src/lib/encoding/pem.c

   1 /* Copyright (c) 2001, Matej Pfajfar.
   2  * Copyright (c) 2001-2004, Roger Dingledine.
   3  * Copyright (c) 2004-2006, Roger Dingledine, Nick Mathewson.
   4  * Copyright (c) 2007-2019, The Tor Project, Inc. */
   5 /* See LICENSE for licensing information */
   6
   7 /**
   8  * \file pem.c
   9  *
  10  * \brief Implement a trivial version of PEM encoding, for use with NSS.
  11  *
  12  * We deliberately do not support any encryption here.
  13  **/
  14
  15 #include "orconfig.h"
  16
  17 #include "lib/encoding/pem.h"
  18
  19 #include "lib/ctime/di_ops.h"
  20 #include "lib/encoding/binascii.h"
  21 #include "lib/log/util_bug.h"
  22 #include "lib/malloc/malloc.h"
  23 #include "lib/string/printf.h"
  24 #include "lib/string/util_string.h"
  25
  26 #include <string.h>
  27
  28 /**
  29  * Return the length of a <b>src_len</b>-byte object when tagged with
  30  * <b>objtype</b> and PEM-encoded.  Includes terminating NUL.
  31  */
  32 size_t
  33 pem_encoded_size(size_t src_len, const char *objtype)
  34 {
  35   return
  36     strlen("-----BEGIN -----\n") +
  37     strlen("-----END -----\n") +
  38     strlen(objtype) * 2 +
  39     base64_encode_size(src_len, BASE64_ENCODE_MULTILINE)
  40     + 1;
  41 }
  42
  43 /**
  44  * PEM-encode the <b>srclen</b>-byte object at <b>src</b> into the
  45  * <b>destlen<\b>-byte buffer at <b>dest</b>, tagging it with <b>objtype</b>.
  46  * Return 0 on success and -1 on failure.
  47  */
  48 int
  49 pem_encode(char *dest, size_t destlen, const uint8_t *src, size_t srclen,
  50            const char *objtype)
  51 {
  52   if (tor_snprintf(dest, destlen, "-----BEGIN %s-----\n", objtype) < 0)
  53     return -1;
  54
  55   size_t offset = strlen(dest);
  56
  57   int n = base64_encode(dest + offset, destlen - offset,
  58                         (const char *)src, srclen, BASE64_ENCODE_MULTILINE);
  59   if (n < 0)
  60     return -1;
  61   offset += n;
  62   if (BUG(offset > destlen))
  63     return -1;
  64
  65   if (tor_snprintf(dest + offset, destlen - offset,
  66                    "-----END %s-----\n", objtype) < 0)
  67     return -1;
  68
  69   tor_assert(strlen(dest) + 1 <= pem_encoded_size(srclen, objtype));
  70   return 0;
  71 }
  72
  73 /**
  74  * Given a PEM-encoded block of size <b>srclen</b> in <b>src</b>, if it has
  75  * object type <b>objtype</b>, decode it into the <b>destlen</b>-byte buffer
  76  * at <b>dest</b>.  Return the number of characters decoded on success, or -1
  77  * on failure.
  78  */
  79 int
  80 pem_decode(uint8_t *dest, size_t destlen, const char *src, size_t srclen,
  81            const char *objtype)
  82 {
  83   const char *eos = src + srclen;
  84
  85   src = eat_whitespace_eos(src, eos);
  86
  87   char *tag = NULL;
  88   tor_asprintf(&tag, "-----BEGIN %s-----", objtype);
  89   if ((size_t)(eos-src) < strlen(tag) || fast_memneq(src, tag, strlen(tag))) {
  90     tor_free(tag);
  91     return -1;
  92   }
  93   src += strlen(tag);
  94   tor_free(tag);
  95   /* At this point we insist on spaces (including CR), then an LF. */
  96   src = eat_whitespace_eos_no_nl(src, eos);
  97   if (src == eos || *src != '\n') {
  98     /* Extra junk at end of line: this isn't valid. */
  99     return -1;
 100   }
 101
 102   // NOTE lack of trailing \n.  We do not enforce its presence.
 103   tor_asprintf(&tag, "\n-----END %s-----", objtype);
 104   const char *end_of_base64 = tor_memstr(src, eos-src, tag);
 105   tor_free(tag);
 106   if (end_of_base64 == NULL)
 107     return -1;
 108
 109   /* Should we actually allow extra stuff at the end? */
 110
 111   return base64_decode((char*)dest, destlen, src, end_of_base64-src);
 112 }