BIGNUM *BN_mod_sqrt(BIGNUM *in, const BIGNUM *a, const BIGNUM *p, BN_CTX *ctx)
/* Returns 'ret' such that
* ret^2 == a (mod p),
* using the Tonelli/Shanks algorithm (cf. Henri Cohen, "A Course
* in Algebraic Computational Number Theory", algorithm 1.5.1).
* 'p' must be prime!
*/
{
BIGNUM *ret = in;
int err = 1;
int r;
BIGNUM *A, *b, *q, *t, *x, *y;
int e, i, j;
if (!BN_is_odd(p) || BN_abs_is_word(p, 1))
{
if (BN_abs_is_word(p, 2))
{
if (ret == NULL)
ret = BN_new();
if (ret == NULL)
goto end;
if (!BN_set_word(ret, BN_is_bit_set(a, 0)))
{
if (ret != in)
BN_free(ret);
return NULL;
}
bn_check_top(ret);
return ret;
}
BNerr(BN_F_BN_MOD_SQRT, BN_R_P_IS_NOT_PRIME);
return(NULL);
}
if (BN_is_zero(a) || BN_is_one(a))
{
if (ret == NULL)
ret = BN_new();
if (ret == NULL)
goto end;
if (!BN_set_word(ret, BN_is_one(a)))
{
if (ret != in)
BN_free(ret);
return NULL;
}
bn_check_top(ret);
return ret;
}
BN_CTX_start(ctx);
A = BN_CTX_get(ctx);
b = BN_CTX_get(ctx);
q = BN_CTX_get(ctx);
t = BN_CTX_get(ctx);
x = BN_CTX_get(ctx);
y = BN_CTX_get(ctx);
if (y == NULL) goto end;
if (ret == NULL)
ret = BN_new();
if (ret == NULL) goto end;
/* A = a mod p */
if (!BN_nnmod(A, a, p, ctx)) goto end;
/* now write |p| - 1 as 2^e*q where q is odd */
e = 1;
while (!BN_is_bit_set(p, e))
e++;
/* we'll set q later (if needed) */
if (e == 1)
{
/* The easy case: (|p|-1)/2 is odd, so 2 has an inverse
* modulo (|p|-1)/2, and square roots can be computed
* directly by modular exponentiation.
* We have
* 2 * (|p|+1)/4 == 1 (mod (|p|-1)/2),
* so we can use exponent (|p|+1)/4, i.e. (|p|-3)/4 + 1.
*/
if (!BN_rshift(q, p, 2)) goto end;
q->neg = 0;
if (!BN_add_word(q, 1)) goto end;
if (!BN_mod_exp(ret, A, q, p, ctx)) goto end;
err = 0;
goto vrfy;
}
if (e == 2)
{
/* |p| == 5 (mod 8)
*
* In this case 2 is always a non-square since
* Legendre(2,p) = (-1)^((p^2-1)/8) for any odd prime.
* So if a really is a square, then 2*a is a non-square.
* Thus for
* b := (2*a)^((|p|-5)/8),
* i := (2*a)*b^2
* we have
* i^2 = (2*a)^((1 + (|p|-5)/4)*2)
* = (2*a)^((p-1)/2)
* = -1;
* so if we set
* x := a*b*(i-1),
* then
* x^2 = a^2 * b^2 * (i^2 - 2*i + 1)
* = a^2 * b^2 * (-2*i)
* = a*(-i)*(2*a*b^2)
* = a*(-i)*i
* = a.
*
* (This is due to A.O.L. Atkin,
* <URL: http://listserv.nodak.edu/scripts/wa.exe?A2=ind9211&L=nmbrthry&O=T&P=562>,
* November 1992.)
*/
/* t := 2*a */
if (!BN_mod_lshift1_quick(t, A, p)) goto end;
/* b := (2*a)^((|p|-5)/8) */
if (!BN_rshift(q, p, 3)) goto end;
q->neg = 0;
if (!BN_mod_exp(b, t, q, p, ctx)) goto end;
/* y := b^2 */
if (!BN_mod_sqr(y, b, p, ctx)) goto end;
/* t := (2*a)*b^2 - 1*/
if (!BN_mod_mul(t, t, y, p, ctx)) goto end;
if (!BN_sub_word(t, 1)) goto end;
/* x = a*b*t */
if (!BN_mod_mul(x, A, b, p, ctx)) goto end;
if (!BN_mod_mul(x, x, t, p, ctx)) goto end;
if (!BN_copy(ret, x)) goto end;
err = 0;
goto vrfy;
}
/* e > 2, so we really have to use the Tonelli/Shanks algorithm.
* First, find some y that is not a square. */
if (!BN_copy(q, p)) goto end; /* use 'q' as temp */
q->neg = 0;
i = 2;
do
{
/* For efficiency, try small numbers first;
* if this fails, try random numbers.
*/
if (i < 22)
{
if (!BN_set_word(y, i)) goto end;
}
else
{
if (!BN_pseudo_rand(y, BN_num_bits(p), 0, 0)) goto end;
if (BN_ucmp(y, p) >= 0)
{
if (!(p->neg ? BN_add : BN_sub)(y, y, p)) goto end;
}
/* now 0 <= y < |p| */
if (BN_is_zero(y))
if (!BN_set_word(y, i)) goto end;
}
r = BN_kronecker(y, q, ctx); /* here 'q' is |p| */
if (r < -1) goto end;
if (r == 0)
{
/* m divides p */
BNerr(BN_F_BN_MOD_SQRT, BN_R_P_IS_NOT_PRIME);
goto end;
}
}
while (r == 1 && ++i < 82);
if (r != -1)
{
/* Many rounds and still no non-square -- this is more likely
* a bug than just bad luck.
* Even if p is not prime, we should have found some y
* such that r == -1.
*/
BNerr(BN_F_BN_MOD_SQRT, BN_R_TOO_MANY_ITERATIONS);
goto end;
}
/* Here's our actual 'q': */
if (!BN_rshift(q, q, e)) goto end;
/* Now that we have some non-square, we can find an element
* of order 2^e by computing its q'th power. */
if (!BN_mod_exp(y, y, q, p, ctx)) goto end;
if (BN_is_one(y))
{
BNerr(BN_F_BN_MOD_SQRT, BN_R_P_IS_NOT_PRIME);
goto end;
}
/* Now we know that (if p is indeed prime) there is an integer
* k, 0 <= k < 2^e, such that
*
* a^q * y^k == 1 (mod p).
