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Tink is a small cryptographic library that provides a safe, simple, agile and fast way to accomplish some common cryptographic tasks.
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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.signature;

import com.google.crypto.tink.AccessesPartialKey;
import com.google.crypto.tink.Key;
import com.google.crypto.tink.annotations.Alpha;
import com.google.crypto.tink.util.Bytes;
import com.google.errorprone.annotations.Immutable;
import com.google.errorprone.annotations.RestrictedApi;
import java.nio.ByteBuffer;
import java.security.GeneralSecurityException;
import java.util.Objects;
import javax.annotation.Nullable;

/**
 * Ed25519PublicKey represents the public portion of the Ed25519 signature primitive.
 *
 * This API is annotated with Alpha because it is not yet stable and might be changed in the
 * future.
 */
@Alpha
@Immutable
public final class Ed25519PublicKey extends SignaturePublicKey {
  private final Ed25519Parameters parameters;
  private final Bytes publicKeyBytes;
  private final Bytes outputPrefix;
  @Nullable private final Integer idRequirement;

  private Ed25519PublicKey(
      Ed25519Parameters parameters,
      Bytes publicKeyBytes,
      Bytes outputPrefix,
      @Nullable Integer idRequirement) {
    this.parameters = parameters;
    this.publicKeyBytes = publicKeyBytes;
    this.outputPrefix = outputPrefix;
    this.idRequirement = idRequirement;
  }

  private static Bytes createOutputPrefix(
      Ed25519Parameters parameters, @Nullable Integer idRequirement) {
    if (parameters.getVariant() == Ed25519Parameters.Variant.NO_PREFIX) {
      return Bytes.copyFrom(new byte[] {});
    }
    if (parameters.getVariant() == Ed25519Parameters.Variant.CRUNCHY
        || parameters.getVariant() == Ed25519Parameters.Variant.LEGACY) {
      return Bytes.copyFrom(
          ByteBuffer.allocate(5).put((byte) 0).putInt(idRequirement.intValue()).array());
    }
    if (parameters.getVariant() == Ed25519Parameters.Variant.TINK) {
      return Bytes.copyFrom(
          ByteBuffer.allocate(5).put((byte) 1).putInt(idRequirement.intValue()).array());
    }
    throw new IllegalStateException("Unknown Variant: " + parameters.getVariant());
  }

  @Override
  public Bytes getOutputPrefix() {
    return outputPrefix;
  }

  @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})
  @AccessesPartialKey
  public static Ed25519PublicKey create(Bytes publicKeyBytes) throws GeneralSecurityException {
    return create(Ed25519Parameters.Variant.NO_PREFIX, publicKeyBytes, null);
  }

  @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 Ed25519PublicKey create(
      Ed25519Parameters.Variant variant, Bytes publicKeyBytes, @Nullable Integer idRequirement)
      throws GeneralSecurityException {
    Ed25519Parameters parameters = Ed25519Parameters.create(variant);
    if (!variant.equals(Ed25519Parameters.Variant.NO_PREFIX) && idRequirement == null) {
      throw new GeneralSecurityException(
          "For given Variant " + variant + " the value of idRequirement must be non-null");
      }

    if (variant.equals(Ed25519Parameters.Variant.NO_PREFIX) && idRequirement != null) {
      throw new GeneralSecurityException(
          "For given Variant NO_PREFIX the value of idRequirement must be null");
    }
    if (publicKeyBytes.size() != 32) {
      throw new GeneralSecurityException(
          "Ed25519 key must be constructed with key of length 32 bytes, not "
              + publicKeyBytes.size());
    }

    return new Ed25519PublicKey(
        parameters, publicKeyBytes, createOutputPrefix(parameters, idRequirement), idRequirement);
  }

  @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 Bytes getPublicKeyBytes() {
    return publicKeyBytes;
  }

  @Override
  public Ed25519Parameters getParameters() {
    return parameters;
  }

  @Override
  @Nullable
  public Integer getIdRequirementOrNull() {
    return idRequirement;
  }

  @Override
  public boolean equalsKey(Key o) {
    if (!(o instanceof Ed25519PublicKey)) {
      return false;
    }
    Ed25519PublicKey that = (Ed25519PublicKey) o;
    // Since outputPrefix is a function of parameters, we can ignore it here.
    return that.parameters.equals(parameters)
        && that.publicKeyBytes.equals(publicKeyBytes)
        && Objects.equals(that.idRequirement, idRequirement);
  }
}