Secure Real-Time Protocol (SRTP) for Software

The Secure Real-Time Transport Protocol, as described in RFC 3711, The Secure Real-time Transport Protocol (SRTP), provides a framework for the encryption and authentication of Real-time Transport Protocol (RTP) and RTP Control Protocol (RTCP) streams. Both RTP and RTCP are defined by RFC 3550, RTP: A Transport Protocol for Real-Time Applications.

Encryption ensures that the call content and associated signalling remains private during transmission.

Authentication ensures the following.

• Received packets are from the purported source
• Packets have not been tampered with during transmission
• A packet has not been replayed by a malicious server

Protocol Overview

While the RFC 3711 framework provides encryption and authentication procedures and defines a set of default cryptographic transforms required for RFC compliance, it does not specify a key management protocol to securely derive and exchange cryptographic keys. RFC 4568, Session Description Protocol (SDP) Security Description for Media Streams, defines such a protocol specifically designed to exchange cryptographic material using a newly defined SDP crypto attribute. Cryptographic parameters are established with only a single message or in single round-trip exchange using the offer/answer model defined in RFC 3264, An Offer/Answer Model with the Session Description Protocol.

The current release provides support for an initial SDP Security Descriptions (SDES) implementation that generates keys used to encrypt SRTP/SRTCP packets.

Authentication of packets will be added to a subsequent release.

A sample SDP exchange is shown below:

The SDP offerer sends:

v=0
o=sam 2890844526 2890842807 IN IP4 10.47.16.5
s=SRTP Discussion
i=A discussion of Secure RTP
u=http://www.example.com/seminars/srtp.pdf
e=[e-mail] (Marge Simpson)
c=IN IP4 168.2.17.12
t=2873397496 2873404696
m=audio 49170 RTP/SAVP 0
a=crypto:1 AES_CM_128_HMAC_SHA1_80
inline:WVNfX19zZW1jdGwgKCkgewkyMjA7fQp9CnVubGVz|2^20|1:4

The SDP answerer replies:

v=0
o=jill 25690844 8070842634 IN IP4 10.47.16.5
s=SRTP Discussion
i=A discussion of Secure RTP
u=http://www.example.com/seminars/srtp.pdf
e=[e-mail] (Homer Simpson)
c=IN IP4 168.2.17.11
t=2873397526 2873405696
m=audio 32640 RTP/SAVP 0
a=crypto:1 AES_CM_128_HMAC_SHA1_80
inline:PS1uQCVeeCFCanVmcjkpPywjNWhcYD0mXXtxaVBR|2^20|1:4

The media-level SDP attribute, crypto, describes the cryptographic suite, key parameters, and session parameters for the preceding unicast media line. The crypto attribute takes the form:

a=crypto: tag crypto-suite key-parameter [session-parameters]

tag

The tag field contains a decimal number that identifies a specific attribute instance. When an offer contains multiple crypto attributes, the answer uses the tag value to identify the accepted offer.

In the sample offer the tag value is 1.

crypto-suite

The crypto-suite field contains the encryption and authentication algorithms, either AES_CM_128_HMAC_SHA1_80 or AES_CM_128_HMAC_SHA1_32.

key-parameter

The key-parameter field contains one or more sets of keying material for the selected crypto-suite and it has following format.

"inline:" <key||salt> ["|" lifetime] ["|" MKI ":" length]

inline is a method and specifies that the crypto material to be used by the offerer is transmitted via the SDP.

The key||salt field contains a base64-encoded concatenated master key and salt.

Assuming the offer is accepted, the key || salt provides the crypto material used by the offerer to encrypt SRTP/SRTCP packets, and used by the answerer to decrypt SRTP/SRTCP packets.

Conversely the key || salt contained in the answer to the offer provides the crypto material used by the answerer to encrypt SRTP/SRTCP packets, and used by the offerer to decrypt SRTP/SRTCP packets.

The lifetime field optionally contains the master key lifetime (maximum number of SRTP or SRTCP packets encoded using this master key).