*
* As a^q is a square and y is not, k must be even.
* q+1 is even, too, so there is an element
*
* X := a^((q+1)/2) * y^(k/2),
*
* and it satisfies
*
* X^2 = a^q * a * y^k
* = a,
*
* so it is the square root that we are looking for.
*/
/* t := (q-1)/2 (note that q is odd) */
if (!BN_rshift1(t, q)) goto end;
/* x := a^((q-1)/2) */
if (BN_is_zero(t)) /* special case: p = 2^e + 1 */
{
if (!BN_nnmod(t, A, p, ctx)) goto end;
if (BN_is_zero(t))
{
/* special case: a == 0 (mod p) */
BN_zero(ret);
err = 0;
goto end;
}
else
if (!BN_one(x)) goto end;
}
else
{
if (!BN_mod_exp(x, A, t, p, ctx)) goto end;
if (BN_is_zero(x))
{
/* special case: a == 0 (mod p) */
BN_zero(ret);
err = 0;
goto end;
}
}
/* b := a*x^2 (= a^q) */
if (!BN_mod_sqr(b, x, p, ctx)) goto end;
if (!BN_mod_mul(b, b, A, p, ctx)) goto end;
/* x := a*x (= a^((q+1)/2)) */
if (!BN_mod_mul(x, x, A, p, ctx)) goto end;
while (1)
{
/* Now b is a^q * y^k for some even k (0 <= k < 2^E
* where E refers to the original value of e, which we
* don't keep in a variable), and x is a^((q+1)/2) * y^(k/2).
*
* We have a*b = x^2,
* y^2^(e-1) = -1,
* b^2^(e-1) = 1.
*/
if (BN_is_one(b))
{
if (!BN_copy(ret, x)) goto end;
err = 0;
goto vrfy;
}
/* find smallest i such that b^(2^i) = 1 */
i = 1;
if (!BN_mod_sqr(t, b, p, ctx)) goto end;
while (!BN_is_one(t))
{
i++;
if (i == e)
{
BNerr(BN_F_BN_MOD_SQRT, BN_R_NOT_A_SQUARE);
goto end;
}
if (!BN_mod_mul(t, t, t, p, ctx)) goto end;
}
/* t := y^2^(e - i - 1) */
if (!BN_copy(t, y)) goto end;
for (j = e - i - 1; j > 0; j--)
{
if (!BN_mod_sqr(t, t, p, ctx)) goto end;
}
if (!BN_mod_mul(y, t, t, p, ctx)) goto end;
if (!BN_mod_mul(x, x, t, p, ctx)) goto end;
if (!BN_mod_mul(b, b, y, p, ctx)) goto end;
e = i;
}
vrfy:
if (!err)
{
/* verify the result -- the input might have been not a square
* (test added in 0.9.8) */
if (!BN_mod_sqr(x, ret, p, ctx))
err = 1;
if (!err && 0 != BN_cmp(x, A))
{
BNerr(BN_F_BN_MOD_SQRT, BN_R_NOT_A_SQUARE);
err = 1;
}
}
end:
if (err)
{
if (ret != NULL && ret != in)
{
BN_clear_free(ret);
}
ret = NULL;
}
BN_CTX_end(ctx);
bn_check_top(ret);
return ret;
}
int ec_GFp_simple_set_compressed_coordinates(const EC_GROUP *group,
EC_POINT *point, const BIGNUM *x_,
int y_bit, BN_CTX *ctx) {
BN_CTX *new_ctx = NULL;
BIGNUM *tmp1, *tmp2, *x, *y;
int ret = 0;
ERR_clear_error();
if (ctx == NULL) {
ctx = new_ctx = BN_CTX_new();
if (ctx == NULL) {
return 0;
}
}
y_bit = (y_bit != 0);
BN_CTX_start(ctx);
tmp1 = BN_CTX_get(ctx);
tmp2 = BN_CTX_get(ctx);
x = BN_CTX_get(ctx);
y = BN_CTX_get(ctx);
if (y == NULL) {
goto err;
}
/* Recover y. We have a Weierstrass equation
* y^2 = x^3 + a*x + b,
* so y is one of the square roots of x^3 + a*x + b. */
/* tmp1 := x^3 */
if (!BN_nnmod(x, x_, &group->field, ctx)) {
goto err;
}
if (group->meth->field_decode == 0) {
/* field_{sqr,mul} work on standard representation */
if (!group->meth->field_sqr(group, tmp2, x_, ctx) ||
!group->meth->field_mul(group, tmp1, tmp2, x_, ctx)) {
goto err;
}
} else {
if (!BN_mod_sqr(tmp2, x_, &group->field, ctx) ||
!BN_mod_mul(tmp1, tmp2, x_, &group->field, ctx)) {
goto err;
}
}
/* tmp1 := tmp1 + a*x */
if (group->a_is_minus3) {
if (!BN_mod_lshift1_quick(tmp2, x, &group->field) ||
!BN_mod_add_quick(tmp2, tmp2, x, &group->field) ||
!BN_mod_sub_quick(tmp1, tmp1, tmp2, &group->field)) {
goto err;
}
} else {
if (group->meth->field_decode) {
if (!group->meth->field_decode(group, tmp2, &group->a, ctx) ||
!BN_mod_mul(tmp2, tmp2, x, &group->field, ctx)) {
goto err;
}
} else {
/* field_mul works on standard representation */
if (!group->meth->field_mul(group, tmp2, &group->a, x, ctx)) {
goto err;
}
}
if (!BN_mod_add_quick(tmp1, tmp1, tmp2, &group->field)) {
goto err;
}
}
/* tmp1 := tmp1 + b */
if (group->meth->field_decode) {
if (!group->meth->field_decode(group, tmp2, &group->b, ctx) ||
!BN_mod_add_quick(tmp1, tmp1, tmp2, &group->field)) {
goto err;
}
} else {
if (!BN_mod_add_quick(tmp1, tmp1, &group->b, &group->field)) {
goto err;
}
}
if (!BN_mod_sqrt(y, tmp1, &group->field, ctx)) {
unsigned long err = ERR_peek_last_error();
if (ERR_GET_LIB(err) == ERR_LIB_BN &&
ERR_GET_REASON(err) == BN_R_NOT_A_SQUARE) {
ERR_clear_error();
OPENSSL_PUT_ERROR(EC, ec_GFp_simple_set_compressed_coordinates, EC_R_INVALID_COMPRESSED_POINT);
} else {
OPENSSL_PUT_ERROR(EC, ec_GFp_simple_set_compressed_coordinates, ERR_R_BN_LIB);
}
goto err;
}
if (y_bit != BN_is_odd(y)) {
if (BN_is_zero(y)) {
int kron;
