draft-ietf-tls-rfc4347-bis-01.txt		draft-ietf-tls-rfc4347-bis-02.txt
	INTERNET-DRAFT E. Rescorla		INTERNET-DRAFT E. Rescorla
	Obsoletes (if approved): RFC 4347 RTFM, Inc.		Obsoletes (if approved): RFC 4347 RTFM, Inc.
	Intended Status: Proposed Standard N. Modadugu		Intended Status: Proposed Standard N. Modadugu
	<draft-ietf-tls-rfc4347-bis-01.txt> Stanford University		<draft-ietf-tls-rfc4347-bis-02.txt> Stanford University
	November 2008 (Expires May 2009)		March 7, 2009 (Expires September 2009)
	Datagram Transport Layer Security version 1.2		Datagram Transport Layer Security version 1.2
	Status of This Memo		Status of This Memo
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	Abstract		Abstract
	This document specifies Version 1.2 of the Datagram Transport Layer		This document specifies Version 1.2 of the Datagram Transport Layer
	Security (DTLS) protocol. The DTLS protocol provides communications		Security (DTLS) protocol. The DTLS protocol provides communications
	privacy for datagram protocols. The protocol allows client/server		privacy for datagram protocols. The protocol allows client/server
	applications to communicate in a way that is designed to prevent		applications to communicate in a way that is designed to prevent
	eavesdropping, tampering, or message forgery. The DTLS protocol is		eavesdropping, tampering, or message forgery. The DTLS protocol is
	based on the Transport Layer Security (TLS) protocol and provides		based on the Transport Layer Security (TLS) protocol and provides
	equivalent security guarantees. Datagram semantics of the underlying		equivalent security guarantees. Datagram semantics of the underlying
	transport are preserved by the DTLS protocol. This document		transport are preserved by the DTLS protocol. This document updates
	updates DTLS 1.0 to work with TLS version 1.2.		DTLS 1.0 to work with TLS version 1.2.
			Legal
			This documents and the information contained therein 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 THEREIN WILL NOT INFRINGE
			ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS
			FOR A PARTICULAR PURPOSE.
	Table of Contents		Table of Contents
	1. Introduction 2		1. Introduction 3
	1.1. Requirements Terminology 3		1.1. Requirements Terminology 4
	2. Usage Model 3		2. Usage Model 4
	3. Overview of DTLS 4		3. Overview of DTLS 5
	3.1. Loss-Insensitive Messaging 4		3.1. Loss-Insensitive Messaging 5
	3.2. Providing Reliability for Handshake 5		3.2. Providing Reliability for Handshake 5
	3.2.1. Packet Loss 5		3.2.1. Packet Loss 6
	3.2.2. Reordering 5		3.2.2. Reordering 6
	3.2.3. Message Size 6		3.2.3. Message Size 6
	3.3. Replay Detection 6		3.3. Replay Detection 7
	4. Differences from TLS 6		4. Differences from TLS 7
	4.1. Record Layer 6		4.1. Record Layer 7
	4.1.1. Transport Layer Mapping 8		4.1.1. Transport Layer Mapping 9
	4.1.1.1. PMTU Issues 9		4.1.1.1. PMTU Issues 10
	4.1.2. Record Payload Protection 10		4.1.2. Record Payload Protection 11
	4.1.2.1. MAC 10		4.1.2.1. MAC 11
	4.1.2.2. Null or Standard Stream Cipher 11		4.1.2.2. Null or Standard Stream Cipher 12
	4.1.2.3. Block Cipher 11		4.1.2.3. Block Cipher 12
	4.1.2.3. AEAD Ciphers 11		4.1.2.3. AEAD Ciphers 12
	4.1.2.5. New Cipher Suites 11		4.1.2.5. New Cipher Suites 12
	4.1.2.6. Anti-replay 11		4.1.2.6. Anti-replay 13
	4.2. The DTLS Handshake Protocol 12		4.2. The DTLS Handshake Protocol 13
	4.2.1. Denial of Service Countermeasures 12		4.2.1. Denial of Service Countermeasures 14
	4.2.2. Handshake Message Format 15		4.2.2. Handshake Message Format 16
	4.2.3. Message Fragmentation and Reassembly 16		4.2.3. Message Fragmentation and Reassembly 18
	4.2.4. Timeout and Retransmission 17		4.2.4. Timeout and Retransmission 18
	4.2.4.1. Timer Values 21		4.2.4.1. Timer Values 22
	4.2.5. ChangeCipherSpec 21		4.2.5. ChangeCipherSpec 22
	4.2.6. CertificateVerify and Finished Messages 21		4.2.6. CertificateVerify and Finished Messages 22
	4.2.7. Alert Messages 21		4.2.7. Alert Messages 22
	4.3. Summary of new syntax 22		4.3. Summary of new syntax 23
	4.3.1. Record Layer 23		4.3.1. Record Layer 24
	4.3.2. Handshake Protocol 23		4.3.2. Handshake Protocol 24
	5. Security Considerations 24		5. Security Considerations 25
	6. Acknowledgements 25		6. Acknowledgements 26
	7. IANA Considerations 25		7. IANA Considerations 26
	8. References 25		8. References 26
	8.1. Normative References 25		8.1. Normative References 26
	8.2. Informative References 26		8.2. Informative References 27
	1. Introduction		1. Introduction
	TLS [TLS] is the most widely deployed protocol for securing network		TLS [TLS] is the most widely deployed protocol for securing network
	traffic. It is widely used for protecting Web traffic and for e-mail		traffic. It is widely used for protecting Web traffic and for e-mail
	protocols such as IMAP [IMAP] and POP [POP]. The primary advantage		protocols such as IMAP [IMAP] and POP [POP]. The primary advantage
	of TLS is that it provides a transparent connection-oriented channel.		of TLS is that it provides a transparent connection-oriented channel.
