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// Copyright 2023 Google LLC
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//
////////////////////////////////////////////////////////////////////////////////
package com.google.crypto.tink.jwt;
import com.google.crypto.tink.AccessesPartialKey;
import com.google.crypto.tink.Key;
import com.google.crypto.tink.subtle.Base64;
import com.google.crypto.tink.util.SecretBytes;
import com.google.errorprone.annotations.CanIgnoreReturnValue;
import com.google.errorprone.annotations.RestrictedApi;
import java.nio.ByteBuffer;
import java.security.GeneralSecurityException;
import java.util.Optional;
import javax.annotation.Nullable;
/** Represents a JWT HMAC key to create and verify JWT using HMAC. */
public class JwtHmacKey extends JwtMacKey {
private final JwtHmacParameters parameters;
private final SecretBytes key;
private final Optional<Integer> idRequirement;
private final Optional<String> kid;
/** Helps creating new {@code JwtHmacKey} objects. */
public static class Builder {
private Optional<JwtHmacParameters> parameters = Optional.empty();
private Optional<SecretBytes> keyBytes = Optional.empty();
private Optional<Integer> idRequirement = Optional.empty();
private Optional<String> customKid = Optional.empty();
private Builder() {}
@CanIgnoreReturnValue
public Builder setParameters(JwtHmacParameters parameters) {
this.parameters = Optional.of(parameters);
return this;
}
@CanIgnoreReturnValue
public Builder setKeyBytes(SecretBytes keyBytes) {
this.keyBytes = Optional.of(keyBytes);
return this;
}
@CanIgnoreReturnValue
public Builder setIdRequirement(int idRequirement) {
this.idRequirement = Optional.of(idRequirement);
return this;
}
@CanIgnoreReturnValue
public Builder setCustomKid(String customKid) {
this.customKid = Optional.of(customKid);
return this;
}
private Optional<String> computeKid() throws GeneralSecurityException {
if (parameters
.get()
.getKidStrategy()
.equals(JwtHmacParameters.KidStrategy.BASE64_ENCODED_KEY_ID)) {
byte[] bigEndianKeyId = ByteBuffer.allocate(4).putInt(idRequirement.get()).array();
if (customKid.isPresent()) {
throw new GeneralSecurityException(
"customKid must not be set for KidStrategy BASE64_ENCODED_KEY_ID");
}
return Optional.of(Base64.urlSafeEncode(bigEndianKeyId));
}
if (parameters.get().getKidStrategy().equals(JwtHmacParameters.KidStrategy.CUSTOM)) {
if (!customKid.isPresent()) {
throw new GeneralSecurityException("customKid needs to be set for KidStrategy CUSTOM");
}
return customKid;
}
if (parameters.get().getKidStrategy().equals(JwtHmacParameters.KidStrategy.IGNORED)) {
if (customKid.isPresent()) {
throw new GeneralSecurityException("customKid must not be set for KidStrategy IGNORED");
}
return Optional.empty();
}
throw new IllegalStateException("Unknown kid strategy");
}
public JwtHmacKey build() throws GeneralSecurityException {
if (!parameters.isPresent()) {
throw new GeneralSecurityException("Parameters are required");
}
if (!keyBytes.isPresent()) {
throw new GeneralSecurityException("KeyBytes are required");
}
if (parameters.get().getKeySizeBytes() != keyBytes.get().size()) {
throw new GeneralSecurityException("Key size mismatch");
}
if (parameters.get().hasIdRequirement() && !idRequirement.isPresent()) {
throw new GeneralSecurityException(
"Cannot create key without ID requirement with parameters with ID requirement");
}
if (!parameters.get().hasIdRequirement() && idRequirement.isPresent()) {
throw new GeneralSecurityException(
"Cannot create key with ID requirement with parameters without ID requirement");
}
return new JwtHmacKey(parameters.get(), keyBytes.get(), idRequirement, computeKid());
}
}
@RestrictedApi(
explanation = "Accessing parts of keys can produce unexpected incompatibilities, annotate the function with @AccessesPartialKey",
link = "https://developers.google.com/tink/design/access_control#accessing_partial_keys",
allowedOnPath = ".*Test\\.java",
allowlistAnnotations = {AccessesPartialKey.class})
public static Builder builder() {
return new Builder();
}
private JwtHmacKey(
JwtHmacParameters parameters,
SecretBytes key,
Optional<Integer> idRequirement,
Optional<String> kid) {
this.parameters = parameters;
this.key = key;
this.idRequirement = idRequirement;
this.kid = kid;
}
@RestrictedApi(
explanation = "Accessing parts of keys can produce unexpected incompatibilities, annotate the function with @AccessesPartialKey",
link = "https://developers.google.com/tink/design/access_control#accessing_partial_keys",
allowedOnPath = ".*Test\\.java",
allowlistAnnotations = {AccessesPartialKey.class})
public SecretBytes getKeyBytes() {
return key;
}
/**
* Returns the "kid" to be used for this key.
*
* <p>If present, this kid will be written into the {@code kid} header during {@code
* computeMacAndEncode}. If absent, no kid will be written.
*
* <p>If present, and the {@code kid} header is present, the contents of the {@code kid} header
* needs to match the return value of this function.
*/
@Override
public Optional<String> getKid() {
return kid;
}
@Nullable
@Override
public Integer getIdRequirementOrNull() {
return idRequirement.orElse(null);
}
@Override
public JwtHmacParameters getParameters() {
return parameters;
}
@Override
public boolean equalsKey(Key o) {
if (!(o instanceof JwtHmacKey)) {
return false;
}
JwtHmacKey that = (JwtHmacKey) o;
return that.parameters.equals(parameters)
&& that.key.equalsSecretBytes(key)
&& that.kid.equals(kid)
&& that.idRequirement.equals(idRequirement);
}
}
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