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    1 /* base64.c -- Encode binary data using printable characters.
    2    Copyright (C) 1999-2001, 2004-2006, 2009-2018 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 2, 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 <https://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 <https://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
   57 to_uchar (char ch)
   58 {
   59   return ch;
   60 }
   61 
   62 static const char b64c[64] =
   63   "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
   64 
   65 /* Base64 encode IN array of size INLEN into OUT array. OUT needs
   66    to be of length >= BASE64_LENGTH(INLEN), and INLEN needs to be
   67    a multiple of 3.  */
   68 static void
   69 base64_encode_fast (const char *in, size_t inlen, char *out)
   70 {
   71   while (inlen)
   72     {
   73       *out++ = b64c[to_uchar (in[0]) >> 2];
   74       *out++ = b64c[((to_uchar (in[0]) << 4) + (to_uchar (in[1]) >> 4)) & 0x3f];
   75       *out++ = b64c[((to_uchar (in[1]) << 2) + (to_uchar (in[2]) >> 6)) & 0x3f];
   76       *out++ = b64c[to_uchar (in[2]) & 0x3f];
   77 
   78       inlen -= 3;
   79       in += 3;
   80     }
   81 }
   82 
   83 /* Base64 encode IN array of size INLEN into OUT array of size OUTLEN.
   84    If OUTLEN is less than BASE64_LENGTH(INLEN), write as many bytes as
   85    possible.  If OUTLEN is larger than BASE64_LENGTH(INLEN), also zero
   86    terminate the output buffer. */
   87 void
   88 base64_encode (const char *in, size_t inlen,
   89                char *out, size_t outlen)
   90 {
   91   /* Note this outlen constraint can be enforced at compile time.
   92      I.E. that the output buffer is exactly large enough to hold
   93      the encoded inlen bytes.  The inlen constraints (of corresponding
   94      to outlen, and being a multiple of 3) can change at runtime
   95      at the end of input.  However the common case when reading
   96      large inputs is to have both constraints satisfied, so we depend
   97      on both in base_encode_fast().  */
   98   if (outlen % 4 == 0 && inlen == outlen / 4 * 3)
   99     {
  100       base64_encode_fast (in, inlen, out);
  101       return;
  102     }
  103 
  104   while (inlen && outlen)
  105     {
  106       *out++ = b64c[to_uchar (in[0]) >> 2];
  107       if (!--outlen)
  108         break;
  109       *out++ = b64c[((to_uchar (in[0]) << 4)
  110                        + (--inlen ? to_uchar (in[1]) >> 4 : 0))
  111                       & 0x3f];
  112       if (!--outlen)
  113         break;
  114       *out++ =
  115         (inlen
  116          ? b64c[((to_uchar (in[1]) << 2)
  117                    + (--inlen ? to_uchar (in[2]) >> 6 : 0))
  118                   & 0x3f]
  119          : '=');
  120       if (!--outlen)
  121         break;
  122       *out++ = inlen ? b64c[to_uchar (in[2]) & 0x3f] : '=';
  123       if (!--outlen)
  124         break;
  125       if (inlen)
  126         inlen--;
  127       if (inlen)
  128         in += 3;
  129     }
  130 
  131   if (outlen)
  132     *out = '\0';
  133 }
  134 
  135 /* Allocate a buffer and store zero terminated base64 encoded data
  136    from array IN of size INLEN, returning BASE64_LENGTH(INLEN), i.e.,
  137    the length of the encoded data, excluding the terminating zero.  On
  138    return, the OUT variable will hold a pointer to newly allocated
  139    memory that must be deallocated by the caller.  If output string
  140    length would overflow, 0 is returned and OUT is set to NULL.  If
  141    memory allocation failed, OUT is set to NULL, and the return value
  142    indicates length of the requested memory block, i.e.,
  143    BASE64_LENGTH(inlen) + 1. */
  144 size_t
  145 base64_encode_alloc (const char *in, size_t inlen, char **out)
  146 {
  147   size_t outlen = 1 + BASE64_LENGTH (inlen);
  148 
  149   /* Check for overflow in outlen computation.
