Internet DRAFT - draft-hajjeh-tls-identity-protection
draft-hajjeh-tls-identity-protection
TLS Working Group I. Hajjeh
Internet Draft INEOVATION
M. Badra
LIMOS Laboratory
Intended status: Experimental November 14, 2009
Expires: May 2010
Credential Protection Ciphersuites for Transport Layer Security
(TLS)
draft-hajjeh-tls-identity-protection-09.txt
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Abstract
This document defines a set of cipher suites to add client credential
protection to the Transport Layer Security (TLS) protocol. By
negotiating one of those ciphersuites, the TLS clients will be able
to determine for themselves when, how, to what extent and for what
purpose information about them is communicated to others. The
ciphersuites defined in this document can be used only when public
key certificates are used in the client authentication process.
Table of Contents
1. Introduction...................................................3
1.1. Conventions used in this document.........................5
2. TLS credential protection overview.............................5
2.1. Certificate and CertificateVerify protection..............6
2.1.1. Stream cipher encryption.............................6
2.1.2. Block cipher encryption..............................7
2.2. Key derivation............................................7
2.3. Structure of Certificate and CertificateVerify............8
2.3.1. Certificate structure................................9
2.3.1.1. Case TLS version 1.2............................9
2.3.1.2. Case TLS version 1.1...........................10
2.3.1.3. Case TLS version 1.0...........................11
2.3.2. CertificateVerify structure.........................11
2.3.2.1. Case TLS version 1.2...........................11
2.3.2.2. Case TLS version 1.1...........................12
2.3.2.3. Case TLS version 1.0...........................13
2.4. Message Flow.............................................14
2.5. New ciphersuites.........................................14
3. CP_RSA Key Exchange Algorithm.................................15
4. CP_DHE Key Exchange Algorithm.................................15
5. CP_ECDHE Key Exchange Algorithm...............................16
6. Security Considerations.......................................16
7. References....................................................18
7.1. Normative References.....................................18
7.2. Informative References...................................19
Author's Addresses...............................................19
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1. Introduction
The Transport Layer Security (TLS) protocol (TLS v1.0 [RFC2246], TLS
v1.1 [RFC4346], and TLS v1.2 [RFC5246]), 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 cipher suites. However,
anonymous cipher suites are strongly discouraged because they cannot
prevent man-in-the-middle (MITM) attacks.
The TLS authentication is usually based on either preshared keys or
public key certificates. If a public key certificate is used to
authenticate the TLS client, the TLS client credentials are sent in
clear text over the wire. Thus, any observer can determine the
credentials used by the client; learn who is reaching the network,
when, and from where, and hence correlate the client credentials to
the connection location.
Credentials protection and privacy are the right to informational
self-determination, i.e., individuals must be able to determine for
themselves when, how, to what extent and for what purpose information
about them is communicated to others.
TLS client credential protection may be established by changing the
order of the messages that the client sends after receiving
ServerHelloDone [CORELLA]. It consists of sending the
ChangeCipherSpec message before the Certificate and the
CertificateVerify messages and after the ClientKeyExchange message.
The ChangeCipherSpec message is sent to notify the receiving party
that subsequent messages will be protected under the cipher suite and
keys negotiated during the TLS Handshake. However, this solution
requires a major change to the TLS state machine as well as a new TLS
version.
TLS client credential protection may also be done through a DHE
exchange before establishing an ordinary handshake with identity
information [SSLTLS]. This wouldn't however be secure enough against
active attackers, which will be able to disclose the client's
credentials. Moreover, it wouldn't be favorable for some environments
(e.g., performance-constrained environments with limited CPU power),
due to the additional cryptographic computations and round trips.
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TLS client credential protection may also be possible, assuming that
the client permits renegotiation after the first server
authentication [RFC5246]: The client and the server establish a TLS
session with only server-side authentication and then perform a new
full TLS Handshake with mutual authentication; the client credentials
transferred in this stage thus are protected by the secure channel
established in the first TLS Handshake. This solution doesn't
require a change to TLS. However, this solution requires more
asymmetric cryptographic computations, which in many environments (in
particular for less powerful mobile nodes) are the rate limiting step
in TLS, and therefore, the renegotiation has negative performance
consequences. In fact, renegotiation requires another round of an
asymmetric encryption/decryption, which means the double number of
asymmetric en-/decryption operations (e.g., with an RSA key) for TLS
Handshake message processing, for both server and client. Moreover,
renegotiation requires twice the number of messages and roundtrips
than a single TLS handshake, thus significantly increasing the
overall delay in the session setup. Additionally, the server is
forced to complete a full first TLS handshake before it becomes able
to confirm whether the client has a valid certificate or not. This
increased misbalance in processing load in the failure case might
open an opportunity for misbehaving clients to perform resource
exhaustion attacks against such servers.
