py_ecc bad prime_field_inv implementation

UID: CL-2020-19

Severity: medium

Type: Crypto

Affected Clients: None

Summary: Reproduction:
prime_field_inv(7, 7)
prime_field_inv(0, 7)

Output:
1
0

Links: https://github.com/ethereum/py_ecc/pull/114

Reported: 2020-12-07

Fixed: 2020-12-14

Published: 2021-12-01

Bounty Hunter: Quan

Bounty Points: 500