In the sample offer the lifetime value is 1,048, 576 (220) packets.

The MKI:length field optionally contains the Master Key Index (MKI) value and the MKI length.

The MKI is used only when the offer contains multiple keys; it provides a means to differentiate one key from another. The MKI takes the form of an integer, followed by its byte length when included in SRTP/SRTCP packets. For hardware-based platforms, the length value can be up to 32 bytes. For software-based platforms, the length value is 4 bytes.

In the sample offer the MKI value is 1 with a length of 4 bytes.

The session-parameters field contains a set of optional parameters that may override SRTP session defaults for the SRTP and SRTCP streams.

UNENCRYPTED_SRTP — SRTP messages are not encrypted

UNENCRYPTED_SRTCP — SRTCP messages are not encrypted

UNAUTHENTICATED_SRTP — SRTP messages are not authenticated

When generating an initial offer, the offerer ensures that there is at least one crypto attribute for each media stream for which security is desired. Each crypto attribute for a given media stream must contain a unique tag. The ordering of multiple crypto attributes is significant — the most preferred crypto suite is listed first.

Upon receiving the initial offer, the answerer must either accept one of the offered crypto attributes, or reject the offer in its entirety.

When an offered crypto attribute is accepted, the crypto attribute contained in the answer MUST contain the tag and crypto-suite from the accepted crypto attribute in the offer, and the key(s) the answerer will use to encrypt media sent to the offerer.

The crypto-suite is bidirectional and specifies encryption and authentication algorithms for both ends of the connection. The keys are unidirectional in that one key or key set encrypts and decrypts traffic originated by the offerer, while the other key or key set encrypts and decrypts traffic originated by the answerer.

Key exchange via text-based SDP is unacceptable in that malicious network elements could easily eavesdrop and obtain the plaintext keys, thus compromising the privacy and integrity of the encrypted media stream. Consequently, the SDP exchange must be protected by a security protocol such as TLS.

Operational Modes

SRTP topologies can be reduced to three basic topologies which are described in the following sections.

Single-Ended SRTP Termination

Single-ended SRTP termination is illustrated in the following figure.

If SRTP is enabled for the inbound realm/interface, the Oracle® Enterprise Session Border Controller handles the incoming call as specified by the Media Security Policy assigned to the inbound realm. If there is crypto attribute contained in the offer, the Oracle® Enterprise Session Border Controller parses the crypto attributes and optional parameters, if any. If the offer contains a crypto attribute or attributes compatible with the requirements specified by the SDES profile assigned to the Media Security policy, it selects the most preferred compatible attribute. Otherwise, the Oracle® Enterprise Session Border Controller rejects the offer. Before the SDP is forwarded to the called party, the Oracle® Enterprise Session Border Controller allocates resources, established SRTP and SRTCP Security Associations and updates the SDP by removing the crypto attribute and inserting possibly NAT’ed media addresses and ports. At the same time, the original crypto attribute is also removed from the SDP.

Once the reply from the called party is received, the Oracle® Enterprise Session Border Controller inserts appropriate crypto attribute(s) to form a new SDP, and forward the response back to the calling party.

Refer to ACLI Example Configurations for a sample ACLI configuration.

Back-to-Back SRTP Termination

The following figure illustrates Back-to-back SRTP termination.

Initial processing is similar to the single-ended termination described above. Before forwarding the request to the called party, the Oracle® Enterprise Session Border Controller (E-SBC) replaces the original crypto attribute with a new one whose crypto attribute conforms to the media security policy for the outbound realm/interface. Upon receiving the answer from the called party, the E-SBC accepts or rejects it, again based upon conformity to the media security policy. If accepted, the E-SBC replaces the original crypto attribute from the called party with its own to form a new SDP, which it forwards back to the calling party. At this point, SRTP media sessions are established on both sides for both calling and called parties.

SRTP Pass-Thru

The following figure illustrates SRTP pass-thru.

