ISAKMP ● RFC 2408 ● Internet Security Association & Key Management Protocol ● Protocol –...

ISAKMP

● RFC 2408

● Internet Security Association & Key Management Protocol

● Protocol

– Establish, modify, and delete SAs

– Negotiate crypto keys

● Procedures

– Authentication of peers

– Threat mitigation

ISAKMP

● Defines procedures and packet formats to deal with SAs

and keys

● Provides a framework for secure communication on the

Internet

● Does not specify algorithms, formats, or protocols

● ISAKMP is a framework in which a specific secure

communication definition can be implemented

ISAKMP

● Security Associations

● Authentication

● Public Key Cryptography

● Protection

● DoS – Anti-Clogging

● Hijacking a connection

● Man in the middle attacks

ISAKMP Terminology

● DOI – Domain Of Interpretation: defines payload

formats, exchange types, naming conventions

IISAKMP – Phases

● Phase 1: Two entities agree on how to protect further

negotiation traffic. They negotiate an ISAKMP SA for

an authenticated and secure channel

● Phase 2:The phase 1 secure channel is used to negotiate

security services for IPSec.

ISAKMP Header

Next Payload Exchange Type

Initiator Cookie

Message ID

Length

Responder Cookie

MajorVersion

MinorVersion Flags

Header Fields

● Initiator Cookie (8 octets) – Cookie of entity that initiated SA

establishment, notification or deletion.

● Responder Cookie (8 octets) – Cookie of the responder

● Next Payload (1 octet) – Type of first payload

● Major/Minor Version (4 bits each) – Version of ISAKMP in use

● Exchange Type (1 octet) – Type of exchange being used

● Flags (1 octet) – More stinking flags, encrypt, commit authentication

only

● Message ID (4 octets) – Unique ID to identify things in Phase 2

● Length (4 octets) – Length of total message (headers + payloads)

Next Payload Types

Next Payload Type Value

NONE 0

SA 1

Proposal 2

Transform 3

Key Exchange 4

Identification 5

Certificate 6

Cert Request 7

Next Payload Type Value

Hash 8

Signature 9

Nonce 10

Notification 11

Delete 12

Vendor ID 13

Reserved 14 –

127

Private Use 128 -

255

Exchange Types

Exchange Type

Value

NONE 0

Base 1

Id Protection 2

Auth Only 3

Aggressive 4

Informational 5

Exchange Type Value

ISAKMP Future Use 6 - 31

DOI Specific Use 32 –

127

Private Use 128 -

255

Generic Payload Header

Next Payload Payload Length

Payload Data

Reserved

SA Payload

Next Payload Payload Length

Situation

Reserved

Domain of Interpretation (DOI)

~

DOI (4 octets) – Identifies the DOI under which this negotiation is taking place. A

value of 0 (zero) during Phase 1 specifies a Generic ISAKMP SA

which can be used for any protocol during Phase 2.

Situation - A DOI-specific field that identifies the situation under which this

negotiation is taking place.

Proposal Payload

Next Payload Payload Length

SPI (variable)

Reserved

Proposal No. Proposal ID SPI Size No. of Transforms

Proposal Payload

●Payload Length (2 octets) – Length is octets of the entire Proposal payload

including the generic payload header, the Proposal payload, and all

Transform payloads associated with this proposal.

●Proposal No. - Identifies the Proposal number for the current payload.

●Proposal ID – Specifies the protocol identifier such as IPSEC ESP, IPSEC

AH, OSPF, TLS, etc.

●SPI Size – Length in octets of the SPI as defined by the Protocol ID.

●No. of Transforms – Specifies the number of transforms for the proposal.

●SPI (variable) – The sending entity's SPI.

Transform Payload

Next Payload Payload Length

SA Attributes

Reserved

Transform No. Transform ID Reserved2

~

Transform Payload

●Payload Length (2 octets) – Length is octets of the current payload,

including the generic payload header, Transform values, and all SA

attributes

●Transform No. - Identifies the Transform number for the current payload.

●Transform ID – Specifies the Transform identifier fmor the protocol within

the current proposal.

●Reserved 2 (2 octets) – Set to zero.

●SA Attributes (Variable length) – SA attributes should be represented using

the Data Attributes format.

