We recommend the HMAC_SHA256 key type for most use cases. For all supported key types, see Supported Key Types.
If you want to ensure that nobody can tamper with your data, we recommend the Message Authentication Code (MAC) primitive. It uses a single key to generate message authentication codes and verify them. MAC does not encrypt data. In most cases, protecting data with AEAD, which includes encryption and MAC, is preferable to MAC alone.
The following examples get you started using the MAC primitive.
C++
// A command-line utility for showcasing using the Tink MAC primitive.
#include <cstdlib>
#include <fstream>
#include <iostream>
#include <memory>
#include <ostream>
#include <sstream>
#include <string>
#include <utility>
#include "absl/flags/flag.h"
#include "absl/flags/parse.h"
#include "absl/log/check.h"
#include "absl/strings/string_view.h"
#include "tink/config/global_registry.h"
#include "util/util.h"
#include "tink/keyset_handle.h"
#include "tink/mac.h"
#include "tink/mac/mac_config.h"
#include "tink/util/status.h"
ABSL_FLAG(std::string, keyset_filename, "", "Keyset file in JSON format");
ABSL_FLAG(std::string, mode, "", "Mode of operation {compute|verify}");
ABSL_FLAG(std::string, data_filename, "", "Data file name");
ABSL_FLAG(std::string, tag_filename, "", "Authentication tag file name");
namespace {
using ::crypto::tink::KeysetHandle;
using ::crypto::tink::Mac;
using ::crypto::tink::MacConfig;
using ::crypto::tink::util::Status;
using ::crypto::tink::util::StatusOr;
constexpr absl::string_view kCompute = "compute";
constexpr absl::string_view kVerify = "verify";
void ValidateParams() {
// ...
}
} // namespace
namespace tink_cc_examples {
// MAC example CLI implementation.
Status MacCli(absl::string_view mode, const std::string keyset_filename,
const std::string& data_filename,
const std::string& tag_filename) {
Status result = MacConfig::Register();
if (!result.ok()) return result;
// Read the keyset from file.
StatusOr<std::unique_ptr<KeysetHandle>> keyset_handle =
ReadJsonCleartextKeyset(keyset_filename);
if (!keyset_handle.ok()) return keyset_handle.status();
// Get the primitive.
StatusOr<std::unique_ptr<Mac>> mac_primitive =
(*keyset_handle)
->GetPrimitive<crypto::tink::Mac>(
crypto::tink::ConfigGlobalRegistry());
if (!mac_primitive.ok()) return mac_primitive.status();
// Read the input.
StatusOr<std::string> data_file_content = ReadFile(data_filename);
if (!data_file_content.ok()) return data_file_content.status();
std::string output;
if (mode == kCompute) {
// Compute authentication tag.
StatusOr<std::string> compute_result =
(*mac_primitive)->ComputeMac(*data_file_content);
if (!compute_result.ok()) return compute_result.status();
// Write out the authentication tag to tag file.
return WriteToFile(*compute_result, tag_filename);
} else { // operation == kVerify.
// Read the authentication tag from tag file.
StatusOr<std::string> tag_result = ReadFile(tag_filename);
if (!tag_result.ok()) {
std::cerr << tag_result.status().message() << '\n';
exit(1);
}
// Verify authentication tag.
Status verify_result =
(*mac_primitive)->VerifyMac(*tag_result, *data_file_content);
if (verify_result.ok()) std::clog << "Verification succeeded!" << '\n';
return verify_result;
}
}
} // namespace tink_cc_examples
int main(int argc, char** argv) {
absl::ParseCommandLine(argc, argv);
ValidateParams();
std::string mode = absl::GetFlag(FLAGS_mode);
std::string keyset_filename = absl::GetFlag(FLAGS_keyset_filename);
std::string data_filename = absl::GetFlag(FLAGS_data_filename);
std::string tag_filename = absl::GetFlag(FLAGS_tag_filename);
std::clog << "Using keyset from file '" << keyset_filename << "' to " << mode
<< " authentication tag from file '" << tag_filename
<< "' for data file '" << data_filename << "'." << '\n';
std::clog << "The tag will be "
<< ((mode == kCompute) ? "written to" : "read from") << " file '"
<< tag_filename << "'." << '\n';
CHECK_OK(tink_cc_examples::MacCli(mode, keyset_filename, data_filename,
tag_filename));
return 0;
}
Go
import (
"bytes"
"fmt"
"log"
"github.com/tink-crypto/tink-go/v2/insecurecleartextkeyset"
"github.com/tink-crypto/tink-go/v2/keyset"
"github.com/tink-crypto/tink-go/v2/mac"
)
func Example() {
// A keyset created with "tinkey create-keyset --key-template=HMAC_SHA256_128BITTAG".
// Note that this keyset has the secret key information in cleartext.
jsonKeyset := `{
"key": [{
"keyData": {
"keyMaterialType":
"SYMMETRIC",
"typeUrl":
"type.googleapis.com/google.crypto.tink.HmacKey",
"value":
"EgQIAxAQGiA0LQjovcydWhVQV3k8W9ZSRkd7Ei4Y/TRWApE8guwV4Q=="
},
"keyId": 1892702217,
"outputPrefixType": "TINK",
"status": "ENABLED"
}],
"primaryKeyId": 1892702217
}`
// Create a keyset handle from the cleartext keyset in the previous
// step. The keyset handle provides abstract access to the underlying keyset to
// limit the exposure of accessing the raw key material. WARNING: In practice,
// it is unlikely you will want to use a insecurecleartextkeyset, as it implies
// that your key material is passed in cleartext, which is a security risk.
