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Tink for C++ HOW-TO

The following subsections present instructions and/or C++ snippets for some common tasks in Tink.

Installing Tink

Tink is built with Bazel, so it is quite easy to use Tink in a project built with Bazel, and this is the recommended way. See for example tink-examples repo on how to import Tink using Bazel's WORKSPACE file.

Still, there are definitely projects for which using Bazel is not an option, and for such situations we offer a library that can be used with other build tools. Currently only we offer support for Linux machines, but are working on supporting other operating systems as well.

Warning: In any case, the use of Tink without Bazel is at experimental stage, so the instructions given below might not work in some environments.

Supported Platforms

  • Linux x86_64
  • macOS x86_64, 10.12.6 (Sierra) or newer

Caveats

Tink depends on Abseil, Protocol Buffers, and BoringSSL, so any project that wants to use Tink should either depend on the same versions of these libraries (cf. versions in the corresponding entries in WORKSPACE file), or not depend directly on these libraries at all (i.e. have only the indirect dependence via Tink).

Installing pre-built binaries

  1. Download and extract the Tink library into /usr/local/lib by invoking the following shell commands:

    OS="linux" # Change to "darwin" for macOS
TARGET_DIR="/usr/local"
curl -L \
"https://storage.googleapis.com/tink/releases/libtink-${OS}-x86_64-1.2.0-rc2.tar.gz" |
sudo tar -xz -C $TARGET_DIR

The tar command extracts the Tink library into the lib subdirectory of TARGET_DIR. For example, specifying /usr/local as TARGET_DIR causes tar to extract the Tink library into /usr/local/lib.

If you'd prefer to extract the library into a different directory, adjust TARGET_DIR accordingly.

  1. On Linux, if in Step 2 you specified a system directory (for example, /usr/local) as the TARGET_DIR, then run ldconfig to configure the linker. For example:

    sudo ldconfig

    If you assigned a TARGET_DIR other than a system directory (for example, ~/mydir), then you must append the extraction directory (for example, ~/mydir/lib) to two environment variables:

    export LIBRARY_PATH=$LIBRARY_PATH:$TARGET_DIR/lib
export LD_LIBRARY_PATH=$LD_LIBRARY_PATH:$TARGET_DIR/lib

Installing from the source

Prerequisites

To install Tink from the source code, the following prerequisites must be installed:

  • git - to download the source of Tink
  • Bazel - to build the Tink library

Step-by-step instructions to build and use libtink.so

  1. clone Tink from GitHub:

    git clone https://github.com/google/tink/

  2. build the library and header-file bundles, and install them in appropriate directories of the target project (TARGET_DIR):

    cd tink
TARGET_DIR="/usr/local"
mkdir -p $TARGET_DIR/lib $TARGET_DIR/include
bazel build -c opt cc:libtink.so
sudo cp bazel-bin/cc/libtink.so $TARGET_DIR/lib/
bazel build cc:tink_headers cc:tink_deps_headers
sudo tar xfv bazel-genfiles/cc/tink_headers.tar -C $TARGET_DIR/include/
sudo tar xfv bazel-genfiles/cc/tink_deps_headers.tar -C $TARGET_DIR/include/

  3. On Linux, if in Step 2 you specified a system directory (for example, /usr/local) as the TARGET_DIR, then run ldconfig to configure the linker. For example:

    sudo ldconfig

    If you assigned a TARGET_DIR other than a system directory (for example, ~/mydir), then you must append the extraction directory (for example, ~/mydir/lib) to two environment variables:

    export LIBRARY_PATH=$LIBRARY_PATH:$TARGET_DIR/lib
export LD_LIBRARY_PATH=$LD_LIBRARY_PATH:$TARGET_DIR/lib

Validate your installation

To validate the installation compile and run hello_world.cc.

  1. Copy the source code and a test cryptographic key, create some plaintext to encrypt.

    cd /tmp
GITHUB_DIR=https://raw.githubusercontent.com/google/tink/master/examples/helloworld/cc/
curl $GITHUB_DIR/hello_world.cc -O $GITHUB_DIR/aes128_gcm_test_keyset_json.txt -O
echo "some message to be encrypted" > plaintext.txt

  2. Compile the source code.

     g++ -std=c++11 -I$TARGET_DIR/include/ -L$TARGET_DIR/lib/ hello_world.cc -ltink -o hello_world

  3. Run hello_world application to encrypt and decrypt some data.

    ./hello_world aes128_gcm_test_keyset_json.txt encrypt plaintext.txt "associated data" ciphertext.bin
./hello_world aes128_gcm_test_keyset_json.txt decrypt ciphertext.bin "associated data" decrypted.txt
cat decrypted.txt

Initializing Tink

Tink provides customizable initialization, which allows for choosing specific implementations (identified by key types) of desired primitives. This initialization happens via registration of the implementations.

For example, if you want to use all standard implementations of all primitives in the current release of Tink, the initialization would look as follows:

   #include "tink/config/tink_config.h"

   // ...
   auto status = TinkConfig::Register();
   if (!status.ok()) /* ... handle failure */;
   // ...

To use standard implementations of only one primitive, say AEAD, proceed as follows:

   #include "tink/aead/aead_config.h"

   // ...
   auto status = AeadConfig::Register();
   if (!status.ok()) /* ... handle failure */;
   // ...

