Stuck on an issue?

Lightrun Answers was designed to reduce the constant googling that comes with debugging 3rd party libraries. It collects links to all the places you might be looking at while hunting down a tough bug.

And, if you’re still stuck at the end, we’re happy to hop on a call to see how we can help out.

Mention how to seed PRNG before activating Filevault

See original GitHub issue

For example:

cat > /dev/random
[type random letters for a while and press ctrl-c]

Issue Analytics

State:
Created 7 years ago
Comments:11

Top GitHub Comments

1reaction

felixgrcommented, Sep 30, 2016

In this issue I’m asking for a more practical advice for users that want to additionally seed the Yarrow PRNG by writing to /dev/random before activating FileVault. FileVault keys are generated from the PRNG and my estimate is that the entropy that went into the PRNG before that is rather low. We did experiments with 1000 fresh install boots and the estimated effective fresh reboot seed entropy is around 320 bits:

prngInitialize()
prngInput(inbuflen = 8)     source: microtime()
prngForceReseed(ticks = 50) recalculate pool
prngInput(inbuflen = 20)        source: /var/db/SystemEntropyCache (updated every 6h)
prngForceReseed(ticks = 50)
prngInput(inbuflen = 256)   source: mach_absolute_time() (41 * sizeof(mach_timespec_t)) via kdbg_getentropy(), collectEntropy(), and also 1 * current time
prngInput(inbuflen = 72)
prngForceReseed(ticks = 50)

From those seeds, microtime and current time are predictable. SystemEntropyCache is empty. 7 of 8 bytes of mach_timespec_t is also predictable.

In most systems, SystemEntropyCache from the first boot saves the day so we didn’t go to DEFCON 😃 but it’s still pretty low entropy.

See https://eprint.iacr.org/2012/374.pdf for more info. This is based on 10.7. I would be interested in your comments on this assessment 😃

0reactions

savchenkocommented, Sep 30, 2016

@felixgr , I’ve meant situation if the HD was encrypted after the 1st boot.

Top Results From Across the Web

Use FileVault to encrypt your Mac startup disk - Apple Support

FileVault full-disk encryption uses XTS-AES-128 encryption with a 256-bit key to help prevent unauthorized access to the information on your ...

Security Analysis and Decryption of Filevault 2 - ins3cure.com

In a security-critical scenario, the PRNG should be reseeded by man- ually writing entropy to /dev/random before activating FileVault 2.

Security Analysis and Decryption of Lion Full Disk Encryption

For highly security-critical scenarios, the PRNG should be reseeded by manually writing entropy to. /dev/random before activation of FileVault 2. 4.2 Plaintext ...

MSC32-C. Properly seed pseudorandom number generators

A properly seeded PRNG will generate a different sequence of random numbers each ... Call srandom() before invoking random() to seed the random...

What exactly is a seed in a random number generator?

Most pseudo-random number generators (PRNGs) are build on algorithms involving some kind of recursive method starting from a base value that ...