kron = BN_kronecker(x, &group->field, ctx);
if (kron == -2) {
goto err;
}
if (kron == 1) {
OPENSSL_PUT_ERROR(EC, ec_GFp_simple_set_compressed_coordinates,
EC_R_INVALID_COMPRESSION_BIT);
} else {
/* BN_mod_sqrt() should have cought this error (not a square) */
OPENSSL_PUT_ERROR(EC, ec_GFp_simple_set_compressed_coordinates,
EC_R_INVALID_COMPRESSED_POINT);
}
goto err;
}
if (!BN_usub(y, &group->field, y)) {
goto err;
}
}
if (y_bit != BN_is_odd(y)) {
OPENSSL_PUT_ERROR(EC, ec_GFp_simple_set_compressed_coordinates,
ERR_R_INTERNAL_ERROR);
goto err;
}
if (!EC_POINT_set_affine_coordinates_GFp(group, point, x, y, ctx))
goto err;
ret = 1;
err:
BN_CTX_end(ctx);
if (new_ctx != NULL)
BN_CTX_free(new_ctx);
return ret;
}
int ec_GFp_simple_dbl(const EC_GROUP *group, EC_POINT *r, const EC_POINT *a,
BN_CTX *ctx)
{
int (*field_mul) (const EC_GROUP *, BIGNUM *, const BIGNUM *,
const BIGNUM *, BN_CTX *);
int (*field_sqr) (const EC_GROUP *, BIGNUM *, const BIGNUM *, BN_CTX *);
const BIGNUM *p;
BN_CTX *new_ctx = NULL;
BIGNUM *n0, *n1, *n2, *n3;
int ret = 0;
if (EC_POINT_is_at_infinity(group, a)) {
BN_zero(r->Z);
r->Z_is_one = 0;
return 1;
}
field_mul = group->meth->field_mul;
field_sqr = group->meth->field_sqr;
p = group->field;
if (ctx == NULL) {
ctx = new_ctx = BN_CTX_new();
if (ctx == NULL)
return 0;
}
BN_CTX_start(ctx);
n0 = BN_CTX_get(ctx);
n1 = BN_CTX_get(ctx);
n2 = BN_CTX_get(ctx);
n3 = BN_CTX_get(ctx);
if (n3 == NULL)
goto err;
/*
* Note that in this function we must not read components of 'a' once we
* have written the corresponding components of 'r'. ('r' might the same
* as 'a'.)
*/
/* n1 */
if (a->Z_is_one) {
if (!field_sqr(group, n0, a->X, ctx))
goto err;
if (!BN_mod_lshift1_quick(n1, n0, p))
goto err;
if (!BN_mod_add_quick(n0, n0, n1, p))
goto err;
if (!BN_mod_add_quick(n1, n0, group->a, p))
goto err;
/* n1 = 3 * X_a^2 + a_curve */
} else if (group->a_is_minus3) {
if (!field_sqr(group, n1, a->Z, ctx))
goto err;
if (!BN_mod_add_quick(n0, a->X, n1, p))
goto err;
if (!BN_mod_sub_quick(n2, a->X, n1, p))
goto err;
if (!field_mul(group, n1, n0, n2, ctx))
goto err;
if (!BN_mod_lshift1_quick(n0, n1, p))
goto err;
if (!BN_mod_add_quick(n1, n0, n1, p))
goto err;
/*-
* n1 = 3 * (X_a + Z_a^2) * (X_a - Z_a^2)
* = 3 * X_a^2 - 3 * Z_a^4
*/
} else {
if (!field_sqr(group, n0, a->X, ctx))
goto err;
if (!BN_mod_lshift1_quick(n1, n0, p))
goto err;
if (!BN_mod_add_quick(n0, n0, n1, p))
goto err;
if (!field_sqr(group, n1, a->Z, ctx))
goto err;
if (!field_sqr(group, n1, n1, ctx))
goto err;
if (!field_mul(group, n1, n1, group->a, ctx))
goto err;
if (!BN_mod_add_quick(n1, n1, n0, p))
goto err;
/* n1 = 3 * X_a^2 + a_curve * Z_a^4 */
}
/* Z_r */
if (a->Z_is_one) {
if (!BN_copy(n0, a->Y))
goto err;
} else {
if (!field_mul(group, n0, a->Y, a->Z, ctx))
goto err;
}
if (!BN_mod_lshift1_quick(r->Z, n0, p))
goto err;
r->Z_is_one = 0;
/* Z_r = 2 * Y_a * Z_a */
/* n2 */
if (!field_sqr(group, n3, a->Y, ctx))
goto err;
if (!field_mul(group, n2, a->X, n3, ctx))
goto err;
if (!BN_mod_lshift_quick(n2, n2, 2, p))
goto err;
/* n2 = 4 * X_a * Y_a^2 */
/* X_r */
if (!BN_mod_lshift1_quick(n0, n2, p))
goto err;
if (!field_sqr(group, r->X, n1, ctx))
goto err;
if (!BN_mod_sub_quick(r->X, r->X, n0, p))
goto err;
/* X_r = n1^2 - 2 * n2 */
/* n3 */
if (!field_sqr(group, n0, n3, ctx))
goto err;
if (!BN_mod_lshift_quick(n3, n0, 3, p))
goto err;
/* n3 = 8 * Y_a^4 */
/* Y_r */
if (!BN_mod_sub_quick(n0, n2, r->X, p))
goto err;
if (!field_mul(group, n0, n1, n0, ctx))
goto err;
if (!BN_mod_sub_quick(r->Y, n0, n3, p))
goto err;
/* Y_r = n1 * (n2 - X_r) - n3 */
ret = 1;
err:
BN_CTX_end(ctx);
BN_CTX_free(new_ctx);
return ret;
}
int ec_GFp_simple_is_on_curve(const EC_GROUP *group, const EC_POINT *point,
BN_CTX *ctx)
{
int (*field_mul) (const EC_GROUP *, BIGNUM *, const BIGNUM *,
const BIGNUM *, BN_CTX *);
int (*field_sqr) (const EC_GROUP *, BIGNUM *, const BIGNUM *, BN_CTX *);
const BIGNUM *p;
BN_CTX *new_ctx = NULL;
BIGNUM *rh, *tmp, *Z4, *Z6;
int ret = -1;
if (EC_POINT_is_at_infinity(group, point))
return 1;
field_mul = group->meth->field_mul;
field_sqr = group->meth->field_sqr;
p = group->field;
if (ctx == NULL) {
ctx = new_ctx = BN_CTX_new();
if (ctx == NULL)
return -1;
}
BN_CTX_start(ctx);
rh = BN_CTX_get(ctx);
tmp = BN_CTX_get(ctx);
Z4 = BN_CTX_get(ctx);
Z6 = BN_CTX_get(ctx);
if (Z6 == NULL)
goto err;
/*-
* We have a curve defined by a Weierstrass equation
* y^2 = x^3 + a*x + b.
