Module 'cryptography.utils' has no attribute 'bit_length'

[Melih-Celik]

I am currently trying to figure out how to use netmiko to automate some of my routine work.Such as getting configuration backup, creating vlans etc.I've managed to use it on Aruba and Huawei Switches without problem.But on alcatel switch I'm facing this issue:

Unknown exception: module 'cryptography.utils' has no attribute 'bit_length'
Traceback (most recent call last):
File "C:\Users\melih.celik\AppData\Local\Programs\Python\Python39\lib\site-packages\paramiko\transport.py", line 2075, in run
self.kex_engine.parse_next(ptype, m)
File "C:\Users\melih.celik\AppData\Local\Programs\Python\Python39\lib\site-packages\paramiko\kex_gex.py", line 101, in parse_next
return self._parse_kexdh_gex_reply(m)
File "C:\Users\melih.celik\AppData\Local\Programs\Python\Python39\lib\site-packages\paramiko\kex_gex.py", line 281, in _parse_kexdh_gex_reply
self.transport._verify_key(host_key, sig)
File "C:\Users\melih.celik\AppData\Local\Programs\Python\Python39\lib\site-packages\paramiko\transport.py", line 1886, in _verify_key
if not key.verify_ssh_sig(self.H, Message(sig)):
File "C:\Users\melih.celik\AppData\Local\Programs\Python\Python39\lib\site-packages\paramiko\dsskey.py", line 148, in verify_ssh_sig
key = dsa.DSAPublicNumbers(
File "C:\Users\melih.celik\AppData\Local\Programs\Python\Python39\lib\site-packages\cryptography\hazmat\primitives\asymmetric\dsa.py", line 212, in public_key
return backend.load_dsa_public_numbers(self)
File "C:\Users\melih.celik\AppData\Local\Programs\Python\Python39\lib\site-packages\cryptography\hazmat\backends\openssl\backend.py", line 871, in load_dsa_public_numbers
dsa._check_dsa_parameters(numbers.parameter_numbers)
File "C:\Users\melih.celik\AppData\Local\Programs\Python\Python39\lib\site-packages\netmiko\tplink\tplink_jetstream.py", line 145, in _override_check_dsa_parameters
if crypto_utils.bit_length(parameters.q) not in [160, 256]:
AttributeError: module 'cryptography.utils' has no attribute 'bit_length'

Traceback (most recent call last):
File "C:\Users\melih.celik\Desktop\New_Backup\Yedek\Coding\Rand stuff\ssh_deneme(toplu).py", line 75, in
config_backup(cihaz_secim,ip_address,username,password)
File "C:\Users\melih.celik\Desktop\New_Backup\Yedek\Coding\Rand stuff\ssh_deneme(toplu).py", line 12, in config_backup
net_connect=ConnectHandler(**switch) #Baglanti kuruldu.
File "C:\Users\melih.celik\AppData\Local\Programs\Python\Python39\lib\site-packages\netmiko\ssh_dispatcher.py", line 312, in ConnectHandler
return ConnectionClass(*args, **kwargs)
File "C:\Users\melih.celik\AppData\Local\Programs\Python\Python39\lib\site-packages\netmiko\base_connection.py", line 346, in init
self._open()
File "C:\Users\melih.celik\AppData\Local\Programs\Python\Python39\lib\site-packages\netmiko\base_connection.py", line 351, in _open
self.establish_connection()
File "C:\Users\melih.celik\AppData\Local\Programs\Python\Python39\lib\site-packages\netmiko\base_connection.py", line 920, in establish_connection
self.remote_conn_pre.connect(**ssh_connect_params)
File "C:\Users\melih.celik\AppData\Local\Programs\Python\Python39\lib\site-packages\paramiko\client.py", line 406, in connect
t.start_client(timeout=timeout)
File "C:\Users\melih.celik\AppData\Local\Programs\Python\Python39\lib\site-packages\paramiko\transport.py", line 660, in start_client
raise e
File "C:\Users\melih.celik\AppData\Local\Programs\Python\Python39\lib\site-packages\paramiko\transport.py", line 2075, in run
self.kex_engine.parse_next(ptype, m)
File "C:\Users\melih.celik\AppData\Local\Programs\Python\Python39\lib\site-packages\paramiko\kex_gex.py", line 101, in parse_next
return self._parse_kexdh_gex_reply(m)
File "C:\Users\melih.celik\AppData\Local\Programs\Python\Python39\lib\site-packages\paramiko\kex_gex.py", line 281, in _parse_kexdh_gex_reply
self.transport._verify_key(host_key, sig)
File "C:\Users\melih.celik\AppData\Local\Programs\Python\Python39\lib\site-packages\paramiko\transport.py", line 1886, in _verify_key
if not key.verify_ssh_sig(self.H, Message(sig)):
File "C:\Users\melih.celik\AppData\Local\Programs\Python\Python39\lib\site-packages\paramiko\dsskey.py", line 148, in verify_ssh_sig
key = dsa.DSAPublicNumbers(
File "C:\Users\melih.celik\AppData\Local\Programs\Python\Python39\lib\site-packages\cryptography\hazmat\primitives\asymmetric\dsa.py", line 212, in public_key
return backend.load_dsa_public_numbers(self)
File "C:\Users\melih.celik\AppData\Local\Programs\Python\Python39\lib\site-packages\cryptography\hazmat\backends\openssl\backend.py", line 871, in load_dsa_public_numbers
dsa._check_dsa_parameters(numbers.parameter_numbers)
File "C:\Users\melih.celik\AppData\Local\Programs\Python\Python39\lib\site-packages\netmiko\tplink\tplink_jetstream.py", line 145, in _override_check_dsa_parameters
if crypto_utils.bit_length(parameters.q) not in [160, 256]:
AttributeError: module 'cryptography.utils' has no attribute 'bit_length'

