We recommend the Digital Signature primitive with ECDSA_P256 key type for most use cases.
A digital signature ensures that no one tampers with your data and proves that the data came from you. It is asymmetric, using the private key to sign the data and the public key verify it.
The following examples get you started using the Digital Signature primitive:
C++
// A utility for signing and verifying files using digital signatures.
#include <iostream>
#include <memory>
#include <ostream>
#include <string>
#include <utility>
#include "absl/flags/flag.h"
#include "absl/flags/parse.h"
#include "util/util.h"
#include "tink/keyset_handle.h"
#include "tink/public_key_sign.h"
#include "tink/public_key_verify.h"
#include "tink/signature/signature_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 (sign|verify)");
ABSL_FLAG(std::string, input_filename, "", "Filename to operate on");
ABSL_FLAG(std::string, signature_filename, "", "Path to the signature file");
namespace {
using ::crypto::tink::KeysetHandle;
using ::crypto::tink::PublicKeySign;
using ::crypto::tink::PublicKeyVerify;
using ::crypto::tink::util::Status;
using ::crypto::tink::util::StatusOr;
constexpr absl::string_view kSign = "sign";
constexpr absl::string_view kVerify = "verify";
// ...
} // namespace
namespace tink_cc_examples {
// Digital signature example CLI implementation.
Status DigitalSignatureCli(absl::string_view mode,
const std::string& keyset_filename,
const std::string& input_filename,
const std::string& signature_filename) {
Status result = crypto::tink::SignatureConfig::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();
// Read the input.
StatusOr<std::string> input_file_content = ReadFile(input_filename);
if (!input_file_content.ok()) return input_file_content.status();
if (mode == kSign) {
StatusOr<std::unique_ptr<PublicKeySign>> public_key_sign =
(*keyset_handle)->GetPrimitive<PublicKeySign>();
if (!public_key_sign.ok()) return public_key_sign.status();
StatusOr<std::string> signature =
(*public_key_sign)->Sign(*input_file_content);
if (!signature.ok()) return signature.status();
return WriteToFile(*signature, signature_filename);
} else { // mode == kVerify
StatusOr<std::unique_ptr<PublicKeyVerify>> public_key_verify =
(*keyset_handle)->GetPrimitive<PublicKeyVerify>();
if (!public_key_verify.ok()) return public_key_verify.status();
// Read the signature.
StatusOr<std::string> signature_file_content = ReadFile(signature_filename);
if (!signature_file_content.ok()) return signature_file_content.status();
return (*public_key_verify)
->Verify(*signature_file_content, *input_file_content);
}
}
} // 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 input_filename = absl::GetFlag(FLAGS_input_filename);
std::string signature_filename = absl::GetFlag(FLAGS_signature_filename);
std::clog << "Using keyset in " << keyset_filename << " to " << mode;
if (mode == kSign) {
std::clog << " file " << input_filename
<< "; the resulting signature is written to "
<< signature_filename << std::endl;
} else { // mode == kVerify
std::clog << " the signature in " << signature_filename
<< " over the content of " << input_filename << std::endl;
}
Status result = tink_cc_examples::DigitalSignatureCli(
mode, keyset_filename, input_filename, signature_filename);
if (!result.ok()) {
std::cerr << result.message() << std::endl;
exit(1);
}
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/signature"
)
func Example() {
// A private keyset created with
// "tinkey create-keyset --key-template=ECDSA_P256 --out private_keyset.cfg".