The registration of custom key managers can proceed directly via Registry-class:

   #include "tink/registry.h"
   #include "custom_project/custom_aead_key_manager.h"

   // ...
   auto status = Registry::RegisterKeyManager(new CustomAeadKeyManager());
   if (!status.ok()) /* ... handle failure */;

A more complex custom initialization (especially when registering a mix of standard and custom key managers) can take advantage of Config-class, which enables use of human-readable configuration files for Tink initialization. Please note however that to use such configurations one must first add to the Registry so-called catalogues, which provide a bridge between text descriptions of key managers and their implementations (see e.g. AeadConfig::Register()-method).

Generating New Key(set)s

Each KeyManager-implementation provides NewKey(template)-method that generates new keys of the corresponding key type. However to avoid accidental leakage of sensitive key material one should be careful with mixing key(set) generation with key(set) usage in code. To support the separation between these activities Tink package provides a command-line tool called Tinkey, which can be used for common key management tasks.

Still, if there is a need to generate a KeysetHandle with fresh key material directly in C++ code, one can use KeysetHandle:

    auto new_keyset_handle_result = KeysetHandle::GenerateNew(key_template);
    if (!new_keyset_handle_result.ok()) return new_keyset_handle_result.status();
    auto keyset_handle = std::move(new_keyset_handle_result.ValueOrDie());
    // use the keyset...

where key_template can be initialized with one of pre-generated templates from examples/keytemplates-folder.

Loading Existing Keysets

To load cleartext keysets, use CleartextKeysetHandle and an appropriate KeysetReader, depending on the wire format of the stored keyset, for example a BinaryKeysetReader or a JsonKeysetReader.

    #include "tink/binary_keyset_reader.h"
    #include "tink/cleartext_keyset_handle.h"

    // ...
    std::string binary_keyset = ...;
    auto reader_result = BinaryKeysetReader::New(binary_keyset);
    if (!reader_result.ok()) return reader_result.status();
    auto reader = std::move(reader_result.ValueOrDie());
    auto handle_result = CleartextKeysetHandle::Read(std::move(reader));
    if (!handle_result.ok()) return handle_result.status();
    auto keyset_handle = std::move(handle_result.ValueOrDie());

To load encrypted keysets, one can use KeysetHandle and an appropriate KeysetReader:

    #include "tink/aead.h"
    #include "tink/json_keyset_reader.h"
    #include "tink/cleartext_keyset_handle.h"
    #include "tink/integration/aws_kms_client.h"

    // ...
    std::string json_encrypted_keyset = ...;
    auto reader_result = JsonKeysetReader::New(json_encrypted_keyset);
    if (!reader_result.ok()) return reader_result.status();
    auto reader = std::move(reader_result.ValueOrDie());
    std::string master_key_uri =
        "aws-kms://arn:aws:kms:us-east-1:007084425826:key/84a65985-f868-4bfc-83c2-366618acf147";
    auto aead = std::move(AwsKmsClient::NewAead(master_key_uri).ValueOrDie());
    auto handle_result = KeysetHandle::Read(std::move(reader), *aead);
    if (!handle_result.ok()) return handle_result.status();
    auto keyset_handle = std::move(handle_result.ValueOrDie());

Obtaining and Using Primitives

Primitives represent cryptographic operations offered by Tink, hence they form the core of Tink API. A primitive is just an interface that specifies what operations are offered by the primitive. A primitive can have multiple implementations, and user chooses a desired implementation by using a key of corresponding type (see the this section for details).

The following table summarizes C++ implementations of primitives that are currently available or planned (the latter are listed in brackets).

Primitive Implementations
AEAD AES-GCM, AES-CTR-HMAC, AES-EAX
Deterministic AEAD AES-SIV
MAC HMAC-SHA2
Digital Signatures ECDSA over NIST curves, (Ed25519)
Hybrid Encryption ECIES with AEAD and HKDF

The user obtains a primitive by calling the function getPrimitive<> of the KeysetHandle.

Symmetric Key Encryption

Here is how you can obtain and use an AEAD (Authenticated Encryption with Associated Data) primitive to encrypt or decrypt data:

    #include "tink/aead.h"
    #include "tink/keyset_handle.h"


    // 1. Get a handle to the key material.
    KeysetHandle keyset_handle = ...;

    // 2. Get the primitive.
    auto aead_result= keyset_handle.GetPrimitive<Aead>();
    if (!aead_result.ok()) return aead_result.status();
    auto aead = std::move(aead_result.ValueOrDie());

    // 3. Use the primitive.
    auto ciphertext_result = aead.Encrypt(plaintext, aad);
    if (!ciphertext_result.ok()) return ciphertext_result.status();
    auto ciphertext = std::move(ciphertext_result.ValueOrDie());

Hybrid Encryption

To decrypt using a combination of public key encryption and symmetric key encryption:

    #include "tink/hybrid_decrypt.h"
    #include "tink/keyset_handle.h"


    // 1. Get a handle to the key material.
    KeysetHandle keyset_handle = ...;

    // 2. Get the primitive.
    auto hybrid_decrypt_result = keyset_handle.GetPrimitive<HybridDecrypt>();
    if (!hybrid_decrypt_result.ok()) return hybrid_decrypt_result.status();
    auto hybrid_decrypt = std::move(hybrid_decrypt_result.ValueOrDie());

    // 3. Use the primitive.
    auto plaintext_result = hybrid_decrypt.Decrypt(ciphertext, context_info);
    if (!plaintext_result.ok()) return plaintext_result.status();
    auto plaintext = std::move(plaintext_result.ValueOrDie());