doc.: IEEE Submission November 18, 2004 Poor & Struik / Ember & CerticomSlide 1 Project: IEEE P Working Group for Wireless Personal Area Networks (WPANs) Submission Title: [Security Resolutions] Date Submitted: [November 18, 2004] Source: [Rene Struik] Company [Certicom Research] Address [5520 Explorer Drive, Fourth Floor, Mississauga, ON, L4W 5L1, Canada] Voice:[ ], FAX: [ ], Re: [] Abstract:[This document proposes resolutions to a set of issues relating to the security suite in IEEE ] Purpose:[This document is submitted for consideration for revisions to the specification.] Notice:This document has been prepared to assist the IEEE P It is offered as a basis for discussion and is not binding on the contributing individual(s) or organization(s). The material in this document is subject to change in form and content after further study. The contributor(s) reserve(s) the right to add, amend or withdraw material contained herein. Release:The contributor acknowledges and accepts that this contribution becomes the property of IEEE and may be made publicly available by P

doc.: IEEE Submission November 18, 2004 Poor & Struik / Ember & CerticomSlide 2 Security Resolutions Rene Struik (Certicom Research) New items/updates in blue

doc.: IEEE Submission November 18, 2004 Poor & Struik / Ember & CerticomSlide 3 Compatibility issues is unclear about how to interpret reserved fields. Interpretation 1 Reserved fields may be ignored upon reception (don’t care approach) Consequence: Reserved fields cannot be given meaningful value, since this would break existing implementations. Interpretation 2 Reserved fields shall be set to zero. The receiver shall inspect these fields and, if found to be nonzero, it shall discard the frame with no indication to higher layers. Consequence: Reserved fields can be given meaningful value, without breaking existing implementations. Subsequent interpretations still unclear: - Minutes Berlin meeting ( b) - Document Phil Beecher ( b) Proposal: Adopt interpretation 2, since it allows use of reserved fields for updates to

doc.: IEEE Submission November 18, 2004 Poor & Struik / Ember & CerticomSlide 4 #14, #45: CCM* Description: The current 15.4 security suite is composed of three components: AES-CCM (for encryption and authentication), CBC-MAC (for authentication only), and AES-CTR (encryption only). Problem 1: These three separate components require a larger implementation (counted in gates or code) than the unified CCM* implementation. Problem 2: Switching between these modes compromises security unless you keep separate keys, which requires additional storage. Problem 3: CBC-MAC doesn’t provide freshness and is subject to replay attacks. Proposal: Replace security suite with CCM* as described in (replaces r0). (Note on backward compatibility: current specification allows devices to negotiate security, falling back to ‘no security’ as required.) PAR Compliance: “remove inflexible security use”

doc.: IEEE Submission November 18, 2004 Poor & Struik / Ember & CerticomSlide 5 #30: What fields are authenticated? Problem: The IEEE spec is ambiguous or unclear as to what components of a packet are subject to authentication. Proposal: Authenticate MAC header and MAC payload, i.e. everything except the FCS. (Refer to figure 34 in ). PAR Compliance: Resolving ambiguities. Guiding principle: - contiguous frame portions are authenticated, resp. encrypted

doc.: IEEE Submission November 18, 2004 Poor & Struik / Ember & CerticomSlide 6 Details of frame protection (1) Option 1: Aux Security Frame Header as extension of MHR a  b 

doc.: IEEE Submission November 18, 2004 Poor & Struik / Ember & CerticomSlide 7 Details of frame protection (2) Option 2: Aux Security Frame Header right ahead of Payload field

doc.: IEEE Submission November 18, 2004 Poor & Struik / Ember & CerticomSlide 8 Details of frame protection (3) AttributeOption 1Option 2 Security: Encrypt Bcn Pending Address Field YESNO Processing: Availability security material required for decryption Early, since on MHR boundary (allows minimal decryption delays) Late, since just prior to frame payload (maximizes decryption delays) Processing: Avoidance frame type discrimination YESNO Processing: Similarity to handling MHR YESNO Processing: Similarity to security handling For Data FramesFor all frame types Esthetics:Beauty pageantLess appealing

doc.: IEEE Submission November 18, 2004 Poor & Struik / Ember & CerticomSlide 9 Details of frame protection (4) Proposal: Adopt frame protection, Option 1b. PAR Compliance: Resolving ambiguities.

