- {
- unsigned int i, b;
- unsigned char pad, padding_good;
- *outl=0;
-
- if (ctx->cipher->flags & EVP_CIPH_FLAG_CUSTOM_CIPHER)
- {
- int ret = ctx->cipher->do_cipher(ctx, out, NULL, 0);
- if (ret < 0)
- return 0;
- else
- *outl = ret;
- return 1;
- }
-
- b=(unsigned int)(ctx->cipher->block_size);
- if (ctx->flags & EVP_CIPH_NO_PADDING)
- {
- if(ctx->buf_len)
- {
- EVPerr(EVP_F_EVP_DECRYPTFINAL_EX,EVP_R_DATA_NOT_MULTIPLE_OF_BLOCK_LENGTH);
- return 0;
- }
- *outl = 0;
- return 1;
- }
- if (b > 1)
- {
- if (ctx->buf_len || !ctx->final_used)
- {
- EVPerr(EVP_F_EVP_DECRYPTFINAL_EX,EVP_R_WRONG_FINAL_BLOCK_LENGTH);
- return(0);
- }
- OPENSSL_assert(b <= sizeof ctx->final);
- pad=ctx->final[b-1];
-
- padding_good = (unsigned char)(~constant_time_is_zero_8(pad));
- padding_good &= constant_time_ge_8(b, pad);
-
- for (i = 1; i < b; ++i)
- {
- unsigned char is_pad_index = constant_time_lt_8(i, pad);
- unsigned char pad_byte_good = constant_time_eq_8(ctx->final[b-i-1], pad);
- padding_good &= constant_time_select_8(is_pad_index, pad_byte_good, 0xff);
- }
-
- /*
- * At least 1 byte is always padding, so we always write b - 1
- * bytes to avoid a timing leak. The caller is required to have |b|
- * bytes space in |out| by the API contract.
- */
- for (i = 0; i < b - 1; ++i)
- out[i] = ctx->final[i] & padding_good;
- /* Safe cast: for a good padding, EVP_MAX_IV_LENGTH >= b >= pad */
- *outl = padding_good & ((unsigned char)(b - pad));
- return padding_good & 1;
- }
- else
- {
- *outl = 0;
- return 1;
- }
- }
+{
+ int i, n;
+ unsigned int b;
+ *outl = 0;
+
+ if (ctx->cipher->flags & EVP_CIPH_FLAG_CUSTOM_CIPHER) {
+ i = ctx->cipher->do_cipher(ctx, out, NULL, 0);
+ if (i < 0)
+ return 0;
+ else
+ *outl = i;
+ return 1;
+ }
+
+ b = ctx->cipher->block_size;
+ if (ctx->flags & EVP_CIPH_NO_PADDING) {
+ if (ctx->buf_len) {
+ EVPerr(EVP_F_EVP_DECRYPTFINAL_EX,
+ EVP_R_DATA_NOT_MULTIPLE_OF_BLOCK_LENGTH);
+ return 0;
+ }
+ *outl = 0;
+ return 1;
+ }
+ if (b > 1) {
+ if (ctx->buf_len || !ctx->final_used) {
+ EVPerr(EVP_F_EVP_DECRYPTFINAL_EX, EVP_R_WRONG_FINAL_BLOCK_LENGTH);
+ return (0);
+ }
+ OPENSSL_assert(b <= sizeof ctx->final);
+
+ /*
+ * The following assumes that the ciphertext has been authenticated.
+ * Otherwise it provides a padding oracle.
+ */
+ n = ctx->final[b - 1];
+ if (n == 0 || n > (int)b) {
+ EVPerr(EVP_F_EVP_DECRYPTFINAL_EX, EVP_R_BAD_DECRYPT);
+ return (0);
+ }
+ for (i = 0; i < n; i++) {
+ if (ctx->final[--b] != n) {
+ EVPerr(EVP_F_EVP_DECRYPTFINAL_EX, EVP_R_BAD_DECRYPT);
+ return (0);
+ }
+ }
+ n = ctx->cipher->block_size - n;
+ for (i = 0; i < n; i++)
+ out[i] = ctx->final[i];
+ *outl = n;
+ } else
+ *outl = 0;
+ return (1);
+}