From cb4e889b249907d65de247a6ae5f107483f124cd Mon Sep 17 00:00:00 2001
From: Toni Uhlig <matzeton@googlemail.com>
Date: Tue, 11 Dec 2018 12:53:53 +0100
Subject: basic ascii85 encoder/decoder
Signed-off-by: Toni Uhlig <matzeton@googlemail.com>
---
scrambler.c | 341 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 341 insertions(+)
create mode 100644 scrambler.c
(limited to 'scrambler.c')
diff --git a/scrambler.c b/scrambler.c
new file mode 100644
index 0000000..b3e09e8
--- /dev/null
+++ b/scrambler.c
@@ -0,0 +1,341 @@
+/** @file ascii85.c
+ *
+ * @brief Ascii85 encoder and decoder
+ *
+ * @par
+ * @copyright Copyright © 2017 Doug Currie, Londonderry, NH, USA. All rights reserved.
+ *
+ * @par
+ * Permission is hereby granted, free of charge, to any person obtaining a copy of this software
+ * and associated documentation files (the "Software"), to deal in the Software without
+ * restriction, including without limitation the rights to use, copy, modify, merge, publish,
+ * distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all copies or
+ * substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING
+ * BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
+ * DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+**/
+
+/* from: https://github.com/dcurrie/ascii85 */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <stdint.h>
+#include <stdbool.h>
+
+enum ascii85_errs_e
+{
+ ascii85_err_out_buf_too_small = -255,
+ ascii85_err_in_buf_too_large,
+ ascii85_err_bad_decode_char,
+ ascii85_err_decode_overflow
+};
+
+int32_t encode_ascii85 (const uint8_t *inp, int32_t in_length, uint8_t *outp, int32_t out_max_length);
+
+int32_t decode_ascii85 (const uint8_t *inp, int32_t in_length, uint8_t *outp, int32_t out_max_length);
+
+// From Wikipedia re: Ascii85 length...
+// Adobe adopted the basic btoa encoding, but with slight changes, and gave it the name Ascii85.
+// The characters used are the ASCII characters 33 (!) through 117 (u) inclusive (to represent
+// the base-85 digits 0 through 84), together with the letter z (as a special case to represent
+// a 32-bit 0 value), and white space is ignored. Adobe uses the delimiter "~>" to mark the end
+// of an Ascii85-encoded string, and represents the length by truncating the final group: If the
+// last block of source bytes contains fewer than 4 bytes, the block is padded with up to three
+// null bytes before encoding. After encoding, as many bytes as were added as padding are
+// removed from the end of the output.
+// The reverse is applied when decoding: The last block is padded to 5 bytes with the Ascii85
+// character "u", and as many bytes as were added as padding are omitted from the end of the
+// output (see example).
+// NOTE: The padding is not arbitrary. Converting from binary to base 64 only regroups bits and
+// does not change them or their order (a high bit in binary does not affect the low bits in the
+// base64 representation). In converting a binary number to base85 (85 is not a power of two)
+// high bits do affect the low order base85 digits and conversely. Padding the binary low (with
+// zero bits) while encoding and padding the base85 value high (with 'u's) in decoding assures
+// that the high order bits are preserved (the zero padding in the binary gives enough room so
+// that a small addition is trapped and there is no "carry" to the high bits).
+
+// NOTE: ths implementation does not ignore white space!
+//
+// The motivation for this implementation is as a binary message wrapper for serial
+// communication; in that application, white space is used for message framing.
+
+static const uint8_t base_char = 33u; // '!' -- note that (85 + 33) < 128
+
+static const int32_t ascii85_in_length_max = 65536;
+
+static const bool ascii85_decode_z_for_zero = true;
+static const bool ascii85_encode_z_for_zero = true;
+
+static const bool ascii85_check_decode_chars = true;
+
+#if 0
+static inline bool ascii85_char_ok (uint8_t c)
+{
+ return ((c >= 33u) && (c <= 117u));
+}
+#endif
+
+static inline bool ascii85_char_ng (uint8_t c)
+{
+ return ((c < 33u) || (c > 117u));
+}
+
+/*!
+ * @brief encode_ascii85: encode binary input into Ascii85
+ * @param[in] inp pointer to a buffer of unsigned bytes
+ * @param[in] in_length the number of bytes at inp to encode
+ * @param[in] outp pointer to a buffer for the encoded data
+ * @param[in] out_max_length available space at outp in bytes; must be >= 5 * ceiling(in_length/4)
+ * @return number of bytes in the encoded value at outp if non-negative; error code from
+ * ascii85_errs_e if negative
+ * @par Possible errors include: ascii85_err_in_buf_too_large, ascii85_err_out_buf_too_small
+ */
+int32_t encode_ascii85 (const uint8_t *inp, int32_t in_length, uint8_t *outp, int32_t out_max_length)
+{
+ // Note that (in_length + 3) below may overflow, but this is inconsequental
+ // since ascii85_in_length_max is < (INT32_MAX - 3), and we check in_length before
+ // using the calculated out_length.