TLS client credential protection may as well be done by allowing the
client and the server to add a TLS extension to their Hello messages
in order to negotiate specific crypto algorithms, and use these to
protect the client certificate [EAPIP]. This solution may suffer
from interoperability issues related to TLS Extensions, TLS 1.0 and
TLS 1.1 implementations, as described in [INTEROP]. Moreover, it
provides imperfect privacy guarantees. In fact, the
CertificateVerify message is sent in clear text over the wire. As a
consequence, if an attacker ever obtains a client's certificate it
can do trial verification to determine whether a new handshake uses
that certificate.
This document defines a set of cipher suites to add client credential
protection to the TLS protocol. When one of the cipher suites
defined through this document is negotiated, a symmetric encryption
is used to encrypt the TLS client Certificate and the
CertificateVerify messages as following:
o The keys for the symmetric encryption and MAC are generated
uniquely for each TLS Handshake and are based on a secret
negotiated during the TLS Handshake. These keys don't replace
the other keys and secrets (master_secret and key_block).
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o Each encrypted message includes a message integrity check using
a keyed MAC. Secure hash functions (e.g., SHA, etc.) are used
for MAC computations.
o The encryption and MAC algorithms are determined by the
cipher_suite selected by the server and revealed in the
ServerHello message.
o Any key generated by this document should be deleted from
memory once the CertificateVerify message has been encrypted or
decrypted.
The reader is expected to become familiar with the TLS standards
([RFC5246] and, if needed, [RFC4346] and [RFC2246] for its
predecessors) prior to studying this document.
1.1. Conventions used in this document
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 [RFC2119].
2. TLS credential protection overview
This document specifies a set of cipher suites for TLS. These cipher
suites reuse existing key exchange algorithms with certificate-based
authentication, and reuse existing cipher and MAC algorithms from
[RFC5246], [RFC4492], and [RFC4132].
The name of cipher suites defined in this document includes the text
"CP" to refer to the client credential protection. An example is
shown below.
CipherSuite Key Exchange Cipher Hash
TLS_CP_RSA_WITH_AES_128_CBC_SHA RSA AES_128_CBC SHA1
TLS_CP_DHE_DSS_WITH_AES_128_CBC_SHA DHE AES_128_CBC SHA1
If no certificates are available, the client MUST NOT include any
credential protection cipher suite in the ClientHello.cipher_suites.
If the server selects a cipher suite with client credential
protection, the server MUST send a certificate appropriate for the
negotiated cipher suite's key exchange algorithm, and MUST request a
certificate from the client. If the server, agreeing on using a
credential protection cipher suite, does not receive a client
certificate in response to the subsequent certificate request, then
it MUST abort the session by sending a fatal handshake failure alert.
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The client certificate MUST be appropriate for the negotiated cipher
suite's key exchange algorithm, and any negotiated extensions.
2.1. Certificate and CertificateVerify protection
If the server selects one of the cipher suites defined in this
document, the client MUST symmetrically encrypt and integrity-protect
the Certificate and the CertificateVerify messages.
The encryption and MAC algorithms are determined by the cipher_suite
selected by the server and revealed in the ServerHello message.
The keys for the symmetric encryption and MAC are derived from the
pre_master_secret.
This document reuses the hash algorithm and the two symmetric
encryption modes defined by TLS: stream cipher encryption and block
cipher encryption, in a manner dependent on the negotiated TLS
version.
2.1.1. Stream cipher encryption
In stream cipher encryption, the client symmetrically encrypts the
Certificate and the CertificateVerify messages without any padding
byte. The encryption key cp_client_write_key is computed as
described in Section 2.2.
The MAC notation slightly varies with the TLS version being employed.
Symbolically, the MAC in this document is generated as follow:
In TLS version 1.2:
MAC(cp_client_write_MAC_key, plaintext)
The cp_client_write_MAC_key is generated as described in Section
2.2.
In TLS versions prior to 1.2:
HMAC_hash(cp_client_write_MAC_secret, plaintext)
The cp_client_write_MAC_secret is generated as described in
Section 2.2.
