1 /* base64.c -- Encode binary data using printable characters.
2    Copyright (C) 1999-2001, 2004-2006, 2009-2013 Free Software Foundation, Inc.
3 
4    This program is free software; you can redistribute it and/or modify
5    it under the terms of the GNU General Public License as published by
6    the Free Software Foundation; either version 3, or (at your option)
7    any later version.
8 
9    This program is distributed in the hope that it will be useful,
10    but WITHOUT ANY WARRANTY; without even the implied warranty of
11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
12    GNU General Public License for more details.
13 
14    You should have received a copy of the GNU General Public License
15    along with this program; if not, see <http://www.gnu.org/licenses/>.  */
16 
17 /* Written by Simon Josefsson.  Partially adapted from GNU MailUtils
18  * (mailbox/filter_trans.c, as of 2004-11-28).  Improved by review
19  * from Paul Eggert, Bruno Haible, and Stepan Kasal.
20  *
21  * See also RFC 4648 <http://www.ietf.org/rfc/rfc4648.txt>.
22  *
23  * Be careful with error checking.  Here is how you would typically
24  * use these functions:
25  *
26  * bool ok = base64_decode_alloc (in, inlen, &out, &outlen);
27  * if (!ok)
28  *   FAIL: input was not valid base64
29  * if (out == NULL)
30  *   FAIL: memory allocation error
31  * OK: data in OUT/OUTLEN
32  *
33  * size_t outlen = base64_encode_alloc (in, inlen, &out);
34  * if (out == NULL && outlen == 0 && inlen != 0)
35  *   FAIL: input too long
36  * if (out == NULL)
37  *   FAIL: memory allocation error
38  * OK: data in OUT/OUTLEN.
39  *
40  */
41 
42 #include <config.h>
43 
44 /* Get prototype. */
45 #include "base64.h"
46 
47 /* Get malloc. */
48 #include <stdlib.h>
49 
50 /* Get UCHAR_MAX. */
51 #include <limits.h>
52 
53 #include <string.h>
54 
55 /* C89 compliant way to cast 'char' to 'unsigned char'. */
56 static unsigned char
to_uchar(char ch)57 to_uchar (char ch)
58 {
59   return ch;
60 }
61 
62 /* Base64 encode IN array of size INLEN into OUT array of size OUTLEN.
63    If OUTLEN is less than BASE64_LENGTH(INLEN), write as many bytes as
64    possible.  If OUTLEN is larger than BASE64_LENGTH(INLEN), also zero
65    terminate the output buffer. */
66 void
base64_encode(const char * restrict in,size_t inlen,char * restrict out,size_t outlen)67 base64_encode (const char *restrict in, size_t inlen,
68                char *restrict out, size_t outlen)
69 {
70   static const char b64str[64] =
71     "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
72 
73   while (inlen && outlen)
74     {
75       *out++ = b64str[(to_uchar (in[0]) >> 2) & 0x3f];
76       if (!--outlen)
77         break;
78       *out++ = b64str[((to_uchar (in[0]) << 4)
79                        + (--inlen ? to_uchar (in[1]) >> 4 : 0))
80                       & 0x3f];
81       if (!--outlen)
82         break;
83       *out++ =
84         (inlen
85          ? b64str[((to_uchar (in[1]) << 2)
86                    + (--inlen ? to_uchar (in[2]) >> 6 : 0))
87                   & 0x3f]
88          : '=');
89       if (!--outlen)
90         break;
91       *out++ = inlen ? b64str[to_uchar (in[2]) & 0x3f] : '=';
92       if (!--outlen)
93         break;
94       if (inlen)
95         inlen--;
96       if (inlen)
97         in += 3;
98     }
99 
100   if (outlen)
101     *out = '\0';
102 }
103 
104 /* Allocate a buffer and store zero terminated base64 encoded data
105    from array IN of size INLEN, returning BASE64_LENGTH(INLEN), i.e.,
106    the length of the encoded data, excluding the terminating zero.  On
107    return, the OUT variable will hold a pointer to newly allocated
108    memory that must be deallocated by the caller.  If output string
109    length would overflow, 0 is returned and OUT is set to NULL.  If
110    memory allocation failed, OUT is set to NULL, and the return value
111    indicates length of the requested memory block, i.e.,
112    BASE64_LENGTH(inlen) + 1. */
113 size_t
base64_encode_alloc(const char * in,size_t inlen,char ** out)114 base64_encode_alloc (const char *in, size_t inlen, char **out)
115 {
116   size_t outlen = 1 + BASE64_LENGTH (inlen);
117 
118   /* Check for overflow in outlen computation.
