With the exception of the last five bytes, an obfuscated filename is simply a random string of (filesystem-acceptable) characters. The last five bytes are chosen, based on the random portion before them, such that the resulting obfuscated name has the same hash value as the original filename. This is done by essentially working backwards from the difference between the original hash and the hash value computed for the obfuscated name so far, picking final bytes based on how that difference gets manipulated by completing the hash computation. Of those last 5 bytes, all but the upper half of the first one are completely determined by this process. The upper part of the first one is currently computed as 4 random bits, just like the entire first part of the obfuscated name. But the lower nibble of that byte is already effectively random, resulting from the hash computation (or the difference between two of them). We can choose to use 0's for that upper nibble and it will have no significant effect on the randomoness of the result. Doing this simplifies the generation of two of the final five characters, and makes all five of them get computed in a consistent way. Add the use of a mask in the one case it wasn't used to be even more consistent. Signed-off-by: Alex Elder <aelder@xxxxxxx> --- db/metadump.c | 6 ++---- 1 file changed, 2 insertions(+), 4 deletions(-) Index: b/db/metadump.c =================================================================== --- a/db/metadump.c +++ b/db/metadump.c @@ -472,8 +472,7 @@ generate_obfuscated_name( */ newhash = rol32(newhash, 3) ^ hash; - newp[namelen - 5] = (newhash >> 28) | - (random_filename_char() & 0xf0); + newp[namelen - 5] = (newhash >> 28) & 0x7f; if (is_invalid_char(newp[namelen - 5])) continue; newp[namelen - 4] = (newhash >> 21) & 0x7f; @@ -485,8 +484,7 @@ generate_obfuscated_name( newp[namelen - 2] = (newhash >> 7) & 0x7f; if (is_invalid_char(newp[namelen - 2])) continue; - newp[namelen - 1] = ((newhash >> 0) ^ - (newp[namelen - 5] >> 4)) & 0x7f; + newp[namelen - 1] = (newhash >> 0) & 0x7f; if (is_invalid_char(newp[namelen - 1])) continue; break; _______________________________________________ xfs mailing list xfs@xxxxxxxxxxx http://oss.sgi.com/mailman/listinfo/xfs
