Auth Identity module provides functionalities for securely identifying originators of SIP messages. This module has two basic service:
authorizer - authorizes a message and adds Identity and Identity-Info headers
verifier - verifies an authorized message
Known limitations in this version:
authorizer and verifier support all SIP requests except for CANCEL and REGISTER
verifier does not support the subjectAltName extension of certificates
This module needs the following headers and libraries:
OpenSSL (version 0.9.8 or higher) for cryptographic functions
libcurl for HTTP, HTTPS functions
If you'd like to use TLS module too then use the corresponding LIB line in auth_identity's Makefile
the Authorizer service needs to make the public key, which conveyed in a certificate, available over HTTPS or HTTP for verifiers. The domain the authorizer is responsible for and the domain part of the URL of the certificate must be the same. This service needs access to the private key too.
Note: this parameter is for authorizer service.
The path of private key of the authentication service. The key must be in PEM format.
This parameter is required by authentication service.
Example 1. Set privatekey_path parameter
...
modparam("auth_identity","privatekey_path","/etc/ssl/private/key.pem")
...
Note: this parameter is for authorizer service.
The path of certificate of the authentication service. The certificate must be in PEM format.
This parameter is required by authentication service.
Example 2. Set certificate_path parameter
...
modparam("auth_identity","certificate_path","/var/www/ssl/mycert.pem")
...
Note: this parameter is for authorizer service.
The url where certificate is available for other verifier services. (value of Identity-info header) The certificate should be in DER format.
This parameter is required by authentication service.
Example 3. Set certificate_url parameter
...
modparam("auth_identity","certificate_url","https://foo.bar/mycert.der")
...
Note: this parameter is for authorizer service.
If the Date header of message which is needed to be authenticated contains a time different by more than this seconds from the current time noted by the authentication service then it rejects the message.
This parameter is optional. The default value is "600".
Note: this parameter is for verifier service.
The validity time of an authenticated message. The message will be refused if it contains a time different by more than this seconds from the current time noted by the verification service.
This parameter is optional. The default value is "3600".
Example 5. Set auth_validity_time parameter
...
modparam("auth_identity","auth_validity_time",3600)
...
Note: this parameter is for verifier service.
The number of Call-IDs stored in order to recognize call replay
attacks. A Call-ID is stored auth_validity_time long and
uses approximately 100 bytes memory.
This parameter is optional. The default value is "32768". (you should increase the size of shared memory with -m command line switch if you liked to store more callid than 10000)
Example 6. Set auth_validity_time parameter
...
modparam("auth_identity","callid_cache_limit",32768)
...
Note: this parameter is for verifier service.
The number of certificates stored in order to avoid needless download. A certificate is stored until its expiration date and uses approximately 600 bytes memory.
This parameter is optional. The default value is "4096".
Example 7. Set certificate_cache_limit parameter
...
modparam("auth_identity","certificate_cache_limit",4096)
...
Note: this parameter is for verifier service.
A file of trusted certificates. The file should contain multiple certificates in PEM format concatenated together. It could be useful for verifying a certificate signed by a private CA.
This parameter is optional. It has not got default value.
Example 8. Set cainfo_path parameter
...
modparam("auth_identity","cainfo_path","/etc/ssl/certs/ca-certificates.crt")
...
Note: this function is for authorizer service.
If a message, the auth service should authorize, contains Date header then this function checks whether it falls in message timeout (set by msg_timeout parameter). If there is not any Date header then the module adds one. This function also checks whether the certificate of the authentication service (set by certificate_path parameter) has been expired.
Note: this function is for authorizer service.
Assembles digest-string from the message, calculates its SHA1 hash, encrypts it with the private key (set by privatekey_path parameter) of the authorizer service, base64 encodes it and adds to the outgoing message as the value of Identity header. This function also adds Identity-Info header which contains an URI (set by certificate_url parameter) from which the certificate of auth service can be acquired.
Note: this function needs the final outgoing message for authorization, so no module may modify any digest string related headers (From, To, Call-ID, CSeq, Date, Contact) and body after auth_add_identity()'s been called
Note: this function is for verifier service.
Checks Date header of the incoming message whether falls in validity time (set by auth_validity_time parameter)
Note: this function is for verifier service.
Tries to get certificate defined by the value of Identity-info header from certificate table (which size is set by certificate_cache_limit parameter). If the required certificate is not found there then this function downloads it.
Note: this function is for verifier service.
Checks whether the downloaded certificate is valid (is not expired, its subject and the domain part of the URL are the same) and adds it to certificate table.
Note: this function is for verifier service.
Assembles digest-string from the message, create SHA1 hash and compares it with the decrypted value of Identity header.
Note: this function is for verifier service.
Checks whether the current call's been already processed in validity time (set by auth_validity_time) to recognize call replay attacks. If this call (identified by Call-id, Cseq, and tag of From header triple) has not been replayed then adds it to callid table (which size is set by callid_cache_limit parameter).
...
route[INIT]
{
# we process new transactions only
if (!t_newtran()) {
sl_reply("500", "Internal error newtran");
drop;
}
...
route[OUTBOUND]
{
# If we are responsible for the domain of the sender of this message
if ($f.did && !$t.did) {
# Authentication service
if (method=="INVITE" || method=="BYE"
|| method=="OPTION" || method=="ACK") {
# Identity and Identity-info headers must not exist
if (@identity) {
t_reply("403", "Invalid Identity header");
drop;
}
if (@identity_info) {
t_reply("403", "Invalid Identity-info header");
drop;
}
if (!auth_date_proc()) {
t_reply("403", "Invalid Date value");
drop;
}
if (!auth_add_identity()) {
t_reply("480", "Authentication error");
drop;
}
}
route(FORWARD);
}
}
...
...
route[INIT]
{
# we process new transactions only
if (!t_newtran()) {
sl_reply("500", "Internal error newtran");
drop;
}
...
route[VERIFY]
{
# if we've already processed this message then we drop it
if (!t_newtran()) {
sl_reply("500", "Internal error newtran");
drop;
}
if (method=="INVITE" || method=="BYE"
|| method=="OPTION" || method=="ACK") {
# Identity and Identity-info are required for verification
if (!@identity) {
t_reply("428", "Use Identity Header");
drop;
}
if (!@identity_info) {
t_reply("436", "Bad Identity-Info");
drop;
}
if (!vrfy_check_date()) {
t_reply("403", "Outdated Date header value");
drop;
}
if (!vrfy_get_certificate()) {
t_reply("436", "Bad Identity-Info");
drop;
}
if (!vrfy_check_certificate()) {
t_reply("437", "Unsupported Certificate");
drop;
}
if (!vrfy_check_msgvalidity()) {
t_reply("438", "Invalid Identity Header");
drop;
}
if (!vrfy_check_callid()) {
t_reply("403", "Message is replayed");
drop;
}
}
}
...