// SPDX-License-Identifier: GPL-2.0-or-later /* * Common Twofish algorithm parts shared between the c and assembler * implementations * * Originally Twofish for GPG * By Matthew Skala <mskala@ansuz.sooke.bc.ca>, July 26, 1998 * 256-bit key length added March 20, 1999 * Some modifications to reduce the text size by Werner Koch, April, 1998 * Ported to the kerneli patch by Marc Mutz <Marc@Mutz.com> * Ported to CryptoAPI by Colin Slater <hoho@tacomeat.net> * * The original author has disclaimed all copyright interest in this * code and thus put it in the public domain. The subsequent authors * have put this under the GNU General Public License. * * This code is a "clean room" implementation, written from the paper * _Twofish: A 128-Bit Block Cipher_ by Bruce Schneier, John Kelsey, * Doug Whiting, David Wagner, Chris Hall, and Niels Ferguson, available * through http://www.counterpane.com/twofish.html * * For background information on multiplication in finite fields, used for * the matrix operations in the key schedule, see the book _Contemporary * Abstract Algebra_ by Joseph A. Gallian, especially chapter 22 in the * Third Edition.
*/
/* These MDS tables are actually tables of MDS composed with q0 and q1, * because it is only ever used that way and we can save some time by * precomputing. Of course the main saving comes from precomputing the * GF(2^8) multiplication involved in the MDS matrix multiply; by looking * things up in these tables we reduce the matrix multiply to four lookups * and three XORs. Semi-formally, the definition of these tables is: * mds[0][i] = MDS (q1[i] 0 0 0)^T mds[1][i] = MDS (0 q0[i] 0 0)^T * mds[2][i] = MDS (0 0 q1[i] 0)^T mds[3][i] = MDS (0 0 0 q0[i])^T * where ^T means "transpose", the matrix multiply is performed in GF(2^8) * represented as GF(2)[x]/v(x) where v(x)=x^8+x^6+x^5+x^3+1 as described * by Schneier et al, and I'm casually glossing over the byte/word
* conversion issues. */
/* The exp_to_poly and poly_to_exp tables are used to perform efficient * operations in GF(2^8) represented as GF(2)[x]/w(x) where * w(x)=x^8+x^6+x^3+x^2+1. We care about doing that because it's part of the * definition of the RS matrix in the key schedule. Elements of that field * are polynomials of degree not greater than 7 and all coefficients 0 or 1, * which can be represented naturally by bytes (just substitute x=2). In that * form, GF(2^8) addition is the same as bitwise XOR, but GF(2^8) * multiplication is inefficient without hardware support. To multiply * faster, I make use of the fact x is a generator for the nonzero elements, * so that every element p of GF(2)[x]/w(x) is either 0 or equal to (x)^n for * some n in 0..254. Note that caret is exponentiation in GF(2^8), * *not* polynomial notation. So if I want to compute pq where p and q are * in GF(2^8), I can just say: * 1. if p=0 or q=0 then pq=0 * 2. otherwise, find m and n such that p=x^m and q=x^n * 3. pq=(x^m)(x^n)=x^(m+n), so add m and n and find pq * The translations in steps 2 and 3 are looked up in the tables * poly_to_exp (for step 2) and exp_to_poly (for step 3). To see this * in action, look at the CALC_S macro. As additional wrinkles, note that * one of my operands is always a constant, so the poly_to_exp lookup on it * is done in advance; I included the original values in the comments so * readers can have some chance of recognizing that this *is* the RS matrix * from the Twofish paper. I've only included the table entries I actually * need; I never do a lookup on a variable input of zero and the biggest * exponents I'll ever see are 254 (variable) and 237 (constant), so they'll * never sum to more than 491. I'm repeating part of the exp_to_poly table * so that I don't have to do mod-255 reduction in the exponent arithmetic. * Since I know my constant operands are never zero, I only have to worry * about zero values in the variable operand, and I do it with a simple * conditional branch. I know conditionals are expensive, but I couldn't * see a non-horrible way of avoiding them, and I did manage to group the
* statements so that each if covers four group multiplications. */
/* Macro to perform one column of the RS matrix multiplication. The * parameters a, b, c, and d are the four bytes of output; i is the index * of the key bytes, and w, x, y, and z, are the column of constants from
* the RS matrix, preprocessed through the poly_to_exp table. */
/* Macros to calculate the key-dependent S-boxes for a 128-bit key using * the S vector from CALC_S. CALC_SB_2 computes a single entry in all * four S-boxes, where i is the index of the entry to compute, and a and b * are the index numbers preprocessed through the q0 and q1 tables
* respectively. */
/* Macros to calculate the whitening and round subkeys. CALC_K_2 computes the * last two stages of the h() function for a given index (either 2i or 2i+1). * a, b, c, and d are the four bytes going into the last two stages. For * 128-bit keys, this is the entire h() function and a and c are the index * preprocessed through q0 and q1 respectively; for longer keys they are the * output of previous stages. j is the index of the first key byte to use. * CALC_K computes a pair of subkeys for 128-bit Twofish, by calling CALC_K_2 * twice, doing the Pseudo-Hadamard Transform, and doing the necessary * rotations. Its parameters are: a, the array to write the results into, * j, the index of the first output entry, k and l, the preprocessed indices * for index 2i, and m and n, the preprocessed indices for index 2i+1. * CALC_K192_2 expands CALC_K_2 to handle 192-bit keys, by doing an * additional lookup-and-XOR stage. The parameters a, b, c and d are the * four bytes going into the last three stages. For 192-bit keys, c = d * are the index preprocessed through q0, and a = b are the index * preprocessed through q1; j is the index of the first key byte to use. * CALC_K192 is identical to CALC_K but for using the CALC_K192_2 macro * instead of CALC_K_2. * CALC_K256_2 expands CALC_K192_2 to handle 256-bit keys, by doing an * additional lookup-and-XOR stage. The parameters a and b are the index * preprocessed through q0 and q1 respectively; j is the index of the first * key byte to use. CALC_K256 is identical to CALC_K but for using the
* CALC_K256_2 macro instead of CALC_K_2. */
#define CALC_K256(a, j, k, l, m, n) \
x = CALC_K256_2 (k, l, 0); \
y = CALC_K256_2 (m, n, 4); \
y = rol32(y, 8); \
x += y; y += x; ctx->a[j] = x; \
ctx->a[(j) + 1] = rol32(y, 9)
/* Perform the key setup. */ int __twofish_setkey(struct twofish_ctx *ctx, const u8 *key, unsignedint key_len)
{ int i, j, k;
/* Temporaries for CALC_K. */
u32 x, y;
/* The S vector used to key the S-boxes, split up into individual bytes.
