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Diffstat (limited to 'gs/base/sarc4.c')
| -rw-r--r-- | gs/base/sarc4.c | 128 |
1 files changed, 128 insertions, 0 deletions
diff --git a/gs/base/sarc4.c b/gs/base/sarc4.c new file mode 100644 index 000000000..fe75e4a15 --- /dev/null +++ b/gs/base/sarc4.c @@ -0,0 +1,128 @@ +/* Copyright (C) 2001-2006 Artifex Software, Inc. + All Rights Reserved. + + This software is provided AS-IS with no warranty, either express or + implied. + + This software is distributed under license and may not be copied, modified + or distributed except as expressly authorized under the terms of that + license. Refer to licensing information at http://www.artifex.com/ + or contact Artifex Software, Inc., 7 Mt. Lassen Drive - Suite A-134, + San Rafael, CA 94903, U.S.A., +1(415)492-9861, for further information. +*/ + +/* $Id$ */ + +/* Arcfour cipher and filter implementation */ + +#include "memory_.h" +#include "gserrors.h" +#include "gserror.h" +#include "strimpl.h" +#include "sarc4.h" + +/* This is an independent implementation of the symmetric block + * cipher commonly known as 'arcfour' based on Bruce Schneier's + * description of the algorithm in _Applied Cryptography_. Arcfour + * is believed to be functionally equivalent to the RC4(tm) cipher + * mentioned in the PDF specification. (RC4 is a registered + * trademark of RSA Data Security, Inc.) + */ + +/* stream implementation */ + +private_st_arcfour_state(); /* creates a gc object for our state, defined in sarc4.h */ + +/* initialize the S box using the given key */ +int +s_arcfour_set_key(stream_arcfour_state * state, const unsigned char *key, + int keylength) +{ + unsigned int x, y; + unsigned char s, *S = state->S; + + if (keylength < 1) + return_error(gs_error_rangecheck); + + /* initialize to eponymous values */ + for (x = 0; x < 256; x++) + S[x] = x; + + /* scramble based on the key */ + y = 0; + for (x = 0; x < 256; x++) { + y = (y + S[x] + key[x % keylength]) & 0xFF; + s = S[x]; + S[x] = S[y]; + S[y] = s; + } + + /* initialize the indicies */ + state->x = 0; + state->y = 0; + + /* return successfully */ + return 0; +} + +/* (de)crypt a section of text--the procedure is the same + * in each direction. see strimpl.h for return codes. + */ +static int +s_arcfour_process(stream_state * ss, stream_cursor_read * pr, + stream_cursor_write * pw, bool last) +{ + stream_arcfour_state *const state = (stream_arcfour_state *) ss; + unsigned int x = state->x; + unsigned int y = state->y; + unsigned char s, *S = state->S; + unsigned char z; + const unsigned char *limit; + int status; + + /* figure out if we're going to run out of space */ + if ((pr->limit - pr->ptr) > (pw->limit - pw->ptr)) { + limit = pr->ptr + (pw->limit - pw->ptr); + status = 1; + } else { + limit = pr->limit; + status = last ? EOFC : 0; + } + /* generate a pseudorandom byte stream and xor it with the input */ + while (pr->ptr < limit) { + x = (x + 1) & 0xFF; + y = (y + S[x]) & 0xFF; + s = S[x]; + S[x] = S[y]; + S[y] = s; + z = S[(S[x] + S[y]) & 0xFF]; + + *++pw->ptr = (*++pr->ptr) ^ z; + } + /* save state */ + state->x = x; + state->y = y; + + return status; +} + +/* stream template */ +const stream_template s_arcfour_template = { + &st_arcfour_state, NULL, s_arcfour_process, 1, 1 +}; + +/* (de)crypt a section of text in a buffer -- the procedure is the same + * in each direction. see strimpl.h for return codes. + */ +int +s_arcfour_process_buffer(stream_arcfour_state *ss, byte *buf, int buf_size) +{ + stream_cursor_read r; + stream_cursor_write w; + const bool unused = false; + + r.ptr = w.ptr = buf - 1; + r.limit = w.limit = buf - 1 + buf_size; + return s_arcfour_process((stream_state *)ss, &r, &w, unused); +} + |