G. Appenzeller
L. Martin
S/MIME Working Group M. Schertler
Internet Draft Voltage Security
Expires: September 2007 March 2007
Identity-based Encryption Architecture
<draft-ietf-smime-ibearch-03.txt>
Status of this Document
By submitting this Internet-Draft, each author represents that any
applicable patent or other IPR claims of which he or she is aware
have been or will be disclosed, and any of which he or she becomes
aware will be disclosed, in accordance with Section 6 of BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html
Abstract
This document describes the security architecture required to implement
identity-based encryption, a public-key encryption technology that uses
a user's identity to generate their public key.
Appenzeller, et al. Expires September 2007 [Page 1]
Internet-Draft IBE Architecture March 2007
Table of Contents
1. Introduction...................................................3
1.1. Terminology...............................................3
2. Identity-based Encryption......................................3
2.1. Overview..................................................3
2.2. Sending a Message that is Encrypted Using IBE.............4
2.2.1. Sender Obtains Recipient's IBE Public Parameters.....5
2.2.2. Construct and Send IBE-encrypts Message..............5
2.3. Receiving and Viewing an IBE-encrypted Message............6
2.3.1. Recipient Obtains IBE Public Parameters from PPS.....7
2.3.2. Recipient Obtains IBE Private Key from PKG...........7
2.3.3. Recipient Decrypts IBE-encrypted Message.............7
3. Public Parameter Lookup........................................8
3.1. Request Method............................................9
3.2. Parameter and Policy Format...............................9
4. Private Key Request Protocol..................................12
4.1. Overview.................................................12
4.2. Private Key Request......................................12
4.3. Request Structure........................................13
4.4. Authentication...........................................13
4.5. Server Response Format...................................14
4.6. Response Containing a Private Key........................14
4.7. Responses Containing a Redirect..........................15
4.8. Responses Indicating an Error............................16
5. ASN.1 Module..................................................17
6. Security Considerations.......................................19
6.1. Attacks that are outside the scope of this document......19
6.2. Attacks that are within the scope of this document.......20
6.2.1. Attacks to which the protocols defined in this document
are susceptible............................................20
7. IANA Considerations...........................................21
8. References....................................................22
8.1. Normative References.....................................22
Authors' Addresses...............................................24
Intellectual Property Statement..................................24
Disclaimer of Validity...........................................25
Copyright Statement..............................................25
Acknowledgment...................................................25
Appenzeller, et al. Expires September 2007 [Page 2]
Internet-Draft IBE Architecture March 2007
1. Introduction
This document describes the security architecture required to
implement identity-based encryption, a public-key encryption
technology that uses a user's identity as a public key.
1.1. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [KEY].
2. Identity-based Encryption
2.1. Overview
Identity-based encryption (IBE) is a public-key encryption technology
that allows a public key to be calculated from an identity and the
corresponding private key to be calculated from the public key.
Calculation of both the public and private keys in an IBE-based
system can occur as needed, resulting in just-in-time key material.
This contrasts with other public-key systems [P1363], in which keys
are generated randomly and distributed prior to secure communication
commencing. The ability to calculate a recipient's public key, in
particular, eliminates the need for the sender and receiver in an
IBE-based messaging system to interact with each other, either
directly or through a proxy such as a directory server, before
sending secure messages.
This document describes an IBE-based messaging system and how the
components of the system work together. The components required for a
complete IBE messaging system are the following:
o A Private-key Generator (PKG). The PKG contains the
cryptographic material, known as a master secret, for
generating an individual's IBE private key. A PKG accepts an
IBE user's private key request and after successfully
authenticating them in some way returns the IBE private key.
o A Public Parameter Server (PPS). IBE System Parameters
include publicly sharable cryptographic material, known as
IBE public parameters, and policy information for the PKG. A
PPS provides a well-known location for secure distribution
of IBE public parameters and policy information for the IBE
PKG.
Appenzeller, et al. Expires September 2007 [Page 3]
Internet-Draft IBE Architecture March 2007
A logical architecture would be to have a PKG/PPS per a name space,
such as a DNS zone. The organization that controls the DNS zone would
also control the PKG/PPS and thus the determination of which PKG/PSS
to use when creating public and private keys for the organization's
members. In this case the PPS URI can be uniquely created by the form
of the identity that it supports. This architecture would make it
clear which set of public parameters to use and where to retrieve
them for a given identity (i.e. an RFC822 address).
IBE encrypted messages can use standard message formats, such as the
Cryptographic Message Syntax [CMS]. How to use IBE with CMS is
defined in [IBECMS].
Note that IBE algorithms are used only for encryption, so if digital
signatures are required they will need to be provided by an
additional mechanism.
