/*
* Software implementation of AES.
*
* This implementation uses a bit-sliced representation. Instead of
* the obvious approach of storing the cipher state so that each byte
* (or field element, or entry in the cipher matrix) occupies 8
* contiguous bits in a machine integer somewhere, we organise the
* cipher state as an array of 8 integers, in such a way that each
* logical byte of the cipher state occupies one bit in each integer,
* all at the same position. This allows us to do parallel logic on
* all bytes of the state by doing bitwise operations between the 8
* integers; in particular, the S-box (SubBytes) lookup is done this
* way, which takes about 110 operations - but for those 110 bitwise
* ops you get 64 S-box lookups, not just one.
*/
#include "ssh.h"
#include "aes.h"
#include "mpint_i.h" /* we reuse the BignumInt system */
static bool aes_sw_available(void)
{
/* Software AES is always available */
return true;
}
#define SLICE_PARALLELISM (BIGNUM_INT_BYTES / 2)
#ifdef BITSLICED_DEBUG
/* Dump function that undoes the bitslicing transform, so you can see
* the logical data represented by a set of slice words. */
static inline void dumpslices_uint16_t(
const char *prefix, const uint16_t slices[8])
{
printf("%-30s", prefix);
for (unsigned byte = 0; byte < 16; byte++) {
unsigned byteval = 0;
for (unsigned bit = 0; bit < 8; bit++)
byteval |= (1 & (slices[bit] >> byte)) << bit;
printf("%02x", byteval);
}
printf("\n");
}
static inline void dumpslices_BignumInt(
const char *prefix, const BignumInt slices[8])
{
printf("%-30s", prefix);
for (unsigned iter = 0; iter < SLICE_PARALLELISM; iter++) {
for (unsigned byte = 0; byte < 16; byte++) {
unsigned byteval = 0;
for (unsigned bit = 0; bit < 8; bit++)
byteval |= (1 & (slices[bit] >> (iter*16+byte))) << bit;
printf("%02x", byteval);
}
if (iter+1 < SLICE_PARALLELISM)
printf(" ");
}
printf("\n");
}
#else
#define dumpslices_uintN_t(prefix, slices) ((void)0)
#define dumpslices_BignumInt(prefix, slices) ((void)0)
#endif
/* -----
* Bit-slicing transformation: convert between an array of 16 uint8_t
* and an array of 8 uint16_t, so as to interchange the bit index
* within each element and the element index within the array. (That
* is, bit j of input[i] == bit i of output[j].
*/
#define SWAPWORDS(shift) do \
{ \
uint64_t mask = ~(uint64_t)0 / ((1ULL << shift) + 1); \
uint64_t diff = ((i0 >> shift) ^ i1) & mask; \
i0 ^= diff << shift; \
i1 ^= diff; \
} while (0)
#define SWAPINWORD(i, bigshift, smallshift) do \
{ \
uint64_t mask = ~(uint64_t)0; \
mask /= ((1ULL << bigshift) + 1); \
mask /= ((1ULL << smallshift) + 1); \
mask <<= smallshift; \
unsigned shift = bigshift - smallshift; \
uint64_t diff = ((i >> shift) ^ i) & mask; \
i ^= diff ^ (diff << shift); \
} while (0)
#define TO_BITSLICES(slices, bytes, uintN_t, assign_op, shift) do \
{ \
uint64_t i0 = GET_64BIT_LSB_FIRST(bytes); \
uint64_t i1 = GET_64BIT_LSB_FIRST(bytes + 8); \
SWAPINWORD(i0, 8, 1); \
SWAPINWORD(i1, 8, 1); \
SWAPINWORD(i0, 16, 2); \
SWAPINWORD(i1, 16, 2); \
SWAPINWORD(i0, 32, 4); \
SWAPINWORD(i1, 32, 4); \
SWAPWORDS(8); \
slices[0] assign_op (uintN_t)((i0 >> 0) & 0xFFFF) << (shift); \
slices[2] assign_op (uintN_t)((i0 >> 16) & 0xFFFF) << (shift); \
slices[4] assign_op (uintN_t)((i0 >> 32) & 0xFFFF) << (shift); \
slices[6] assign_op (uintN_t)((i0 >> 48) & 0xFFFF) << (shift); \
slices[1] assign_op (uintN_t)((i1 >> 0) & 0xFFFF) << (shift); \
slices[3] assign_op (uintN_t)((i1 >> 16) & 0xFFFF) << (shift); \
slices[5] assign_op (uintN_t)((i1 >> 32) & 0xFFFF) << (shift); \
slices[7] assign_op (uintN_t)((i1 >> 48) & 0xFFFF) << (shift); \
} while (0)
#define FROM_BITSLICES(bytes, slices, shift) do \
{ \
uint64_t i1 = ((slices[7] >> (shift)) & 0xFFFF); \
i1 = (i1 << 16) | ((slices[5] >> (shift)) & 0xFFFF); \
i1 = (i1 << 16) | ((slices[3] >> (shift)) & 0xFFFF); \
i1 = (i1 << 16) | ((slices[1] >> (shift)) & 0xFFFF); \
uint64_t i0 = ((slices[6] >> (shift)) & 0xFFFF); \
i0 = (i0 << 16) | ((slices[4] >> (shift)) & 0xFFFF); \
i0 = (i0 << 16) | ((slices[2] >> (shift)) & 0xFFFF); \
i0 = (i0 << 16) | ((slices[0] >> (shift)) & 0xFFFF); \
SWAPWORDS(8); \
SWAPINWORD(i0, 32, 4); \
SWAPINWORD(i1, 32, 4); \
SWAPINWORD(i0, 16, 2); \
SWAPINWORD(i1, 16, 2); \
SWAPINWORD(i0, 8, 1); \
SWAPINWORD(i1, 8, 1); \
PUT_64BIT_LSB_FIRST(bytes, i0); \
PUT_64BIT_LSB_FIRST((bytes) + 8, i1); \
} while (0)
/* -----
* Some macros that will be useful repeatedly.
