nettle.texinfo 156 KB
Newer Older
Niels Möller's avatar
Niels Möller committed
1
2
3
\input texinfo          @c -*-texinfo-*-
@c %**start of header
@setfilename nettle.info
4
@settitle Nettle: a low-level cryptographic library
Niels Möller's avatar
Niels Möller committed
5
@documentencoding UTF-8
6
@footnotestyle separate
Niels Möller's avatar
Niels Möller committed
7
@syncodeindex fn cp
8
@c %**end of header
Niels Möller's avatar
Niels Möller committed
9

10
@set UPDATED-FOR 2.7
Niels Möller's avatar
Niels Möller committed
11
@set AUTHOR Niels Möller
12

13
14
15
@copying
This manual is for the Nettle library (version @value{UPDATED-FOR}), a
low-level cryptographic library.
Niels Möller's avatar
Niels Möller committed
16

17
Originally written 2001 by @value{AUTHOR}, updated 2013.
Niels Möller's avatar
Niels Möller committed
18

19
@quotation
20
21
22
This manual is placed in the public domain. You may freely copy it, in
whole or in part, with or without modification. Attribution is
appreciated, but not required.
23
24
@end quotation
@end copying
Niels Möller's avatar
Niels Möller committed
25

26
27
28
29
30
31
@ifnottex
@macro pmod {m} 
(mod \m\)
@end macro
@end ifnottex

Niels Möller's avatar
Niels Möller committed
32
33
34
35
36
37
@titlepage
@title Nettle Manual
@subtitle For the Nettle Library version @value{UPDATED-FOR}
@author @value{AUTHOR}
@page
@vskip 0pt plus 1filll
38
@insertcopying
Niels Möller's avatar
Niels Möller committed
39
40
@end titlepage

41
42
43
44
45
@dircategory Encryption
@direntry
* Nettle: (nettle).             A low-level cryptographic library.
@end direntry

46
47
@contents

Niels Möller's avatar
Niels Möller committed
48
49
50
@ifnottex
@node     Top, Introduction, (dir), (dir)
@comment  node-name,  next,  previous,  up
51
@top Nettle
Niels Möller's avatar
Niels Möller committed
52

53
54
55
This document describes the Nettle low-level cryptographic library. You
can use the library directly from your C programs, or write or use an
object-oriented wrapper for your favorite language or application.
Niels Möller's avatar
Niels Möller committed
56

57
@insertcopying
Niels Möller's avatar
Niels Möller committed
58
59

@menu
Niels Möller's avatar
Niels Möller committed
60
61
* Introduction::                What is Nettle?
* Copyright::                   Your rights.
62
63
* Conventions::                 General interface conventions.
* Example::                     An example program.
64
* Linking::                     Linking with the libnettle and libhogweed.
Niels Möller's avatar
Niels Möller committed
65
66
67
* Reference::                   All Nettle functions and features.
* Nettle soup::                 For the serious nettle hacker.
* Installation::                How to install Nettle.
68
* Index::                       Function and concept index.
69
70
71
72
73
74
75
76
77
78

@detailmenu
 --- The Detailed Node Listing ---

Reference

* Hash functions::              
* Cipher functions::            
* Cipher modes::                
* Keyed hash functions::        
Simon Josefsson's avatar
Simon Josefsson committed
79
* Key derivation functions::    
80
81
* Public-key algorithms::       
* Randomness::                  
82
* ASCII encoding::              
83
84
85
86
87
88
89
90
91
92
93
94
95
* Miscellaneous functions::     
* Compatibility functions::     

Cipher modes

* CBC::                         
* CTR::                         
* GCM::                         

Public-key algorithms

* RSA::                         The RSA public key algorithm.
* DSA::                         The DSA digital signature algorithm.
96
* Elliptic curves::             Elliptic curves and ECDSA
97
98

@end detailmenu
Niels Möller's avatar
Niels Möller committed
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
@end menu

@end ifnottex

@node Introduction, Copyright, Top, Top
@comment  node-name,  next,  previous,  up
@chapter Introduction

Nettle is a cryptographic library that is designed to fit easily in more
or less any context: In crypto toolkits for object-oriented languages
(C++, Python, Pike, ...), in applications like LSH or GNUPG, or even in
kernel space. In most contexts, you need more than the basic
cryptographic algorithms, you also need some way to keep track of available
algorithms, their properties and variants. You often have some algorithm
selection process, often dictated by a protocol you want to implement.

115
And as the requirements of applications differ in subtle and not so
Niels Möller's avatar
Niels Möller committed
116
117
118
119
120
121
122
123
124
125
subtle ways, an API that fits one application well can be a pain to use
in a different context. And that is why there are so many different
cryptographic libraries around.

Nettle tries to avoid this problem by doing one thing, the low-level
crypto stuff, and providing a @emph{simple} but general interface to it.
In particular, Nettle doesn't do algorithm selection. It doesn't do
memory allocation. It doesn't do any I/O.

The idea is that one can build several application and context specific
Niels Möller's avatar
Niels Möller committed
126
interfaces on top of Nettle, and share the code, test cases, benchmarks,
Niels Möller's avatar
Niels Möller committed
127
128
129
documentation, etc. Examples are the Nettle module for the Pike
language, and LSH, which both use an object-oriented abstraction on top
of the library.
Niels Möller's avatar
Niels Möller committed
130

131
132
133
134
This manual explains how to use the Nettle library. It also tries to
provide some background on the cryptography, and advice on how to best
put it to use.

Niels Möller's avatar
Niels Möller committed
135
136
137
138
@node Copyright, Conventions, Introduction, Top
@comment  node-name,  next,  previous,  up
@chapter Copyright

139
140
141
142
Nettle is distributed under the GNU Lesser General Public License
(LGPL), see the file COPYING.LIB for details. A few of the individual
files are in the public domain. To find the current status of particular
files, you have to read the copyright notices at the top of the files.
Niels Möller's avatar
Niels Möller committed
143

144
145
146
147
148
This manual is in the public domain. You may freely copy it in whole or
in part, e.g., into documentation of programs that build on Nettle.
Attribution, as well as contribution of improvements to the text, is of
course appreciated, but it is not required.

Niels Möller's avatar
Niels Möller committed
149
150
151
152
153
A list of the supported algorithms, their origins and licenses:

@table @emph
@item AES
The implementation of the AES cipher (also known as rijndael) is written
154
155
156
by Rafael Sevilla. Assembler for x86 by Rafael Sevilla and
@value{AUTHOR}, Sparc assembler by @value{AUTHOR}. Released under the
LGPL.
Niels Möller's avatar
Niels Möller committed
157
158
159

@item ARCFOUR
The implementation of the ARCFOUR (also known as RC4) cipher is written
160
by @value{AUTHOR}. Released under the LGPL.
Niels Möller's avatar
Niels Möller committed
161

Niels Möller's avatar
Niels Möller committed
162
163
164
165
166
@item ARCTWO
The implementation of the ARCTWO (also known as RC2) cipher is written
by Nikos Mavroyanopoulos and modified by Werner Koch and Simon
Josefsson. Released under the LGPL.

Niels Möller's avatar
Niels Möller committed
167
168
@item BLOWFISH
The implementation of the BLOWFISH cipher is written by Werner Koch,
169
copyright owned by the Free Software Foundation. Also hacked by Simon
Niels Möller's avatar
Niels Möller committed
170
Josefsson and Niels Möller. Released under the LGPL.
Niels Möller's avatar
Niels Möller committed
171

172
@item CAMELLIA
173
The C implementation is by Nippon Telegraph and Telephone Corporation
174
175
(NTT), heavily modified by @value{AUTHOR}. Assembler for x86 and x86_64
by @value{AUTHOR}. Released under the LGPL.
176

Niels Möller's avatar
Niels Möller committed
177
178
179
180
181
182
183
184
@item CAST128
The implementation of the CAST128 cipher is written by Steve Reid.
Released into the public domain.