119    *
120    * If there is no overflow, outlen >= inlen.
121    *
122    * If the operation (inlen + 2) overflows then it yields at most +1, so
123    * outlen is 0.
124    *
125    * If the multiplication overflows, we lose at least half of the
126    * correct value, so the result is < ((inlen + 2) / 3) * 2, which is
127    * less than (inlen + 2) * 0.66667, which is less than inlen as soon as
128    * (inlen > 4).
129    */
130   if (inlen > outlen)
131     {
132       *out = NULL;
133       return 0;
134     }
135 
136   *out = malloc (outlen);
137   if (!*out)
138     return outlen;
139 
140   base64_encode (in, inlen, *out, outlen);
141 
142   return outlen - 1;
143 }
144 
145 /* With this approach this file works independent of the charset used
146    (think EBCDIC).  However, it does assume that the characters in the
147    Base64 alphabet (A-Za-z0-9+/) are encoded in 0..255.  POSIX
148    1003.1-2001 require that char and unsigned char are 8-bit
149    quantities, though, taking care of that problem.  But this may be a
150    potential problem on non-POSIX C99 platforms.
151 
152    IBM C V6 for AIX mishandles "#define B64(x) ...'x'...", so use "_"
153    as the formal parameter rather than "x".  */
154 #define B64(_)                                  \
155   ((_) == 'A' ? 0                               \
156    : (_) == 'B' ? 1                             \
157    : (_) == 'C' ? 2                             \
158    : (_) == 'D' ? 3                             \
159    : (_) == 'E' ? 4                             \
160    : (_) == 'F' ? 5                             \
161    : (_) == 'G' ? 6                             \
162    : (_) == 'H' ? 7                             \
163    : (_) == 'I' ? 8                             \
164    : (_) == 'J' ? 9                             \
165    : (_) == 'K' ? 10                            \
166    : (_) == 'L' ? 11                            \
167    : (_) == 'M' ? 12                            \
168    : (_) == 'N' ? 13                            \
169    : (_) == 'O' ? 14                            \
170    : (_) == 'P' ? 15                            \
171    : (_) == 'Q' ? 16                            \
172    : (_) == 'R' ? 17                            \
173    : (_) == 'S' ? 18                            \
174    : (_) == 'T' ? 19                            \
175    : (_) == 'U' ? 20                            \
176    : (_) == 'V' ? 21                            \
177    : (_) == 'W' ? 22                            \
178    : (_) == 'X' ? 23                            \
179    : (_) == 'Y' ? 24                            \
180    : (_) == 'Z' ? 25                            \
181    : (_) == 'a' ? 26                            \
182    : (_) == 'b' ? 27                            \
183    : (_) == 'c' ? 28                            \
184    : (_) == 'd' ? 29                            \
185    : (_) == 'e' ? 30                            \
186    : (_) == 'f' ? 31                            \
187    : (_) == 'g' ? 32                            \
188    : (_) == 'h' ? 33                            \
189    : (_) == 'i' ? 34                            \
190    : (_) == 'j' ? 35                            \
191    : (_) == 'k' ? 36                            \
192    : (_) == 'l' ? 37                            \
193    : (_) == 'm' ? 38                            \
