Add JwtRsaSsaPkcs1PublicKey class in Java.

PiperOrigin-RevId: 549607483

5 files changed, 591 insertions, 0 deletions

diff --git a/java_src/BUILD.bazel b/java_src/BUILD.bazel
index e8e3432ce..6bf76aa8e 100644
--- a/java_src/BUILD.bazel
+++ b/java_src/BUILD.bazel
@@ -240,6 +240,7 @@ gen_maven_jar_rules(
         "//src/main/java/com/google/crypto/tink/jwt:jwt_public_key_verify_internal",
         "//src/main/java/com/google/crypto/tink/jwt:jwt_public_key_verify_wrapper",
         "//src/main/java/com/google/crypto/tink/jwt:jwt_rsa_ssa_pkcs1_parameters",
+        "//src/main/java/com/google/crypto/tink/jwt:jwt_rsa_ssa_pkcs1_public_key",
         "//src/main/java/com/google/crypto/tink/jwt:jwt_rsa_ssa_pkcs1_sign_key_manager",
         "//src/main/java/com/google/crypto/tink/jwt:jwt_rsa_ssa_pkcs1_verify_key_manager",
         "//src/main/java/com/google/crypto/tink/jwt:jwt_rsa_ssa_pss_sign_key_manager",
@@ -670,6 +671,7 @@ gen_maven_jar_rules(
         "//src/main/java/com/google/crypto/tink/jwt:jwt_public_key_verify_internal-android",
         "//src/main/java/com/google/crypto/tink/jwt:jwt_public_key_verify_wrapper-android",
         "//src/main/java/com/google/crypto/tink/jwt:jwt_rsa_ssa_pkcs1_parameters-android",
+        "//src/main/java/com/google/crypto/tink/jwt:jwt_rsa_ssa_pkcs1_public_key-android",
         "//src/main/java/com/google/crypto/tink/jwt:jwt_rsa_ssa_pkcs1_sign_key_manager-android",
         "//src/main/java/com/google/crypto/tink/jwt:jwt_rsa_ssa_pkcs1_verify_key_manager-android",
         "//src/main/java/com/google/crypto/tink/jwt:jwt_rsa_ssa_pss_sign_key_manager-android",
diff --git a/java_src/src/main/java/com/google/crypto/tink/jwt/BUILD.bazel b/java_src/src/main/java/com/google/crypto/tink/jwt/BUILD.bazel
index 5f205a5ee..1f11a87b2 100644
--- a/java_src/src/main/java/com/google/crypto/tink/jwt/BUILD.bazel
+++ b/java_src/src/main/java/com/google/crypto/tink/jwt/BUILD.bazel
@@ -1143,3 +1143,31 @@ java_library(
         "@maven//:com_google_errorprone_error_prone_annotations",
     ],
 )
+
+java_library(
+    name = "jwt_rsa_ssa_pkcs1_public_key",
+    srcs = ["JwtRsaSsaPkcs1PublicKey.java"],
+    deps = [
+        ":jwt_rsa_ssa_pkcs1_parameters",
+        ":jwt_signature_public_key",
+        "//src/main/java/com/google/crypto/tink:accesses_partial_key",
+        "//src/main/java/com/google/crypto/tink:key",
+        "//src/main/java/com/google/crypto/tink/subtle:base64",
+        "@maven//:com_google_code_findbugs_jsr305",
+        "@maven//:com_google_errorprone_error_prone_annotations",
+    ],
+)
+
+android_library(
+    name = "jwt_rsa_ssa_pkcs1_public_key-android",
+    srcs = ["JwtRsaSsaPkcs1PublicKey.java"],
+    deps = [
+        ":jwt_rsa_ssa_pkcs1_parameters-android",
+        ":jwt_signature_public_key-android",
+        "//src/main/java/com/google/crypto/tink:accesses_partial_key-android",
+        "//src/main/java/com/google/crypto/tink:key-android",
+        "//src/main/java/com/google/crypto/tink/subtle:base64-android",
+        "@maven//:com_google_code_findbugs_jsr305",
+        "@maven//:com_google_errorprone_error_prone_annotations",
+    ],
+)
diff --git a/java_src/src/main/java/com/google/crypto/tink/jwt/JwtRsaSsaPkcs1PublicKey.java b/java_src/src/main/java/com/google/crypto/tink/jwt/JwtRsaSsaPkcs1PublicKey.java
new file mode 100644
index 000000000..e0d7d6459
--- /dev/null
+++ b/java_src/src/main/java/com/google/crypto/tink/jwt/JwtRsaSsaPkcs1PublicKey.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 PKCS1 signature primitive.