Thanks for your help in advance.

[Marshall700]

This looks like a cryptography fault. Using the latest version of netmiko and cryptography i can see this issue.

Traceback (most recent call last):
  File "testCommit.py", line 97, in <module>
    connect_handler = ConnectHandler(**data_dict)
  File "/usr/local/lib/python3.6/site-packages/netmiko/ssh_dispatcher.py", line 312, in ConnectHandler
    return ConnectionClass(*args, **kwargs)
  File "/usr/local/lib/python3.6/site-packages/netmiko/cisco/cisco_xr.py", line 10, in __init__
    return super().__init__(*args, **kwargs)
  File "/usr/local/lib/python3.6/site-packages/netmiko/base_connection.py", line 346, in __init__
    self._open()
  File "/usr/local/lib/python3.6/site-packages/netmiko/base_connection.py", line 351, in _open
    self.establish_connection()
  File "/usr/local/lib/python3.6/site-packages/netmiko/cisco/cisco_xr.py", line 14, in establish_connection
    super().establish_connection(width=511, height=511)
  File "/usr/local/lib/python3.6/site-packages/netmiko/base_connection.py", line 920, in establish_connection
    self.remote_conn_pre.connect(**ssh_connect_params)
  File "/usr/local/lib/python3.6/site-packages/paramiko/client.py", line 406, in connect
    t.start_client(timeout=timeout)
  File "/usr/local/lib/python3.6/site-packages/paramiko/transport.py", line 660, in start_client
    raise e
  File "/usr/local/lib/python3.6/site-packages/paramiko/transport.py", line 2075, in run
    self.kex_engine.parse_next(ptype, m)
  File "/usr/local/lib/python3.6/site-packages/paramiko/kex_ecdh_nist.py", line 53, in parse_next
    return self._parse_kexecdh_reply(m)
  File "/usr/local/lib/python3.6/site-packages/paramiko/kex_ecdh_nist.py", line 136, in _parse_kexecdh_reply
    self.transport._verify_key(K_S, sig)
  File "/usr/local/lib/python3.6/site-packages/paramiko/transport.py", line 1886, in _verify_key
    if not key.verify_ssh_sig(self.H, Message(sig)):
  File "/usr/local/lib/python3.6/site-packages/paramiko/dsskey.py", line 153, in verify_ssh_sig
    ).public_key(backend=default_backend())
  File "/usr/local/lib64/python3.6/site-packages/cryptography/hazmat/primitives/asymmetric/dsa.py", line 212, in public_key
    return backend.load_dsa_public_numbers(self)
  File "/usr/local/lib64/python3.6/site-packages/cryptography/hazmat/backends/openssl/backend.py", line 871, in load_dsa_public_numbers
    dsa._check_dsa_parameters(numbers.parameter_numbers)
  File "/usr/local/lib/python3.6/site-packages/netmiko/tplink/tplink_jetstream.py", line 145, in _override_check_dsa_parameters
    if crypto_utils.bit_length(parameters.q) not in [160, 256]:
AttributeError: module 'cryptography.utils' has no attribute 'bit_length'

I downgraded the cryptography module and this issue went away. pip install -U cryptography==2.5 (there might be a better version of cryptography to use that is more recent than 2.5).