@item DES
The implementation of the DES cipher is written by Dana L. How, and
released under the LGPL.

185
186
@item MD2
The implementation of MD2 is written by Andrew Kuchling, and hacked
187
some by Andreas Sigfridsson and @value{AUTHOR}. Python Cryptography
188
189
190
191
192
193
Toolkit license (essentially public domain).

@item MD4
This is almost the same code as for MD5 below, with modifications by
Marcus Comstedt. Released into the public domain.

Niels Möller's avatar
Niels Möller committed
194
195
@item MD5
The implementation of the MD5 message digest is written by Colin Plumb.
196
It has been hacked some more by Andrew Kuchling and @value{AUTHOR}.
Niels Möller's avatar
Niels Möller committed
197
198
Released into the public domain.

199
@item RIPEMD160
200
201
202
203
The implementation of RIPEMD160 message digest is based on the code in
libgcrypt, copyright owned by the Free Software Foundation. Ported to
Nettle by Andres Mejia. Released under the LGPL.

Niels Möller's avatar
Niels Möller committed
204
205
@item SALSA20
The C implementation of SALSA20 is based on D. J. Bernstein's reference
206
207
208
implementation (in the public domain), adapted to Nettle by Simon
Josefsson, and heavily modified by Niels Möller. Assembly for x86_64 by
Niels Möller. Released under the LGPL.
Niels Möller's avatar
Niels Möller committed
209

Simon Josefsson's avatar
Simon Josefsson committed
210
211
212
213
@item PBKDF2
The C implementation of PBKDF2 is based on earlier work for Shishi and
GnuTLS by Simon Josefsson.  Released under the LGPL.

Niels Möller's avatar
Niels Möller committed
214
@item SERPENT
215
The implementation of the SERPENT cipher is based on the code in libgcrypt,
216
copyright owned by the Free Software Foundation. Adapted to Nettle by
Niels Möller's avatar
Niels Möller committed
217
218
Simon Josefsson and heavily modified by Niels Möller. Assembly for
x86_64 by Niels Möller. Released under the LGPL.
Niels Möller's avatar
Niels Möller committed
219
220

@item SHA1
221
222
223
224
The C implementation of the SHA1 message digest is written by Peter
Gutmann, and hacked some more by Andrew Kuchling and @value{AUTHOR}.
Released into the public domain. Assembler for x86 by @value{AUTHOR},
released under the LGPL.
Niels Möller's avatar
Niels Möller committed
225

Niels Möller's avatar
Niels Möller committed
226
@item SHA2
Niels Möller's avatar
Niels Möller committed
227
228
229
Written by @value{AUTHOR}, using Peter Gutmann's SHA1 code as a model. 
Released under the LGPL.

Niels Möller's avatar
Niels Möller committed
230
@item SHA3
231
232
Written by @value{AUTHOR}. Released under the LGPL.

233
234
235
236
237
@item GOSTHASH94
The C implementation of the GOST94 message digest is written by 
Aleksey Kravchenko and was ported from the rhash library by Nikos
Mavrogiannopoulos. It is released under the MIT license.

Niels Möller's avatar
Niels Möller committed
238
239
240
@item TWOFISH
The implementation of the TWOFISH cipher is written by Ruud de Rooij.
Released under the LGPL.
Niels Möller's avatar
Niels Möller committed
241
242
243
244
245
246
247
248

@item RSA
Written by @value{AUTHOR}, released under the LGPL. Uses the GMP library
for bignum operations.

@item DSA
Written by @value{AUTHOR}, released under the LGPL. Uses the GMP library
for bignum operations.
249
250
251
252
253

@item ECDSA
Written by @value{AUTHOR}, released under the LGPL. Uses the GMP library
for bignum operations. Development of Nettle's ECC support was funded by
Internetfonden.
Niels Möller's avatar
Niels Möller committed
254
255
256
257
258
259
260
261
@end table

@node Conventions, Example, Copyright, Top
@comment  node-name,  next,  previous,  up
@chapter Conventions

For each supported algorithm, there is an include file that defines a
@emph{context struct}, a few constants, and declares functions for
262
operating on the context. The context struct encapsulates all information
Niels Möller's avatar
Niels Möller committed
263
264
265
needed by the algorithm, and it can be copied or moved in memory with no
unexpected effects.

266
267
For consistency, functions for different algorithms are very similar,
but there are some differences, for instance reflecting if the key setup
268
or encryption function differ for encryption and decryption, and whether
269
270
271
272
273
or not key setup can fail. There are also differences between algorithms
that don't show in function prototypes, but which the application must
nevertheless be aware of. There is no big difference between the
functions for stream ciphers and for block ciphers, although they should
be used quite differently by the application.
Niels Möller's avatar
Niels Möller committed
274

275
276
277
If your application uses more than one algorithm of the same type, you
should probably create an interface that is tailor-made for your needs,
and then write a few lines of glue code on top of Nettle.
Niels Möller's avatar
Niels Möller committed
278
279
280
281
282
283
284

By convention, for an algorithm named @code{foo}, the struct tag for the
context struct is @code{foo_ctx}, constants and functions uses prefixes
like @code{FOO_BLOCK_SIZE} (a constant) and @code{foo_set_key} (a
function).

In all functions, strings are represented with an explicit length, of
285
type @code{unsigned}, and a pointer of type @code{uint8_t *} or
Niels Möller's avatar
Niels Möller committed
286
287
288
289
@code{const uint8_t *}. For functions that transform one string to
another, the argument order is length, destination pointer and source
pointer. Source and destination areas are of the same length. Source and
destination may be the same, so that you can process strings in place,
290
but they @emph{must not} overlap in any other way.
Niels Möller's avatar
Niels Möller committed
291

292
293
294
Many of the functions lack return value and can never fail. Those
functions which can fail, return one on success and zero on failure.

295
296
@c FIXME: Say something about the name mangling.

297
@node Example, Linking, Conventions, Top
Niels Möller's avatar
Niels Möller committed
298
299
300
@comment  node-name,  next,  previous,  up
@chapter Example

301
A simple example program that reads a file from standard input and
302
writes its SHA1 check-sum on standard output should give the flavor of
303
Nettle.
Niels Möller's avatar
Niels Möller committed
304
305

@example
306
@verbatiminclude sha-example.c
Niels Möller's avatar
Niels Möller committed
307
308
@end example

309
310
311
On a typical Unix system, this program can be compiled and linked with
the command line 
@example
312
gcc sha-example.c -o sha-example -lnettle
313
314
315
316
317
318
319
320
321
322
323
324
@end example

@node Linking, Reference, Example, Top
@comment  node-name,  next,  previous,  up
@chapter Linking

Nettle actually consists of two libraries, @file{libnettle} and
@file{libhogweed}. The @file{libhogweed} library contains those
functions of Nettle that uses bignum operations, and depends on the GMP
library. With this division, linking works the same for both static and
dynamic libraries.

325
326
327
328
329
330
331
If an application uses only the symmetric crypto algorithms of Nettle
(i.e., block ciphers, hash functions, and the like), it's sufficient to
link with @code{-lnettle}. If an application also uses public-key
algorithms, the recommended linker flags are @code{-lhogweed -lnettle
-lgmp}. If the involved libraries are installed as dynamic libraries, it
may be sufficient to link with just @code{-lhogweed}, and the loader
will resolve the dependencies automatically.
332
333

@node Reference, Nettle soup, Linking, Top
Niels Möller's avatar
Niels Möller committed
334
335
336
337
338
339
340
341
@comment  node-name,  next,  previous,  up
@chapter Reference

This chapter describes all the Nettle functions, grouped by family.