194    : (_) == 'n' ? 39                            \
195    : (_) == 'o' ? 40                            \
196    : (_) == 'p' ? 41                            \
197    : (_) == 'q' ? 42                            \
198    : (_) == 'r' ? 43                            \
199    : (_) == 's' ? 44                            \
200    : (_) == 't' ? 45                            \
201    : (_) == 'u' ? 46                            \
202    : (_) == 'v' ? 47                            \
203    : (_) == 'w' ? 48                            \
204    : (_) == 'x' ? 49                            \
205    : (_) == 'y' ? 50                            \
206    : (_) == 'z' ? 51                            \
207    : (_) == '0' ? 52                            \
208    : (_) == '1' ? 53                            \
209    : (_) == '2' ? 54                            \
210    : (_) == '3' ? 55                            \
211    : (_) == '4' ? 56                            \
212    : (_) == '5' ? 57                            \
213    : (_) == '6' ? 58                            \
214    : (_) == '7' ? 59                            \
215    : (_) == '8' ? 60                            \
216    : (_) == '9' ? 61                            \
217    : (_) == '+' ? 62                            \
218    : (_) == '/' ? 63                            \
219    : -1)
220 
221 static const signed char b64[0x100] = {
222   B64 (0), B64 (1), B64 (2), B64 (3),
223   B64 (4), B64 (5), B64 (6), B64 (7),
224   B64 (8), B64 (9), B64 (10), B64 (11),
225   B64 (12), B64 (13), B64 (14), B64 (15),
226   B64 (16), B64 (17), B64 (18), B64 (19),
227   B64 (20), B64 (21), B64 (22), B64 (23),
228   B64 (24), B64 (25), B64 (26), B64 (27),
229   B64 (28), B64 (29), B64 (30), B64 (31),
230   B64 (32), B64 (33), B64 (34), B64 (35),
231   B64 (36), B64 (37), B64 (38), B64 (39),
232   B64 (40), B64 (41), B64 (42), B64 (43),
233   B64 (44), B64 (45), B64 (46), B64 (47),
234   B64 (48), B64 (49), B64 (50), B64 (51),
235   B64 (52), B64 (53), B64 (54), B64 (55),
236   B64 (56), B64 (57), B64 (58), B64 (59),
237   B64 (60), B64 (61), B64 (62), B64 (63),
238   B64 (64), B64 (65), B64 (66), B64 (67),
239   B64 (68), B64 (69), B64 (70), B64 (71),
240   B64 (72), B64 (73), B64 (74), B64 (75),
241   B64 (76), B64 (77), B64 (78), B64 (79),
242   B64 (80), B64 (81), B64 (82), B64 (83),
243   B64 (84), B64 (85), B64 (86), B64 (87),
244   B64 (88), B64 (89), B64 (90), B64 (91),
245   B64 (92), B64 (93), B64 (94), B64 (95),
246   B64 (96), B64 (97), B64 (98), B64 (99),
247   B64 (100), B64 (101), B64 (102), B64 (103),
248   B64 (104), B64 (105), B64 (106), B64 (107),
249   B64 (108), B64 (109), B64 (110), B64 (111),
250   B64 (112), B64 (113), B64 (114), B64 (115),
251   B64 (116), B64 (117), B64 (118), B64 (119),
252   B64 (120), B64 (121), B64 (122), B64 (123),
253   B64 (124), B64 (125), B64 (126), B64 (127),
254   B64 (128), B64 (129), B64 (130), B64 (131),
255   B64 (132), B64 (133), B64 (134), B64 (135),
256   B64 (136), B64 (137), B64 (138), B64 (139),
257   B64 (140), B64 (141), B64 (142), B64 (143),
258   B64 (144), B64 (145), B64 (146), B64 (147),
259   B64 (148), B64 (149), B64 (150), B64 (151),
260   B64 (152), B64 (153), B64 (154), B64 (155),
261   B64 (156), B64 (157), B64 (158), B64 (159),
262   B64 (160), B64 (161), B64 (162), B64 (163),