2.2. Sending a Message that is Encrypted Using IBE
In order to send an encrypted message, an IBE user must perform the
following steps:
1. Obtain the recipient's public parameters
The recipient's IBE public parameters allow the creation of
unique public and private keys for the recipient's domain. A
user of an IBE system is capable of calculating the public key
of a recipient after he obtains the public parameters for their
IBE system. Once the public parameters for a recipient's domain
are obtained, IBE-encrypted messages can be sent to all members
of that domain.
2. Construct and Send IBE-encrypted Message
All that is needed, in addition to the IBE public parameters,
is the recipient's identity in order to generate their public
key for use in encrypting messages to them. When this identity
is the same as the identity that a message would be addressed
to, then no more information is needed from a user to send
someone a secure message then is needed to send them an
unsecured message. This is one of the major benefits of an IBE-
based secure messaging system. Examples of identities can be an
individual, group, or role identifiers.
Appenzeller, et al. Expires September 2007 [Page 4]
Internet-Draft IBE Architecture March 2007
2.2.1. Sender Obtains Recipient's IBE Public Parameters
The sender of a message obtains the IBE public parameters that he
needs for calculating the IBE public key of the recipient from a PPS
that is hosted at a well-known URI. The IBE public parameters contain
all of the information that the sender needs to create an IBE-
encrypted message except for the identity of the recipient. Section 3
of this document describes the URI where a PPS is located, the format
of IBE public parameters, and how to obtain them. The URI from which
users obtain IBE public parameters MUST be authenticated in some way;
PPS servers MUST support TLS 1.1 [TLS] to satisfy this requirement.
Section 3 also describes the way in which identity formats are
defined and a minimum interoperable format that all PPSs and PKGs
MUST support. This step is shown below in Figure 1.
IBE Public Parameter Request
----------------------------->
Sender Public Parameter Server
<-----------------------------
IBE Public Parameters
Figure 1 Requesting IBE Public Parameters
The sender of an IBE-encrypted message selects the PPS and
corresponding PKG based on his local security policy. Different PPSs
may provide public parameters that specify different IBE algorithms
or different key strengths, for example, or require the use of PKGs
that require different levels of authentication before granting IBE
private keys.
2.2.2. Construct and Send IBE-encrypts Message
To IBE-encrypt a message, the sender chooses a content encryption key
(CEK) and uses it to encrypt his message and then encrypts the CEK
with the recipient's IBE public key as described in [CMS]. This
operation is shown below in Figure 2. [IBCS] describes the algorithms
needed to implement two forms of IBE and [IBECMS] describes how to
use the Cryptographic Message Syntax (CMS) to encapsulate the
encrypted message along with the IBE information that the recipient
needs to decrypt the message.
Appenzeller, et al. Expires September 2007 [Page 5]
Internet-Draft IBE Architecture March 2007
CEK ----> Sender ----> IBE-encrypted CEK
^
|
|
Recipient's Identity
and IBE Public Parameters
Figure 2 Using an IBE Public-key Algorithm to Encrypt
2.3. Receiving and Viewing an IBE-encrypted Message
In order to read an encrypted message, a recipient of an IBE-
encrypted message parses the message as described in [IBECMS]. This
gives him the URI he needs to obtain the IBE public parameters
required to perform IBE calculations as well as the identity that was
used to encrypt the message. Next the recipient must carry out the
following steps:
1. Obtain the recipient's public parameters
An IBE system's public parameters allow it to uniquely create
public and private keys. The recipient of an IBE-encrypted
message can decrypt an IBE-encrypted message if he has both the
IBE public parameters and the necessary IBE private key. The
PPS can also provide the URI of the PKG where the recipient of
an IBE-encrypted message can obtain the IBE private keys.
2. Obtain the IBE private key from the PKG
To decrypt an IBE-encrypted message, in addition to the IBE
public parameters the recipient needs to obtain the private key
that corresponds to the public key that the sender used. The
IBE private key is obtained after successfully authenticating
to a private key generator (PKG), a trusted third party that
calculates private keys for users. The recipient receives the
IBE private key over an HTTPS connection.
3. Decrypt IBE-encrypted message
The IBE private key decrypts the CEK (see section 2.2.2). The
CEK is then used to decrypt encrypted message.
The PKG may allow users other than the intended recipient to receive
some IBE private keys. Giving a mail filtering appliance permission
to obtain IBE private keys on behalf of users, for example, can allow
Appenzeller, et al. Expires September 2007 [Page 6]
Internet-Draft IBE Architecture March 2007
the appliance to decrypt and scan encrypted messages for viruses or
other malicious features.
2.3.1. Recipient Obtains IBE Public Parameters from PPS
Before he can perform any IBE calculations related to the message
that he has received, the recipient of an IBE-encrypted message needs
to obtain the IBE public parameters that were used in the encryption
operation. This operation is shown below in Figure 3. The comments in
Section 2.2.1 also apply to this operation.