@menu
* Hash functions::              
* Cipher functions::            
342
* Cipher modes::                
Niels Möller's avatar
Niels Möller committed
343
* Keyed hash functions::        
Simon Josefsson's avatar
Simon Josefsson committed
344
* Key derivation functions::    
345
346
* Public-key algorithms::       
* Randomness::                  
347
* ASCII encoding::              
Niels Möller's avatar
Niels Möller committed
348
* Miscellaneous functions::     
349
* Compatibility functions::     
Niels Möller's avatar
Niels Möller committed
350
351
352
353
@end menu

@node Hash functions, Cipher functions, Reference, Reference
@comment  node-name,  next,  previous,  up
354

Niels Möller's avatar
Niels Möller committed
355
@section Hash functions
356
@cindex Hash function
Niels Möller's avatar
Niels Möller committed
357
358
359
360
361
362
363
364
365
366
A cryptographic @dfn{hash function} is a function that takes variable
size strings, and maps them to strings of fixed, short, length. There
are naturally lots of collisions, as there are more possible 1MB files
than 20 byte strings. But the function is constructed such that is hard
to find the collisions. More precisely, a cryptographic hash function
@code{H} should have the following properties:

@table @emph

@item One-way
367
@cindex One-way
Niels Möller's avatar
Niels Möller committed
368
369
370
371
Given a hash value @code{H(x)} it is hard to find a string @code{x}
that hashes to that value.

@item Collision-resistant
372
@cindex Collision-resistant
Niels Möller's avatar
Niels Möller committed
373
374
375
376
377
378
It is hard to find two different strings, @code{x} and @code{y}, such
that @code{H(x)} = @code{H(y)}.

@end table

Hash functions are useful as building blocks for digital signatures,
379
message authentication codes, pseudo random generators, association of
380
unique ids to documents, and many other things.
Niels Möller's avatar
Niels Möller committed
381

Niels Möller's avatar
Niels Möller committed
382
383
The most commonly used hash functions are MD5 and SHA1. Unfortunately,
both these fail the collision-resistance requirement; cryptologists have
384
385
386
387
388
389
found ways to construct colliding inputs. The recommended hash functions
for new applications are SHA2 (with main variants SHA256 and SHA512). At
the time of this writing (December 2012), the winner of the NIST SHA3
competition has recently been announced, and the new SHA3 (earlier known
as Keccak) and other top SHA3 candidates may also be reasonable
alternatives.
390

391
392
393
394
395
@menu
* Recommended hash functions::
* Legacy hash functions::
* nettle_hash abstraction::
@end menu
Niels Möller's avatar
Niels Möller committed
396

397
398
399
@node Recommended hash functions, Legacy hash functions,, Hash functions
@comment  node-name,  next,  previous,  up
@subsection Recommended hash functions
Niels Möller's avatar
Niels Möller committed
400

401
402
403
404
405
406
407
408
409
410
The following hash functions have no known weaknesses, and are suitable
for new applications. The SHA2 family of hash functions were specified
by @dfn{NIST}, intended as a replacement for @acronym{SHA1}.

@subsubsection @acronym{SHA256}

SHA256 is a member of the SHA2 family. It outputs hash values of 256
bits, or 32 octets. Nettle defines SHA256 in @file{<nettle/sha2.h>}.

@deftp {Context struct} {struct sha256_ctx}
Niels Möller's avatar
Niels Möller committed
411
412
@end deftp

413
@defvr Constant SHA256_DIGEST_SIZE
Niels Möller's avatar
Niels Möller committed
414
The size of a SHA256 digest, i.e. 32.
Niels Möller's avatar
Niels Möller committed
415
416
@end defvr

417
418
419
@defvr Constant SHA256_DATA_SIZE
The internal block size of SHA256. Useful for some special constructions,
in particular HMAC-SHA256.
Niels Möller's avatar
Niels Möller committed
420
421
@end defvr

422
423
@deftypefun void sha256_init (struct sha256_ctx *@var{ctx})
Initialize the SHA256 state.
Niels Möller's avatar
Niels Möller committed
424
425
@end deftypefun

426
@deftypefun void sha256_update (struct sha256_ctx *@var{ctx}, unsigned @var{length}, const uint8_t *@var{data})
Niels Möller's avatar
Niels Möller committed
427
428
429
Hash some more data.
@end deftypefun

430
@deftypefun void sha256_digest (struct sha256_ctx *@var{ctx}, unsigned @var{length}, uint8_t *@var{digest})
431
432
Performs final processing and extracts the message digest, writing it
to @var{digest}. @var{length} may be smaller than
433
@code{SHA256_DIGEST_SIZE}, in which case only the first @var{length}
434
octets of the digest are written.
Niels Möller's avatar
Niels Möller committed
435

436
This function also resets the context in the same way as
437
@code{sha256_init}.
Niels Möller's avatar
Niels Möller committed
438
439
@end deftypefun

440
441
442
Earlier versions of nettle defined SHA256 in the header file
@file{<nettle/sha.h>}, which is now deprecated, but kept for
compatibility.
Niels Möller's avatar
Niels Möller committed
443

444
@subsubsection @acronym{SHA224}
445

446
447
448
449
SHA224 is a variant of SHA256, with a different initial state, and with
the output truncated to 224 bits, or 28 octets. Nettle defines SHA224 in
@file{<nettle/sha2.h>} (and in @file{<nettle/sha.h>}, for backwards
compatibility).
450

451
@deftp {Context struct} {struct sha224_ctx}
452
453
@end deftp

454
@defvr Constant SHA224_DIGEST_SIZE
Niels Möller's avatar
Niels Möller committed
455
The size of a SHA224 digest, i.e. 28.
456
457
@end defvr

458
459
460
@defvr Constant SHA224_DATA_SIZE
The internal block size of SHA224. Useful for some special constructions,
in particular HMAC-SHA224.
461
462
@end defvr

463
464
@deftypefun void sha224_init (struct sha224_ctx *@var{ctx})
Initialize the SHA224 state.
465
466
@end deftypefun

467
@deftypefun void sha224_update (struct sha224_ctx *@var{ctx}, unsigned @var{length}, const uint8_t *@var{data})
468
469
470
Hash some more data.
@end deftypefun

471
@deftypefun void sha224_digest (struct sha224_ctx *@var{ctx}, unsigned @var{length}, uint8_t *@var{digest})
472
473
Performs final processing and extracts the message digest, writing it
to @var{digest}. @var{length} may be smaller than
474
@code{SHA224_DIGEST_SIZE}, in which case only the first @var{length}
475
476
477
octets of the digest are written.

This function also resets the context in the same way as
478
@code{sha224_init}.
479
480
@end deftypefun

481
@subsubsection @acronym{SHA512}
482

483
484
485
486
487
488
SHA512 is a larger sibling to SHA256, with a very similar structure but
with both the output and the internal variables of twice the size. The
internal variables are 64 bits rather than 32, making it significantly
slower on 32-bit computers. It outputs hash values of 512 bits, or 64
octets. Nettle defines SHA512 in @file{<nettle/sha2.h>} (and in
@file{<nettle/sha.h>}, for backwards compatibility).
489

490
@deftp {Context struct} {struct sha512_ctx}
491
492
@end deftp

493
@defvr Constant SHA512_DIGEST_SIZE
Niels Möller's avatar
Niels Möller committed
494
The size of a SHA512 digest, i.e. 64.
495
496
@end defvr

497
498
499
@defvr Constant SHA512_DATA_SIZE
The internal block size of SHA512. Useful for some special constructions,
in particular HMAC-SHA512.
500
501
@end defvr

502
503
@deftypefun void sha512_init (struct sha512_ctx *@var{ctx})
Initialize the SHA512 state.
504
505
@end deftypefun

506
@deftypefun void sha512_update (struct sha512_ctx *@var{ctx}, unsigned @var{length}, const uint8_t *@var{data})
507
508
509
Hash some more data.
@end deftypefun

510
@deftypefun void sha512_digest (struct sha512_ctx *@var{ctx}, unsigned @var{length}, uint8_t *@var{digest})
511
512
Performs final processing and extracts the message digest, writing it
to @var{digest}. @var{length} may be smaller than
513
@code{SHA512_DIGEST_SIZE}, in which case only the first @var{length}
514
515
516
octets of the digest are written.