Key Exchange Payload

Next Payload Payload Length

Key Exchange Data

Reserved

~

Key Exchange Data (variable length) – Data required to generate a session key.

This data is specified by the DOI and the associated Key

Exchange algorithm.

Certificate Payload

Next Payload Payload Length

Key Exchange Data

Reserved

~

Cert Encoding (1 octet) – Indicates the type of certificate contained in the

Certificate field.

Cert Encoding

Certificate Types

Certificate Type

Value

NONE 0

PKCS #7 1

PGP Certificate 2

DNS Signed Key 3

X.509 Cert - Signature 4

X.509 Cert – Key Exchange 5

Certificate Type Value

Kerberos Token 6

Cert Revoc List 7

Authority Revoc List 8

SPKI Cert. 9

X.509 Cert – Attribute 10

Reserved 11 -

255

Other Payloads

Next Payload Payload Length

Hash Data

Reserved

~

Next Payload Payload Length

Signature Data

Reserved

~

Next Payload Payload Length

Nonce Data

Reserved

~

Notification Payload

Next Payload Payload Length

SPI

Reserved

Protocol ID SPI Size Notify Message Type

~

DOI

Notification Data~

Notify Messages

Errors Value

INVALID-PAYLOAD-TYPE 1 DOI-NOT-SUPPORTED 2 SITUATION-NOT-SUPPORTED 3 INVALID-COOKIE 4 INVALID-MAJOR-VERSION 5 INVALID-MINOR-VERSION 6 INVALID-EXCHANGE-TYPE 7 INVALID-FLAGS 8 INVALID-MESSAGE-ID 9 INVALID-PROTOCOL-ID 10 INVALID-SPI 11 INVALID-TRANSFORM-ID 12 ATTRIBUTES-NOT-SUPPORTED 13 NO-PROPOSAL-CHOSEN 14 BAD-PROPOSAL-SYNTAX 15

Errors Value

PAYLOAD-MALFORMED 16 INVALID-KEY-INFORMATION 17 INVALID-ID-INFORMATION 18 INVALID-CERT-ENCODING 19 INVALID-CERTIFICATE 20 CERT-TYPE-UNSUPPORTED 21 INVALID-CERT-AUTHORITY 22 INVALID-HASH-INFORMATION 23 AUTHENTICATION-FAILED 24 INVALID-SIGNATURE 25 ADDRESS-NOTIFICATION 26 NOTIFY-SA-LIFETIME 27 CERTIFICATE-UNAVAILABLE 28 UNSUPPORTED-EXCHANGE-TYPE 29 UNEQUAL-PAYLOAD-LENGTHS 30 RESERVED (Future Use) 31 - 8191 Private Use 8192 – 16383

ISAKMP Message Construction

NP = Nonce KE Payload Length

Key Exchange Data

Reserved

NP = 0 Nonce Payload Length

Nonce Data

Reserved

NP = KE Exchange Type

Initiator Cookie

Message ID

Total Message Length

Responder Cookie

MajorVersion

MinorVersion

Flags

Proposal Syntax

Proposal #

Transform #

Transform #

Proposal #

Transform #

Proposals with the same Proposal

number are taken as a logical AND.

Proposals with different numbers are

taken as a logical OR.

Different Transform within a proposal

are taken as a logical OR.

Proposal Example

Proposal 1: AH

Transform 1: HMAC-SHA

Transform 2: HMAC-MD5

Proposal 2: ESP

Transform 1: 3DES with HMAC-SHA

Transform 2: 3DES with HMAC-MD5

Transform 3: AES with HMAC-SHA-256

Proposal 3: ESP

Transform 1: 3DES with HMAC-SHA

Proposal 4: PCP

Transform 1: LZS

Exchange Types

Exchange Type

Value

NONE 0

Base 1

Id Protection 2

Auth Only 3

Aggressive 4

Informational 5

Exchange Type Value

ISAKMP Future Use 6 - 31

DOI Specific Use 32 –

127

Private Use 128 -

255

Base Exchange

Initiator Direction Responder Note

Header, SA, Nonce => Begin ISAKMP-SA

negotiation

<= HDR, SA, Nonce Basic SA agreed

upon

Header, KE, Idii, Auth => Key generated by responder

Initiator Ident verified

<= HDR, KE, Idir, Auth Responder Ident verified

Initiator key generated, SA est.