Check HKDF-Expand length of output <= 255*HashLen #2956
Merged
Conversation
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
wolfcrypt/src/hmac.c
Outdated
| @@ -1215,11 +1215,18 @@ int wolfSSL_GetHmacMaxSize(void) | |||
| word32 outIdx = 0; | |||
| word32 hashSz = wc_HmacSizeByType(type); | |||
| byte n = 0x1; | |||
| word32 N = 0; /* rf5869: N = ceil(L/HashLen)*/ | |||
There was a problem hiding this comment.
Why add an additional variable to the stack when we can just check that L <= (255 * hashSz)? Also please put a comment on why 255 is used here to explain the hard set number
There was a problem hiding this comment.
@JacobBarthelmeh, Good point. Fixed. FYI. The additional variable was for clarity and I wanted to avoid multiplications.
JacobBarthelmeh
approved these changes
May 8, 2020
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
This PR adds a length check in wc_HKDF_Expand() to address issues reported in ZD#10261 and GitHub issues #2951.
RFC 5869 section 2.3 states that the length of output keying material in octets must be L <= 255*HashLen
where HashLen is the size in octets of the hash function's digest.
However, wc_HKDF_Expand was missing this check.