* The point to consider is given in Jacobian projective coordinates
* where (X, Y, Z) represents (x, y) = (X/Z^2, Y/Z^3).
* Substituting this and multiplying by Z^6 transforms the above equation into
* Y^2 = X^3 + a*X*Z^4 + b*Z^6.
* To test this, we add up the right-hand side in 'rh'.
*/
/* rh := X^2 */
if (!field_sqr(group, rh, point->X, ctx))
goto err;
if (!point->Z_is_one) {
if (!field_sqr(group, tmp, point->Z, ctx))
goto err;
if (!field_sqr(group, Z4, tmp, ctx))
goto err;
if (!field_mul(group, Z6, Z4, tmp, ctx))
goto err;
/* rh := (rh + a*Z^4)*X */
if (group->a_is_minus3) {
if (!BN_mod_lshift1_quick(tmp, Z4, p))
goto err;
if (!BN_mod_add_quick(tmp, tmp, Z4, p))
goto err;
if (!BN_mod_sub_quick(rh, rh, tmp, p))
goto err;
if (!field_mul(group, rh, rh, point->X, ctx))
goto err;
} else {
if (!field_mul(group, tmp, Z4, group->a, ctx))
goto err;
if (!BN_mod_add_quick(rh, rh, tmp, p))
goto err;
if (!field_mul(group, rh, rh, point->X, ctx))
goto err;
}
/* rh := rh + b*Z^6 */
if (!field_mul(group, tmp, group->b, Z6, ctx))
goto err;
if (!BN_mod_add_quick(rh, rh, tmp, p))
goto err;
} else {
/* point->Z_is_one */
/* rh := (rh + a)*X */
if (!BN_mod_add_quick(rh, rh, group->a, p))
goto err;
if (!field_mul(group, rh, rh, point->X, ctx))
goto err;
/* rh := rh + b */
if (!BN_mod_add_quick(rh, rh, group->b, p))
goto err;
}
/* 'lh' := Y^2 */
if (!field_sqr(group, tmp, point->Y, ctx))
goto err;
ret = (0 == BN_ucmp(tmp, rh));
err:
BN_CTX_end(ctx);
BN_CTX_free(new_ctx);
return ret;
}
int ec_GFp_simple_add(const EC_GROUP *group, EC_POINT *r, const EC_POINT *a,
const EC_POINT *b, BN_CTX *ctx)
{
int (*field_mul) (const EC_GROUP *, BIGNUM *, const BIGNUM *,
const BIGNUM *, BN_CTX *);
int (*field_sqr) (const EC_GROUP *, BIGNUM *, const BIGNUM *, BN_CTX *);
const BIGNUM *p;
BN_CTX *new_ctx = NULL;
BIGNUM *n0, *n1, *n2, *n3, *n4, *n5, *n6;
int ret = 0;
if (a == b)
return EC_POINT_dbl(group, r, a, ctx);
if (EC_POINT_is_at_infinity(group, a))
return EC_POINT_copy(r, b);
if (EC_POINT_is_at_infinity(group, b))
return EC_POINT_copy(r, a);
field_mul = group->meth->field_mul;
field_sqr = group->meth->field_sqr;
p = group->field;
if (ctx == NULL) {
ctx = new_ctx = BN_CTX_new();
if (ctx == NULL)
return 0;
}
BN_CTX_start(ctx);
n0 = BN_CTX_get(ctx);
n1 = BN_CTX_get(ctx);
n2 = BN_CTX_get(ctx);
n3 = BN_CTX_get(ctx);
n4 = BN_CTX_get(ctx);
n5 = BN_CTX_get(ctx);
n6 = BN_CTX_get(ctx);
if (n6 == NULL)
goto end;
/*
* Note that in this function we must not read components of 'a' or 'b'
* once we have written the corresponding components of 'r'. ('r' might
* be one of 'a' or 'b'.)