This function also resets the context in the same way as
517
@code{sha512_init}.
518
519
@end deftypefun

520
@subsubsection @acronym{SHA384}
521

522
523
524
525
SHA384 is a variant of SHA512, with a different initial state, and with
the output truncated to 384 bits, or 48 octets. Nettle defines SHA384 in
@file{<nettle/sha2.h>} (and in @file{<nettle/sha.h>}, for backwards
compatibility).
526

527
@deftp {Context struct} {struct sha384_ctx}
528
529
@end deftp

530
@defvr Constant SHA384_DIGEST_SIZE
Niels Möller's avatar
Niels Möller committed
531
The size of a SHA384 digest, i.e. 48.
532
533
@end defvr

534
535
536
@defvr Constant SHA384_DATA_SIZE
The internal block size of SHA384. Useful for some special constructions,
in particular HMAC-SHA384.
537
538
@end defvr

539
540
@deftypefun void sha384_init (struct sha384_ctx *@var{ctx})
Initialize the SHA384 state.
541
542
@end deftypefun

543
@deftypefun void sha384_update (struct sha384_ctx *@var{ctx}, unsigned @var{length}, const uint8_t *@var{data})
544
545
546
Hash some more data.
@end deftypefun

547
@deftypefun void sha384_digest (struct sha384_ctx *@var{ctx}, unsigned @var{length}, uint8_t *@var{digest})
548
549
Performs final processing and extracts the message digest, writing it
to @var{digest}. @var{length} may be smaller than
550
@code{SHA384_DIGEST_SIZE}, in which case only the first @var{length}
551
552
553
octets of the digest are written.

This function also resets the context in the same way as
554
@code{sha384_init}.
555
556
@end deftypefun

557
@subsubsection @acronym{SHA3-224}
Niels Möller's avatar
Niels Möller committed
558

559
The SHA3 hash functions were specified by NIST in response to weaknesses
560
561
562
563
564
565
566
in SHA1, and doubts about SHA2 hash functions which structurally are
very similar to SHA1. The standard is a result of a competition, where
the winner, also known as Keccak, was designed by Guido Bertoni, Joan
Daemen, Michaël Peeters and Gilles Van Assche. It is structurally very
different from all widely used earlier hash functions. Like SHA2, there
are several variants, with output sizes of 224, 256, 384 and 512 bits
(28, 32, 48 and 64 octets, respectively).
Niels Möller's avatar
Niels Möller committed
567

568
Nettle defines SHA3-224 in @file{<nettle/sha3.h>}.
Niels Möller's avatar
Niels Möller committed
569

570
@deftp {Context struct} {struct sha3_224_ctx}
Niels Möller's avatar
Niels Möller committed
571
572
@end deftp

573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
@defvr Constant SHA3_224_DIGEST_SIZE
The size of a SHA3_224 digest, i.e., 28.
@end defvr

@defvr Constant SHA3_224_DATA_SIZE
The internal block size of SHA3_224.
@end defvr

@deftypefun void sha3_224_init (struct sha3_224_ctx *@var{ctx})
Initialize the SHA3-224 state.
@end deftypefun

@deftypefun void sha3_224_update (struct sha3_224_ctx *@var{ctx}, unsigned @var{length}, const uint8_t *@var{data})
Hash some more data.
@end deftypefun

@deftypefun void sha3_224_digest (struct sha3_224_ctx *@var{ctx}, unsigned @var{length}, uint8_t *@var{digest})
Performs final processing and extracts the message digest, writing it
to @var{digest}. @var{length} may be smaller than
@code{SHA3_224_DIGEST_SIZE}, in which case only the first @var{length}
octets of the digest are written.

This function also resets the context.
@end deftypefun

@subsubsection @acronym{SHA3-256}

This is SHA3 with 256-bit output size, and possibly the most useful
of the SHA3 hash functions.

Nettle defines SHA3-256 in @file{<nettle/sha3.h>}.

@deftp {Context struct} {struct sha3_256_ctx}
@end deftp

608
@defvr Constant SHA3_256_DIGEST_SIZE
609
The size of a SHA3_256 digest, i.e., 32.
Niels Möller's avatar
Niels Möller committed
610
611
@end defvr

612
613
@defvr Constant SHA3_256_DATA_SIZE
The internal block size of SHA3_256.
Niels Möller's avatar
Niels Möller committed
614
615
@end defvr

616
617
@deftypefun void sha3_256_init (struct sha3_256_ctx *@var{ctx})
Initialize the SHA3-256 state.
Niels Möller's avatar
Niels Möller committed
618
619
@end deftypefun

620
@deftypefun void sha3_256_update (struct sha3_256_ctx *@var{ctx}, unsigned @var{length}, const uint8_t *@var{data})
Niels Möller's avatar
Niels Möller committed
621
622
623
Hash some more data.
@end deftypefun

624
@deftypefun void sha3_256_digest (struct sha3_256_ctx *@var{ctx}, unsigned @var{length}, uint8_t *@var{digest})
625
626
Performs final processing and extracts the message digest, writing it
to @var{digest}. @var{length} may be smaller than
627
@code{SHA3_256_DIGEST_SIZE}, in which case only the first @var{length}
628
629
octets of the digest are written.

630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
This function also resets the context.
@end deftypefun

@subsubsection @acronym{SHA3-384}

This is SHA3 with 384-bit output size.

Nettle defines SHA3-384 in @file{<nettle/sha3.h>}.

@deftp {Context struct} {struct sha3_384_ctx}
@end deftp

@defvr Constant SHA3_384_DIGEST_SIZE
The size of a SHA3_384 digest, i.e., 48.
@end defvr

@defvr Constant SHA3_384_DATA_SIZE
The internal block size of SHA3_384.
@end defvr

@deftypefun void sha3_384_init (struct sha3_384_ctx *@var{ctx})
Initialize the SHA3-384 state.
@end deftypefun

@deftypefun void sha3_384_update (struct sha3_384_ctx *@var{ctx}, unsigned @var{length}, const uint8_t *@var{data})
Hash some more data.
@end deftypefun

@deftypefun void sha3_384_digest (struct sha3_384_ctx *@var{ctx}, unsigned @var{length}, uint8_t *@var{digest})
Performs final processing and extracts the message digest, writing it
to @var{digest}. @var{length} may be smaller than
@code{SHA3_384_DIGEST_SIZE}, in which case only the first @var{length}
octets of the digest are written.

This function also resets the context.
@end deftypefun

@subsubsection @acronym{SHA3-512}

This is SHA3 with 512-bit output size.

Nettle defines SHA3-512 in @file{<nettle/sha3.h>}.

