Check HKDF-Expand length of output <= 255*HashLen #2956
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wolfcrypt/src/hmac.c
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| word32 outIdx = 0; | ||
| word32 hashSz = wc_HmacSizeByType(type); | ||
| byte n = 0x1; | ||
| word32 N = 0; /* rf5869: N = ceil(L/HashLen)*/ |
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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
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@JacobBarthelmeh, Good point. Fixed. FYI. The additional variable was for clarity and I wanted to avoid multiplications.
JacobBarthelmeh
approved these changes
May 8, 2020
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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.