IBE Public Parameter Request
----------------------------->
Recipient Public Parameter Server
<-----------------------------
IBE Public Parameters
Figure 3 Requesting IBE Public Parameters
2.3.2. Recipient Obtains IBE Private Key from PKG
To obtain an IBE private key, the recipient of an IBE-encrypted
message provides the IBE public key used to encrypt the message and
their authentication credentials to a PKG and requests the private
key that corresponds to the IBE public key. Section 4 of this
document defines the protocol for communicating with a PKG as well as
a minimum interoperable way to authenticate to a PKG that all IBE
implementations MUST support. Because the security of IBE private
keys is vital to the overall security of an IBE system, IBE private
keys MUST be transported to recipients over a secure protocol. PKGs
MUST support TLS 1.1 [TLS] for transport of IBE private keys. This
operation is shown below in Figure 4.
IBE Private Key Request
---------------------------->
Recipient PKG
<----------------------------
IBE Private Key
Figure 4 Obtaining an IBE Private Key
2.3.3. Recipient Decrypts IBE-encrypted Message
After obtaining the necessary IBE private key, the recipient uses
that IBE private key and the corresponding IBE public parameters to
decrypt the CEK. This operation is shown below in Figure 5. He then
Appenzeller, et al. Expires September 2007 [Page 7]
Internet-Draft IBE Architecture March 2007
uses the CEK to decrypt the encrypted message content as specified in
[IBECMS].
IBE-encrypted CEK ----> Recipient ----> CEK
^
|
|
IBE Private Key
and IBE Public Parameters
Figure 5 Using an IBE Public-key Algorithm to Decrypt
3. Public Parameter Lookup
For an identity-based encryption (IBE) system to operate, the sender,
receiver and the private key generator (PKG) must agree on a number
of parameters, specifically:
1. The Public Parameters of the PKG. The public parameters are part
of the encryption (and in some cases decryption) operation of
the IBE system. Generation of public parameters and the master
secret, as well as the mathematical structure of the public
parameters for the BF and BB1 algorithms are described in
[IBCS].
2. The URI of the PKG. Knowledge of this URI allows recipients to
request a private key as described in Section 4 of this
document.
3. The schema to format the identity strings. When issuing a
private key, the PKG often wants to limit who can obtain private
keys. For example for an identity string that contains
"bob@example.com", only the owner of the identity string should
be able to request the private key. To ensure that the PKG can
interpret the identity string for which a private key is
requested, the encryption engine and the PKG have to use the
same schema for identity strings. Identity schemas are described
in [IBECMS]
This section specifies how a component of an IBE system can retrieve
these parameters. A sending or receiving client MUST allow
configuration of these parameters manually, e.g. through editing a
configuration file. However for simplified configuration a client MAY
also implement the PP URI request method described in this document
Appenzeller, et al. Expires September 2007 [Page 8]
Internet-Draft IBE Architecture March 2007
to fetch the system parameters based on a configured URI. This is
especially useful for federating between IBE systems. By specifying a
single URI a client can be configured to fetch all the relevant
parameters for a remote PKG. These public parameters can then be used
to encrypt messages to recipients who authenticate to and retrieve
private keys from that PKG.
The following section outlines the URI request method to retrieve a
parameter block and describes the structure of the parameter block
itself.
3.1. Request Method
The configuration URI SHOULD be an HTTPS URI [HTTP] of the format:
http_URI = "https:" "//" host [ ":" port ] [ abs_path ]
An example URI for ibe system parameters is
https://ibe-0000.example.com/example.com.pem
To retrieve the IBE system parameters, the client SHOULD use the HTTP
GET method as defined in [HTTP]. The request MUST happen over a
secure protocol. The requesting client MUST support TLS 1.1 [TLS].
When requesting the URI the client MUST only accept the system
parameter block if the server identity was verified successfully by
TLS 1.1.
A successful GET request returns in its body the Base64 encoding of
the DER-encoded [DER] ASN.1 structure that is described in the next
section.
3.2. Parameter and Policy Format
The IBE System parameters are a set of
IBESysParams ::= SEQUENCE {
version INTEGER { v2(2) },
districtName UTF8String,
districtSerial INTEGER,
validity Validity,
ibePublicParameters IBEPublicParameters,
ibeIdentitySchema OBJECT IDENTIFIER,
ibeParamExtensions IBEParamExtensions
}
Appenzeller, et al. Expires September 2007 [Page 9]
Internet-Draft IBE Architecture March 2007
The version specifies the version of the IBESysParams format. For the
format described in this document it MUST be set to 2. The district
name is an UTF8String that MUST be a valid domain name as defined by
[DOM]. The districtSerial is a serial number that represents a unique
set of IBE public parameters. If new parameters are published for a
district, it MUST be increased to a number greater than the
previously-used serial number.