Note that the MAC is computed before encryption. The stream cipher
encrypts the entire block, including the MAC.
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2.1.2. Block cipher encryption
In block cipher encryption, every block of plaintext encrypts to a
block of ciphertext. All block cipher encryption is done in CBC
(Cipher Block Chaining) mode, and all items that are block-ciphered
will be an exact multiple of the cipher block length.
In block cipher encryption, the client uses an explicit
initialization vector, generated as described through this document.
The client adds a padding value to force the structure's length of
each the Certificate and the CertificateVerify messages to be an
integral multiple of the block cipher's block length, as it is
described later through this document.
2.2. Key derivation
For all key exchange methods, the same algorithm is used to convert
the pre_master_secret into the cp_key_block (credential protection
key block). The cp_key_block MUST be deleted from memory as soon as
possible during the TLS handshake, i.e.
o on the client: after encoding the CertificateVerify message;
o on the server: after decoding and verifying this message.
All the keys and parameters generated in this section are used only
to encrypt and compute the MAC of the client Certificate and the
CertificateVerify messages. The name of these keys includes the text
"cp" to refer to this use.
The pending premaster secret is used as an entropy source. To
generate the CP encryption and MAC keys, compute using the pending
connection state (see Section 6.1 of [RFC5246])
cp_key_block = PRF(pre_master_secret, "cp key block",
SecurityParameters.server_random +
SecurityParameters.client_random);
until enough output has been generated. Then the cp_key_block is
partitioned as follows:
Case TLS version 1.2:
cp_client_write_MAC_key[SecurityParameters.mac_key_length]
cp_client_write_key[SecurityParameters.enc_key_length]
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Case TLS version 1.1:
cp_client_write_MAC_secret[SecurityParameters.hash_size]
cp_client_write_key[SecurityParameters.key_material_length]
Case TLS version 1.0:
cp_client_write_MAC_secret[SecurityParameters.hash_size]
cp_client_write_key[SecurityParameters.key_material_length]
cp_client_write_IV[SecurityParameters.IV_size]
Note 1: There are always four TLS connection states outstanding
[RFC5246]: the current read and write states, and the pending read
and write states. All records (conveying the Handshake messages)
are processed under the current read and write states per standard
TLS rules (i.e., usually no encryption or MAC will be used unless
renegotiation is in progress).
When one of the ciphersuites described in this document is
negotiated, the encryption and MAC keys generated above are used
to encrypt the content of the Certificate and the
CertificateVerify messages in the ciphersuite specific part of the
TLS Handshake Layer, independent of the current processing in the
TLS Record Layer.
Note 2: During the handshake, the client MUST send the Certificate
message before the ClientKeyExchange message. Because the
ClientKeyExchange message conveys the encrypted pre_master_secret,
o the client has to use the pre_master_secret before sending
the ClientKeyExchange message in order to perform the
credential protection key derivation necessary to encrypt
the Certificate and the CertificateVerify messages;
o the server cannot decrypt and verify the content of the
Certificate and the CertificateVerify messages until it has
received the ClientKeyExchange message, which allows the
server to assemble the pre_master_secret needed to perform
the credential protection key derivation necessary to this
end.
2.3. Structure of Certificate and CertificateVerify
The stream-ciphered, block-ciphered and digitally-signed structures
vary with the TLS version being employed.
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2.3.1. Certificate structure
2.3.1.1. Case TLS version 1.2
opaque ASN.1Cert<1..2^24-1>;
struct {
select (SecurityParameters.cipher_type) {
case stream:
stream-ciphered struct {
ASN.1Cert certificate_list<0..2^24-1>;
opaque MAC[SecurityParameters.mac_length];
};
case block:
opaque IV[SecurityParameters.record_iv_length];
block-ciphered struct {
ASN.1Cert certificate_list<0..2^24-1>;
opaque MAC[SecurityParameters.mac_length];
uint8 padding[Certificate.padding_length];
uint8 padding_length;
};
};
} Certificate;
The MAC is generated as described in Section 2.1.1 (the plaintext is
the certificate_list).
IV
As part of the TLS Handshake, the standard TLS IV (Initialization
Vector) is generated and therefore used by the TLS Record protocol.
This document uses a second IV, generated in the same way as
described in Section 6.2.3.2 of [RFC5246]. This IV is only used
during the encryption/decryption of the content of the Certificate
message (concatenation of certificate_list and MAC).