@deftp {Context struct} {struct sha3_512_ctx}
@end deftp

@defvr Constant SHA3_512_DIGEST_SIZE
The size of a SHA3_512 digest, i.e. 64.
@end defvr

@defvr Constant SHA3_512_DATA_SIZE
The internal block size of SHA3_512.
@end defvr

@deftypefun void sha3_512_init (struct sha3_512_ctx *@var{ctx})
Initialize the SHA3-512 state.
@end deftypefun

@deftypefun void sha3_512_update (struct sha3_512_ctx *@var{ctx}, unsigned @var{length}, const uint8_t *@var{data})
Hash some more data.
@end deftypefun

@deftypefun void sha3_512_digest (struct sha3_512_ctx *@var{ctx}, unsigned @var{length}, uint8_t *@var{digest})
Performs final processing and extracts the message digest, writing it
to @var{digest}. @var{length} may be smaller than
@code{SHA3_512_DIGEST_SIZE}, in which case only the first @var{length}
octets of the digest are written.

This function also resets the context.
Niels Möller's avatar
Niels Möller committed
699
700
@end deftypefun

701
702
703
@node Legacy hash functions, nettle_hash abstraction, Recommended hash functions, Hash functions
@comment  node-name,  next,  previous,  up
@subsection Legacy hash functions
704

705
706
707
708
709
710
711
712
713
The hash functions in this section all have some known weaknesses, and
should be avoided for new applications. These hash functions are mainly
useful for compatibility with old applications and protocols. Some are
still considered safe as building blocks for particular constructions,
e.g., there seems to be no known attacks against HMAC-SHA1 or even
HMAC-MD5. In some important cases, use of a ``legacy'' hash function
does not in itself make the application insecure; if a known weakness is
relevant depends on how the hash function is used, and on the threat
model.
714

715
@subsubsection @acronym{MD5}
716

717
718
719
720
721
MD5 is a message digest function constructed by Ronald Rivest, and
described in @cite{RFC 1321}. It outputs message digests of 128 bits, or
16 octets. Nettle defines MD5 in @file{<nettle/md5.h>}.

@deftp {Context struct} {struct md5_ctx}
722
723
@end deftp

724
725
@defvr Constant MD5_DIGEST_SIZE
The size of an MD5 digest, i.e. 16.
726
727
@end defvr

728
729
730
@defvr Constant MD5_DATA_SIZE
The internal block size of MD5. Useful for some special constructions,
in particular HMAC-MD5.
731
732
@end defvr

733
734
@deftypefun void md5_init (struct md5_ctx *@var{ctx})
Initialize the MD5 state.
735
736
@end deftypefun

737
@deftypefun void md5_update (struct md5_ctx *@var{ctx}, unsigned @var{length}, const uint8_t *@var{data})
738
739
740
Hash some more data.
@end deftypefun

741
@deftypefun void md5_digest (struct md5_ctx *@var{ctx}, unsigned @var{length}, uint8_t *@var{digest})
742
743
Performs final processing and extracts the message digest, writing it
to @var{digest}. @var{length} may be smaller than
744
@code{MD5_DIGEST_SIZE}, in which case only the first @var{length}
745
octets of the digest are written.
Niels Möller's avatar
Niels Möller committed
746

747
This function also resets the context in the same way as
748
@code{md5_init}.
Niels Möller's avatar
Niels Möller committed
749
750
@end deftypefun

751
752
753
754
755
The normal way to use MD5 is to call the functions in order: First
@code{md5_init}, then @code{md5_update} zero or more times, and finally
@code{md5_digest}. After @code{md5_digest}, the context is reset to
its initial state, so you can start over calling @code{md5_update} to
hash new data.
756

757
To start over, you can call @code{md5_init} at any time.
758

759
@subsubsection @acronym{MD2}
760

761
762
763
764
765
MD2 is another hash function of Ronald Rivest's, described in
@cite{RFC 1319}. It outputs message digests of 128 bits, or 16 octets.
Nettle defines MD2 in @file{<nettle/md2.h>}.

@deftp {Context struct} {struct md2_ctx}
766
767
@end deftp

768
769
@defvr Constant MD2_DIGEST_SIZE
The size of an MD2 digest, i.e. 16.
770
771
@end defvr

772
773
@defvr Constant MD2_DATA_SIZE
The internal block size of MD2.
774
775
@end defvr

776
777
@deftypefun void md2_init (struct md2_ctx *@var{ctx})
Initialize the MD2 state.
778
779
@end deftypefun

780
@deftypefun void md2_update (struct md2_ctx *@var{ctx}, unsigned @var{length}, const uint8_t *@var{data})
781
782
783
Hash some more data.
@end deftypefun

784
@deftypefun void md2_digest (struct md2_ctx *@var{ctx}, unsigned @var{length}, uint8_t *@var{digest})
785
786
Performs final processing and extracts the message digest, writing it
to @var{digest}. @var{length} may be smaller than
787
@code{MD2_DIGEST_SIZE}, in which case only the first @var{length}
788
789
790
octets of the digest are written.

This function also resets the context in the same way as
791
@code{md2_init}.
792
793
@end deftypefun

794
@subsubsection @acronym{MD4}
795

796
797
798
799
800
MD4 is a predecessor of MD5, described in @cite{RFC 1320}. Like MD5, it
is constructed by Ronald Rivest. It outputs message digests of 128 bits,
or 16 octets. Nettle defines MD4 in @file{<nettle/md4.h>}. Use of MD4 is
not recommended, but it is sometimes needed for compatibility with
existing applications and protocols.
801

802
@deftp {Context struct} {struct md4_ctx}
803
804
@end deftp

805
806
@defvr Constant MD4_DIGEST_SIZE
The size of an MD4 digest, i.e. 16.
807
808
@end defvr

809
810
@defvr Constant MD4_DATA_SIZE
The internal block size of MD4.
811
812
@end defvr

813
814
@deftypefun void md4_init (struct md4_ctx *@var{ctx})
Initialize the MD4 state.
815
816
@end deftypefun

817
@deftypefun void md4_update (struct md4_ctx *@var{ctx}, unsigned @var{length}, const uint8_t *@var{data})
818
819
820
Hash some more data.
@end deftypefun

821
@deftypefun void md4_digest (struct md4_ctx *@var{ctx}, unsigned @var{length}, uint8_t *@var{digest})
822
823
Performs final processing and extracts the message digest, writing it
to @var{digest}. @var{length} may be smaller than
824
@code{MD4_DIGEST_SIZE}, in which case only the first @var{length}
825
826
827
octets of the digest are written.

This function also resets the context in the same way as
828
@code{md4_init}.
829
830
@end deftypefun

831
@subsubsection @acronym{RIPEMD160}
832

833
834
835
836
837
RIPEMD160 is a hash function designed by Hans Dobbertin, Antoon
Bosselaers, and Bart Preneel, as a strengthened version of RIPEMD
(which, like MD4 and MD5, fails the collision-resistance requirement).
It produces message digests of 160 bits, or 20 octets. Nettle defined
RIPEMD160 in @file{nettle/ripemd160.h}.
838

839
840
@deftp {Context struct} {struct ripemd160_ctx}
@end deftp
841

842
@defvr Constant RIPEMD160_DIGEST_SIZE
Niels Möller's avatar
Niels Möller committed
843
The size of a RIPEMD160 digest, i.e. 20.
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
@end defvr

@defvr Constant RIPEMD160_DATA_SIZE
The internal block size of RIPEMD160.
@end defvr

@deftypefun void ripemd160_init (struct ripemd160_ctx *@var{ctx})
Initialize the RIPEMD160 state.
@end deftypefun

@deftypefun void ripemd160_update (struct ripemd160_ctx *@var{ctx}, unsigned @var{length}, const uint8_t *@var{data})
Hash some more data.
@end deftypefun

@deftypefun void ripemd160_digest (struct ripemd160_ctx *@var{ctx}, unsigned @var{length}, uint8_t *@var{digest})
Performs final processing and extracts the message digest, writing it
to @var{digest}. @var{length} may be smaller than
@code{RIPEMD160_DIGEST_SIZE}, in which case only the first @var{length}
octets of the digest are written.