*/
/* Iterate a unary transformation over all 8 slices. */
#define ITERATE(MACRO, output, input, uintN_t) do \
{ \
MACRO(output[0], input[0], uintN_t); \
MACRO(output[1], input[1], uintN_t); \
MACRO(output[2], input[2], uintN_t); \
MACRO(output[3], input[3], uintN_t); \
MACRO(output[4], input[4], uintN_t); \
MACRO(output[5], input[5], uintN_t); \
MACRO(output[6], input[6], uintN_t); \
MACRO(output[7], input[7], uintN_t); \
} while (0)
/* Simply add (i.e. XOR) two whole sets of slices together. */
#define BITSLICED_ADD(output, lhs, rhs) do \
{ \
output[0] = lhs[0] ^ rhs[0]; \
output[1] = lhs[1] ^ rhs[1]; \
output[2] = lhs[2] ^ rhs[2]; \
output[3] = lhs[3] ^ rhs[3]; \
output[4] = lhs[4] ^ rhs[4]; \
output[5] = lhs[5] ^ rhs[5]; \
output[6] = lhs[6] ^ rhs[6]; \
output[7] = lhs[7] ^ rhs[7]; \
} while (0)
/* -----
* The AES S-box, in pure bitwise logic so that it can be run in
* parallel on whole words full of bit-sliced field elements.
*
* Source: 'A new combinational logic minimization technique with
* applications to cryptology', https://eprint.iacr.org/2009/191
*
* As a minor speed optimisation, I use a modified version of the
* S-box which omits the additive constant 0x63, i.e. this S-box
* consists of only the field inversion and linear map components.
* Instead, the addition of the constant is deferred until after the
* subsequent ShiftRows and MixColumns stages, so that it happens at
* the same time as adding the next round key - and then we just make
* it _part_ of the round key, so it doesn't cost any extra
* instructions to add.
*
* (Obviously adding a constant to each byte commutes with ShiftRows,
* which only permutes the bytes. It also commutes with MixColumns:
* that's not quite so obvious, but since the effect of MixColumns is
* to multiply a constant polynomial M into each column, it is obvious
* that adding some polynomial K and then multiplying by M is
* equivalent to multiplying by M and then adding the product KM. And
* in fact, since the coefficients of M happen to sum to 1, it turns
* out that KM = K, so we don't even have to change the constant when
* we move it to the far side of MixColumns.)
*
* Of course, one knock-on effect of this is that the use of the S-box
* *during* key setup has to be corrected by manually adding on the
* constant afterwards!
*/
/* Initial linear transformation for the forward S-box, from Fig 2 of
* the paper. */
#define SBOX_FORWARD_TOP_TRANSFORM(input, uintN_t) \
uintN_t y14 = input[4] ^ input[2]; \
uintN_t y13 = input[7] ^ input[1]; \
uintN_t y9 = input[7] ^ input[4]; \
uintN_t y8 = input[7] ^ input[2]; \
uintN_t t0 = input[6] ^ input[5]; \
uintN_t y1 = t0 ^ input[0]; \
uintN_t y4 = y1 ^ input[4]; \
uintN_t y12 = y13 ^ y14; \
uintN_t y2 = y1 ^ input[7]; \
uintN_t y5 = y1 ^ input[1]; \
uintN_t y3 = y5 ^ y8; \
uintN_t t1 = input[3] ^ y12; \
uintN_t y15 = t1 ^ input[2]; \
uintN_t y20 = t1 ^ input[6]; \
uintN_t y6 = y15 ^ input[0]; \
uintN_t y10 = y15 ^ t0; \
uintN_t y11 = y20 ^ y9; \
uintN_t y7 = input[0] ^ y11; \
uintN_t y17 = y10 ^ y11; \
uintN_t y19 = y10 ^ y8; \
uintN_t y16 = t0 ^ y11; \
uintN_t y21 = y13 ^ y16; \
uintN_t y18 = input[7] ^ y16; \
/* Make a copy of input[0] under a new name, because the core
* will refer to it, and in the inverse version of the S-box
