_ Git - BearSSL/blob - inc/bearssl_pem.h

   1 /*
   2  * Copyright (c) 2016 Thomas Pornin <pornin@bolet.org>
   3  *
   4  * Permission is hereby granted, free of charge, to any person obtaining
   5  * a copy of this software and associated documentation files (the
   6  * "Software"), to deal in the Software without restriction, including
   7  * without limitation the rights to use, copy, modify, merge, publish,
   8  * distribute, sublicense, and/or sell copies of the Software, and to
   9  * permit persons to whom the Software is furnished to do so, subject to
  10  * the following conditions:
  11  *
  12  * The above copyright notice and this permission notice shall be
  13  * included in all copies or substantial portions of the Software.
  14  *
  15  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
  16  * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
  17  * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
  18  * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
  19  * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
  20  * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
  21  * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
  22  * SOFTWARE.
  23  */
  24
  25 #ifndef BR_BEARSSL_PEM_H__
  26 #define BR_BEARSSL_PEM_H__
  27
  28 #include <stddef.h>
  29 #include <stdint.h>
  30
  31 #ifdef __cplusplus
  32 extern "C" {
  33 #endif
  34
  35 /** \file bearssl_pem.h
  36  *
  37  * # PEM Support
  38  *
  39  * PEM is a traditional encoding layer use to store binary objects (in
  40  * particular X.509 certificates, and private keys) in text files. While
  41  * the acronym comes from an old, defunct standard ("Privacy Enhanced
  42  * Mail"), the format has been reused, with some variations, by many
  43  * systems, and is a _de facto_ standard, even though it is not, actually,
  44  * specified in all clarity anywhere.
  45  *
  46  * ## Format Details
  47  *
  48  * BearSSL contains a generic, streamed PEM decoder, which handles the
  49  * following format:
  50  *
  51  *   - The input source (a sequence of bytes) is assumed to be the
  52  *     encoding of a text file in an ASCII-compatible charset. This
  53  *     includes ISO-8859-1, Windows-1252, and UTF-8 encodings. Each
  54  *     line ends on a newline character (U+000A LINE FEED). The
  55  *     U+000D CARRIAGE RETURN characters are ignored, so the code
  56  *     accepts both Windows-style and Unix-style line endings.
  57  *
  58  *   - Each object begins with a banner that occurs at the start of
  59  *     a line; the first banner characters are "`-----BEGIN `" (five
  60  *     dashes, the word "BEGIN", and a space). The banner matching is
  61  *     not case-sensitive.
  62  *
  63  *   - The _object name_ consists in the characters that follow the
  64  *     banner start sequence, up to the end of the line, but without
  65  *     trailing dashes (in "normal" PEM, there are five trailing
  66  *     dashes, but this implementation is not picky about these dashes).
  67  *     The BearSSL decoder normalises the name characters to uppercase
  68  *     (for ASCII letters only) and accepts names up to 127 characters.
  69  *
  70  *   - The object ends with a banner that again occurs at the start of
  71  *     a line, and starts with "`-----END `" (again case-insensitive).
  72  *
  73  *   - Between that start and end banner, only Base64 data shall occur.
  74  *     Base64 converts each sequence of three bytes into four
  75  *     characters; the four characters are ASCII letters, digits, "`+`"
  76  *     or "`-`" signs, and one or two "`=`" signs may occur in the last
  77  *     quartet. Whitespace is ignored (whitespace is any ASCII character
  78  *     of code 32 or less, so control characters are whitespace) and
  79  *     lines may have arbitrary length; the only restriction is that the
  80  *     four characters of a quartet must appear on the same line (no
  81  *     line break inside a quartet).
  82  *
  83  *   - A single file may contain more than one PEM object. Bytes that
  84  *     occur between objects are ignored.
  85  *
  86  *
  87  * ## PEM Decoder API
  88  *
  89  * The PEM decoder offers a state-machine API. The caller allocates a
  90  * decoder context, then injects source bytes. Source bytes are pushed
  91  * with `br_pem_decoder_push()`. The decoder stops accepting bytes when
  92  * it reaches an "event", which is either the start of an object, the
  93  * end of an object, or a decoding error within an object.
  94  *
  95  * The `br_pem_decoder_event()` function is used to obtain the current
  96  * event; it also clears it, thus allowing the decoder to accept more
  97  * bytes. When a object start event is raised, the decoder context
  98  * offers the found object name (normalised to ASCII uppercase).
  99  *
 100  * When an object is reached, the caller must set an appropriate callback
 101  * function, which will receive (by chunks) the decoded object data.
 102  *
 103  * Since the decoder context makes no dynamic allocation, it requires
 104  * no explicit deallocation.
