Rename spec to be useful ; remove redundant copy of matt's spec draft.

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diff --git a/specs/U2-formats.txt b/specs/U2-formats.txt
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-
-0. Preliminaries
-
-0.0. Scope
-
-   This document describes a system for distributing Tor bundle updates.
-
-0.1. Proposed code name
-
-   Since "auto-update" is so generic, I've been thinking about going with
-   "glider", based on the sugar glider you get when you search for "handy
-   pocket creature".  I haven't yet done a search to find out whether
-   somebody else is using the name, so we shouldn't get too attached to it
-   before we see if it's taken.
-
-0.2. Goals
-
-   Once Tor was a single executable that you could just run.  Then it
-   required Privoxy.  Now, thanks to the Tor Browser Bundle and related
-   projects, a full installation can contain Tor, Privoxy, Torbutton,
-   Firefox, and more.
-
-   We need to keep this software updated.  When we make security fixes,
-   quick uptake helps narrow the window in which attackers can exploit
-   them.
-
-   We need updates to be easy.  Each additional step a user must take to
-   get updated means that more users will stay with older insecure
-   versions.
-
-   We need updates to be secure.  We're supposed to be good at crypto;
-   let's act like it.  There is no good reason in this day and age to
-   subject users to rollback attacks or unsigned packages or whatever.
-
-   We need administration to be simple.  Tor doesn't have a release
-   engineering team, so we can't add too many hard steps to putting out
-   a new release.
-
-   The system should be easy to implement; we may need to do multiple
-   implementations on the client side at least.
-
-0.2.1. Goals for package formats and PKIs
-
-   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 formats and protocols should be pretty future-proof.
-
-0.3. Non-goals
-
-   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 arbitrary selection of packages dependant on one
-   another.  (Rationale: these systems do what they do pretty well.)
-
-   This is also not a general-purpose package format.  It assumes the
-   existence of an external package format that can handle install,
-   update, remove, and version query.  (Rationale:
-
-1. System overview
-
-   The basic unit of updatability is a "bundle".  A bundle is a set of
-   software components, or "packages", plus some rules about installing
-   them.  Example bundles could be "Tor Browser, stable series" or
-   "Basic Tor, development series".
-
-   When Glider has responsibility for keeping a bundle up to date, we
-   say that a user has "subscribed" to that bundle.
-
-   Conceptually, there are four parts to keeping a bundle up to date:
-
-      Polling:
-        - Periodically, Glider asks a mirror whether there is a newer
-          version of some bundle that a user has subscribed to.  If so,
-          Glider determines what's in the bundle.
-
-      Fetching:
-        - If the bundle contains packages that Glider hasn't installed
-          or hasn't cached, it needs to download them from a mirror.
-          This can happen over any protocol; v1 should support at least
-          http and https-over-Tor.  V1 should also support resuming
-          partial downloads, since many users have unreliable
-          connections.
-
-          Later versions could support Bittorrent, or whatever.
-
-      Validation:
-        - Throughout the process, Glider must ensure that all the
-          bundles are signed correctly, all the packages are signed
-          correctly, and everything is up-to-date.
-
-          We want to specify this so that users can't be tricked about
-          the contents of a bundle, can't install a malicious package,
-          and can't be fooled into believing that an old bundle is
-          actually the latest.
-
-      Installation:
-        - Now Glider has a set of packages to install.  The format of
-          these packages will be platform-dependent: they could be pkg
-          files on OSX, MSI files on Win32, RPMs or DEBs on Linux, and
-          so on.  Glider should query the user for permission to start,
-          then install the packages.
-
-1.1. The repository
-
-   Each Glider instance knows about one or more "repositories".  A
-   repository is a filesystem somewhere that contains the packages in a
-   set of bundles, and some associated metadata.  A repository must
-   exist at one or more canonical hosts, and may have a number of full
-   or partial mirrors.
-
-   In v1, each Glider instance will know about only one repository.
-
-1.2. The PKI
-
-   The trust root for the whole system is, necessarily, whatever users
-   download when they first download a copy of Glider.  We need to make
-   sure that the first download happens from a site we trust, using
-   HTTPS.
-
-   Glider ships with root keys, which in turn are used to verify the
-   keys for all the other roles.  There are a few root keys, operated by
-   trusted admins for the system.  If root keys ever need to be changed,
-   we can just ship an update of Glider: it's supposed to be
-   self-updating anyway.
-
-   The root keys are only used to sign a 'key list' of all the other
-   keys and their roles.  A key list is valid if it has been signed by a
-   threshold of root keys.
-
-   Each package is signed with the key of its authorized builder.  For
-   example, one volunteer may be authorized to build the mac versions of
-   several packages, and another may be authorized to build the windows
-   version of just one.
-
-   Each bundle is signed with the key of its maintainer.  It's assumed
-   that the bundle maintainer might be the package maintainer for some
-   but not all of the packages.
-
-   The list of mirrors is also signed.  If the mirror list is
-   automatically updated, this key must be kept online; otherwise, it
-   can be offline.
-
-   To prevent an adversary from replaying an out-of-date signed
-   document, an automated process periodically signs a timestamped
-   statement containing the hashes of the mirror list, the latest
-   bundles, and the key list, using yet another special-purpose key.
-   This key must be kept online.
