Category : C Source Code
Archive   : SNIP1292.ZIP
Filename : CRYPT.C

/****************************************************************/
/* */
/* S-CODER - Encrypt/decrypt data */
/* */
/* Copyright 1987-1989 by Robert B. Stout dba MicroFirm */
/* */
/* Originally written by Bob Stout with modifications */
/* suggested by Mike Smedley. */
/* */
/* This code may be used freely in any program for any */
/* application, personal or commercial. */
/* */
/* Current commercial availability: */
/* */
/* 1. MicroFirm Toolkit ver 3.00: LYNX and CRYPT utilities */
/* 2. CXL libraries (MSC, TC, ZTC/C++, PC): fcrypt() */
/* dedicated file encryption function */
/* 3. SMTC & MFLZT libraries: crypt() function */
/* */
/****************************************************************/

char *cryptext; /* The actual encryption/decryption key */
int crypt_ptr = 0; /* Circular pointer to elements of key */
int crypt_length; /* Set externally to strlen(cryptext) */

/* NOTES: cryptext should be set and qualified (to something over
5-6 chars, minimum) by the calling program, which should
also set crypt_ptr in the range of 0 to strlen(cryptext)
before each use. If crypt() is used to encrypt several
buffers, cryptext should be reloaded and crypt_ptr reset
before each buffer is encrypted. The encryption is both
reversible - to decrypt data, pass it back through crypt()
using the original key and original initial value of
crypt_ptr - and multiple passes are commutative.
*/

/**** Encrypt/decrypt buffer datum ******************************/
void crypt(char *buf)
{
*buf ^= cryptext[crypt_ptr] ^ (cryptext[0] * crypt_ptr);
cryptext[crypt_ptr] += ((crypt_ptr < (crypt_length - 1)) ?
cryptext[crypt_ptr + 1] : cryptext[0]);
if (!cryptext[crypt_ptr])
cryptext[crypt_ptr] += 1;
if (++crypt_ptr >= crypt_length)
crypt_ptr = 0;
}