HMAC appears to be a variant of NMAC where the two independent keys required by NMAC are derived through the hash function of the HMAC ( since H(k || m) --> H[iv=H(k)] (m) )
Why is it so important for the two keys of NMAC to be independent (or pseudo-independent in the case of HMAC)?
What happens when k1=k2? Scheme still appears secure to me.
Another way of asking the above is what happens if the "ipad" and "opad" in HMAC are identical?
