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

/****************************************************************/
/* */
/* Encrypt/decrypt data */
/* */
/* Copyright 1987-1989 by Robert B. Stout dba MicroFirm */
/* */
/* This code may be used freely in any program for any */
/* application, personal or commercial. */
/* */
/* Available as part of Steve Margison's C library for the */
/* Zortech C/C++ and Turbo C compilers. */
/* */
/* Also available for dedciated file encryption as part of */
/* Mike Smedley's CXL windowing library, and for stand-alone */
/* file encryption as part of the LYNX and CRYPT utilities */
/* in the MicroFirm Toolkit, versions 3.00 and above. */
/* */
/****************************************************************/

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 reset crypt_ptr before each use. In other words, if
crypt() is used to encrypt several files, crypt_ptr
should be reset to zero before each is encrypted. Also
note the encryption is perfectly reversible - to decrypt
data, pass it back through crypt() using the original
key and original initial value of crypt_ptr.
*/

/**** 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;
}