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Oblivous Go maps

This package provides secure storage of map[string]string objects. The contents of the structure cannot be deduced from its public representation, and querying it requires knowledge of a secret key. It is suitable for client/server protocols where the service is trusted only to provide storage. In addition to providing confidentiality, it allows the client to verify the integrity of the server's responses.

An overview and installation instructions follow; the package documentation is indexed on GoDoc.

#b8b8b8 DISCLAIMER: This code is related to a research paper, which will be up on ePrint at some point.

#b8b8b8 FUTURE WORK: Currently this package only provides immutable storage of maps, meaning once you've created a data store, you can't change its contents. However, with some modifications it should be possible to insert, remove, and update input/output pairs securely. I'll be working on this next.

The store package

The main package provides two data structures: Store and Dict. The former offers confidentiality and integrity for map[string]string objects with arbitrary-length inputs and outputs. Its security follows from the combination of authenticated encryption with associated data (AEAD) and the latter structure, which offers only confidentiality and is only suitable for maps who's outputs are of length at most 60.

Store. The client possesses a secret key K and data M (of type map[string]string). It executes:

pub, priv, err := store.NewStore(K, M)

and transmits pub, the public representation of M, to the server. To compute M[input], the client executes:

x, y, err := priv.GetIdx(input)

and sends x and y (both of type int) to the server. The pair (x,y) is called the index and is used by the server to compute its share of the output. The server computes:

pubShare, err := pub.GetShare(x, y)

and sends pubShare (of type []byte) to the client. Finally, the client executes:

output, err := priv.GetOutput(input, pubShare)

This combines pubShare with a private share computed from input and K. The result is output = M[input]. Note that the server is not entrusted with the key; its only job is to look up the index requested by the client. The underlying data structure is designed so that no information about input or output is leaked to any party not in possession of the secret key.

For convenience, this package also provides an interface for querying pub directly:

output, err := priv.Get(pub, input)

Dict. This light-weight structure is the core of Store. The Go package is an interface for the underlying C implementation. It can be used in exactly the same way as Store, but is only suitable for short (60 byte) outputs. See the package documentation for an explanation of this limitation. To construct it, the client executes:

pub, priv, err := store.NewDict(K, M)

The remaining functions are as above.

The store/pb package

File pb/store.proto specifies a bare-bones remote procedure call for the client and server roles in the protocol above.

The StoreProvider service. The user computes pub from its map M and key K and provisions the service provider (out-of-band) with pub. The request consists of the user and (x,y), and the response consists of the pubShare computed from x, y, and pub.

This simple RPC provides no authentication of the user, so any anyone can get the entire public store of any user. This is not a problem, however, as long as the adversary doesn't know (or can't guess) K. But if K is derived from a password, for example, then the contents of pub are susceptible to dictionary attacks.

For documentation of this package, check out the GoDoc index.

Installation

First, you'll need Go. To get the latest version on Ubuntu, do

$ sudo add-apt-repository ppa:longsleep/golang-backports
$ sudo apt update
$ sudo apt install golang-go

On Mac, download the pkg and install it. Next, add the following lines to the end of.bashrc on Ubuntu or .bash_profile on Mac:

export GOPATH="$HOME/go"
export PATH="$PATH:$GOPATH/bin"

In a new terminal, make the directory $HOME/go, go to the directory and type:

go get github.com/cjpatton/store

This downloads this repository and puts it in go/src/github.com/cjpatton/store.

Next, the core data structures are implemented in C. (Navigate to go/src/github.com/cjpatton/store/c/.) The Makefile compiles a shared object for which the Go code has bindings. They depend on OpenSSL (SHA512 and HMAC-SHA512), so you'll need to install this library in advance. On Ubuntu:

$ sudo apt-get install libssl-dev

On Mac via Homebrew:

$ brew install openssl

(Homebrew puts the includes in /usr/local/opt/openssl/include, which is a non-standard location. Makefile passes this directory to the compioler via -I, so this shouldn't be a problem.) To build the C code and run tests do:

$ make && make test

Note that, since the data strucutres are probabilistic, the tests will produce warnings from time to time. (This is OK as long as it doesn't produce a lot of warnings.) To install, do

$ sudo make install && sudo ldconfig

This builds a file called libstructsec.so and moves it to /usr/local/lib and copies the header files to /usr/local/include/structsec.

Now you should be able to build the package. To run tests, do

$ go test github.com/cjpatton/store

Running the toy application

hadee/server/hadee_server.go implements the RPC service and serves a single user. It takes as input the user name and a file containing the public store. To run it, first generate a sample store by doing:

$ cd hadee/gen && go install && hadee_gen

It will prompt you for a "master password" used to derive a key, which is used to generate the structure. This writes a file store.pub to the current directory. (The map it represents is hard-coded in the Go code.) To run the server, do:

$ cd hadee/server && go install && hadee_server cjpatton store.pub

This opens a TCP socket on localhost:50051 and begins serving requests. To run the client, do:

$ cd hadee/client && go install && hadee_client cjpatton

#f03c15 SECURITY WARNING: Do NOT use this for anything real. As is, the protocol is susceptible to dictionary attacks on the master password.

Modifying store.proto

You only need to do this if you want to modify the protocol buffers or RPC. This project uses protcool buffers and remote procedure calls. To build you'll first need the lastest version of protoc. Go to protobuf documentation for instructions. To build store.pb.go, go to $HOME/go/src/github.com/cjpatton/store/pb and run

  $ protoc -I . store.proto --go_out=plugins=grpc:.

Note that you only need to do this if you modify store.proto.

Copyright notice

This software is distributed under the terms of the 3-Clause BSD License; see LICENSE in the root project directory for details.

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