FreeCalypso > hg > gsm-net-reveng
view tfo/find-is-hdr.c @ 16:2daf8f209707
tcsm2-notes: initial observations on boards
author | Mychaela Falconia <falcon@freecalypso.org> |
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date | Wed, 29 May 2024 02:26:13 +0000 |
parents | 98c0881c2af0 |
children |
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/* * This program reads a binary file containing a G.711 PCM stream capture * and looks for an IS_Header pattern as defined in ETSI TS 101 504 * (GSM 08.62) section A.1.2. The objective is to analyze PCM streams * originating from extant commercial GSM network operators and see if * they implement in-band TFO. */ #include <sys/types.h> #include <sys/file.h> #include <sys/stat.h> #include <sys/mman.h> #include <stdio.h> #include <stdlib.h> #include <unistd.h> static char *pcmfile; static size_t pcm_file_size; static u_char *filemap; static const u_char hdr_pattern[20] = {0, 1, 0, 1, 0, 1, 1, 0, 1, 0, 0, 1, 1, 0, 1, 0, 1, 0, 0, 1}; static void mmap_pcm_file() { int fd; struct stat st; fd = open(pcmfile, O_RDONLY); if (fd < 0) { perror(pcmfile); exit(1); } fstat(fd, &st); if (!S_ISREG(st.st_mode)) { fprintf(stderr, "error: %s is not a regular file\n", pcmfile); exit(1); } pcm_file_size = st.st_size; if (pcm_file_size < 320) { fprintf(stderr, "error: %s is too short\n", pcmfile); exit(1); } filemap = mmap(NULL, pcm_file_size, PROT_READ, MAP_PRIVATE, fd, 0L); if (filemap == MAP_FAILED) { perror("mmap"); exit(1); } close(fd); } static void try_offset(offset) size_t offset; { unsigned n; for (n = 0; n < 20; n++) { if ((filemap[offset + n * 16] & 1) != hdr_pattern[n]) return; } printf("Found IS_Header at offset %lu (0x%lx)\n", (u_long) offset, (u_long) offset); } main(argc, argv) char **argv; { size_t offset, endoff; if (argc != 2) { fprintf(stderr, "usage: %s pcm-capture-file\n", argv[0]); exit(1); } pcmfile = argv[1]; mmap_pcm_file(); endoff = pcm_file_size - 320; for (offset = 0; offset <= endoff; offset++) try_offset(offset); exit(0); }