  150    *
  151    * If there is no overflow, outlen >= inlen.
  152    *
  153    * If the operation (inlen + 2) overflows then it yields at most +1, so
  154    * outlen is 0.
  155    *
  156    * If the multiplication overflows, we lose at least half of the
  157    * correct value, so the result is < ((inlen + 2) / 3) * 2, which is
  158    * less than (inlen + 2) * 0.66667, which is less than inlen as soon as
  159    * (inlen > 4).
  160    */
  161   if (inlen > outlen)
  162     {
  163       *out = NULL;
  164       return 0;
  165     }
  166 
  167   *out = malloc (outlen);
  168   if (!*out)
  169     return outlen;
  170 
  171   base64_encode (in, inlen, *out, outlen);
  172 
  173   return outlen - 1;
  174 }
  175 
  176 /* With this approach this file works independent of the charset used
  177    (think EBCDIC).  However, it does assume that the characters in the
  178    Base64 alphabet (A-Za-z0-9+/) are encoded in 0..255.  POSIX
  179    1003.1-2001 require that char and unsigned char are 8-bit
  180    quantities, though, taking care of that problem.  But this may be a
  181    potential problem on non-POSIX C99 platforms.
  182 
  183    IBM C V6 for AIX mishandles "#define B64(x) ...'x'...", so use "_"
  184    as the formal parameter rather than "x".  */
  185 #define B64(_)                                  \
  186   ((_) == 'A' ? 0                               \
  187    : (_) == 'B' ? 1                             \
  188    : (_) == 'C' ? 2                             \
  189    : (_) == 'D' ? 3                             \
  190    : (_) == 'E' ? 4                             \
  191    : (_) == 'F' ? 5                             \
  192    : (_) == 'G' ? 6                             \
  193    : (_) == 'H' ? 7                             \
  194    : (_) == 'I' ? 8                             \
  195    : (_) == 'J' ? 9                             \
  196    : (_) == 'K' ? 10                            \
  197    : (_) == 'L' ? 11                            \
  198    : (_) == 'M' ? 12                            \
  199    : (_) == 'N' ? 13                            \
  200    : (_) == 'O' ? 14                            \
  201    : (_) == 'P' ? 15                            \
  202    : (_) == 'Q' ? 16                            \
  203    : (_) == 'R' ? 17                            \
  204    : (_) == 'S' ? 18                            \
  205    : (_) == 'T' ? 19                            \
  206    : (_) == 'U' ? 20                            \
  207    : (_) == 'V' ? 21                            \
  208    : (_) == 'W' ? 22                            \
  209    : (_) == 'X' ? 23                            \
  210    : (_) == 'Y' ? 24                            \
  211    : (_) == 'Z' ? 25                            \
  212    : (_) == 'a' ? 26                            \
  213    : (_) == 'b' ? 27                            \
  214    : (_) == 'c' ? 28                            \
  215    : (_) == 'd' ? 29                            \
  216    : (_) == 'e' ? 30                            \
  217    : (_) == 'f' ? 31                            \
  218    : (_) == 'g' ? 32                            \
  219    : (_) == 'h' ? 33                            \
  220    : (_) == 'i' ? 34                            \
  221    : (_) == 'j' ? 35                            \
  222    : (_) == 'k' ? 36                            \
  223    : (_) == 'l' ? 37                            \
