cryptography.x509.verification
cryptography.x509.verification
Support for X.509 certificate verification, also known as path validation or chain building.
Note
While usable, these APIs should be considered unstable and not yet subject to our backwards compatibility policy.
Example usage, with certifi providing the root of trust:
from cryptography.x509 import load_pem_x509_certificate, load_pem_x509_certificates from datetime import datetime
peer = load_pem_x509_certificate(b""" -----BEGIN CERTIFICATE-----MIIDgTCCAwegAwIBAgISBJUzlK20QGqPf5xI0aoE8OIBMAoGCCqGSM49BAMDMDIx CzAJBgNVBAYTAlVTMRYwFAYDVQQKEw1MZXQncyBFbmNyeXB0MQswCQYDVQQDEwJF MTAeFw0yMzExMjIyMDUyNDBaFw0yNDAyMjAyMDUyMzlaMBoxGDAWBgNVBAMTD2Ny eXB0b2dyYXBoeS5pbzBZMBMGByqGSM49AgEGCCqGSM49AwEHA0IABAh2A0yuOByJ lxK3ps5vbSOT6ZmvAlflGLn8kEseeodIAockm0ISTb/NGSpu/SY4ITefAOSaulKn BzDgmqjGRKujggITMIICDzAOBgNVHQ8BAf8EBAMCB4AwHQYDVR0lBBYwFAYIKwYB BQUHAwEGCCsGAQUFBwMCMAwGA1UdEwEB/wQCMAAwHQYDVR0OBBYEFJu7f03HjjwJ MU6rfwDBzxySTrs5MB8GA1UdIwQYMBaAFFrz7Sv8NsI3eblSMOpUb89Vyy6sMFUG CCsGAQUFBwEBBEkwRzAhBggrBgEFBQcwAYYVaHR0cDovL2UxLm8ubGVuY3Iub3Jn MCIGCCsGAQUFBzAChhZodHRwOi8vZTEuaS5sZW5jci5vcmcvMBoGA1UdEQQTMBGC D2NyeXB0b2dyYXBoeS5pbzATBgNVHSAEDDAKMAgGBmeBDAECATCCAQYGCisGAQQB 1nkCBAIEgfcEgfQA8gB3AEiw42vapkc0D+VqAvqdMOscUgHLVt0sgdm7v6s52IRz AAABi/kFXv4AAAQDAEgwRgIhAI9uF526YzU/DEfpmWRA28fn9gryrWMUCXQnEejQ K/trAiEA12ePSql3sGJ/QgXc6ceQB/XAdwzwDB+2CHr6T14vvvUAdwDuzdBk1dsa zsVct520zROiModGfLzs3sNRSFlGcR+1mwAAAYv5BV8kAAAEAwBIMEYCIQD1mqTn b1hOpZWAUlwVM4EJLYA9HtlOvF70bfrGHpAX4gIhAI8pktDxrUwfTXPuA+eMFPbC QraG6dMkB+HOmTz+hgKyMAoGCCqGSM49BAMDA2gAMGUCMQC+PwiHciKMaJyRJkGa KFjT/1ICAUsCm8o5h4Xxm0LoOCJVggaXeamDEYnPWbxGETgCME5TJzLIDuF3z6vX 1SLZDdvHEHLKfOL8/h8KctkjLQ8OJycxwIc+zK+xexVoIuxRhA== -----END CERTIFICATE-----""" )
untrusted_intermediates = load_pem_x509_certificates(b""" -----BEGIN CERTIFICATE-----MIICxjCCAk2gAwIBAgIRALO93/inhFu86QOgQTWzSkUwCgYIKoZIzj0EAwMwTzEL MAkGA1UEBhMCVVMxKTAnBgNVBAoTIEludGVybmV0IFNlY3VyaXR5IFJlc2VhcmNo IEdyb3VwMRUwEwYDVQQDEwxJU1JHIFJvb3QgWDIwHhcNMjAwOTA0MDAwMDAwWhcN MjUwOTE1MTYwMDAwWjAyMQswCQYDVQQGEwJVUzEWMBQGA1UEChMNTGV0J3MgRW5j cnlwdDELMAkGA1UEAxMCRTEwdjAQBgcqhkjOPQIBBgUrgQQAIgNiAAQkXC2iKv0c S6Zdl3MnMayyoGli72XoprDwrEuf/xwLcA/TmC9N/A8AmzfwdAVXMpcuBe8qQyWj +240JxP2T35p0wKZXuskR5LBJJvmsSGPwSSB/GjMH2m6WPUZIvd0xhajggEIMIIB BDAOBgNVHQ8BAf8EBAMCAYYwHQYDVR0lBBYwFAYIKwYBBQUHAwIGCCsGAQUFBwMB MBIGA1UdEwEB/wQIMAYBAf8CAQAwHQYDVR0OBBYEFFrz7Sv8NsI3eblSMOpUb89V yy6sMB8GA1UdIwQYMBaAFHxClq7eS0g7+pL4nozPbYupcjeVMDIGCCsGAQUFBwEB BCYwJDAiBggrBgEFBQcwAoYWaHR0cDovL3gyLmkubGVuY3Iub3JnLzAnBgNVHR8E IDAeMBygGqAYhhZodHRwOi8veDIuYy5sZW5jci5vcmcvMCIGA1UdIAQbMBkwCAYG Z4EMAQIBMA0GCysGAQQBgt8TAQEBMAoGCCqGSM49BAMDA2cAMGQCMHt01VITjWH+ Dbo/AwCd89eYhNlXLr3pD5xcSAQh8suzYHKOl9YST8pE9kLJ03uGqQIwWrGxtO3q YJkgsTgDyj2gJrjubi1K9sZmHzOa25JK1fUpE8ZwYii6I4zPPS/Lgul/ -----END CERTIFICATE-----""")
verification_time = datetime.fromisoformat("2024-01-12T00:00:00Z")