SRTP Pass-Thru

If the media security policy specifies pass-through mode, the Oracle® Enterprise Session Border Controller (E-SBC) does not alter the crypto attribute exchange between the calling and the called party; the attribute is transparently passed.

ACLI Instructions

SDES configuration consists of the following steps.

1. Create one or more SDES profiles which specify parameter values negotiated during the offer/answer exchange.
2. Create one or more Media Security Policies that specify key exchange protocols and protocol-specific profiles.
3. Assign a Media Security Policy to a realm.
4. Create an interface-specific Security Policy (refer to Security Policy for a sample ACLI configuration)

Configure an SDES Profile

A Session Description Protocol Security Descriptions (SDES) profile specifies the parameter values offered or accepted during SDES negotiation.

In the following procedure, use the key and salt parameters to generate the synchronous key used to encrypt and decrypt SRTP/SRTCP traffic originated by theOracle® Enterprise Session Border Controller (E-SBC). The E-SBC passes these concatenated values to the remote SRTP peer. Upon reception, the remote peer inputs the key and salt values to the negotiated encryption algorithm (AES in the current implementation), and derives the key required to decrypt SRTP/SRTCP traffic received from the E-SBC. The key parameter provides the basic keying material, while the salt (a bit string) provides the randomsess/entropy required by the encryption algorithm.

1. Access the sdes-profile configuration element.

   ORACLE# configure terminal
   ORACLE(configure)# security
   ORACLE(security)# media-security
   ORACLE(media-security)# sdes-profile
   ORACLE(sdes-profile)# 

2. In sdes-profile, do the following:

   name	Type the unique name of this profile.
   crypto-suite	Add one or more cryptography suites to this profile. Default: AES_CM_128_HMAC_SHA1_80. Valid values: AES_CM_128_HMAC_SHA1_80 | AES_CM_128_HMAC_SHA1_32.
   srtp-auth	Enable authentication of RTP packets. Default: enable. Valid values: enable | disable.
   srtp-encrypt	Enable to reject an answer that contains an UNENCRYPTED_SRTP session parameter in the crypto attribute. Disable to not to offer RTP encryption and include an UNENCRYPTED_SRTP session parameter in the SDP crypto attribute and accept an answer that contains an UNENCRYPTED_SRTP session parameter. Default: enable. Valid values: enable | disable.
   srtcp-encrypt	Enable to offer RTCP encryption, and reject an answer that contains an UNENCRYPTED_SRTCP session parameter in the crypto attribute. Disable to not offer RTCP encryption and include an UNENCRYPTED_SRTCP session parameter in the SDP crypto attribute; accepting an answer that contains an UNENCRYPTED_SRTCP session parameter. Default: enable. Valid values: enable | disable.
   mki	Enable or disable the use of the master key identifier within the SDP crypto attribute that differentiates one key from another. Enable—The E-SBC sends an MKI field within the crypto attribute (16 bytes maximum). Express MKI as a pair of decimal numbers in the form: |mki:mki_length| where MKI is the MKI integer value and MKI length is the length of the MKI field in bytes. Disable—The E-SBC sends no MKI field. Default: disable. Valid values: enable | disable.
   egress-offer-format	Set the egress offer format for this profile to use when you also set the outbound mode in the associated media security policy to "any." If the media security policy requires either RTP or SRTP, ignore this parameter. same-as-ingress—The E-SBC does not change the profile of the media lines. simultaneous-best- effort—The E-SBC inspects the incoming offer SDP, and adds one of the following: an RTP/SAVP media line for any media profile that has only the RTP/AVP media profile an RTP/AVP media line for any media profile that has only the RTP/SAVP media profile Default: same as ingress. Valid values: same as ingress | simultaneous best effort.
   use-ingress-session-params	Add one or more allowable ingress session parameters. Default: none. Valid values: srtcp-encrypt | srtcp-auth | srtcp-encrypt.
   lifetime	Add the lifetime parameter value to a=crypto in the SDP offer. Default: 0 (Do not add lifetime to a=crypto.) Valid values: 20-48. (Express as 2^<value>. For example, using the value 2^20: inline:zYALksQps3ntUw/KsbDdNuxChEQ81Z3BqvTJH|2^20)
   options	Add one or more optional features and parameters.
   key	Type the master key. (for testing purposes)
   salt	Type the master salt. (for testing purposes)
   srtp-rekey-on-re-invite	Enable to generate new outbound srtp keys on every re-invite. Default: disable. Valid values: enable | disable.