+ //
+ int32_t out_length = (((in_length + 3) / 4) * 5); // ceiling
+
+ if (in_length > ascii85_in_length_max)
+ {
+ out_length = (int32_t )ascii85_err_in_buf_too_large;
+ }
+ else if (out_length > out_max_length)
+ {
+ out_length = (int32_t )ascii85_err_out_buf_too_small;
+ }
+ else
+ {
+ int32_t in_rover = 0;
+
+ out_length = 0; // we know we can increment by 5 * ceiling(in_length/4)
+
+ while (in_rover < in_length)
+ {
+ uint32_t chunk;
+ int32_t chunk_len = in_length - in_rover;
+
+ if (chunk_len >= 4)
+ {
+ chunk = (((uint32_t )inp[in_rover++]) << 24u);
+ chunk |= (((uint32_t )inp[in_rover++]) << 16u);
+ chunk |= (((uint32_t )inp[in_rover++]) << 8u);
+ chunk |= (((uint32_t )inp[in_rover++]) );
+ }
+ else
+ {
+ chunk = (((uint32_t )inp[in_rover++]) << 24u);
+ chunk |= ((in_rover < in_length) ? (((uint32_t )inp[in_rover++]) << 16u) : 0u);
+ chunk |= ((in_rover < in_length) ? (((uint32_t )inp[in_rover++]) << 8u) : 0u);
+ chunk |= ((in_rover < in_length) ? (((uint32_t )inp[in_rover++]) ) : 0u);
+ }
+
+ if (/*lint -e{506} -e{774}*/ascii85_encode_z_for_zero && (0u == chunk) && (chunk_len >= 4))
+ {
+ outp[out_length++] = (uint8_t )'z';
+ }
+ else
+ {
+ outp[out_length + 4] = (chunk % 85u) + base_char;
+ chunk /= 85u;
+ outp[out_length + 3] = (chunk % 85u) + base_char;
+ chunk /= 85u;
+ outp[out_length + 2] = (chunk % 85u) + base_char;
+ chunk /= 85u;
+ outp[out_length + 1] = (chunk % 85u) + base_char;
+ chunk /= 85u;
+ outp[out_length ] = (uint8_t )chunk + base_char;
+ // we don't need (chunk % 85u) on the last line since (((((2^32 - 1) / 85) / 85) / 85) / 85) = 82.278
+
+ if (chunk_len >= 4)
+ {
+ out_length += 5;
+ }
+ else
+ {
+ out_length += (chunk_len + 1); // see note above re: Ascii85 length
+ }
+ }
+ }
+ }
+
+ return out_length;
+}
+
+/*!
+ * @brief decode_ascii85: decode Ascii85 input to binary output
+ * @param[in] inp pointer to a buffer of Ascii85 encoded unsigned bytes
+ * @param[in] in_length the number of bytes at inp to decode
+ * @param[in] outp pointer to a buffer for the decoded data
+ * @param[in] out_max_length available space at outp in bytes; must be >= 4 * ceiling(in_length/5)
+ * @return number of bytes in the decoded value at outp if non-negative; error code from
+ * ascii85_errs_e if negative
+ * @par Possible errors include: ascii85_err_in_buf_too_large, ascii85_err_out_buf_too_small,
+ * ascii85_err_bad_decode_char, ascii85_err_decode_overflow
+ */
+int32_t decode_ascii85 (const uint8_t *inp, int32_t in_length, uint8_t *outp, int32_t out_max_length)
+{
+ // Note that (in_length + 4) below may overflow, but this is inconsequental
+ // since ascii85_in_length_max is < (INT32_MAX - 4), and we check in_length before
+ // using the calculated out_length.