doc.: IEEE Submission November 18, 2004 Poor & Struik / Ember & CerticomSlide 10 Eliminate Key Sequence Counter Problem: In practice, Key Sequence Counter serves no useful function (is always fixed at 0), and generates one byte overhead in each security-enabled frame. Proposal: Eliminate Key Sequence Counter. This increases over the air efficiency, reduces the size of the ACL tables, simplifies processing in CCM. (Note on backward compatibility: If this change is introduced as part of CCM* update, there will be no backward compatibility issue.) PAR compliance: Removing unnecessary complexity, reduce MAC overhead, MAC header compression.

doc.: IEEE Submission November 18, 2004 Poor & Struik / Ember & CerticomSlide 11 #44: Security Endianess Clarification Problem: The definition of Least Significant Bit and Most Significant Bit is inconsistent between Section 7.6 and Annex B. Solution: Integers that are communicated over the air are represented as octet strings, in lowest-octet-first order and lowest- bit-first order. PAR compliance: Resolve ambiguities.

doc.: IEEE Submission November 18, 2004 Poor & Struik / Ember & CerticomSlide 12 Broadcast Encryption Problem: Broadcast encryption does not provide freshness when using the default (broadcast) key, making the system subject to replay attacks. Proposal: Implement fix as described in document Receiver keeps track of the frame counter for each device sending to it using default key, similar to what is currently done for peer-to-peer traffic (which uses peer-to-peer keys). PAR Compliance: remove inflexible key usage, fix security holes, remove ambiguities The frame counter element and the explicit key identification part of the proposal are covered by 13, resp. 17

doc.: IEEE Submission November 18, 2004 Poor & Struik / Ember & CerticomSlide 13 Which Key to use for Peer to Peer Problem: Node A may have a shared key to use with Node B. If node B lacks that shared key, it will try to use the default key (aka broadcast key) when receiving a packet from Node A, resulting in a decryption failure. Higher level code cannot determine why the decryption failed. Proposal: Explicitly identify key in a Key Identification Field in the Security Control field, if the key is not a function of source and destination device. PAR compliance: remove inflexible key usage, remove ambiguities, reduce complexities

doc.: IEEE Submission November 18, 2004 Poor & Struik / Ember & CerticomSlide 14 Dynamic protection levels Problem: Nodes can only derive applicable security/protection level from statically maintained information, thus leading to unworkable broadcast encryption (if recipients have different security expectations) and high-cost system set-up Proposal 1: Differentiate applicable protection level on frame-by- frame basis; Proposal 2: Allow acceptance of incoming frames depending on minimum required protection level (this may depend on frame type and command type) Proposal 3: Allow the communication of expected protection levels between devices, by incorporating this in the Security Control Field (this level will be passed to higher layer, who may act on this) PAR compliance: remove inflexible key usage, reduce complexities, reduce cost, reduce latency

doc.: IEEE Submission November 18, 2004 Poor & Struik / Ember & CerticomSlide 15 Group keying and multicast Problem: secure broadcast is not possible, if devices would change key over lifetime; secure multicast is also not possible Proposal 1: Incorporate secure broadcast over network’s lifetime; Proposal 2: incorporate secure multicast (and unsecured multicast) See also PAR compliance: remove inflexible key usage, reduce complexities, reduce key storage cost, reduce latency, incorporate multicast See also b, Slides 6-8

doc.: IEEE Submission November 18, 2004 Poor & Struik / Ember & CerticomSlide 16 Compress security overhead if possible Problem: security overhead is substantial (currently 5 bytes per secured frame). Proposal 1: reduce frame counter overhead from 4 to 2 bytes per frame Proposal 2: piggyback on DSN entry for reduction of frame counter size by 1 further octet (thus reducing this to 1) Proposal 3: allow automatic resynchronization See also 02/474r2 and (slight impact on frame receipt) PAR compliance: remove security overhead, reduce battery usage at no computational cost (1 integer increment only), eliminate risk of Denial of Service attack by insiders (!)

doc.: IEEE Submission November 18, 2004 Poor & Struik / Ember & CerticomSlide 17 Centralized frame counters Problem: frame counters depend on device and key, thus invoking quite a big key storage cost (Example: 16 RFD talk with coordinator using n versions of broadcast key  16 X n X 4=64 n bytes for frame counters) Proposal: centralize frame counters, such as to have these depend on device only (this requires #stored frame counter = # devices sending) PAR compliance: reduce storage requirements keying material