// Consider encrypting it with a remote key in Cloud KMS, AWS KMS or HashiCorp Vault.
// See https://github.com/google/tink/blob/master/docs/GOLANG-HOWTO.md#storing-and-loading-existing-keysets.
keysetHandle, err := insecurecleartextkeyset.Read(
keyset.NewJSONReader(bytes.NewBufferString(jsonKeyset)))
if err != nil {
log.Fatal(err)
}
// Retrieve the MAC primitive we want to use from the keyset handle.
primitive, err := mac.New(keysetHandle)
if err != nil {
log.Fatal(err)
}
// Use the primitive to create a MAC tag for some data. In this case the primary
// key of the keyset will be used (which is also the only key in this example).
data := []byte("data")
tag, err := primitive.ComputeMAC(data)
if err != nil {
log.Fatal(err)
}
// Use the primitive to verify the tag. VerifyMAC finds the correct key in
// the keyset. If no key is found or verification fails, it returns an error.
err = primitive.VerifyMAC(tag, data)
if err != nil {
log.Fatal(err)
}
fmt.Printf("tag is valid")
// Output: tag is valid
}
Java
package mac;
import static java.nio.charset.StandardCharsets.UTF_8;
import com.google.crypto.tink.InsecureSecretKeyAccess;
import com.google.crypto.tink.KeysetHandle;
import com.google.crypto.tink.Mac;
import com.google.crypto.tink.TinkJsonProtoKeysetFormat;
import com.google.crypto.tink.mac.MacConfig;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
/**
* A command-line utility for checking file integrity with a Message Authentication Code (MAC).
*
* <p>It loads cleartext keys from disk - this is not recommended!
*
* <p>It requires the following arguments:
*
* <ul>
* <li>mode: either 'compute' or 'verify'.
* <li>key-file: Read the key material from this file.
* <li>input-file: Read the input from this file.
* <li>mac-file: name of the file containing a hexadecimal MAC of the input data.
*/
public final class MacExample {
public static void main(String[] args) throws Exception {
if (args.length != 4) {
System.err.printf("Expected 4 parameters, got %d\n", args.length);
System.err.println("Usage: java MacExample compute/verify key-file input-file mac-file");
System.exit(1);
}
String mode = args[0];
if (!mode.equals("compute") && !mode.equals("verify")) {
System.err.println("Incorrect mode. Please select compute or verify.");
System.exit(1);
}
Path keyFile = Paths.get(args[1]);
byte[] msg = Files.readAllBytes(Paths.get(args[2]));
Path macFile = Paths.get(args[3]);
// Register all MAC key types with the Tink runtime.
MacConfig.register();
// Read the keyset into a KeysetHandle.
KeysetHandle handle =
TinkJsonProtoKeysetFormat.parseKeyset(
new String(Files.readAllBytes(keyFile), UTF_8), InsecureSecretKeyAccess.get());
// Get the primitive.
Mac macPrimitive = handle.getPrimitive(Mac.class);
if (mode.equals("compute")) {
byte[] macTag = macPrimitive.computeMac(msg);
Files.write(macFile, macTag);
} else {
byte[] macTag = Files.readAllBytes(macFile);
// This will throw a GeneralSecurityException if verification fails.
macPrimitive.verifyMac(macTag, msg);
}
}
private MacExample() {}
}
Python
import tink
from tink import mac
from tink import secret_key_access
def example():
"""Compute and verify MAC tags."""
# Register the MAC key managers. This is needed to create a Mac primitive
# later.
mac.register()
# Created with "tinkey create-keyset --key-template=HMAC_SHA256_128BITTAG".
# Note that this keyset has the secret key information in cleartext.
keyset = r"""{
"key": [{
"keyData": {
"keyMaterialType":
"SYMMETRIC",
"typeUrl":
"type.googleapis.com/google.crypto.tink.HmacKey",
"value":
"EgQIAxAQGiA0LQjovcydWhVQV3k8W9ZSRkd7Ei4Y/TRWApE8guwV4Q=="
},
"keyId": 1892702217,
"outputPrefixType": "TINK",
"status": "ENABLED"
}],
"primaryKeyId": 1892702217
}"""
# Create a keyset handle from the cleartext keyset in the previous
# step. The keyset handle provides abstract access to the underlying keyset to
# limit access of the raw key material. WARNING: In practice, it is unlikely
# you will want to use tink.json_proto_keyset_format.parse, as it implies that
# your key material is passed in cleartext, which is a security risk.
keyset_handle = tink.json_proto_keyset_format.parse(
keyset, secret_key_access.TOKEN
)
# Retrieve the Mac primitive we want to use from the keyset handle.
primitive = keyset_handle.primitive(mac.Mac)
# Use the primitive to compute the MAC for a message. In this case the primary
# key of the keyset will be used (which is also the only key in this example).
data = b'data'
tag = primitive.compute_mac(data)
# Use the primitive to verify the MAC for the message. Verify finds the
# correct key in the keyset and verifies the MAC. If no key is found or
# verification fails, it raises an error.
primitive.verify_mac(tag, data)