Internet Engineering Task Force I. Hajjeh
ESRGroups
M. Badra
ISIMA Laboratory
Expires: April 2007 November, 2006
Identity Protection Ciphersuites for Transport Layer Security
<draft-hajjeh-tls-identity-protection-00.txt>
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Abstract
TLS defines several ciphersuites providing authentication, data
protection and session key exchange between two communicating
entities. Some of these ciphersuites are used for completely
anonymous key exchange, in which neither party is authenticated.
However, they are vulnerable to man-in-the-middle attacks and are
therefore deprecated.
This document defines a set of ciphersuites to add client identity
protection to the Transport Layer Security (TLS) protection.
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1. Introduction
TLS is the most deployed security protocol for securing exchanges.
It provides end-to-end secure communications between two entities
with authentication and data protection.
TLS supports three authentication modes: authentication of both
parties, only server-side authentication, and anonymous key
exchange. For each mode, TLS specifies a set of ciphersuites.
However, anonymous ciphersuites are strongly discouraged because
they cannot prevent man-in-the-middle attacks.
Client identity protection may be established by changing the order
of the messages that the client sends after receiving
ServerHelloDone [CORELLA]. This is done by sending the
ChangeCipherSpec message before the Certificate and the
CertificateVerify messages and after the ClientKeyExchange message.
However, it requires a major change to TLS machine state as long as
a new TLS version.
Client identity protection may also be done through a EDH exchange
before establishing an ordinary handshake with identity information
[RESCORLA]. This wouldn't however be secure enough against active
attackers and wouldn't be favorable for some environments (e.g.
mobile), due to the additional cryptographic computations.
Client identity protection may be also possible, assuming that the
client permits renegotiation after the first server authentication.
However, this requires more cryptographic computations and augments
significantly the number of rounds trips.
Finally, client identity protection may be realized by exchanging a
TLS extension that negotiates the symmetric encryption algorithm to
be used for client certificate encrypting/decrypting [EAPTLSIP].
This solution may suffer from interoperability issues related to TLS
Extensions, TLS 1.0 and TLS 1.1 implementations, as described in
[INTEROP].
This document defines a set of ciphersuites to add client identity
protection to TLS protocol. Client identity protection is provided
by symmetrically encrypting the client certificate with a key
derived from the SecurityParameters.master_secret,
SecurityParameters.server_random and
SecurityParameters.client_random. The symmetric encryption algorithm
is set to the cipher algorithm of the ServerHello.cipher_suite.
1.2. Requirements language
The key words "MUST", "MUST NOT" and "MAY" in this document are to
be interpreted as described in RFC-2119.
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2. TLS Identity Protection overview
This document specifies a set of ciphersuites for TLS. These
ciphersuites reuse existing key exchange algorithms that require
based-certificates authentication, and reuse also existing MAC,
stream and bloc ciphers algorithms from [TLS] and [TLSCTR],
[TLSECC], [TLSAES] and [TLSCAM]. Their names include the text "IP"
to refer to the client identity protection. An example is shown
below.
CipherSuite Key Exchange Cipher Hash
TLS_IP_RSA_EXPORT_WITH_RC4_40_MD5 RSA RC4 40 MD5
TLS_IP_DHE_DSS_WITH_AES_128_CBC_SHA DHE AES 128_CBC SHA
If the client has not a certificate with a type appropriate for one
of the supported cipher key exchange algorithms or if the client
will not be able to send such a certificate, it MUST NOT include any
ciphersuite with client identity protection in the
ClientHello.cipher_suites.
If the server selects a ciphersuite with client identity protection,
the server MUST request a certificate from the client.
If the server selects one of the ciphersuites defined in this
document, the client MUST encrypt its certificate using the
symmetric algorithm selected by the server from the list in
ClientHello.cipher_suites and a key derived from the
SecurityParameters.master_secret (see section 3 for the key
computation).
In the case of DH_DSS and DH_RSA ciphersuites with client
authentication, the ClientKeyExchange message always contains
explicit Diffie-Hellman public value and it is possible to correlate
sessions by the same client. Consequently, DH_DSS and DH_RSA are not
currently omitted from this document.
