summaryrefslogtreecommitdiff
path: root/ext/openssl/ossl_cipher.c
blob: 4e758b6a26827f88f7c4b978ee57f77d203e666c (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
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
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
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
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
/*
 * $Id$
 * 'OpenSSL for Ruby' project
 * Copyright (C) 2001-2002  Michal Rokos <m.rokos@sh.cvut.cz>
 * All rights reserved.
 */
/*
 * This program is licenced under the same licence as Ruby.
 * (See the file 'LICENCE'.)
 */
#include "ossl.h"

#define WrapCipher(obj, klass, ctx) \
    (obj) = Data_Wrap_Struct((klass), 0, ossl_cipher_free, (ctx))
#define MakeCipher(obj, klass, ctx) \
    (obj) = Data_Make_Struct((klass), EVP_CIPHER_CTX, 0, ossl_cipher_free, (ctx))
#define AllocCipher(obj, ctx) \
    memset(DATA_PTR(obj) = (ctx) = ALLOC(EVP_CIPHER_CTX), 0, sizeof(EVP_CIPHER_CTX))
#define GetCipherInit(obj, ctx) do { \
    Data_Get_Struct((obj), EVP_CIPHER_CTX, (ctx)); \
} while (0)
#define GetCipher(obj, ctx) do { \
    GetCipherInit((obj), (ctx)); \
    if (!(ctx)) { \
	ossl_raise(rb_eRuntimeError, "Cipher not inititalized!"); \
    } \
} while (0)
#define SafeGetCipher(obj, ctx) do { \
    OSSL_Check_Kind((obj), cCipher); \
    GetCipher((obj), (ctx)); \
} while (0)

/*
 * Classes
 */
VALUE cCipher;
VALUE eCipherError;

static VALUE ossl_cipher_alloc(VALUE klass);

/*
 * PUBLIC
 */
const EVP_CIPHER *
GetCipherPtr(VALUE obj)
{
    EVP_CIPHER_CTX *ctx;

    SafeGetCipher(obj, ctx);

    return EVP_CIPHER_CTX_cipher(ctx);
}

VALUE
ossl_cipher_new(const EVP_CIPHER *cipher)
{
    VALUE ret;
    EVP_CIPHER_CTX *ctx;

    ret = ossl_cipher_alloc(cCipher);
    AllocCipher(ret, ctx);
    EVP_CIPHER_CTX_init(ctx);
    if (EVP_CipherInit_ex(ctx, cipher, NULL, NULL, NULL, -1) != 1)
	ossl_raise(eCipherError, NULL);

    return ret;
}

/*
 * PRIVATE
 */
static void
ossl_cipher_free(EVP_CIPHER_CTX *ctx)
{
    if (ctx) {
	EVP_CIPHER_CTX_cleanup(ctx);
	ruby_xfree(ctx);
    }
}

static VALUE
ossl_cipher_alloc(VALUE klass)
{
    VALUE obj;

    WrapCipher(obj, klass, 0);

    return obj;
}

/*
 *  call-seq:
 *     Cipher.new(string) -> cipher
 *
 *  The string must contain a valid cipher name like "AES-128-CBC" or "3DES".
 *
 *  A list of cipher names is available by calling OpenSSL::Cipher.ciphers.
 */
static VALUE
ossl_cipher_initialize(VALUE self, VALUE str)
{
    EVP_CIPHER_CTX *ctx;
    const EVP_CIPHER *cipher;
    char *name;
    unsigned char key[EVP_MAX_KEY_LENGTH];

    name = StringValuePtr(str);
    GetCipherInit(self, ctx);
    if (ctx) {
	ossl_raise(rb_eRuntimeError, "Cipher already inititalized!");
    }
    AllocCipher(self, ctx);
    EVP_CIPHER_CTX_init(ctx);
    if (!(cipher = EVP_get_cipherbyname(name))) {
	ossl_raise(rb_eRuntimeError, "unsupported cipher algorithm (%s)", name);
    }
    /*
     * The EVP which has EVP_CIPH_RAND_KEY flag (such as DES3) allows
     * uninitialized key, but other EVPs (such as AES) does not allow it.
     * Calling EVP_CipherUpdate() without initializing key causes SEGV so we
     * set the data filled with "\0" as the key by default.
     */
    memset(key, 0, EVP_MAX_KEY_LENGTH);
    if (EVP_CipherInit_ex(ctx, cipher, NULL, key, NULL, -1) != 1)
	ossl_raise(eCipherError, NULL);