// Note that this keyset has the secret key information in cleartext.
privateJSONKeyset := `{
"key": [{
"keyData": {
"keyMaterialType":
"ASYMMETRIC_PRIVATE",
"typeUrl":
"type.googleapis.com/google.crypto.tink.EcdsaPrivateKey",
"value":
"EkwSBggDEAIYAhogEiSZ9u2nDtvZuDgWgGsVTIZ5/V08N4ycUspTX0RYRrkiIHpEwHxQd1bImkyMvV2bqtUbgMh5uPSTdnUEGrPXdt56GiEA3iUi+CRN71qy0fOCK66xAW/IvFyjOGtxjppRhSFUneo="
},
"keyId": 611814836,
"outputPrefixType": "TINK",
"status": "ENABLED"
}],
"primaryKeyId": 611814836
}`
// The corresponding public keyset created with
// "tinkey create-public-keyset --in private_keyset.cfg"
publicJSONKeyset := `{
"key": [{
"keyData": {
"keyMaterialType":
"ASYMMETRIC_PUBLIC",
"typeUrl":
"type.googleapis.com/google.crypto.tink.EcdsaPublicKey",
"value":
"EgYIAxACGAIaIBIkmfbtpw7b2bg4FoBrFUyGef1dPDeMnFLKU19EWEa5IiB6RMB8UHdWyJpMjL1dm6rVG4DIebj0k3Z1BBqz13beeg=="
},
"keyId": 611814836,
"outputPrefixType": "TINK",
"status": "ENABLED"
}],
"primaryKeyId": 611814836
}`
// Create a keyset handle from the cleartext private keyset in the previous
// step. The keyset handle provides abstract access to the underlying keyset to
// limit the access of 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.
privateKeysetHandle, err := insecurecleartextkeyset.Read(
keyset.NewJSONReader(bytes.NewBufferString(privateJSONKeyset)))
if err != nil {
log.Fatal(err)
}
// Retrieve the Signer primitive from privateKeysetHandle.
signer, err := signature.NewSigner(privateKeysetHandle)
if err != nil {
log.Fatal(err)
}
// Use the primitive to sign a message. In this case, the primary key of the
// keyset will be used (which is also the only key in this example).
data := []byte("data")
sig, err := signer.Sign(data)
if err != nil {
log.Fatal(err)
}
// Create a keyset handle from the keyset containing the public key. Because the
// public keyset does not contain any secrets, we can use [keyset.ReadWithNoSecrets].
publicKeysetHandle, err := keyset.ReadWithNoSecrets(
keyset.NewJSONReader(bytes.NewBufferString(publicJSONKeyset)))
if err != nil {
log.Fatal(err)
}
// Retrieve the Verifier primitive from publicKeysetHandle.
verifier, err := signature.NewVerifier(publicKeysetHandle)
if err != nil {
log.Fatal(err)
}
if err = verifier.Verify(sig, data); err != nil {
log.Fatal(err)
}
fmt.Printf("sig is valid")
// Output: sig is valid
}
Java
package signature;
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.PublicKeySign;
import com.google.crypto.tink.PublicKeyVerify;
import com.google.crypto.tink.TinkJsonProtoKeysetFormat;
import com.google.crypto.tink.signature.SignatureConfig;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
/**
* A command-line utility for digitally signing and verifying a file.
*
* <p>It loads cleartext keys from disk - this is not recommended!
*
* <p>It requires the following arguments:
*
* <ul>
* <li>mode: either 'sign' or 'verify'.
* <li>key-file: Read the key material from this file.
* <li>input-file: Read the input from this file.
* <li>signature-file: name of the file containing a hexadecimal signature of the input file.
*/
public final class SignatureExample {
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 SignatureExample sign/verify key-file input-file signature-file");
System.exit(1);
}
String mode = args[0];
if (!mode.equals("sign") && !mode.equals("verify")) {
System.err.println("Incorrect mode. Please select sign or verify.");
System.exit(1);
}
Path keyFile = Paths.get(args[1]);
byte[] msg = Files.readAllBytes(Paths.get(args[2]));
Path signatureFile = Paths.get(args[3]);
// Register all signature key types with the Tink runtime.
SignatureConfig.register();
// Read the keyset into a KeysetHandle.
KeysetHandle handle =
TinkJsonProtoKeysetFormat.parseKeyset(
new String(Files.readAllBytes(keyFile), UTF_8), InsecureSecretKeyAccess.get());
if (mode.equals("sign")) {
// Get the primitive.