  224    : (_) == 'm' ? 38                            \
  225    : (_) == 'n' ? 39                            \
  226    : (_) == 'o' ? 40                            \
  227    : (_) == 'p' ? 41                            \
  228    : (_) == 'q' ? 42                            \
  229    : (_) == 'r' ? 43                            \
  230    : (_) == 's' ? 44                            \
  231    : (_) == 't' ? 45                            \
  232    : (_) == 'u' ? 46                            \
  233    : (_) == 'v' ? 47                            \
  234    : (_) == 'w' ? 48                            \
  235    : (_) == 'x' ? 49                            \
  236    : (_) == 'y' ? 50                            \
  237    : (_) == 'z' ? 51                            \
  238    : (_) == '0' ? 52                            \
  239    : (_) == '1' ? 53                            \
  240    : (_) == '2' ? 54                            \
  241    : (_) == '3' ? 55                            \
  242    : (_) == '4' ? 56                            \
  243    : (_) == '5' ? 57                            \
  244    : (_) == '6' ? 58                            \
  245    : (_) == '7' ? 59                            \
  246    : (_) == '8' ? 60                            \
  247    : (_) == '9' ? 61                            \
  248    : (_) == '+' ? 62                            \
  249    : (_) == '/' ? 63                            \
  250    : -1)
  251 
  252 static const signed char b64[0x100] = {
  253   B64 (0), B64 (1), B64 (2), B64 (3),
  254   B64 (4), B64 (5), B64 (6), B64 (7),
  255   B64 (8), B64 (9), B64 (10), B64 (11),
  256   B64 (12), B64 (13), B64 (14), B64 (15),
  257   B64 (16), B64 (17), B64 (18), B64 (19),
  258   B64 (20), B64 (21), B64 (22), B64 (23),
  259   B64 (24), B64 (25), B64 (26), B64 (27),
  260   B64 (28), B64 (29), B64 (30), B64 (31),
  261   B64 (32), B64 (33), B64 (34), B64 (35),
  262   B64 (36), B64 (37), B64 (38), B64 (39),
  263   B64 (40), B64 (41), B64 (42), B64 (43),
  264   B64 (44), B64 (45), B64 (46), B64 (47),
  265   B64 (48), B64 (49), B64 (50), B64 (51),
  266   B64 (52), B64 (53), B64 (54), B64 (55),
  267   B64 (56), B64 (57), B64 (58), B64 (59),
  268   B64 (60), B64 (61), B64 (62), B64 (63),
  269   B64 (64), B64 (65), B64 (66), B64 (67),
  270   B64 (68), B64 (69), B64 (70), B64 (71),
  271   B64 (72), B64 (73), B64 (74), B64 (75),
  272   B64 (76), B64 (77), B64 (78), B64 (79),
  273   B64 (80), B64 (81), B64 (82), B64 (83),
  274   B64 (84), B64 (85), B64 (86), B64 (87),
  275   B64 (88), B64 (89), B64 (90), B64 (91),
  276   B64 (92), B64 (93), B64 (94), B64 (95),
  277   B64 (96), B64 (97), B64 (98), B64 (99),
  278   B64 (100), B64 (101), B64 (102), B64 (103),
  279   B64 (104), B64 (105), B64 (106), B64 (107),
  280   B64 (108), B64 (109), B64 (110), B64 (111),
  281   B64 (112), B64 (113), B64 (114), B64 (115),
  282   B64 (116), B64 (117), B64 (118), B64 (119),
  283   B64 (120), B64 (121), B64 (122), B64 (123),
  284   B64 (124), B64 (125), B64 (126), B64 (127),
  285   B64 (128), B64 (129), B64 (130), B64 (131),
  286   B64 (132), B64 (133), B64 (134), B64 (135),
  287   B64 (136), B64 (137), B64 (138), B64 (139),
  288   B64 (140), B64 (141), B64 (142), B64 (143),
  289   B64 (144), B64 (145), B64 (146), B64 (147),
  290   B64 (148), B64 (149), B64 (150), B64 (151),
  291   B64 (152), B64 (153), B64 (154), B64 (155),