The validity period or lifetime of a specific instance of the
IBESysParams is defined as follows:
ValidityPeriod ::= SEQUENCE {
notBefore GeneralizedTime,
notAfter GeneralizedTime
}
A client MUST verify that the date on which it utilizes the IBE
system parameters falls between the notBefore time and the notAfter
times of the IBE system parameters and SHOULD not use the parameters
if they do not.
IBE system parameters MUST be regenerated and republished whenever
the ibePublicParameters, ibeIdentitySchema, or ibeParamExtensions
change for a district. A client SHOULD refetch the IBE system
parameters at an application configurable interval to ensure that it
has the most current version on the IBE system parameters.
It is possible to create identities for use in IBE that have a time
component, as described in [IBECMS]. If such an identity is used, the
time component of the identity MUST fall between the notBefore time
and the notAfter times of the IBE system parameters.
IBEPublicParameters is a set of public parameters that correspond to
IBE algorithms that the PKG associated with this district
understands.
IBEPublicParameters ::= SEQUENCE OF IBEPublicParameter
IBEPublicParameter ::= SEQUENCE {
ibeAlgorithm OBJECT IDENTIFIER,
publicParameterData OCTET STRING
}
The ibeAlgorithm OID specifies an IBE algorithm. The
publicParameterData is a DER encoded ASN.1 structure that contains
the actual cryptographic parameters. Its specific structure depends
on the algorithm. The OIDs for two IBE algorithms, the Boneh-Franklin
Appenzeller, et al. Expires September 2007 [Page 10]
Internet-Draft IBE Architecture March 2007
and Boneh-Boyen algorithms and their publicParameterData structures
are defined in [IBCS].
The IBESysParams of a district MUST contain at least one algorithm
and MAY contain several algorithms. It MUST NOT contain two or more
IBEPublicParameter entries with the same algorithm. A client that
wants to use IBESysParams can chose any of the algorithms specified
in the publicParameterData structure. A client MUST implement at
least the Boneh-Franklin algorithm and MAY implement the Boneh-Boyen
and other algorithms. If a client does not support any of the
supported algorithms it MUST generate an error message and fail.
ibeIdentitySchema is an OID that defines the type of identities that
are used with this district. The OIDs and the required and optional
fields for each OID are described in [IBECMS].
IBEParamExtensions is a set of extensions that can be used to define
additional parameters that particular implementations may require.
IBEParamExtensions ::= SEQUENCE OF IBEParamExtension
IBEParamExtension ::= SEQUENCE {
ibeParamExtensionOID OBJECT IDENTIFIER,
ibeParamExtensionValue OCTET STRING
}
The contents of the octet string are defined by the specific
extension type. The System Parameters of a district MAY have any
number of extensions, including zero.
The IBEParamExtension pkgURI defines the URI of the Private Key
Generator of the district. If the PKG is publicly accessible, this
extension SHOULD be present to allow the automatic retrieval of
private keys for recipients of encrypted messages. For this extension
the OCTET STRING contains a UTF8String with the URI of the key
server.
Appenzeller, et al. Expires September 2007 [Page 11]
Internet-Draft IBE Architecture March 2007
ibeParamExt OBJECT IDENTIFIER ::= {
ibcs ibcs3(3) parameter-extensions(2)
}
pkgURI OBJECT IDENTIFIER ::= { ibeParamExt pkgURI(1) }
4. Private Key Request Protocol
4.1. Overview
In an identity-based encryption (IBE) system messages are encrypted
using a public key that is locally calculated from public parameters
and a user`s identity and decrypted using a private key that
corresponds to the user`s public key. These private keys are
generated by a private key generator (PKG) based on a global secret
called a master secret.
When requesting a private key, a client has to transmit two
parameters:
1. The identity for which it is requesting a key
2. Authentication credentials for the individual requesting the
key
These two are often not the same as a single user may have access to
multiple aliases. For example an email user may have access to the
keys that correspond to two different email addresses, e.g.
bob@example.com and bob.smith@example.com.
This section defines the protocol to request private keys, a minimum
user authentication method for interoperability, and how to pass
authentication credentials to the server. It assumes that a client
has already determined the URI of the PKG. This can be done from
hints included in the IBE message format [IBECMS] and the system
parameters of the IBE system.
4.2. Private Key Request
To request a private key, a client performs a HTTP POST method as
defined in [HTTP]. The request MUST happen over a secure protocol.
