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Network Working Group                                    J. StrombergsonRequest for Comments: 4194                                 InformAsic ABCategory: Standards Track                                     L. Walleij                                                 Lunds Tekniska Hogskola                                                            P. Faltstrom                                                       Cisco Systems Inc                                                            October 2005The S Hexdump FormatStatus 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 differentStrombergson, 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 inRFC 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 theRFC3174      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 20054.2.  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 byRFC 3275 [3].Strombergson, et al.        Standards Track                     [Page 8]

RFC 4194                  The S Hexdump Format              October 20059.  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 200511.  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 2005Authors' 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.comStrombergson, et al.        Standards Track                    [Page 12]

RFC 4194                  The S Hexdump Format              October 2005Full Copyright Statement   Copyright (C) The Internet Society (2005).   This document is subject to the rights, licenses and restrictions   contained inBCP 78, and except as set forth therein, the authors   retain all their rights.   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 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.Intellectual Property   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 inBCP 78 andBCP 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 athttp://www.ietf.org/ipr.   The IETF invites any interested party to bring to its attention any   copyrights, patents or patent applications, or other proprietary   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.Acknowledgement   Funding for the RFC Editor function is currently provided by the   Internet Society.Strombergson, et al.        Standards Track                    [Page 13]