+ *
+ * <p>Standard: https://datatracker.ietf.org/doc/html/rfc7518
+ */
+public final class JwtRsaSsaPkcs1PublicKey extends JwtSignaturePublicKey {
+  private final JwtRsaSsaPkcs1Parameters parameters;
+  private final BigInteger modulus;
+  private final Optional<Integer> idRequirement;
+  private final Optional<String> kid;
+
+  /** Builder for JwtRsaSsaPkcs1PublicKey. */
+  public static class Builder {
+    private Optional<JwtRsaSsaPkcs1Parameters> 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(JwtRsaSsaPkcs1Parameters 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(JwtRsaSsaPkcs1Parameters.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(JwtRsaSsaPkcs1Parameters.KidStrategy.CUSTOM)) {
+        if (!customKid.isPresent()) {
+          throw new GeneralSecurityException("customKid needs to be set for KidStrategy CUSTOM");
+        }
+        return customKid;
+      }
+      if (parameters.get().getKidStrategy().equals(JwtRsaSsaPkcs1Parameters.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 JwtRsaSsaPkcs1PublicKey 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 JwtRsaSsaPkcs1PublicKey(
+          parameters.get(), modulus.get(), idRequirement, computeKid());
+    }
+  }
+
+  private JwtRsaSsaPkcs1PublicKey(
+      JwtRsaSsaPkcs1Parameters 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 JwtRsaSsaPkcs1Parameters getParameters() {
+    return parameters;
+  }
+
+  @Override
+  @Nullable
+  public Integer getIdRequirementOrNull() {
+    return idRequirement.orElse(null);
+  }
+
+  @Override
+  public boolean equalsKey(Key o) {
+    if (!(o instanceof JwtRsaSsaPkcs1PublicKey)) {
+      return false;
+    }
+    JwtRsaSsaPkcs1PublicKey that = (JwtRsaSsaPkcs1PublicKey) o;
+    return that.parameters.equals(parameters)
+        && that.modulus.equals(modulus)
+        && that.kid.equals(kid)
+        && that.idRequirement.equals(idRequirement);
+  }
+}
diff --git a/java_src/src/test/java/com/google/crypto/tink/jwt/BUILD.bazel b/java_src/src/test/java/com/google/crypto/tink/jwt/BUILD.bazel
index 6371ee03d..337614535 100644
--- a/java_src/src/test/java/com/google/crypto/tink/jwt/BUILD.bazel
+++ b/java_src/src/test/java/com/google/crypto/tink/jwt/BUILD.bazel
@@ -510,3 +510,17 @@ java_test(
         "@maven//:junit_junit",
     ],
 )
+
+java_test(
+    name = "JwtRsaSsaPkcs1PublicKeyTest",
+    size = "small",
+    srcs = ["JwtRsaSsaPkcs1PublicKeyTest.java"],
+    deps = [
+        "//src/main/java/com/google/crypto/tink/internal:key_tester",
+        "//src/main/java/com/google/crypto/tink/jwt:jwt_rsa_ssa_pkcs1_parameters",
+        "//src/main/java/com/google/crypto/tink/jwt:jwt_rsa_ssa_pkcs1_public_key",
+        "//src/main/java/com/google/crypto/tink/subtle:base64",
+        "@maven//:com_google_truth_truth",
+        "@maven//:junit_junit",
+    ],
+)
diff --git a/java_src/src/test/java/com/google/crypto/tink/jwt/JwtRsaSsaPkcs1PublicKeyTest.java b/java_src/src/test/java/com/google/crypto/tink/jwt/JwtRsaSsaPkcs1PublicKeyTest.java
new file mode 100644
index 000000000..4239f47ef
--- /dev/null
+++ b/java_src/src/test/java/com/google/crypto/tink/jwt/JwtRsaSsaPkcs1PublicKeyTest.java
@@ -0,0 +1,345 @@
