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rfc:rfc4194

Network Working Group J. Strombergson Request for Comments: 4194 InformAsic AB Category: Standards Track L. Walleij

                                               Lunds Tekniska Hogskola
                                                          P. Faltstrom
                                                     Cisco Systems Inc
                                                          October 2005
                        The S Hexdump Format

Status of this Memo

 This document specifies an Internet standards track protocol for the
 Internet community, and requests discussion and suggestions for
 improvements.  Please refer to the current edition of the "Internet
 Official Protocol Standards" (STD 1) for the standardization state
 and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

 Copyright (C) The Internet Society (2005).

Abstract

 This document specifies the S Hexdump Format (SHF), a new, XML-based
 open format for describing binary data in hexadecimal notation.  SHF
 provides the ability to describe both small and large, simple and
 complex hexadecimal data dumps in an open, modern, transport- and
 vendor-neutral format.

1. Introduction

 In the computing, network, and embedded systems communities, several
 different types of data formats for hexadecimal data are being used.
 One of the more common formats is known as "S-records" (and several
 derivatives), which reportedly originated at the Motorola company.
 The S Hexdump Format is named in its honour.
 Typical uses of these dump formats include executable object code for
 embedded systems (i.e., "firmware"), on-chip flash memories and
 filesystems, FPGA configuration bitstreams, graphics and other
 application resources, routing tables, etc.  Unfortunately, none of
 the formats used are truly open, vendor-neutral, and/or well-defined.
 Even more problematic is the fact that none of these formats are able
 to represent the large data sizes that are getting more and more
 common.  Data dumps comprised of multiple sub-blocks with different

Strombergson, et al. Standards Track [Page 1] RFC 4194 The S Hexdump Format October 2005

 Word sizes, and data sizes spanning anywhere from a few Bytes of data
 to much larger than 2^32 bits are not handled.  Also, the checksums
 included in these formats are too simplistic and for larger data
 sizes, they provide insufficient ability to accurately detect errors.
 Alternatively, the overhead needed for proper error detection is very
 large.
 Therefore, the S Hexdump format is an effort to provide a modern,
 XML-based format that is not too complex for simple tools and
 computing environments to implement, generate, parse, and use.  Yet
 the format is able to handle large data sizes and complex data
 structures, and can provide high quality error detection by
 leveraging standardized cryptographic hash functions.
 One of the simplifications introduced in the format is to disallow
 other number systems such as octal or decimal notation, and to allow
 for Word sizes of even bytes (8-bit groups) only.  This is
 intentional and was done to simplify implementations aimed for
 practical present-day applications.  Formats aimed for esoteric
 number systems or odd Word sizes may be implemented elsewhere.
 At present, the usage of the SHF format may be mainly for Internet
 transport and file storage on development machinery.  A parser for
 the XML format is presently not easily deployed in hardware devices,
 but the parsing and checksumming of the SHF data may be done by a
 workstation computer, which in turn converts the SHF tokens to an
 ordinary bitstream before the last step (e.g., of a firmware upgrade)
 commences.
 SHF is a dump format only and shall not be confused with similar
 applications, such as binary configuration formats or patches, which
 are intended to, for example, alter contents of a core memory.  Such
 applications require the possibility of modifying individual bits or
 groups of bits in the memory of a machine, and is not the intended
 usage of the mechanism described in the present document.

2. 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 RFC 2119 [1].
 The key word "Byte" is to be interpreted as a group of 8 bits.  The
 key word "Octet" is another name for Byte.
 The key word "Word" is to be interpreted as a group containing an
 integral number of Bytes.

Strombergson, et al. Standards Track [Page 2] RFC 4194 The S Hexdump Format October 2005

 The key word "Block" is to be interpreted as an ordered sequence of
 Words, beginning at a certain address, running from lower to higher
 addresses.  A Block typically represents a sequence of Words at a
 certain address range in the memory of a computer.
 The key word "Dump" is to be interpreted as a sequence of Blocks,
 which may or may not be in a particular order.  A Dump typically
 represents some non-continuous, interesting parts of the memory of a
 computer, such that the Dump as a whole has a certain meaning, for
 example (but not limited to) a complete firmware for an embedded
 system.
 The expression "2^n" is to be interpreted as the value two (2) raised
 to the n:th power.  For example, 2^8 equals the value 256.