-
-1.3. Threat Model And Analysis
-
-   We assume an adversary who can operate compromised mirrors, and who
-   can possibly compromise the main repository.  At worst, such an
-   adversary can DOS users in a way that they can detect.
-
-   We're assuming for the moment an OSX/Win32-like execution model,
-   where all packages will run equal privilege, but occasionally
-   installation will require higher privilege.  This means that once a
-   hostile package is installed, it can basically do whatever it
-   wants.  As rootkit writers demonstrate, compromise is really
-   tenuous: any attacker who can induce a user to install a hostile
-   piece of code has, in effect, permanently compromised that user
-   until they reinstall.
-
-   Thus, if an adversary compromises enough keys to sign a compromised
-   package, or tricks a packager into signing a compromised package,
-   and manages to get that package into a signed bundle, the best we
-   can do is to limit the number of users who are affected.  We do
-   this by compartmentalizing signing keys so that only the package
-   and bundle in question are at risk.
-
-   (If we had replicated build processes and a bit-by-bit reliable
-   build process, we could have multiple packagers test that a binary
-   was built properly, and multiply sign it.  This would be effective
-   against an adversary compromising a single packaging key, but not
-   against one compromising a source repository.)
-
-2. The repository layout
-
-   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.
-
-   The following files exist in all repositories and mirrors:
-
-    /meta/keys.txt
-
-         Signed by the root keys; indicates keys and roles.
-         [???? I'm using the txt extension here.  Is that smart?]
-
-    /meta/mirrors.txt
-
-         Signed by the mirror key; indicates which parts of the
-         repository are mirrored at what mirrors.
-
-    /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.
-
-         This is the only file that needs to be downloaded for polling.
-
-    /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 a package, its hash, and what procedure
-         is used to install it.
-
-    /packages/packagename/os-arch/version/(some filename)
-
-         The actual package file.  Its naming convention will depend
-         on the underlying packaging system.
-
-3. Document formats
-
-3.1. 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.
-
-   (We use SEXP because it's really easy to parse, really portable,
-   and unlike most other tagged data formats, has a
-   trivially-specified canonical format suitable for hashing.)
-
-   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 one or
-   more  of flours, zero or one occurrences of eggs, and one
-   occurrence of yeast, in any order.  This pattern matches (bread eggs
-   yeast flour) but not (bread yeast) or (bread flour eggs yeast
-   macadamias).
-
-3.2. 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 first 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 n), with both values given in big-endian
-   binary format.  [This makes keys 45-60% more compact than using
-   decimal integers.]
-
-   All RSA keys must be at least 2048 bits long.
-
-
-   Every role in the system is 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.)
-
-3.3. File formats: key list
-
-   The key list file is signed by multiple root keys.  It indicates
-   which keys are authorized to sign which parts of the repository.
-
-   (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.
-
-3.4. File formats: mirror list
-
-   The mirror list is signed by a mirror key.  It indicates which
-   mirrors are active and believed to be mirroring which parts of the
-   repository.
-
-   (mirrorlist
-     (ts TIME)
-     (mirrors
-       ( (mirror ({(name N) (urlbase U) (contents PATH+) (weight W)
-                   (official)?  (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.
-
-  W is an integer used to weight mirrors when picking at random;
-  mirrors with more bandwidth should have higher weigths.   The
-  "official" element should only be present if the mirror is (one of
-  the) official repositories operated by the Tor Project.
-
-3.5. File formats: timestamp files
-
-  The timestamp file is signed by a timestamp key.  It indicates the
-  latest versions of other files, and contains a regularly updated
-  timestamp to prevent rollback attacks.
-
-  (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.
-
-3.6. 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 a 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.")
-
-  Multiple gloss strings are allowed; each should have a different
-  language. The UI should display the must appropriate language to the
-  user.
-
-3.7. 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.
-
-  Descriptions are tagged with languages in the same way as glosses.
-
-4. Detailed Workflows
-
-4.1. 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.
-
-4.1.1. Download preferences
-
-  Users should be able to specify that packages must be only
-  downloaded over Tor, or must only be downloaded over encrypted
-  protocols, or both.  Users should also be able to force 
-
-4.2. 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 inconsistent state.  Mirrors SHOULD validate the information
-  they receive, and not serve partial or inconsistent files.
-
-4.3. 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.
-
-4.4. 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.
-
-4.5. 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.
-
-5. Parameter setting and corner cases.
-
-5.1. 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.
-
-5.2. 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.
-
-5.3. 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 root 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.
-
-
-
-F. Future directions and open questions
-
-F.1. Package decomposition
-
-  It would be neat to decouple existing packages.  Right now, we'd
-  never want a windows user to have to fetch an openssl dll and Tor
-  separately.  But if they're using an auto-update tool, it'd be
-  pretty keen to have them not need to fetch a new openssl every time
-  Tor has a bugfix.
-
-F.2. Caching at Tor servers.
-
-  See Tor Proposal number 127.
-
-F.3. Support for more download methods
-
-  Ozymandns, chunked downloads, and bittorrent would all be neat
-  ideas.
-
-
-R. Ideas I'm rejecting for the moment
-
-R.1. Considering recommended versions from Tor consensus directory documents
-
-  This requires a working Tor to update Tor; that's not necessarily a
-  great idea.
-
-R.2. Integration with existing GPG signatures
-
-  The OpenPGP signature and key format is so complicated that you'd
-  have to be mad to touch it.
-
-
-
-
-