  292   B64 (156), B64 (157), B64 (158), B64 (159),
  293   B64 (160), B64 (161), B64 (162), B64 (163),
  294   B64 (164), B64 (165), B64 (166), B64 (167),
  295   B64 (168), B64 (169), B64 (170), B64 (171),
  296   B64 (172), B64 (173), B64 (174), B64 (175),
  297   B64 (176), B64 (177), B64 (178), B64 (179),
  298   B64 (180), B64 (181), B64 (182), B64 (183),
  299   B64 (184), B64 (185), B64 (186), B64 (187),
  300   B64 (188), B64 (189), B64 (190), B64 (191),
  301   B64 (192), B64 (193), B64 (194), B64 (195),
  302   B64 (196), B64 (197), B64 (198), B64 (199),
  303   B64 (200), B64 (201), B64 (202), B64 (203),
  304   B64 (204), B64 (205), B64 (206), B64 (207),
  305   B64 (208), B64 (209), B64 (210), B64 (211),
  306   B64 (212), B64 (213), B64 (214), B64 (215),
  307   B64 (216), B64 (217), B64 (218), B64 (219),
  308   B64 (220), B64 (221), B64 (222), B64 (223),
  309   B64 (224), B64 (225), B64 (226), B64 (227),
  310   B64 (228), B64 (229), B64 (230), B64 (231),
  311   B64 (232), B64 (233), B64 (234), B64 (235),
  312   B64 (236), B64 (237), B64 (238), B64 (239),
  313   B64 (240), B64 (241), B64 (242), B64 (243),
  314   B64 (244), B64 (245), B64 (246), B64 (247),
  315   B64 (248), B64 (249), B64 (250), B64 (251),
  316   B64 (252), B64 (253), B64 (254), B64 (255)
  317 };
  318 
  319 #if UCHAR_MAX == 255
  320 # define uchar_in_range(c) true
  321 #else
  322 # define uchar_in_range(c) ((c) <= 255)
  323 #endif
  324 
  325 /* Return true if CH is a character from the Base64 alphabet, and
  326    false otherwise.  Note that '=' is padding and not considered to be
  327    part of the alphabet.  */
  328 bool
  329 isbase64 (char ch)
  330 {
  331   return uchar_in_range (to_uchar (ch)) && 0 <= b64[to_uchar (ch)];
  332 }
  333 
  334 /* Initialize decode-context buffer, CTX.  */
  335 void
  336 base64_decode_ctx_init (struct base64_decode_context *ctx)
  337 {
  338   ctx->i = 0;
  339 }
  340 
  341 /* If CTX->i is 0 or 4, there are four or more bytes in [*IN..IN_END), and
  342    none of those four is a newline, then return *IN.  Otherwise, copy up to
  343    4 - CTX->i non-newline bytes from that range into CTX->buf, starting at
  344    index CTX->i and setting CTX->i to reflect the number of bytes copied,
  345    and return CTX->buf.  In either case, advance *IN to point to the byte
  346    after the last one processed, and set *N_NON_NEWLINE to the number of
  347    verified non-newline bytes accessible through the returned pointer.  */
  348 static char *
  349 get_4 (struct base64_decode_context *ctx,
  350        char const **in, char const *in_end,
  351        size_t *n_non_newline)
  352 {
  353   if (ctx->i == 4)
  354     ctx->i = 0;
  355 
  356   if (ctx->i == 0)
  357     {
  358       char const *t = *in;
  359       if (4 <= in_end - *in && memchr (t, '\n', 4) == NULL)
  360         {
  361           /* This is the common case: no newline.  */
  362           *in += 4;
  363           *n_non_newline = 4;
  364           return (char *) t;
  365         }
  366     }
  367 
  368   {
  369     /* Copy non-newline bytes into BUF.  */
  370     char const *p = *in;
  371     while (p < in_end)
  372       {
  373         char c = *p++;
  374         if (c != '\n')
  375           {
  376             ctx->buf[ctx->i++] = c;
  377             if (ctx->i == 4)
  378               break;
  379           }
  380       }
  381 
  382     *in = p;
