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Diffstat (limited to 'src/lib/crypto/krb/nfold.c')
| -rw-r--r-- | src/lib/crypto/krb/nfold.c | 130 |
1 files changed, 130 insertions, 0 deletions
diff --git a/src/lib/crypto/krb/nfold.c b/src/lib/crypto/krb/nfold.c new file mode 100644 index 0000000..1f1902d --- /dev/null +++ b/src/lib/crypto/krb/nfold.c @@ -0,0 +1,130 @@ +/* + * Copyright (C) 1998 by the FundsXpress, INC. + * + * All rights reserved. + * + * Export of this software from the United States of America may require + * a specific license from the United States Government. It is the + * responsibility of any person or organization contemplating export to + * obtain such a license before exporting. + * + * WITHIN THAT CONSTRAINT, permission to use, copy, modify, and + * distribute this software and its documentation for any purpose and + * without fee is hereby granted, provided that the above copyright + * notice appear in all copies and that both that copyright notice and + * this permission notice appear in supporting documentation, and that + * the name of FundsXpress. not be used in advertising or publicity pertaining + * to distribution of the software without specific, written prior + * permission. FundsXpress makes no representations about the suitability of + * this software for any purpose. It is provided "as is" without express + * or implied warranty. + * + * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR + * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED + * WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE. + */ + +#include "k5-int.h" +#ifdef HAVE_MEMORY_H +#include <memory.h> +#endif + +/* +n-fold(k-bits): + l = lcm(n,k) + r = l/k + s = k-bits | k-bits rot 13 | k-bits rot 13*2 | ... | k-bits rot 13*(r-1) + compute the 1's complement sum: + n-fold = s[0..n-1]+s[n..2n-1]+s[2n..3n-1]+..+s[(k-1)*n..k*n-1] +*/ + +/* representation: msb first, assume n and k are multiples of 8, and + that k>=16. this is the case of all the cryptosystems which are + likely to be used. this function can be replaced if that + assumption ever fails. */ + +/* input length is in bits */ + +void +krb5_nfold(unsigned int inbits, const unsigned char *in, unsigned int outbits, + unsigned char *out) +{ + int a,b,c,lcm; + int byte, i, msbit; + + /* the code below is more readable if I make these bytes + instead of bits */ + + inbits >>= 3; + outbits >>= 3; + + /* first compute lcm(n,k) */ + + a = outbits; + b = inbits; + + while(b != 0) { + c = b; + b = a%b; + a = c; + } + + lcm = outbits*inbits/a; + + /* now do the real work */ + + memset(out, 0, outbits); + byte = 0; + + /* this will end up cycling through k lcm(k,n)/k times, which + is correct */ + for (i=lcm-1; i>=0; i--) { + /* compute the msbit in k which gets added into this byte */ + msbit = (/* first, start with the msbit in the first, unrotated + byte */ + ((inbits<<3)-1) + /* then, for each byte, shift to the right for each + repetition */ + +(((inbits<<3)+13)*(i/inbits)) + /* last, pick out the correct byte within that + shifted repetition */ + +((inbits-(i%inbits))<<3) + )%(inbits<<3); + + /* pull out the byte value itself */ + byte += (((in[((inbits-1)-(msbit>>3))%inbits]<<8)| + (in[((inbits)-(msbit>>3))%inbits])) + >>((msbit&7)+1))&0xff; + + /* do the addition */ + byte += out[i%outbits]; + out[i%outbits] = byte&0xff; + +#if 0 + printf("msbit[%d] = %d\tbyte = %02x\tsum = %03x\n", i, msbit, + (((in[((inbits-1)-(msbit>>3))%inbits]<<8)| + (in[((inbits)-(msbit>>3))%inbits])) + >>((msbit&7)+1))&0xff, byte); +#endif + + /* keep around the carry bit, if any */ + byte >>= 8; + +#if 0 + printf("carry=%d\n", byte); +#endif + } + + /* if there's a carry bit left over, add it back in */ + if (byte) { + for (i=outbits-1; i>=0; i--) { + /* do the addition */ + byte += out[i]; + out[i] = byte&0xff; + + /* keep around the carry bit, if any */ + byte >>= 8; + } + } +} + |