263   B64 (164), B64 (165), B64 (166), B64 (167),
264   B64 (168), B64 (169), B64 (170), B64 (171),
265   B64 (172), B64 (173), B64 (174), B64 (175),
266   B64 (176), B64 (177), B64 (178), B64 (179),
267   B64 (180), B64 (181), B64 (182), B64 (183),
268   B64 (184), B64 (185), B64 (186), B64 (187),
269   B64 (188), B64 (189), B64 (190), B64 (191),
270   B64 (192), B64 (193), B64 (194), B64 (195),
271   B64 (196), B64 (197), B64 (198), B64 (199),
272   B64 (200), B64 (201), B64 (202), B64 (203),
273   B64 (204), B64 (205), B64 (206), B64 (207),
274   B64 (208), B64 (209), B64 (210), B64 (211),
275   B64 (212), B64 (213), B64 (214), B64 (215),
276   B64 (216), B64 (217), B64 (218), B64 (219),
277   B64 (220), B64 (221), B64 (222), B64 (223),
278   B64 (224), B64 (225), B64 (226), B64 (227),
279   B64 (228), B64 (229), B64 (230), B64 (231),
280   B64 (232), B64 (233), B64 (234), B64 (235),
281   B64 (236), B64 (237), B64 (238), B64 (239),
282   B64 (240), B64 (241), B64 (242), B64 (243),
283   B64 (244), B64 (245), B64 (246), B64 (247),
284   B64 (248), B64 (249), B64 (250), B64 (251),
285   B64 (252), B64 (253), B64 (254), B64 (255)
286 };
287 
288 #if UCHAR_MAX == 255
289 # define uchar_in_range(c) true
290 #else
291 # define uchar_in_range(c) ((c) <= 255)
292 #endif
293 
294 /* Return true if CH is a character from the Base64 alphabet, and
295    false otherwise.  Note that '=' is padding and not considered to be
296    part of the alphabet.  */
297 bool
isbase64(char ch)298 isbase64 (char ch)
299 {
300   return uchar_in_range (to_uchar (ch)) && 0 <= b64[to_uchar (ch)];
301 }
302 
303 /* Initialize decode-context buffer, CTX.  */
304 void
base64_decode_ctx_init(struct base64_decode_context * ctx)305 base64_decode_ctx_init (struct base64_decode_context *ctx)
306 {
307   ctx->i = 0;
308 }
309 
310 /* If CTX->i is 0 or 4, there are four or more bytes in [*IN..IN_END), and
311    none of those four is a newline, then return *IN.  Otherwise, copy up to
312    4 - CTX->i non-newline bytes from that range into CTX->buf, starting at
313    index CTX->i and setting CTX->i to reflect the number of bytes copied,
314    and return CTX->buf.  In either case, advance *IN to point to the byte
315    after the last one processed, and set *N_NON_NEWLINE to the number of
316    verified non-newline bytes accessible through the returned pointer.  */
317 static char *
get_4(struct base64_decode_context * ctx,char const * restrict * in,char const * restrict in_end,size_t * n_non_newline)318 get_4 (struct base64_decode_context *ctx,
319        char const *restrict *in, char const *restrict in_end,
320        size_t *n_non_newline)
321 {
322   if (ctx->i == 4)
323     ctx->i = 0;
324 
325   if (ctx->i == 0)
326     {
327       char const *t = *in;
328       if (4 <= in_end - *in && memchr (t, '\n', 4) == NULL)
329         {
330           /* This is the common case: no newline.  */
331           *in += 4;
332           *n_non_newline = 4;
333           return (char *) t;
334         }
335     }
336 
337   {
338     /* Copy non-newline bytes into BUF.  */
339     char const *p = *in;
340     while (p < in_end)
341       {
342         char c = *p++;
343         if (c != '\n')
344           {
345             ctx->buf[ctx->i++] = c;
346             if (ctx->i == 4)
347               break;
348           }
349       }
350 
351     *in = p;