* the corresponding value will be one of the calculated ones
* and not in input[0] itself. */ \
uintN_t i0 = input[0]; \
/* end */
/* Core nonlinear component, from Fig 3 of the paper. */
#define SBOX_CORE(uintN_t) \
uintN_t t2 = y12 & y15; \
uintN_t t3 = y3 & y6; \
uintN_t t4 = t3 ^ t2; \
uintN_t t5 = y4 & i0; \
uintN_t t6 = t5 ^ t2; \
uintN_t t7 = y13 & y16; \
uintN_t t8 = y5 & y1; \
uintN_t t9 = t8 ^ t7; \
uintN_t t10 = y2 & y7; \
uintN_t t11 = t10 ^ t7; \
uintN_t t12 = y9 & y11; \
uintN_t t13 = y14 & y17; \
uintN_t t14 = t13 ^ t12; \
uintN_t t15 = y8 & y10; \
uintN_t t16 = t15 ^ t12; \
uintN_t t17 = t4 ^ t14; \
uintN_t t18 = t6 ^ t16; \
uintN_t t19 = t9 ^ t14; \
uintN_t t20 = t11 ^ t16; \
uintN_t t21 = t17 ^ y20; \
uintN_t t22 = t18 ^ y19; \
uintN_t t23 = t19 ^ y21; \
uintN_t t24 = t20 ^ y18; \
uintN_t t25 = t21 ^ t22; \
uintN_t t26 = t21 & t23; \
uintN_t t27 = t24 ^ t26; \
uintN_t t28 = t25 & t27; \
uintN_t t29 = t28 ^ t22; \
uintN_t t30 = t23 ^ t24; \
uintN_t t31 = t22 ^ t26; \
uintN_t t32 = t31 & t30; \
uintN_t t33 = t32 ^ t24; \
uintN_t t34 = t23 ^ t33; \
uintN_t t35 = t27 ^ t33; \
uintN_t t36 = t24 & t35; \
uintN_t t37 = t36 ^ t34; \
uintN_t t38 = t27 ^ t36; \
uintN_t t39 = t29 & t38; \
uintN_t t40 = t25 ^ t39; \
uintN_t t41 = t40 ^ t37; \
uintN_t t42 = t29 ^ t33; \
uintN_t t43 = t29 ^ t40; \
uintN_t t44 = t33 ^ t37; \
uintN_t t45 = t42 ^ t41; \
uintN_t z0 = t44 & y15; \
uintN_t z1 = t37 & y6; \
uintN_t z2 = t33 & i0; \
uintN_t z3 = t43 & y16; \
uintN_t z4 = t40 & y1; \
uintN_t z5 = t29 & y7; \
uintN_t z6 = t42 & y11; \
uintN_t z7 = t45 & y17; \
uintN_t z8 = t41 & y10; \
uintN_t z9 = t44 & y12; \
uintN_t z10 = t37 & y3; \
uintN_t z11 = t33 & y4; \
uintN_t z12 = t43 & y13; \
uintN_t z13 = t40 & y5; \
uintN_t z14 = t29 & y2; \
uintN_t z15 = t42 & y9; \
uintN_t z16 = t45 & y14; \
uintN_t z17 = t41 & y8; \
/* end */
/* Final linear transformation for the forward S-box, from Fig 4 of
* the paper. */
#define SBOX_FORWARD_BOTTOM_TRANSFORM(output, uintN_t) \
uintN_t t46 = z15 ^ z16; \
uintN_t t47 = z10 ^ z11; \
uintN_t t48 = z5 ^ z13; \
uintN_t t49 = z9 ^ z10; \
uintN_t t50 = z2 ^ z12; \
uintN_t t51 = z2 ^ z5; \
uintN_t t52 = z7 ^ z8; \
uintN_t t53 = z0 ^ z3; \
uintN_t t54 = z6 ^ z7; \
uintN_t t55 = z16 ^ z17; \
uintN_t t56 = z12 ^ t48; \
uintN_t t57 = t50 ^ t53; \
uintN_t t58 = z4 ^ t46; \
uintN_t t59 = z3 ^ t54; \
uintN_t t60 = t46 ^ t57; \
uintN_t t61 = z14 ^ t57; \
uintN_t t62 = t52 ^ t58; \
uintN_t t63 = t49 ^ t58; \
uintN_t t64 = z4 ^ t59; \
uintN_t t65 = t61 ^ t62; \
uintN_t t66 = z1 ^ t63; \
output[7] = t59 ^ t63; \
output[1] = t56 ^ t62; \
output[0] = t48 ^ t60; \
uintN_t t67 = t64 ^ t65; \
output[4] = t53 ^ t66; \
output[3] = t51 ^ t66; \
output[2] = t47 ^ t65; \
output[6] = t64 ^ output[4]; \
output[5] = t55 ^ t67; \
/* end */
#define BITSLICED_SUBBYTES(output, input, uintN_t) do { \
SBOX_FORWARD_TOP_TRANSFORM(input, uintN_t); \
SBOX_CORE(uintN_t); \
SBOX_FORWARD_BOTTOM_TRANSFORM(output, uintN_t); \
} while (0)
/*
* Initial and final linear transformations for the backward S-box. I
* generated these myself, by implementing the linear-transform
* optimisation algorithm in the paper, and applying it to the
* matrices calculated by _their_ top and bottom transformations, pre-
* and post-multiplied as appropriate by the linear map in the inverse
* S_box.