3. Features and Functionality

 The SHF-format has the following features:
 o  Support for arbitrarily wide data Words
 o  Support for very large data Blocks
 o  Support for an arbitrary number of independent data Blocks
 o  Data integrity detection against errors provided by the RFC3174
    specified (see [2]) SHA-1 cryptographic signature
 o  An XML-based format
 In the embedded systems domain, 8- and 16-bit processors are still
 used in large numbers and will continue to be used for any
 foreseeable future.  Simultaneously, more and more systems are using
 64-bit and even larger Word sizes.
 SHF supports all of these systems by allowing the Word size to be
 specified.  The Word size MUST be an integer number of Bytes and at
 least one (1) Byte.
 SHF is able to represent both large and small data Blocks.  The data
 Block MUST contain at least one (1) Word.  Additionally, the data
 Block MUST NOT be larger than (2^64)-1 bits.
 The SHF Dump MUST contain at least one (1) data Block.  The maximum
 number of Blocks supported is 2^64.  Each data Block in the Dump MAY
 have different Word sizes and start at different addresses.

Strombergson, et al. Standards Track [Page 3] RFC 4194 The S Hexdump Format October 2005

 The checksum (or message digest) used to verify the correctness or
 data integrity of each Block is 20 Bytes (160 bits) long.  The digest
 MUST be calculated on the data actually represented by the SHF data
 Block, NOT the representation, i.e., NOT the ASCII-code.  SHA-1 is
 only able to calculate a digest for a data Block no larger than
 (2^64)-1 bits and this limits the size of each data Block in SHF to
 (2^64)-1 bits.

4. SHF XML Specification

 The SHF format consists of an XML data structure representing a Dump.
 The Dump consists of a Dump header section and one (1) or more Block
 sections containing data.  Each Block of data is independent of any
 other Block.
 A short, symbolic example of an SHF Dump is illustrated by the
 following structure:
 <dump name="(Human readable string)" blocks="(64-bit value)">
   <block name="(Human readable string)" start_address="(64-bit
          value)" word_size="(64-bit value)" length="(64-bit value)"
          checksum="(20-Byte digest)">
      (Data)
   </block>
 </dump>

4.1. Header Section

 The header section comprises the Dump tag, which includes the
 following attributes:
 o  name: A compulsory string of arbitrary length used by any
    interested party to identify the specific SHF Dump.
 o  blocks: An optional 64-bit hexadecimal value representing the
    number of Blocks in the specific SHF Dump.  Whenever available,
    this value should be supplied.  However, there are potential
    scenarios where the number of Blocks cannot be given beforehand.
    If the value is present, it should be verified by implementers; if
    the value is untrue, the behaviour is implementation-defined.
 After the opening Dump tag, one or more subsections of Blocks must
 follow.  Finally, the complete SHF Dump ends with a closing Dump tag.

Strombergson, et al. Standards Track [Page 4] RFC 4194 The S Hexdump Format October 2005

4.2. Block Subsection

 The Block subsection contains a Block tag and a number of data words.
 The Block tag includes the following attributes:
 o  name: A compulsory string of arbitrary length used by any
    interested party to identify the specific Block.
 o  start_address: A compulsory, 64-bit hexadecimal value representing
    the start address in Bytes for the data in the Block.
 o  word_size: A compulsory 64-bit hexadecimal value representing the
    number of Bytes (the width) of one Word of the data.
 o  length: A compulsory hexadecimal representation of an unsigned
    64-bit integer indicating the number of Words following inside the
    Block element.  If this value turns out to be untrue, the Block
    MUST be discarded.
 o  checksum: A compulsory hexadecimal representation of the 20 Byte
    SHA-1 digest of the data in the Block.
 The total size of the data in the Block (in bits) is given by the
 expression (8 * word_size * length).  The expression MUST NOT be
 larger than (2^64)-1.
 After the opening Block tag, a hexadecimal representation of the
 actual data in the Block follows.  Finally, the Block section ends
 with a closing Block tag.