    return self;
}

static VALUE
ossl_cipher_copy(VALUE self, VALUE other)
{
    EVP_CIPHER_CTX *ctx1, *ctx2;

    rb_check_frozen(self);
    if (self == other) return self;

    GetCipherInit(self, ctx1);
    if (!ctx1) {
	AllocCipher(self, ctx1);
    }
    SafeGetCipher(other, ctx2);
    if (EVP_CIPHER_CTX_copy(ctx1, ctx2) != 1)
	ossl_raise(eCipherError, NULL);

    return self;
}

#ifdef HAVE_OBJ_NAME_DO_ALL_SORTED
static void*
add_cipher_name_to_ary(const OBJ_NAME *name, VALUE ary)
{
    rb_ary_push(ary, rb_str_new2(name->name));
    return NULL;
}
#endif

#ifdef HAVE_OBJ_NAME_DO_ALL_SORTED
/*
 *  call-seq:
 *     Cipher.ciphers -> array[string...]
 *
 *  Returns the names of all available ciphers in an array.
 */
static VALUE
ossl_s_ciphers(VALUE self)
{
    VALUE ary;

    ary = rb_ary_new();
    OBJ_NAME_do_all_sorted(OBJ_NAME_TYPE_CIPHER_METH,
                    (void(*)(const OBJ_NAME*,void*))add_cipher_name_to_ary,
                    (void*)ary);

    return ary;
}
#else
#define ossl_s_ciphers rb_f_notimplement
#endif

/*
 *  call-seq:
 *     cipher.reset -> self
 *
 *  Fully resets the internal state of the Cipher. By using this, the same
 *  Cipher instance may be used several times for en- or decryption tasks.
 *
 *  Internally calls EVP_CipherInit_ex(ctx, NULL, NULL, NULL, NULL, -1).
 */
static VALUE
ossl_cipher_reset(VALUE self)
{
    EVP_CIPHER_CTX *ctx;

    GetCipher(self, ctx);
    if (EVP_CipherInit_ex(ctx, NULL, NULL, NULL, NULL, -1) != 1)
	ossl_raise(eCipherError, NULL);

    return self;
}

static VALUE
ossl_cipher_init(int argc, VALUE *argv, VALUE self, int mode)
{
    EVP_CIPHER_CTX *ctx;
    unsigned char key[EVP_MAX_KEY_LENGTH], *p_key = NULL;
    unsigned char iv[EVP_MAX_IV_LENGTH], *p_iv = NULL;
    VALUE pass, init_v;

    if(rb_scan_args(argc, argv, "02", &pass, &init_v) > 0){
	/*
	 * oops. this code mistakes salt for IV.
	 * We deprecated the arguments for this method, but we decided
	 * keeping this behaviour for backward compatibility.
	 */
	const char *cname  = rb_class2name(rb_obj_class(self));
	rb_warn("arguments for %s#encrypt and %s#decrypt were deprecated; "
                "use %s#pkcs5_keyivgen to derive key and IV",
                cname, cname, cname);
	StringValue(pass);
	GetCipher(self, ctx);
	if (NIL_P(init_v)) memcpy(iv, "OpenSSL for Ruby rulez!", sizeof(iv));
	else{
	    StringValue(init_v);
	    if (EVP_MAX_IV_LENGTH > RSTRING_LEN(init_v)) {
		memset(iv, 0, EVP_MAX_IV_LENGTH);
		memcpy(iv, RSTRING_PTR(init_v), RSTRING_LEN(init_v));
	    }
	    else memcpy(iv, RSTRING_PTR(init_v), sizeof(iv));
	}
	EVP_BytesToKey(EVP_CIPHER_CTX_cipher(ctx), EVP_md5(), iv,
		       (unsigned char *)RSTRING_PTR(pass), RSTRING_LENINT(pass), 1, key, NULL);
	p_key = key;
	p_iv = iv;
    }
    else {
	GetCipher(self, ctx);
    }
    if (EVP_CipherInit_ex(ctx, NULL, NULL, p_key, p_iv, mode) != 1) {
	ossl_raise(eCipherError, NULL);
    }