Media Security Policy Configuration

Use the following procedure to create a Media Security Policy that specifies the role of the Oracle® Enterprise Session Border Controller (E-SBC) in the security negotiation. When the E-SBC takes part in the negotiation, the policy specifies a key exchange protocol and SDES profile for both incoming and outgoing calls.

1. Access the media-sec-policy configuration element.

   ORACLE# configure terminal
   ORACLE(configure)# security
   ORACLE(security)# media-security
   ORACLE(media-security)# media-sec-policy
   ORACLE(media-sec-policy)#

2. Use the required name parameter to provide a unique identifier for this media-sec-policy instance.

   name enables the creation of multiple media-sec-policy instances.

3. Use optional pass-through parameter to enable or disable pass-thru mode.

   With pass-through mode disabled (the default state), the E-SBC disallows end-to-end negotiation — rather the Oracle® Enterprise Session Border Controller initiates and terminates SRTP connections with both endpoints.

   With pass-through mode enabled, the SRTP endpoints negotiate security parameters between each other; consequently, the E-SBC simply relays SRTP traffic between the two endpoints.

4. Use the outbound navigation command to move to media-sec-outbound configuration mode. While in this configuration mode you specify security parameters applied to the outbound call leg, that is calls sent by the E-SBC.
5. Use the profile parameter to specify the name of the SDES profile applied to calls sent by the E-SBC.
6. Use the mode parameter to select the real time transport protocol.

   Allowable values are rtp (the default) | srtp | any (either rtp | srtp)

   mode identifies the transport protocol (RTP or SRTP) included in an SDP offer when this media-security-policy is in effect.

7. Use the protocol parameter to select the key exchange protocol.

   Select sdes for SDES key exchange.

8. Use the done and exit parameters to return to media-sec-policy configuration mode.
9. Use the inbound navigation command to move to media-sec-inbound configuration mode. While in this configuration mode you specify security parameters applied to the inbound call leg, that is calls received by the E-SBC.
10. Use the profile parameter to specify the name of the SDES profile applied to calls received by the E-SBC.
11. Use the mode parameter to select the real time transport protocol.

    Allowable values are rtp (the default) | srtp | any (either rtp | srtp)

    mode identifies the transport protocol (RTP or SRTP) included in an SDP offer when this media-security-policy is in effect.

12. Use the protocol parameter to select the key exchange protocol.

    Select sdes for SDES key exchange.

13. Use done, exit, and verify-config to complete configuration of this media security policy instance.
14. Repeat Steps 1 through 13 to configure additional media-security policies.

Assign the Media Security Policy to a Realm

To assign a media-security-policy to a realm:

1. From superuser mode, use the following command sequence to access realm-config configuration mode. While in this mode, you assign an existing media-security-policy to an existing realm.

   ORACLE# configure terminal
   ORACLE(configure)# media-manager
   ORACLE(media-manager)# realm-config
   ORACLE(realm-config)# select
   identifier:
   1. access-12
   ...
   ...
   selection: 1
   ORACLE(realm-config)#

2. Use the media-sec-policy parameter to assign the policy to the target realm.
3. Use done, exit, and verify-config to complete assignment of the media-security-policy to the realm.

ACLI Example Configurations

The following section contain XML representations of system configurations for basic operational modes.

