John Hood
114 lines
3.4 KiB
C++
114 lines
3.4 KiB
C++
/*
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Mosh: the mobile shell
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Copyright 2012 Keith Winstein
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This program is free software: you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation, either version 3 of the License, or
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(at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program. If not, see <http://www.gnu.org/licenses/>.
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In addition, as a special exception, the copyright holders give
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permission to link the code of portions of this program with the
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OpenSSL library under certain conditions as described in each
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individual source file, and distribute linked combinations including
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the two.
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You must obey the GNU General Public License in all respects for all
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of the code used other than OpenSSL. If you modify file(s) with this
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exception, you may extend this exception to your version of the
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file(s), but you are not obligated to do so. If you do not wish to do
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so, delete this exception statement from your version. If you delete
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this exception statement from all source files in the program, then
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also delete it here.
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*/
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#include <string.h>
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#include <stdlib.h>
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#include "fatal_assert.h"
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#include "base64.h"
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static const char table[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
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/* Reverse maps from an ASCII char to a base64 sixbit value. Returns > 0x3f on failure. */
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static unsigned char base64_char_to_sixbit(char c)
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{
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/*
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* Yes, this is slow. But it's also very simple, and easy to verify.
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* We don't need performance here.
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*/
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const char *match = NULL;
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for ( const char *search = table; *search; search++ ) {
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if ( *search == c ) {
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match = search;
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}
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}
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if ( !match ) {
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return 0xff;
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}
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return match - table;
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}
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bool base64_decode( const char *b64, const size_t b64_len,
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uint8_t *raw, size_t *raw_len )
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{
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fatal_assert( b64_len == 24 ); /* only useful for Mosh keys */
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fatal_assert( *raw_len == 16 );
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uint32_t bytes = 0;
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for (int i = 0; i < 22; i++) {
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unsigned char sixbit = base64_char_to_sixbit(*(b64++));
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if (sixbit > 0x3f) {
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return false;
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}
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bytes <<= 6;
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bytes |= sixbit;
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/* write groups of 3 */
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if (i % 4 == 3) {
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raw[0] = bytes >> 16;
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raw[1] = bytes >> 8;
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raw[2] = bytes;
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raw += 3;
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bytes = 0;
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}
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}
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/* last byte of output */
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*raw = bytes >> 4;
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if (b64[0] != '=' || b64[1] != '=') {
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return false;
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}
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return true;
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}
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void base64_encode( const uint8_t *raw, const size_t raw_len,
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char *b64, const size_t b64_len )
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{
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fatal_assert( b64_len == 24 ); /* only useful for Mosh keys */
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fatal_assert( raw_len == 16 );
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/* first 15 bytes of input */
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for (int i = 0; i < 5; i++) {
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uint32_t bytes = (raw[0] << 16) | (raw[1] << 8) | raw[2];
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b64[0] = table[(bytes >> 18) & 0x3f];
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b64[1] = table[(bytes >> 12) & 0x3f];
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b64[2] = table[(bytes >> 6) & 0x3f];
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b64[3] = table[(bytes) & 0x3f];
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raw += 3;
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b64 += 4;
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}
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/* last byte of input, last 4 of output */
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b64[0] = table[*raw >> 2];
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b64[1] = table[(*raw << 4) & 0x3f];
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b64[2] = '=';
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b64[3] = '=';
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}
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