Certificate authority management¶

django-ca supports managing multiple certificate authorities as well as child certificate authorities.

The command-line interface is the only way to create certificate authorities. It is obviously most important that the private keys are never exposed to any attacker, and any web interface would pose an unnecessary risk. Some details, like the x509 extensions used for signing certificates, can be configured using the web interface.

For the same reason, the private key of a certificate authority is stored on the file system and not in the database. The initial location of the private key is configured by the CA_DIR setting. This also means that you can run your django-ca on two hosts, where one host has the private key and only uses the command line, and one with the web interface that can still be used to revoke certificates.

Index of commands¶

To manage certificate authorities, use the following manage.py commands:

Command	Description
`dump_ca`	Write the CA certificate to a file.
`edit_ca`	Edit a certificate authority.
`import_ca`	Import an existing certificate authority.
`init_ca`	Create a new certificate authority.
`list_cas`	List all currently configured certificate authorities.
`view_ca`	View details of a certificate authority.

Like all manage.py subcommands, you can run manage.py <subcommand> -h to get a list of available parameters.

Create a new CA¶

There are many options when creating a new certificate authority, but the defaults are carefully chosen to be secure. To create a simple setup with a root certificate authority and an intermediate certificate authority that has ACMEv2 enabled, simply use:

$ python manage.py init_ca --path-length=1 --subject-format=rfc4514 Root CN=Root
$ python manage.py init_ca --parent=Root --acme-enable --subject-format=rfc4514 Intermediate CN=Intermediate

Note

How you invoke manage.py differs depending on how you installed django-ca. Refer to the installation guide you followed for further instructions and complete examples.

You should be very careful when creating a new certificate authority, especially if it is used by a large number of clients. If you make a mistake here, it could make your CA unusable and you have to redistribute new public keys to all clients, which is usually a lot of work.

Please think carefully about how you want to run your CA: Do you want intermediate CAs? Do you want to use CRLs and/or run an OCSP responder?

Private key parameters¶

The private key generated for your certificate authority may vary based on key type, key size and elliptic curve used.

Key type¶

The type of private key can be configured with the --key-type parameter. Currently supported values are RSA (the default), EC (for elliptic curve cryptography based keys), Ed448, and Ed25519. DSA is also supported but the use is discouraged.

Key size¶

For RSA and DSA keys, you can specify the size of the private key using the --key-size option. The value must be an integer and a power of two. 2048 or 4096 are reasonable values.

The default is specified using the CA_DEFAULT_KEY_SIZE setting, the minimum value is set by the CA_MIN_KEY_SIZE setting.

Elliptic curve¶

When generating an EC (elliptic curve) private key, you can chose the elliptic curve used with the --elliptic-curve parameter. The default curve is configured using the CA_DEFAULT_ELLIPTIC_CURVE setting.

The supported elliptic curves are the curves found in the ELLIPTIC_CURVE_TYPES constant. Please see the cryptography information on elliptic curves for more information on each curve.

Hostname¶

Running a CA with an OCSP responder or CRLs for certificate validation requires a web server providing HTTP. Please configure CA_DEFAULT_HOSTNAME accordingly. You can always override that setting by passing manual URLs when creating a new CA.

Signature hash algorithm¶

The hash algorithm used for signing the public key can be configured using the --algorithm parameter.

For root certificate authorities, the default is configured via the CA_DEFAULT_SIGNATURE_HASH_ALGORITHM setting for RSA and Elliptic Curve (EC) keys, and via the CA_DEFAULT_DSA_SIGNATURE_HASH_ALGORITHM setting for DSA keys. Intermediate certificate authorities will use the same hash algorithm as their parent by default.

The supported signature hash algorithms are the hash algorithms defined by HashAlgorithms. For example, to use SHA-384 as signature hash algorithm:

$ python manage.py init_ca --algorithm=SHA-384 ...

Ed448 and and Ed25519 keys do not use a signature hash algorithm and an error will be raised if you pass the --algorithm option with these key types.

