Messages in this thread | | | From | Petr Ovtchenkov <> | Subject | constant half-byte from /proc/sys/kernel/random/uuid | Date | Tue, 1 Jun 2010 16:22:58 +0400 |
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Lack of randomness during generating uuid.
Sample:
for i in 1 2 3 4 5 6 7 8 9; do cat /proc/sys/kernel/random/uuid ; done
3faf5c7e-5e1b-4b3c-a318-979653d85404 a929d2d3-e229-42ca-9f33-9c09801f41fb c2a96cb6-0dba-401c-a9c6-dabe1dec89d6 df341de3-eb97-4327-bb63-46afd8dbfaa8 9d84d61c-0c55-4914-8bd6-7f1601110908 6d82e69b-418e-4189-b5a4-0661b6e24dcf eb38de66-4e0b-4bd0-827b-e75ba273e85a 5585c367-754f-4bbf-81f6-8a728380860d c074480b-ad5c-4e10-81d2-82225c449b91
See on 7th high half-byte: it '4' in all cases---4b, 42, 40, 43, 49, 41, 4b, 4b, 4e. Checked three comps, with similar results. All Linux-generated UUID (boot_id) that I see in internet has '4' in this half-byte.
cat /proc/version Linux version 2.6.27.15 (yeti@peak) (gcc version 4.1.2 20060928 (prerelease) (Ubuntu 4.1.1-13ubuntu5)) #1 SMP Thu Feb 12 17:28:11 MSK 2009
or
Linux version 2.6.27.21 (ptr@localhost) (gcc version 4.2.4) #6 SMP Sat Apr 25 00:29:08 MSD 2009
or
Linux version 2.6.33-ARCH (thomas@evey) (gcc version 4.5.0 (GCC) ) #1 SMP PREEMPT Thu May 13 12:06:25 CEST 2010
cat /proc/cpuinfo processor : 0 vendor_id : GenuineIntel cpu family : 6 model : 15 model name : Intel(R) Core(TM)2 Quad CPU Q6600 @ 2.40GHz stepping : 11 cpu MHz : 2400.000 cache size : 4096 KB physical id : 0 siblings : 4 core id : 0 cpu cores : 4 apicid : 0 initial apicid : 0 fdiv_bug : no hlt_bug : no f00f_bug : no coma_bug : no fpu : yes fpu_exception : yes cpuid level : 10 wp : yes flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe nx lm constant_tsc arch_perfmon pebs bts pni monitor ds_cpl vmx est tm2 ssse3 cx16 xtpr lahf_lm bogomips : 4799.97 clflush size : 64 power management: ...
or
processor : 0 vendor_id : AuthenticAMD cpu family : 15 model : 75 model name : AMD Athlon(tm) 64 X2 Dual Core Processor 4200+ stepping : 2 cpu MHz : 2204.555 cache size : 512 KB physical id : 0 siblings : 2 core id : 0 cpu cores : 2 apicid : 0 initial apicid : 0 fdiv_bug : no hlt_bug : no f00f_bug : no coma_bug : no fpu : yes fpu_exception : yes cpuid level : 1 wp : yes flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush mmx fxsr sse sse2 ht syscall nx mmxext fxsr_opt rdtscp lm 3dnowext 3dnow pni cx16 lahf_lm cmp_legacy svm extapic cr8_legacy bogomips : 4409.11 clflush size : 64 power management: ts fid vid ttp tm stc
...
or processor : 0 vendor_id : GenuineIntel cpu family : 6 model : 15 model name : Intel(R) Core(TM)2 CPU T7200 @ 2.00GHz stepping : 6 cpu MHz : 1995.264 cache size : 4096 KB physical id : 0 siblings : 2 core id : 0 cpu cores : 2 apicid : 0 initial apicid : 0 fdiv_bug : no hlt_bug : no f00f_bug : no coma_bug : no fpu : yes fpu_exception : yes cpuid level : 10 wp : yes flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe nx lm constant_tsc arch_perfmon pebs bts aperfmperf pni dtes64 monitor ds_cpl vmx est tm2 ssse3 cx16 xtpr pdcm lahf_lm tpr_shadow bogomips : 3992.80 clflush size : 64 cache_alignment : 64 address sizes : 36 bits physical, 48 bits virtual power management:
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