The requesting client MUST support TLS 1.1 [TLS]. When requesting the
URI the client MUST verify the server certificate [RFC2818], and MUST
abort the key request if the server certificate verification of the
TLS connection fails. Doing so is critical to protect the
authentication credentials and the private key against man-in-the-
Appenzeller, et al. Expires September 2007 [Page 12]
Internet-Draft IBE Architecture March 2007
middle attacks when it is transmitted from the key server to the
client.
4.3. Request Structure
The POST method contains in its body the following XML structure:
<ibe:request xmlns:ibe="urn:ietf:params:xml:ns:ibe">
<ibe:header>
<ibe:client version="clientID"/>
</ibe:header>
<ibe:body>
<ibe:keyRequest>
<ibe:algorithm>
<oid> algorithmOID </oid>
</ibe:algorithm>
<ibe:id>
ibeIdentityInfo
</ibe:id>
</ibe:keyRequest>
</ibe:body>
</ibe:request>
A <ibe:request> SHOULD include a <ibe:clientID> element that
identifies the client type and client version.
A key request MUST contain a valid ibeIdentityInfo that the private
key is requested for. This identity is the base64 encoding of the DER
encoding of the ASN.1 structure IBEIdentityInfo as defined in
[IBECMS].
A key request MUST contain a <ibe:algorithm> element that contains a
XER encoded ASN.1 OBJECT IDENTIFIER that identifies the algorithm for
which a key is requested. OIDs for the BB1 and BF algorithms are
listed in [IBCS].
A client MAY include optional additional XML elements in the
<ibe:body> part of the key request.
4.4. Authentication
When a client requests a key from a PKG, the PKG SHOULD authenticate
the client before issuing the key. Authentication may either be done
through the key request structure or as part of the secure transport
protocol.
Appenzeller, et al. Expires September 2007 [Page 13]
Internet-Draft IBE Architecture March 2007
A client or server implementing the request protocol MUST support
HTTP Basic Auth as described in [AUTH]. A client and server SHOULD
also support HTTP Digest Auth as defined in [AUTH].
For authentication methods that are not done by the transport
protocol, a client MAY include additional authentication information
in xml elements in the body part of the key request. If a client does
not know how to authenticate to a server, the client MAY send a key
request without authentication information. If the key server
requires the client to authenticate externally, it MAY reply with a
201 response code as defined below to redirect the client to the
correct authentication mechanism.
4.5. Server Response Format
The key server replies to the HTTP request with an HTTP response. If
the response contains a client error or server error status code, the
client MUST abort the key request and fail.
If the PKG replies with a HTTP response that has a status code
indicating success, the body of the reply MUST contain the following
XML structure:
<ibe:response xmlns:ibe="urn:ietf:params:xml:ns:ibe">
<ibe:responseType value="responseCode"/>
<ibe:body>
bodyTags
</ibe:body>
</ibe:response>
The responseCode describes the type of response from the key server.
The list of currently defined response codes is:
100 KEY_FOLLOWS
101 RESERVED
201 FOLLOW_ENROLL_URI
300 SYSTEM_ERROR
301 INVALID_REQUEST
303 CLIENT_OBSOLETE
304 AUTHORIZATION DENIED
4.6. Response Containing a Private Key
If the key request was successful, the key server responds with KEY
FOLLOWS, and the <ibe:body> must contain a <ibe:privateKey> tag with
a valid private key. An example of this is shown below.
Appenzeller, et al. Expires September 2007 [Page 14]
Internet-Draft IBE Architecture March 2007
<ibe:response xmlns:ibe="urn:ietf:params:xml:ns:ibe">
<ibe:responseType value="100"/>
<ibe:body>
<ibe:privateKey>
privateKey
</ibe:privateKey>
</ibe:body>
</ibe:response>
The privateKey is the Base64 [B64] encoding of the DER encoding of
the following ASN.1 structure:
IBEPrivateKeyReply ::= SEQUENCE {
pkgIdentity IBEIdentityInfo,
pgkAlgorithm OBJECT IDENTIFIER
pkgKeyData OCTET STRING
pkgOptions SEQUENCE OF Extensions
}
The pkgIdentity is an IBEIdentityInfo structure as defined in
[IBECMS]. It MUST be identical to the IBEIdentityInfo structure that
was sent in the key request.
The pkgAlgorithm is an OID that identifies the algorithm of the
returned private key. The OIDs for the BB and BF algorithms are
defined in [IBCS].
The pkgKeyData is an ASN.1 structure that contains the actual private
key. Private-key formats for the BB and BF algorithms are defined in
[IBCS].
A server MAY pass back additional information to a client in the
pkgOptions structure. The contents of the structure are defined in
the ASN.1 module below.
4.7. Responses Containing a Redirect
A Key Server MAY support authenticating user to external
authentication mechanism. If this is the case, the server replies to
the client with response code 201 and the body MUST contain a
<ibe:location> element that specifies the URI of the authentication
mechanism. An example is shown below.