*/
#define SBOX_BACKWARD_TOP_TRANSFORM(input, uintN_t) \
uintN_t y5 = input[4] ^ input[6]; \
uintN_t y19 = input[3] ^ input[0]; \
uintN_t itmp8 = y5 ^ input[0]; \
uintN_t y4 = itmp8 ^ input[1]; \
uintN_t y9 = input[4] ^ input[3]; \
uintN_t y2 = y9 ^ y4; \
uintN_t itmp9 = y2 ^ input[7]; \
uintN_t y1 = y9 ^ input[0]; \
uintN_t y6 = y5 ^ input[7]; \
uintN_t y18 = y9 ^ input[5]; \
uintN_t y7 = y18 ^ y2; \
uintN_t y16 = y7 ^ y1; \
uintN_t y21 = y7 ^ input[1]; \
uintN_t y3 = input[4] ^ input[7]; \
uintN_t y13 = y16 ^ y21; \
uintN_t y8 = input[4] ^ y6; \
uintN_t y10 = y8 ^ y19; \
uintN_t y14 = y8 ^ y9; \
uintN_t y20 = itmp9 ^ input[2]; \
uintN_t y11 = y9 ^ y20; \
uintN_t i0 = y11 ^ y7; \
uintN_t y15 = i0 ^ y6; \
uintN_t y17 = y16 ^ y15; \
uintN_t y12 = itmp9 ^ input[3]; \
/* end */
#define SBOX_BACKWARD_BOTTOM_TRANSFORM(output, uintN_t) \
uintN_t otmp18 = z15 ^ z6; \
uintN_t otmp19 = z13 ^ otmp18; \
uintN_t otmp20 = z12 ^ otmp19; \
uintN_t otmp21 = z16 ^ otmp20; \
uintN_t otmp22 = z8 ^ otmp21; \
uintN_t otmp23 = z0 ^ otmp22; \
uintN_t otmp24 = otmp22 ^ z3; \
uintN_t otmp25 = otmp24 ^ z4; \
uintN_t otmp26 = otmp25 ^ z2; \
uintN_t otmp27 = z1 ^ otmp26; \
uintN_t otmp28 = z14 ^ otmp27; \
uintN_t otmp29 = otmp28 ^ z10; \
output[4] = z2 ^ otmp23; \
output[7] = z5 ^ otmp24; \
uintN_t otmp30 = z11 ^ otmp29; \
output[5] = z13 ^ otmp30; \
uintN_t otmp31 = otmp25 ^ z8; \
output[1] = z7 ^ otmp31; \
uintN_t otmp32 = z11 ^ z9; \
uintN_t otmp33 = z17 ^ otmp32; \
uintN_t otmp34 = otmp30 ^ otmp33; \
output[0] = z15 ^ otmp33; \
uintN_t otmp35 = z12 ^ otmp34; \
output[6] = otmp35 ^ z16; \
uintN_t otmp36 = z1 ^ otmp23; \
uintN_t otmp37 = z5 ^ otmp36; \
output[2] = z4 ^ otmp37; \
uintN_t otmp38 = z11 ^ output[1]; \
uintN_t otmp39 = z2 ^ otmp38; \
uintN_t otmp40 = z17 ^ otmp39; \
uintN_t otmp41 = z0 ^ otmp40; \
uintN_t otmp42 = z5 ^ otmp41; \
uintN_t otmp43 = otmp42 ^ z10; \
uintN_t otmp44 = otmp43 ^ z3; \
output[3] = otmp44 ^ z16; \
/* end */
#define BITSLICED_INVSUBBYTES(output, input, uintN_t) do { \
SBOX_BACKWARD_TOP_TRANSFORM(input, uintN_t); \
SBOX_CORE(uintN_t); \
SBOX_BACKWARD_BOTTOM_TRANSFORM(output, uintN_t); \
} while (0)
/* -----
* The ShiftRows transformation. This operates independently on each
* bit slice.
*/
#define SINGLE_BITSLICE_SHIFTROWS(output, input, uintN_t) do \
{ \
uintN_t mask, mask2, mask3, diff, x = (input); \
/* Rotate rows 2 and 3 by 16 bits */ \
mask = 0x00CC * (((uintN_t)~(uintN_t)0) / 0xFFFF); \
diff = ((x >> 8) ^ x) & mask; \
x ^= diff ^ (diff << 8); \
/* Rotate rows 1 and 3 by 8 bits */ \
mask = 0x0AAA * (((uintN_t)~(uintN_t)0) / 0xFFFF); \
mask2 = 0xA000 * (((uintN_t)~(uintN_t)0) / 0xFFFF); \
mask3 = 0x5555 * (((uintN_t)~(uintN_t)0) / 0xFFFF); \
x = ((x >> 4) & mask) | ((x << 12) & mask2) | (x & mask3); \
/* Write output */ \
(output) = x; \
} while (0)
#define SINGLE_BITSLICE_INVSHIFTROWS(output, input, uintN_t) do \
{ \
uintN_t mask, mask2, mask3, diff, x = (input); \
/* Rotate rows 2 and 3 by 16 bits */ \
mask = 0x00CC * (((uintN_t)~(uintN_t)0) / 0xFFFF); \
diff = ((x >> 8) ^ x) & mask; \
x ^= diff ^ (diff << 8); \
/* Rotate rows 1 and 3 by 8 bits, the opposite way to ShiftRows */ \
mask = 0x000A * (((uintN_t)~(uintN_t)0) / 0xFFFF); \
mask2 = 0xAAA0 * (((uintN_t)~(uintN_t)0) / 0xFFFF); \
mask3 = 0x5555 * (((uintN_t)~(uintN_t)0) / 0xFFFF); \
x = ((x >> 12) & mask) | ((x << 4) & mask2) | (x & mask3); \
/* Write output */ \
(output) = x; \
} while (0)
#define BITSLICED_SHIFTROWS(output, input, uintN_t) do \
{ \
ITERATE(SINGLE_BITSLICE_SHIFTROWS, output, input, uintN_t); \
} while (0)
#define BITSLICED_INVSHIFTROWS(output, input, uintN_t) do \
{ \
ITERATE(SINGLE_BITSLICE_INVSHIFTROWS, output, input, uintN_t); \
} while (0)
/* -----
* The MixColumns transformation. This has to operate on all eight bit
* slices at once, and also passes data back and forth between the
* bits in an adjacent group of 4 within each slice.
*
* Notation: let F = GF(2)[X]/<X^8+X^4+X^3+X+1> be the finite field
* used in AES, and let R = F[Y]/<Y^4+1> be the ring whose elements
* represent the possible contents of a column of the matrix. I use X
* and Y below in those senses, i.e. X is the value in F that
* represents the byte 0x02, and Y is the value in R that cycles the
* four bytes around by one if you multiply by it.