The IV SHOULD be chosen at random, and MUST be unpredictable. For
block ciphers, the IV length is SecurityParameters.record_iv_length
which is equal to the SecurityParameters.block_size.
padding
Padding that is added to force the length of the Certificate
structure to be an integral multiple of the block cipher's block
length. The padding MAY be any length up to 255 bytes, as long as
it results in the length of the encrypted Certificate being an
integral multiple of the block length. Lengths longer than
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necessary might be desirable to frustrate attacks on a protocol
that are based on analysis of the lengths of exchanged messages.
Each uint8 in the padding data vector MUST be filled with the
padding length value. The receiver MUST check this padding and
SHOULD use the bad_record_mac alert to indicate padding errors.
padding_length
The padding length MUST be such that the total size of the
Certificate structure is a multiple of the cipher's block length.
Legal values range from zero to 255, inclusive. This length
specifies the length of the padding field exclusive of the
padding_length field itself.
2.3.1.2. Case TLS version 1.1
opaque ASN.1Cert<1..2^24-1>;
struct {
select (SecurityParameters.cipher_type) {
case stream:
stream-ciphered struct {
ASN.1Cert certificate_list<0..2^24-1>;
opaque MAC[SecurityParameters.hash_size];
};
case block:
block-ciphered struct {
opaque IV[SecurityParameters.block_length];
ASN.1Cert certificate_list<0..2^24-1>;
opaque MAC[SecurityParameters.hash_size];
uint8 padding[Certificate.padding_length];
uint8 padding_length;
};
};
} Certificate;
The MAC is generated as described in Section 2.1.1 (the plaintext is
the certificate_list). For the generation and handling of the IV see
[RFC4346], Section 6.2.3.2; this document supports both sample
algorithms described there. The padding and padding_length are
generated and handled as described in Section 2.3.1.1.
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2.3.1.3. Case TLS version 1.0
opaque ASN.1Cert<1..2^24-1>;
struct {
select (SecurityParameters.cipher_type) {
case stream:
stream-ciphered struct {
ASN.1Cert certificate_list<0..2^24-1>;
opaque MAC[SecurityParameters.hash_size];
};
case block:
block-ciphered struct {
ASN.1Cert certificate_list<0..2^24-1>;
opaque MAC[SecurityParameters.hash_size];
uint8 padding[Certificate.padding_length];
uint8 padding_length;
};
};
} Certificate;
The MAC is generated as described in Section 2.1.1 (the plaintext is
the certificate_list).
The padding is generated as described in Section 2.3.1.1.
Note: With block ciphers in CBC mode (Cipher Block Chaining), the IV
for the Certificate content is generated with the other keys and
secrets, as described in Section 2.2. The IV for CertificateVerify
content (Section 2.3.2.3) is the last ciphertext block from the
Certificate content. For more details of TLS 1.0 IV handling, see
Sections 6.1, 6.2.3.2, and 6.3, of [RFC2246].
2.3.2. CertificateVerify structure
2.3.2.1. Case TLS version 1.2
digitally-signed struct {
opaque handshake_messages[handshake_messages_length];
} Signature;
The digitally-signed type is described in Sections 4.7 of [RFC5246].
We use the above shorthand type notation 'Signature' for the standard
content of the CertificateVerify struct (Section 7.4.8 of [RFC4346])
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in a similar manner as a variant of it was defined for TLS versions
1.1 and 1.0 (Section 7.4.3 in [RFC4346] and [RFC2246] -- see below).
struct {
select (SecurityParameters.cipher_type) {
case stream:
stream-ciphered struct {
Signature signature;
opaque MAC[SecurityParameters.mac_length];
};
case block:
opaque IV[SecurityParameters.record_iv_length];
block-ciphered struct {
Signature signature;
opaque MAC[SecurityParameters.mac_length];
uint8 padding[CertificateVerify.padding_length];
uint8 padding_length;
};
};
} CertificateVerify;
The padding, IV and the MAC are described in Section 2.3.1.1,
replacing Certificate with CertificateVerify and the certificate_list
with the signature. Semantically, the CertificateVerify content is
the signature and the MAC of the certificate_list. The basic
Certificate Verify handshake message is described in Section 7.4.8 of
[RFC5246].
