Some CRL source data is very slow in tbs_cert_list dump(), regardless of CRL size

[pr0x1ma-byte]

I am having a problem when the TbsCertList.dump() gets called, and it's quite confusing as to why. The problem is that when that function is called, it takes a very long time for it to complete (we're talking minutes). We need the dump method because it is used in the verification process of a CRL.

Here is some example code to reproduce the problem and a fix which works by rebuilding the CertificateList object (could you explain why this works?):

I'm also using python 3.6.8

I attached the source crl file as a .txt, but you can rename it to source.crl (same with the python file)

import os

import asn1crypto.core
from asn1crypto import crl

from asn1crypto.crl import TbsCertList, CertificateList

def fix_certificate_list(in_list):
    ''' some certificate lists take a long time to dump(), but this appears to fix the problem '''
    tbslist = TbsCertList()

    if not isinstance(in_list['tbs_cert_list']['version'], asn1crypto.core.Void):
        tbslist['version'] = in_list['tbs_cert_list']['version']

    tbslist['signature'] = in_list['tbs_cert_list']['signature']
    tbslist['issuer'] = in_list['tbs_cert_list']['issuer']
    tbslist['this_update'] = in_list['tbs_cert_list']['this_update']

    if not isinstance(in_list['tbs_cert_list']['next_update'], asn1crypto.core.Void):
        tbslist['next_update'] = in_list['tbs_cert_list']['next_update']

    if not isinstance(in_list['tbs_cert_list']['revoked_certificates'], asn1crypto.core.Void):
        tbslist['revoked_certificates'] = in_list['tbs_cert_list']['revoked_certificates']

    if not isinstance(in_list['tbs_cert_list']['crl_extensions'], asn1crypto.core.Void):
        tbslist['crl_extensions'] = in_list['tbs_cert_list']['crl_extensions']

    outlist = CertificateList()
    outlist['tbs_cert_list'] = tbslist
    outlist['signature_algorithm'] = in_list['signature_algorithm']
    outlist['signature'] = in_list['signature']

    return outlist

print("load")
certificate_list = None
with open('source.crl', 'rb') as f:
    slow_list = crl.CertificateList.load(f.read())
    fast_list = fix_certificate_list(slow_list)

print("dump fast_list")
print(len(fast_list['tbs_cert_list'].dump()))
print("done")

print("dump slow_list")
print(len(slow_list['tbs_cert_list'].dump()))
print("done")

crl_dump_demo.py.txt
source.crl.txt

[wbond]

Unfortunately I won't likely have time to look into this soon.

If you are keen to figure out what is going on, I'd recommend using https://pypi.org/project/line-profiler/ and see where the slowdown is.