Attribute-Based Encryption (Relic)

Installation

1. Install Opam.

• In Ubuntu,

apt-get install -y ocaml ocaml-native-compilers opam m4 camlp4-extra

• In OS X, use homebrew,

brew install opam

2. Install Relic:

To install relic, clone the repository from https://github.com/relic-toolkit/relic and follow the instructions below:

mkdir build
cd build
cmake build --ALLOC=DYNAMIC --SHLIB=on ../

The flag --ALLOC=DYNAMIC may not work. Check that the file include/relic_conf.h contains the line "#define ALLOC DYNAMIC" and fix it if necessary.

make
sudo make install

The installation works for commit 0e239a842b89126080e998e3836f83aff1078576 of relic.

3. Install the Ocaml Bindings for Relic:

Install opam packages:

git clone https://github.com/ZooCrypt/relic-ocaml-bindings.git
opam pin add relic-ocaml-bindings RELIC_OCAML_BINDINGS_DIR -n
opam install relic-ocaml-bindings --deps-only

Compile and install the bindings:

oasis setup
./configure
make
opam install relic-ocaml-bindings

4. To compile and test our ABE implementation from Relic, execute the following commands:

make
make test

Usage (Batch mode)

The tool supports four modes (corresponding to the four ABE algorithms) given as first argument:

• setup: this algorithm gets as input the public parameters (security parameter, attribute universe, predicate universe...) and outputs the master public key (mpk) and the master secret key (msk).

• encrypt: the encryption algorithm takes as input the master public key (mpk), a message and a value x (corresponding to a set of attributes in KP-ABE or a policy in CP-ABE) and outputs a ciphertext ct_x.

• keygen: the key generation algorithm gets as input mpk and msk and a value y (corresponding to a poliy in KP-ABE or a set of attributes in CP-ABE) and outputs a secret key sk_y. Note that this algorithm needs the msk as input and thus, it is not a public algorithm. It is supposed to be runned by the master authority of the system.

• decrypt: the decryption algorithm takes as input sk_y and ct_x and outputs a message. It will succeed if and only if x and y are such that the policy is satisfied by the set of attributes.

Example

We set the file public_parameters.txt as:

scheme = CP_ABE.
encoding = PREDICATE_ENCODING.
predicate = boolean_formula(2 repetitions, 4 and-gates).
attributes = [tall, dark, handsome, phd, cs, maths].

We run the algorithm:

$ ./abe_relic.native setup -pp public_parameters.txt -mpk mpk.txt -msk msk.txt

This will produce two files, mpk.txt and msk.txt, containing the information of the master public key and the master secret key respectively.

We will encrypt the message in file message.txt containing:

L'essentiel est invisible pour les yeux

For this, we run the encryption algorithm:

$ ./abe_relic.native encrypt -mpk mpk.txt -msg message.txt -out ciphertext.txt \
                   -policy "(tall and handsome and dark) or (phd and cs)"

Only users with a secret key satisfying the policy will be able to decrypt. As an example, we create two secret keys corresponding to different attributes:

$ ./abe_relic.native keygen -mpk mpk.txt -msk msk.txt -out key1.txt -attrs "[phd, cs]"
$ ./abe_relic.native keygen -mpk mpk.txt -msk msk.txt -out key2.txt -attrs "[tall, dark, phd, maths]"

Decryption will succeed only for the first key:

$ ./abe_relic.native decrypt -mpk mpk.txt -ct ciphertext.txt -sk key1.txt
L'essentiel est invisible pour les yeux

$ ./abe_relic.native decrypt -mpk mpk.txt -ct ciphertext.txt -sk key2.txt
bad decrypt