* 128-bit keys use only sa through sh; 256-bit use all of them. */
u8 sa = 0, sb = 0, sc = 0, sd = 0, se = 0, sf = 0, sg = 0, sh = 0;
u8 si = 0, sj = 0, sk = 0, sl = 0, sm = 0, sn = 0, so = 0, sp = 0;
if (key_len == 32) { /* 256-bit key */ /* Calculate the fourth word of the S vector */
CALC_S (sm, sn, so, sp, 24, 0x00, 0x2D, 0x01, 0x2D); /* 01 A4 02 A4 */
CALC_S (sm, sn, so, sp, 25, 0x2D, 0xA4, 0x44, 0x8A); /* A4 56 A1 55 */
CALC_S (sm, sn, so, sp, 26, 0x8A, 0xD5, 0xBF, 0xD1); /* 55 82 FC 87 */
CALC_S (sm, sn, so, sp, 27, 0xD1, 0x7F, 0x3D, 0x99); /* 87 F3 C1 5A */
CALC_S (sm, sn, so, sp, 28, 0x99, 0x46, 0x66, 0x96); /* 5A 1E 47 58 */
CALC_S (sm, sn, so, sp, 29, 0x96, 0x3C, 0x5B, 0xED); /* 58 C6 AE DB */
CALC_S (sm, sn, so, sp, 30, 0xED, 0x37, 0x4F, 0xE0); /* DB 68 3D 9E */
CALC_S (sm, sn, so, sp, 31, 0xE0, 0xD0, 0x8C, 0x17); /* 9E E5 19 03 */
/* Compute the S-boxes. */ for ( i = j = 0, k = 1; i < 256; i++, j += 2, k += 2 ) {
CALC_SB256_2( i, calc_sb_tbl[j], calc_sb_tbl[k] );
}
/* CALC_K256/CALC_K192/CALC_K loops were unrolled. * Unrolling produced x2.5 more code (+18k on i386), * and speeded up key setup by 7%: * unrolled: twofish_setkey/sec: 41128 * loop: twofish_setkey/sec: 38148 * CALC_K256: ~100 insns each * CALC_K192: ~90 insns * CALC_K: ~70 insns
*/ /* Calculate whitening and round subkeys */ for ( i = 0; i < 8; i += 2 ) {
CALC_K256 (w, i, q0[i], q1[i], q0[i+1], q1[i+1]);
} for ( i = 0; i < 32; i += 2 ) {
CALC_K256 (k, i, q0[i+8], q1[i+8], q0[i+9], q1[i+9]);
}
} elseif (key_len == 24) { /* 192-bit key */ /* Compute the S-boxes. */ for ( i = j = 0, k = 1; i < 256; i++, j += 2, k += 2 ) {
CALC_SB192_2( i, calc_sb_tbl[j], calc_sb_tbl[k] );
}
/* Calculate whitening and round subkeys */ for ( i = 0; i < 8; i += 2 ) {
CALC_K192 (w, i, q0[i], q1[i], q0[i+1], q1[i+1]);
} for ( i = 0; i < 32; i += 2 ) {
CALC_K192 (k, i, q0[i+8], q1[i+8], q0[i+9], q1[i+9]);
}
} else { /* 128-bit key */ /* Compute the S-boxes. */ for ( i = j = 0, k = 1; i < 256; i++, j += 2, k += 2 ) {
CALC_SB_2( i, calc_sb_tbl[j], calc_sb_tbl[k] );
}
/* Calculate whitening and round subkeys */ for ( i = 0; i < 8; i += 2 ) {
CALC_K (w, i, q0[i], q1[i], q0[i+1], q1[i+1]);
} for ( i = 0; i < 32; i += 2 ) {
CALC_K (k, i, q0[i+8], q1[i+8], q0[i+9], q1[i+9]);
}
}
MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("Twofish cipher common functions");
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