 105  */
 106
 107 /**
 108  * \brief PEM decoder context.
 109  *
 110  * Contents are opaque (they should not be accessed directly).
 111  */
 112 typedef struct {
 113 #ifndef BR_DOXYGEN_IGNORE
 114         /* CPU for the T0 virtual machine. */
 115         struct {
 116                 uint32_t *dp;
 117                 uint32_t *rp;
 118                 const unsigned char *ip;
 119         } cpu;
 120         uint32_t dp_stack[32];
 121         uint32_t rp_stack[32];
 122         int err;
 123
 124         const unsigned char *hbuf;
 125         size_t hlen;
 126
 127         void (*dest)(void *dest_ctx, const void *src, size_t len);
 128         void *dest_ctx;
 129
 130         unsigned char event;
 131         char name[128];
 132         unsigned char buf[255];
 133         size_t ptr;
 134 #endif
 135 } br_pem_decoder_context;
 136
 137 /**
 138  * \brief Initialise a PEM decoder structure.
 139  *
 140  * \param ctx   decoder context to initialise.
 141  */
 142 void br_pem_decoder_init(br_pem_decoder_context *ctx);
 143
 144 /**
 145  * \brief Push some bytes into the decoder.
 146  *
 147  * Returned value is the number of bytes actually consumed; this may be
 148  * less than the number of provided bytes if an event is raised. When an
 149  * event is raised, it must be read (with `br_pem_decoder_event()`);
 150  * until the event is read, this function will return 0.
 151  *
 152  * \param ctx    decoder context.
 153  * \param data   new data bytes.
 154  * \param len    number of new data bytes.
 155  * \return  the number of bytes actually received (may be less than `len`).
 156  */
 157 size_t br_pem_decoder_push(br_pem_decoder_context *ctx,
 158         const void *data, size_t len);
 159
 160 /**
 161  * \brief Set the receiver for decoded data.
 162  *
 163  * When an object is entered, the provided function (with opaque context
 164  * pointer) will be called repeatedly with successive chunks of decoded
 165  * data for that object. If `dest` is set to 0, then decoded data is
 166  * simply ignored. The receiver can be set at any time, but, in practice,
 167  * it should be called immediately after receiving a "start of object"
 168  * event.
 169  *
 170  * \param ctx        decoder context.
 171  * \param dest       callback for receiving decoded data.
 172  * \param dest_ctx   opaque context pointer for the `dest` callback.
 173  */
 174 static inline void
 175 br_pem_decoder_setdest(br_pem_decoder_context *ctx,
 176         void (*dest)(void *dest_ctx, const void *src, size_t len),
 177         void *dest_ctx)
 178 {
 179         ctx->dest = dest;
 180         ctx->dest_ctx = dest_ctx;
 181 }
 182
 183 /**
 184  * \brief Get the last event.
 185  *
 186  * If an event was raised, then this function returns the event value, and
 187  * also clears it, thereby allowing the decoder to proceed. If no event
 188  * was raised since the last call to `br_pem_decoder_event()`, then this
 189  * function returns 0.
 190  *
 191  * \param ctx   decoder context.
 192  * \return  the raised event, or 0.
 193  */
 194 int br_pem_decoder_event(br_pem_decoder_context *ctx);
 195
 196 /**
 197  * \brief Event: start of object.
 198  *
 199  * This event is raised when the start of a new object has been detected.
 200  * The object name (normalised to uppercase) can be accessed with
 201  * `br_pem_decoder_name()`.
 202  */
 203 #define BR_PEM_BEGIN_OBJ   1
 204
 205 /**
 206  * \brief Event: end of object.
 207  *
 208  * This event is raised when the end of the current object is reached
 209  * (normally, i.e. with no decoding error).
 210  */
 211 #define BR_PEM_END_OBJ     2
 212
 213 /**
 214  * \brief Event: decoding error.
 215  *
 216  * This event is raised when decoding fails within an object.
 217  * This formally closes the current object and brings the decoder back
 218  * to the "out of any object" state. The offending line in the source
 219  * is consumed.
 220  */
 221 #define BR_PEM_ERROR       3
 222
 223 /**
 224  * \brief Get the name of the encountered object.
 225  *
 226  * The encountered object name is defined only when the "start of object"
 227  * event is raised. That name is normalised to uppercase (for ASCII letters
 228  * only) and does not include trailing dashes.
 229  *
 230  * \param ctx   decoder context.
 231  * \return  the current object name.
 232  */
 233 static inline const char *
 234 br_pem_decoder_name(br_pem_decoder_context *ctx)
 235 {
 236         return ctx->name;
 237 }
 238
 239 #ifdef __cplusplus
 240 }
 241 #endif
 242
 243 #endif