+// 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 static com.google.common.truth.Truth.assertThat;
+import static org.junit.Assert.assertThrows;
+
+import com.google.crypto.tink.internal.KeyTester;
+import com.google.crypto.tink.subtle.Base64;
+import java.math.BigInteger;
+import java.security.GeneralSecurityException;
+import java.util.Optional;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.junit.runners.JUnit4;
+
+@RunWith(JUnit4.class)
+public final class JwtRsaSsaPkcs1PublicKeyTest {
+
+  // Test vector from https://datatracker.ietf.org/doc/html/rfc7515#appendix-A.2
+  static final BigInteger MODULUS =
+      new BigInteger(
+          1,
+          Base64.urlSafeDecode(
+              "ofgWCuLjybRlzo0tZWJjNiuSfb4p4fAkd_wWJcyQoTbji9k0l8W26mPddx"
+                  + "HmfHQp-Vaw-4qPCJrcS2mJPMEzP1Pt0Bm4d4QlL-yRT-SFd2lZS-pCgNMs"
+                  + "D1W_YpRPEwOWvG6b32690r2jZ47soMZo9wGzjb_7OMg0LOL-bSf63kpaSH"
+                  + "SXndS5z5rexMdbBYUsLA9e-KXBdQOS-UTo7WTBEMa2R2CapHg665xsmtdV"
+                  + "MTBQY4uDZlxvb3qCo5ZwKh9kG4LT6_I5IhlJH7aGhyxXFvUK-DWNmoudF8"
+                  + "NAco9_h9iaGNj8q2ethFkMLs91kzk2PAcDTW9gb54h4FRWyuXpoQ"));
+
+  @Test
+  public void build_kidStrategyIgnored_hasExpectedValues() throws Exception {
+    JwtRsaSsaPkcs1Parameters parameters =
+        JwtRsaSsaPkcs1Parameters.builder()
+            .setModulusSizeBits(2048)
+            .setPublicExponent(JwtRsaSsaPkcs1Parameters.F4)
+            .setKidStrategy(JwtRsaSsaPkcs1Parameters.KidStrategy.IGNORED)
+            .setAlgorithm(JwtRsaSsaPkcs1Parameters.Algorithm.RS256)
+            .build();
+    JwtRsaSsaPkcs1PublicKey key =
+        JwtRsaSsaPkcs1PublicKey.builder().setParameters(parameters).setModulus(MODULUS).build();
+    assertThat(key.getParameters()).isEqualTo(parameters);
+    assertThat(key.getModulus()).isEqualTo(MODULUS);
+    assertThat(key.getKid()).isEqualTo(Optional.empty());
+    assertThat(key.getIdRequirementOrNull()).isNull();
+  }
+
+  @Test
+  public void build_kidStrategyIgnored_setCustomKid_fails() throws Exception {
+    JwtRsaSsaPkcs1Parameters parameters =
+        JwtRsaSsaPkcs1Parameters.builder()
+            .setModulusSizeBits(2048)
+            .setPublicExponent(JwtRsaSsaPkcs1Parameters.F4)
+            .setKidStrategy(JwtRsaSsaPkcs1Parameters.KidStrategy.IGNORED)
+            .setAlgorithm(JwtRsaSsaPkcs1Parameters.Algorithm.RS256)
+            .build();
+    JwtRsaSsaPkcs1PublicKey.Builder builder =
+        JwtRsaSsaPkcs1PublicKey.builder()
+            .setParameters(parameters)
+            .setModulus(MODULUS)
+            .setCustomKid("customKid23");
+    assertThrows(GeneralSecurityException.class, builder::build);
+  }
+
+  @Test
+  public void build_kidStrategyIgnored_setIdRequirement_fails() throws Exception {
+    JwtRsaSsaPkcs1Parameters parameters =
+        JwtRsaSsaPkcs1Parameters.builder()
+            .setModulusSizeBits(2048)
+            .setPublicExponent(JwtRsaSsaPkcs1Parameters.F4)
+            .setKidStrategy(JwtRsaSsaPkcs1Parameters.KidStrategy.IGNORED)
+            .setAlgorithm(JwtRsaSsaPkcs1Parameters.Algorithm.RS256)
+            .build();
+    JwtRsaSsaPkcs1PublicKey.Builder builder =