This function also resets the context in the same way as
@code{ripemd160_init}.
@end deftypefun

@subsubsection @acronym{SHA1}

SHA1 is a hash function specified by @dfn{NIST} (The U.S. National
Institute for Standards and Technology). It outputs hash values of 160
bits, or 20 octets. Nettle defines SHA1 in @file{<nettle/sha1.h>} (and
in @file{<nettle/sha.h>}, for backwards compatibility).

@deftp {Context struct} {struct sha1_ctx}
876
877
@end deftp

878
@defvr Constant SHA1_DIGEST_SIZE
Niels Möller's avatar
Niels Möller committed
879
The size of a SHA1 digest, i.e. 20.
880
881
@end defvr

882
883
884
@defvr Constant SHA1_DATA_SIZE
The internal block size of SHA1. Useful for some special constructions,
in particular HMAC-SHA1.
885
886
@end defvr

887
888
@deftypefun void sha1_init (struct sha1_ctx *@var{ctx})
Initialize the SHA1 state.
889
890
@end deftypefun

891
@deftypefun void sha1_update (struct sha1_ctx *@var{ctx}, unsigned @var{length}, const uint8_t *@var{data})
892
893
894
Hash some more data.
@end deftypefun

895
@deftypefun void sha1_digest (struct sha1_ctx *@var{ctx}, unsigned @var{length}, uint8_t *@var{digest})
896
897
Performs final processing and extracts the message digest, writing it
to @var{digest}. @var{length} may be smaller than
898
@code{SHA1_DIGEST_SIZE}, in which case only the first @var{length}
899
900
901
octets of the digest are written.

This function also resets the context in the same way as
902
@code{sha1_init}.
903
904
@end deftypefun

905
906

@subsubsection @acronym{GOSTHASH94}
907
908
909
910
911
912
913
914
915
916

The GOST94 or GOST R 34.11-94 hash algorithm is a Soviet-era algorithm 
used in Russian government standards (see @cite{RFC 4357}).
It outputs message digests of 256 bits, or 32 octets.
Nettle defines GOSTHASH94 in @file{<nettle/gosthash94.h>}.

@deftp {Context struct} {struct gosthash94_ctx}
@end deftp

@defvr Constant GOSTHASH94_DIGEST_SIZE
Niels Möller's avatar
Niels Möller committed
917
The size of a GOSTHASH94 digest, i.e. 32.
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
@end defvr

@defvr Constant GOSTHASH94_DATA_SIZE
The internal block size of GOSTHASH94, i.e., 32.
@end defvr

@deftypefun void gosthash94_init (struct gosthash94_ctx *@var{ctx})
Initialize the GOSTHASH94 state.
@end deftypefun

@deftypefun void gosthash94_update (struct gosthash94_ctx *@var{ctx}, unsigned @var{length}, const uint8_t *@var{data})
Hash some more data.
@end deftypefun

@deftypefun void gosthash94_digest (struct gosthash94_ctx *@var{ctx}, unsigned @var{length}, uint8_t *@var{digest})
Performs final processing and extracts the message digest, writing it
to @var{digest}. @var{length} may be smaller than
@code{GOSTHASH94_DIGEST_SIZE}, in which case only the first @var{length}
octets of the digest are written.

This function also resets the context in the same way as
@code{gosthash94_init}.
@end deftypefun

942
943
944
@node nettle_hash abstraction,, Legacy hash functions, Hash functions
@comment  node-name,  next,  previous,  up
@subsection The nettle_hash abstraction
Niels Möller's avatar
Niels Möller committed
945
946
947

Nettle includes a struct including information about the supported hash
functions. It is defined in @file{<nettle/nettle-meta.h>}, and is used
948
949
by Nettle's implementation of @acronym{HMAC} (@pxref{Keyed hash
functions}).
Niels Möller's avatar
Niels Möller committed
950
951
952
953
954

@deftp {Meta struct} @code{struct nettle_hash} name context_size digest_size block_size init update digest
The last three attributes are function pointers, of types
@code{nettle_hash_init_func}, @code{nettle_hash_update_func}, and
@code{nettle_hash_digest_func}. The first argument to these functions is
955
@code{void *} pointer to a context struct, which is of size
Niels Möller's avatar
Niels Möller committed
956
957
958
@code{context_size}. 
@end deftp

959
960
961
@deftypevr {Constant Struct} {struct nettle_hash} nettle_md2
@deftypevrx {Constant Struct} {struct nettle_hash} nettle_md4
@deftypevrx {Constant Struct} {struct nettle_hash} nettle_md5
962
@deftypevrx {Constant Struct} {struct nettle_hash} nettle_ripemd160
963
964
965
966
967
@deftypevrx {Constant Struct} {struct nettle_hash} nettle_sha1
@deftypevrx {Constant Struct} {struct nettle_hash} nettle_sha224
@deftypevrx {Constant Struct} {struct nettle_hash} nettle_sha256
@deftypevrx {Constant Struct} {struct nettle_hash} nettle_sha384
@deftypevrx {Constant Struct} {struct nettle_hash} nettle_sha512
968
@deftypevrx {Constant Struct} {struct nettle_hash} nettle_sha3_256
969
@deftypevrx {Constant Struct} {struct nettle_hash} nettle_gosthash94
Niels Möller's avatar
Niels Möller committed
970
These are all the hash functions that Nettle implements.
971
@end deftypevr
972

973
Nettle also exports a list of all these hashes.
974

975
976
977
@deftypevr {Constant Array} {struct nettle_hash **} nettle_hashes
This list can be used to dynamically enumerate or search the supported
algorithms. NULL-terminated.
Niels Möller's avatar
Niels Möller committed
978
979
@end deftypevr

980
@node Cipher functions, Cipher modes, Hash functions, Reference
Niels Möller's avatar
Niels Möller committed
981
982
@comment  node-name,  next,  previous,  up
@section Cipher functions
983
@cindex Cipher
Niels Möller's avatar
Niels Möller committed
984
985
986
987

A @dfn{cipher} is a function that takes a message or @dfn{plaintext}
and a secret @dfn{key} and transforms it to a @dfn{ciphertext}. Given
only the ciphertext, but not the key, it should be hard to find the
Niels Möller's avatar
Niels Möller committed
988
plaintext. Given matching pairs of plaintext and ciphertext, it should
Niels Möller's avatar
Niels Möller committed
989
990
be hard to find the key.

991
992
993
@cindex Block Cipher
@cindex Stream Cipher

Niels Möller's avatar
Niels Möller committed
994
995
996
997
998
999
1000
1001
There are two main classes of ciphers: Block ciphers and stream ciphers.

A block cipher can process data only in fixed size chunks, called
@dfn{blocks}. Typical block sizes are 8 or 16 octets. To encrypt
arbitrary messages, you usually have to pad it to an integral number of
blocks, split it into blocks, and then process each block. The simplest
way is to process one block at a time, independent of each other. That
mode of operation is called @dfn{ECB}, Electronic Code Book mode.
1002
However, using @acronym{ECB} is usually a bad idea. For a start, plaintext blocks
Niels Möller's avatar
Niels Möller committed
1003
1004
that are equal are transformed to ciphertext blocks that are equal; that
leaks information about the plaintext. Usually you should apply the
1005
1006
1007
1008
cipher is some ``feedback mode'', @dfn{CBC} (Cipher Block Chaining) and
@dfn{CTR} (Counter mode) being two of
of the most popular. See @xref{Cipher modes}, for information on
how to apply @acronym{CBC} and @acronym{CTR} with Nettle.
Niels Möller's avatar
Niels Möller committed
1009

Niels Möller's avatar
Niels Möller committed
1010
A stream cipher can be used for messages of arbitrary length. A typical
Niels Möller's avatar
Niels Möller committed
1011
stream cipher is a keyed pseudo-random generator. To encrypt a plaintext
Niels Möller's avatar
Niels Möller committed
1012
message of @var{n} octets, you key the generator, generate @var{n}
Niels Möller's avatar
Niels Möller committed
1013
octets of pseudo-random data, and XOR it with the plaintext. To decrypt,
Niels Möller's avatar
Niels Möller committed
1014
1015
1016
1017
1018
1019
1020
1021
regenerate the same stream using the key, XOR it to the ciphertext, and
the plaintext is recovered.

