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- This is just a very rough draft. If anyone wants to take this up as a FOSS
- project, feel free; I only ask that Taylor and I be mentioned somewhere in the
- credits.
- ################################################################################
- _____ __ _____ _ _
- / ____| / _| / ____| (_) | |
- | (___ __ _| |_ ___ _ _| (___ ___ _ __ _ _ __ | |_
- \___ \ / _` | _/ _ \ '__\___ \ / __| '__| | '_ \| __|
- ____) | (_| | || __/ | ____) | (__| | | | |_) | |_
- |_____/ \__,_|_| \___|_| |_____/ \___|_| |_| .__/ \__|
- | |
- |_| (The name is negotiable)
- _______________________________________________________________________________
- \ ;
- \ Making Javascript Safer, Preventing XSS Payloads ;
- \ @voodooKobra (Scott Arciszewski) ;
- \ Further suggestions by @DefuseSec (Taylor Hornby) ;
- \__________________________________________________________________________;
- WHAT IS IT?
- An optional way to configure only digitally signed Javascript for websites
- set up to use it.
- COMPONENTS
- o Browser plugin (Firefox at first, eventually Chrome & Opera?)
- o Netbeans plugin (for developers)
- o CLI Program (integrates with gnupg) for the server
- o Source file on the server
- o Publicly accessible whitelist file
- o Network of notaries which audit the signed whitelists to detect abuse
- _____________________
- | The Browser Plugin \______________________________________________________
- | |
- | For security-conscious users, the SaferScript browser plugin would request |
- | a whitelist of .js files (and their sha256 checksums), which should be |
- | signed by the developer's GPG private key. |
- | |
- | (Note: In case SHA-256 is ever broken it needs to be able to support other |
- | hash functions, such as the SHA-3 family, Whirlpool, and RIPEMD.) |
- | |
- | If we do not know the public key, we will request it from the server and |
- | check with notaries that the user trusts that they see the same key. If |
- | the website has been queried before, the notary will also compare the |
- | public key it received with the one archived. |
- | |
- | The code will then verify the signature of the whitelist. If it matches, |
- | then each .js file will be downloaded and their checksums will be verified |
- | before they are loaded into memory. If any of their checksums doesn't |
- | match, then that .js file is not loaded and the user is notified. |
- | |
- | For public key verification, The browser will then send an SHA-256 digest |
- | of the whitelist to a notary. If the notary does not have a record of that |
- | whitelist, our network will request the whitelist and compare the digest |
- | with the one submitted by the user. If it doesn't match, the user is |
- | notified and they fail back to a copy that was signed and stored in the |
- | public record. |
- | |
- | If the signature matches but it is an updated version of the Javascript |
- | (and the notary has cached a copy of the same whitelist), the user will be |
- | notified of the change and asked if they wish to examine the differences |
- | between the old version and the new version. (This can be turned off for |
- | non-tech-savvy users; all changes that any user experiences should be |
- | mirrored on the notaries, assuming they have opted in.) |
- | |
- | No other Javascript will load. Even inline function calls (onClick="" etc) |
- | will have to be rewritten as $("#objectID").click( function() { }); |
- | |
- | If the GPG signature doesn't match, NO Javascript will load for the entire |
- | domain until the developer updates the signed whitelist with new checksums |
- | and an updated signature. |
- | |
- | Two further levels of paranoia will also be available: If a .css file is |
- | specified in the whitelist, no other stylesheet changes (outside of those |
- | made by trusted Javascript) will be registered. Additionally, if a .png, |
- | .jpg, .gif (etc) file is listed, all other images will be blacklisted. |
- | These paranoid modes are entirely optional and suited to self-contained |
- | apps rather than content portals that depend on user-generated content. |
- | |
- | Notaries are selected when a user first installs the addon. Trust may be |
- | revoked by the user at any time should they change their mind. |
- |____________________________________________________________________________|
- __________________
- | The CLI Program \_________________________________________________________
- | |
- | For developers who prever to SSH directly into their production system, |
- | the CLI program would reconstruct (calculate sha256 checksums and GPG sign |
- | the list) the whitelist textfile. |
- | |
- | root@server~$: saferscript /root/whitelist.src /var/www/white.list |
- | Calculating SHA-256 checksums: |
- | /var/www/jquery.js: |
- | ea3b35ed94f9e600c29ca51d2ee1f6efb03d1389ea5455d2596ca32af1f6aadd |
- | /var/www/interface.js: |
- | f75062d19a9e56f0d002f9a93c909636e559ff16b0c8c712e84d207a434e66d8 |
- | Enter GnuPG Password to sign the new whitelist: |
- | Your SaferScript whitelist is located at /var/www/white.list |
- | root@server~$: _ |
- |____________________________________________________________________________|
- _____________________
- | The Whitelist Files \______________________________________________________
- | |
- | There would be two files: One you edit that tells the CLI script which .js |
- | files should be checksummed and included in the GPG-signed whitelist, and |
- | the latter file which should be served publicly (http://domain/white.list) |
- | |
- | Source File (typically whitelist.src) |
- | - Line 1 should contain the document root folder |
- | - Lines 2-n should contain the relative path of each script to be included |
- | |
- | Public Whitelist (should be /white.list) |
- | /jquery.js:sha256:ea3b35ed94f9e600c29ca51d2ee1f6efb03d1389ea5455d2596ca... |
- | /interface.js:sha256:f75062d19a9e56f0d002f9a93c909636e559ff16b0c8c712e8... |
- | (Truncated here for the sake of formatting) |
- | (Then, the PGP signature goes below) |
- | |
- | As stated above, the source public whitelist can also contain image or CSS |
