Initial auto-updater commit: s-expression libray and format spec.

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+Filename: xxx-automatic-updates.txt
+Title: Automatic Software Update Protocol
+Version: $Revision$
+Last-Modified: $Date$
+Author: Matt Edman
+Created: 30-July-2008
+Status: Open
+
+
+Scope
+
+  This proposal specifies the method by which an automatic update client can
+  determine the most recent recommended Tor installation package for the
+  user's platform, download the package, and then verify that the package was
+  downloaded successfully. While this proposal focuses on only the Tor
+  software, the protocol defined is sufficiently extensible such that other
+  components of the Tor bundles, like Vidalia, Polipo, and Torbutton, can be
+  managed and updated by the automatic update client as well.
+
+  The initial target platform for the automatic update framework is Windows,
+  given that's the platform used by a majority of our users and that it lacks
+  a sane package management system that many Linux distributions already have.
+  Our second target platform will be Mac OS X, and so the protocol will be
+  designed with this near-future direction in mind.
+
+  Other client-side aspects of the automatic update process, such as user
+  interaction, the interface presented, and actual package installation
+  procedure, are outside the scope of this proposal.
+
+
+Motivation
+
+  Tor releases new versions frequently, often with important security,
+  anonymity, and stability fixes. Thus, it is important for users to be able
+  to promptly recognize when new versions are available and to easily
+  download, authenticate, and install updated Tor and Tor-related software
+  packages.
+  
+  Tor's control protocol [2] provides a method by which controllers can
+  identify when the user's Tor software is obsolete or otherwise no longer
+  recommended. Currently, however, no mechanism exists for clients to
+  automatically download and install updated Tor and Tor-related software for
+  the user.
+
+
+Design Overview
+
+  The core of the automatic update framework is a well-defined file called a
+  "recommended-packages" file. The recommended-packages file is accessible via
+  HTTP[S] at one or more well-defined URLs. An example recommended-packages
+  URL may be:
+
+    https://updates.torproject.org/recommended-packages
+
+  The recommended-packages document is formatted according to Section 1.2
+  below and specifies the most recent recommended installation package
+  versions for Tor or Tor-related software, as well as URLs at which the
+  packages and their signatures can be downloaded.
+
+  An automatic update client process runs on the Tor user's computer and
+  periodically retrieves the recommended-packages file according to the method
+  described in Section 2.0. As described further in Section 1.2, the
+  recommended-packages file is signed and can be verified by the automatic
+  update client with one or more public keys included in the client software.
+  Since it is signed, the recommended-packages file can be mirrored by
+  multiple hosts (e.g., Tor directory authorities), whose URLs are included in
+  the automatic update client's configuration.
+
+  After retrieving and verifying the recommended-packages file, the automatic
+  update client compares the versions of the recommended software packages
+  listed in the file with those currently installed on the end-user's
+  computer. If one or more of the installed packages is determined to be out
+  of date, an updated package and its signature will be downloaded from one of
+  the package URLs listed in the recommended-packages file as described in
+  Section 2.2.
+
+  The automatic update system uses a multilevel signing key scheme for package
+  signatures. There are a small number of entities we call "packaging
+  authorities" that each have their own signing key. A packaging authority is
+  responsible for signing and publishing the recommended-packages file.
+  Additionally, each individual packager responsible for producing an
+  installation package for one or more platforms has their own signing key.
+  Every packager's signing key must be signed by at least one of the packaging
+  authority keys.
+
+
+Specification
+
+  1. recommended-packages Specification
+
+  In this section we formally specify the format of the published
+  recommended-packages file.
+
+  1.1. Document Meta-format
+  
+  The recommended-packages document follows the lightweight extensible
+  information format defined in Tor's directory protocol specification [1]. In
+  the interest of self-containment, we have reproduced the relevant portions
+  of that format's specification in this Section. (Credits to Nick Mathewson
+  for much of the original format definition language.)
+  
+  The highest level object is a Document, which consists of one or more
+  Items.  Every Item begins with a KeywordLine, followed by zero or more
+  Objects. A KeywordLine begins with a Keyword, optionally followed by
+  whitespace and more non-newline characters, and ends with a newline.  A
+  Keyword is a sequence of one or more characters in the set [A-Za-z0-9-].