@strong{Caution:} The first rule for this kind of cipher is the
same as for a One Time Pad: @emph{never} ever use the same key twice.

A common misconception is that encryption, by itself, implies
authentication. Say that you and a friend share a secret key, and you
Niels Möller's avatar
Niels Möller committed
1022
receive an encrypted message. You apply the key, and get a plaintext
1023
message that makes sense to you. Can you then be sure that it really was
Niels Möller's avatar
Niels Möller committed
1024
your friend that wrote the message you're reading? The answer is no. For
Niels Möller's avatar
Niels Möller committed
1025
1026
1027
1028
example, if you were using a block cipher in ECB mode, an attacker may
pick up the message on its way, and reorder, delete or repeat some of
the blocks. Even if the attacker can't decrypt the message, he can
change it so that you are not reading the same message as your friend
Niels Möller's avatar
Niels Möller committed
1029
1030
1031
1032
wrote. If you are using a block cipher in @acronym{CBC} mode rather than
ECB, or are using a stream cipher, the possibilities for this sort of
attack are different, but the attacker can still make predictable
changes to the message.
Niels Möller's avatar
Niels Möller committed
1033
1034
1035

It is recommended to @emph{always} use an authentication mechanism in
addition to encrypting the messages. Popular choices are Message
1036
1037
Authentication Codes like @acronym{HMAC-SHA1} (@pxref{Keyed hash
functions}), or digital signatures like @acronym{RSA}.
Niels Möller's avatar
Niels Möller committed
1038

1039
Some ciphers have so called ``weak keys'', keys that results in
Niels Möller's avatar
Niels Möller committed
1040
undesirable structure after the key setup processing, and should be
1041
1042
1043
1044
avoided. In Nettle, most key setup functions have no return value, but
for ciphers with weak keys, the return value indicates whether or not
the given key is weak. For good keys, key setup returns 1, and for weak
keys, it returns 0. When possible, avoid algorithms that
Niels Möller's avatar
Niels Möller committed
1045
1046
1047
have weak keys. There are several good ciphers that don't have any weak
keys.

1048
1049
1050
To encrypt a message, you first initialize a cipher context for
encryption or decryption with a particular key. You then use the context
to process plaintext or ciphertext messages. The initialization is known
1051
as @dfn{key setup}. With Nettle, it is recommended to use each
1052
1053
1054
1055
context struct for only one direction, even if some of the ciphers use a
single key setup function that can be used for both encryption and
decryption.

Niels Möller's avatar
Niels Möller committed
1056
@subsection AES
1057
AES is a block cipher, specified by NIST as a replacement for
Niels Möller's avatar
Niels Möller committed
1058
the older DES standard. The standard is the result of a competition
1059
1060
between cipher designers. The winning design, also known as RIJNDAEL,
was constructed by Joan Daemen and Vincent Rijnmen.
Niels Möller's avatar
Niels Möller committed
1061
1062

Like all the AES candidates, the winning design uses a block size of 128
Niels Möller's avatar
Niels Möller committed
1063
bits, or 16 octets, and variable key-size, 128, 192 and 256 bits (16, 24
Niels Möller's avatar
Niels Möller committed
1064
1065
1066
1067
1068
1069
1070
and 32 octets) being the allowed key sizes. It does not have any weak
keys. Nettle defines AES in @file{<nettle/aes.h>}.
 
@deftp {Context struct} {struct aes_ctx}
@end deftp

@defvr Constant AES_BLOCK_SIZE
Niels Möller's avatar
Niels Möller committed
1071
The AES block-size, 16
Niels Möller's avatar
Niels Möller committed
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
@end defvr

@defvr Constant AES_MIN_KEY_SIZE
@end defvr

@defvr Constant AES_MAX_KEY_SIZE
@end defvr

@defvr Constant AES_KEY_SIZE
Default AES key size, 32
@end defvr

1084
1085
1086
@deftypefun void aes_set_encrypt_key (struct aes_ctx *@var{ctx}, unsigned @var{length}, const uint8_t *@var{key})
@deftypefunx void aes_set_decrypt_key (struct aes_ctx *@var{ctx}, unsigned @var{length}, const uint8_t *@var{key})
Initialize the cipher, for encryption or decryption, respectively.
Niels Möller's avatar
Niels Möller committed
1087
1088
@end deftypefun

1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
@deftypefun void aes_invert_key (struct aes_ctx *@var{dst}, const struct aes_ctx *@var{src})
Given a context @var{src} initialized for encryption, initializes the
context struct @var{dst} for decryption, using the same key. If the same
context struct is passed for both @code{src} and @code{dst}, it is
converted in place. Calling @code{aes_set_encrypt_key} and
@code{aes_invert_key} is more efficient than calling
@code{aes_set_encrypt_key} and @code{aes_set_decrypt_key}. This function
is mainly useful for applications which needs to both encrypt and
decrypt using the @emph{same} key.
@end deftypefun

1100
@deftypefun void aes_encrypt (struct aes_ctx *@var{ctx}, unsigned @var{length}, uint8_t *@var{dst}, const uint8_t *@var{src})
Niels Möller's avatar
Niels Möller committed
1101
1102
1103
1104
1105
1106
Encryption function. @var{length} must be an integral multiple of the
block size. If it is more than one block, the data is processed in ECB
mode. @code{src} and @code{dst} may be equal, but they must not overlap
in any other way.
@end deftypefun

1107
@deftypefun void aes_decrypt (struct aes_ctx *@var{ctx}, unsigned @var{length}, uint8_t *@var{dst}, const uint8_t *@var{src})
Niels Möller's avatar
Niels Möller committed
1108
1109
1110
1111
1112
1113
1114
1115
Analogous to @code{aes_encrypt}
@end deftypefun

@subsection ARCFOUR
ARCFOUR is a stream cipher, also known under the trade marked name RC4,
and it is one of the fastest ciphers around. A problem is that the key
setup of ARCFOUR is quite weak, you should never use keys with
structure, keys that are ordinary passwords, or sequences of keys like
1116
``secret:1'', ``secret:2'', @enddots{}. If you have keys that don't look
Niels Möller's avatar
Niels Möller committed
1117
like random bit strings, and you want to use ARCFOUR, always hash the
Niels Möller's avatar
Niels Möller committed
1118
1119
1120
key before feeding it to ARCFOUR. Furthermore, the initial bytes of the
generated key stream leak information about the key; for this reason, it
is recommended to discard the first 512 bytes of the key stream.
Niels Möller's avatar
Niels Möller committed
1121
1122
1123
1124

@example
/* A more robust key setup function for ARCFOUR */
void
1125
1126
arcfour_set_key_hashed(struct arcfour_ctx *ctx,
                       unsigned length, const uint8_t *key)
Niels Möller's avatar
Niels Möller committed
1127
@{
Niels Möller's avatar
Niels Möller committed
1128
1129
1130
  struct sha256_ctx hash;
  uint8_t digest[SHA256_DIGEST_SIZE];
  uint8_t buffer[0x200];
Niels Möller's avatar
Niels Möller committed
1131

Niels Möller's avatar
Niels Möller committed
1132
1133
1134
  sha256_init(&hash);
  sha256_update(&hash, length, key);
  sha256_digest(&hash, SHA256_DIGEST_SIZE, digest);
Niels Möller's avatar
Niels Möller committed
1135

Niels Möller's avatar
Niels Möller committed
1136
1137
  arcfour_set_key(ctx, SHA256_DIGEST_SIZE, digest);
  arcfour_crypt(ctx, sizeof(buffer), buffer, buffer);
Niels Möller's avatar
Niels Möller committed
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
@}
@end example

Nettle defines ARCFOUR in @file{<nettle/arcfour.h>}.