2.3.2.2. Case TLS version 1.1
struct {
select (SecurityParameters.cipher_type) {
case stream:
stream-ciphered struct {
Signature signature;
opaque MAC[SecurityParameters.hash_size];
};
case block:
block-ciphered struct {
opaque IV[SecurityParameters.block_length];
Signature signature;
opaque MAC[SecurityParameters.hash_size];
uint8 padding[CertificateVerify.padding_length];
uint8 padding_length;
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};
};
} CertificateVerify;
The padding, IV and the MAC are described in Section 2.3.1.2,
replacing Certificate with CertificateVerify and the certificate_list
with the signature. Semantically, the CertificateVerify content is
the signature and the MAC of the certificate_list. The Signature
type and the basic Certificate Verify message structure for TLS
version 1.1 are described in Sections 7.4.3 and 7.4.8 of [RFC4346].
2.3.2.3. Case TLS version 1.0
struct {
select (SecurityParameters.cipher_type) {
case stream:
stream-ciphered struct {
Signature signature;
opaque MAC[SecurityParameters.hash_size];
};
case block:
block-ciphered struct {
Signature signature;
opaque MAC[SecurityParameters.hash_size];
uint8 padding[CertificateVerify.padding_length];
uint8 padding_length;
};
};
} CertificateVerify;
The Signature type and the basic CertificateVerify message structure
for TLS version 1.0 are described in Sections 7.4.3 and 7.4.8 of
[RFC2246].
With block ciphers in CBC mode, the IV is the last ciphertext block
from the Certificate content. The padding and the MAC are generated
as described in Section 2.3.1.3, replacing Certificate with
CertificateVerify and the certificate_list with the signature.
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2.4. Message Flow
Client Server
ClientHello -------->
ServerHello
Certificate
ServerKeyExchange*
<-------- CertificateRequest
{Certificate}
ClientKeyExchange
{CertificateVerify}
ChangeCipherSpec
Finished -------->
ChangeCipherSpec
<-------- Finished
Application Data <-------> Application Data
* Indicates optional or situation-dependent messages that are not
always sent.
{} Indicates messages with symmetrically encrypted and integrity-
protected body.
For the DHE key exchange algorithm, the client always sends the
ClientKeyExchange message conveying its ephemeral DH public key Yc.
For the ECDHE key exchange algorithm, the client always sends the
ClientKeyExchange message conveying its ephemeral ECDH public key Yc.
Current TLS specifications note that if the client certificate
already contains a suitable DH or ECDH public key, then Yc is
implicit and does not need to be sent again and consequently, the
client key exchange message will be sent, but it MUST be empty. Even
if the client key exchange message is used to carry the Yc, using the
same Yc will allow traceability. Consequently, static Diffie-Hellman
SHOULD NOT be used with this document.
2.5. New ciphersuites
The cipher suites in Section 3 (CP_RSA Key Exchange Algorithm) use
RSA based certificates to mutually authenticate an RSA exchange with
client credential protection.
The cipher suites in Section 4 (CP_DHE Key Exchange Algorithm) use
DHE_RSA or DHE_DSS to mutually authenticate an Ephemeral Diffie-
Hellman (DHE) exchange.
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The cipher suites in Section 5 (CP_ECDHE Key Exchange Algorithm) use
ECDHE_RSA or ECDHE_ECDSA to mutually authenticate an Ephemeral
Elliptic Curve Diffie-Hellman (ECDHE) exchange.
3. CP_RSA Key Exchange Algorithm
This section defines additional cipher suites that use RSA based
certificates to authenticate an RSA exchange. These cipher suites
give client credential protection.
CipherSuite Key Cipher Hash
Exchange
TLS_CP_RSA_WITH_RC4_128_MD5 RSA RC4_128 MD5
TLS_CP_RSA_WITH_RC4_128_SHA RSA RC4_128 SHA1
TLS_CP_RSA_WITH_3DES_EDE_CBC_SHA RSA 3DES_EDE SHA1
TLS_CP_RSA_WITH_AES_128_CBC_SHA RSA AES_128_CBC SHA1
TLS_CP_RSA_WITH_AES_256_CBC_SHA RSA AES_256_CBC SHA1
TLS_CP_RSA_WITH_CAMELLIA_128_CBC_SHA RSA CAMELLIA_128_CBC SHA1
TLS_CP_RSA_WITH_CAMELLIA_256_CBC_SHA RSA CAMELLIA_256_CBC SHA1
TLS_CP_RSA_WITH_AES_128_CBC_SHA256 RSA AES_128_CBC SHA256
TLS_CP_RSA_WITH_AES_256_CBC_SHA384 RSA AES_256_CBC SHA384
4. CP_DHE Key Exchange Algorithm
This section defines additional cipher suites that use DHE as key
exchange algorithm, with RSA or DSS based certificates to
authenticate an Ephemeral Diffie-Hellman exchange. These cipher
suites provide client credential protection and Perfect Forward
Secrecy (PFS).
