1 files changed, 202 insertions, 0 deletions
diff --git a/java_src/src/main/java/com/google/crypto/tink/jwt/JwtRsaSsaPssPublicKey.java b/java_src/src/main/java/com/google/crypto/tink/jwt/JwtRsaSsaPssPublicKey.java
new file mode 100644
index 000000000..ebc0ff72d
--- /dev/null
+++ b/java_src/src/main/java/com/google/crypto/tink/jwt/JwtRsaSsaPssPublicKey.java
@@ -0,0 +1,202 @@
+// 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.errorprone.annotations.CanIgnoreReturnValue;
+import com.google.errorprone.annotations.RestrictedApi;
+import java.math.BigInteger;
+import java.nio.ByteBuffer;
+import java.security.GeneralSecurityException;
+import java.util.Optional;
+import javax.annotation.Nullable;
+
+/**
+ * Represents a public key for the JWT RSA SSA PSS signature primitive.
+ *
+ * <p>Standard: https://datatracker.ietf.org/doc/html/rfc7518
+ */
+public final class JwtRsaSsaPssPublicKey extends JwtSignaturePublicKey {
+  private final JwtRsaSsaPssParameters parameters;
+  private final BigInteger modulus;
+  private final Optional<Integer> idRequirement;
+  private final Optional<String> kid;
+
+  /** Builder for JwtRsaSsaPssPublicKey. */
+  public static class Builder {
+    private Optional<JwtRsaSsaPssParameters> parameters = Optional.empty();
+    private Optional<BigInteger> modulus = Optional.empty();
+    private Optional<Integer> idRequirement = Optional.empty();
+    private Optional<String> customKid = Optional.empty();
+
+    private Builder() {}
+
+    @CanIgnoreReturnValue
+    public Builder setParameters(JwtRsaSsaPssParameters parameters) {
+      this.parameters = Optional.of(parameters);
+      return this;
+    }
+
+    @CanIgnoreReturnValue
+    public Builder setModulus(BigInteger modulus) {
+      this.modulus = Optional.of(modulus);
+      return this;
+    }
+
+    @CanIgnoreReturnValue
+    public Builder setIdRequirement(Integer 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(JwtRsaSsaPssParameters.KidStrategy.BASE64_ENCODED_KEY_ID)) {
+        if (customKid.isPresent()) {
+          throw new GeneralSecurityException(
+              "customKid must not be set for KidStrategy BASE64_ENCODED_KEY_ID");
+        }
+        byte[] bigEndianKeyId = ByteBuffer.allocate(4).putInt(idRequirement.get()).array();
+        return Optional.of(Base64.urlSafeEncode(bigEndianKeyId));
+      }
+      if (parameters.get().getKidStrategy().equals(JwtRsaSsaPssParameters.KidStrategy.CUSTOM)) {
+        if (!customKid.isPresent()) {
+          throw new GeneralSecurityException("customKid needs to be set for KidStrategy CUSTOM");
+        }
+        return customKid;
+      }
+      if (parameters.get().getKidStrategy().equals(JwtRsaSsaPssParameters.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 JwtRsaSsaPssPublicKey build() throws GeneralSecurityException {
+      if (!parameters.isPresent()) {
+        throw new GeneralSecurityException("Cannot build without parameters");
+      }
+
+      if (!modulus.isPresent()) {
+        throw new GeneralSecurityException("Cannot build without modulus");
+      }
+      int modulusSize = modulus.get().bitLength();
+      int paramModulusSize = parameters.get().getModulusSizeBits();
+      // https://nvlpubs.nist.gov/nistpubs/FIPS/NIST.FIPS.186-4.pdf, B.3 requires p and q
+      // to be chosen such that 2^(paramModulusSize-1) < modulus < 2^paramModulusSize.
+      if (modulusSize != paramModulusSize) {
+        throw new GeneralSecurityException(
+            "Got modulus size "
+                + modulusSize
+                + ", but parameters requires modulus size "
+                + paramModulusSize);
+      }
+
+      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 JwtRsaSsaPssPublicKey(
+          parameters.get(), modulus.get(), idRequirement, computeKid());
+    }
+  }
+
+  private JwtRsaSsaPssPublicKey(
+      JwtRsaSsaPssParameters parameters,
+      BigInteger modulus,
+      Optional<Integer> idRequirement,
+      Optional<String> kid) {
+    this.parameters = parameters;
+    this.modulus = modulus;
+    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 static Builder builder() {
+    return new Builder();
+  }
+
+  /** Returns the underlying key bytes. */
+  @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 BigInteger getModulus() {
+    return modulus;
+  }
+
+  /**
+   * Returns the "kid" to be used for this key.
+   *
+   * <p>If present, this kid will be written into the {@code kid} header during {{@code
+   * PublicKeySign#signAndEncode}. 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;
+  }
+
+  @Override
+  public JwtRsaSsaPssParameters getParameters() {
+    return parameters;
+  }
+
+  @Override
+  @Nullable
+  public Integer getIdRequirementOrNull() {
+    return idRequirement.orElse(null);
+  }
+
+  @Override
+  public boolean equalsKey(Key o) {
+    if (!(o instanceof JwtRsaSsaPssPublicKey)) {
+      return false;
+    }
+    JwtRsaSsaPssPublicKey that = (JwtRsaSsaPssPublicKey) o;
+    return that.parameters.equals(parameters)
+        && that.modulus.equals(modulus)
+        && that.kid.equals(kid)
+        && that.idRequirement.equals(idRequirement);
+  }
+}