+        JwtRsaSsaPkcs1PublicKey.builder()
+            .setParameters(parameters)
+            .setIdRequirement(123)
+            .setModulus(MODULUS);
+    assertThrows(GeneralSecurityException.class, builder::build);
+  }
+
+  @Test
+  public void build_kidStrategyCustom_hasExpectedValues() throws Exception {
+    JwtRsaSsaPkcs1Parameters parameters =
+        JwtRsaSsaPkcs1Parameters.builder()
+            .setModulusSizeBits(2048)
+            .setPublicExponent(JwtRsaSsaPkcs1Parameters.F4)
+            .setKidStrategy(JwtRsaSsaPkcs1Parameters.KidStrategy.CUSTOM)
+            .setAlgorithm(JwtRsaSsaPkcs1Parameters.Algorithm.RS256)
+            .build();
+    JwtRsaSsaPkcs1PublicKey key =
+        JwtRsaSsaPkcs1PublicKey.builder()
+            .setParameters(parameters)
+            .setModulus(MODULUS)
+            .setCustomKid("customKid777")
+            .build();
+    assertThat(key.getParameters()).isEqualTo(parameters);
+    assertThat(key.getModulus()).isEqualTo(MODULUS);
+    assertThat(key.getKid().get()).isEqualTo("customKid777");
+    assertThat(key.getIdRequirementOrNull()).isNull();
+  }
+
+  @Test
+  public void build_kidStrategyCustom_setIdRequirement_fails() throws Exception {
+    JwtRsaSsaPkcs1Parameters parameters =
+        JwtRsaSsaPkcs1Parameters.builder()
+            .setModulusSizeBits(2048)
+            .setPublicExponent(JwtRsaSsaPkcs1Parameters.F4)
+            .setKidStrategy(JwtRsaSsaPkcs1Parameters.KidStrategy.CUSTOM)
+            .setAlgorithm(JwtRsaSsaPkcs1Parameters.Algorithm.RS256)
+            .build();
+    JwtRsaSsaPkcs1PublicKey.Builder builder =
+        JwtRsaSsaPkcs1PublicKey.builder()
+            .setParameters(parameters)
+            .setIdRequirement(123)
+            .setCustomKid("customKid777")
+            .setModulus(MODULUS);
+    assertThrows(GeneralSecurityException.class, builder::build);
+  }
+
+  @Test
+  public void buildKidStrategyCustom_missingCustomKid_fails() throws Exception {
+    JwtRsaSsaPkcs1Parameters parameters =
+        JwtRsaSsaPkcs1Parameters.builder()
+            .setModulusSizeBits(2048)
+            .setPublicExponent(JwtRsaSsaPkcs1Parameters.F4)
+            .setKidStrategy(JwtRsaSsaPkcs1Parameters.KidStrategy.CUSTOM)
+            .setAlgorithm(JwtRsaSsaPkcs1Parameters.Algorithm.RS256)
+            .build();
+    JwtRsaSsaPkcs1PublicKey.Builder builder =
+        JwtRsaSsaPkcs1PublicKey.builder().setParameters(parameters).setModulus(MODULUS);
+    assertThrows(GeneralSecurityException.class, builder::build);
+  }
+
+  @Test
+  public void build_kidStrategyBase64_getProperties_succeeds() throws Exception {
+    JwtRsaSsaPkcs1Parameters parameters =
+        JwtRsaSsaPkcs1Parameters.builder()
+            .setModulusSizeBits(2048)
+            .setPublicExponent(JwtRsaSsaPkcs1Parameters.F4)
+            .setKidStrategy(JwtRsaSsaPkcs1Parameters.KidStrategy.BASE64_ENCODED_KEY_ID)
+            .setAlgorithm(JwtRsaSsaPkcs1Parameters.Algorithm.RS256)
+            .build();
+    JwtRsaSsaPkcs1PublicKey key =
+        JwtRsaSsaPkcs1PublicKey.builder()
+            .setParameters(parameters)
+            .setModulus(MODULUS)
+            .setIdRequirement(0x1ac6a944)