CipherSuite Key Cipher Hash
Exchange
TLS_CP_DHE_DSS_WITH_3DES_EDE_CBC_SHA DHE_DSS 3DES_EDE_CBC SHA1
TLS_CP_DHE_RSA_WITH_3DES_EDE_CBC_SHA DHE_RSA 3DES_EDE_CBC SHA1
TLS_CP_DHE_DSS_WITH_AES_128_CBC_SHA DHE_DSS AES_128_CBC SHA1
TLS_CP_DHE_RSA_WITH_AES_128_CBC_SHA DHE_RSA AES_128_CBC SHA1
TLS_CP_DHE_DSS_WITH_AES_256_CBC_SHA DHE_DSS AES_256_CBC SHA1
TLS_CP_DHE_RSA_WITH_AES_256_CBC_SHA DHE_RSA AES_256_CBC SHA1
TLS_CP_DHE_DSS_WITH_AES_128_CBC_SHA256 DHE_DSS AES_128_CBC SHA256
TLS_CP_DHE_RSA_WITH_AES_128_CBC_SHA256 DHE_RSA AES_128_CBC SHA256
TLS_CP_DHE_DSS_WITH_AES_256_CBC_SHA384 DHE_DSS AES_256_CBC SHA384
TLS_CP_DHE_RSA_WITH_AES_256_CBC_SHA384 DHE_RSA AES_256_CBC SHA384
TLS_CP_DHE_DSS_WITH_CAMELLIA_128_CBC_SHA DHE_DSS CAMELLIA_128_CBC SHA1
TLS_CP_DHE_RSA_WITH_CAMELLIA_128_CBC_SHA DHE_RSA CAMELLIA_128_CBC SHA1
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TLS_CP_DHE_DSS_WITH_CAMELLIA_256_CBC_SHA DHE_DSS CAMELLIA_256_CBC SHA1
TLS_CP_DHE_RSA_WITH_CAMELLIA_256_CBC_SHA DHE_RSA CAMELLIA_256_CBC SHA1
5. CP_ECDHE Key Exchange Algorithm
This section defines additional cipher suites that use ECDHE as key
exchange algorithm, with RSA or ECDSA based certificates to
authenticate an Ephemeral ECDH exchange. These cipher suites provide
client credential protection and PFS.
CipherSuite Key Exchange Cipher Hash
TLS_CP_ECDHE_ECDSA_WITH_RC4_128_SHA ECDHE_ECDSA RC4_128 SHA1
TLS_CP_ECDHE_RSA_WITH_RC4_128_SHA ECDHE_RSA RC4_128 SHA1
TLS_CP_ECDHE_ECDSA_WITH_3DES_EDE_CBC_SHA ECDHE_ECDSA 3DES_EDE_CBC SHA1
TLS_CP_ECDHE_RSA_WITH_3DES_EDE_CBC_SHA ECDHE_RSA 3DES_EDE_CBC SHA1
TLS_CP_ECDHE_ECDSA_WITH_AES_128_CBC_SHA ECDHE_ECDSA AES_128_CBC SHA1
TLS_CP_ECDHE_ECDSA_WITH_AES_256_CBC_SHA ECDHE_RSA AES_256_CBC SHA1
TLS_CP_ECDHE_RSA_WITH_AES_128_CBC_SHA ECDHE_RSA AES_256_CBC SHA1
TLS_CP_ECDHE_RSA_WITH_AES_256_CBC_SHA ECDHE_RSA AES_256_CBC SHA1
6. Security Considerations
The security considerations described throughout [RFC2246],
[RFC4346], [RFC5246], [RFC4347], and [RFC4492] apply here as well.
In order for the client to be protected against man-in-the-middle
attacks, the client SHOULD verify that the server provided a valid
certificate and that the received public key belongs to the server.