+  An Object is a block of encoded data in pseudo-Open-PGP-style
+  armor. (cf. RFC 2440)
+
+  More formally:
+
+    Document     ::= (Item | NL)+
+    Item         ::= KeywordLine Object*
+    KeywordLine  ::= Keyword NL | Keyword WS ArgumentChar+ NL
+    Keyword      ::= KeywordChar+
+    KeywordChar  ::= 'A' ... 'Z' | 'a' ... 'z' | '0' ... '9' | '-'
+    ArgumentChar ::= any printing ASCII character except NL.
+    WS           ::= (SP | TAB)+
+    Object       ::= BeginLine Base-64-encoded-data EndLine
+    BeginLine    ::= "-----BEGIN " Keyword "-----" NL
+    EndLine      ::= "-----END " Keyword "-----" NL
+
+    The BeginLine and EndLine of an Object must use the same keyword.
+  
+  In our Document description below, we also tag Items with a multiplicity in
+  brackets. Possible tags are:
+
+    "At start, exactly once": These items MUST occur in every instance of the
+    document type, and MUST appear exactly once, and MUST be the first item in
+    their documents.
+        
+    "Exactly once": These items MUST occur exactly one time in every
+    instance of the document type.
+
+    "Once or more": These items MUST occur at least once in any instance
+    of the document type, and MAY occur more than once.
+
+    "At end, exactly once": These items MUST occur in every instance of
+    the document type, and MUST appear exactly once, and MUST be the
+    last item in their documents.
+
+  1.2. recommended-packages Document Format
+
+  When interpreting a recommended-packages Document, software MUST ignore
+  any KeywordLine that starts with a keyword it doesn't recognize; future
+  implementations MUST NOT require current automatic update clients to
+  understand any KeywordLine not currently described.
+
+  In lines that take multiple arguments, extra arguments SHOULD be
+  accepted and ignored.
+
+  The currently defined Items contained in a recommended-packages document
+  are:
+
+    "recommended-packages-format" SP number NL
+
+      [Exactly once]
+
+      This Item specifies the version of the recommended-packages format that
+      is contained in the subsequent document. The version defined in this
+      proposal is version "1". Subsequent iterations of this protocol MUST
+      increment this value if they introduce incompatible changes to the
+      document format and MAY increment this value if they only introduce
+      additional Keywords.
+
+    "published" SP YYYY-MM-DD SP HH:MM:SS NL
+
+      [Exactly once]
+
+      The time, in GMT, when this recommended-packages document was generated.
+      Automatic update clients SHOULD ignore Documents over 60 days old.
+
+    "tor-stable-win32-version" SP TorVersion NL
+
+      [Exactly once]
+
+      This keyword specifies the latest recommended release of Tor's "stable"
+      branch for the Windows platform that has an installation package
+      available. Note that this version does not necessarily correspond to the
+      most recently tagged stable Tor version, since that version may not yet
+      have an installer package available, or may have known issues on
+      Windows.
+
+      The TorVersion field is formatted according to Section 2 of Tor's 
+      version specification [3].
+
+    "tor-stable-win32-package" SP Url NL
+
+      [Once or more]
+
+      This Item specifies the location from which the most recent
+      recommended Windows installation package for Tor's stable branch can be
+      downloaded.
+    
+      When this Item appears multiple times within the Document, automatic
+      update clients SHOULD select randomly from the available package
+      mirrors.
+
+    "tor-dev-win32-version" SP TorVersion NL
+
+      [Exactly once]
+    
+      This Item specifies the latest recommended release of Tor's
+      "development" branch for the Windows platform that has an installation
+      package available. The same caveats from the description of
+      "tor-stable-win32-version" also apply to this keyword.
+
+      The TorVersion field is formatted according to Section 2 of Tor's
+      version specification [3].
+
+    "tor-dev-win32-package" SP Url NL
+  
+      [Once or more]
+
+      This Item specifies the location from which the most recent recommended
+      Windows installation package and its signature for Tor's development
+      branch can be downloaded.
+
+      When this Keyword appears multiple times within the Document, automatic
+      update clients SHOULD select randomly from the available package
+      mirrors.
+
+    "signature" NL SIGNATURE NL
+
+      [At end, exactly once]
+
+      The "SIGNATURE" Object contains a PGP signature (using a packaging
+      authority signing key) of the entire document, taken from the beginning
+      of the "recommended-packages-format" keyword, through the newline after
+      the "signature" Keyword.