*/
/* Multiply every column by Y^3, i.e. cycle it round one place to the
* right. Operates on one bit slice at a time; you have to wrap it in
* ITERATE to affect all the data at once. */
#define BITSLICED_MUL_BY_Y3(output, input, uintN_t) do \
{ \
uintN_t mask, mask2, x; \
mask = 0x8 * (((uintN_t)~(uintN_t)0) / 0xF); \
mask2 = 0x7 * (((uintN_t)~(uintN_t)0) / 0xF); \
x = input; \
output = ((x << 3) & mask) ^ ((x >> 1) & mask2); \
} while (0)
/* Multiply every column by Y^2. */
#define BITSLICED_MUL_BY_Y2(output, input, uintN_t) do \
{ \
uintN_t mask, mask2, x; \
mask = 0xC * (((uintN_t)~(uintN_t)0) / 0xF); \
mask2 = 0x3 * (((uintN_t)~(uintN_t)0) / 0xF); \
x = input; \
output = ((x << 2) & mask) ^ ((x >> 2) & mask2); \
} while (0)
#define BITSLICED_MUL_BY_1_Y3(output, input, uintN_t) do \
{ \
uintN_t tmp = input; \
BITSLICED_MUL_BY_Y3(tmp, input, uintN_t); \
output = input ^ tmp; \
} while (0)
/* Multiply every column by 1+Y^2. */
#define BITSLICED_MUL_BY_1_Y2(output, input, uintN_t) do \
{ \
uintN_t tmp = input; \
BITSLICED_MUL_BY_Y2(tmp, input, uintN_t); \
output = input ^ tmp; \
} while (0)
/* Multiply every field element by X. This has to feed data between
* slices, so it does the whole job in one go without needing ITERATE. */
#define BITSLICED_MUL_BY_X(output, input, uintN_t) do \
{ \
uintN_t bit7 = input[7]; \
output[7] = input[6]; \
output[6] = input[5]; \
output[5] = input[4]; \
output[4] = input[3] ^ bit7; \
output[3] = input[2] ^ bit7; \
output[2] = input[1]; \
output[1] = input[0] ^ bit7; \
output[0] = bit7; \
} while (0)
/*
* The MixColumns constant is
* M = X + Y + Y^2 + (X+1)Y^3
* which we construct by rearranging it into
* M = 1 + (1+Y^3) [ X + (1+Y^2) ]
*/
#define BITSLICED_MIXCOLUMNS(output, input, uintN_t) do \
{ \
uintN_t a[8], aX[8], b[8]; \
/* a = input * (1+Y^3) */ \
ITERATE(BITSLICED_MUL_BY_1_Y3, a, input, uintN_t); \
/* aX = a * X */ \
BITSLICED_MUL_BY_X(aX, a, uintN_t); \
/* b = a * (1+Y^2) = input * (1+Y+Y^2+Y^3) */ \
ITERATE(BITSLICED_MUL_BY_1_Y2, b, a, uintN_t); \
/* output = input + aX + b (reusing a as a temp */ \
BITSLICED_ADD(a, aX, b); \
BITSLICED_ADD(output, input, a); \
} while (0)
/*
* The InvMixColumns constant, written out longhand, is
* I = (X^3+X^2+X) + (X^3+1)Y + (X^3+X^2+1)Y^2 + (X^3+X+1)Y^3
* We represent this as
* I = (X^3+X^2+X+1)(Y^3+Y^2+Y+1) + 1 + X(Y+Y^2) + X^2(Y+Y^3)
*/
#define BITSLICED_INVMIXCOLUMNS(output, input, uintN_t) do \
{ \
/* We need input * X^i for i=1,...,3 */ \
uintN_t X[8], X2[8], X3[8]; \
BITSLICED_MUL_BY_X(X, input, uintN_t); \
BITSLICED_MUL_BY_X(X2, X, uintN_t); \
BITSLICED_MUL_BY_X(X3, X2, uintN_t); \
/* Sum them all and multiply by 1+Y+Y^2+Y^3. */ \
uintN_t S[8]; \
BITSLICED_ADD(S, input, X); \
BITSLICED_ADD(S, S, X2); \
BITSLICED_ADD(S, S, X3); \
ITERATE(BITSLICED_MUL_BY_1_Y3, S, S, uintN_t); \
ITERATE(BITSLICED_MUL_BY_1_Y2, S, S, uintN_t); \
/* Compute the X(Y+Y^2) term. */ \
uintN_t A[8]; \
ITERATE(BITSLICED_MUL_BY_1_Y3, A, X, uintN_t); \
ITERATE(BITSLICED_MUL_BY_Y2, A, A, uintN_t); \
/* Compute the X^2(Y+Y^3) term. */ \
uintN_t B[8]; \
ITERATE(BITSLICED_MUL_BY_1_Y2, B, X2, uintN_t); \
ITERATE(BITSLICED_MUL_BY_Y3, B, B, uintN_t); \
/* And add all the pieces together. */ \
BITSLICED_ADD(S, S, input); \
BITSLICED_ADD(S, S, A); \
BITSLICED_ADD(output, S, B); \
} while (0)
/* -----
* Put it all together into a cipher round.