- | files if the developer is truly paranoid. |
- |____________________________________________________________________________|
- ______________________
- | The Netbeans Plugin \_____________________________________________________
- | |
- | For convenience when updating a project on a remote server, without having |
- | to login through SSH and run the saferscript CLI, a Netbeans plugin would |
- | be created that would run the command for you every time you update your |
- | Javascript files. |
- | |
- | The whitelist generation would take place entirely on the developer's box, |
- | but an option to mirror your whitelist source file would be available. |
- | |
- | (Netbeans was chosen because it's currently the best free and open source |
- | IDE for PHP projects on a remote server.) |
- |____________________________________________________________________________|
- ________________
- | Notary Network \___________________________________________________________
- | |
- | Inspired in part by the EFF's SSL Observatory and Moxie Marlinspike's |
- | Convergence, we would need to set up a robust network capable of handling |
- | three tasks: |
- | 1. When a user passes a hostname:SHA hash of a server's whitelist, the |
- | notaries will see if the hash already exists in its records. If it |
- | doesn't, the notary requests the white.list, records it, and also |
- | verifies that the copy it has on file is the same as the copy the user |
- | forwarded. This should prevent targeted attacks. |
- | 2. When a user passes the hostname:SHA hash of a server's purported GPG |
- | public key, the server will check to see if it's a known key for that |
- | particular host. It will also request the key itself and make sure it |
- | sees the same key, and store a publicly auditable copy. |
- | 3. It allows the general public to verify and audit the signed code on |
- | websites that use this feature, by mirroring this data on a public web |
- | site on a different network. |
- |____________________________________________________________________________|
- .~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~,
- { PROCESS FLOW (PROGRAM LOGIC) }
- `^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^'
- A request is sent to a webserver
- Has the user already established the credibility of the code this session?
- YES:
- > Just load whatever settings were cached to minimize overhead
- NO:
- > Do we have a cached copy of the development team's GPG key?
- > YES:
- >> Continue.
- > NO:
- >> !Fallback feature so we can support Tor Hidden Services
- >> (Make it possible to disable this feature?)
- >> Does /dev.public exist?
- >> YES:
- >>> Fetch /dev.public, which should contain the public key
- >>> SHA2/3 hash the file
- >>> Pass it to the Notaries for GPG key verification
- >>> The notaries will let you know if that's a known public key on
- >>> file for that hostname. This is a weak authentication so...
- >>> Prompt the user whether or not they trust the public key
- >>> YES:
- >>>> Save the public key to cache for the hostname
- >>> NO:
- >>>> Disable Javascript, require user to confirm a security exemption
- >>>> if they wish to still visit the page.
- >> NO:
- >>> Abort; SaferScript is not deployed on this host
- > Does /white.list exist?
- > YES:
- >> GET /white.list
- >> Verify the GPG Signature with the developer's GPG Public Key
- >> Does it match?
- >> YES:
- >>> Download the .js files
- >>> FOR EACH JS FILE:
- >>>> Calculate the hash digest
- >>>> Does it match?
- >>>> YES:
- >>>>> Do we have a cached copy that's any different than the new one?
- >>>>> YES:
- >>>>>> Alert user to the changes, allow them to review the changes between
- >>>>>> both versions and decide whether or not to use the new one or the old
- >>>>>> copy of the file
- >>>>> NO:
- >>>>>> Proceed.
- >>>> NO:
- >>>>> Blacklist that file, make sure the user knows.
- >>> IF(SEND_TO_NOTARIES):
- >>>> SHA2/3 the white.list file
- >>>> Send to a trusted notary over TLS (respect proxy
- >>>> settings so it works with Tor, etc)
- >>>> Notary will request the white.list file and SHA2/3 hash it
- >>>> Does it match?
- >>>> YES:
- >>>>> Is it an old copy or a new copy?
- >>>>> NEW:
- >>>>>> Respond affirmatively, but let the user know it's a new copy
- >>>>> OLD:
- >>>>>> Respond affirmatively
- >>>> NO:
- >>>>> The user is being signled out with different copies of the Javascript
- >>>>> Reply negatively, offer the user a nonce they can use to request
- >>>>> a trusted copy of the white.list if it's needed
- >> NO:
- >>> Danger, Will Robinson! Let the user know it failed.
- >>> Do we have a copy of trusted (signed) code?
- >>> YES:
- >>>> Use that instead, keeping the user notified that something is wrong.
- >>> NO:
- >>>> Disable Javascript, require user to confirm a security exemption
- >>>> if they wish to still visit the page.
- > NO:
- >> Abort. If a GPG key was specified, disable Javascript and require the user
- >> to confirm a security exemption if they wish to still visit the page. It's
- >> fishy if they specify a key but have no white.list file.
- And then everything else proceeds like normal.
- MOTIVATIONS AND DESIGN GOALS
- o Provide a feature analogous to DEP for Javascript (mitigate XSS)
- o Provide a mechanism to deliver signed Javascript code
- o Needs to function even on HTTPS and Tor Hidden Services (no special ports)
- o Needs to use existing cryptographic primitives (GPG, SHA2)
- o Needs to be released as free and open source software
- o All code changes need to be publicly auditable in case of attack
- o All code delivered must be neutral; you and I should see the same code
- o Users should have the option to reject "Updates" published by servers
- ROADMAP
- o Build a browser plugin that only allows "trusted" Javascript
- o Build a GPG signature verification feature for selecting "trusted" code
- o Build the Command Line Interface tool (C, C++)
- o Build the Netbeans plugin
- o Write the documentation
- o Publish an alpha release
- o Get peer review, code audits
- o Possibly publish an Internet Standard?
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