For EDH, the client MUST explicitly send its EDH public value in the
ClientKeyExchange message.
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Client Server
ClientHello -------->
ServerHello
Certificate
ServerKeyExchange*
CertificateRequest
<-------- ServerHelloDone
ClientKeyExchange
{Certificate}
CertificateVerify
[ChangeCipherSpec]
Finished -------->
[ChangeCipherSpec]
<-------- Finished
Application Data <-------> Application Data
* Indicates optional or situation-dependent messages that are not
always sent.
{} Indicates messages that are symmetrically encrypted.
The ciphersuites in Section 4 (IP_RSA Key Exchange Algorithm) use
RSA based certificates to mutually authenticate a RSA exchange with
the client identity protection.
The ciphersuites in Section 5 (IP_EDH Key Exchange Algorithm) use
EDH_RSA or EDH_DSS to mutually authenticate a Diffie-Hellman
exchange with the client identity protection.
The ciphersuites in Section 6 (IP_ECC Key Exchange Algorithm) are
TBC.
3. Key computation to encrypt/decrypt client's certificate
Before sending its certificate, the client is able to compute the
master secret and then the key_block. Thus, the client and the
server derive from the key_block a key called
identity_protection_key. This key is deployed by the client
(respectively the server) to encrypt (respectively decrypt) the
client's certificate.
The identity_protection_key is set to the low order bits of the
key_block, and its length is set appropriately to
ServerHello.cipher_suite. For example, if the client and the server
have agreed on using a ciphersuite with RC4_128 as symmetric
cryptography, they therefore set their key to the low order 128-bits
of the key_block.
Exportable encryption algorithms (for which CipherSpec.is_exportable
is true) require additional processing as follows to derive their
final identity_protection_key:
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final_identity_protection_key =
PRF(SecurityParameters.identity_protection_key,
"identity_protection_key",
SecurityParameters.client_random +
SecurityParameters.server_random);
4. IP_RSA Key Exchange Algorithm
This section defines additional ciphersuites that use RSA based
certificates to authenticate a RSA exchange. These ciphersuites give
client identity protection.
CipherSuite Key Exchange Cipher Hash
TLS_IP_RSA_EXPORT_WITH_RC4_40_MD5 RSA RC4_40 MD5
TLS_IP_RSA_WITH_RC4_128_MD5 RSA RC4_128 MD5
TLS_IP_RSA_WITH_RC4_128_SHA RSA RC4_128 SHA
TLS_IP_RSA_EXPORT_WITH_RC2_CBC_40_MD5 RSA RC2_CBC_40 MD5
TLS_IP_RSA_WITH_IDEA_CBC_SHA RSA IDEA_CBC SHA
TLS_IP_RSA_EXPORT_WITH_DES40_CBC_SHA RSA DES40_CBC_ SHA
TLS_IP_RSA_WITH_DES_CBC_SHA RSA DES_CBC SHA
TLS_IP_RSA_WITH_3DES_EDE_CBC_SHA RSA 3DES_EDE SHA
TLS_IP_RSA_WITH_AES_128_CBC_SHA RSA AES_128_CBC SHA
TLS_IP_RSA_WITH_AES_256_CBC_SHA RSA AES_256_CBC SHA
TLS_IP_RSA_WITH_AES_128_CTR_SHA RSA AES_128_CTR SHA
TLS_IP_RSA_WITH_CAMELLIA_128_CBC_SHA RSA CAMELLIA_128_CBC SHA
TLS_IP_RSA_WITH_AES_256_CTR_SHA RSA AES_256_CTR SHA
TLS_IP_RSA_WITH_CAMELLIA_256_CBC_SHA RSA CAMELLIA_256_CBC SHA
5. IP_EDH Key Exchange Algorithm
This section defines additional ciphersuites that use EDH with RSA
or DSS based certificates to authenticate a Diffie-Hellman exchange.
These ciphersuites give client identity protection.
The client MUST explicitly send its EDH public value in the
ClientKeyExchange message.
Note that this document does not specify any CipherSpec that uses DH
RSA or DSS based certificates.