    return self;
}

/*
 *  call-seq:
 *     cipher.encrypt -> self
 *
 *  Initializes the Cipher for encryption.
 *
 *  Make sure to call Cipher#encrypt or Cipher#decrypt before using any of the
 *  following methods:
 *  * [key=, iv=, random_key, random_iv, pkcs5_keyivgen]
 *
 *  Internally calls EVP_CipherInit_ex(ctx, NULL, NULL, NULL, NULL, 1).
 */
static VALUE
ossl_cipher_encrypt(int argc, VALUE *argv, VALUE self)
{
    return ossl_cipher_init(argc, argv, self, 1);
}

/*
 *  call-seq:
 *     cipher.decrypt -> self
 *
 *  Initializes the Cipher for decryption.
 *
 *  Make sure to call Cipher#encrypt or Cipher#decrypt before using any of the
 *  following methods:
 *  * [key=, iv=, random_key, random_iv, pkcs5_keyivgen]
 *
 *  Internally calls EVP_CipherInit_ex(ctx, NULL, NULL, NULL, NULL, 0).
 */
static VALUE
ossl_cipher_decrypt(int argc, VALUE *argv, VALUE self)
{
    return ossl_cipher_init(argc, argv, self, 0);
}

/*
 *  call-seq:
 *     cipher.pkcs5_keyivgen(pass [, salt [, iterations [, digest]]] ) -> nil
 *
 *  Generates and sets the key/IV based on a password.
 *
 *  WARNING: This method is only PKCS5 v1.5 compliant when using RC2, RC4-40,
 *  or DES with MD5 or SHA1. Using anything else (like AES) will generate the
 *  key/iv using an OpenSSL specific method. This method is deprecated and
 *  should no longer be used. Use a PKCS5 v2 key generation method from
 *  OpenSSL::PKCS5 instead.
 *
 *  === Parameters
 *  +salt+ must be an 8 byte string if provided.
 *  +iterations+ is a integer with a default of 2048.
 *  +digest+ is a Digest object that defaults to 'MD5'
 *
 *  A minimum of 1000 iterations is recommended.
 *
 */
static VALUE
ossl_cipher_pkcs5_keyivgen(int argc, VALUE *argv, VALUE self)
{
    EVP_CIPHER_CTX *ctx;
    const EVP_MD *digest;
    VALUE vpass, vsalt, viter, vdigest;
    unsigned char key[EVP_MAX_KEY_LENGTH], iv[EVP_MAX_IV_LENGTH], *salt = NULL;
    int iter;

    rb_scan_args(argc, argv, "13", &vpass, &vsalt, &viter, &vdigest);
    StringValue(vpass);
    if(!NIL_P(vsalt)){
	StringValue(vsalt);
	if(RSTRING_LEN(vsalt) != PKCS5_SALT_LEN)
	    ossl_raise(eCipherError, "salt must be an 8-octet string");
	salt = (unsigned char *)RSTRING_PTR(vsalt);
    }
    iter = NIL_P(viter) ? 2048 : NUM2INT(viter);
    digest = NIL_P(vdigest) ? EVP_md5() : GetDigestPtr(vdigest);
    GetCipher(self, ctx);
    EVP_BytesToKey(EVP_CIPHER_CTX_cipher(ctx), digest, salt,
		   (unsigned char *)RSTRING_PTR(vpass), RSTRING_LENINT(vpass), iter, key, iv);
    if (EVP_CipherInit_ex(ctx, NULL, NULL, key, iv, -1) != 1)
	ossl_raise(eCipherError, NULL);
    OPENSSL_cleanse(key, sizeof key);
    OPENSSL_cleanse(iv, sizeof iv);