+            .build();
+    assertThat(key.getParameters()).isEqualTo(parameters);
+    assertThat(key.getIdRequirementOrNull()).isEqualTo(0x1ac6a944);
+    // See JwtFormatTest.getKidFromTinkOutputPrefixType_success
+    assertThat(key.getKid()).isEqualTo(Optional.of("GsapRA"));
+  }
+
+  @Test
+  public void build_kidStrategyBase64_noIdRequirement_throws() throws Exception {
+    JwtRsaSsaPkcs1Parameters parameters =
+        JwtRsaSsaPkcs1Parameters.builder()
+            .setModulusSizeBits(2048)
+            .setPublicExponent(JwtRsaSsaPkcs1Parameters.F4)
+            .setKidStrategy(JwtRsaSsaPkcs1Parameters.KidStrategy.BASE64_ENCODED_KEY_ID)
+            .setAlgorithm(JwtRsaSsaPkcs1Parameters.Algorithm.RS256)
+            .build();
+    JwtRsaSsaPkcs1PublicKey.Builder builder =
+        JwtRsaSsaPkcs1PublicKey.builder().setParameters(parameters).setModulus(MODULUS);
+    assertThrows(GeneralSecurityException.class, builder::build);
+  }
+
+  @Test
+  public void build_kidStrategyBase64_setCustomKid_throws() throws Exception {
+    JwtRsaSsaPkcs1Parameters parameters =
+        JwtRsaSsaPkcs1Parameters.builder()
+            .setModulusSizeBits(2048)
+            .setPublicExponent(JwtRsaSsaPkcs1Parameters.F4)
+            .setKidStrategy(JwtRsaSsaPkcs1Parameters.KidStrategy.BASE64_ENCODED_KEY_ID)
+            .setAlgorithm(JwtRsaSsaPkcs1Parameters.Algorithm.RS256)
+            .build();
+    JwtRsaSsaPkcs1PublicKey.Builder builder =
+        JwtRsaSsaPkcs1PublicKey.builder()
+            .setParameters(parameters)
+            .setIdRequirement(0x89abcdef)
+            .setCustomKid("customKid")
+            .setModulus(MODULUS);
+    assertThrows(GeneralSecurityException.class, builder::build);
+  }
+
+  @Test
+  public void emptyBuild_fails() throws Exception {
+    assertThrows(GeneralSecurityException.class, () -> JwtRsaSsaPkcs1PublicKey.builder().build());
+  }
+
+  @Test
+  public void buildWithoutParameters_fails() throws Exception {
+    assertThrows(
+        GeneralSecurityException.class,
+        () -> JwtRsaSsaPkcs1PublicKey.builder().setModulus(MODULUS).build());
+  }
+
+  @Test
+  public void build_withoutModulus_fails() throws Exception {
+    JwtRsaSsaPkcs1Parameters parameters =
+        JwtRsaSsaPkcs1Parameters.builder()
+            .setModulusSizeBits(2048)
+            .setPublicExponent(JwtRsaSsaPkcs1Parameters.F4)
+            .setKidStrategy(JwtRsaSsaPkcs1Parameters.KidStrategy.IGNORED)
+            .setAlgorithm(JwtRsaSsaPkcs1Parameters.Algorithm.RS256)
+            .build();
+    assertThrows(
+        GeneralSecurityException.class,
+        () -> JwtRsaSsaPkcs1PublicKey.builder().setParameters(parameters).build());
+  }
+
+  @Test
+  public void build_invalidModulusSize_fails() throws Exception {
+    JwtRsaSsaPkcs1Parameters parameters =
+        JwtRsaSsaPkcs1Parameters.builder()
+            .setModulusSizeBits(3456)
+            .setPublicExponent(JwtRsaSsaPkcs1Parameters.F4)
+            .setKidStrategy(JwtRsaSsaPkcs1Parameters.KidStrategy.IGNORED)
+            .setAlgorithm(JwtRsaSsaPkcs1Parameters.Algorithm.RS256)
+            .build();
+
+    // Modulus between 2^3455 and 2^3456 are valid.