352     *n_non_newline = ctx->i;
353     return ctx->buf;
354   }
355 }
356 
357 #define return_false                            \
358   do                                            \
359     {                                           \
360       *outp = out;                              \
361       return false;                             \
362     }                                           \
363   while (false)
364 
365 /* Decode up to four bytes of base64-encoded data, IN, of length INLEN
366    into the output buffer, *OUT, of size *OUTLEN bytes.  Return true if
367    decoding is successful, false otherwise.  If *OUTLEN is too small,
368    as many bytes as possible are written to *OUT.  On return, advance
369    *OUT to point to the byte after the last one written, and decrement
370    *OUTLEN to reflect the number of bytes remaining in *OUT.  */
371 static bool
decode_4(char const * restrict in,size_t inlen,char * restrict * outp,size_t * outleft)372 decode_4 (char const *restrict in, size_t inlen,
373           char *restrict *outp, size_t *outleft)
374 {
375   char *out = *outp;
376   if (inlen < 2)
377     return false;
378 
379   if (!isbase64 (in[0]) || !isbase64 (in[1]))
380     return false;
381 
382   if (*outleft)
383     {
384       *out++ = ((b64[to_uchar (in[0])] << 2)
385                 | (b64[to_uchar (in[1])] >> 4));
386       --*outleft;
387     }
388 
389   if (inlen == 2)
390     return_false;
391 
392   if (in[2] == '=')
393     {
394       if (inlen != 4)
395         return_false;
396 
397       if (in[3] != '=')
398         return_false;
399     }
400   else
401     {
402       if (!isbase64 (in[2]))
403         return_false;
404 
405       if (*outleft)
406         {
407           *out++ = (((b64[to_uchar (in[1])] << 4) & 0xf0)
408                     | (b64[to_uchar (in[2])] >> 2));
409           --*outleft;
410         }
411 
412       if (inlen == 3)
413         return_false;
414 
415       if (in[3] == '=')
416         {
417           if (inlen != 4)
418             return_false;
419         }
420       else
421         {
422           if (!isbase64 (in[3]))
423             return_false;
424 
425           if (*outleft)
426             {
427               *out++ = (((b64[to_uchar (in[2])] << 6) & 0xc0)
428                         | b64[to_uchar (in[3])]);
429               --*outleft;
430             }
431         }
432     }
433 
434   *outp = out;
435   return true;
436 }
437 
438 /* Decode base64-encoded input array IN of length INLEN to output array
439    OUT that can hold *OUTLEN bytes.  The input data may be interspersed
440    with newlines.  Return true if decoding was successful, i.e. if the
441    input was valid base64 data, false otherwise.  If *OUTLEN is too
442    small, as many bytes as possible will be written to OUT.  On return,
443    *OUTLEN holds the length of decoded bytes in OUT.  Note that as soon
444    as any non-alphabet, non-newline character is encountered, decoding
445    is stopped and false is returned.  If INLEN is zero, then process
446    only whatever data is stored in CTX.
447 
448    Initially, CTX must have been initialized via base64_decode_ctx_init.
449    Subsequent calls to this function must reuse whatever state is recorded
450    in that buffer.  It is necessary for when a quadruple of base64 input
451    bytes spans two input buffers.