[Melih-Celik]

Thank you for your fast reply.I've tried to downgrade the version of cryptography.And I'm facing this one then.(Even though it is not netmiko's issue,I'm kinda stuck.) :

error: command 'C:\Program Files (x86)\Microsoft Visual Studio\2019\BuildTools\VC\Tools\MSVC\14.28.29333\bin\HostX86\x64\cl.exe' failed with exit code 2
ERROR: Failed building wheel for cryptography
Failed to build cryptography
ERROR: Could not build wheels for cryptography which use PEP 517 and cannot be installed directly

Update : Tried to run my code on fresh install Ubuntu 20.10.This time I'm getting this error:

Traceback (most recent call last):
File "/usr/local/lib/python3.8/dist-packages/tenacity/init.py", line 412, in call
result = fn(*args, **kwargs)
File "/usr/local/lib/python3.8/dist-packages/netmiko/base_connection.py", line 1149, in set_base_prompt
raise ValueError(f"Router prompt not found: {repr(prompt)}")
ValueError: Router prompt not found: 'A2-Blok-Sw'

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
File "ssh_Deneme.py", line 75, in
config_backup(cihaz_secim,ip_address,username,password)
File "ssh_Deneme.py", line 12, in config_backup
net_connect=ConnectHandler(**switch) #Baglanti kuruldu.
File "/usr/local/lib/python3.8/dist-packages/netmiko/ssh_dispatcher.py", line 312, in ConnectHandler
return ConnectionClass(*args, **kwargs)
File "/usr/local/lib/python3.8/dist-packages/netmiko/base_connection.py", line 346, in init
self._open()
File "/usr/local/lib/python3.8/dist-packages/netmiko/base_connection.py", line 352, in _open
self._try_session_preparation()
File "/usr/local/lib/python3.8/dist-packages/netmiko/base_connection.py", line 777, in _try_session_preparation
self.session_preparation()
File "/usr/local/lib/python3.8/dist-packages/netmiko/alcatel/alcatel_aos_ssh.py", line 12, in session_preparation
self.set_base_prompt()
File "/usr/local/lib/python3.8/dist-packages/tenacity/init.py", line 329, in wrapped_f
return self.call(f, *args, **kw)
File "/usr/local/lib/python3.8/dist-packages/tenacity/init.py", line 409, in call
do = self.iter(retry_state=retry_state)
File "/usr/local/lib/python3.8/dist-packages/tenacity/init.py", line 369, in iter
six.raise_from(retry_exc, fut.exception())
File "", line 3, in raise_from
tenacity.RetryError: RetryError[<Future at 0x7feec9bb75e0 state=finished raised ValueError>]

[ktbyers]

The bit_length issue should be fixed in this PR:

https://github.com/ktbyers/netmiko/pull/2043/files

So it should be fixed in the develop branch.

[Melih-Celik]

Does this apply to alcatel_aos as well? Because I'm still having the same error on Alcatel Switches.

Edit: I just downgraded my python version from v3.9.0 to v3.8.6.And installed cryptography v2.8.Seems like it solved the cryptography issue.However this time I'm facing this :

RetryError[<Future at 0x1e13bb81b20 state=finished raised ValueError>]

as I stated above.

[ktbyers]

@yukio4 Can you post the full exception? The RetryError could be due a bunch of causes; the relevant item for this issue is the bit_length error.

Kirk

[nullbitzero]

Hello everyone
I also experience the same in IOS_XR, when I try to validate user through ssh. Will there be any advance of the solution?

I appreciate your comments.