  383     *n_non_newline = ctx->i;
  384     return ctx->buf;
  385   }
  386 }
  387 
  388 #define return_false                            \
  389   do                                            \
  390     {                                           \
  391       *outp = out;                              \
  392       return false;                             \
  393     }                                           \
  394   while (false)
  395 
  396 /* Decode up to four bytes of base64-encoded data, IN, of length INLEN
  397    into the output buffer, *OUT, of size *OUTLEN bytes.  Return true if
  398    decoding is successful, false otherwise.  If *OUTLEN is too small,
  399    as many bytes as possible are written to *OUT.  On return, advance
  400    *OUT to point to the byte after the last one written, and decrement
  401    *OUTLEN to reflect the number of bytes remaining in *OUT.  */
  402 static bool
  403 decode_4 (char const *in, size_t inlen,
  404           char **outp, size_t *outleft)
  405 {
  406   char *out = *outp;
  407   if (inlen < 2)
  408     return false;
  409 
  410   if (!isbase64 (in[0]) || !isbase64 (in[1]))
  411     return false;
  412 
  413   if (*outleft)
  414     {
  415       *out++ = ((b64[to_uchar (in[0])] << 2)
  416                 | (b64[to_uchar (in[1])] >> 4));
  417       --*outleft;
  418     }
  419 
  420   if (inlen == 2)
  421     return_false;
  422 
  423   if (in[2] == '=')
  424     {
  425       if (inlen != 4)
  426         return_false;
  427 
  428       if (in[3] != '=')
  429         return_false;
  430     }
  431   else
  432     {
  433       if (!isbase64 (in[2]))
  434         return_false;
  435 
  436       if (*outleft)
  437         {
  438           *out++ = (((b64[to_uchar (in[1])] << 4) & 0xf0)
  439                     | (b64[to_uchar (in[2])] >> 2));
  440           --*outleft;
  441         }
  442 
  443       if (inlen == 3)
  444         return_false;
  445 
  446       if (in[3] == '=')
  447         {
  448           if (inlen != 4)
  449             return_false;
  450         }
  451       else
  452         {
  453           if (!isbase64 (in[3]))
  454             return_false;
  455 
  456           if (*outleft)
  457             {
  458               *out++ = (((b64[to_uchar (in[2])] << 6) & 0xc0)
  459                         | b64[to_uchar (in[3])]);
  460               --*outleft;
  461             }
  462         }
  463     }
  464 
  465   *outp = out;
  466   return true;
  467 }
  468 
  469 /* Decode base64-encoded input array IN of length INLEN to output array
  470    OUT that can hold *OUTLEN bytes.  The input data may be interspersed
  471    with newlines.  Return true if decoding was successful, i.e. if the
  472    input was valid base64 data, false otherwise.  If *OUTLEN is too
  473    small, as many bytes as possible will be written to OUT.  On return,
  474    *OUTLEN holds the length of decoded bytes in OUT.  Note that as soon
  475    as any non-alphabet, non-newline character is encountered, decoding
  476    is stopped and false is returned.  If INLEN is zero, then process
  477    only whatever data is stored in CTX.
  478 
  479    Initially, CTX must have been initialized via base64_decode_ctx_init.
  480    Subsequent calls to this function must reuse whatever state is recorded
  481    in that buffer.  It is necessary for when a quadruple of base64 input
  482    bytes spans two input buffers.