CRL URLs¶

Certificate Revocation Lists (CRLs) are signed files that contain a list of all revoked certificates. Certificates (including those for CAs) can contain pointers to CRLs, usually a single URL, in the CRL Distribution Points extension. Clients that support this extension can query the URL and refuse to establish a connection if the certificate is revoked.

Since a CRL has to be signed by the issuing CA, root CAs cannot sensibly contain a CRL: You could only revoke the root CA with it, and it would have to be signed by the (compromised) root CA.

If you have correctly configured CA_DEFAULT_HOSTNAME, you can use CRL URLs out of the box. You can also embed custom URLs in certificates, please see Host a Certificate Revocation List (CRL) for more information.

OCSP responder¶

The Online Certificate Status Protocol or OCSP is a service (called “OCSP responder”) run by a certificate authority that allows clients to query for revoked certificates. It is an improvement over CRLs particularly for larger CAs because a full CRL can grow quite big.

The same restrictions as for CRLs apply: You cannot add a OCSP URL to a root CA, it runs via HTTP (not HTTPS) and if you decide to add such URLs, you also have to actually run that service, or clients will refuse to connect.

If you have correctly configured CA_DEFAULT_HOSTNAME, you can use an OCSP responder out of the box, if you use the docker compose. If you installed from source or you have regularly create OCSP responder keys (e.g. via a CRON job):

$ python manage.py regenerate_ocsp_keys

How can configure how long certificates will be valid via the --ocsp-responder-key-validity argument when creating/editing a certificate authority. You can also configure how long responses are valid via the --ocsp-response-validity.

Extensions¶

manage.py init_ca will add mandatory and common extensions for certificate authorities automatically. In most cases, the only extension you really should think about is the path length in the Basic Constraints extension, in case you ever want to create intermediate certificate authorities. Only extensions that make sense in the context of a certificate authority can be added here.

Some important extensions (the Key Usage, CRL Distribution Points and Authority Information Access extensions) are automatically set with sane defaults and you do not typically have to configure them.

Authority Information Access¶

The Authority Information Access extension (RFC 5280, section 4.2.2.1) provides information how to access services of the issuer of a certificate. It can point to either an OCSP responder or to the certificate of the issuer. It can only be used for intermediate CAs: The only valid signer for OCSP responses would be the root CA itself, making such an OCSP request pointless.

django-ca will automatically add this extension for intermediate CAs, as long as the CA_DEFAULT_HOSTNAME is configured, so usually you do not have to add this extension manually.

You can manually add OCSP responders or CA Issuers instead of the default ones using the --ca-issuer and --ocsp-responder options:

$ python manage.py init_ca \
>     --ca-issuer http://issuer.example.com \
>     --ocsp-responder http://ocsp.example.com \
>     ...

Each option can be given multiple times. These options will disable the default values added to intermediate CAs.

String formatting in URIs can be used in this extension. To use the default URIs in addition to your own endpoints, you can use the CA_ISSUER_PATH and OCSP_PATH variables:

$ python manage.py init_ca \
>     --ca-issuer http://example.com/{CA_ISSUER_PATH} \
>     --ca-issuer ... \
>     --ocsp-responder http://example.com/{OCSP_PATH} \
>     --ocsp-responder ... \
>     ...

Basic Constraints¶

The Basic Constraints extension (RFC 5280, section 4.2.1.9) indicates if you are creating a certificate authority. For certificate authorities, the optional path length attribute specifies how many levels of intermediate certificate authorities can exist below itself. If the attribute is not present, the number is unlimited.

This extension is always added, and is always a critical extension. django-ca sets a path length of 0 by default. You can set a different value using --path-length:

$ python manage.py init_ca --path-length 3 ...

If you do not want to set a path length attribute, use --no-path-length:

$ python manage.py init_ca --no-path-length ...

Note that for a valid setup, the attributes in all intermediate CAs must be correct. Here is a typical example:

root   # path length: 2
|- child_A  # path length: 1
   |- child_A.1  # path length: 0
|- child_B  # path length" 0

In this example, root and child_A can have intermediate CAs, while child_B and child_A.1 can not.

Certificate Policies¶

In certificate authorities, the Certificate Policies extension (RFC 5280, section 4.2.1.4) limits the policies that may occur in certification paths that include the certificate authority.

