Impacts of Security Protocols on Real- time Multimedia Communications Kihun Hong 1, Souhwan Jung 1, Luigi Lo Iacono 2, Christoph Ruland 2 1 School of Electronic Engineering, Soongsil University, 1-1, Sangdo-dong, Dongjak-ku, Seoul , KOREA 2 Institute for Data Communications Systems, University of Siegen, Germany {lo_iacono,

2 Outline Motivation for the study Main contributions of the paper Security Standards for Multimedia Communication Comparing Criteria Implementation Conclusion

3 Motivation for the study Which security protocol will you use for real- time multimedia communication ? We have many security protocols as IPsec, TLS, H.235, SRTP, and so on. Media stream has real-time properties. Delay, packet loss, jitter etc. Security service can degrade the quality of real- time multimedia services.

4 Main contributions of the paper We investigated the existing security protocols for real-time multimedia communication. We analyzed the details of the security functions for real- time multimedia communication. Optimized security function for real-time multimedia communication. Protection bound, Encryption algorithm and operation mode, computational delay etc. This work is helpful to choose and design the security protocol for real-time multimedia communication.

5 Security Standards for Multimedia Communication IPsec Security services for the Internet Protocol It is mandatory for IPv6 and optional for IPv4. Encapsulating Security Payload (ESP) Authentication Header (AH) H.235 H.235 standard describes security services for H.323. Baseline Security Profile Message authentication/integrity for the signaling path. Voice encryption profile Signature Security Profile Authentication, integrity, and non-repudiation for the signaling messages by using digital signatures. SRTP The Secure RTP (SRTP) provides confidentiality and authentication for RTP and RTCP. The encryption of SRTP or SRTCP packets is optional whereas the authentication for RTCP is mandatory but optional for RTP.

6 Comparing Criteria Confidentiality Data Integrity and Message Authentication Packet Source Authentication and User Authentication Replay Protection Dos Protection Key Management Data Expansion Error Propagation Computational Delay

7 Confidentiality IPsec IP payload (protection bound) DES CBC-Mode H.235 RTP payload (protection bound) RC2, DES, and 3DES, CBC-Mode SRTP RTP, RTCP payload (protection bound) AES in Segmented Integer Counter (SIC) mode Keystream is XORed with the payload.

8 Data Integrity and Message Authentication IPsec IP packet (AH) H.235 The anti-spamming mechanism provides a light-weighted RTP packet authentication. A part of the RTP header. An attacker can modify RTP payloads. SRTP RTP, RTCP header and the (encrypted) payload MAC is truncated to the leftmost 32 bit. A truncation to less than the half of the generated output of the HMAC increases the possibility to attack the MAC because of the birthday-attack-bound.

9 Packet Source Authentication and User Authentication All of the schemes don’t provide a method for packet source authentication. IPsec User authentication relies on the main mode of the IKE protocol using digital signatures. H.235 Authentication is accomplished by the utilization of pre- shared secrets. (a static password or some other a priori piece of information) The usage of digital certificates is possible. SRTP SRTP depends on a separate protocol for user authentication.

10 Replay Protection and Dos Protection Replay Protection IPsec The AH guards against replay attacks. Sliding window approach This is realized by maintaining a replay list on the receiver-side. H.235 Replay protection is for further study. SRTP It indirectly provides replay protection by authenticating the sequence number. Dos Protection IPsec and SRTP have no countermeasure against message flooding. H.235 A media anti-spamming mechanism …P…SEQ#timestamp……Media datapaddingAUTHpadlen encrypted MAC K (…SEQ#, timestamp) RTP Header

11 Key Management IPsec Internet Key Exchange (IKE) protocol Main Mode and Quick Mode H.235 The master chooses a random session key. The shared secret is used to encrypt the session key material. SRTP SRTP does not define any key establishment protocol. It just describes how to derive the necessary session keys for encryption and authentication from the master keys.

12 Data Expansion IPsec : ESP (or AH) header, pad, auth. field H.235 : pad, auth. field SRTP : auth. tag

13 Error Propagation IPsec and H.235 In case of CBC, a transmission error affects two plaintext blocks. SRTP No error propagation The process of encrypting a packet XORing with the keystream

14 Computational Delay Sender-side IPsec computation delay = Enc(UDP header||RTP header||RTP payload) + GenMAC(ESP header||UDP header||RTP header||RTP payload) H.235 computation delay = Enc(RTP payload) + GenMAC(RTP header) SRTP computation delay = Enc(RTP payload) + GenMAC(RTP header || RTP payload) * Receiver-side IPsec Computation delay = Dec(UDP header||RTP header||RTP payload) + VerMAC(ESP header||UDP header||RTP header||RTP payload) H.235 computation delay = Dec(RTP payload) + VerMAC(RTP header) SRTP computation delay = Dec(RTP payload) + VerMAC(RTP header || RTP payload) * * : XOR operation.

15 Summary of Properties IPsecH.235SRTP Key management  User Authentication  Integrity of RTP Payload  RTCP Protection  Pre-computation  Error Propagation  Data Size Expansion (High) (Medium) (Low)

16 Implementation H.235 OpenH323 supports H.235 for securing RAS messages but doesn’t support security functions for H.225.0, H.245, and RTP. We extended the H and H.245 signaling implementations and added the missing security fields and structures such as CryptoToken, ClearToken, and H.235Key. All encryption algorithms as stated in H.235 Annex D were integrated. SRTP The SRTP framework is considered as a bump in the stack implementation between the RTP application and the transport layer. We integrated our SRTP framework into the openH323 project and extended the OpenPhone application.

17 Communication overheads versus payload size IPsec : ESP (or AH) header, pad, auth. field H.235 : pad, auth. field SRTP : auth. tag

18 Corrupt frames versus Packet error probability We use a 40 bytes payload consisting of 2 frame of G The block size of encryption algorithm is 8 bytes. The error position of packet is random. IPsec and H.235 make more corrupted frames.

19 Conclusions IPsec is a general security protocol for IP datagram and is easy to apply to applications. But IPsec has a high comm. overhead and end-to-end delay. In case of H.235 the offered security for the media stream is incomplete. Furthermore the protection of RTCP is left out completely. That makes H.235 very vulnerable to a variety of attacks. Protection bound, pre-computation, error propagation, data size expansion SRTP defines optimized security functions as integrity of RTP payload, RTCP protection, pre-computation, and low comm. overhead for real-time multimedia application using RTP.