	Thus, it is easy to secure an application protocol by inserting TLS		Thus, it is easy to secure an application protocol by inserting TLS
	between the application layer and the transport layer. However, TLS		between the application layer and the transport layer. However, TLS
	must run over a reliable transport channel -- typically TCP [TCP].		must run over a reliable transport channel -- typically TCP [TCP].
	skipping to change at page 7, line 34		skipping to change at page 8, line 22
	The sequence number for this record.		The sequence number for this record.
	length		length
	Identical to the length field in a TLS 1.2 record. As in TLS		Identical to the length field in a TLS 1.2 record. As in TLS
	1.2, the length should not exceed 2^14.		1.2, the length should not exceed 2^14.
	fragment		fragment
	Identical to the fragment field of a TLS 1.2 record.		Identical to the fragment field of a TLS 1.2 record.
	DTLS uses an explicit sequence number, rather than an implicit one,		DTLS uses an explicit sequence number, rather than an implicit one,
	carried in the sequence_number field of the record. As with TLS, the		carried in the sequence_number field of the record. Sequence numbers
	sequence number is set to zero after each ChangeCipherSpec message is		are maintained separately for each epoch, with each sequence_number
	sent.		initially being 0 for each epoch. For instance, if a handshake
			message from epoch 0 is retransmitted, it might have a sequence
			number after a message from epoch 1, even if the message from epoch 1
			was transmitted first. Note that some care needs to be taken during
			the handshake to ensure that retransmitted messages use the right
			epoch and keying material.
	If several handshakes are performed in close succession, there might		If several handshakes are performed in close succession, there might
	be multiple records on the wire with the same sequence number but		be multiple records on the wire with the same sequence number but
	from different cipher states. The epoch field allows recipients to		from different cipher states. The epoch field allows recipients to
	distinguish such packets. The epoch number is initially zero and is		distinguish such packets. The epoch number is initially zero and is
	incremented each time the ChangeCipherSpec messages is sent. In		incremented each time the ChangeCipherSpec messages is sent. In
	order to ensure that any given sequence/epoch pair is unique,		order to ensure that any given sequence/epoch pair is unique,
	implementations MUST NOT allow the same epoch value to be reused		implementations MUST NOT allow the same epoch value to be reused
	within two times the TCP maximum segment lifetime. In practice, TLS		within two times the TCP maximum segment lifetime. In practice, TLS
	implementations rarely rehandshake and we therefore do not expect		implementations rarely rehandshake and we therefore do not expect
	this to be a problem.		this to be a problem.
	Note that because DTLS records may be reordered, a record from epoch		Note that because DTLS records may be reordered, a record from epoch
	1 may be received after epoch 2 has begun. In general,		1 may be received after epoch 2 has begun. In general,
	implementations SHOULD discard packets from earlier epochs, but if		implementations SHOULD discard packets from earlier epochs, but if
	packet loss causes noticeable problems MAY choose to retain keying		packet loss causes noticeable problems MAY choose to retain keying
	material from previous epochs for up to 120 seconds (the default TCP		material from previous epochs for up to 120 seconds (the default TCP
	MSL) to allow for packet reordering.		MSL) to allow for packet reordering. Until the handshake has
			completed, implementations MUST accept packets from the old epoch.
	Conversely, it is possible for records that are protected by the		Conversely, it is possible for records that are protected by the
	newly negotiated context to be received prior to the completion of a		newly negotiated context to be received prior to the completion of a
	handshake. For instance, the server may send its Finished and then		handshake. For instance, the server may send its Finished and then
	start transmitting data. Implementations MAY either buffer or		start transmitting data. Implementations MAY either buffer or
	discard such packets, though when DTLS is used over reliable		discard such packets, though when DTLS is used over reliable
	transports (e.g., SCTP), they SHOULD be buffered and processed once		transports (e.g., SCTP), they SHOULD be buffered and processed once
	the handshake completes. Note that TLS's restrictions on when		the handshake completes. Note that TLS's restrictions on when
	packets may be sent still apply, and the receiver treats the packets		packets may be sent still apply, and the receiver treats the packets
	as if they were sent in the right order. In particular, it is still		as if they were sent in the right order. In particular, it is still
	impermissible to send data prior to completion of the first		impermissible to send data prior to completion of the first
	handshake.		handshake.