    return Qnil;
}


/*
 *  call-seq:
 *     cipher.update(data [, buffer]) -> string or buffer
 *
 *  Encrypts data in a streaming fashion. Hand consecutive blocks of data
 *  to the +update+ method in order to encrypt it. Returns the encrypted
 *  data chunk. When done, the output of Cipher#final should be additionally
 *  added to the result. 
 *
 *  === Parameters
 *  +data+ is a nonempty string.
 *  +buffer+ is an optional string to store the result.
 */
static VALUE
ossl_cipher_update(int argc, VALUE *argv, VALUE self)
{
    EVP_CIPHER_CTX *ctx;
    unsigned char *in;
    int in_len, out_len;
    VALUE data, str;

    rb_scan_args(argc, argv, "11", &data, &str);

    StringValue(data);
    in = (unsigned char *)RSTRING_PTR(data);
    if ((in_len = RSTRING_LENINT(data)) == 0)
        ossl_raise(rb_eArgError, "data must not be empty");
    GetCipher(self, ctx);
    out_len = in_len+EVP_CIPHER_CTX_block_size(ctx);

    if (NIL_P(str)) {
        str = rb_str_new(0, out_len);
    } else {
        StringValue(str);
        rb_str_resize(str, out_len);
    }

    if (!EVP_CipherUpdate(ctx, (unsigned char *)RSTRING_PTR(str), &out_len, in, in_len))
	ossl_raise(eCipherError, NULL);
    assert(out_len < RSTRING_LEN(str));
    rb_str_set_len(str, out_len);

    return str;
}

/*
 *  call-seq:
 *     cipher.final -> string
 *
 *  Returns the remaining data held in the cipher object.  Further calls to
 *  Cipher#update or Cipher#final will return garbage.
 *
 *  See EVP_CipherFinal_ex for further information.
 */
static VALUE
ossl_cipher_final(VALUE self)
{
    EVP_CIPHER_CTX *ctx;
    int out_len;
    VALUE str;

    GetCipher(self, ctx);
    str = rb_str_new(0, EVP_CIPHER_CTX_block_size(ctx));
    if (!EVP_CipherFinal_ex(ctx, (unsigned char *)RSTRING_PTR(str), &out_len))
	ossl_raise(eCipherError, NULL);
    assert(out_len <= RSTRING_LEN(str));
    rb_str_set_len(str, out_len);

    return str;
}

/*
 *  call-seq:
 *     cipher.name -> string
 *
 *  Returns the name of the cipher which may differ slightly from the original
 *  name provided.
 */
static VALUE
ossl_cipher_name(VALUE self)
{
    EVP_CIPHER_CTX *ctx;

    GetCipher(self, ctx);

    return rb_str_new2(EVP_CIPHER_name(EVP_CIPHER_CTX_cipher(ctx)));
}

/*
 *  call-seq:
 *     cipher.key = string -> string
 *
 *  Sets the cipher key. To generate a key, you should either use a secure
 *  random byte string or, if the key is to be derived from a password, you
 *  should rely on PBKDF2 functionality provided by OpenSSL::PKCS5. To
 *  generate a secure random-based key, Cipher#random_key may be used.
 *
 *  Only call this method after calling Cipher#encrypt or Cipher#decrypt.
 */
static VALUE
ossl_cipher_set_key(VALUE self, VALUE key)
{
    EVP_CIPHER_CTX *ctx;