+
+
+  2. Automatic Update Client Behavior
+
+  The client-side component of the automatic update framework is an
+  application that runs on the end-user's machine. It is responsible for
+  fetching and verifying a recommended-packages document, as well as
+  downloading, verifying, and subsequently installing any necessary updated
+  software packages.
+
+  2.1. Download and verify a recommended-packages document
+
+  The first step in the automatic update process is for the client to download
+  a copy of the recommended-packages file. The automatic update client
+  contains a (hardcoded and/or user-configurable) list of URLs from which it
+  will attempt to retrieve a recommended-packages file.
+
+  Connections to each of the recommended-packages URLs SHOULD be attempted in
+  the following order:
+
+    1) HTTPS over Tor
+    2) HTTP over Tor
+    3) Direct HTTPS
+    4) Direct HTTP
+
+  If the client fails to retrieve a recommended-packages document via any of
+  the above connection methods from any of the configured URLs, the client
+  SHOULD retry its download attempts following an exponential back-off
+  algorithm. After the first failed attempt, the client SHOULD delay one hour
+  before attempting again, up to a maximum of 24 hours delay between retry
+  attempts.
+
+  After successfully downloading a recommended-packages file, the automatic
+  update client will verify the signature using one of the public keys
+  distributed with the client software. If more than one recommended-packages
+  file is downloaded and verified, the file with the most recent "published"
+  date that is verified will be retained and the rest discarded.
+
+  2.2. Download and verify the updated packages
+
+  The automatic update client next compares the latest recommended package
+  version from the recommended-packages document with the currently installed
+  Tor version. If the user currently has installed a Tor version from Tor's
+  "development" branch, then the version specified in "tor-dev-*-version" Item
+  is used for comparison. Similarly, if the user currently has installed a Tor
+  version from Tor's "stable" branch, then the version specified in the
+  "tor-stable-*version" Item is used for comparison. Version comparisons are
+  done according to Tor's version specification [3].
+
+  If the automatic update client determines an installation package newer than
+  the user's currently installed version is available, it will attempt to
+  download a package appropriate for the user's platform and Tor branch from a
+  URL specified by a "tor-[branch]-[platform]-package" Item. If more than one
+  mirror for the selected package is available, a mirror will be chosen at
+  random from all those available.
+
+  The automatic update client must also download a ".asc" signature file for
+  the retrieved package. The URL for the package signature is the same as that
+  for the package itself, except with the extension ".asc" appended to the
+  package URL.
+
+  Connections to download the updated package and its signature SHOULD be
+  attempted in the same order described in Section 2.1.
+
+  After completing the steps described in Sections 2.1 and 2.2, the automatic
+  update client will have downloaded and verified a copy of the latest Tor
+  installation package. It can then take whatever subsequent platform-specific
+  steps are necessary to install the downloaded software updates.
+
+  2.3. Periodic checking for updates
+
+  The automatic update client SHOULD maintain a local state file in which it
+  records (at a minimum) the timestamp at which it last retrieved a
+  recommended-packages file and the timestamp at which the client last
+  successfully downloaded and installed a software update.
+
+  Automatic update clients SHOULD check for an updated recommended-packages
+  document at most once per day but at least once every 30 days.
+
+
+  3. Future Extensions
+
+  There are several possible areas for future extensions of this framework.
+  The extensions below are merely suggestions and should be the subject of
+  their own proposal before being implemented.
+  
+  3.1. Additional Software Updates
+  
+  There are several software packages often included in Tor bundles besides
+  Tor, such as Vidalia, Privoxy or Polipo, and Torbutton. The versions and
+  download locations of updated installation packages for these bundle
+  components can be easily added to the recommended-packages document
+  specification above.
+
+  3.2. Including ChangeLog Information
+
+  It may be useful for automatic update clients to be able to display for
+  users a summary of the changes made in the latest Tor or Tor-related
+  software release, before the user chooses to install the update. In the
+  future, we can add keywords to the specification in Section 1.2 that specify
+  the location of a ChangeLog file for the latest recommended package
+  versions. It may also be desirable to allow localized ChangeLog information,
+  so that the automatic update client can fetch release notes in the
+  end-user's preferred language.