CipherSuite Key Exchange Cipher Hash
TLS_IP_DHE_DSS_WITH_DES_CBC_SHA DHE DES_CBC SHA
TLS_IP_DHE_DSS_WITH_3DES_EDE_CBC_SHA DHE 3DES_EDE_CBC SHA
TLS_IP_DHE_RSA_WITH_DES_CBC_SHA DHE DES_CBC SHA
TLS_IP_DHE_RSA_WITH_3DES_EDE_CBC_SHA DHE 3DES_EDE_CBC SHA
TLS_IP_DHE_DSS_WITH_AES_128_CBC_SHA DHE AES_128_CBC SHA
TLS_IP_DHE_RSA_WITH_AES_128_CBC_SHA DHE AES_128_CBC SHA
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TLS_IP_DHE_DSS_WITH_AES_256_CBC_SHA DHE AES_256_CBC SHA
TLS_IP_DHE_RSA_WITH_AES_256_CBC_SHA DHE AES_256_CBC SHA
TLS_IP_DHE_DSS_WITH_CAMELLIA_128_CBC_SHA DHE CAMELLIA_128_CBC SHA
TLS_IP_DHE_RSA_WITH_CAMELLIA_128_CBC_SHA DHE CAMELLIA_128_CBC SHA
TLS_IP_DHE_DSS_WITH_CAMELLIA_256_CBC_SHA DHE CAMELLIA_256_CBC SHA
TLS_IP_DHE_RSA_WITH_CAMELLIA_256_CBC_SHA DHE CAMELLIA_256_CBC SHA
TLS_IP_DHE_DSS_WITH_AES_128_CTR_SHA DHE AES_128_CTR SHA
TLS_IP_DHE_RSA_WITH_AES_128_CTR_SHA DHE AES_128_CTR SHA
TLS_IP_DHE_DSS_WITH_AES_256_CTR_SHA DHE AES_256_CTR SHA
TLS_IP_DHE_RSA_WITH_AES_256_CTR_SHA DHE AES_256_CTR SHA
6. IP_ECC Key Exchange Algorithm
TBC.
7. Security Considerations
The security considerations described throughout [TLS], [DTLS],
[TLS1.1], [TLSAES] and [TLSAES] apply here as well.
8. IANA Considerations
This section provides guidance to the IANA regarding registration of
values related to the identity protection ciphersuites.
CipherSuite TLS_IP_RSA_EXPORT_WITH_RC4_40_MD5 = { 0xXX,0xXX };
CipherSuite TLS_IP_RSA_WITH_RC4_128_MD5 = { 0xXX,0xXX };
CipherSuite TLS_IP_RSA_WITH_RC4_128_SHA = { 0xXX,0xXX };
CipherSuite TLS_IP_RSA_EXPORT_WITH_RC2_CBC_40_MD5 = { 0xXX,0xXX };
CipherSuite TLS_IP_RSA_WITH_IDEA_CBC_SHA = { 0xXX,0xXX };
CipherSuite TLS_IP_RSA_EXPORT_WITH_DES40_CBC_SHA = { 0xXX,0xXX };
CipherSuite TLS_IP_RSA_WITH_DES_CBC_SHA = { 0xXX,0xXX };
CipherSuite TLS_IP_RSA_WITH_3DES_EDE_CBC_SHA = { 0xXX,0xXX };
CipherSuite TLS_IP_RSA_WITH_AES_128_CBC_SHA = { 0xXX,0xXX };
CipherSuite TLS_IP_RSA_WITH_AES_256_CBC_SHA = { 0xXX,0xXX };
CipherSuite TLS_IP_RSA_WITH_AES_128_CTR_SHA = { 0xXX,0xXX };
CipherSuite TLS_IP_RSA_WITH_CAMELLIA_128_CBC_SHA = { 0xXX,0xXX };
CipherSuite TLS_IP_RSA_WITH_AES_256_CTR_SHA = { 0xXX,0xXX };
CipherSuite TLS_IP_RSA_WITH_CAMELLIA_256_CBC_SHA = { 0xXX,0xXX };
CipherSuite TLS_IP_DHE_DSS_WITH_DES_CBC_SHA = { 0xXX,0xXX };
CipherSuite TLS_IP_DHE_DSS_WITH_3DES_EDE_CBC_SHA = { 0xXX,0xXX };
CipherSuite TLS_IP_DHE_RSA_WITH_DES_CBC_SHA = { 0xXX,0xXX };
CipherSuite TLS_IP_DHE_RSA_WITH_3DES_EDE_CBC_SHA = { 0xXX,0xXX };
CipherSuite TLS_IP_DHE_DSS_WITH_AES_128_CBC_SHA = { 0xXX,0xXX };
CipherSuite TLS_IP_DHE_RSA_WITH_AES_128_CBC_SHA = { 0xXX,0xXX };
CipherSuite TLS_IP_DHE_DSS_WITH_AES_256_CBC_SHA = { 0xXX,0xXX };
