If you xor the hashes together, it may be as weak as the weaker of the two functions, though it probably depends on their structure. Getting much stronger hash

If you xor the hashes together, it may be as weak as the weaker of the two functions, though it probably depends on their structure. Getting much stronger hashing with double compute time is easy. Double the number of round - most alorithms have about 30-60% security margins. It would probably avoid any breaks of the hash (so 80 bits for SHA1), though it can't be enough if the hash is simply too small (64 bit security for MD5/4/2).