@deftp {Context struct} {struct arcfour_ctx}
@end deftp

@defvr Constant ARCFOUR_MIN_KEY_SIZE
Minimum key size, 1
@end defvr

@defvr Constant ARCFOUR_MAX_KEY_SIZE
Maximum key size, 256
@end defvr

@defvr Constant ARCFOUR_KEY_SIZE
Default ARCFOUR key size, 16
@end defvr

@deftypefun void arcfour_set_key (struct arcfour_ctx *@var{ctx}, unsigned @var{length}, const uint8_t *@var{key})
Initialize the cipher. The same function is used for both encryption and
decryption. 
@end deftypefun

1163
@deftypefun void arcfour_crypt (struct arcfour_ctx *@var{ctx}, unsigned @var{length}, uint8_t *@var{dst}, const uint8_t *@var{src})
Niels Möller's avatar
Niels Möller committed
1164
1165
1166
1167
1168
1169
1170
Encrypt some data. The same function is used for both encryption and
decryption. Unlike the block ciphers, this function modifies the
context, so you can split the data into arbitrary chunks and encrypt
them one after another. The result is the same as if you had called
@code{arcfour_crypt} only once with all the data.
@end deftypefun

Niels Möller's avatar
Niels Möller committed
1171
1172
1173
1174
@subsection ARCTWO
ARCTWO (also known as the trade marked name RC2) is a block cipher
specified in RFC 2268. Nettle also include a variation of the ARCTWO
set key operation that lack one step, to be compatible with the
1175
reverse engineered RC2 cipher description, as described in a Usenet
Niels Möller's avatar
Niels Möller committed
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
post to @code{sci.crypt} by Peter Gutmann.

ARCTWO uses a block size of 64 bits, and variable key-size ranging
from 1 to 128 octets. Besides the key, ARCTWO also has a second
parameter to key setup, the number of effective key bits, @code{ekb}.
This parameter can be used to artificially reduce the key size. In
practice, @code{ekb} is usually set equal to the input key size.
Nettle defines ARCTWO in @file{<nettle/arctwo.h>}.

We do not recommend the use of ARCTWO; the Nettle implementation is
provided primarily for interoperability with existing applications and
standards.

@deftp {Context struct} {struct arctwo_ctx}
@end deftp

@defvr Constant ARCTWO_BLOCK_SIZE
1193
The ARCTWO block-size, 8
Niels Möller's avatar
Niels Möller committed
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
@end defvr

@defvr Constant ARCTWO_MIN_KEY_SIZE
@end defvr

@defvr Constant ARCTWO_MAX_KEY_SIZE
@end defvr

@defvr Constant ARCTWO_KEY_SIZE
Default ARCTWO key size, 8
@end defvr

@deftypefun void arctwo_set_key_ekb (struct arctwo_ctx *@var{ctx}, unsigned @var{length}, const uint8_t *@var{key}, unsigned @var{ekb})
@deftypefunx void arctwo_set_key (struct arctwo_ctx *@var{ctx}, unsigned @var{length}, const uint8_t *@var{key})
@deftypefunx void arctwo_set_key_gutmann (struct arctwo_ctx *@var{ctx}, unsigned @var{length}, const uint8_t *@var{key})
Initialize the cipher. The same function is used for both encryption
and decryption. The first function is the most general one, which lets
you provide both the variable size key, and the desired effective key
size (in bits). The maximum value for @var{ekb} is 1024, and for
convenience, @code{ekb = 0} has the same effect as @code{ekb = 1024}.

@code{arctwo_set_key(ctx, length, key)} is equivalent to
@code{arctwo_set_key_ekb(ctx, length, key, 8*length)}, and
@code{arctwo_set_key_gutmann(ctx, length, key)} is equivalent to
@code{arctwo_set_key_ekb(ctx, length, key, 1024)}
@end deftypefun

1221
@deftypefun void arctwo_encrypt (struct arctwo_ctx *@var{ctx}, unsigned @var{length}, uint8_t *@var{dst}, const uint8_t *@var{src})
Niels Möller's avatar
Niels Möller committed
1222
1223
1224
1225
1226
1227
Encryption function. @var{length} must be an integral multiple of the
block size. If it is more than one block, the data is processed in ECB
mode. @code{src} and @code{dst} may be equal, but they must not
overlap in any other way.
@end deftypefun

1228
@deftypefun void arctwo_decrypt (struct arctwo_ctx *@var{ctx}, unsigned @var{length}, uint8_t *@var{dst}, const uint8_t *@var{src})
Niels Möller's avatar
Niels Möller committed
1229
1230
1231
Analogous to @code{arctwo_encrypt}
@end deftypefun

Niels Möller's avatar
Niels Möller committed
1232
1233
@subsection BLOWFISH

1234
1235
1236
1237
1238
1239
1240
1241
BLOWFISH is a block cipher designed by Bruce Schneier. It uses a block
size of 64 bits (8 octets), and a variable key size, up to 448 bits. It
has some weak keys. Nettle defines BLOWFISH in @file{<nettle/blowfish.h>}.

@deftp {Context struct} {struct blowfish_ctx}
@end deftp

@defvr Constant BLOWFISH_BLOCK_SIZE
Niels Möller's avatar
Niels Möller committed
1242
The BLOWFISH block-size, 8
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
@end defvr

@defvr Constant BLOWFISH_MIN_KEY_SIZE
Minimum BLOWFISH key size, 8
@end defvr

@defvr Constant BLOWFISH_MAX_KEY_SIZE
Maximum BLOWFISH key size, 56
@end defvr

@defvr Constant BLOWFISH_KEY_SIZE
Default BLOWFISH key size, 16
@end defvr

@deftypefun int blowfish_set_key (struct blowfish_ctx *@var{ctx}, unsigned @var{length}, const uint8_t *@var{key})
Initialize the cipher. The same function is used for both encryption and
1259
1260
1261
1262
decryption. Checks for weak keys, returning 1
for good keys and 0 for weak keys. Applications that don't care about
weak keys can ignore the return value.

1263
1264
1265
1266
@code{blowfish_encrypt} or @code{blowfish_decrypt} with a weak key will
crash with an assert violation.
@end deftypefun

1267
@deftypefun void blowfish_encrypt (struct blowfish_ctx *@var{ctx}, unsigned @var{length}, uint8_t *@var{dst}, const uint8_t *@var{src})
1268
1269
1270
1271
1272
1273
Encryption function. @var{length} must be an integral multiple of the
block size. If it is more than one block, the data is processed in ECB
mode. @code{src} and @code{dst} may be equal, but they must not overlap
in any other way.
@end deftypefun

1274
@deftypefun void blowfish_decrypt (struct blowfish_ctx *@var{ctx}, unsigned @var{length}, uint8_t *@var{dst}, const uint8_t *@var{src})
1275
Analogous to @code{blowfish_encrypt}
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
<