Single-Ended SRTP Termination Configuration

<sdesProfile name='sdes'
    srtpAuth='enabled'
    srtpEncrypt='enabled'
    srtcpEncrypt='enabled'
    mki='disabled'
    egressOfferFormat='same-as-ingress'
    useIngressSessionParams=''
    options=''
    key=''
    salt=''
    lastModifiedBy='admin@172.30.11.55'
    lastModifiedDate='2013-03-04 19:29:40' objectId='21'>
    <cipherSuites name='AES_CM_128_HMAC_SHA1_80'/>
    key>sdes</key>
</sdesProfile>

<mediaSecPolicy name='sdes'
    passThrough='disabled'
    options=''
    lastModifiedBy='admin@172.30.11.55'
    lastModifiedDate='2013-03-04 19:30:23' objectId='22'>

    <inbound profile='sdes'
        mode='srtp'
        protocol='sdes'/>

    <outbound profile='sdes'
        mode='sdes'
        protocol='sdes'/>

    key>sdes</key>
        </mediaSecPolicy>

...
...
...
realm-config
    identifier                peer
    description
    addr-prefix               192.168.0.0/16
    network-interfaces        M00:0
    mm-in-realm               enabled
    mm-in-network             enabled
    mm-same-ip                enabled
    mm-in-system              enabled
    bw-cac-non-mm             disabled
    msm-release               disabled
    qos-enable                disabled
    generate-UDP-checksum     disabled
    max-bandwidth             0
    fallback-bandwidth        0
    max-priority-bandwidth    0
    max-latency               0
    max-jitter                0
    max-packet-loss           0
    observ-window-size        0
    parent-realm
    dns-realm
    media-policy
    media-sec-policy          msp2
    in-translationid
    ...
    ...
    ...
    last-modified-by         admin@console
    last-modified-date       2009-11-10 15:38:19

Back-to-Back SRTP Termination Configuration

ORACLE# show running-config
...
...
...
sdes-profile
     name                           sdes1
     crypto-list                    AES_CM_128_HMAC_SHA1_80
     srtp-auth                      enabled
     srtp-encrypt                   enabled
     srtcp-encrypt                  enabled
     mki                            disabled
     key
     salt
     last-modified-by               admin@console
     last-modified-date             2009-11-16 15:37:13
media-sec-policy
     name                           msp2
     pass-through                   disabled
     inbound
          profile                   sdes1
     mode                           srtp
     protocol                       sdes
     outbound
          profile                   sdes1
     mode                           srtp
     protocol                       sdes
     last-modified-by               admin@console
     last-modified-date             2009-11-16 15:37:51
...
...
...
realm-config
     identifier                     peer
     description
     addr-prefix                    192.168.0.0/16
     network-interfaces	M00:0
     mm-in-realm	enabled
     mm-in-network                  enabled
     mm-same-ip                     enabled
     mm-in-system                   enabled
     bw-cac-non-mm                  disabled
     msm-release                    disabled
     qos-enable                     disabled
     generate-UDP-checksum          disabled
     max-bandwidth                  0
     fallback-bandwidth             0
     max-priority-bandwidth         0
     max-latency                    0
     max-jitter                     0
     max-packet-loss                0
     observ-window-size             0
     parent-realm
     dns-realm
     media-policy
     media-sec-policy               msp2
     in-translationid
     ...
     ...
     ...
realm-config
     identifier                     backOffice
     description
     addr-prefix                   	172.16.0.0/16
     network-interfaces	M10:0
     mm-in-realm                    enabled
     mm-in-network                  enabled
     mm-same-ip                     enabled
     mm-in-system                   enabled
     bw-cac-non-mm                  disabled
     msm-release                    disabled
     qos-enable                     disabled
     generate-UDP-checksum          disabled
     max-bandwidth                  0
     fallback-bandwidth             0
     max-priority-bandwidth         0
     max-latency                    0
     max-jitter                     0
     max-packet-loss                0
     observ-window-size             0
     parent-realm
     dns-realm
     media-policy
     media-sec-policy               msp2
     in-translationid
     ...
     ...
     ...
     last-modified-by              admin@console
     last-modified-date            2009-11-10 15:38:19