Appenzeller, et al. Expires September 2007 [Page 15]
Internet-Draft IBE Architecture March 2007
<ibe:response xmlns:ibe="urn:ietf:params:xml:ns:ibe">
<ibe:responseType value="201"/>
<ibe:body>
<ibe:location URI="http://www.example.com/enroll.asp"/>
</ibe:body>
</ibe:response>
The client can now contact the authentication mechanism to obtain
authentication credentials. Once the client has obtained the
credential, it sends a new key request to the PKG with the correct
authentication credentials contained in the request.
4.8. Responses Indicating an Error
If the server replies with a 3xx error code, the client MUST abort
the request and discard any data that is part of the response.
The meaning of the response codes for errors is as follows:
300 - This indicates an internal server error of the PKG.
301 - The request to the server is invalid or the server is not able
to fulfill this type of request.
303 - The server is not able to serve key requests for this type of
client. A client with a newer version of the protocol is required.
304 - The key request was processed correctly, but the authentication
credentials provided by the user were invalid, could not be verified,
or do not allow access to keys for this identity.
Appenzeller, et al. Expires September 2007 [Page 16]
Internet-Draft IBE Architecture March 2007
5. ASN.1 Module
IBE1-module { joint-iso-itu(2) country(16) us(840) organization(1)
identicrypt(114334) ibcs(1) cms(4) module(5) version(1)
}
DEFINITIONS IMPLICIT TAGS ::= BEGIN
IBEOtherRecipientInfo ::= SEQUENCE {
oriType OBJECT IDENTIFIER,
oriValue IBERecipientInfo
}
ibeORIType OBJECT IDENTIFIER ::= { joint-iso-itu(2) country(16)
us(840) organization(1) identicrypt(114334) ibcs(1)
cms(4) ori-oid(1)
}
IBERecipientInfo ::= SEQUENCE {
cmsVersion INTEGER { v0(0) },
keyFetchMethod OBJECT IDENTIFIER,
recipientIdentity IBEIdentityInfo,
serverInfo SEQUENCE OF OIDValuePairs OPTIONAL,
encryptedKey EncryptedKey
}
IBEIdentityInfo ::= SEQUENCE {
District UTF8STRING,
Serial INTEGER,
identitySchema OBJECT IDENTIFIER,
identityData OCTET STRING
}
OIDValuePairs ::= SEQUENCE {
fieldID OBJECT IDENTIFIER,
fieldData OCTET STRING
}
EmailIdentitySchema ::= SEQUENCE {
rfc822Email UTF8STRING,
time GeneralizedTime
}
cmsIdentityOID OBJECT IDENTIFIER ::= { joint-iso-itu(2) country(16)
us(840) organization(1) identicrypt(114334) keyschemas(2)
icschemas(1) rfc822email(1)
}
Appenzeller, et al. Expires September 2007 [Page 17]
Internet-Draft IBE Architecture March 2007
cmsPPSOID OBJECT IDENTIFIER ::= { joint-iso-itu(2) country(16)
us(840) organization(1) identicrypt(114334) pps-schemas(3)
ic-schemas(1) pps-uri(1)
}
ibcs OBJECT IDENTIFIER ::= {
joint-iso-itu(2) country(16) us(840) organization(1)
identicrypt(114334) ibcs(1)
}
-- The IBE System parameters consist of a set of public parameters
-- for the encryption algorithms supported by the district,
-- the identity schema, the URI of the PKG and further optional
-- parameters
IBESysParams ::= SEQUENCE {
Version INTEGER { v2(2) },
districtName UTF8String,
districtSerial INTEGER,
validity Validity,
ibePublicParameters IBEPublicParameters,
ibeIdentitySchema OBJECT IDENTIFIER,
ibeParamExtensions IBEParamExtensions
}
-- Validity designates the time interval for which these parameters
-- are valid.