+ //
+ int32_t out_length = (((in_length + 4) / 5) * 4); // ceiling
+
+ if (in_length > ascii85_in_length_max)
+ {
+ out_length = (int32_t )ascii85_err_in_buf_too_large;
+ }
+ else if (out_length > out_max_length)
+ {
+ out_length = (int32_t )ascii85_err_out_buf_too_small;
+ }
+ else
+ {
+ int32_t in_rover = 0;
+
+ out_length = 0; // we know we can increment by 4 * ceiling(in_length/5)
+
+ while (in_rover < in_length)
+ {
+ uint32_t chunk;
+ int32_t chunk_len = in_length - in_rover;
+
+ if (/*lint -e{506} -e{774}*/ascii85_decode_z_for_zero && ((uint8_t )'z' == inp[in_rover]))
+ {
+ in_rover += 1;
+ chunk = 0u;
+ chunk_len = 5; // to make out_length increment correct
+ }
+ else if (/*lint -e{506} -e{774}*/ascii85_check_decode_chars
+ && ( ascii85_char_ng(inp[in_rover ])
+ || ((chunk_len > 1) && ascii85_char_ng(inp[in_rover + 1]))
+ || ((chunk_len > 2) && ascii85_char_ng(inp[in_rover + 2]))
+ || ((chunk_len > 3) && ascii85_char_ng(inp[in_rover + 3]))
+ || ((chunk_len > 4) && ascii85_char_ng(inp[in_rover + 4]))))
+ {
+ out_length = (int32_t )ascii85_err_bad_decode_char;
+ break; // leave while loop early to report error
+ }
+ else if (chunk_len >= 5)
+ {
+ chunk = inp[in_rover++] - base_char;
+ chunk *= 85u; // max: 84 * 85 = 7,140
+ chunk += inp[in_rover++] - base_char;
+ chunk *= 85u; // max: (84 * 85 + 84) * 85 = 614,040
+ chunk += inp[in_rover++] - base_char;
+ chunk *= 85u; // max: (((84 * 85 + 84) * 85) + 84) * 85 = 52,200,540
+ chunk += inp[in_rover++] - base_char;
+ // max: (((((84 * 85 + 84) * 85) + 84) * 85) + 84) * 85 = 4,437,053,040 oops! 0x108780E70
+ if (chunk > (UINT32_MAX / 85u))
+ {
+ // multiply would overflow
+ out_length = (int32_t )ascii85_err_decode_overflow; // bad input
+ break; // leave while loop early to report error
+ }
+ else
+ {
+ uint8_t addend = inp[in_rover++] - base_char;
+
+ chunk *= 85u; // multiply will not overflow due to test above
+
+ if (chunk > (UINT32_MAX - addend))
+ {
+ /// add would overflow
+ out_length = (int32_t )ascii85_err_decode_overflow; // bad input
+ break; // leave while loop early to report error
+ }
+ else
+ {
+ chunk += addend;
+ }
+ }
+ }
+ else
+ {
+ chunk = inp[in_rover++] - base_char;
+ chunk *= 85u; // max: 84 * 85 = 7,140
+ chunk += ((in_rover < in_length) ? (inp[in_rover++] - base_char) : 84u);
+ chunk *= 85u; // max: (84 * 85 + 84) * 85 = 614,040
+ chunk += ((in_rover < in_length) ? (inp[in_rover++] - base_char) : 84u);
+ chunk *= 85u; // max: (((84 * 85 + 84) * 85) + 84) * 85 = 52,200,540
+ chunk += ((in_rover < in_length) ? (inp[in_rover++] - base_char) : 84u);
+ // max: (((((84 * 85 + 84) * 85) + 84) * 85) + 84) * 85 = 4,437,053,040 oops! 0x108780E70
+ if (chunk > (UINT32_MAX / 85u))
+ {
+ // multiply would overflow
+ out_length = (int32_t )ascii85_err_decode_overflow; // bad input
+ break; // leave while loop early to report error
+ }
+ else
+ {
+ uint8_t addend = (uint8_t )((in_rover < in_length) ? (inp[in_rover++] - base_char) : 84u);
+
+ chunk *= 85u; // multiply will not overflow due to test above
+
+ if (chunk > (UINT32_MAX - addend))
+ {
+ /// add would overflow
+ out_length = (int32_t )ascii85_err_decode_overflow; // bad input
+ break; // leave while loop early to report error
+ }
+ else
+ {
+ chunk += addend;
+ }
+ }
+ }
+
+ outp[out_length + 3] = (chunk % 256u);
+ chunk /= 256u;
+ outp[out_length + 2] = (chunk % 256u);
+ chunk /= 256u;
+ outp[out_length + 1] = (chunk % 256u);
+ chunk /= 256u;
+ outp[out_length ] = (uint8_t )chunk;
+ // we don't need (chunk % 256u) on the last line since ((((2^32 - 1) / 256u) / 256u) / 256u) = 255
+
+ if (chunk_len >= 5)
+ {
+ out_length += 4;
+ }
+ else
+ {
+ out_length += (chunk_len - 1); // see note above re: Ascii85 length
+ }
+ }
+ }
+
+ return out_length;
+}
+
+int main(int argc, char **argv) {
+ uint8_t out_enc[BUFSIZ], out_dec[BUFSIZ];
+ size_t buflen;
+ int32_t siz_enc, siz_dec;
+
+ if (argc != 2) {
+ printf("usage: %s [BINARY-DATA]\n", (argc > 0 ? argv[0] : "null"));
+ exit(1);
+ }
+
+ memset(out_enc, 0, sizeof out_enc);
+ memset(out_dec, 0, sizeof out_dec);
+
+ buflen = strlen(argv[1]);
+ siz_enc = encode_ascii85((uint8_t *) argv[1], buflen, out_enc, sizeof out_enc - 1);
+ printf("Encoded: \"%.*s\"\n", siz_enc, (char *) out_enc);
+ siz_dec = decode_ascii85(out_enc, siz_enc, out_dec, sizeof out_dec - 1);
+ printf("Decoded: \"%.*s\"\n", siz_dec, (char *) out_dec);
+
+ return 0;
+}
--
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