*/
/* n1, n2 */
if (b->Z_is_one) {
if (!BN_copy(n1, a->X))
goto end;
if (!BN_copy(n2, a->Y))
goto end;
/* n1 = X_a */
/* n2 = Y_a */
} else {
if (!field_sqr(group, n0, b->Z, ctx))
goto end;
if (!field_mul(group, n1, a->X, n0, ctx))
goto end;
/* n1 = X_a * Z_b^2 */
if (!field_mul(group, n0, n0, b->Z, ctx))
goto end;
if (!field_mul(group, n2, a->Y, n0, ctx))
goto end;
/* n2 = Y_a * Z_b^3 */
}
/* n3, n4 */
if (a->Z_is_one) {
if (!BN_copy(n3, b->X))
goto end;
if (!BN_copy(n4, b->Y))
goto end;
/* n3 = X_b */
/* n4 = Y_b */
} else {
if (!field_sqr(group, n0, a->Z, ctx))
goto end;
if (!field_mul(group, n3, b->X, n0, ctx))
goto end;
/* n3 = X_b * Z_a^2 */
if (!field_mul(group, n0, n0, a->Z, ctx))
goto end;
if (!field_mul(group, n4, b->Y, n0, ctx))
goto end;
/* n4 = Y_b * Z_a^3 */
}
/* n5, n6 */
if (!BN_mod_sub_quick(n5, n1, n3, p))
goto end;
if (!BN_mod_sub_quick(n6, n2, n4, p))
goto end;
/* n5 = n1 - n3 */
/* n6 = n2 - n4 */
if (BN_is_zero(n5)) {
if (BN_is_zero(n6)) {
/* a is the same point as b */
BN_CTX_end(ctx);
ret = EC_POINT_dbl(group, r, a, ctx);
ctx = NULL;
goto end;
} else {
/* a is the inverse of b */
BN_zero(r->Z);
r->Z_is_one = 0;
ret = 1;
goto end;
}
}
/* 'n7', 'n8' */
if (!BN_mod_add_quick(n1, n1, n3, p))
goto end;
if (!BN_mod_add_quick(n2, n2, n4, p))
goto end;
/* 'n7' = n1 + n3 */
/* 'n8' = n2 + n4 */
/* Z_r */
if (a->Z_is_one && b->Z_is_one) {
if (!BN_copy(r->Z, n5))
goto end;
} else {
if (a->Z_is_one) {
if (!BN_copy(n0, b->Z))
goto end;
} else if (b->Z_is_one) {
if (!BN_copy(n0, a->Z))
goto end;
} else {
if (!field_mul(group, n0, a->Z, b->Z, ctx))
goto end;
}
if (!field_mul(group, r->Z, n0, n5, ctx))
goto end;
}
r->Z_is_one = 0;
/* Z_r = Z_a * Z_b * n5 */
/* X_r */
if (!field_sqr(group, n0, n6, ctx))
goto end;
if (!field_sqr(group, n4, n5, ctx))
goto end;
if (!field_mul(group, n3, n1, n4, ctx))
goto end;
if (!BN_mod_sub_quick(r->X, n0, n3, p))
goto end;
/* X_r = n6^2 - n5^2 * 'n7' */
/* 'n9' */
if (!BN_mod_lshift1_quick(n0, r->X, p))
goto end;
if (!BN_mod_sub_quick(n0, n3, n0, p))
goto end;
/* n9 = n5^2 * 'n7' - 2 * X_r */
/* Y_r */
if (!field_mul(group, n0, n0, n6, ctx))
goto end;
if (!field_mul(group, n5, n4, n5, ctx))
goto end; /* now n5 is n5^3 */
if (!field_mul(group, n1, n2, n5, ctx))
goto end;
if (!BN_mod_sub_quick(n0, n0, n1, p))
goto end;
if (BN_is_odd(n0))
if (!BN_add(n0, n0, p))
goto end;
/* now 0 <= n0 < 2*p, and n0 is even */
if (!BN_rshift1(r->Y, n0))
goto end;
/* Y_r = (n6 * 'n9' - 'n8' * 'n5^3') / 2 */
ret = 1;
end:
if (ctx) /* otherwise we already called BN_CTX_end */
BN_CTX_end(ctx);
BN_CTX_free(new_ctx);
return ret;
}
/*-
* Recovers the y-coordinate of r using Eq. (8) from Brier-Joye, "Weierstrass
* Elliptic Curves and Side-Channel Attacks", modified to work in projective
* coordinates and return r in Jacobian projective coordinates.
*
* X4 = two*Y1*X2*Z3*Z2*Z1;
* Y4 = two*b*Z3*SQR(Z2*Z1) + Z3*(a*Z2*Z1+X1*X2)*(X1*Z2+X2*Z1) - X3*SQR(X1*Z2-X2*Z1);
* Z4 = two*Y1*Z3*SQR(Z2)*Z1;
*
* Z4 != 0 because:
* - Z1==0 implies p is at infinity, which would have caused an early exit in
* the caller;
* - Z2==0 implies r is at infinity (handled by the BN_is_zero(r->Z) branch);
* - Z3==0 implies s is at infinity (handled by the BN_is_zero(s->Z) branch);
* - Y1==0 implies p has order 2, so either r or s are infinity and handled by
* one of the BN_is_zero(...) branches.
*/
int ec_GFp_simple_ladder_post(const EC_GROUP *group,
EC_POINT *r, EC_POINT *s,
EC_POINT *p, BN_CTX *ctx)
{
int ret = 0;
BIGNUM *t0, *t1, *t2, *t3, *t4, *t5, *t6 = NULL;
if (BN_is_zero(r->Z))
return EC_POINT_set_to_infinity(group, r);
if (BN_is_zero(s->Z)) {
/* (X,Y,Z) -> (XZ,YZ**2,Z) */
if (!group->meth->field_mul(group, r->X, p->X, p->Z, ctx)
|| !group->meth->field_sqr(group, r->Z, p->Z, ctx)
|| !group->meth->field_mul(group, r->Y, p->Y, r->Z, ctx)
|| !BN_copy(r->Z, p->Z)
|| !EC_POINT_invert(group, r, ctx))
return 0;
return 1;
}
BN_CTX_start(ctx);
t0 = BN_CTX_get(ctx);
t1 = BN_CTX_get(ctx);
t2 = BN_CTX_get(ctx);
t3 = BN_CTX_get(ctx);
t4 = BN_CTX_get(ctx);
t5 = BN_CTX_get(ctx);
t6 = BN_CTX_get(ctx);
if (t6 == NULL
|| !BN_mod_lshift1_quick(t0, p->Y, group->field)
|| !group->meth->field_mul(group, t1, r->X, p->Z, ctx)
|| !group->meth->field_mul(group, t2, r->Z, s->Z, ctx)
|| !group->meth->field_mul(group, t2, t1, t2, ctx)
|| !group->meth->field_mul(group, t3, t2, t0, ctx)
|| !group->meth->field_mul(group, t2, r->Z, p->Z, ctx)
|| !group->meth->field_sqr(group, t4, t2, ctx)
|| !BN_mod_lshift1_quick(t5, group->b, group->field)
|| !group->meth->field_mul(group, t4, t4, t5, ctx)
