2005-08-28: Kernel Entropy
There seems to be an issue with linux kernels > 2.6.10 and kernel generated entropy. As /dev/random is required for almost every cryptographic procedure in linux, the amount of available entroy is important. With kernel version 2.6.10 available entropy is about 4000 bytes. With kernel version 2.6.12, however, the entropy oscillates between 600 and 3500 bytes with a median of 800 bytes. This behavior has been observed independently on three different systems. The diagram below points out the problem. Today at 11:40 I downgraded to a 2.6.10 kernel.
Maybe it’s a kernel bug? We’ll keep track of it…
Update: It seems to be a feature. Maybe it’s the “periodicity detection fix” patch introduced in 2.6.11? It primarily targeted the input layer, though. This is a server, it has no keyboard or mouse input.