+
+  3.3. Weighted Package Mirror Selection
+
+  We defined in Section 1.2 a method by which automatic update clients can
+  select from multiple available package mirrors. We may want to add a Weight
+  argument to the "*-package" Items that allows the recommended-packages file
+  to suggest to clients the probability with which a package mirror should be
+  chosen. This will allow clients to more appropriately distribute package
+  downloads across available mirrors proportional to their approximate
+  bandwidth.
+
+
+Implementation
+
+  Implementation of this proposal will consist of two separate components.
+
+  The first component is a small "au-publish" tool that takes as input a
+  configuration file specifying the information described in Section 1.2 and a
+  private key. The tool is run by a "packaging authority" (someone responsible
+  for publishing updated installation packages), who will be prompted to enter
+  the passphrase for the private key used to sign the recommended-packages
+  document. The output of the tool is a document formatted according to
+  Section 1.2, with a signature appended at the end. The resulting document
+  can then be published to any of the update mirrors.
+
+  The second component is an "au-client" tool that is run on the end-user's
+  machine. It periodically checks for updated installation packages according
+  to Section 2 and fetches the packages if necessary. The public keys used
+  to sign the recommended-packages file and any of the published packages are
+  included in the "au-client" tool.
+
+
+References
+  
+  [1] Tor directory protocol (version 3),
+  https://tor-svn.freehaven.net/svn/tor/trunk/doc/spec/dir-spec.txt
+  
+  [2] Tor control protocol (version 2),
+  https://tor-svn.freehaven.net/svn/tor/trunk/doc/spec/control-spec.txt
+
+  [3] Tor version specification,
+  https://tor-svn.freehaven.net/svn/tor/trunk/doc/spec/version-spec.txt
diff --git a/specs/U2-formats.txt b/specs/U2-formats.txt
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+
+
+Scope
+
+   This document descibes a repository and document format for use in
+   distributing Tor bundle updates.  It is meant to be a component of
+   an overall automatic update system.
+
+   Not described in this document is the design the packages or their
+   install process, though some requirements are listed.
+
+Proposed code name
+
+   Since "auto-update" is so generic, I've been thinking about going with
+   with "hapoc" or "glider" or "petaurus", all based on the sugar
+   glider you get when you search for "handy pocket creature".
+
+Metaformat
+
+   All documents use Rivest's SEXP meta-format as documented at
+     http://people.csail.mit.edu/rivest/sexp.html
+   with the restriction that no "display hint" fields are to be used,
+   and the base64 transit encoding isn't used either.
+
+   In descriptions of syntax below, we use regex-style qualifiers, so
+   that in
+        (sofa slipcover? occupant* leg+)
+   the sofa will have an optional slipcover, zero or more occupants,
+   and one or more legs.  This pattern matches (sofa leg) and (sofa
+   slipcover occupant occupant leg leg leg leg) but not (sofa leg
+   slipcover).
+
+   We also use a braces notation to indicate elements that can occur
+   in any order.  For example,
+        (bread {flour+ eggs? yeast})
+   matches a list starting with "bread", and then containing a one or
+   more occurances of flours, zero or one occurances of eggs, and one
+   occurance of yeast, in any order.  This pattern matches (bread eggs
+   yeast flour) but not (bread yeast) or (bread flour eggs yeast
+   macadamias).
+
+
+Goals
+
+   It should be possible to mirror a repository using only rsync and cron.
+
+   Separate keys should be used for different people and different
+   roles.
+
+   Only a minimal set of keys should have to be kept online to keep
+   the system running.
+
+   The system should handle any single computer or system or person
+   being unavailable.
+
+   The system should be pretty future-proof.
+
+   The client-side of the architecture should be really easy to implement.
+
+Non-goals:
+
+   This is not a package format.  Instead, we reuse existing package
+   formats for each platform.
+
+   This is not a general-purpose package manager like yum or apt: it
+   assumes that users will want to have one or more of a set of
+   "bundles", not an arbitary selection of packages dependant on one
+   another.
+
+   This is also not a general-purpose package format.  It assumes the
+   existance of an external package format that can handle install,
+   update, remove, and version query.
+
+Architecture: Repository
+
+   A "repository" is a directory hierarchy containing packages,
+   bundles, and metadata, all signed.
