Group Key Management Architecture Howie Weiss NASA/JPL/SPARTA hsw@sparta.com

Types of Key Management Manual key generation & distribution Hardcopy, paper tape, key cards, floppy disks, magnetic tape Hand carried and manually loaded Electronic key generation & distribution EKMS (electronic key management system) LMD/KP (local KPs, dial-up to download keys) KDC (e.g., STU-III Central Facility, STU-II Bellfield) Public Key Key agreements between key pairs Public/private key negotiation to establish symmetric key Group Key Generate, distribute, manage keys and policies for a group of systems

We Gotta Get Away From This… Bank of KW-26s in service from ‘60s – ‘80s.

A Bit Better …. Key order processing Electronic generation & dist FIREFLY generation Seed Key conversion CRL OTAR Central Office of Record Phys key dist Elect key dist Key generation Key ordering KOK-22 Key Processor Local key generation Digital signature KYK-13 KOI-18 CYZ-10 New fill devices

IPsec Requirements IPsec “lives” between the network (IP) layer and transport (TCP or UDP) layer Requires a “security policy database” to determine what services are applied to what connections E.g., connection A-B requires encryption+auth E.g., connection C-D requires encryption E.g., all other connections require no security services Crypto keys Manually loaded, or IKEv2 negotiated Policy: Manually loaded in each individual device, or RFC 4807 (IPsec Security Policy Database Configuration MIB) IPsec Security Policy IPsec Action MIB (ID) IPsec Security Policy IKE Action MIB (ID)

Application Layer Security A la SSL/TLS (but TBD) Requires keys SSL/TLS would use Diffie-Helman key negotiation which may not be possible for Cx flight systems. Pre-shared symmetric keys a la RFC 4279. e.g., TLS_PSK_WITH_AES_128_CBC_SHA Requires policy SSL/TLS really has no policy database “https” == encrypt connection Mutual authentication (dual cert) vs. server-side authentication (single cert) Messaging security Pub/Sub messaging security mechanims

Conundrums Keys are required by heterogeneous systems Policy is required by heterogeneous systems Ground/Mission systems have good, broadband connectivity Space systems may have intermittent, lossy, and limited bandwidth connectivity

So….. Public Key technology and Electronic Key Distribution are the ‘modern’ ways to generate and distribute keys, but……. Not a problem for ground-based systems with good connectivity Can be a problem for space-based systems with not so good connectivity

Therefore….. How do we combine ‘modern’ electronic key distribution with varying types of connectivity across the entire program? 1) go with PKI and hope for the best (a la cellular phone systems)? 2) use only PKI in control centers and do something else for space? 3) use symmetric keys everywhere and deliver them manually (e.g., floppy, flash drive, paper tape)? 4) LMD/KP local site generation and manual loading? 5) Central key distribution center (KDC) that all systems must contact to obtain keys? 6) ‘Group keying’ techniques doing what’s best and available for the given part of the system?

Group Key Overview From RFC 2094: “GKMP combines techniques developed for creation of pair-wise keys with techniques used to distribute keys from a KDC (i.e., symmetric encryption of keys) to distribute symmetric key to a group of hosts.” Defined in RFC 4535 - GSAKMP: Group Secure Association Key Management Protocol Parameters for a given GSAKMP group are provided in the Group Security Policy Token, whose structure is defined in RFC 4534

Group Security Use of cryptography to protect data shared between multiple endpoints Encryption of data Network layer Application layer Key management for groups Definition of mutual suspicious key exchanges for groups Security policy and policy dissemination Key creation and dissemination Security management for groups Scalability of security infrastructure Coalitions and diverse mechanisms Low latency group establishment Management of group membership

GSAKMP Entities Group Owner responsible for creating the security policy rules for a group and expressing these in the policy token Group Controller/Key Server responsible for creating/obtaining keys, maintaining the keys, and enforcing the group policy by granting access to potential Group Members (GMs) in accordance with the policy token In a distributed mode, there can be multiple subordinate GC/KSs Group Member responsible for verifying key and policy disseminations and for protecting group data according to group policy

Group Controller/Key Server GSAKMP Architecture Group Owner Policy Group Controller/Key Server [Keys] Key Infrastructure Sub GC/KS Sub GC/KS Sub GC/KS Sub GC/KS Policy & Keys M M M M M M M M

Group Trust Group policy vs. Peer Policies Alice Bob Sue ? A and B have 1st hand knowledge A and S have 1st hand knowledge B and S have never communicated Who owns the data? How can S trust B? B trust S? Was the A to B key exchange as strong As the A to S exchange? Will A and B protect the data equally? Is A authorized to distribute key? Is A controlling the group? Alice Bob A and B have 1st hand knowledge A and B are sharing their own data A and B participate in key creation

GSAKMP / Group Policy All actors must prove they are authorized Must support mutual suspicion All actors must prove they are authorized Policy creation authorities Key dissemination Key possession Group management Must provide flexible group definitions Rule based access control Limited only by infrastructures available Mechanism flexibility Algorithms Infrastructures Protocols Operational flexibility DoS controls Protocol latency controls

GSAKMP - Group Joins Group Controller Defines group policy Creates initial keys Members join the group Can become subordinate GCs Can be key consumers Member can get keys from GC or S-GC Group membership is managed using group cryptography One message can reconfigure membership of receivers Member Member Member Member Member Member

Binary Key Trees A B C D E F 1 2 3 4 5 6 7 8 1,C,A 2,C,A 3,DA 4,DA 1 2 3 4 5 6 7 8 1,C,A 2,C,A 3,DA 4,DA 5,E,B 6,E,B 7,F,B 8,F,B

Bottom Line GSAKMP can provide key and policy management for scalable groups (large or small). Group members can perform a full, negotiated group join or can just receive keys from a group or sub-group controller Combines the best of public key, symmetric key, and policy management. Can provide keys (with work on the host side) to applications, IPsec (using multicast SAs), and even bulk encryptors if they can be controlled by the system.

By The Way….. Cisco is using an alternative group key (GDOI – RFC 3547) to more easily establish VPN groups.