    StringValue(key);
    GetCipher(self, ctx);

    if (RSTRING_LEN(key) < EVP_CIPHER_CTX_key_length(ctx))
        ossl_raise(eCipherError, "key length too short");

    if (EVP_CipherInit_ex(ctx, NULL, NULL, (unsigned char *)RSTRING_PTR(key), NULL, -1) != 1)
        ossl_raise(eCipherError, NULL);

    return key;
}

/*
 *  call-seq:
 *     cipher.iv = string -> string
 *
 *  Sets the cipher IV. Please note that since you should never be using ECB
 *  mode, an IV is always explicitly required and should be set prior to
 *  encryption. The IV itself can be safely transmitted in public, but it
 *  should be unpredictable to prevent certain kinds of attacks. You may use
 *  Cipher#random_iv to create a secure random IV.
 *
 *  Only call this method after calling Cipher#encrypt or Cipher#decrypt.
 *
 *  If not explicitly set, the OpenSSL default of an all-zeroes ("\\0") IV is
 *  used.
 */
static VALUE
ossl_cipher_set_iv(VALUE self, VALUE iv)
{
    EVP_CIPHER_CTX *ctx;

    StringValue(iv);
    GetCipher(self, ctx);

    if (RSTRING_LEN(iv) < EVP_CIPHER_CTX_iv_length(ctx))
        ossl_raise(eCipherError, "iv length too short");

    if (EVP_CipherInit_ex(ctx, NULL, NULL, NULL, (unsigned char *)RSTRING_PTR(iv), -1) != 1)
	ossl_raise(eCipherError, NULL);

    return iv;
}


/*
 *  call-seq:
 *     cipher.key_len = integer -> integer
 *
 *  Sets the key length of the cipher.  If the cipher is a fixed length cipher
 *  then attempting to set the key length to any value other than the fixed
 *  value is an error.
 *
 *  Under normal circumstances you do not need to call this method (and probably shouldn't).
 *
 *  See EVP_CIPHER_CTX_set_key_length for further information.
 */
static VALUE
ossl_cipher_set_key_length(VALUE self, VALUE key_length)
{
    int len = NUM2INT(key_length);
    EVP_CIPHER_CTX *ctx;

    GetCipher(self, ctx);
    if (EVP_CIPHER_CTX_set_key_length(ctx, len) != 1)
        ossl_raise(eCipherError, NULL);

    return key_length;
}

#if defined(HAVE_EVP_CIPHER_CTX_SET_PADDING)
/*
 *  call-seq:
 *     cipher.padding = integer -> integer
 *
 *  Enables or disables padding. By default encryption operations are padded using standard block padding and the
 *  padding is checked and removed when decrypting. If the pad parameter is zero then no padding is performed, the
 *  total amount of data encrypted or decrypted must then be a multiple of the block size or an error will occur.
 *
 *  See EVP_CIPHER_CTX_set_padding for further information.
 */
static VALUE
ossl_cipher_set_padding(VALUE self, VALUE padding)
{
    EVP_CIPHER_CTX *ctx;
    int pad = NUM2INT(padding);

    GetCipher(self, ctx);
    if (EVP_CIPHER_CTX_set_padding(ctx, pad) != 1)
	ossl_raise(eCipherError, NULL);
    return padding;
}
#else
#define ossl_cipher_set_padding rb_f_notimplement
#endif

#define CIPHER_0ARG_INT(func)					\
    static VALUE						\
    ossl_cipher_##func(VALUE self)				\
    {								\
	EVP_CIPHER_CTX *ctx;					\
	GetCipher(self, ctx);					\
	return INT2NUM(EVP_CIPHER_##func(EVP_CIPHER_CTX_cipher(ctx)));	\
    }

/*
 *  call-seq:
 *     cipher.key_len -> integer
 *
 *  Returns the key length in bytes of the Cipher.
 */
CIPHER_0ARG_INT(key_length)
/*
 *  call-seq:
 *     cipher.iv_len -> integer
 *
 *  Returns the expected length in bytes for an IV for this Cipher.
 */
CIPHER_0ARG_INT(iv_length)
/*
 *  call-seq:
 *     cipher.block_size -> integer
 *
 *  Returns the size in bytes of the blocks on which this Cipher operates on.
 */
CIPHER_0ARG_INT(block_size)

/*
 * INIT
 */
void
Init_ossl_cipher(void)
{
#if 0
    mOSSL = rb_define_module("OpenSSL"); /* let rdoc know about mOSSL */
#endif