[2020-12-11 13:49:11.343210]:Validando Credenciales
Unknown exception: module 'cryptography.utils' has no attribute 'bit_length'
Traceback (most recent call last):
  File "/usr/lib/python3/dist-packages/paramiko/transport.py", line 2075, in run
    self.kex_engine.parse_next(ptype, m)
  File "/usr/lib/python3/dist-packages/paramiko/kex_group1.py", line 75, in parse_next
    return self._parse_kexdh_reply(m)
  File "/usr/lib/python3/dist-packages/paramiko/kex_group1.py", line 120, in _parse_kexdh_reply
    self.transport._verify_key(host_key, sig)
  File "/usr/lib/python3/dist-packages/paramiko/transport.py", line 1886, in _verify_key
    if not key.verify_ssh_sig(self.H, Message(sig)):
  File "/usr/lib/python3/dist-packages/paramiko/dsskey.py", line 148, in verify_ssh_sig
    key = dsa.DSAPublicNumbers(
  File "/usr/lib/python3/dist-packages/cryptography/hazmat/primitives/asymmetric/dsa.py", line 212, in public_key
    return backend.load_dsa_public_numbers(self)
  File "/usr/lib/python3/dist-packages/cryptography/hazmat/backends/openssl/backend.py", line 871, in load_dsa_public_numbers
    dsa._check_dsa_parameters(numbers.parameter_numbers)
  File "/usr/local/lib/python3.9/dist-packages/netmiko/tplink/tplink_jetstream.py", line 145, in _override_check_dsa_parameters
    if crypto_utils.bit_length(parameters.q) not in [160, 256]:
AttributeError: module 'cryptography.utils' has no attribute 'bit_length'
=========================================================================
File "/usr/local/lib/python3.9/dist-packages/netmiko/ssh_dispatcher.py", line 312, in ConnectHandler
    return ConnectionClass(*args, **kwargs)
  File "/usr/local/lib/python3.9/dist-packages/netmiko/cisco/cisco_xr.py", line 10, in __init__
    return super().__init__(*args, **kwargs)
  File "/usr/local/lib/python3.9/dist-packages/netmiko/base_connection.py", line 346, in __init__
    self._open()
  File "/usr/local/lib/python3.9/dist-packages/netmiko/base_connection.py", line 351, in _open
    self.establish_connection()
  File "/usr/local/lib/python3.9/dist-packages/netmiko/cisco/cisco_xr.py", line 14, in establish_connection
    super().establish_connection(width=511, height=511)
  File "/usr/local/lib/python3.9/dist-packages/netmiko/base_connection.py", line 920, in establish_connection
    self.remote_conn_pre.connect(**ssh_connect_params)
  File "/usr/lib/python3/dist-packages/paramiko/client.py", line 406, in connect
    t.start_client(timeout=timeout)
  File "/usr/lib/python3/dist-packages/paramiko/transport.py", line 660, in start_client
    raise e
  File "/usr/lib/python3/dist-packages/paramiko/transport.py", line 2075, in run
    self.kex_engine.parse_next(ptype, m)
  File "/usr/lib/python3/dist-packages/paramiko/kex_group1.py", line 75, in parse_next
    return self._parse_kexdh_reply(m)
  File "/usr/lib/python3/dist-packages/paramiko/kex_group1.py", line 120, in _parse_kexdh_reply
    self.transport._verify_key(host_key, sig)
  File "/usr/lib/python3/dist-packages/paramiko/transport.py", line 1886, in _verify_key
    if not key.verify_ssh_sig(self.H, Message(sig)):
  File "/usr/lib/python3/dist-packages/paramiko/dsskey.py", line 148, in verify_ssh_sig
    key = dsa.DSAPublicNumbers(
  File "/usr/lib/python3/dist-packages/cryptography/hazmat/primitives/asymmetric/dsa.py", line 212, in public_key
    return backend.load_dsa_public_numbers(self)
  File "/usr/lib/python3/dist-packages/cryptography/hazmat/backends/openssl/backend.py", line 871, in load_dsa_public_numbers
    dsa._check_dsa_parameters(numbers.parameter_numbers)
  File "/usr/local/lib/python3.9/dist-packages/netmiko/tplink/tplink_jetstream.py", line 145, in _override_check_dsa_parameters
    if crypto_utils.bit_length(parameters.q) not in [160, 256]:
AttributeError: module 'cryptography.utils' has no attribute 'bit_length'

[ktbyers]

It is fixed, use the Netmiko develop branch.

Kirk