OpenSSH public key parser for Python
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README.rst

OpenSSH Public Key Parser for Python

https://travis-ci.org/ojarva/python-sshpubkeys.svg?branch=master

Major changes between versions 2 and 3

  • Dropped support for Python 2.6 and 3.3
  • Even in loose mode, DSA keys must be 1024, 2048, or 3072 bits (earlier this was looser)
  • The interface (API) is exactly the same

Usage

Native implementation for validating OpenSSH public keys.

Currently ssh-rsa, ssh-dss (DSA), ssh-ed25519 and ecdsa keys with NIST curves are supported.

Installation:

pip install sshpubkeys

or clone the repository and use

python setup.py install

Usage:

import sys
from sshpubkeys import SSHKey

ssh = SSHKey("ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAAAYQCxO38tKAJXIs9ivPxt7AY"
      "dfybgtAR1ow3Qkb9GPQ6wkFHQqcFDe6faKCxH6iDRteo4D8L8B"
      "xwzN42uZSB0nfmjkIxFTcEU3mFSXEbWByg78aoddMrAAjatyrh"
      "H1pON6P0= ojarva@ojar-laptop", strict=True)
try:
    ssh.parse()
except InvalidKeyError as err:
    print("Invalid key:", err)
    sys.exit(1)
except NotImplementedError as err:
    print("Invalid key type:", err)
    sys.exit(1)

print(ssh.bits)  # 768
print(ssh.hash_md5())  # 56:84:1e:90:08:3b:60:c7:29:70:5f:5e:25:a6:3b:86
print(ssh.hash_sha256())  # SHA256:xk3IEJIdIoR9MmSRXTP98rjDdZocmXJje/28ohMQEwM
print(ssh.hash_sha512())  # SHA512:1C3lNBhjpDVQe39hnyy+xvlZYU3IPwzqK1rVneGavy6O3/ebjEQSFvmeWoyMTplIanmUK1hmr9nA8Skmj516HA
print(ssh.comment)  # ojar@ojar-laptop
print(ssh.options_raw)  # None (string of optional options at the beginning of public key)
print(ssh.options)  # None (options as a dictionary, parsed and validated)

Parsing of authorized_keys files:

import os
from sshpubkeys import AuthorizedKeysFile
f = open(os.environ["HOME"] + "/.ssh/authorized_keys", "r")
key_file = AuthorizedKeysFile(f, strict=False)

for key in key_file.keys:
    print(key.key_type, key.bits, key.hash_sha512())

Options

Set options in constructor as a keywords (i.e., SSHKey(None, strict=False))

  • strict: defaults to True. Disallows keys OpenSSH's ssh-keygen refuses to create. For instance, this includes DSA keys where length != 1024 bits and RSA keys shorter than 1024-bit. If set to False, tries to allow all keys OpenSSH accepts, including highly insecure 1-bit DSA keys.
  • skip_option_parsing: if set to True, options string is not parsed (ssh.options_raw is populated, but ssh.options is not).
  • disallow_options: if set to True, options are not allowed and it will raise an InvalidOptionsError.

Exceptions

  • NotImplementedError if invalid ecdsa curve or unknown key type is encountered.
  • InvalidKeyError if any other error is encountered:
    • TooShortKeyError if key is too short (<768 bits for RSA, <1024 for DSA, <256 for ED25519)
    • TooLongKeyError if key is too long (>16384 for RSA, >1024 for DSA, >256 for ED25519)
    • InvalidTypeError if key type ("ssh-rsa" in above example) does not match to what is included in base64 encoded data.
    • MalformedDataError if decoding and extracting the data fails.
    • InvalidOptionsError if options string is invalid.
      • InvalidOptionNameError if option name contains invalid characters.
        • UnknownOptionNameError if option name is not recognized.
      • MissingMandatoryOptionValueError if option needs to have parameter, but it is absent.

Tests

See "tests/" folder for unit tests. Use

python setup.py test

or

python3 setup.py test

to run test suite. If you have keys that are not parsed properly, or malformed keys that raise incorrect exception, please send your public key to olli@jarva.fi, and I'll include it. Alternatively, create a new issue or make a pull request in github.