Skip to content

ASN PemToDer: remove padding when AES_CBC encrypted #4911

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
dgarske merged 1 commit into from
Mar 2, 2022
Merged

ASN PemToDer: remove padding when AES_CBC encrypted #4911

Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
15 changes: 14 additions & 1 deletion wolfcrypt/src/asn.c
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -19709,7 +19709,9 @@ int PemToDer(const unsigned char* buff, long longSz, int type,
word32 algId = 0;
word32 idx;
#if defined(WOLFSSL_ENCRYPTED_KEYS)
#if defined(WOLFSSL_ENCRYPTED_KEYS) && !defined(NO_DES3) && \
#if ((defined(WOLFSSL_ENCRYPTED_KEYS) && !defined(NO_DES3)) || \
(!defined(NO_AES) && defined(HAVE_AES_CBC) && \
defined(HAVE_AES_DECRYPT))) && \
!defined(NO_WOLFSSL_SKIP_TRAILING_PAD)
int padVal = 0;
#endif
Expand Down Expand Up @@ -20051,6 +20053,17 @@ int PemToDer(const unsigned char* buff, long longSz, int type,
}
}
#endif /* !NO_DES3 */
#if !defined(NO_AES) && defined(HAVE_AES_CBC) && \
defined(HAVE_AES_DECRYPT)
if (info->cipherType == WC_CIPHER_AES_CBC) {
if (der->length > AES_BLOCK_SIZE) {
Copy link
Contributor

@dgarske dgarske Mar 2, 2022

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

What if der->length is a multiple of AES_BLOCK_SIZE? Will there still be padding? If not this logic isn't right. Perhaps the check should be if ((der->length % AES_BLOCK_SIZE) != 0) {?

Copy link
Contributor Author

@SparkiDev SparkiDev Mar 2, 2022

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

The check is to see whether there is enough bytes for at least one block - a padded block. Must have a full block of padding if the plaintext is a multiple of the block size - otherwise you don't know whether there is padding there or not.
The decryption will fail if the encrypted data isn't a multiple of the block size.

padVal = der->buffer[der->length-1];
if (padVal <= AES_BLOCK_SIZE) {
Copy link
Contributor

@dgarske dgarske Mar 2, 2022

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Then use if (padVal <= der->length)?

Copy link
Contributor Author

@SparkiDev SparkiDev Mar 2, 2022 •
edited
Loading

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

The padding value cannot be more than the block size if using PKCS #5/#7 padding.

der->length -= padVal;
}
}
}
#endif
#endif /* !NO_WOLFSSL_SKIP_TRAILING_PAD */
}
}
Expand Down