# &adminguide;

## Overview

This module implements STIR (Secure Telephony Identity Revisited) and SHAKEN (Signature-based Handling of Asserted information using toKENs) (RFC8224, RFC8588), with X509 certificate path check (ATIS "Signature-based Handling of Asserted information using toKENs (SHAKEN)", RFC5280 "6. Certification Path Validation").

stirshaken module exports the functions to check and to generate PASSporT, wrapped into SIP Identity header. For call authentication two functions are available: stirshaken_add_identity(...) and stirshaken_add_identity_with_key(key). stirshaken_add_identity() uses default key (through Authentication Service), stirshaken_add_identity_with_key(..., key) uses key specified as argument. For call verification three methods are available: stirshaken_check_identity() (through Verification Service), stirshaken_check_identity_with_key(key) and stirshaken_check_identity_with_cert(cert). stirshaken_check_identity() offers the most comprehensive check as only this method may download certificate (if needed), cache it, and check it with X509 certificate path check algorithm. This method is therefore to be used as a default verification mechanism, while stirshaken_check_identity_with_key(key) and stirshaken_check_identity_with_cert(cert) are only for completeness.

## Dependencies

### &kamailio; Modules

The following modules must be loaded before this module:

- No dependencies on other &kamailio; modules.

### External Libraries or Applications

The following libraries or applications must be installed before running &kamailio; with this module loaded:

- libstirshaken - https://github.com/signalwire/libstirshaken.

## Parameters

### `as_default_key` (str)

SSL private key to be used as default. Default key must be set if calls to stirshaken_add_identity() are executed. When set, module starts Authentication Service which makes each call to stirshaken_add_identity() using this key. Default key doesn't need to be set (Authentication Service doesn't need to be running) for the stirshaken_add_identity_with_key(..., key) to be available. This param has no meaning for calls to stirshaken_add_identity_with_key(..., key).

Default value is "" (not set).

#### Set `as_default_key` parameter

    ...
    modparam("stirshaken", "as_default_key", "/path/to/key")
    ...

### `vs_verify_x509_cert_path` (int)

If set, then stirshaken_check_identity() will execute X509 certificate path check on certificate referenced in PASSporT. This param has no meaning for calls to stirshaken_check_identity_with_key(key) and stirshaken_check_identity_with_cert(cert).

Default value is 1, (turned on).

#### Set `vs_verify_x509_cert_path` parameter

    ...
    modparam("stirshaken", "vs_verify_x509_cert_path", 1)
    ...

### `vs_ca_dir` (str)

The path to folder containing CA root certificates with names hashed. If set then must point to existing directory. This must be set when enabled X509 certificate path check, otherwise no end entity certificate will pass that check. This param has no meaning for calls to stirshaken_check_identity_with_key(key) and stirshaken_check_identity_with_cert(cert).

Default value is "" (not set).

#### Set `vs_ca_dir` parameter

    ...
    modparam("stirshaken", "vs_ca_dir", "/path/to/ca_dir")
    ...

### `vs_crl_dir` (str)

The path to folder containing CRLs. If set, then must point to existing directory. This is optional when X509 certificate path check is enabled, only vs_ca_dir is mandatory. If X509 certificate path check is enabled, and vs_crl_dir is set, then CRLs are loaded from this directory, which renders revoked certificates invalid (not trusted). This param has no meaning for calls to stirshaken_check_identity_with_key(key) and stirshaken_check_identity_with_cert(cert).

Default value is "" (not set).

#### Set `vs_crl_dir` parameter

    ...
    modparam("stirshaken", "vs_crl_dir", "/path/to/crl_dir")
    ...

### `vs_identity_expire_s` (int)

This parameter defines a maximum time in seconds for which PASSporT is considered valid.

Default value is 60 seconds.

#### Set `vs_identity_expire_s` parameter

    ...
    modparam("stirshaken", "vs_identity_expire_s", 20)
    ...

### `vs_connect_timeout_s` (int)

During a call verification with stirshaken_check_identity() a blocking HTTP(s) call is executed to download certificate referenced in PASSporT (unless certificate caching is turned on and a valid cert is found in cache). This parameter defines a maximum time in seconds for this blocking HTTP(s) connection to be established. After this time had passed and connection did not succeed (could not resolve host, address unreachable or other network errors) a call to stirshaken_check_identity() will return with error. This param has no meaning for calls to stirshaken_check_identity_with_key(key) and stirshaken_check_identity_with_cert(cert).

Default value is 5 seconds.

#### Set `vs_connect_timeout_s` parameter

    ...
    modparam("stirshaken", "vs_connect_timeout_s", 10)
    ...