+
+   A "package" is a single independent downloadable, installable
+   binary archive.  It could be an MSI, an RPM, a DMG, or so on.
+   Every package is compiled version of some version of some piece of
+   software (an 'application') for some (os, architecture,
+   version) combinations.  Some packages are "glue" that make other
+   packages work well together or get configured properly.
+
+   A "bundle" is a list of of packages to be installed together.
+   Examples might be "Tor Browser Bundle" or "Tor plus controller".  A
+   bundle is versioned, and every bundle is for a particular (os,
+   architecture) combination.  Bundles specify which order to install
+   or update their components.
+
+   Metadata is used to:
+     - Find mirrors
+     - Validate packages, bundles, and metadata
+     - Make sure information is up-to-date
+     - Determine which packages are in a bundle
+
+   The filesystem layout in the repository is used for two purposes:
+     - To give mirrors an easy way to mirror only some of the repository.
+     - To specify which parts of the repository a given key has the
+       authority to sign.
+
+Architecture: Roles
+
+   Every role in the system are associated with a key.  Replacing
+   anything but a root key is supposed to be relatively easy.
+
+   Root-keys sign other keys, and certify them as belonging to roles.
+   Clients are configured to know the root keys.
+
+   Bundle keys certify the contents of a bundle.
+
+   Package keys certify packages for a given program or set of
+   programs.
+
+   Mirror keys certify a list of mirrors.  We expect this to be an
+   automated process.
+
+   Timestamp keys certify that given versions of other metadata
+   documents are up-to-date.  They are the only keys that absolutely
+   need to be kept online.  (If they are not, timestamps won't be
+   generated.)
+
+Directory layout
+
+   The following files exist in all repositories and mirrors:
+
+    /meta/keys.txt
+
+         Signed by the root keys; indicates keys and roles.
+         [XXXX I'm using the txt extension here.  Is that smart?]
+
+    /meta/mirrors.txt
+
+         Signed by the mirror key; indicates which parts of the repo
+         are mirrored where.
+
+    /meta/timestamp.txt
+
+         Signed by the timestamp key; indicates hashes and timestamps
+         for the latest versions of keys.txt and mirrors.txt.  Also
+         indicates the latest version of each bundle for each os/arch.
+
+    /bundleinfo/bundlename/os-arch/bundlename-os-arch-bundleversion.txt
+
+         Signed by the appropriate bundle key.  Describes what
+         packages make up a bundle, and what order to install,
+         uninstall, and upgrade them in.
+
+    /pkginfo/packagename/os-arch/version/packagename-os-arch-packageversion.txt
+
+         Signed by the appropriate package key.  Tells the name of the
+         file that makes up the bundle, its hash, and what procedure
+         is used to install it.
+
+    /packages/packagename/os-arch/version/(some filename)
+
+         The actual files 
+
+File formats: general principles
+
+   We use tagged lists (lists whose first element is a string) to
+   indicate typed objects.  Tags are generally lower-case, with
+   hyphens used for separation.  Think Lispy.
+
+   We use attrlists [lists of (key value) lists] to indicate a
+   multimap from keys to values.  Clients MUST accept unrecognized
+   keys in these attrlists.  The syntax for an attrlist with two
+   recognized and required keys is typically given as ({(key1 val1)
+   (key2 val2) (ATTR VAL)*}), indicating that the keys can occur in
+   any order, intermixed with other attributes.
+
+   Timestamp files will be downloaded very frequently; all other files
+   will be much smaller in size than package files.  Thus,
+   size-optimization for timestamp files makes sense and most other
+   other space optimizations don't.
+
+   Versions are represented as lists of the form (v I1 I2 I3 I4 ...)
+   where each item is a number or alphanumeric version component.  For
+   example, the version "0.2.1.5-alpha" is represented as (v 0 2 1 5
+   alpha).
+
+   All signed files are of the format:
+
+       (signed
+          X
+          (signature ({(keyid K) (method M) (ATTR VAL)*}) SIG)+
+       )
+
+   where: X is a list whose fist element describes the signed object.
+          K is the identifier of a key signing the document
+          M is the method to be used to make the signature
+          (ATTR VAL) is an arbitrary list whose first element is a
+             string.
+          SIG is a signature of the canonical encoding of X using the
+          identified key.