452 
453    If CTX is NULL then newlines are treated as garbage and the input
454    buffer is processed as a unit.  */
455 
456 bool
base64_decode_ctx(struct base64_decode_context * ctx,const char * restrict in,size_t inlen,char * restrict out,size_t * outlen)457 base64_decode_ctx (struct base64_decode_context *ctx,
458                    const char *restrict in, size_t inlen,
459                    char *restrict out, size_t *outlen)
460 {
461   size_t outleft = *outlen;
462   bool ignore_newlines = ctx != NULL;
463   bool flush_ctx = false;
464   unsigned int ctx_i = 0;
465 
466   if (ignore_newlines)
467     {
468       ctx_i = ctx->i;
469       flush_ctx = inlen == 0;
470     }
471 
472 
473   while (true)
474     {
475       size_t outleft_save = outleft;
476       if (ctx_i == 0 && !flush_ctx)
477         {
478           while (true)
479             {
480               /* Save a copy of outleft, in case we need to re-parse this
481                  block of four bytes.  */
482               outleft_save = outleft;
483               if (!decode_4 (in, inlen, &out, &outleft))
484                 break;
485 
486               in += 4;
487               inlen -= 4;
488             }
489         }
490 
491       if (inlen == 0 && !flush_ctx)
492         break;
493 
494       /* Handle the common case of 72-byte wrapped lines.
495          This also handles any other multiple-of-4-byte wrapping.  */
496       if (inlen && *in == '\n' && ignore_newlines)
497         {
498           ++in;
499           --inlen;
500           continue;
501         }
502 
503       /* Restore OUT and OUTLEFT.  */
504       out -= outleft_save - outleft;
505       outleft = outleft_save;
506 
507       {
508         char const *in_end = in + inlen;
509         char const *non_nl;
510 
511         if (ignore_newlines)
512           non_nl = get_4 (ctx, &in, in_end, &inlen);
513         else
514           non_nl = in;  /* Might have nl in this case. */
515 
516         /* If the input is empty or consists solely of newlines (0 non-newlines),
517            then we're done.  Likewise if there are fewer than 4 bytes when not
518            flushing context and not treating newlines as garbage.  */
519         if (inlen == 0 || (inlen < 4 && !flush_ctx && ignore_newlines))
520           {
521             inlen = 0;
522             break;
523           }
524         if (!decode_4 (non_nl, inlen, &out, &outleft))
525           break;
526 
527         inlen = in_end - in;
528       }
529     }
530 
531   *outlen -= outleft;
532 
533   return inlen == 0;
534 }
535 
536 /* Allocate an output buffer in *OUT, and decode the base64 encoded
537    data stored in IN of size INLEN to the *OUT buffer.  On return, the
538    size of the decoded data is stored in *OUTLEN.  OUTLEN may be NULL,
539    if the caller is not interested in the decoded length.  *OUT may be
540    NULL to indicate an out of memory error, in which case *OUTLEN
541    contains the size of the memory block needed.  The function returns
542    true on successful decoding and memory allocation errors.  (Use the
543    *OUT and *OUTLEN parameters to differentiate between successful
544    decoding and memory error.)  The function returns false if the
545    input was invalid, in which case *OUT is NULL and *OUTLEN is
546    undefined. */
547 bool
base64_decode_alloc_ctx(struct base64_decode_context * ctx,const char * in,size_t inlen,char ** out,size_t * outlen)548 base64_decode_alloc_ctx (struct base64_decode_context *ctx,
549                          const char *in, size_t inlen, char **out,
550                          size_t *outlen)
551 {
552   /* This may allocate a few bytes too many, depending on input,
553      but it's not worth the extra CPU time to compute the exact size.
554      The exact size is 3 * (inlen + (ctx ? ctx->i : 0)) / 4, minus 1 if the
555      input ends with "=" and minus another 1 if the input ends with "==".
556      Dividing before multiplying avoids the possibility of overflow.  */
557   size_t needlen = 3 * (inlen / 4) + 3;
558 
559   *out = malloc (needlen);
560   if (!*out)
561     return true;
562 
563   if (!base64_decode_ctx (ctx, in, inlen, *out, &needlen))
564     {
565       free (*out);
566       *out = NULL;
567       return false;
568     }
569 
570   if (outlen)
571     *outlen = needlen;
572 
573   return true;
574 }
575