### `vs_cache_certificates` (int)

If set, then certificates caching is turned on. This means that certificates downloaded during call verification with stirshaken_check_identity() are cached inside vs_cache_dir, and will be loaded from that cache as long as they are not there for more than vs_cache_expire_s seconds (see vs_cache_expire_s). If vs_cache_certificates is set then vs_cache_dir must be set too and pointing to existing directory. This param has no meaning for calls to stirshaken_check_identity_with_key(key) and stirshaken_check_identity_with_cert(cert).

Default value is 0 (turned off).

#### Set `vs_cache_certificates` parameter

    ...
    modparam("stirshaken", "vs_cache_certificates", 1)
    ...

### `vs_cache_dir` (str)

If vs_cache_certificates is set then vs_cache_dir must be set too and pointing to existing directory. Cached certificates are saved in this directory and loaded from there when needed during a call verification executed with stirshaken_check_identity(), as long as they are not there for more than vs_cache_expire_s seconds. This param has no meaning for calls to stirshaken_check_identity_with_key(key) and stirshaken_check_identity_with_cert(cert).

Default value is "" (not set).

#### Set `vs_cache_dir` parameter

    ...
    modparam("stirshaken", "vs_cache_dir", "/tmp/cert_cache")
    ...

### `vs_cache_expire_s` (int)

If vs_cache_certificates is set then cached certificates are saved in vs_cache_dir directory and loaded from there when needed during a call verification executed with stirshaken_check_identity(), as long as they are not there for more than vs_cache_expire_s seconds. If they are in cache for more than vs_cache_expire_s seconds, then a blocking HTTP(s) call is executed to download a new version of (expired) certificate. If this is successful then old version is removed and new version is saved in cache. This param has no meaning for calls to stirshaken_check_identity_with_key(key) and stirshaken_check_identity_with_cert(cert).

Default value is 120 seconds.

#### Set `vs_cache_expire_s` parameter

    ...
    modparam("stirshaken", "vs_cache_expire_s", 15)
    ...

### `vs_certsubject_pvname` (str)

If vs_certsubject_pvname is set then the Subject of the authenticated x509 certificate will be written to this pseudo-variable when stirshaken_check_identity() is executed. If the Identity header cannot be fully authenticated the pseudo-variable will be set to $null.

Default value is blank (disabled).

#### Set `vs_certsubject_pvname` parameter

    ...
    modparam("stirshaken", "vs_certsubject_pvname", "$vn(certsubject)")
    ...

### `vs_pptgrants_pvname` (str)

If vs_pptgrants_pvname is set then the JSON string of the authenticated PASSporT's grants will be written to this pseudo-variable when stirshaken_check_identity() is executed. If the Identity header cannot be fully authenticated the pseudo-variable will be set to $null.

Default value is blank (disabled).

#### Set `vs_pptgrants_pvname` parameter

    ...
    modparam("stirshaken", "vs_pptgrants_pvname", "$vn(grants)")
    ...

## Functions

### `stirshaken_check_identity()`

Check the validity of the Identity header by decoding PASSporT's signature with a certificate referenced in its x5u header and (optionally) checking that certificate for being trusted by X509 certificate check with CA root certificates in vs_ca_dir (and optionally CRLs in vs_crl_dir). PASSporT's iat grant is also checked for being too fresh or expired against vs_identity_expire_s seconds. This function executes a call to a callback which may supply certificates from cache (see vs_cache_certificates param). If certificate needs to be downloaded this call will block for a maximum of vs_connect_timeout_s seconds (see vs_connect_timeout_s param);

This function takes no parameters (only SIP message is passed implicitly).

This function can be used from ANY_ROUTE.

#### `stirshaken_check_identity` usage

    ...
    modparam("stirshaken", "vs_verify_x509_cert_path", 1)
    modparam("stirshaken", "vs_ca_dir", "/path/to/ca")
    modparam("stirshaken", "vs_cache_certificates", 1)
    modparam("stirshaken", "vs_cache_dir", "/path/to/cert_cache")
    modparam("stirshaken", "vs_cache_expire_s", 100)

    request_route {
        ...
    		if (1 == stirshaken_check_identity()) {
    			xlog("Shaken Identity is OK\n");
    		} else {
    			xlog("Shaken Identity is invalid\n");
    		}
        ...
    }
    ...

### `stirshaken_check_identity_with_key(keyPath)`

Check the validity of the Identity header by decoding PASSporT's signature with a key read from the location provided. PASSporT's iat grant is also checked for being too fresh or expired against vs_identity_expire_s seconds. This method does not involve HTTP(s) transcations. This method does not execute a call to a callback (vs_cache_certificates param has no meaning for this method). WARNING: This method only checks if SIP Identity Header was signed by a key corresponding to specified public key. This method doesn't attempt to obtain certificate referenced in PASSporT (but PASSporT should be checked with key corresponding to that certificate). Therefore it is possible that this check will be successful, while PASSporT is not valid (could be signed with key that doesn't match certificate referenced in x5u header). If you want a complete Shaken check or if you are not sure what you're doing, then you should execute w_stirshaken_check_identity() instead (and configure Verification Service to perform X509 certificate path verification with stirshaken_vs_verify_x509_cert_path param set to 1).