|| !group->meth->field_mul(group, t6, t2, group->a, ctx)
|| !group->meth->field_mul(group, t5, r->X, p->X, ctx)
|| !BN_mod_add_quick(t5, t6, t5, group->field)
|| !group->meth->field_mul(group, t6, r->Z, p->X, ctx)
|| !BN_mod_add_quick(t2, t6, t1, group->field)
|| !group->meth->field_mul(group, t5, t5, t2, ctx)
|| !BN_mod_sub_quick(t6, t6, t1, group->field)
|| !group->meth->field_sqr(group, t6, t6, ctx)
|| !group->meth->field_mul(group, t6, t6, s->X, ctx)
|| !BN_mod_add_quick(t4, t5, t4, group->field)
|| !group->meth->field_mul(group, t4, t4, s->Z, ctx)
|| !BN_mod_sub_quick(t4, t4, t6, group->field)
|| !group->meth->field_sqr(group, t5, r->Z, ctx)
|| !group->meth->field_mul(group, r->Z, p->Z, s->Z, ctx)
|| !group->meth->field_mul(group, r->Z, t5, r->Z, ctx)
|| !group->meth->field_mul(group, r->Z, r->Z, t0, ctx)
/* t3 := X, t4 := Y */
/* (X,Y,Z) -> (XZ,YZ**2,Z) */
|| !group->meth->field_mul(group, r->X, t3, r->Z, ctx)
|| !group->meth->field_sqr(group, t3, r->Z, ctx)
|| !group->meth->field_mul(group, r->Y, t4, t3, ctx))
goto err;
ret = 1;
err:
BN_CTX_end(ctx);
return ret;
}
/*-
* Differential addition-and-doubling using Eq. (9) and (10) from Izu-Takagi
* "A fast parallel elliptic curve multiplication resistant against side channel
* attacks", as described at
* https://hyperelliptic.org/EFD/g1p/auto-shortw-xz.html#ladder-ladd-2002-it-4
*/
int ec_GFp_simple_ladder_step(const EC_GROUP *group,
EC_POINT *r, EC_POINT *s,
EC_POINT *p, BN_CTX *ctx)
{
int ret = 0;
BIGNUM *t0, *t1, *t2, *t3, *t4, *t5, *t6, *t7 = NULL;
BN_CTX_start(ctx);
t0 = BN_CTX_get(ctx);
t1 = BN_CTX_get(ctx);
t2 = BN_CTX_get(ctx);
t3 = BN_CTX_get(ctx);
t4 = BN_CTX_get(ctx);
t5 = BN_CTX_get(ctx);
t6 = BN_CTX_get(ctx);
t7 = BN_CTX_get(ctx);
if (t7 == NULL
|| !group->meth->field_mul(group, t0, r->X, s->X, ctx)
|| !group->meth->field_mul(group, t1, r->Z, s->Z, ctx)
|| !group->meth->field_mul(group, t2, r->X, s->Z, ctx)
|| !group->meth->field_mul(group, t3, r->Z, s->X, ctx)
|| !group->meth->field_mul(group, t4, group->a, t1, ctx)
|| !BN_mod_add_quick(t0, t0, t4, group->field)
|| !BN_mod_add_quick(t4, t3, t2, group->field)
|| !group->meth->field_mul(group, t0, t4, t0, ctx)
|| !group->meth->field_sqr(group, t1, t1, ctx)
|| !BN_mod_lshift_quick(t7, group->b, 2, group->field)
|| !group->meth->field_mul(group, t1, t7, t1, ctx)
|| !BN_mod_lshift1_quick(t0, t0, group->field)
|| !BN_mod_add_quick(t0, t1, t0, group->field)
|| !BN_mod_sub_quick(t1, t2, t3, group->field)
|| !group->meth->field_sqr(group, t1, t1, ctx)
|| !group->meth->field_mul(group, t3, t1, p->X, ctx)
|| !group->meth->field_mul(group, t0, p->Z, t0, ctx)
/* s->X coord output */
|| !BN_mod_sub_quick(s->X, t0, t3, group->field)
/* s->Z coord output */
|| !group->meth->field_mul(group, s->Z, p->Z, t1, ctx)
|| !group->meth->field_sqr(group, t3, r->X, ctx)
|| !group->meth->field_sqr(group, t2, r->Z, ctx)
|| !group->meth->field_mul(group, t4, t2, group->a, ctx)
|| !BN_mod_add_quick(t5, r->X, r->Z, group->field)
|| !group->meth->field_sqr(group, t5, t5, ctx)
|| !BN_mod_sub_quick(t5, t5, t3, group->field)
|| !BN_mod_sub_quick(t5, t5, t2, group->field)
|| !BN_mod_sub_quick(t6, t3, t4, group->field)
|| !group->meth->field_sqr(group, t6, t6, ctx)
|| !group->meth->field_mul(group, t0, t2, t5, ctx)
|| !group->meth->field_mul(group, t0, t7, t0, ctx)
/* r->X coord output */
|| !BN_mod_sub_quick(r->X, t6, t0, group->field)
|| !BN_mod_add_quick(t6, t3, t4, group->field)
|| !group->meth->field_sqr(group, t3, t2, ctx)
|| !group->meth->field_mul(group, t7, t3, t7, ctx)
|| !group->meth->field_mul(group, t5, t5, t6, ctx)
|| !BN_mod_lshift1_quick(t5, t5, group->field)
/* r->Z coord output */
|| !BN_mod_add_quick(r->Z, t7, t5, group->field))
goto err;
ret = 1;
err:
BN_CTX_end(ctx);
return ret;
}
int ec_GFp_simple_dbl(const EC_GROUP *group, EC_POINT *r, const EC_POINT *a,
BN_CTX *ctx) {
int (*field_mul)(const EC_GROUP *, BIGNUM *, const BIGNUM *, const BIGNUM *,
BN_CTX *);
int (*field_sqr)(const EC_GROUP *, BIGNUM *, const BIGNUM *, BN_CTX *);
const BIGNUM *p;
BN_CTX *new_ctx = NULL;
BIGNUM *n0, *n1, *n2, *n3;
int ret = 0;
if (EC_POINT_is_at_infinity(group, a)) {
BN_zero(&r->Z);
return 1;
}
field_mul = group->meth->field_mul;
field_sqr = group->meth->field_sqr;
p = &group->field;
if (ctx == NULL) {
ctx = new_ctx = BN_CTX_new();
if (ctx == NULL) {
return 0;
}
}
BN_CTX_start(ctx);
n0 = BN_CTX_get(ctx);
n1 = BN_CTX_get(ctx);
n2 = BN_CTX_get(ctx);
n3 = BN_CTX_get(ctx);
if (n3 == NULL) {
goto err;
}
/* Note that in this function we must not read components of 'a'
* once we have written the corresponding components of 'r'.