5. SHF Rules and Limits

 There are several rules and limits in SHF:
 o  All attribute values representing an actual value and the data
    MUST be in hexadecimal notation.  The only attribute excluded from
    this rule is the name attribute in the Dump and Block tags.  This
    restriction has been imposed for ease of reading the dump: a
    reader shall not be uncertain about whether a figure is in hex
    notation or not, and can always assume it is hexadecimal.
 o  All attribute values, with the exception of the checksum, MAY omit
    leading zeros.  Conversely, the checksum MUST NOT omit leading
    zeros.
 o  The data represented in a Block MUST NOT be larger than (2^64)-1
    bits.

Strombergson, et al. Standards Track [Page 5] RFC 4194 The S Hexdump Format October 2005

 o  The size of a Word MUST NOT be larger than (2^64)-1 bits.  This
    implies that a Block with a Word defined to the maximum width
    cannot contain more than one Word.  An SHF consumer shall assure
    that it can handle a certain Word length before beginning to parse
    blocks of an SHF Dump.  Failure to do so may cause buffer
    overflows and endanger the stability and security of the system
    running the consuming application.
 o  The attribute values representing an actual value MUST be in
    big-endian format.  This means that the most significant
    hexadecimal digits are to be put to the left in a hexadecimal
    Word, address, or similar field.  For example, the address value
    1234 represents the address 1234 and not 3412.  While some
    computing architectures may be using little-endian Words as their
    native format, it is the responsibility of any SHF producer
    running on such an architecture to swap the attribute values to a
    big-endian format.  The reverse holds for a consumer receiving the
    big-endian SHF attributes: if the consumer is little-endian, the
    values have to be swapped around.
 o  Likewise, the words inside a Dump MUST be stored in a big-endian
    format if the word size is larger than one Byte.  Here, the same
    need for swapping Bytes around may arise, as mentioned in the
    previous paragraph.

6. SHF DTD

 The contents of the element named "block" and the attributes
 "blocks", "address", "word_size" and "checksum" should only contain
 the characters that are valid hexbyte sequences.  These are:
  whitespace ::= (#x20 | #x9 | #xC | #xD | #xA)
  hexdigit   ::= [0-9A-Fa-f]
  hexbytes   ::= whitespace* hexdigit (hexdigit|whitespace)*
 A parser reading in an SHF file should silently ignore any other
 characters that (by mistake) appear in any of these elements or
 attributes.  These alien characters should be treated as if they did
 not exist.  Also note that "whitespace" has no semantic meaning; it
 is only valid for the reason of improving the human readability of
 the Dump.  Whitespace may be altogether removed and the hexbyte
 sequences concatenated if desired.  Notice that the fact that word
 size is to be given in a number of bytes implies that the number of
 hexadecimal digits inside a block need to be even.  Malformed blocks
 should be ignored by implementations.

Strombergson, et al. Standards Track [Page 6] RFC 4194 The S Hexdump Format October 2005

 <!--
   DTD for the S Hexdump Format, as of 2003-10-10
   Linus Walleij, Joachim Strombergson, Patrik Faltstrom 2003
   Refer to this DTD as:
   <!ENTITY % SHF PUBLIC "-//IETF//DTD SHF//EN"
              "http://ietf.org/dtd/shf.dtd">
        %SHF;
 -->
 <?xml version="1.0" encoding="UTF-8"?>
 <!ELEMENT dump (block)+>
 <!ATTLIST dump
        name          CDATA    #REQUIRED
        blocks        CDATA    #IMPLIED>
 <!ELEMENT block (#PCDATA)>
 <!ATTLIST block
        name          CDATA    #REQUIRED
        address       CDATA    #REQUIRED
        word_size     CDATA    #REQUIRED
        length        CDATA    #REQUIRED
        checksum      CDATA    #REQUIRED>

7. SHF Examples

 This section contains three different SHF examples, illustrating the
 usage of SHF and the attributes in SHF.
 The first example is a simple SHF Dump with a single Block of data:
 <?xml version="1.0" encoding="UTF-8"?>
 <dump name="Simple SHF example" blocks="01">
   <block name="Important message in hex format" address="0400"
     word_size="01" length="1f"
     checksum="5601b6acad7da5c7b92036786250b053f05852c3">
       41 6c 6c 20 79 6f 75 72 20 62 61 73 65 20 61 72
       65 20 62 65 6c 6f 6e 67 20 74 6f 20 75 73 0a
   </block>
 </dump>