SRTP Pass-Thru Configuration

ORACLE# show running-config
...
...
...
sdes-profile
     name                           sdes1
     crypto-list                    AES_CM_128_HMAC_SHA1_80
     srtp-auth                      enabled
     srtp-encrypt                   enabled
     srtcp-encrypt                  enabled
     mki                            disabled
     key
     salt
     last-modified-by               admin@console
     last-modified-date             2009-11-16 15:37:13
     media-sec-policy
     name                           msp2
     pass-through                   enabled
     inbound
     profile                        sdes1
     mode                           srtp
     protocol                       sdes
     outbound
     profile                        sdes1
     mode                           srtp
     protocol                       sdes
     last-modified-by               admin@console
     last-modified-date             2009-11-16 15:37:51
     ...
     ...
     ...
realm-config
     identifier                     peer
     description
     addr-prefix                    192.168.0.0/16
     network-interfaces             M00:0
     mm-in-realm                    enabled
     mm-in-network                  enabled
     mm-same-ip                     enabled
     mm-in-system                   enabled
     bw-cac-non-mm                  disabled
     msm-release                    disabled
     qos-enable                     disabled
     generate-UDP-checksum          disabled
     max-bandwidth                  0
     fallback-bandwidth             0
     max-priority-bandwidth         0
     max-latency                    0
     max-jitter                     0
     max-packet-loss                0
     observ-window-size             0
     parent-realm
     dns-realm
     media-policy
     media-sec-policy               msp2
     ...
     ...
     ...
realm-config
     identifier                     core
     description
     addr-prefix                    172.16.0.0/16
     network-interfaces             M10:0
     mm-in-realm                    enabled
     mm-in-network                  enabled
     mm-same-ip                     enabled
     mm-in-system                   enabled
     bw-cac-non-mm                  disabled
     msm-release                    disabled
     qos-enable                     disabled
     generate-UDP-checksum          disabled
     max-bandwidth                  0
     fallback-bandwidth             0
     max-priority-bandwidth         0
     max-latency                    0
     max-jitter                     0
     max-packet-loss                0
     observ-window-size             0
     parent-realm
     dns-realm
     media-policy
     media-sec-policy               msp2
     in-translationid
     ...
     ...
     ...
     last-modified-by              admin@console
     last-modified-date            2009-11-10 15:38:19

Security Policy

A Security Policy enables the Oracle® Enterprise Session Border Controller to identify inbound and outbound media streams that are treated as SRTP/SRTCP. The high-priority Security Policy, p1, (shown below) allows signaling traffic from source 172.16.1.3 to destination 172.16.1.10:5060. The lower-priority Security Policy, p2, (also shown below) matches media traffic with the same source and destination, but without any specific ports. Consequently, SIP signaling traffic (from local port 5060) go through, but the media stream will be handled by appropriate SRTP SA.

security-policy
     name                          p1
     network-interface             private:0
     priority                      0
     local-ip-addr-match           172.16.1.3
     remote-ip-addr-match          172.16.1.10
     local-port-match              5060
     remote-port-match             0
     trans-protocol-match          UDP
     direction                     both
     local-ip-mask                 255.255.255.255
     remote-ip-mask                255.255.255.255
     action                        allow
     ike-sainfo-name
     outbound-sa-fine-grained-mask
          local-ip-mask            255.255.255.255
          remote-ip-mask           255.255.255.255
          local-port-mask          0
          remote-port-mask         0
          trans-protocol-mask      0
          valid                    enabled
          vlan-mask                0xFFF
     last-modified-by              admin@console
     last-modified-date            2009-11-09 15:01:55
     
     security-policy
     name                          p2
     network-interface             private:0
     priority                      10
     local-ip-addr-match           172.16.1.3
     remote-ip-addr-match          172.16.1.10
     local-port-match              0
     remote-port-match             0
     trans-protocol-match          UDP
     direction                     both
     local-ip-mask                 255.255.255.255
     remote-ip-mask                255.255.255.255
     action                        ipsec
     ike-sainfo-name
     outbound-sa-fine-grained-mask
     local-ip-mask                 0.0.0.0
     remote-ip-mask                255.255.255.255
     local-port-mask               0
     remote-port-mask              65535
     trans-protocol-mask           255
     valid                         enabled
     vlan-mask                     0xFFF
     last-modified-by              admin@console
     last-modified-date            2009-11-09 15:38:19

SRTP Re-keying

Initialization of SRTP re-keying is supported by the Oracle® Enterprise Session Border Controller.

