/**
* @brief Perform a single Barrett reduction.
* @param ctx [in] The bigint session context.
* @param bi [in] A bigint.
* @return The result of the Barrett reduction.
*/
bigint * ICACHE_FLASH_ATTR bi_barrett(BI_CTX *ctx, bigint *bi)
{
bigint *q1, *q2, *q3, *r1, *r2, *r;
uint8_t mod_offset = ctx->mod_offset;
bigint *bim = ctx->bi_mod[mod_offset];
int k = bim->size;
check(bi);
check(bim);
/* use Classical method instead - Barrett cannot help here */
if (bi->size > k*2)
{
return bi_mod(ctx, bi);
}
q1 = comp_right_shift(bi_clone(ctx, bi), k-1);
/* do outer partial multiply */
q2 = regular_multiply(ctx, q1, ctx->bi_mu[mod_offset], 0, k-1);
q3 = comp_right_shift(q2, k+1);
r1 = comp_mod(bi, k+1);
/* do inner partial multiply */
r2 = comp_mod(regular_multiply(ctx, q3, bim, k+1, 0), k+1);
r = bi_subtract(ctx, r1, r2, NULL);
/* if (r >= m) r = r - m; */
if (bi_compare(r, bim) >= 0)
{
r = bi_subtract(ctx, r, bim, NULL);
}
return r;
}
/*
* Karatsuba improves on regular multiplication due to only 3 multiplications
* being done instead of 4. The additional additions/subtractions are O(N)
* rather than O(N^2) and so for big numbers it saves on a few operations
*/
static bigint * ICACHE_FLASH_ATTR karatsuba(BI_CTX *ctx, bigint *bia, bigint *bib, int is_square)
{
bigint *x0, *x1;
bigint *p0, *p1, *p2;
int m;
if (is_square)
{
m = (bia->size + 1)/2;
}
else
{
m = (max(bia->size, bib->size) + 1)/2;
}
x0 = bi_clone(ctx, bia);
x0->size = m;
x1 = bi_clone(ctx, bia);
comp_right_shift(x1, m);
bi_free(ctx, bia);
/* work out the 3 partial products */
if (is_square)
{
p0 = bi_square(ctx, bi_copy(x0));
p2 = bi_square(ctx, bi_copy(x1));
p1 = bi_square(ctx, bi_add(ctx, x0, x1));
}
else /* normal multiply */
{
bigint *y0, *y1;
y0 = bi_clone(ctx, bib);
y0->size = m;
y1 = bi_clone(ctx, bib);
comp_right_shift(y1, m);
bi_free(ctx, bib);
p0 = bi_multiply(ctx, bi_copy(x0), bi_copy(y0));
p2 = bi_multiply(ctx, bi_copy(x1), bi_copy(y1));
p1 = bi_multiply(ctx, bi_add(ctx, x0, x1), bi_add(ctx, y0, y1));
}
p1 = bi_subtract(ctx,
bi_subtract(ctx, p1, bi_copy(p2), NULL), bi_copy(p0), NULL);
comp_left_shift(p1, m);
comp_left_shift(p2, 2*m);
return bi_add(ctx, p1, bi_add(ctx, p0, p2));
}
/**
* @brief Use the Chinese Remainder Theorem to quickly perform RSA decrypts.
*
* @param ctx [in] The bigint session context.
* @param bi [in] The bigint to perform the exp/mod.
* @param dP [in] CRT's dP bigint
* @param dQ [in] CRT's dQ bigint
* @param p [in] CRT's p bigint
* @param q [in] CRT's q bigint
* @param qInv [in] CRT's qInv bigint
* @return The result of the CRT operation
*/
bigint * ICACHE_FLASH_ATTR bi_crt(BI_CTX *ctx, bigint *bi,
bigint *dP, bigint *dQ,
bigint *p, bigint *q, bigint *qInv)
{
bigint *m1, *m2, *h;
/* Montgomery has a condition the 0 < x, y < m and these products violate
* that condition. So disable Montgomery when using CRT */
#if defined(CONFIG_BIGINT_MONTGOMERY)
ctx->use_classical = 1;
#endif
ctx->mod_offset = BIGINT_P_OFFSET;
m1 = bi_mod_power(ctx, bi_copy(bi), dP);
ctx->mod_offset = BIGINT_Q_OFFSET;
m2 = bi_mod_power(ctx, bi, dQ);
h = bi_subtract(ctx, bi_add(ctx, m1, p), bi_copy(m2), NULL);
h = bi_multiply(ctx, h, qInv);
ctx->mod_offset = BIGINT_P_OFFSET;
h = bi_residue(ctx, h);
#if defined(CONFIG_BIGINT_MONTGOMERY)
ctx->use_classical = 0; /* reset for any further operation */
#endif
return bi_add(ctx, m2, bi_multiply(ctx, q, h));
}
/**
* @brief Perform a single montgomery reduction.
* @param ctx [in] The bigint session context.
* @param bixy [in] A bigint.
* @return The result of the montgomery reduction.