			Note that in the special case of a rehandshake on an existing
			association, it is safe to process a data packet immediately even if
			the CSS or Finished has not yet been received provided that either
			the rehandshake resumes the existing session or that it uses exactly
			the same security parameters as the existing association. In an
			other case, the implementation MUST wait for the receipt of the
			Finished to prevent downgrade attack.
	4.1.1. Transport Layer Mapping		4.1.1. Transport Layer Mapping
	Each DTLS record MUST fit within a single datagram. In order to		Each DTLS record MUST fit within a single datagram. In order to
	avoid fragmentation, that clients of the DTLS record layer SHOULD		avoid fragmentation, that clients of the DTLS record layer SHOULD
	attempt to size records so that they fit within any PMTU estimates		attempt to size records so that they fit within any PMTU estimates
	obtained from the record layer.		obtained from the record layer.
	Note that unlike IPsec, DTLS records do not contain any association		Note that unlike IPsec, DTLS records do not contain any association
	identifiers. Applications must arrange to multiplex between		identifiers. Applications must arrange to multiplex between
	associations. With UDP, this is presumably done with host/port		associations. With UDP, this is presumably done with host/port
	skipping to change at page 9, line 41		skipping to change at page 10, line 45
	particular:		particular:
	- For DTLS over UDP, the upper layer protocol SHOULD be allowed		- For DTLS over UDP, the upper layer protocol SHOULD be allowed
	to obtain the PMTU estimate maintained in the IP layer.		to obtain the PMTU estimate maintained in the IP layer.
	- For DTLS over DCCP, the upper layer protocol		- For DTLS over DCCP, the upper layer protocol
	SHOULD be allowed to obtain the current estimate of the		SHOULD be allowed to obtain the current estimate of the
	PMTU.		PMTU.
	- For DTLS over TCP or SCTP, which automatically fragment		- For DTLS over TCP or SCTP, which automatically fragment
	and reassemble datagrams, the upper layer protocol		and reassemble datagrams, there is no PMTU limitation.
	SHOULD be informed that the PMTU is effectively infinite.		However, the upper layer protocol MUST NOT write any
			record that exceeds the maximum record size of 2^14 bytes.
	The DTLS record layer SHOULD allow the upper layer protocol to		The DTLS record layer SHOULD allow the upper layer protocol to
	discover the amount of record expansion expected by the DTLS		discover the amount of record expansion expected by the DTLS
	processing. Note that this number is only an estimate because of		processing. Note that this number is only an estimate because of
	block padding and the potential use of DTLS compression.		block padding and the potential use of DTLS compression.
	If there is a transport protocol indication (either via ICMP or via a		If there is a transport protocol indication (either via ICMP or via a
	refusal to send the datagram as in DCCP Section 14), then DTLS record		refusal to send the datagram as in DCCP Section 14), then DTLS record
	layer should inform the upper layer protocol of the error.		layer should inform the upper layer protocol of the error.
	skipping to change at page 15, line 26		skipping to change at page 16, line 34
	handshake.		handshake.
	If HelloVerifyRequest is used, the initial ClientHello and		If HelloVerifyRequest is used, the initial ClientHello and
	HelloVerifyRequest are not included in the calculation of the		HelloVerifyRequest are not included in the calculation of the
	handshake_messages (for the CertificateVerify message) and		handshake_messages (for the CertificateVerify message) and
	verify_data (for the Finished message).		verify_data (for the Finished message).
	If a server receives a ClientHello with an invalid cookie, it SHOULD		If a server receives a ClientHello with an invalid cookie, it SHOULD
	treat it the same as a ClientHello with no cookie. This avoids		treat it the same as a ClientHello with no cookie. This avoids
	race/deadlock conditions if the client somehow gets a bad cookie		race/deadlock conditions if the client somehow gets a bad cookie
	(e.g., because the server changes its cookie signing key).		(e.g., because the server changes its cookie signing key). Note to
			implementors: this may results in clients receiving multiple
			HelloVerifyRequest messages with different cookies. Clients SHOULD
			handle this by sending a new HelloVerify in response to the new
			HelloVerifyRequest.
	4.2.2. Handshake Message Format		4.2.2. Handshake Message Format
	In order to support message loss, reordering, and fragmentation, DTLS		In order to support message loss, reordering, and fragmentation, DTLS
	modifies the TLS 1.2 handshake header:		modifies the TLS 1.2 handshake header:
	struct {		struct {
	HandshakeType msg_type;		HandshakeType msg_type;
	uint24 length;		uint24 length;
	uint16 message_seq; // New field		uint16 message_seq; // New field
	skipping to change at page 28, line 4		skipping to change at line 1261
	EMail: ekr@rtfm.com		EMail: ekr@rtfm.com
	Nagendra Modadugu		Nagendra Modadugu
	Computer Science Department		Computer Science Department
	Stanford University		Stanford University
	353 Serra Mall		353 Serra Mall
	Stanford, CA 94305		Stanford, CA 94305
	EMail: nagendra@cs.stanford.edu		EMail: nagendra@cs.stanford.edu
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