The RFC (5869) for this implementation defines two functions,
HKDF-Extract and HKDF-Expand. The existing 'hkdf_256' was implementing
the Extract function, so it was renamed appropriately. The name was
changed for consistency when the Expand function will be added in the
future.
The "H" function used by SAE and EAP-PWD was effectively the same
function, EAP-PWD just used a zero key for its calls. This removes
the duplicate implementations and merges them into crypto.c as
"hkdf_256".
Since EAP-PWD always uses a zero'ed key, passing in a NULL key to
hkdf_256 will actually use a 32 byte zero'ed array as the key. This
avoids the need for EAP-PWD to store or create a zero'ed key for
every call.
Both the original "H" functions never called va_end, so that was
added to hkdf_256.
==40686== Syscall param sendmsg(msg.msg_iov[0]) points to uninitialised byte(s)
==40686== at 0x5147037: sendmsg (in /usr/lib64/libc-2.24.so)
==40686== by 0x43957C: operate_cipher (cipher.c:354)
==40686== by 0x439C18: l_cipher_decrypt (cipher.c:415)
==40686== by 0x40FAB8: arc4_skip (crypto.c:181)
Initialize the skip buffer to 0s. This isn't strictly necessary, but
hides the above valgrind warning.
The aim of arc4 skip is simply to seed some data into the RC4 cipher so
it makes it harder for the attacker to decrypt. This 'initialization'
doesn't really care what data is fed.
James Prestwood