*/
/* Dummy macro to get rid of the MixColumns in the final round. */
#define NO_MIXCOLUMNS(out, in, uintN_t) do {} while (0)
#define ENCRYPT_ROUND_FN(suffix, uintN_t, mixcol_macro) \
static void aes_sliced_round_e_##suffix( \
uintN_t output[8], const uintN_t input[8], const uintN_t roundkey[8]) \
{ \
BITSLICED_SUBBYTES(output, input, uintN_t); \
BITSLICED_SHIFTROWS(output, output, uintN_t); \
mixcol_macro(output, output, uintN_t); \
BITSLICED_ADD(output, output, roundkey); \
}
ENCRYPT_ROUND_FN(serial, uint16_t, BITSLICED_MIXCOLUMNS)
ENCRYPT_ROUND_FN(serial_last, uint16_t, NO_MIXCOLUMNS)
ENCRYPT_ROUND_FN(parallel, BignumInt, BITSLICED_MIXCOLUMNS)
ENCRYPT_ROUND_FN(parallel_last, BignumInt, NO_MIXCOLUMNS)
#define DECRYPT_ROUND_FN(suffix, uintN_t, mixcol_macro) \
static void aes_sliced_round_d_##suffix( \
uintN_t output[8], const uintN_t input[8], const uintN_t roundkey[8]) \
{ \
BITSLICED_ADD(output, input, roundkey); \
mixcol_macro(output, output, uintN_t); \
BITSLICED_INVSUBBYTES(output, output, uintN_t); \
BITSLICED_INVSHIFTROWS(output, output, uintN_t); \
}
#if 0 /* no cipher mode we support requires serial decryption */
DECRYPT_ROUND_FN(serial, uint16_t, BITSLICED_INVMIXCOLUMNS)
DECRYPT_ROUND_FN(serial_first, uint16_t, NO_MIXCOLUMNS)
#endif
DECRYPT_ROUND_FN(parallel, BignumInt, BITSLICED_INVMIXCOLUMNS)
DECRYPT_ROUND_FN(parallel_first, BignumInt, NO_MIXCOLUMNS)
/* -----
* Key setup function.
*/
typedef struct aes_sliced_key aes_sliced_key;
struct aes_sliced_key {
BignumInt roundkeys_parallel[MAXROUNDKEYS * 8];
uint16_t roundkeys_serial[MAXROUNDKEYS * 8];
unsigned rounds;
};
static void aes_sliced_key_setup(
aes_sliced_key *sk, const void *vkey, size_t keybits)
{
const unsigned char *key = (const unsigned char *)vkey;
size_t key_words = keybits / 32;
sk->rounds = key_words + 6;
size_t sched_words = (sk->rounds + 1) * 4;
unsigned rconpos = 0;
uint16_t *outslices = sk->roundkeys_serial;
unsigned outshift = 0;
memset(sk->roundkeys_serial, 0, sizeof(sk->roundkeys_serial));
uint8_t inblk[16];
memset(inblk, 0, 16);
uint16_t slices[8];
for (size_t i = 0; i < sched_words; i++) {
/*
* Prepare a word of round key in the low 4 bits of each
* integer in slices[].
*/
if (i < key_words) {
memcpy(inblk, key + 4*i, 4);
TO_BITSLICES(slices, inblk, uint16_t, =, 0);
} else {
unsigned wordindex, bitshift;
uint16_t *prevslices;
/* Fetch the (i-1)th key word */
wordindex = i-1;
bitshift = 4 * (wordindex & 3);
prevslices = sk->roundkeys_serial + 8 * (wordindex >> 2);
for (size_t i = 0; i < 8; i++)
slices[i] = prevslices[i] >> bitshift;
/* Decide what we're doing in this expansion stage */
bool rotate_and_round_constant = (i % key_words == 0);
bool sub = rotate_and_round_constant ||
(key_words == 8 && i % 8 == 4);
if (rotate_and_round_constant) {
for (size_t i = 0; i < 8; i++)
slices[i] = ((slices[i] << 3) | (slices[i] >> 1)) & 0xF;
}
if (sub) {
/* Apply the SubBytes transform to the key word. But
* here we need to apply the _full_ SubBytes from the
* spec, including the constant which our S-box leaves
* out. */
BITSLICED_SUBBYTES(slices, slices, uint16_t);
slices[0] ^= 0xFFFF;
slices[1] ^= 0xFFFF;
slices[5] ^= 0xFFFF;
slices[6] ^= 0xFFFF;
}
if (rotate_and_round_constant) {
assert(rconpos < lenof(aes_key_setup_round_constants));
uint8_t rcon = aes_key_setup_round_constants[rconpos++];
for (size_t i = 0; i < 8; i++)
slices[i] ^= 1 & (rcon >> i);
}
/* Combine with the (i-Nk)th key word */
wordindex = i - key_words;
bitshift = 4 * (wordindex & 3);
prevslices = sk->roundkeys_serial + 8 * (wordindex >> 2);
for (size_t i = 0; i < 8; i++)
slices[i] ^= prevslices[i] >> bitshift;
}
/*
* Now copy it into sk.
*/
for (unsigned b = 0; b < 8; b++)
outslices[b] |= (slices[b] & 0xF) << outshift;
outshift += 4;
if (outshift == 16) {
outshift = 0;
outslices += 8;
}
}
smemclr(inblk, sizeof(inblk));
smemclr(slices, sizeof(slices));
/*
* Add the S-box constant to every round key after the first one,
* compensating for it being left out in the main cipher.
*/
for (size_t i = 8; i < 8 * (sched_words/4); i += 8) {
sk->roundkeys_serial[i+0] ^= 0xFFFF;
sk->roundkeys_serial[i+1] ^= 0xFFFF;
sk->roundkeys_serial[i+5] ^= 0xFFFF;
sk->roundkeys_serial[i+6] ^= 0xFFFF;
}
/*
* Replicate that set of round keys into larger integers for the
* parallel versions of the cipher.
*/
for (size_t i = 0; i < 8 * (sched_words / 4); i++) {
sk->roundkeys_parallel[i] = sk->roundkeys_serial[i] *
((BignumInt)~(BignumInt)0 / 0xFFFF);
}
}
/* -----
* The full cipher primitive, including transforming the input and
* output to/from bit-sliced form.