* ('r' might the same as 'a'.)
*/
/* n1 */
if (BN_cmp(&a->Z, &group->one) == 0) {
if (!field_sqr(group, n0, &a->X, ctx) ||
!BN_mod_lshift1_quick(n1, n0, p) ||
!BN_mod_add_quick(n0, n0, n1, p) ||
!BN_mod_add_quick(n1, n0, &group->a, p)) {
goto err;
}
/* n1 = 3 * X_a^2 + a_curve */
} else {
/* ring: This assumes a == -3. */
if (!field_sqr(group, n1, &a->Z, ctx) ||
!BN_mod_add_quick(n0, &a->X, n1, p) ||
!BN_mod_sub_quick(n2, &a->X, n1, p) ||
!field_mul(group, n1, n0, n2, ctx) ||
!BN_mod_lshift1_quick(n0, n1, p) ||
!BN_mod_add_quick(n1, n0, n1, p)) {
goto err;
}
/* n1 = 3 * (X_a + Z_a^2) * (X_a - Z_a^2)
* = 3 * X_a^2 - 3 * Z_a^4 */
}
/* Z_r */
if (BN_cmp(&a->Z, &group->one) == 0) {
if (!BN_copy(n0, &a->Y)) {
goto err;
}
} else if (!field_mul(group, n0, &a->Y, &a->Z, ctx)) {
goto err;
}
if (!BN_mod_lshift1_quick(&r->Z, n0, p)) {
goto err;
}
/* Z_r = 2 * Y_a * Z_a */
/* n2 */
if (!field_sqr(group, n3, &a->Y, ctx) ||
!field_mul(group, n2, &a->X, n3, ctx) ||
!BN_mod_lshift_quick(n2, n2, 2, p)) {
goto err;
}
/* n2 = 4 * X_a * Y_a^2 */
/* X_r */
if (!BN_mod_lshift1_quick(n0, n2, p) ||
!field_sqr(group, &r->X, n1, ctx) ||
!BN_mod_sub_quick(&r->X, &r->X, n0, p)) {
goto err;
}
/* X_r = n1^2 - 2 * n2 */
/* n3 */
if (!field_sqr(group, n0, n3, ctx) ||
!BN_mod_lshift_quick(n3, n0, 3, p)) {
goto err;
}
/* n3 = 8 * Y_a^4 */
/* Y_r */
if (!BN_mod_sub_quick(n0, n2, &r->X, p) ||
!field_mul(group, n0, n1, n0, ctx) ||
!BN_mod_sub_quick(&r->Y, n0, n3, p)) {
goto err;
}
/* Y_r = n1 * (n2 - X_r) - n3 */
ret = 1;
err:
BN_CTX_end(ctx);
BN_CTX_free(new_ctx);
return ret;
}
BIGNUM *BN_mod_sqrt(BIGNUM *in, const BIGNUM *a, const BIGNUM *p, BN_CTX *ctx) {
// Compute a square root of |a| mod |p| using the Tonelli/Shanks algorithm
// (cf. Henri Cohen, "A Course in Algebraic Computational Number Theory",
// algorithm 1.5.1). |p| is assumed to be a prime.
BIGNUM *ret = in;
int err = 1;
int r;
BIGNUM *A, *b, *q, *t, *x, *y;
int e, i, j;
if (!BN_is_odd(p) || BN_abs_is_word(p, 1)) {
if (BN_abs_is_word(p, 2)) {
if (ret == NULL) {
ret = BN_new();
}
if (ret == NULL) {
goto end;
}
if (!BN_set_word(ret, BN_is_bit_set(a, 0))) {
if (ret != in) {
BN_free(ret);
}
return NULL;
}
return ret;
}
OPENSSL_PUT_ERROR(BN, BN_R_P_IS_NOT_PRIME);
return (NULL);
}
if (BN_is_zero(a) || BN_is_one(a)) {
if (ret == NULL) {
ret = BN_new();
}
if (ret == NULL) {
goto end;
}
if (!BN_set_word(ret, BN_is_one(a))) {
if (ret != in) {
BN_free(ret);
}
return NULL;
}
return ret;
}
BN_CTX_start(ctx);
A = BN_CTX_get(ctx);
b = BN_CTX_get(ctx);
q = BN_CTX_get(ctx);
t = BN_CTX_get(ctx);
x = BN_CTX_get(ctx);
y = BN_CTX_get(ctx);
if (y == NULL) {
goto end;
}
if (ret == NULL) {
ret = BN_new();
}
if (ret == NULL) {
goto end;
}
// A = a mod p
if (!BN_nnmod(A, a, p, ctx)) {
goto end;
}
// now write |p| - 1 as 2^e*q where q is odd
e = 1;
while (!BN_is_bit_set(p, e)) {
e++;
}
// we'll set q later (if needed)
if (e == 1) {
// The easy case: (|p|-1)/2 is odd, so 2 has an inverse
// modulo (|p|-1)/2, and square roots can be computed
// directly by modular exponentiation.
// We have
// 2 * (|p|+1)/4 == 1 (mod (|p|-1)/2),
// so we can use exponent (|p|+1)/4, i.e. (|p|-3)/4 + 1.
if (!BN_rshift(q, p, 2)) {
goto end;
}
q->neg = 0;
if (!BN_add_word(q, 1) ||
!BN_mod_exp_mont(ret, A, q, p, ctx, NULL)) {
goto end;
}
err = 0;
goto vrfy;
}
if (e == 2) {
// |p| == 5 (mod 8)
//
// In this case 2 is always a non-square since
// Legendre(2,p) = (-1)^((p^2-1)/8) for any odd prime.
// So if a really is a square, then 2*a is a non-square.
// Thus for
// b := (2*a)^((|p|-5)/8),
// i := (2*a)*b^2
// we have
// i^2 = (2*a)^((1 + (|p|-5)/4)*2)
// = (2*a)^((p-1)/2)
// = -1;
// so if we set
// x := a*b*(i-1),
// then
// x^2 = a^2 * b^2 * (i^2 - 2*i + 1)
// = a^2 * b^2 * (-2*i)
// = a*(-i)*(2*a*b^2)
// = a*(-i)*i
// = a.