    /* Document-class: OpenSSL::Cipher
     *
     * Provides symmetric algorithms for encryption and decryption. The
     * algorithms that are available depend on the particular version
     * of OpenSSL that is installed.
     *
     * === Listing all supported algorithms
     *
     * A list of supported algorithms can be obtained by
     *
     *   puts OpenSSL::Cipher.ciphers
     *
     * === Instantiating a Cipher
     *
     * There are several ways to create a Cipher instance. Generally, a
     * Cipher algorithm is categorized by its name, the key length in bits
     * and the cipher mode to be used. The most generic way to create a
     * Cipher is the following
     *
     *   cipher = OpenSSL::Cipher.new('<name>-<key length>-<mode>')
     *
     * That is, a string consisting of the hyphenated concatenation of the
     * individual components name, key length and mode. Either all uppercase
     * or all lowercase strings may be used, for example:
     *
     *  cipher = OpenSSL::Cipher.new('AES-128-CBC')
     *
     * For each algorithm supported, there is a class defined under the
     * Cipher class that goes by the name of the cipher, e.g. to obtain an
     * instance of AES, you could also use
     *
     *   # these are equivalent
     *   cipher = OpenSSL::Cipher::AES.new(128, :CBC)
     *   cipher = OpenSSL::Cipher::AES.new(128, 'CBC')
     *   cipher = OpenSSL::Cipher::AES.new('128-CBC')
     *
     * Finally, due to its wide-spread use, there are also extra classes
     * defined for the different key sizes of AES
     *
     *   cipher = OpenSSL::Cipher::AES128.new(:CBC)
     *   cipher = OpenSSL::Cipher::AES192.new(:CBC)
     *   cipher = OpenSSL::Cipher::AES256.new(:CBC)
     *
     * === Choosing either encryption or decryption mode
     *
     * Encryption and decryption are often very similar operations for
     * symmetric algorithms, this is reflected by not having to choose
     * different classes for either operation, both can be done using the
     * same class. Still, after obtaining a Cipher instance, we need to
     * tell the instance what it is that we intend to do with it, so we
     * need to call either
     *
     *   cipher.encrypt
     *
     * or
     *
     *   cipher.decrypt
     *
     * on the Cipher instance. This should be the first call after creating
     * the instance, otherwise configuration that has already been set could
     * get lost in the process.
     *
     * === Choosing a key
     *
     * Symmetric encryption requires a key that is the same for the encrypting
     * and for the decrypting party and after initial key establishment should
     * be kept as private information. There are a lot of ways to create
     * insecure keys, the most notable is to simply take a password as the key
     * without processing the password further. A simple and secure way to
     * create a key for a particular Cipher is
     *
     *  cipher = OpenSSL::AES256.new(:CFB)
     *  cipher.encrypt
     *  key = cipher.random_key # also sets the generated key on the Cipher
     *
     * If you absolutely need to use passwords as encryption keys, you
     * should use Password-Based Key Derivation Function 2 (PBKDF2) by
     * generating the key with the help of the functionality provided by
     * OpenSSL::PKCS5.pbkdf2_hmac_sha1 or OpenSSL::PKCS5.pbkdf2_hmac.
     *
     * Although there is Cipher#pkcs5_keyivgen, its use is deprecated and
     * it should only be used in legacy applications because it does not use
     * the newer PKCS#5 v2 algorithms.
     *
     * === Choosing an IV
     *
     * The cipher modes CBC, CFB, OFB and CTR all need an "initialization
     * vector", or short, IV. ECB mode is the only mode that does not require
     * an IV, but there is almost no legitimate use case for this mode
     * because of the fact that it does not sufficiently hide plaintext
     * patterns. Therefore
     *
     * <b>You should never use ECB mode unless you are absolutely sure that
     * you absolutely need it</b>
     *
     * Because of this, you will end up with a mode that explicitly requires
     * an IV in any case. Note that for backwards compatibility reasons,
     * setting an IV is not explicitly mandated by the Cipher API. If not
     * set, OpenSSL itself defaults to an all-zeroes IV ("\\0", not the
     * character). Although the IV can be seen as public information, i.e.
     * it may be transmitted in public once generated, it should still stay
     * unpredictable to prevent certain kinds of attacks. Therefore, ideally
     *
     * <b>Always create a secure random IV for every encryption of your
     * Cipher</b>
     *
     * A new, random IV should be created for every encryption of data. Think
     * of the IV as a nonce (number used once) - it's public but random and
     * unpredictable. A secure random IV can be created as follows
     *
     *  cipher = ...
     *  cipher.encrypt
     *  key = cipher.random_key
     *  iv = cipher.random_iv # also sets the generated IV on the Cipher
     *
     *  Although the key is generally a random value, too, it is a bad choice
     *  as an IV. There are elaborate ways how an attacker can take advantage
     *  of such an IV. As a general rule of thumb, exposing the key directly
     *  or indirectly should be avoided at all cost and exceptions only be
     *  made with good reason. 
     *
     * === Calling Cipher#final
     *
     * ECB (which should not be used) and CBC are both block-based modes.
     * This means that unlike for the other streaming-based modes, they
     * operate on fixed-size blocks of data, and therefore they require a
     * "finalization" step to produce or correctly decrypt the last block of
     * data by appropriately handling some form of padding. Therefore it is
     * essential to add the output of OpenSSL::Cipher#final to your
     * encryption/decryption buffer or you will end up with decryption errors
     * or truncated data.
     *
     * Although this is not really necessary for streaming-mode ciphers, it is
     * still recommended to apply the same pattern of adding the output of
     * Cipher#final there as well - it also enables you to switch between
     * modes more easily in the future.
     *
     * === Encrypting and decrypting some data
     *
     *   data = "Very, very confidential data"
     *
     *   cipher = OpenSSL::Cipher::AES.new(128, :CBC)
     *   cipher.encrypt
     *   key = cipher.random_key
     *   iv = cipher.random_iv
     *
     *   encrypted = cipher.update(data) + cipher.final
     *   ...
     *   decipher = OpenSSL::Cipher::AES.new(128, :CBC)
     *   decipher.decrypt
     *   decipher.key = key
     *   decipher.iv = iv
     *
     *   plain = decipher.update(encrypted) + decipher.final
     *
     *   puts data == plain #=> true
     *
     */
    cCipher = rb_define_class_under(mOSSL, "Cipher", rb_cObject);
    eCipherError = rb_define_class_under(cCipher, "CipherError", eOSSLError);