To add this extension to a certificate authority, use the --policy-identifier option to add a policy with the given OID:

$ python manage.py init_ca --policy-identifier=1.2.3 ...

The special value anyPolicy is recognized as an alias for the OID 2.5.29.32.0. To add a certification practice statement (CPS) and/or user notices, use:

$ python manage.py init_ca \
>     --policy-identifier=anyPolicy \
>     --certification-practice-statement=https://example.com/cps/ \
>     --user-notice="Example user notice text" \
>     ...

To add multiple policies, repeat the --policy-identifier option. The options for CPS and user notices will be added to the last named policy:

$ python manage.py init_ca \
>     --policy-identifier=1.2.3 \
>     --certification-practice-statement=https://example.com/cps-for-1.2.3/ \
>     --policy-identifier=1.2.4 \
>     --user-notice="User notice for 1.2.4" \
>     ...

Adding notice references via the command line is not supported.

CRL Distribution Points¶

The CRL Distribution Points extension (RFC 5280, section 4.2.1.13) specifies endpoints where to retrieve Certificate Revocation Lists (CRLs). When including it in a CA, the retrieved CRL can be used to determine if the CA itself has been revoked. revoked. It can only be used for intermediate CAs, as root CAs are trusted by identity, and no trusted CA could then sign the CRL.

django-ca will automatically add this extension for intermediate CAs, as long as the CA_DEFAULT_HOSTNAME is configured, so usually you do not have to add this extension manually.

If you need to specify your own CRL endpoint(s), you can use the --crl-full-name argument:

$ python manage.py init_ca \
>     --crl-full-name http://example.com/crl --crl-full-name http://example.net/crl ...

This will add a single Distribution Point with two URLs. Other, more complex configurations are not supported via the command-line.

String formatting in URIs can be used in this extension. To use the default URIs in addition to your own endpoint(s), you can use the CRL_PATH variable:

$ python manage.py init_ca \
>     --crl-full-name http://example.com/{CRL_PATH} \
>     --crl-full-name ... \
>     ...

Manually adding a CRL via the command-line will disable the default CRL added to intermediate CAs.

Extended Key Usage¶

The Extended Key Usage extension (RFC 5280, section 4.2.1.12) indicates additional purposes that this certificate may be used for. It is often not present in certificate authorities, and django-ca does not add it by default.

Note

This option must be given after the mandatory name and subject arguments:

$ python manage.py init_ca --subject-format=rfc4514 NameOfCa CN=example.com --key-usage ...

The option has a variable number of values and parsing the command-line would not be unambiguous otherwise.

The extension can be added using the --extended-key-usage option. Valid values are given by the values of the EXTENDED_KEY_USAGE_NAMES mapping. For example:

$ python manage.py init_ca --subject-format=rfc4514 NameOfCa CN=example.com --extended-key-usage clientAuth serverAuth

If you need to add OIDs not understood by django-ca, you can also pass any valid OID as a dotted string instead. In this example, the OID for serverAuth is used:

$ python manage.py init_ca --subject-format=rfc4514 NameOfCa CN=example.com --extended-key-usage 1.3.6.1.5.5.7.3.1

Inhibit anyPolicy¶

The Inhibit anyPolicy extension (RFC 5280, section 4.2.1.14) indicates that the special anyPolicy is not considered a match when it appears in the Certificate Policies extension after the given number of certificates in the validation path.

The extension can be added using the --inhibit-any-policy option. The value must an integer larger then 0:

$ python manage.py init_ca --inhibit-any-policy 1 ...

Issuer Alternative Name¶

The Issuer Alternative Name extension (RFC 5280, section 4.2.1.7) is used to associate alternative names with the certificate issuer. It is rarely used in practice.

You can set this extension using the --issuer-alternative-name option. The option can be given multiple times. Values are any valid name, see Names on the command-line for detailed documentation:

$ python manage.py init_ca --issuer-alternative-name DNS:example.com ...

Key Usage¶

The Key Usage extension (RFC 5280, section 4.2.1.3) defines what the certificate can be used for and is always added. By default, the keyCertSign and cRLSign bits are set, matching most public certificate authorities.

