+/* Calculates and sets the affine coordinates of an EC_POINT from the given
+ * compressed coordinates. Uses algorithm 2.3.4 of SEC 1.
+ * Note that the simple implementation only uses affine coordinates.
+ *
+ * The method is from the following publication:
+ *
+ * Harper, Menezes, Vanstone:
+ * "Public-Key Cryptosystems with Very Small Key Lengths",
+ * EUROCRYPT '92, Springer-Verlag LNCS 658,
+ * published February 1993
+ *
+ * US Patents 6,141,420 and 6,618,483 (Vanstone, Mullin, Agnew) describe
+ * the same method, but claim no priority date earlier than July 29, 1994
+ * (and additionally fail to cite the EUROCRYPT '92 publication as prior art).
+ */
+int ec_GF2m_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 *tmp, *x, *y, *z;
+ int ret = 0, z0;
+
+ /* clear error queue */
+ ERR_clear_error();
+
+ if (ctx == NULL)
+ {
+ ctx = new_ctx = BN_CTX_new();
+ if (ctx == NULL)
+ return 0;
+ }
+
+ y_bit = (y_bit != 0) ? 1 : 0;
+
+ BN_CTX_start(ctx);
+ tmp = BN_CTX_get(ctx);
+ x = BN_CTX_get(ctx);
+ y = BN_CTX_get(ctx);
+ z = BN_CTX_get(ctx);
+ if (z == NULL) goto err;
+
+ if (!BN_GF2m_mod_arr(x, x_, group->poly)) goto err;
+ if (BN_is_zero(x))
+ {
+ if (!BN_GF2m_mod_sqrt_arr(y, &group->b, group->poly, ctx)) goto err;
+ }
+ else
+ {
+ if (!group->meth->field_sqr(group, tmp, x, ctx)) goto err;
+ if (!group->meth->field_div(group, tmp, &group->b, tmp, ctx)) goto err;
+ if (!BN_GF2m_add(tmp, &group->a, tmp)) goto err;
+ if (!BN_GF2m_add(tmp, x, tmp)) goto err;
+ if (!BN_GF2m_mod_solve_quad_arr(z, tmp, group->poly, ctx))
+ {
+ unsigned long err = ERR_peek_last_error();
+
+ if (ERR_GET_LIB(err) == ERR_LIB_BN && ERR_GET_REASON(err) == BN_R_NO_SOLUTION)
+ {
+ ERR_clear_error();
+ ECerr(EC_F_EC_GF2M_SIMPLE_SET_COMPRESSED_COORDINATES, EC_R_INVALID_COMPRESSED_POINT);
+ }
+ else
+ ECerr(EC_F_EC_GF2M_SIMPLE_SET_COMPRESSED_COORDINATES, ERR_R_BN_LIB);
+ goto err;
+ }
+ z0 = (BN_is_odd(z)) ? 1 : 0;
+ if (!group->meth->field_mul(group, y, x, z, ctx)) goto err;
+ if (z0 != y_bit)
+ {
+ if (!BN_GF2m_add(y, y, x)) goto err;
+ }
+ }
+
+ if (!EC_POINT_set_affine_coordinates_GF2m(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;
+ }