+ const unsigned char *buf, size_t len, BN_CTX *ctx)
+ {
+ point_conversion_form_t form;
+ int y_bit;
+ BN_CTX *new_ctx = NULL;
+ BIGNUM *x, *y;
+ size_t field_len, enc_len;
+ int ret = 0;
+
+ if (len <= 0)
+ {
+ ECerr(EC_F_EC_GFP_SIMPLE_OCT2POINT, EC_R_BUFFER_TOO_SMALL);
+ return 0;
+ }
+ form = buf[0];
+ y_bit = form & 1;
+ form = form & ~1;
+ if ((form != 0) && (form != POINT_CONVERSION_COMPRESSED)
+ && (form != POINT_CONVERSION_UNCOMPRESSED)
+ && (form != POINT_CONVERSION_HYBRID))
+ {
+ ECerr(EC_F_EC_GFP_SIMPLE_OCT2POINT, EC_R_INVALID_ENCODING);
+ return 0;
+ }
+ if ((form == 0 || form == POINT_CONVERSION_UNCOMPRESSED) && y_bit)
+ {
+ ECerr(EC_F_EC_GFP_SIMPLE_OCT2POINT, EC_R_INVALID_ENCODING);
+ return 0;
+ }
+
+ if (form == 0)
+ {
+ if (len != 1)
+ {
+ ECerr(EC_F_EC_GFP_SIMPLE_OCT2POINT, EC_R_INVALID_ENCODING);
+ return 0;
+ }
+
+ return EC_POINT_set_to_infinity(group, point);
+ }
+
+ field_len = BN_num_bytes(&group->field);
+ enc_len = (form == POINT_CONVERSION_COMPRESSED) ? 1 + field_len : 1 + 2*field_len;
+
+ if (len != enc_len)
+ {
+ ECerr(EC_F_EC_GFP_SIMPLE_OCT2POINT, EC_R_INVALID_ENCODING);
+ return 0;
+ }
+
+ if (ctx == NULL)
+ {
+ ctx = new_ctx = BN_CTX_new();
+ if (ctx == NULL)
+ return 0;
+ }
+
+ BN_CTX_start(ctx);
+ x = BN_CTX_get(ctx);
+ y = BN_CTX_get(ctx);
+ if (y == NULL) goto err;
+
+ if (!BN_bin2bn(buf + 1, field_len, x)) goto err;
+ if (BN_ucmp(x, &group->field) >= 0)
+ {
+ ECerr(EC_F_EC_GFP_SIMPLE_OCT2POINT, EC_R_INVALID_ENCODING);
+ goto err;
+ }
+
+ if (form != POINT_CONVERSION_COMPRESSED)
+ {
+ if (!BN_bin2bn(buf + 1 + field_len, field_len, y)) goto err;
+ if (BN_ucmp(y, &group->field) >= 0)
+ {
+ ECerr(EC_F_EC_GFP_SIMPLE_OCT2POINT, EC_R_INVALID_ENCODING);
+ goto err;
+ }
+ if (form == POINT_CONVERSION_HYBRID)
+ {
+ if (y_bit != BN_is_bit_set(y, 0))
+ {
+ ECerr(EC_F_EC_GFP_SIMPLE_OCT2POINT, EC_R_INVALID_ENCODING);
+ goto err;
+ }
+ }
+ }
+
+ if (form == POINT_CONVERSION_COMPRESSED)
+ {
+ /* 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.
+ */
+
+ BIGNUM *tmp1, *tmp2;
+
+ tmp1 = BN_CTX_get(ctx);
+ tmp2 = BN_CTX_get(ctx);
+ if (tmp2 == NULL) goto err;
+
+ /* tmp1 := x^3 */
+ if (!BN_mod_sqr(tmp2, x, &group->field, ctx)) goto err;
+ if (!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)) goto err;
+ if (!BN_mod_add_quick(tmp2, tmp2, x, &group->field)) goto err;
+ if (!BN_mod_sub_quick(tmp1, tmp1, tmp2, &group->field)) goto err;
+ }
+ else
+ {
+ if (!BN_mod_mul(tmp2, &group->a, x, &group->field, ctx)) goto err;
+ if (!BN_mod_add_quick(tmp1, tmp1, tmp2, &group->field)) goto err;
+ }
+
+ /* tmp1 := tmp1 + b */
+ if (!BN_mod_add_quick(tmp1, tmp1, &group->b, &group->field)) goto err;
+
+ if (!BN_mod_sqrt(y, tmp1, &group->field, ctx))
+ {
+ ECerr(EC_F_EC_GFP_SIMPLE_OCT2POINT, ERR_R_BN_LIB);
+ goto err;
+ }
+
+ if (y_bit != BN_is_bit_set(y, 0))
+ {
+ if (!BN_usub(y, &group->field, y)) goto err;
+ }
+ if (y_bit != BN_is_bit_set(y, 0))
+ {
+ ECerr(EC_F_EC_GFP_SIMPLE_OCT2POINT, ERR_R_INTERNAL_ERROR);
+ goto err;
+ }
+ }
+
+ if (!EC_POINT_set_affine_coordinates_GFp(group, point, x, y, ctx)) goto err;
+
+ if (!EC_POINT_is_on_curve(group, point, ctx)) /* test required by X9.62 */
+ {
+ ECerr(EC_F_EC_GFP_SIMPLE_OCT2POINT, EC_R_POINT_IS_NOT_ON_CURVE);
+ goto err;
+ }
+
+ ret = 1;
+
+ err:
+ BN_CTX_end(ctx);
+ if (new_ctx != NULL)
+ BN_CTX_free(new_ctx);
+ return ret;
+ }
projects / openssl.git / commitdiff