CipherSuite TLS_IP_DHE_RSA_WITH_AES_256_CBC_SHA = { 0xXX,0xXX };
CipherSuite TLS_IP_DHE_DSS_WITH_CAMELLIA_128_CBC_SHA= { 0xXX,0xXX };
CipherSuite TLS_IP_DHE_RSA_WITH_CAMELLIA_128_CBC_SHA= { 0xXX,0xXX };
CipherSuite TLS_IP_DHE_DSS_WITH_CAMELLIA_256_CBC_SHA= { 0xXX,0xXX };
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CipherSuite TLS_IP_DHE_RSA_WITH_CAMELLIA_256_CBC_SHA= { 0xXX,0xXX };
CipherSuite TLS_IP_DHE_DSS_WITH_AES_128_CTR_SHA = { 0xXX,0xXX };
CipherSuite TLS_IP_DHE_RSA_WITH_AES_128_CTR_SHA = { 0xXX,0xXX };
CipherSuite TLS_IP_DHE_DSS_WITH_AES_256_CTR_SHA = { 0xXX,0xXX };
CipherSuite TLS_IP_DHE_RSA_WITH_AES_256_CTR_SHA = { 0xXX,0xXX };
Note: For implementation and deployment facilities, it is helpful to
reserve a specific registry sub-range (minor, major) for identity
protection ciphersuites.
References
[TLS] Dierks, T. and C. Allen, "The TLS Protocol Version 1.0",
RFC 2246, January 1999.
[TLS1.1] Dierks, T. and E. Rescorla, "The TLS Protocol Version
1.1", RFC 4346, April 2005.
[DTLS] Rescorla, E. and N. Modadugu, "Datagram Transport Layer
Security", RFC 4347, April 2006.
[TLSCAM] Moriai, S., Kato, A., Kanda M., "Addition of Camellia
Cipher Suites to Transport Layer Security (TLS)",
RFC 4132, July 2005.
[TLSAES] Chown, P., "Advanced Encryption Standard (AES)
Ciphersuites for Transport Layer Security (TLS)",
RFC 3268, June 2002.
[TLSECC] Blake-Wilson, S., Bolyard, N., Gupta, V., Hawk, C.,
Moeller, B., "Elliptic Curve Cryptography (ECC) Cipher
Suites for Transport Layer Security (TLS)", RFC 4492, May
2006
[TLSCTR] Modadugu, N. and E. Rescorla, "AES Counter Mode Cipher
Suites for TLS and DTLS", draft-ietf-tls-ctr-01.txt (work
in progress), June 2006.
[EAPTLSIP] Urien, P. and M. Badra, "Identity Protection within EAP-
TLS",
draft-urien-badra-eap-tls-identity-protection-01.txt
(work in progress), October 2006.
[INTEROP] Pettersen, Y., "Clientside interoperability
experiences for the SSL and TLS protocols", draft-ietf-
tls-interoperability-00 (work in progress), October 2006.
[CORELLA] Corella, F., "adding client identity protection to TLS",
message on ietf-tls@lists.certicom.com mailing list,
http://www.imc.org/ietf-tls/mail-archive/msg02004.html,
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August 2000.
[RESCORLA] Rescorla, E., "SSL and TLS: Designing and Building Secure
Systems", Addison-Wesley, March 2001.
Author's Addresses
Ibrahim Hajjeh
ESRGroups, Security WG
France Email: Ibrahim.Hajjeh@esrgroups.org
Mohamad Badra
LIMOS Laboratory - UMR (6158), CNRS
France Email: badra@isima.fr
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