Because the question of whether this is the correct certificate is
outside of TLS, applications that do implement credential protection
cipher suites SHOULD enable the client to carefully examine the
certificate presented by the server to determine if it meets its
expectations. Particularly, the client MUST check its understanding
of the server hostname against the server's identity as presented in
the server Certificate message.
In the absence of an application profile specifying otherwise, the
matching is performed according to the following rules, as described
in [RFC4642]:
- The client MUST use the server hostname it used to open the
connection (or the hostname specified in the TLS "server_name"
extension [RFC4366]) as the value to compare against the server
name as expressed in the server certificate. The client MUST
NOT use any form of the server hostname derived from an
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insecure remote source (e.g., insecure DNS lookup). CNAME
canonicalization is not done.
- If a subjectAltName extension of type dNSName is present in the
certificate, it MUST be used as the source of the server's
identity.
- Matching is case-insensitive.
- A "*" wildcard character MAY be used as the left-most name
component in the certificate. For example, *.example.com would
match a.example.com, foo.example.com, etc., but would not match
example.com.
- If the certificate contains multiple names (e.g., more than one
dNSName field), then a match with any one of the fields is
considered acceptable.
If the match fails, the client MUST either ask for explicit user
confirmation or terminate the connection and indicate the server's
identity is suspect.
Additionally, the client MUST verify the binding between the identity
of the server to which it connects and the public key presented by
this server. The client SHOULD implement the algorithm in Section 6
of [RFC5280] for general certificate validation, but MAY supplement
that algorithm with other validation methods that achieve equivalent
levels of verification (such as comparing the server certificate
against a local store of already-verified certificates and identity
bindings).
If the client has external information as to the expected identity of
the server, the hostname check MAY be omitted.
It will depend on the application whether or not the server will have
external knowledge of what the client's identity ought to be and what
degree of assurance it needs to obtain of it. In any case, the
server typically will have to check that the client has a valid
certificate chained to an application-specific trust anchor it is
configured with, following the rules of [RFC5280], before it
successfully finishes the TLS handshake.
One widely accepted layering principle is to decouple service
authorization from client authentication on access. We therefore
recommend that authorization decisions be performed and communicated
at the application layer after the TLS handshake has been completed.
Acknowledgment
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Internet-Draft Credential Protection Ciphersuites for TLS November 2009
People who should be acknowledged include Alfred Hoenes, Pasi Eronen
and Eric Rescorla. Listing their names here does not mean that they
endorse this document, but that they have reviewed it and have
contributed to its improvement.
7. References
7.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2246] Dierks, T. and C. Allen, "The TLS Protocol Version 1.0",
RFC 2246, January 1999.
[RFC4132] Moriai, S., Kato, A., Kanda M., "Addition of Camellia
Cipher Suites to Transport Layer Security (TLS)", RFC 4132,
July 2005.
[RFC4346] Dierks, T. and E. Rescorla, "The TLS Protocol Version 1.1",
RFC 4346, April 2005.
[RFC4347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer
Security", RFC 4347, April 2006.
[RFC4366] Blake-Wilson, S., Nystrom, M., Hopwood, D., Mikkelsen, J.,
and T. Wright, "Transport Layer Security (TLS) Extensions",
RFC 4366, April 2006.
[RFC4492] 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.
[RFC4642] Murchison, K., Vinocur, J., Newman, C., "Using Transport
Layer Security (TLS) with Network News Transfer Protocol
(NNTP)", RFC 4642, October 2006.
[RFC5246] Dierks, T. and E. Rescorla, "The TLS Protocol Version 1.2",
RFC 5246, August 2008.
[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 5280, May 2008.
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Internet-Draft Credential Protection Ciphersuites for TLS November 2009
7.2. Informative References
[SSLTLS] Rescorla, E., "SSL and TLS: Designing and Building Secure
Systems", Addison-Wesley, March 2001.
[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,
August 2000.
[INTEROP] Pettersen, Y., "Clientside interoperability experiences for
the SSL and TLS protocols",
draft-ietf-tls-interoperability-00 (expired work in
progress), October 2006.
[EAPIP] Urien, P. and M. Badra, "Identity Protection within EAP-
TLS", draft-urien-badra-eap-tls-identity-protection-01.txt
(expired work in progress), October 2006.
Author's Addresses
Ibrahim Hajjeh
INEOVATION
France
Email: hajjeh@ineovation.fr
Mohamad Badra
LIMOS Laboratory - UMR6158, CNRS
France
Email: mbadra@gmail.com
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