The Oracle® Enterprise Session Border Controller can generate a new outbound crypto attribute in the SDP offer in a SIP re-INVITE when the srtp-rekey-on-reinvite parameter is set to enabled. The system generates the attribute regardless of the state of the flow, active or not.

This capability is important for some clients that reside on the SRTP side in a single SRTP termination mode configuration. Any media changes that happen in the RTP side are hidden by the Oracle® Enterprise Session Border Controller. This concealment may cause issues in some configurations, where media servers are involved. When the media changes from media server to called phone, the SRTP endpoint is not aware the media source changed because the SDP offer from the Oracle® Enterprise Session Border Controller is the same as original invite. The result is that some devices drop packets because of Synchronization Source Identifier (SSRC) values mismatch, unexpected jumps in sequence number, sequence number reversions back to 1 triggering replay attack defense, and so forth. In certain environment is has been found that re-keying on every re-invite eliminates all these issues especially in customer setups that use Microsoft Lync products.

The processing of standard RE-INVITES (those containing an SDP offer) and offerless RE-INVITES is shown below.

With SDP:

No SDP:

If the re-invite message is a refresh and srtp-rekey-on-reinvite is enabled, the outbound crypto will change but the SDP version will not be incremented on the outgoing invite. If this scenario causes incompatibility issues with customer equipment then add the unique-sdp-id option to media-manager, option configuration so the Oracle® Enterprise Session Border Controller increments the SDP version in the outgoing invite.

SRTP Re-keying Configuration

Configure srtp-rekey-on-reinvite to enable the negotiation and generation of new SRTP keys upon the receipt of a SIP RE-INVITE message that contains SDP.

Confirm that an sdes-profile exists.

In the following procedure, change the default state to enabled.

1. Access the sdes-profile configuration element.

   ORACLE# configure terminal
   ORACLE(configure)# security
   ORACLE(security)# media-security
   ORACLE(media-security)# sdes-profile
   ORACLE(sdes-profile)# 

2. Type select to choose and configure an existing object.

   ORACLE(sdes-profile)# select
   <name>:
   1:  name=sdesprofile01
   
   selection: 1
   ORACLE(sdes-profile)#

3. srtp-rekey-on-reinvite—Set this parameter to enabled for re-keying upon the receipt of an SIP reINVITE that contains SDP.
4. Type done to save your configuration.

Modified ALCI Configuration Elements

The action parameter in security-policy configuration mode has been modified to accept additional values, srtp and srtcp.

1. From superuser mode, use the following command sequence to access media-sec-policy configuration mode.

   ORACLE# configure terminal
   ORACLE(configure)# security
   ORACLE(security)# ipsec
   ORACLE(ipsec)# security-policy
   ORACLE(security-policy)# action ?
   <enumeration> action (default: ipsec)
   ipsec, allow, discard, srtp, srtcp
   ORACLE(security-policy)#

   Refer to Security Policy for sample Security Policies.

   The show security command has been updated with an srtp option.

   ORACLE# show security srtp
   sad
   spd
   statistics
   SRTP Statistics
   status

   The srtp option is similar to the ipsec option save for the sad sub-option that provides data for only SRTP SAs.

   The show sa stats command has been updated with an srtp option.