Note

This option must be given after the mandatory name and subject arguments:

$ python manage.py init_ca --subject-format=rfc4514 NameOfCa CN=example.com --key-usage ...

The option has a variable number of values and parsing the command-line would not be unambiguous otherwise.

You can set a different extension value using the --key-usage option. Note that this will overwrite (and not append to) the default, so you have to name the default values as well. Valid values are given by the values of the KEY_USAGE_NAMES mapping. For example, to also set the digitalSignature flag:

$ python manage.py init_ca --subject-format=rfc4514 Name CN=example.com \
>    --key-usage keyCertSign cRLSign digitalSignature \
>    ...

Name Constraints¶

The Name Constraints extension (RFC 5280, section 4.2.1.10) allows you to create CAs that are limited to issuing certificates for a particular set of names. The parsing of this syntax is quite complex, see e.g. this blog post for a good explanation.

Warning

This extension is marked as “critical”. Any client that does not understand this extension will refuse a connection.

To add name constraints to a CA, use the --permit-name and --exclude-name, both of which can be given multiple times. Values are any valid name, see Names on the command-line for detailed documentation:

$ python manage.py init_ca --permit-name DNS:example.com --exclude-name DNS:example.net ...

This will restrict the CA to issuing certificates for .com and .net subdomains, except for evil.com, which obviously should never have a certificate (evil.net is good, though).

Policy Constraints¶

The Policy Constraints extension (RFC 5280, section 4.2.1.11) can be used to require an explicit policy and/or prohibit policy mapping.

The extension can be added via the --inhibit-policy-mapping and/or --require-explicit-policy options:

$ python manage.py init_ca --inhibit-policy-mapping 1 --require-explicit-policy 2 ...

Subject Alternative Name¶

The Subject Alternative Name extension (RFC 5280, section 4.2.1.6) lists the names a certificate is valid for. It is usually only used in end entity certificates, certificate authorities do not use this extension: certificate validation does not require this information for certificate authorities.

Since RFC 5280 does not rule out this extension occurring in certificate authorities, you can still add this extension:

$ python manage.py init_ca --subject-alternative-name DNS:example.com ...

TLS Feature¶

In certificate authorities, the TLS Feature extension (RFC 7633) will require end entity certificates signed by this certificate authority to include at least the same features. This is not commonly used in practice.

Note

This option must be given after the mandatory name and subject arguments:

$ python manage.py init_ca --subject-format=rfc4514 NameOfCa CN=example.com --key-usage ...

The option has a variable number of values and parsing the command-line would not be unambiguous otherwise.

For example, if a root certificate authority includes a TLS Feature extension that sets status_request, any certificate signed by it (or any intermediate CA) will also have to set status_request.

You can set the TLS Feature extension with --tls-feature:

$ python manage.py init_ca --subject-format=rfc4514 NameOfCA CN=example.com --tls-feature status_request ...

String formatting in URIs¶

For some extensions, you can apply string formatting operations to URIs to create URIs that contain the serial (or other dynamic values) of the certificate you about to create.

Note

String formatting is only available in URIs, and only in the extensions where noted.

String formatting is available for Authority Information Access and the CRL Distribution Points extension. The strings are passed to str.format(), so you can use any feature of the Format String Syntax.

For example, if you want to create a certificate authority that specifies the default CA Issuer URI in its Authority Information Access extension, but also specifies a second URI that includes its own serial:

$ python manage.py init_ca \
>     --ca-issuer http://example.com/{CA_ISSUER_PATH} \
>     --ca-issuer http://ca-issuer.example.com/{SERIAL}/ \
>     --parent 00:11:22... \
>     --subject-format=rfc4514 \
>     NameOfCA CN=example.com

The following variables are available:

