os.urandom for Pico/RP2040 not supported #4196

joelburton · 2021-02-13T20:17:16Z

Attempts to use os.urandom(n) on the Pico currently report:

>>> os.urandom(1)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
NotImplementedError: No hardware random available

The datasheet for the Pico indicate that the ring oscillator can be used for this (RP2040 datasheet, page 240). They do note that there are potential cryptographic attacks possible on this, but could this still be a considered "random hardware"? There are CircuitPython libraries that require os.urandom().

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ladyada · 2021-02-13T20:22:08Z

which library requires os.urandom?

jepler · 2021-02-13T21:24:06Z

In the bundle, adafruit_rsa uses os.urandom. In the community bundle, circuitpython_nrf24l01 does. In Learn, CPB_Quick_Draw_Duo (gracefully works around it if it's missing) and CLUE_Rock_Paper_Scissors (advanced version only) do.

ladyada · 2021-02-13T22:18:42Z

@joelburton you cant use random.randint() ?

joelburton · 2021-02-14T02:22:07Z

I can and can fork those (it’s RSA lib I want). But thought it would be helpful to get this on someone’s non-urgent list for implementation for the pico. Thanks!

…

On Feb 13, 2021, at 2:19 PM, ladyada ***@***.***> wrote: @joelburton you cant use random.randint() ? — You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub, or unsubscribe.

ladyada · 2021-02-14T02:41:29Z

well tbf i dont know the crypto implications - i am not sure how we seed the pico's RNG. i will leave open but yah maybe can you submit a PR to change RSA lib to use random. instead of os.urandom if it throws an exception?

what are you doing with the pico and RSA anyways? makin a U2F? :)

joelburton · 2021-02-14T03:32:24Z

I teach Computer Science; I'm making graduation gifts for my students of a pico with various CS challenges built in, and one of them is decrypting a message using RSA. :-)

…

On Sat, Feb 13, 2021 at 6:41 PM ladyada ***@***.***> wrote: well tbf i dont know the crypto implications - i am not sure how we seed the pico's RNG. i will leave open but yah maybe can you submit a PR to change RSA lib to use random. instead of os.urandom if it throws an exception? what are you doing with the pico and RSA anyways? makin a U2F? :) — You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub <#4196 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AAI7XFTF2NAOP26LMZOD3F3S64Z6TANCNFSM4XSO7DOQ> .

-- Joel Burton - joel@joelburton.com GTalk: joel@joelburton.com, Mobile/SMS: +1 415 513 2470

ladyada · 2021-02-14T03:53:01Z

ahh ok, random.* would be fine for your purposes then! if you submit a PR we will review it and merge

tannewt · 2021-02-17T00:47:47Z

well tbf i dont know the crypto implications - i am not sure how we seed the pico's RNG. i will leave open but yah maybe can you submit a PR to change RSA lib to use random. instead of os.urandom if it throws an exception?

random will use the time you first call it to seed the pseudo-random number generation if urandom isn't provided. It should NOT be used for cryptography. This true in CPython as well: https://docs.python.org/3/library/random.html Anything that doesn't do cryptography should use random instead of os.urandom because it provides a way to seed the random in cases where we'd want to have fixed behavior for testing.

CPython's secrets module is the right higher level random for cryptography and also the reason we should stop using secrets.py for storing secret information. (Filed #4212 to track it.)

hierophect added rp2040 Raspberry Pi RP2040 enhancement labels Feb 16, 2021

tannewt added this to the Long term milestone Feb 17, 2021

jepler mentioned this issue Feb 17, 2021

raspberrypi: implement os.urandom #4213

Merged

tannewt closed this as completed in #4213 Feb 18, 2021

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os.urandom for Pico/RP2040 not supported #4196

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os.urandom for Pico/RP2040 not supported #4196

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