*/
#define ENCRYPT_FN(suffix, uintN_t, nblocks) \
static void aes_sliced_e_##suffix( \
uint8_t *output, const uint8_t *input, const aes_sliced_key *sk) \
{ \
uintN_t state[8]; \
TO_BITSLICES(state, input, uintN_t, =, 0); \
for (unsigned i = 1; i < nblocks; i++) { \
input += 16; \
TO_BITSLICES(state, input, uintN_t, |=, i*16); \
} \
const uintN_t *keys = sk->roundkeys_##suffix; \
BITSLICED_ADD(state, state, keys); \
keys += 8; \
for (unsigned i = 0; i < sk->rounds-1; i++) { \
aes_sliced_round_e_##suffix(state, state, keys); \
keys += 8; \
} \
aes_sliced_round_e_##suffix##_last(state, state, keys); \
for (unsigned i = 0; i < nblocks; i++) { \
FROM_BITSLICES(output, state, i*16); \
output += 16; \
} \
}
#define DECRYPT_FN(suffix, uintN_t, nblocks) \
static void aes_sliced_d_##suffix( \
uint8_t *output, const uint8_t *input, const aes_sliced_key *sk) \
{ \
uintN_t state[8]; \
TO_BITSLICES(state, input, uintN_t, =, 0); \
for (unsigned i = 1; i < nblocks; i++) { \
input += 16; \
TO_BITSLICES(state, input, uintN_t, |=, i*16); \
} \
const uintN_t *keys = sk->roundkeys_##suffix + 8*sk->rounds; \
aes_sliced_round_d_##suffix##_first(state, state, keys); \
keys -= 8; \
for (unsigned i = 0; i < sk->rounds-1; i++) { \
aes_sliced_round_d_##suffix(state, state, keys); \
keys -= 8; \
} \
BITSLICED_ADD(state, state, keys); \
for (unsigned i = 0; i < nblocks; i++) { \
FROM_BITSLICES(output, state, i*16); \
output += 16; \
} \
}
ENCRYPT_FN(serial, uint16_t, 1)
#if 0 /* no cipher mode we support requires serial decryption */
DECRYPT_FN(serial, uint16_t, 1)
#endif
ENCRYPT_FN(parallel, BignumInt, SLICE_PARALLELISM)
DECRYPT_FN(parallel, BignumInt, SLICE_PARALLELISM)
/* -----
* The SSH interface and the cipher modes.
*/
#define SDCTR_WORDS (16 / BIGNUM_INT_BYTES)
typedef struct aes_sw_context aes_sw_context;
struct aes_sw_context {
aes_sliced_key sk;
union {
struct {
/* In CBC mode, the IV is just a copy of the last seen
* cipher block. */
uint8_t prevblk[16];
} cbc;
struct {
/* In SDCTR mode, we keep the counter itself in a form
* that's easy to increment. We also use the parallel
* version of the core AES function, so we'll encrypt
* multiple counter values in one go. That won't align
* nicely with the sizes of data we're asked to encrypt,
* so we must also store a cache of the last set of
* keystream blocks we generated, and our current position
* within that cache. */
BignumInt counter[SDCTR_WORDS];
uint8_t keystream[SLICE_PARALLELISM * 16];
uint8_t *keystream_pos;
} sdctr;
} iv;
ssh_cipher ciph;
};
static ssh_cipher *aes_sw_new(const ssh_cipheralg *alg)
{
aes_sw_context *ctx = snew(aes_sw_context);
ctx->ciph.vt = alg;
return &ctx->ciph;
}
static void aes_sw_free(ssh_cipher *ciph)
{
aes_sw_context *ctx = container_of(ciph, aes_sw_context, ciph);
smemclr(ctx, sizeof(*ctx));
sfree(ctx);
}
static void aes_sw_setkey(ssh_cipher *ciph, const void *vkey)
{
aes_sw_context *ctx = container_of(ciph, aes_sw_context, ciph);
aes_sliced_key_setup(&ctx->sk, vkey, ctx->ciph.vt->real_keybits);
}
static void aes_sw_setiv_cbc(ssh_cipher *ciph, const void *iv)
{
aes_sw_context *ctx = container_of(ciph, aes_sw_context, ciph);
memcpy(ctx->iv.cbc.prevblk, iv, 16);
}
static void aes_sw_setiv_sdctr(ssh_cipher *ciph, const void *viv)
{
aes_sw_context *ctx = container_of(ciph, aes_sw_context, ciph);
const uint8_t *iv = (const uint8_t *)viv;
/* Import the initial counter value into the internal representation */
for (unsigned i = 0; i < SDCTR_WORDS; i++)
ctx->iv.sdctr.counter[i] =
GET_BIGNUMINT_MSB_FIRST(
iv + 16 - BIGNUM_INT_BYTES - i*BIGNUM_INT_BYTES);
/* Set keystream_pos to indicate that the keystream cache is
* currently empty */
ctx->iv.sdctr.keystream_pos =
ctx->iv.sdctr.keystream + sizeof(ctx->iv.sdctr.keystream);
}
typedef void (*aes_sw_fn)(uint32_t v[4], const uint32_t *keysched);
static inline void memxor16(void *vout, const void *vlhs, const void *vrhs)
{
uint8_t *out = (uint8_t *)vout;
const uint8_t *lhs = (const uint8_t *)vlhs, *rhs = (const uint8_t *)vrhs;
uint64_t w;
w = GET_64BIT_LSB_FIRST(lhs);
w ^= GET_64BIT_LSB_FIRST(rhs);
PUT_64BIT_LSB_FIRST(out, w);
w = GET_64BIT_LSB_FIRST(lhs + 8);
w ^= GET_64BIT_LSB_FIRST(rhs + 8);
PUT_64BIT_LSB_FIRST(out + 8, w);
}
static inline void aes_cbc_sw_encrypt(
ssh_cipher *ciph, void *vblk, int blklen)
{
aes_sw_context *ctx = container_of(ciph, aes_sw_context, ciph);
/*
* CBC encryption has to be done serially, because the input to
* each run of the cipher includes the output from the previous
* run.