Variable	Description
SERIAL	Serial (as `int`) of the certificate (CA or end entity) that is created.
SERIAL_HEX	Same as `SERIAL`, but in hex form (e.g. `aabbcc...`).
SERIAL_HEX_COLONS	Same as `SERIAL` but in colon hex-form (e.g. `aa:bb:cc:...`).
SIGNER_SERIAL	Serial (as `int`) of the CA that will sign the certificate.
SIGNER_SERIAL_HEX	Same as `SIGNER_SERIAL`, but in hex form (e.g. `aabbcc...`).
SIGNER_SERIAL_HEX_COLONS	Same as `SIGNER_SERIAL_HEX` but in colon hex-form (e.g. `aa:bb:cc:...`).
CA_ISSUER_PATH	The URL path (without a leading slash) to the CA issuer URL provided by django-ca.
OCSP_PATH	The URL path (without a leading slash) to the OCSP URL provided by django-ca.
CRL_PATH	The URL path (without a leading slash) to the CRL URL provided by django-ca.

Mark extensions as (non-)critical¶

Extensions that may or may not be critical according to the RFC where they are defined (usually RFC 5280), can be marked as either in the command line. The default matches the defining RFC (and what is commonly found in the wild).

For example, to mark the Key Usage extension as non-critical, and the Extended Key Usage as critical, use:

$ python manage.py init_ca --key-usage-non-critical --extended-key-usage-critical ...

Extensions that either MUST or MUST NOT be marked as critical, cannot be changed via the command-line.

Examples¶

Here is a shell session that illustrates the respective manage.py commands:

$ python manage.py init_ca --path-length=2
>     --crl-url=http://ca.example.com/crl \
>     --ocsp-url=http://ocsp.ca.example.com \
>     --issuer-url=http://ca.example.com/ca.crt \
>     --subject-format=rfc4514 \
>     TestCA C=AT,L=Vienna,L=Vienna,O=Example,OU=ExampleUnit,CN=ca.example.com
$ python manage.py list_cas
BD:5B:AB:5B:A2:1C:49:0D:9A:B2:AA:BC:68:ED:ED:7D - TestCA

$ python manage.py view_ca BD:5B:AB:5B:A2
...
* OCSP URL: http://ocsp.ca.example.com
$ python manage.py edit_ca --ocsp-url=http://new-ocsp.ca.example.com \
>     BD:5B:AB:5B:A2
$ python manage.py view_ca BD:5B:AB:5B:A2
...
* OCSP URL: http://new-ocsp.ca.example.com

Note that you can just use the start of a serial to identify the CA, as long as that still uniquely identifies the CA.

Create intermediate CAs¶

Intermediate CAs are created, just like normal CAs, using manage.py init_ca. For intermediate CAs to be valid, CAs however must have a correct path length in the BasicConstraints x509 extension. Its value is an integer describing how many levels of intermediate CAs a CA may have. A path length of “0” means that a CA cannot have any intermediate CAs, if it is not present, a CA may have an infinite number of intermediate CAs.

Note

django-ca by default sets a path length of “0”, as it aims to be secure by default. The path length attribute cannot be changed in hindsight (not without resigning the CA). If you plan to create intermediate CAs, you have to consider this when creating the root CA.

So for example, if you want two levels of intermediate CAs, , you’d need the following path length values (the path length value is the minimum value, it could always be a larger number):

index	CA	`path length`	description
1	example.com	2	Your root CA.
2	sub1.example.com	1	Your first intermediate CA, a sub-CA from (1).
3	sub2.example.com	0	A second intermediate CA, also a sub-CA from (1).
4	sub.sub1.example.com	0	An intermediate CA of (2).

If in the above example, CA (1) had path length of “1” or CA (2) had a path length of “0”, CA (4) would no longer be a valid CA.

By default, django-ca sets a path length of 0, so CAs will not be able to have any intermediate CAs. You can configure the value by passing --path-length to init_ca:

$ python manage.py init_ca --path-length=2 ...

When creating a sub-ca, you must name its parent using the --parent parameter:

$ python manage.py list_cas
BD:5B:AB:5B:A2:1C:49:0D:9A:B2:AA:BC:68:ED:ED:7D - Root CA
$ python manage.py init_ca --parent=BD:5B:AB:5B ...

Note

Just like throughout the system, you can always just give the start of the serial, as long as it still is a unique identifier for the CA.