>>> from cryptography.x509 import Certificate, DNSName, load_pem_x509_certificates >>> from cryptography.x509.verification import PolicyBuilder, Store >>> import certifi >>> from datetime import datetime >>> with open(certifi.where(), "rb") as pems: ... store = Store(load_pem_x509_certificates(pems.read())) >>> builder = PolicyBuilder().store(store) >>> builder = builder.time(verification_time) >>> verifier = builder.build_server_verifier(DNSName("cryptography.io")) >>> # NOTE: peer and untrusted_intermediates are Certificate and >>> # list[Certificate] respectively, and should be loaded from the >>> # application context that needs them verified, such as a >>> # TLS socket. >>> chain = verifier.verify(peer, untrusted_intermediates)
42.0.0
A Store is an opaque set of public keys and subject identifiers that are considered trusted a priori. Stores are typically created from the host OS's root of trust, from a well-known source such as a browser CA bundle, or from a small set of manually pre-trusted entities.
- param certs
A list of one or more
cryptography.x509.Certificateinstances.
42.0.0
Type alias: A union of all subject types supported: cryptography.x509.general_name.DNSName, cryptography.x509.general_name.IPAddress.
42.0.0
A ServerVerifier verifies server certificates.
It contains and describes various pieces of configurable path validation logic, such as which subject to expect, how deep prospective validation chains may go, which signature algorithms are allowed, and so forth.
ServerVerifier instances cannot be constructed directly; PolicyBuilder must be used.
subject
- type
:class:Subject
The verifier's subject.
validation_time
- type
datetime.datetime
The verifier's validation time.
max_chain_depth
- type
int
The verifier's maximum intermediate CA chain depth.
store
- type
Store
The verifier's trust store.
verify(leaf, intermediates)
Performs path validation on leaf, returning a valid path if one exists. The path is returned in leaf-first order: the first member is leaf, followed by the intermediates used (if any), followed by a member of the store.
- param leaf
The leaf
~cryptography.x509.Certificateto validate- param intermediates
A
listof intermediate~cryptography.x509.Certificateto attempt to use- returns
A list containing a valid chain from
leafto a member ofServerVerifier.store.- raises VerificationError
If a valid chain cannot be constructed
42.0.0
The error raised when path validation fails.
42.0.0
A PolicyBuilder provides a builder-style interface for constructing a Verifier.
time(new_time)
Sets the verifier's verification time.
If not called explicitly, this is set to datetime.datetime.now when build_server_verifier is called.
- param new_time
The
datetime.datetimeto use in the verifier- returns
A new instance of
PolicyBuilder
store(new_store)
Sets the verifier's trust store.
- param new_store
The
Storeto use in the verifier- returns
A new instance of
PolicyBuilder
max_chain_depth(new_max_chain_depth)
Sets the verifier's maximum chain building depth.
This depth behaves tracks the length of the intermediate CA chain: a maximum depth of zero means that the leaf must be directly issued by a member of the store, a depth of one means no more than one intermediate CA, and so forth. Note that self-issued intermediates don't count against the chain depth, per RFC 5280.
- param new_max_chain_depth
The maximum depth to allow in the verifier
- returns
A new instance of
PolicyBuilder
build_server_verifier(subject)
Builds a verifier for verifying server certificates.
- param subject
A
Subjectto use in the verifier- returns
An instance of
ServerVerifier