muterra/donna25519

Python wrapper of AGL's Curve25519-donna library

donna25519's Issues

donna25519.PrivateKey writes to read-only buffers

Here's an example:

import donna25519

mybuffer = bytes(32)
print(list(mybuffer))
donna25519.PrivateKey(mybuffer)
print(list(mybuffer))

assert mybuffer == bytes(32)

[0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]
[0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 64]
Traceback (most recent call last):
  File "/home/jacko/tmp/donna.py", line 8, in <module>
    assert mybuffer == bytes(32)
AssertionError

I think the culprit is the clamping happening in these lines. Probably the caller's buffer should be copied to a local array?