PublicKeySign signer = handle.getPrimitive(PublicKeySign.class);
// Use the primitive to sign data.
byte[] signature = signer.sign(msg);
Files.write(signatureFile, signature);
} else {
byte[] signature = Files.readAllBytes(signatureFile);
// Get the primitive.
PublicKeyVerify verifier = handle.getPrimitive(PublicKeyVerify.class);
verifier.verify(signature, msg);
}
}
private SignatureExample() {}
}
Obj-C
Python
import tink
from tink import cleartext_keyset_handle
from tink import signature
def example():
"""Sign and verify using digital signatures."""
# Register the signature key managers. This is needed to create
# PublicKeySign and PublicKeyVerify primitives later.
signature.register()
# A private keyset created with
# "tinkey create-keyset --key-template=ECDSA_P256 --out private_keyset.cfg".
# Note that this keyset has the secret key information in cleartext.
private_keyset = r"""{
"key": [{
"keyData": {
"keyMaterialType":
"ASYMMETRIC_PRIVATE",
"typeUrl":
"type.googleapis.com/google.crypto.tink.EcdsaPrivateKey",
"value":
"EkwSBggDEAIYAhogEiSZ9u2nDtvZuDgWgGsVTIZ5/V08N4ycUspTX0RYRrkiIHpEwHxQd1bImkyMvV2bqtUbgMh5uPSTdnUEGrPXdt56GiEA3iUi+CRN71qy0fOCK66xAW/IvFyjOGtxjppRhSFUneo="
},
"keyId": 611814836,
"outputPrefixType": "TINK",
"status": "ENABLED"
}],
"primaryKeyId": 611814836
}"""
# The corresponding public keyset created with
# "tinkey create-public-keyset --in private_keyset.cfg"
public_keyset = r"""{
"key": [{
"keyData": {
"keyMaterialType":
"ASYMMETRIC_PUBLIC",
"typeUrl":
"type.googleapis.com/google.crypto.tink.EcdsaPublicKey",
"value":
"EgYIAxACGAIaIBIkmfbtpw7b2bg4FoBrFUyGef1dPDeMnFLKU19EWEa5IiB6RMB8UHdWyJpMjL1dm6rVG4DIebj0k3Z1BBqz13beeg=="
},
"keyId": 611814836,
"outputPrefixType": "TINK",
"status": "ENABLED"
}],
"primaryKeyId": 611814836
}"""
# 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 cleartext_keyset_handle, as it implies
# that your key material is passed in cleartext which is a security risk.
private_keyset_handle = cleartext_keyset_handle.read(
tink.JsonKeysetReader(private_keyset))
# Retrieve the PublicKeySign primitive we want to use from the keyset
# handle.
sign_primitive = private_keyset_handle.primitive(signature.PublicKeySign)
# Use the primitive to sign a message. In this case the primary key of the
# keyset will be used (which is also the only key in this example).
sig = sign_primitive.sign(b'msg')
# Create a keyset handle from the keyset containing the public key. Because
# this keyset does not contain any secrets, we can use
# `tink.read_no_secret_keyset_handle`.
public_keyset_handle = tink.read_no_secret_keyset_handle(
tink.JsonKeysetReader(public_keyset))
# Retrieve the PublicKeyVerify primitive we want to use from the keyset
# handle.
verify_primitive = public_keyset_handle.primitive(signature.PublicKeyVerify)
# Use the primitive to verify that `sig` is valid signature for the message.
# Verify finds the correct key in the keyset. If no key is found or
# verification fails, it raises an error.
verify_primitive.verify(sig, b'msg')
# Note that we can also get the public keyset handle from the private keyset
# handle. The verification works the same as above.
public_keyset_handle2 = private_keyset_handle.public_keyset_handle()
verify_primitive2 = public_keyset_handle2.primitive(signature.PublicKeyVerify)
verify_primitive2.verify(sig, b'msg')