   ORACLE# show sa stats <ENTER>	Show statistics summary of all Security Associations
   <ike>       Show statistics for IKE Security Associations
   <ims-aka>   Show statistics for IMS-AKA Security Associations
   <srtp>      Show statistics for SRTP Security Associations
   sd# show sa stats srtp
   20:06:24-114
   SA Statistics                   ---- Lifetime ----
                               Recent     Total      PerMax
   SRTP Statistics
   ADD-SA Req Rcvd             0          0          0
   ADD-SA Success Resp Sent    0          0          0
   ADD-SA Fail Resp Sent       0          0          0
   DEL-SA Req Rcvd             0          0          0
   DEL-SA Success Resp Sent    0          0          0
   DEL-SA Fail Resp Sent       0          0          0

ARIA Cipher Support

Previous and the current Oracle® Enterprise Session Border Controller releases have provided support for the Secure Real-Time Transport Protocol (SRTP), as defined in RFC 3711, to encrypt and authenticate Real-Time Transport Protocol (RTP) and Real-Time Transport Control Protocol (RTCP) media streams. Concurrent support for Session Description Protocol Security Descriptions (SDES) enabled the exchange of SRTP keying material. These releases have supported a single encryption algorithm, Advanced Encryption System (AES) counter mod with 128-bit keys

This release supports ARIA, a block cipher selected by the Korean Agency for Technology and Standards as a standard cryptographic Technique. The Oracle Oracle® Enterprise Session Border Controller now supports the ARIA cipher with a 192-bit key in counter mode for RTP and RTCP encryption; authentication is supported by HMAC_SHA1 with either 32-bit or 80-bit keys.

Call Flow

An example call flow between a ARIA endpoint, the OracleSD, and a Gateway/Application Server illustrates a successful call establishment where the call is originated from an ARIA enabled phone and destined to a core network server.

      ARIA phone            Acme SD          Gateway/App Server
 1.       |  INVITE/SDP        |                    |
          | ---------------->  |                    |
                               |  INVITE/SDP        |
          |                    | ---------------->  |
 2.       |  100 TRYING        |                    |
          | <----------------  |                    |
          |                    |  180 RINGING       |
          |                    | <----------------  |
          |  180 RINGING       |                    |
          | <----------------  |                    |
          |                    |  200 OK/SDP        |
          |                    | <----------------  |
 3.       |  200 OK/SDP        |                    |
          | <----------------  |                    |
          |  ACK               |                    |
          | ---------------->  |                    |
          |                    |  ACK               |
          |                    | ---------------->  |
          |                    |                    |
 4.       | <-SRTP/ARIA media->| <- RTPmedia flow ->|

1. The ARIA-enabled phone sends an INVITE request to the SD with the crypto attribute in the SDP specifying the ARIA 192 CM cipher for encryption and HMAC_SHA1_80 for authentication. The crypto attribute also has the master key encoded in base-64 format, as well the mki parameters (optionally). The SD forwards the INVITE to the called party via the gateway according to the media-security-policy on the outbound realm.
2. The SD sends provisional response to INVITE request
3. Assuming that the SD gets successful answer from called party, the SD sends a 200 OK response to the caller, with the crypto attribute in the accompanying SDP specifying the ARIA 192 CM cipher for encryption and HMAC_SHA1_80 for authentication. The crypto attribute also has the master key, as well the mki parameters (optionally).
4. The ARIA-enabled phone acknowledges the reception of 200 OK final response. At this point, encrypted SRTP traffic using the ARIA 192 counter mode cipher flows between the phone and the SD, and unencrypted traffic flows between the SD and the core network.

ARIA Support Configuration

ARIA support is enabled at the sdes-profile level.

1. Use the following command sequence to move to sdes-profile Configuration Mode.

   ORACLE# configure terminal			 
   ORACLE(configure)# security			 
   ORACLE(security)# media-security 
   ORACLE(sdes-profile)# 

2. Use the crypto-list parameter to specify the crypto suite used for SDES-based encryption.

   Use either aria_cm_192_hmac_32, or aria_cm_192_hmac_32 to specify ARIA encryption.

   ORACLE(sdes-profile)# crypto-list aria_cm_192_hmac_80			 
   ORACLE(sdes-profile)# 

3. Use done, exit, and verify-config to complete cipher suite selection.