Validity ::= SEQUENCE {
notBefore GeneralizedTime,
notAfter GeneralizedTime
}
-- Public Parameters for the IBE Algorithm
-- ibeAlgorithm is the algorithm OID from IBCS, e.g. "bb" or "bf"
-- publicParameterData is a DER encoded ASN.1 public parameter
-- block, e.g. BFPublicParamaters, BBPublicParamaters
IBEPublicParameters ::= SEQUENCE OF IBEPublicParameter
IBEPublicParameter ::= SEQUENCE {
ibeAlgorithm OBJECT IDENTIFIER,
publicParameterData OCTET STRING
}
IBEParamExtensions ::= SEQUENCE OF IBEParamExtension
Appenzeller, et al. Expires September 2007 [Page 18]
Internet-Draft IBE Architecture March 2007
IBEParamExtension ::= SEQUENCE {
ibeParamExtensionOID OBJECT IDENTIFIER,
ibeParamExtensionValue OCTET STRING
}
ibeParamExt OBJECT IDENTIFIER ::= {
ibcs ibcs3(3) parameter-extensions(2)
}
-- Defined Extensions:
-- pkgURI: URI of the PKG, value is a UTF8String
pkgURI OBJECT IDENTIFIER ::= { ibeParamExt pkgURI(1) }
-- Private Key Format
IBEPrivateKeyReply ::= SEQUENCE {
pkgIdentity IBEIdentityInfo,
pgkKeyType OBJECT IDENTIFIER,
pkgKeyData OCTET STRING,
pkgOptions IBEParamExtensions
}
END
6. Security Considerations
6.1. Attacks that are outside the scope of this document
Attacks on the cryptographic algorithms that are used to implement
IBE are outside the scope of this document. Such attacks are detailed
in [IBCS], which defines parameters that give 80-bit, 112-bit and
128-bit encryption strength. We assume that capable administrators of
an IBE system will select parameters that provide a sufficient
resistance to cryptanalytic attacks by adversaries.
Attacks that give an adversary the ability to access or change the
information on a PPS or PKG, especially the cryptographic material
(referred to in this document as the master secret), will defeat the
security of an IBE system. In particular, if the cryptographic
material is compromised the adversary will have the ability to
recreate any user's private key and therefore decrypt all messages
protected with the corresponding public key. To address this concern,
it is highly RECOMMENDED that best practices for physical and
operational security for PPS and PKG servers be followed and that
these servers be configured (sometimes known as hardened) in
accordance with best current practices [NIST]. An IBE system SHOULD
Appenzeller, et al. Expires September 2007 [Page 19]
Internet-Draft IBE Architecture March 2007
be operated in an environment where illicit access is infeasible for
attackers to obtain.
Attacks that require administrative or IBE user equivalent access to
machines used by either the client or the server components defined
in this document are also outside the scope of this document.
We also assume that all administrators of a system implementing the
protocols that are defined in this document are trustworthy and will
not abuse their authority to bypass the security provided by an IBE
system. Similarly, we assume that users of an IBE system will behave
responsibly, not sharing their authentication credentials with
others. Thus attacks that require such assumptions are outside the
scope of this document.
6.2. Attacks that are within the scope of this document
Attacks within the scope of this document are those that allow an
adversary to:
o passively monitor information transmitted between users of
an IBE system and the PPS and PKG
o masquerade as a PPS or PKG
o perform a DOS attack on a PPS or PKG
o easily guess an IBE users authentication credential
6.2.1. Attacks to which the protocols defined in this document are
susceptible
All communications between users of an IBE system and the PPS or PKG
are protected using TLS 1.1 [TLS]. The IBE system defined in this
document provides no additional security protections for the
communications between IBE users and the PPS or PKG. Therefore the
described IBE system is completely dependent on the TLS security
mechanisms for authentication of the PKG or PPS server and for
confidentiality and integrity of the communications. Should there be
a compromise of the TLS security mechanisms, the integrity of all
communications between an IBE user and the PPS or PKG will be
suspect.
The protocols defined in this document do not explicitly defend
against an attacker masquerading as a legitimate IBE PPS or PKG. The
protocols rely on the server authentication mechanism of TLS [TLS].
In addition to the TLS server authentication mechanism IBE client
Appenzeller, et al. Expires September 2007 [Page 20]
Internet-Draft IBE Architecture March 2007
software can provide protection against this possibility by providing
user interface capabilities that allows users to visually determine
that a connection to PPS and PKG servers is legitimate. This
additional capability can help ensure that users cannot easily be
tricked into providing valid authorization credentials to an
attacker.
The protocols defined in this document are also vulnerable to attacks
against an IBE PPS or PKG. Denial of service attacks against either
component can result in users unable to encrypt or decrypt using IBE,
and users of an IBE system SHOULD take the appropriate
countermeasures [RFC2827, RFC3882] that their use of IBE requires.
The IBE user authentication method selected by an IBE PKG SHOULD be
of sufficient strength to prevent attackers from easily guessing the
IBE user's authentication credentials through trial and error.
7. IANA Considerations
The XML defined in this document will be registered with the IANA per
the instructions in RFC 3688, The IETF XML Registry.
