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Tink for C++ HOW-TO

This document contains instructions and C++ code snippets for common tasks in Tink.

Setup instructions

Bazel

Tink is built using Bazel.

Using Tink in projects built with Bazel is straighforward and is the recommended approach. For an example, see this project which specifies Tink as a dependency in a Bazel WORKSPACE file.

Caveats

Tink has a number of library dependencies specified in the "cc" section of the Bazel WORKSPACE file.

Any project using Tink should either:

  • explicitly depend on the same versions of these libraries
  • not depend directly on these libraries at all (i.e. have only the indirect dependence via Tink).

Precompiled library

There are projects where using Bazel is not an option. For such situations, we offer a precompiled library that can be used with other build tools.

Supported platforms

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

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

Using the precompiled library

  1. Download and extract the Tink library.

    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.

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

    sudo ldconfig

    If you set TARGET_DIR to a non-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

Compiling the library from 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

Note: You need to use Bazel to build the library, but you will be able to use the resultant build artifacts in a non-Bazel project.

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.

    cd tink
bazel build -c opt cc:libtink.so
bazel build cc:tink_headers cc:tink_deps_headers

  3. Prepare the installation target directory.

    TARGET_DIR="/usr/local"
mkdir -p ${TARGET_DIR}/lib ${TARGET_DIR}/include

  4. Install the libary and header file bundles.

    sudo cp bazel-bin/cc/libtink.so ${TARGET_DIR}/lib/
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/

  5. On Linux, if you specified a system directory as the TARGET_DIR (for example, /usr/local), then run ldconfig to configure the linker.

    sudo ldconfig

    If you set TARGET_DIR to a non-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. Download the source code and a test cryptographic key. Also, create some plaintext to encrypt.

    cd /tmp
GITHUB_URL=https://raw.githubusercontent.com/google/tink/master/examples/helloworld/cc/
curl ${GITHUB_URL}/hello_world.cc -O ${GITHUB_URL}/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. Use the hello_world application to encrypt and decrypt the plaintext 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 be:

   #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:

   #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 */;

Generating new keys and keysets

Each KeyManager implementation provides a NewKey(template) method that generates new keys of the corresponding key type. However, to avoid accidental leakage of sensitive key material, you should avoid mixing key(set) generation with key(set) usage in code. To support the separation between these activities, Tink 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, you 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...

Recommended key templates can be obtained from util classes corresponding to Tink primitives, e.g. MacKeyTemplates, AeadKeyTemplates, and HybridKeyTemplates.

Loading existing keysets

To load encrypted keysets, use KeysetHandle and an appropriate KeysetReader depending on the wire format of the stored keyset, for example a BinaryKeysetReader or a JsonKeysetReader:

    #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());

To load cleartext keysets, use CleartextKeysetHandle and an appropriate KeysetReader,

    #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());

Obtaining and using primitives

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

A list of primitives and the implementations currently supported by Tink in C++ can be found here.

You obtain a primitive by calling the method GetPrimitive<> of a KeysetHandle.

Symmetric key encryption

You can 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

You can encrypt and 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());