*/
for (uint8_t *blk = (uint8_t *)vblk, *finish = blk + blklen;
blk < finish; blk += 16) {
/*
* We use the IV array itself as the location for the
* encryption, because there's no reason not to.
*/
/* XOR the new plaintext block into the previous cipher block */
memxor16(ctx->iv.cbc.prevblk, ctx->iv.cbc.prevblk, blk);
/* Run the cipher over the result, which leaves it
* conveniently already stored in ctx->iv */
aes_sliced_e_serial(
ctx->iv.cbc.prevblk, ctx->iv.cbc.prevblk, &ctx->sk);
/* Copy it to the output location */
memcpy(blk, ctx->iv.cbc.prevblk, 16);
}
}
static inline void aes_cbc_sw_decrypt(
ssh_cipher *ciph, void *vblk, int blklen)
{
aes_sw_context *ctx = container_of(ciph, aes_sw_context, ciph);
uint8_t *blk = (uint8_t *)vblk;
/*
* CBC decryption can run in parallel, because all the
* _ciphertext_ blocks are already available.
*/
size_t blocks_remaining = blklen / 16;
uint8_t data[SLICE_PARALLELISM * 16];
/* Zeroing the data array is probably overcautious, but it avoids
* technically undefined behaviour from leaving it uninitialised
* if our very first iteration doesn't include enough cipher
* blocks to populate it fully */
memset(data, 0, sizeof(data));
while (blocks_remaining > 0) {
/* Number of blocks we'll handle in this iteration. If we're
* dealing with fewer than the maximum, it doesn't matter -
* it's harmless to run the full parallel cipher function
* anyway. */
size_t blocks = (blocks_remaining < SLICE_PARALLELISM ?
blocks_remaining : SLICE_PARALLELISM);
/* Parallel-decrypt the input, in a separate array so we still
* have the cipher stream available for XORing. */
memcpy(data, blk, 16 * blocks);
aes_sliced_d_parallel(data, data, &ctx->sk);
/* Write the output and update the IV */
for (size_t i = 0; i < blocks; i++) {
uint8_t *decrypted = data + 16*i;
uint8_t *output = blk + 16*i;
memxor16(decrypted, decrypted, ctx->iv.cbc.prevblk);
memcpy(ctx->iv.cbc.prevblk, output, 16);
memcpy(output, decrypted, 16);
}
/* Advance the input pointer. */
blk += 16 * blocks;
blocks_remaining -= blocks;
}
smemclr(data, sizeof(data));
}
static inline void aes_sdctr_sw(
ssh_cipher *ciph, void *vblk, int blklen)
{
aes_sw_context *ctx = container_of(ciph, aes_sw_context, ciph);
/*
* SDCTR encrypt/decrypt loops round one block at a time XORing
* the keystream into the user's data, and periodically has to run
* a parallel encryption operation to get more keystream.
*/
uint8_t *keystream_end =
ctx->iv.sdctr.keystream + sizeof(ctx->iv.sdctr.keystream);
for (uint8_t *blk = (uint8_t *)vblk, *finish = blk + blklen;
blk < finish; blk += 16) {
if (ctx->iv.sdctr.keystream_pos == keystream_end) {
/*
* Generate some keystream.
*/
for (uint8_t *block = ctx->iv.sdctr.keystream;
block < keystream_end; block += 16) {
/* Format the counter value into the buffer. */
for (unsigned i = 0; i < SDCTR_WORDS; i++)
PUT_BIGNUMINT_MSB_FIRST(
block + 16 - BIGNUM_INT_BYTES - i*BIGNUM_INT_BYTES,
ctx->iv.sdctr.counter[i]);
/* Increment the counter. */
BignumCarry carry = 1;
for (unsigned i = 0; i < SDCTR_WORDS; i++)
BignumADC(ctx->iv.sdctr.counter[i], carry,
ctx->iv.sdctr.counter[i], 0, carry);
}
/* Encrypt all those counter blocks. */
aes_sliced_e_parallel(ctx->iv.sdctr.keystream,
ctx->iv.sdctr.keystream, &ctx->sk);
/* Reset keystream_pos to the start of the buffer. */
ctx->iv.sdctr.keystream_pos = ctx->iv.sdctr.keystream;
}
memxor16(blk, blk, ctx->iv.sdctr.keystream_pos);
ctx->iv.sdctr.keystream_pos += 16;
}
}
#define SW_ENC_DEC(len) \
static void aes##len##_sw_cbc_encrypt( \
ssh_cipher *ciph, void *vblk, int blklen) \
{ aes_cbc_sw_encrypt(ciph, vblk, blklen); } \
static void aes##len##_sw_cbc_decrypt( \
ssh_cipher *ciph, void *vblk, int blklen) \
{ aes_cbc_sw_decrypt(ciph, vblk, blklen); } \
static void aes##len##_sw_sdctr( \
ssh_cipher *ciph, void *vblk, int blklen) \
{ aes_sdctr_sw(ciph, vblk, blklen); }
SW_ENC_DEC(128)
SW_ENC_DEC(192)
SW_ENC_DEC(256)
AES_EXTRA(_sw);
AES_ALL_VTABLES(_sw, "unaccelerated");