URI:
urn:ietf:params:xml:ns:ibe
Registrant Contact:
Mark Schertler
Voltage Security
1070 Arastradero Rd Suite 100
Palo Alto CA 94304
Phone: +1 650 543 1280
Email: mark@voltage.com
XML:
Appenzeller, et al. Expires September 2007 [Page 21]
Internet-Draft IBE Architecture March 2007
BEGIN
<ibe:request xmlns:ibe="urn:ietf:params:xml:ns:ibe">
<ibe:header>
<ibe:client version="clientID"/>
</ibe:header>
<ibe:body>
<ibe:keyRequest>
<ibe:algorithm>
<oid> algorithmOID </oid>
</ibe:algorithm>
<ibe:id>
ibeIdentityInfo
</ibe:id>
</ibe:keyRequest>
</ibe:body>
</ibe:request>
<ibe:response xmlns:ibe="urn:ietf:params:xml:ns:ibe">
<ibe:responseType value="responseCode"/>
<ibe:body>
bodyTags
</ibe:body>
</ibe:response>
END
8. References
8.1. Normative References
[AUTH] Franks, J., Hallam-Baker, P., Hostetler, J., Lawrence, S.,
Leach, P., Luotonen, A., Sink, E. and L. Stewart, "HTTP
Authentication: Basic and Digest Access Authentication", RFC
2617, June 1999.
[B64] N. Freed, N. Borenstein, Multipurpose Internet Mail
Extensions(MIME) Part One: Format of Internet Message Bodies,"
RFC 2045, November 1996.
[CMS] R. Housley, "Cryptographic Message Syntax," RFC 3369, August
2002.
[DER] ITU-T Recommendation X.680: Information Technology - Abstract
Syntax Notation One, 1997.
[DOM] P. Mockapetris, "Domain Names - Implementation and
Specification," RFC 1035, November 1987.
Appenzeller, et al. Expires September 2007 [Page 22]
Internet-Draft IBE Architecture March 2007
[HTTP] Fielding, R., Gettys, J., Mogul, J., Frysyk, H., Masinter, L.,
Leach, P. and T. Berners-Lee, "Hypertext Transfer Protocol --
HTTP/1.1", RFC 2616, June 1999.
[IBCS] X. Boyen, L. Martin, "Identity-Based Cryptography Standard
(IBCS) #1: Supersingular Curve Implementations of the BF and
BB1 Cryptosystems," draft-ietf-martin-ibcs-00.txt, September
2006.
[IBECMS] L. Martin, M. Schertler, "Using the Boneh-Franklin identity-
based encryption algorithm with the Cryptographic Message
Syntax (CMS)," draft-ietf-smime-bfibecms-01.txt, September
2006.
[KEY] S. Brander, "Key Words for Use in RFCs to Indicate Requirement
Levels," BCP 14, RFC 2119, March 1997.
[NIST] M. Souppaya, J. Wack, K. Kent, "Security Configuration
Checklist Program for IT Products - Guidance for Checklist
Users and Developers," NIST Special Publication SP 800-70, May
2005.
[P1363] IEEE P1363, "Standards Specifications for Public-Key
Cryptography," 2001.
[RFC2818] E. Rescorla, "HTTP over TLS," RFC 2818, May 2000.
[RFC2827] P. Ferguson, D. Senie, "Network Ingress Filtering:
Defeating Denial of Service Attacks which employ IP Source
Address Spoofing," RFC 2827, BCP 38, May 2000.
[RFC3882] D. Turk, "Configuring BGP to Block Denial-of-Service
Attacks," RFC 3882, September 2004.
[TLS] T. Dierks, E. Rescorla, "The Transport Layer Security (TLS)
Protocol Version 1.1," RFC 4346, April 2006.
[URI] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifiers (URI): Generic Syntax", RFC 2396, August
1998.
Appenzeller, et al. Expires September 2007 [Page 23]
Internet-Draft IBE Architecture March 2007
Authors' Addresses
Guido Appenzeller
Voltage Security
1070 Arastradero Rd Suite 100
Palo Alto CA 94304
Phone: +1 650 543 1280
Email: guido@voltage.com
Luther Martin
Voltage Security
1070 Arastradero Rd Suite 100
Palo Alto CA 94304
Phone: +1 650 543 1280
Email: martin@voltage.com
Mark Schertler
Voltage Security
1070 Arastradero Rd Suite 100
Palo Alto CA 94304
Phone: +1 650 543 1280
Email: mark@voltage.com
Intellectual Property Statement
The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79.
Copies of IPR disclosures made to the IETF Secretariat and any
assurances of licenses to be made available, or the result of an
attempt made to obtain a general license or permission for the use of
such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
Appenzeller, et al. Expires September 2007 [Page 24]
Internet-Draft IBE Architecture March 2007
rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at ietf-
ipr@ietf.org.
Disclaimer of Validity
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS
OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Copyright Statement
Copyright (C) The IETF Trust (2007).
This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors
retain all their rights.
Acknowledgment
Funding for the RFC Editor function is currently provided by the
Internet Society.
Appenzeller, et al. Expires September 2007 [Page 25]