dropbear - "random source" blocked??

[seandarcy]

Using dropbear:

dbclient xx.yy.zz.oo
dbclient: Warning: Reading the random source seems to have blocked.
If you experience problems, you probably need to find a better entropy source.

And then it hangs.

googling was little help.

Anybody else seeing this?

sean

[sevo]

Do something - that is, browse the web, read mail or whatever...

On computers without a hardware random source (or whereever that is not used), /dev/random uses the more unpredictable types of system activity (that is, mostly I/O) to gather cryptographically strong entropy bits. On single purpose computers (like small routers and APs) or low-system-activity portables (like the 770) that can cause a deadlock, when the few currently active processes (in your case ssh daemon and network driver) all are blocked waiting for /dev/random to deliver some more bits - which it only could if they'd do some I/O...

You could also recompile dropbear with the unblocking /dev/urandom instead of /dev/random - urandom is theoretically unsafe as it will generate pseudorandom numbers whenever its entropy source runs dry, but in practice only somebody with some degree of control over your computer can exploit that (which is why ssh daemons usually shun urandom - a local user could suck the entropy pool dry, thereby gaining the seed of the pseudorandom string used for a remote root session of some admin, to eavesdrop on that) .

But attack scenarios with another user on your 770 are very unlikely indeed, so that urandom should do no harm there...

Sevo

[seandarcy]

Recompiling dropbear is somewhat beyond my competence. Though I may Xmas vacation to try setting it up.

In the meantime, can I just remove /dev/random, and symlink /dev/urandom?

i.e.:

rm -f /dev/random
ln -s /dev/urandom /dev/random

Or would it cause the 770 to transform into an expensive brick?

sean