The parameters can contain pseudo-variables.

This function can be used from ANY_ROUTE.

#### `stirshaken_check_identity_with_key` usage

    ...
    request_route {
     	...
    		if (1 == stirshaken_check_identity_with_key("/path/to/key")) {
    			xlog("Shaken Identity is OK\n");
    		} else {
    			xlog("Shaken Identity is invalid\n");
    		}
     	...
    }
    ...

### `stirshaken_check_identity_with_cert(certPath)`

Same as stirshaken_check_identity_with_key(keyPath) but the key is read from the certificate which is read from the location provided.

The parameters can contain pseudo-variables.

This function can be used from ANY_ROUTE.

#### `stirshaken_check_identity_with_cert` usage

    ...
    request_route {
     	...
    		if (1 == stirshaken_check_identity_with_cert("/path/to/cert")) {
    			xlog("Shaken Identity is OK\n");
    		} else {
    			xlog("Shaken Identity is invalid\n");
    		}
     	...
    }
    ...

### `stirshaken_add_identity(x5u, attest, origtn_val, desttn_val, origid)`

Add SIP Identity Header to the call using default private key (see as_default_key param). Authenticate call with STIR-Shaken. If origID is empty, a UUID string is generated to fill the field. The origtn_val represents the origination telephone number; desttn_val, represents the destination telephone number; x5u is the HTTP(s) URL referencing to the public key that should be used to verify the signature; attest represents the attestation level (should be "A", "B" or "C").

The parameters can contain pseudo-variables. If origid is empty, an unique identifier will be generated with libuuid, e.g. "3f31bd2b-9fc4-4084-b0b0-566506c46292".

This function can be used from ANY_ROUTE.

#### `stirshaken_add_identity` with origid usage

    ...
    request_route {
     	...
    		if (1 == stirshaken_add_identity("https://sp.com/sp.pem", "B", "+44100", "+44200", "origid")) {
    			xlog("Shaken authentication added (SIP Identity Header created)\n");
    		} else {
    			xlog("Failed\n");
    		}
    	...
    }
    ...

#### `stirshaken_add_identity` with auto generated uuid as origid usage

If origid is empty, an unique identifier will be generated with libuuid, e.g. "3f31bd2b-9fc4-4084-b0b0-566506c46292".

    ...
    request_route {
    	...
    		if (1 == stirshaken_add_identity("https://sp.com/sp.pem", "B", "+44100", "+44200", "")) {
    			xlog("Shaken authentication added (SIP Identity Header created)\n");
    		} else {
    			xlog("Failed\n");
    		}
    	...
    }
    ...

### `stirshaken_add_identity_with_key(x5u, attest, origtn_val, desttn_val, origid, keyPath)`

Same as stirshaken_add_identity() but using the key read from the location provided as a last parameter.

The parameters can contain pseudo-variables. If origid is empty, an unique identifier will be generated with libuuid, e.g. "3f31bd2b-9fc4-4084-b0b0-566506c46292".

This function can be used from ANY_ROUTE.

#### `stirshaken_add_identity_with_key` usage

    ...
    request_route {
    	...
    		if (1 == stirshaken_add_identity_with_key("https://sp.com/sp.pem", "B", "+44100", "+44200", uuid, "/path/to/key")) {
    			xlog("Shaken authentication added (SIP Identity Header created)\n");
    		} else {
    			xlog("Failed\n");
    		}
    	...
    }
    ...

## Installation

The module depends on "libstirshaken", which is an open source C library from SignalWire. It can be downloaded from https://github.com/signalwire/libstirshaken. Until the libstirshaken is packaged in OS distributions, libstirshaken must be compiled and installed before the stirshaken module can be compiled.

Installing libstirshaken is easy:

### libstirshaken installation

    ...
    		git clone git@github.com:signalwire/libstirshaken.git
    		cd libstirshaken
    		./bootstrap.sh
    		./configure
    		make
    		make check
    		sudo make install
    ...

### Building Kamailio's stirshaken module

After libstirshaken had been installed, Kamailio's stirshaken module can then be built with

    ...
    		cd /path/to/kamailio/
    		make modules modules=src/modules/stirshaken/
    ...

To ensure proper functionality, the Kamailio stirshaken module requires a minimum version of libstirshaken that includes the stir_shaken_verify_cert_path function for performing the x509 certificate path check. This functionality was added to libstirshaken around 2020 (https://github.com/signalwire/libstirshaken/commit/58e740b897ae40e2bb02ada2231a051a7eb55137). If you're using an older version of libstirshaken that predates this commit, the stirshaken module may not function correctly.