passagemath-libecm

10.8.4 verified Fri May 01 auth: no python

passagemath-libecm provides Python bindings to GMP-ECM for elliptic curve method (ECM) integer factorization. Version 10.8.4 supports Python 3.11-3.14. It is part of the passagemath ecosystem and is released on a regular cadence alongside other components.

pip install passagemath-libecm

Common errors

error ImportError: cannot import name 'find_factor' from 'ecm' ↓

cause Importing from the old 'ecm' package instead of 'passagemath.libecm'.

fix

Install passagemath-libecm and import from passagemath.libecm.

error AttributeError: module 'passagemath.libecm' has no attribute 'ECM' ↓

cause Using an older version (pre-10.8.0) where the class name was 'ECMFactory' or simply a different layout.

fix

Upgrade to passagemath-libecm >=10.8.0, and use 'from passagemath.libecm import ECM'.

error TypeError: find_factor() got an unexpected keyword argument 'seed' ↓

cause The 'seed' parameter was removed in version 10.8.3.

fix

Remove the seed argument; RNG is now automatic.

error ValueError: B1 must be less than B2 ↓

cause Stage 2 bound B2 must be larger than stage 1 bound B1.

fix

Ensure B2 > B1.

Warnings

breaking The function signature changed between 10.8.2 and 10.8.3: the 'seed' parameter was removed and replaced by an internal RNG. Code using 'seed' will raise TypeError. ↓

fix Remove the seed argument; RNG is now seeded automatically.

gotcha Do not import directly from 'ecm' or 'libecm' - the correct top-level module is 'passagemath.libecm'. ↓

fix Use 'from passagemath.libecm import ...'

deprecated The 'curves' argument in ECM constructor is deprecated; use 'ncurves' instead. ↓

fix Replace curves=10 with ncurves=10

gotcha Passing large numbers (over ~1000 digits) may hang or exhaust memory; tune B1/B2 appropriately. ↓

fix Reduce B1 bounds or use the 'max_stage2_input' parameter.

Imports

find_factor
wrong
```
from ecm import find_factor
```
correct
```
from passagemath.libecm import find_factor
```
Old package ecm is separate; passagemath-libecm uses the passagemath namespace.

ECM

wrong

from passagemath.libecm import libecm

correct

from passagemath.libecm import ECM

The main class is ECM, not libecm.

Quickstart

Basic usage: attempt integer factorization with ECM using the find_factor function.

from passagemath.libecm import find_factor

# Factor a composite number
n = 9999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999
B1 = 1000000
B2 = 100000000
result = find_factor(n, B1, B2)
print('Found factor:' if result else 'No factor found')