id summary reporter owner description type status priority milestone component version resolution keywords cc launchpad_bug 751 deterministic IV for writecaps for dir entries zooko "Okay, here is a patch which replaces {{{os.urandom(16)}}} with a (tagged) secure hash of the write cap. This protects the directory entries against the ""VM rollback problem"", which otherwise might expose the writecaps of entries to someone who has only the readcap to the dir in the case that the writer of the dir suffered a vm rollback. In addition, this makes packing deterministic, so that pack(unpack(packeddir)) == packeddir. (Kevan's original unit tests for this ticket assumed that would be the case.) Is there any cryptographic problem that making this change would raise? It means that encryption of the writecaps doesn't have ""semantic security"" (which I think corresponds to IND-CPA?), but they actually didn't anyway since each one is accompanied by its readcap. Perhaps surprisingly, this patch appears to reduce the CPU usage a little bit for packing directories (at least on Mac OS X). Please examine this patch, all cryptographers and security experts! Before this patch: {{{ benchmarking N: 64, time: best: 0.07, 2th-best: 0.07, ave: 0.08, 2th-worst: 0.07, worst: 0.09 (of 5), reps/s: 13, ave rate: 837 N: 256, time: best: 0.29, 2th-best: 0.29, ave: 0.30, 2th-worst: 0.30, worst: 0.32 (of 5), reps/s: 3, ave rate: 851 N: 1024, time: best: 1.15, 2th-best: 1.15, ave: 1.18, 2th-worst: 1.15, worst: 1.31 (of 5), reps/s: 0, ave rate: 866 N: 4096, time: best: 4.37, 2th-best: 4.37, ave: 4.49, 2th-worst: 4.41, worst: 4.93 (of 5), reps/s: 0, ave rate: 912 benchmarking N: 64, time: best: 0.07, 2th-best: 0.07, ave: 0.07, 2th-worst: 0.07, worst: 0.08 (of 5), reps/s: 13, ave rate: 862 N: 256, time: best: 0.29, 2th-best: 0.29, ave: 0.29, 2th-worst: 0.29, worst: 0.29 (of 5), reps/s: 3, ave rate: 872 N: 1024, time: best: 1.15, 2th-best: 1.15, ave: 1.15, 2th-worst: 1.15, worst: 1.15 (of 5), reps/s: 0, ave rate: 889 N: 4096, time: best: 4.36, 2th-best: 4.38, ave: 4.39, 2th-worst: 4.38, worst: 4.45 (of 5), reps/s: 0, ave rate: 933 benchmarking N: 64, time: best: 0.07, 2th-best: 0.07, ave: 0.07, 2th-worst: 0.07, worst: 0.08 (of 5), reps/s: 13, ave rate: 857 N: 256, time: best: 0.29, 2th-best: 0.29, ave: 0.29, 2th-worst: 0.29, worst: 0.30 (of 5), reps/s: 3, ave rate: 870 N: 1024, time: best: 1.15, 2th-best: 1.15, ave: 1.15, 2th-worst: 1.15, worst: 1.15 (of 5), reps/s: 0, ave rate: 888 N: 4096, time: best: 4.37, 2th-best: 4.38, ave: 4.38, 2th-worst: 4.38, worst: 4.39 (of 5), reps/s: 0, ave rate: 935 }}} after this patch: {{{ benchmarking N: 64, time: best: 0.07, 2th-best: 0.07, ave: 0.08, 2th-worst: 0.07, worst: 0.08 (of 5), reps/s: 13, ave rate: 844 N: 256, time: best: 0.29, 2th-best: 0.29, ave: 0.30, 2th-worst: 0.29, worst: 0.32 (of 5), reps/s: 3, ave rate: 858 N: 1024, time: best: 1.11, 2th-best: 1.11, ave: 1.15, 2th-worst: 1.11, worst: 1.27 (of 5), reps/s: 0, ave rate: 894 N: 4096, time: best: 4.25, 2th-best: 4.26, ave: 4.37, 2th-worst: 4.27, worst: 4.79 (of 5), reps/s: 0, ave rate: 938 benchmarking N: 64, time: best: 0.07, 2th-best: 0.07, ave: 0.07, 2th-worst: 0.07, worst: 0.08 (of 5), reps/s: 13, ave rate: 859 N: 256, time: best: 0.29, 2th-best: 0.29, ave: 0.29, 2th-worst: 0.29, worst: 0.29 (of 5), reps/s: 3, ave rate: 874 N: 1024, time: best: 1.11, 2th-best: 1.12, ave: 1.12, 2th-worst: 1.12, worst: 1.12 (of 5), reps/s: 0, ave rate: 917 N: 4096, time: best: 4.26, 2th-best: 4.26, ave: 4.27, 2th-worst: 4.28, worst: 4.28 (of 5), reps/s: 0, ave rate: 959 benchmarking N: 64, time: best: 0.07, 2th-best: 0.07, ave: 0.07, 2th-worst: 0.07, worst: 0.08 (of 5), reps/s: 13, ave rate: 856 N: 256, time: best: 0.29, 2th-best: 0.29, ave: 0.29, 2th-worst: 0.29, worst: 0.29 (of 5), reps/s: 3, ave rate: 871 N: 1024, time: best: 1.11, 2th-best: 1.11, ave: 1.13, 2th-worst: 1.12, worst: 1.18 (of 5), reps/s: 0, ave rate: 908 N: 4096, time: best: 4.25, 2th-best: 4.25, ave: 4.25, 2th-worst: 4.26, worst: 4.26 (of 5), reps/s: 0, ave rate: 963 }}} " enhancement closed major 1.5.0 code-dirnodes 1.4.1 invalid confidentiality warner