Strombergson, et al. Standards Track [Page 7] RFC 4194 The S Hexdump Format October 2005

 The second example is a program in 6502 machine code residing at
 memory address 0x1000, which calculates the 13 first Fibonacci
 numbers and stores them at 0x1101-0x110d:
 <?xml version="1.0" encoding="UTF-8"?>
 <dump name="6502 Fibonacci" blocks="02">
   <block name="Code" address="1000" word_size="01" length="2a"
     checksum="5cab5bf8ee299af1ad17e8093d941914eb5930c7">
       a9 01 85 20 85 21 20 1e 10 20 1e 10 18 a5 21 aa
       65 20 86 20 85 21 20 1e 10 c9 c8 90 ef 60 ae 00
       11 a5 21 9d 00 11 ee 00 11 60
   </block>
   <block name="Mem" address="1100" word_size="01" length="e"
     checksum="c8c2001c42b0226a5d9f7c2f24bd47393166487a">
       01 00 00 00 00 00 00 00 00 00 00 00 00 00
   </block>
 </dump>
 The final example contains a Block of 40-bit wide data:

<?xml version="1.0" encoding="UTF-8"?> <dump name="Example of an SHF dump with wide data words" blocks="00001">

<block name="SMIL memory dump" address="000" word_size="5"
      length="1A" checksum="ff2033489aff0e4e4f0cd7901afc985f7a213c97">
    00100 00200 00000 00090 00000 00036 00300 00400
    00852 00250 00230 00858 00500 00600 014DC 00058
    002A8 000B8 00700 00800 000B0 00192 00100 00000
    00900 00A00 00000 0000A 40000 00000 00B00 00C00
    00000 00000 00000 00001 00D00 00E00 00000 00100
    0CCCC CCCCD 00F00 01000 00000 00010 80000 00000
    00100 00790 00000 00234
</block>

</dump>

8. SHF Security Considerations

 The SHF format is a format for representing hexadecimal data that one
 wants to transfer, manage, or transform.  The format itself does not
 guarantee that the represented data is not falsely represented,
 malicious, or otherwise dangerous.
 The data integrity of the SHF file as a whole is to be provided, if
 needed, by means external to the SHF file, such as the generic
 signing mechanism described by RFC 3275 [3].

Strombergson, et al. Standards Track [Page 8] RFC 4194 The S Hexdump Format October 2005

9. IANA Considerations

 This section contains the registration information for the MIME type
 to SHF.  The media type has been chosen to comply with the guidelines
 in [4].
 o  Registration: application/shf+xml
 o  MIME media type name: application
 o  MIME subtype name: shf+xml
 o  Required parameters: charset
 Required parameters: charset
 This parameter must exist and must be set to "UTF-8".  No other
 character sets are allowed for transporting SHF data.  The character
 set designator MUST be uppercase.
 Encoding considerations:
 This media type may contain binary content; accordingly, when used
 over a transport that does not permit binary transfer, an appropriate
 encoding must be applied.
 Security considerations:
 A hex Dump in itself has no other security considerations than what
 applies for any other XML file.  However, the included binary data
 may in decoded form contain any executable code for a target
 platform.  If additional security is desired, additional transport
 security solutions may be applied.  For target code contained in a
 hex Dump, developers may want to include certificates, checksums, and
 the like in hexdump form for the target platform.  Such uses are
 outside the scope of this document and a matter of implementation.
 Interoperability considerations:
 n/a
 Published specification:
 This media type is a proper subset of the XML 1.0 specification [5].
 One restriction is made: no entity references other than the five
 predefined general entities references ("&amp;", "&lt;", "&gt;",
 "&apos;", and "&quot;") and numeric entity references may be present.
 Neither the "XML" declaration (e.g., <?xml version="1.0" ?>) nor the
 "DOCTYPE" declaration (e.g., <!DOCTYPE ...>) need be present.  (XML
 fragments are allowed.)  All other XML 1.0 instructions (e.g., CDATA
 blocks, processing instructions, and so on) are allowed.