+
+   We define two signing methods at present:
+       sha256-oaep : A signature of the SHA256 hash of the canonical
+         encoding of X, using OAEP+ padding. [XXXX say more about mgf]
+
+   All times are given as strings of the format "YYYY-MM-DD HH:MM:SS",
+   in UTC.
+
+   All keys are of the format:
+      (pubkey ({(type TYPE) (ATTR VAL)*}) KEYVAL)
+   where TYPE is a string describing the type of the key and how it's
+   used to sign documents.  The type determines the interpretation of
+   KEYVAL.
+
+   The ID of a key is the type field concatenated with the SHA-256
+   hash of the canonical encoding of the KEYVAL field.
+
+   We define one keytype at present: 'rsa'.  The KEYVAL in this case is a
+   2-element list of (e p), with both values given in big-endian
+   binary format.  [This makes keys 45-60% more compact.]
+
+File formats: key list
+
+   (keylist
+     (ts TIME)
+     (keys
+       ((key ({(roles (ROLE PATH)+) (ATTR VAL)*}) KEY)*)
+     ...
+   )
+
+   The "ts" line describes when the keys file was updated.  Clients
+   MUST NOT replace a file with an older one, and SHOULD NOT accept a
+   file too far in the future.
+
+   A ROLE is one of "timestamp" "mirrors" "bundle" or "package"
+
+   PATH is a path relative to the top of the directory hierarchy.  It
+   may contain "*" elements to indicate "any file", and may end with a
+   "/**" element to indicate all files under a given point.
+
+File formats: mirror list
+
+   (mirrorlist
+     (ts TIME)
+     (mirrors
+       ( (mirror ({(name N) (urlbase U) (contents PATH+) (ATTR VAL)})) * )
+     ...
+  )
+
+  Every mirror is a copy of some or all of the directory hierarchy
+  containing at least the /meta, /bundles/, and /pkginfo directories.
+
+  N is a descriptive name for the mirror; U is the URL of the mirror's
+  base (i.e., the parent of the "meta" directory); and the PATH
+  elements are the components describing how much of the packages
+  directory is mirrored.  Their format is as in the keylist file.
+
+File formats: timestamp files
+  (ts
+    ({(at TIME)
+      (m TIME MIRRORLISTHASH)
+      (k TIME KEYLISTHASH)
+      (b NAME VERSION TIME PATH HASH)*})
+  )
+
+  TIME is when the timestamp was signed.  MIRRORLISTHASH is the digest
+  of the mirror-list file; KEYLISTHASH is the digest of the key list
+  file; and the 'b' entries are a list of the latest version of each
+  bundles and their locations and hashes.
+
+File formats: bundle files
+
+  (bundle
+    (at TIME)
+    (os OS)
+    [(arch ARCH)]
+    (version V)
+    (packages
+      (NAME VERSION PATH HASH ({(order INST UPDATE REMOVE)
+                                (optional)?
+                                (gloss LANG TEXT)*
+                                (longloss LANG TEXT)*
+                                 (ATTR VAL)*})? )* )
+  )
+
+  Most elements are self-explanatory; the INST, UPDATE, and REMOVE
+  elements of the order element are numbers defining the order in
+  which the packages are installed, updated, and removed respectively.
+  The "optional" element is present if the package is optional.
+  "Gloss" is an short utf-8 human-readable string explaining what the
+  package provides for the bundle; "longloss" is a longer such
+  utf-8 string.
+
+  (Note that the gloss strings are meant, not to describe the package,
+  but to describe what the package provides for the bundle.  For
+  example, "The Anonymous Email Bundle needs the Python Runtime to run
+  Mixminion.")
+
+File formats: package files
+  (package
+    ({(name NAME)
+     (version VERSION)
+     (format FMT ((ATTR VAL)*)? )
+     (path PATH)
+     (ts TIME)
+     (digest HASH)
+     (shortdesc LANG TEXT)*
+     (longdesc LANG TEXT)*
+     (ATTR VAL)* })
+  )
+
+  Most elements are self-explanatory.  The "FMT" element describes the
+  file format of the package, which should give enough information
+  about how to install it.
+
+  No two package files in the same repository should have the same
+  name and version.  If a package needs to be changed, the version
+  MUST be incremented.