  483 
  484    If CTX is NULL then newlines are treated as garbage and the input
  485    buffer is processed as a unit.  */
  486 
  487 bool
  488 base64_decode_ctx (struct base64_decode_context *ctx,
  489                    const char *in, size_t inlen,
  490                    char *out, size_t *outlen)
  491 {
  492   size_t outleft = *outlen;
  493   bool ignore_newlines = ctx != NULL;
  494   bool flush_ctx = false;
  495   unsigned int ctx_i = 0;
  496 
  497   if (ignore_newlines)
  498     {
  499       ctx_i = ctx->i;
  500       flush_ctx = inlen == 0;
  501     }
  502 
  503 
  504   while (true)
  505     {
  506       size_t outleft_save = outleft;
  507       if (ctx_i == 0 && !flush_ctx)
  508         {
  509           while (true)
  510             {
  511               /* Save a copy of outleft, in case we need to re-parse this
  512                  block of four bytes.  */
  513               outleft_save = outleft;
  514               if (!decode_4 (in, inlen, &out, &outleft))
  515                 break;
  516 
  517               in += 4;
  518               inlen -= 4;
  519             }
  520         }
  521 
  522       if (inlen == 0 && !flush_ctx)
  523         break;
  524 
  525       /* Handle the common case of 72-byte wrapped lines.
  526          This also handles any other multiple-of-4-byte wrapping.  */
  527       if (inlen && *in == '\n' && ignore_newlines)
  528         {
  529           ++in;
  530           --inlen;
  531           continue;
  532         }
  533 
  534       /* Restore OUT and OUTLEFT.  */
  535       out -= outleft_save - outleft;
  536       outleft = outleft_save;
  537 
  538       {
  539         char const *in_end = in + inlen;
  540         char const *non_nl;
  541 
  542         if (ignore_newlines)
  543           non_nl = get_4 (ctx, &in, in_end, &inlen);
  544         else
  545           non_nl = in;  /* Might have nl in this case. */
  546 
  547         /* If the input is empty or consists solely of newlines (0 non-newlines),
  548            then we're done.  Likewise if there are fewer than 4 bytes when not
  549            flushing context and not treating newlines as garbage.  */
  550         if (inlen == 0 || (inlen < 4 && !flush_ctx && ignore_newlines))
  551           {
  552             inlen = 0;
  553             break;
  554           }
  555         if (!decode_4 (non_nl, inlen, &out, &outleft))
  556           break;
  557 
  558         inlen = in_end - in;
  559       }
  560     }
  561 
  562   *outlen -= outleft;
  563 
  564   return inlen == 0;
  565 }
  566 
  567 /* Allocate an output buffer in *OUT, and decode the base64 encoded
  568    data stored in IN of size INLEN to the *OUT buffer.  On return, the
  569    size of the decoded data is stored in *OUTLEN.  OUTLEN may be NULL,
  570    if the caller is not interested in the decoded length.  *OUT may be
  571    NULL to indicate an out of memory error, in which case *OUTLEN
  572    contains the size of the memory block needed.  The function returns
  573    true on successful decoding and memory allocation errors.  (Use the
  574    *OUT and *OUTLEN parameters to differentiate between successful
  575    decoding and memory error.)  The function returns false if the
  576    input was invalid, in which case *OUT is NULL and *OUTLEN is
  577    undefined. */
  578 bool
  579 base64_decode_alloc_ctx (struct base64_decode_context *ctx,
  580                          const char *in, size_t inlen, char **out,
  581                          size_t *outlen)
  582 {
  583   /* This may allocate a few bytes too many, depending on input,
  584      but it's not worth the extra CPU time to compute the exact size.
  585      The exact size is 3 * (inlen + (ctx ? ctx->i : 0)) / 4, minus 1 if the
  586      input ends with "=" and minus another 1 if the input ends with "==".
  587      Dividing before multiplying avoids the possibility of overflow.  */
  588   size_t needlen = 3 * (inlen / 4) + 3;
  589 
  590   *out = malloc (needlen);
  591   if (!*out)
  592     return true;
  593 
  594   if (!base64_decode_ctx (ctx, in, inlen, *out, &needlen))
  595     {
  596       free (*out);
  597       *out = NULL;
  598       return false;
  599     }
  600 
  601   if (outlen)
  602     *outlen = needlen;
  603 
  604   return true;
  605 }