//
// (This is due to A.O.L. Atkin,
// <URL:
//http://listserv.nodak.edu/scripts/wa.exe?A2=ind9211&L=nmbrthry&O=T&P=562>,
// November 1992.)
// t := 2*a
if (!BN_mod_lshift1_quick(t, A, p)) {
goto end;
}
// b := (2*a)^((|p|-5)/8)
if (!BN_rshift(q, p, 3)) {
goto end;
}
q->neg = 0;
if (!BN_mod_exp_mont(b, t, q, p, ctx, NULL)) {
goto end;
}
// y := b^2
if (!BN_mod_sqr(y, b, p, ctx)) {
goto end;
}
// t := (2*a)*b^2 - 1
if (!BN_mod_mul(t, t, y, p, ctx) ||
!BN_sub_word(t, 1)) {
goto end;
}
// x = a*b*t
if (!BN_mod_mul(x, A, b, p, ctx) ||
!BN_mod_mul(x, x, t, p, ctx)) {
goto end;
}
if (!BN_copy(ret, x)) {
goto end;
}
err = 0;
goto vrfy;
}
// e > 2, so we really have to use the Tonelli/Shanks algorithm.
// First, find some y that is not a square.
if (!BN_copy(q, p)) {
goto end; // use 'q' as temp
}
q->neg = 0;
i = 2;
do {
// For efficiency, try small numbers first;
// if this fails, try random numbers.
if (i < 22) {
if (!BN_set_word(y, i)) {
goto end;
}
} else {
if (!BN_pseudo_rand(y, BN_num_bits(p), 0, 0)) {
goto end;
}
if (BN_ucmp(y, p) >= 0) {
if (!(p->neg ? BN_add : BN_sub)(y, y, p)) {
goto end;
}
}
// now 0 <= y < |p|
if (BN_is_zero(y)) {
if (!BN_set_word(y, i)) {
goto end;
}
}
}
r = bn_jacobi(y, q, ctx); // here 'q' is |p|
if (r < -1) {
goto end;
}
if (r == 0) {
// m divides p
OPENSSL_PUT_ERROR(BN, BN_R_P_IS_NOT_PRIME);
goto end;
}
} while (r == 1 && ++i < 82);
if (r != -1) {
// Many rounds and still no non-square -- this is more likely
// a bug than just bad luck.
// Even if p is not prime, we should have found some y
// such that r == -1.
OPENSSL_PUT_ERROR(BN, BN_R_TOO_MANY_ITERATIONS);
goto end;
}
// Here's our actual 'q':
if (!BN_rshift(q, q, e)) {
goto end;
}
// Now that we have some non-square, we can find an element
// of order 2^e by computing its q'th power.
if (!BN_mod_exp_mont(y, y, q, p, ctx, NULL)) {
goto end;
}
if (BN_is_one(y)) {
OPENSSL_PUT_ERROR(BN, BN_R_P_IS_NOT_PRIME);
goto end;
}
// Now we know that (if p is indeed prime) there is an integer
// k, 0 <= k < 2^e, such that
//
// a^q * y^k == 1 (mod p).
//
// As a^q is a square and y is not, k must be even.
// q+1 is even, too, so there is an element
//
// X := a^((q+1)/2) * y^(k/2),
//
// and it satisfies
//
// X^2 = a^q * a * y^k
// = a,
//
// so it is the square root that we are looking for.
// t := (q-1)/2 (note that q is odd)
if (!BN_rshift1(t, q)) {
goto end;
}
// x := a^((q-1)/2)
if (BN_is_zero(t)) // special case: p = 2^e + 1
{
if (!BN_nnmod(t, A, p, ctx)) {
goto end;
}
if (BN_is_zero(t)) {
// special case: a == 0 (mod p)
BN_zero(ret);
err = 0;
goto end;
} else if (!BN_one(x)) {
goto end;
}
} else {
if (!BN_mod_exp_mont(x, A, t, p, ctx, NULL)) {
goto end;
}
if (BN_is_zero(x)) {
// special case: a == 0 (mod p)
BN_zero(ret);
err = 0;
goto end;
}
}
// b := a*x^2 (= a^q)
if (!BN_mod_sqr(b, x, p, ctx) ||
!BN_mod_mul(b, b, A, p, ctx)) {
goto end;
}
// x := a*x (= a^((q+1)/2))
if (!BN_mod_mul(x, x, A, p, ctx)) {
goto end;
}
while (1) {
// Now b is a^q * y^k for some even k (0 <= k < 2^E
// where E refers to the original value of e, which we
// don't keep in a variable), and x is a^((q+1)/2) * y^(k/2).
//
// We have a*b = x^2,
// y^2^(e-1) = -1,
// b^2^(e-1) = 1.
if (BN_is_one(b)) {
if (!BN_copy(ret, x)) {
goto end;
}
err = 0;
goto vrfy;
}
// find smallest i such that b^(2^i) = 1
i = 1;
if (!BN_mod_sqr(t, b, p, ctx)) {
goto end;
}
while (!BN_is_one(t)) {
i++;
if (i == e) {
OPENSSL_PUT_ERROR(BN, BN_R_NOT_A_SQUARE);
goto end;
}
if (!BN_mod_mul(t, t, t, p, ctx)) {
goto end;
}
}
// t := y^2^(e - i - 1)
if (!BN_copy(t, y)) {
goto end;
}
for (j = e - i - 1; j > 0; j--) {
if (!BN_mod_sqr(t, t, p, ctx)) {
goto end;
}
}
if (!BN_mod_mul(y, t, t, p, ctx) ||
!BN_mod_mul(x, x, t, p, ctx) ||
!BN_mod_mul(b, b, y, p, ctx)) {
goto end;
}
e = i;
}
vrfy:
if (!err) {
// verify the result -- the input might have been not a square
// (test added in 0.9.8)
if (!BN_mod_sqr(x, ret, p, ctx)) {
err = 1;
}
if (!err && 0 != BN_cmp(x, A)) {
OPENSSL_PUT_ERROR(BN, BN_R_NOT_A_SQUARE);
err = 1;
}
}
end:
if (err) {
if (ret != in) {
BN_clear_free(ret);
}
ret = NULL;
}
BN_CTX_end(ctx);
return ret;
}
