Python XML Signature library
Project description
SignXML is an implementation of the W3C XML Signature standard in Python. This standard (also known as XMLDSig and RFC 3275) is used to provide payload security in SAML 2.0, among other uses. Three versions of the standard exist (Version 1 “Second Edition”, Version 1.1, and Version 2.0). SignXML implements all of the required components of the standard, and most recommended ones. Its features are:
Use of defusedxml.lxml to defend against common XML-based attacks when verifying signatures
Extensions to allow signing with and verifying X.509 certificate chains, including hostname/CN validation
Support for exclusive XML canonicalization with inclusive prefixes (InclusiveNamespaces PrefixList, required to verify signatures generated by some SAML implementations)
Modern Python compatibility (2.7-3.4+ and PyPy)
Well-supported, portable, reliable dependencies: lxml, defusedxml, cryptography, eight, pyOpenSSL
Comprehensive testing (including the XMLDSig interoperability suite) and continuous integration
Simple interface with useful defaults
Compactness, readability, and extensibility
Installation
pip install signxml
Note: SignXML depends on lxml and cryptography, which in turn depend on OpenSSL, LibXML, and Python tools to interface with them. You can install those as follows:
Ubuntu, Python 2:
apt-get install python-dev python-cffi libxml2-dev libxslt1-dev libssl-dev
Ubuntu, Python 3:
apt-get install python3-dev python3-cffi libxml2-dev libxslt1-dev libssl-dev
Ubuntu 12.04: python-cffi is not available on 12.04. Use apt-get install libffi-dev followed by pip install cffi.
OS X: Use Homebrew:
brew install libxml2 libxslt brew link --force libxml2 libxslt
Synopsis
SignXML uses the ElementTree API (also supported by lxml) to work with XML data.
from signxml import xmldsig
cert = open("example.pem").read()
key = open("example.key").read()
root = ElementTree.fromstring(signature_data)
signed_root = xmldsig(root).sign(key=key, cert=cert)
verified_data = xmldsig(signed_root).verify()Verifying SAML assertions
Assuming metadata.xml contains SAML metadata for the assertion source:
from lxml import etree
from base64 import b64decode
from signxml import xmldsig
with open("metadata.xml", "rb") as fh:
cert = etree.parse(fh).find("//ds:X509Certificate").text
assertion_data = xmldsig(b64decode(assertion_body)).verify(x509_cert=cert)XML signature methods: enveloped, detached, enveloping
The XML Signature specification defines three ways to compose a signature with the data being signed: enveloped, detached, and enveloping signature. Enveloped is the default method. To specify the type of signature that you want to generate, pass the method argument to sign():
signed_root = xmldsig(root).sign(method=signxml.methods.detached, key=key, cert=cert)
verified_data = xmldsig(signed_root).verify()For detached signatures, the code above will use the Id or ID attribute of root to generate a relative URI (<Reference URI="#value"). You can also override the value of URI by passing a reference_uri argument to sign().
To verify a detached signature that refers to an external entity, pass a callable resolver in xmldsig.verify(uri_resolver=...).
See the API documentation for more.
Links
W3C Recommendation: XML Signature Syntax and Processing (Second Edition)
W3C Recommendation: XML Signature Syntax and Processing Version 1.1
W3C Working Group Note: XML Signature Syntax and Processing Version 2.0
W3C Working Group Note: Test Cases for C14N 1.1 and XMLDSig Interoperability
Bugs
Please report bugs, issues, feature requests, etc. on GitHub.
License
Licensed under the terms of the Apache License, Version 2.0.
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