+    BigInteger tooSmall = BigInteger.valueOf(2).pow(3455).subtract(BigInteger.ONE);
+    BigInteger tooBig = BigInteger.valueOf(2).pow(3456).add(BigInteger.ONE);
+
+    assertThrows(
+        GeneralSecurityException.class,
+        () ->
+            JwtRsaSsaPkcs1PublicKey.builder()
+                .setParameters(parameters)
+                .setModulus(tooSmall)
+                .build());
+    assertThrows(
+        GeneralSecurityException.class,
+        () ->
+            JwtRsaSsaPkcs1PublicKey.builder().setParameters(parameters).setModulus(tooBig).build());
+  }
+
+  @Test
+  public void testEqualities() throws Exception {
+    JwtRsaSsaPkcs1Parameters kidStrategyIgnoredParameters =
+        JwtRsaSsaPkcs1Parameters.builder()
+            .setModulusSizeBits(2048)
+            .setPublicExponent(JwtRsaSsaPkcs1Parameters.F4)
+            .setKidStrategy(JwtRsaSsaPkcs1Parameters.KidStrategy.IGNORED)
+            .setAlgorithm(JwtRsaSsaPkcs1Parameters.Algorithm.RS256)
+            .build();
+    JwtRsaSsaPkcs1Parameters kidStrategyIgnoredParametersCopy =
+        JwtRsaSsaPkcs1Parameters.builder()
+            .setModulusSizeBits(2048)
+            .setPublicExponent(JwtRsaSsaPkcs1Parameters.F4)
+            .setKidStrategy(JwtRsaSsaPkcs1Parameters.KidStrategy.IGNORED)
+            .setAlgorithm(JwtRsaSsaPkcs1Parameters.Algorithm.RS256)
+            .build();
+
+    JwtRsaSsaPkcs1Parameters kidStrategyCustomParameters =
+        JwtRsaSsaPkcs1Parameters.builder()
+            .setModulusSizeBits(2048)
+            .setPublicExponent(JwtRsaSsaPkcs1Parameters.F4)
+            .setKidStrategy(JwtRsaSsaPkcs1Parameters.KidStrategy.CUSTOM)
+            .setAlgorithm(JwtRsaSsaPkcs1Parameters.Algorithm.RS256)
+            .build();
+
+    JwtRsaSsaPkcs1Parameters kidStrategyBase64Parameters =
+        JwtRsaSsaPkcs1Parameters.builder()
+            .setModulusSizeBits(2048)
+            .setPublicExponent(JwtRsaSsaPkcs1Parameters.F4)
+            .setKidStrategy(JwtRsaSsaPkcs1Parameters.KidStrategy.BASE64_ENCODED_KEY_ID)
+            .setAlgorithm(JwtRsaSsaPkcs1Parameters.Algorithm.RS256)
+            .build();
+
+    new KeyTester()
+        .addEqualityGroup(
+            "KID Ignored, R256",
+            JwtRsaSsaPkcs1PublicKey.builder()
+                .setParameters(kidStrategyIgnoredParameters)
+                .setModulus(MODULUS)
+                .build(),
+            // the same key built twice must be equal
+            JwtRsaSsaPkcs1PublicKey.builder()
+                .setParameters(kidStrategyIgnoredParameters)
+                .setModulus(MODULUS)
+                .build(),
+            // the same key built with a copy of parameters must be equal
+            JwtRsaSsaPkcs1PublicKey.builder()
+                .setParameters(kidStrategyIgnoredParametersCopy)
+                .setModulus(MODULUS)
+                .build())
+        // This group checks that keys with different key bytes are not equal
+        .addEqualityGroup(
+            "KID Ignored, different modulus",
+            JwtRsaSsaPkcs1PublicKey.builder()
+                .setParameters(kidStrategyIgnoredParameters)
+                .setModulus(MODULUS.add(BigInteger.ONE))
+                .build())
+        // These groups checks that keys with different customKid are not equal
+        .addEqualityGroup(
+            "KID Custom, customKid1",
+            JwtRsaSsaPkcs1PublicKey.builder()
+                .setParameters(kidStrategyCustomParameters)
+                .setModulus(MODULUS)
+                .setCustomKid("customKid1")
+                .build())
+        .addEqualityGroup(
+            "KID Custom, customKid2",
+            JwtRsaSsaPkcs1PublicKey.builder()
+                .setParameters(kidStrategyCustomParameters)
+                .setModulus(MODULUS)
+                .setCustomKid("customKid2")
+                .build())
+        // These groups checks that keys with different ID Requirements are not equal
+        .addEqualityGroup(
+            "Tink with key id 1907",
+            JwtRsaSsaPkcs1PublicKey.builder()
+                .setParameters(kidStrategyBase64Parameters)
+                .setModulus(MODULUS)
+                .setIdRequirement(1907)
+                .build())
+        .addEqualityGroup(
+            "Tink with key id 1908",
+            JwtRsaSsaPkcs1PublicKey.builder()
+                .setParameters(kidStrategyBase64Parameters)
+                .setModulus(MODULUS)
+                .setIdRequirement(1908)
+                .build())
+        .doTests();
+  }
+}