+
+Workflows: The client application
+
+  Periodically, the client updater fetches a timestamp file from a
+  mirror.  If the timestamp in the file is up-to-date, the client
+  first checks to see whether the keys file listed is one that the
+  client has.  If not, the client fetches it, makes sure the hash of
+  the keys file matches the hash in the timestamp file, makes sure its
+  date is more recent than any keys file they have but not too far in
+  the future, and that it is signed by enough root keys that the
+  client recognizes.
+
+       [If the timestamp file is not up-to-date, the client tries a
+       few mirrors until it finds one with a good timestamp.]
+
+       [If the keys file from a mirror does not match the timestamp
+       file, the client tries a new mirror for both.]
+
+       [If the keys file is not signed by enough root keys, the client
+       warns the user and tries another mirror for both the timestamp
+       file and the keys file.]
+
+  Once the client has an up-to-date keys file, the client checks the
+  signature on the timestamp file.  Assuming it checks out, the client
+  refreshes the mirror list as needed, and refreshes any bundle files
+  to which the user is subscribed if the client does not have
+  the latest version of those files.  The client checks signatures on
+  these files, and fetches package metadata for any packages listed in
+  the bundle file that the client does not have, checks signatures on
+  these, and fetches binaries for packages that might need to be
+  installed or updated.  As the packages arrive, clients check their
+  hashes.
+
+  Once the client has gotten enough packages, it informs the user that
+  new packages have arrived, and asks them if they want to update.
+
+  Clients SHOULD cache at least the latest versions they have received
+  of all files.
+
+Workflow: Mirrors
+
+  Periodically, mirrors do an rsync or equivalent to fetch the latest
+  version of whatever parts of the repository have changed since the
+  version they currently hold.  Mirrors SHOULD replace older versions
+  of the repository idempotently, so that clients are less likely to
+  see inconsistant state.  Mirrors SHOULD validate the information
+  they receive, and not serve partial or inconsistant files.
+
+Workflow: Packagers
+
+  When a new binary package is done, the person making the package
+  runs a tool to generate and sign a package file, and sends both the
+  package and the package file to a repository admin.  Typically, the
+  base package file will be generated by inserting a version into a
+  template.
+
+  Packages MAY have as part of their build process a script to
+  generate the appropriately versioned package file.  This script
+  should at a minimum demand a build version, or use a timestamp in
+  place of a build version, to prevent two packages with the same
+  version from being created.
+
+Workflow: bundlers
+
+  When the packages in a bundle are done, the bundler runs a tool on
+  the package files to generate and sign a bundle file.  Typically,
+  this tool uses a template bundle file.
+
+Workflow: repository administrators
+
+  Repository administrators use a tool to validate signed files into the
+  repository.  The repository should not be altered manually.
+
+  This tool acts as follows:
+     - Package files may be added, but never replaced.
+     - Bundle files may be added, but never replaced.
+     - No file may be added unless it is syntactically valid and
+       signed by a key in the keys file authorized to sign files of
+       this type in this file's location location.
+
+     - A package file may not be added unless all of its binary
+       packages match their hashes.
+
+     - A bundle file may not be added unless all of its package files
+       are present and match their hashes.
+
+     - When adding a new keylist, bundle, or mirrors list, the
+       timestamp file must be regenerated immediately.
+
+Timing:
+
+  The timestamp file SHOULD be regenerated every 15 minutes.  Mirrors
+  SHOULD attempt to update every hour.  Clients SHOULD accept a
+  timestamp file up to 6 hours old.
+
+Format versioning and forward-compatibility:
+
+  All of the above formats include the ability to add more
+  attribute-value fields for backwards-compatible format changes.  If
+  we need to make a backwards incompatible format change, we create a
+  new filename for the new format.
+
+Key management and migration:
+
+  Root keys should be kept offline.  All keys except timestamp and
+  mirror keys should be stored encrypted.
+
+  All the formats above allow for multiple keys to sign a single
+  document.  To replace a compromised master key, it suffices to sign
+  keylist documents with both the compromised key and its replacement
+  until all clients have updated to a new version of the autoupdater.
+
+  To replace another key, it suffices to authorize the new key in the
+  keylist.  Note that a new package or bundle key must re-sign and
+  issue new versions of all packages or bundles it has generated.
+