*/
bigint * ICACHE_FLASH_ATTR bi_mont(BI_CTX *ctx, bigint *bixy)
{
int i = 0, n;
uint8_t mod_offset = ctx->mod_offset;
bigint *bim = ctx->bi_mod[mod_offset];
comp mod_inv = ctx->N0_dash[mod_offset];
check(bixy);
if (ctx->use_classical) /* just use classical instead */
{
return bi_mod(ctx, bixy);
}
n = bim->size;
do
{
bixy = bi_add(ctx, bixy, comp_left_shift(
bi_int_multiply(ctx, bim, bixy->comps[i]*mod_inv), i));
} while (++i < n);
comp_right_shift(bixy, n);
if (bi_compare(bixy, bim) >= 0)
{
bixy = bi_subtract(ctx, bixy, bim, NULL);
}
return bixy;
}
/**
* Use the Chinese Remainder Theorem to quickly perform RSA decrypts.
* This should really be in bigint.c (and was at one stage), but needs
* access to the RSA_CTX context...
*/
static bigint *bi_crt(const RSA_CTX *rsa, bigint *bi)
{
BI_CTX *ctx = rsa->bi_ctx;
bigint *m1, *m2, *h;
/* Montgomery has a condition the 0 < x, y < m and these products violate
* that condition. So disable Montgomery when using CRT */
#if defined(CONFIG_BIGINT_MONTGOMERY)
ctx->use_classical = 1;
#endif
ctx->mod_offset = BIGINT_P_OFFSET;
m1 = bi_mod_power(ctx, bi_copy(bi), rsa->dP);
ctx->mod_offset = BIGINT_Q_OFFSET;
m2 = bi_mod_power(ctx, bi, rsa->dQ);
h = bi_subtract(ctx, bi_add(ctx, m1, rsa->p), bi_copy(m2), NULL);
h = bi_multiply(ctx, h, rsa->qInv);
ctx->mod_offset = BIGINT_P_OFFSET;
h = bi_residue(ctx, h);
#if defined(CONFIG_BIGINT_MONTGOMERY)
ctx->use_classical = 0; /* reset for any further operation */
#endif
return bi_add(ctx, m2, bi_multiply(ctx, rsa->q, h));
}
/**
* @brief Does both division and modulo calculations.
*
* Used extensively when doing classical reduction.
* @param ctx [in] The bigint session context.
* @param u [in] A bigint which is the numerator.
* @param v [in] Either the denominator or the modulus depending on the mode.
* @param is_mod [n] Determines if this is a normal division (0) or a reduction
* (1).
* @return The result of the division/reduction.
*/
bigint * ICACHE_FLASH_ATTR bi_divide(BI_CTX *ctx, bigint *u, bigint *v, int is_mod)
{
int n = v->size, m = u->size-n;
int j = 0, orig_u_size = u->size;
uint8_t mod_offset = ctx->mod_offset;
comp d;
bigint *quotient, *tmp_u;
comp q_dash;
check(u);
check(v);
/* if doing reduction and we are < mod, then return mod */
if (is_mod && bi_compare(v, u) > 0)
{
bi_free(ctx, v);
return u;
}
quotient = alloc(ctx, m+1);
tmp_u = alloc(ctx, n+1);
v = trim(v); /* make sure we have no leading 0's */
d = (comp)((long_comp)COMP_RADIX/(V1+1));
/* clear things to start with */
memset(quotient->comps, 0, ((quotient->size)*COMP_BYTE_SIZE));
/* normalise */
if (d > 1)
{
u = bi_int_multiply(ctx, u, d);
if (is_mod)
{
v = ctx->bi_normalised_mod[mod_offset];
}
else
{
v = bi_int_multiply(ctx, v, d);
}
}
if (orig_u_size == u->size) /* new digit position u0 */
{
more_comps(u, orig_u_size + 1);
}
do
{
/* get a temporary short version of u */
memcpy(tmp_u->comps, &u->comps[u->size-n-1-j], (n+1)*COMP_BYTE_SIZE);
/* calculate q' */
if (U(0) == V1)
{
q_dash = COMP_RADIX-1;
}
else
{
q_dash = (comp)(((long_comp)U(0)*COMP_RADIX + U(1))/V1);
if (v->size > 1 && V2)
{
/* we are implementing the following:
if (V2*q_dash > (((U(0)*COMP_RADIX + U(1) -
q_dash*V1)*COMP_RADIX) + U(2))) ... */
comp inner = (comp)((long_comp)COMP_RADIX*U(0) + U(1) -
(long_comp)q_dash*V1);
if ((long_comp)V2*q_dash > (long_comp)inner*COMP_RADIX + U(2))
{
q_dash--;
}
}
}
/* multiply and subtract */
if (q_dash)
{
int is_negative;
tmp_u = bi_subtract(ctx, tmp_u,
bi_int_multiply(ctx, bi_copy(v), q_dash), &is_negative);
more_comps(tmp_u, n+1);
Q(j) = q_dash;
/* add back */
if (is_negative)
{
Q(j)--;
tmp_u = bi_add(ctx, tmp_u, bi_copy(v));
/* lop off the carry */
tmp_u->size--;
v->size--;
}
}
else
{
Q(j) = 0;
}
/* copy back to u */
memcpy(&u->comps[u->size-n-1-j], tmp_u->comps, (n+1)*COMP_BYTE_SIZE);
} while (++j <= m);
bi_free(ctx, tmp_u);
bi_free(ctx, v);
if (is_mod) /* get the remainder */
{
bi_free(ctx, quotient);
return bi_int_divide(ctx, trim(u), d);
}
else /* get the quotient */
{
bi_free(ctx, u);
return trim(quotient);
}
}