    rb_define_alloc_func(cCipher, ossl_cipher_alloc);
    rb_define_copy_func(cCipher, ossl_cipher_copy);
    rb_define_module_function(cCipher, "ciphers", ossl_s_ciphers, 0);
    rb_define_method(cCipher, "initialize", ossl_cipher_initialize, 1);
    rb_define_method(cCipher, "reset", ossl_cipher_reset, 0);
    rb_define_method(cCipher, "encrypt", ossl_cipher_encrypt, -1);
    rb_define_method(cCipher, "decrypt", ossl_cipher_decrypt, -1);
    rb_define_method(cCipher, "pkcs5_keyivgen", ossl_cipher_pkcs5_keyivgen, -1);
    rb_define_method(cCipher, "update", ossl_cipher_update, -1);
    rb_define_method(cCipher, "final", ossl_cipher_final, 0);
    rb_define_method(cCipher, "name", ossl_cipher_name, 0);
    rb_define_method(cCipher, "key=", ossl_cipher_set_key, 1);
    rb_define_method(cCipher, "key_len=", ossl_cipher_set_key_length, 1);
    rb_define_method(cCipher, "key_len", ossl_cipher_key_length, 0);
    rb_define_method(cCipher, "iv=", ossl_cipher_set_iv, 1);
    rb_define_method(cCipher, "iv_len", ossl_cipher_iv_length, 0);
    rb_define_method(cCipher, "block_size", ossl_cipher_block_size, 0);
    rb_define_method(cCipher, "padding=", ossl_cipher_set_padding, 1);
}