must throw away the first 512 bytes generated from
 263   the PRNG for it to be secure.  I don't know whether OpenBSD do this.
 264   Further, I recall some eprint paper on RC4 security that didn't
 265   inspire confidence.
 266
 267   While I trust the random devices in OpenBSD more than
 268   Solaris/AIX/HPUX/etc, I think that since we need something better on
 269   Solaris/AIX/HPUX we'd might as well use it on OpenBSD or even Linux
 270   too.
 271
 272   > Here is one thought.  The user could specify a desired quality level
 273   > range, and the implementation then would supply random data that is at
 274   > least as good as the lower bound of the range.  I.e., ihe
 275   > implementation refuses to produce any random data if it can't generate
 276   > data that is at least as good as the lower end of the range.  The
 277   > upper bound of the range is advice from the user not to be any more
 278   > expensive than that, but the implementation can ignore the advice if
 279   > it doesn't have anything cheaper.
 280
 281   I'm not sure this is a good idea.  Users can't really be expected to
 282   understand this.  Further, applications need many different kind of
 283   random data.  Selecting the randomness level for each by the user will
 284   be too complicated.
 285
 286   I think it is better if the application decide, from its cryptographic
 287   requirement, what entropy quality it require, and call the proper API.
 288   Meeting the implied semantic properties should be the job for gnulib.
 289
 290   >> Perhaps gc_dev_random and gc_dev_urandom?
 291   >
 292   > To some extent.  I'd rather insulate the user from the details of
 293   > where the random numbers come from.  On the other hand we need to
 294   > provide a way for applications to specify a file that contains
 295   > random bits, so that people can override the defaults.
 296
 297   Agreed.
 298
 299   This may require some thinking before it is finalized.  Is it ok to
 300   install the GC module as-is meanwhile?  Then I can continue to add the
 301   stuff that GnuTLS need, and then come back to re-working the
 302   randomness module.  That way, we have two different projects that use
 303   the code.  GnuTLS includes the same randomness code that was in GNU
 304   SASL and that is in the current gc module.  I feel much more
 305   comfortable working in small steps at a time, rather then working on
 306   this for a long time in gnulib and only later integrate the stuff in
 307   GnuTLS.
 308
 309   Thanks,
 310   Simon
 311  */
 312
 313 #endif /* GC_H */