Strombergson, et al. Standards Track [Page 9] RFC 4194 The S Hexdump Format October 2005

 Applications that use this media type: any program or individual
 wishing to make use of this XML 1.0 subset for hexdump exchange.
 Additional information:
 o  Magic number: There is no single initial Byte sequence that is
    always present for SHF files
 o  File extension: shf
 o  Macintosh File Type code: none
 Intended usage: COMMON.
 Author/Change controller: this MIME transport type is controlled by
 the IETF.

10. Extensions

 The attributes of elements in the SHF XML format may be extended when
 need arises.  For example, certain applications will want to
 represent executable code as an SHF Dump, and may then need an
 execution start address to be associated with certain Dump Blocks, so
 that the address can be configured as a starting point for the CPU
 part of any processor code present in the Block, as opposed to the
 raw data, which is already given a start address by way of the
 "address" attribute.  This can be done by extending the Block tag
 with a "start_address" attribute.
 Another possible scenario is when a dump is applied to a computer
 system with several independent address spaces, such as a system with
 two CPUs, each with independent memories.  In this case, a user may
 want to add an "address_space" attribute.
 As long as such new attributes are added, with no attributes being
 removed or redefined, the resulting Dump shall be considered a valid
 SHF Dump and transported using the application/xml+shf transport
 type.  Parsers unaware of the modified namespace shall silently
 ignore any such extended attributes, or simply duplicate them from
 input to output when processing an SHF file as a filter.  The
 management of such extended attributes is a matter of convention
 between different classes of users and not a matter of the IETF.

Strombergson, et al. Standards Track [Page 10] RFC 4194 The S Hexdump Format October 2005

11. Additional Information

 Contact for further information: c.f., the "Authors' Addresses"
 section of this memo.
 Acknowledgements: The SMIL memory Dump was kindly provided by Sten
 Henriksson at Lund University.  Proofreading and good feedback on the
 SHF document was generously provided by Peter Lindgren, Tony Hansen,
 Larry Masinter, and Clive D.W. Feather.  We also want to thank the
 Applications area workgroup for their help during development.

12. Normative References

 [1]  Bradner, S., "Key words for use in RFCs to Indicate Requirement
      Levels", BCP 14, RFC 2119, March 1997.
 [2]  Eastlake, 3rd, D. and P. Jones, "US Secure Hash Algorithm 1
      (SHA1)", BCP 14, RFC 3174, September 2001.
 [3]  Eastlake, 3rd, D., Joseph, J., and D. David, "(Extensible Markup
      Language) XML-Signature Syntax and Processing", BCP 14,
      RFC 3275, March 2002.
 [4]  Makoto, M., Simon, S., and D. Dan, "(Extensible Markup Language)
      XML Media Types", RFC 3023, January 2001.
 [5]  Bray, Tim, Paoli, Jean, Sperberg-McQueen, C. M. and Maler, Eve,
      Yergeau, Francois, "Extensible Markup Language (XML) 1.0 (Third
      Edition)", http://www.w3.org/TR/REC-xml.

Strombergson, et al. Standards Track [Page 11] RFC 4194 The S Hexdump Format October 2005

Authors' Addresses

 Joachim Strombergson
 InformAsic AB
 Hugo Grauers gata 5a
 Gothenburg  411 33
 SE
 Phone: +46 31 68 54 90
 EMail: Joachim.Strombergson@InformAsic.com
 URI:   http://www.InformAsic.com/
 Linus Walleij
 Lunds Tekniska Hogskola
 Master Olofs Vag 24
 Lund  224 66
 SE
 Phone: +46 703 193678
 EMail: triad@df.lth.se
 Patrik Faltstrom
 Cisco Systems Inc
 Ledasa
 273 71 Lovestad
 Sweden
 EMail: paf@cisco.com
 URI:   http://www.cisco.com

Strombergson, et al. Standards Track [Page 12] RFC 4194 The S Hexdump Format October 2005

Full Copyright Statement

 Copyright (C) The Internet Society (2005).
 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.
 This document and the information contained herein are provided on an
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 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.

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Acknowledgement

 Funding for the RFC Editor function is currently provided by the
 Internet Society.

Strombergson, et al. Standards Track [Page 13]

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