The Ethereum match function in py_ecc_bn128 throws a RecursionError

Ethereum’s peering feature is widely used for secure key exchange and digital signature verification. However, when implementing the matching function using py_ecc_bn128, users often run into a common problem: RecursionError.

Problem

The problem stems from the way py_ecc_bn128 handles exponentiation in its matching function. Specifically, it uses a technique called “incremental squaring” to efficiently calculate matching results.

When we try to multiply the two points G1 and G2 using “G1 * G2”, “py_ecc_bn128” is called recursively to calculate the intermediate result of squaring. In some cases, however, this recursive call may result in a stack overflow error or other unexpected behavior.

Decision

To solve this problem, we need to modify the matching function to avoid calling it recursively when the intermediate score exceeds a certain threshold. Here is the updated code:

from py_ecc.bn128 import G1, G2, pairing, multiplication
def pairing_g1g2(G1, G2):
"""
Computes the pairing of two points using square exponentiation.
Arguments:
G1 (G1): First point.
G2 (G2): Second point.
Returns:
result: Computed pairing result.
"""





Compute pairs
p1 = pair(G1,G2)
q1 = G2.str

Multiply the pairs to get the final result
A = multiplication (p1, q1)
return A

In this updated implementation, we define a new function “pairing_g1g2” that takes two points as input and returns the result of their pairing. We compute the pairs using square exponentiation and multiplying them to get the final result.

Sample usage

To demonstrate how to use the modified matching function, let’s create two instances of objects “G1” and “G2” and perform the matching operation:

Create instances of G1 and G2

G1 = G1.from_pem("your private key")

G2 = G2.from_pem("your public key")



Calculate the pairs

p1 = pair(G1,G2)

q1 = G2.p



Multiply the pairs to get the final result

A = multiplication (p1, q1)


print(A) 
Output: Calculated matching result

By modifying the pairing function in this way, you should no longer encounter a “RecursionError” when using “py_ecc_bn128” for secure key exchange and digital signature verification.

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