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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 2017 Google Inc.
//
// 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;

import java.security.GeneralSecurityException;

/**
 * Interface for hybrid encryption.
 *
 * 

Hybrid Encryption combines the efficiency of symmetric encryption with the convenience of * public-key encryption: to encrypt a message a fresh symmetric key is generated and used to * encrypt the actual plaintext data, while the recipient’s public key is used to encrypt the * symmetric key only, and the final ciphertext consists of the symmetric ciphertext and the * encrypted symmetric key. * *

WARNING

* *

Hybrid Encryption does not provide authenticity, that is the recipient of an encrypted message * does not know the identity of the sender. Similar to general public-key encryption schemes the * security goal of Hybrid Encryption is to provide privacy only. In other words, Hybrid Encryption * is secure if and only if the recipient can accept anonymous messages or can rely on other * mechanisms to authenticate the sender. * *

Security guarantees

* *

The functionality of Hybrid Encryption is represented as a pair of primitives (interfaces): * {@link HybridEncrypt} for encryption of data, and {@link HybridDecrypt} for decryption. * Implementations of these interfaces are secure against adaptive chosen ciphertext attacks. In * addition to {@code plaintext} the encryption takes an extra parameter {@code contextInfo}, which * usually is public data implicit from the context, but should be bound to the resulting * ciphertext, i.e. the ciphertext allows for checking the integrity of {@code contextInfo} (but * there are no guarantees wrt. the secrecy or authenticity of {@code contextInfo}). * *

{@code contextInfo} can be empty or null, but to ensure the correct decryption of a ciphertext * the same value must be provided for the decryption operation as was used during encryption (cf. * {@link HybridEncrypt}). * *

A concrete instantiation of this interface can implement the binding of {@code contextInfo} to * the ciphertext in various ways, for example: * *

    *
  • use {@code contextInfo} as "associated data"-input for the employed AEAD symmetric * encryption (cf. https://tools.ietf.org/html/rfc5116). *
  • use {@code contextInfo} as "CtxInfo"-input for HKDF (if the implementation uses HKDF as key * derivation function, cf. https://tools.ietf.org/html/rfc5869). *
* * @since 1.0.0 */ public interface HybridEncrypt { /** * Encryption operation: encrypts {@code plaintext} binding {@code contextInfo} to the resulting * ciphertext. * * @return resulting ciphertext */ byte[] encrypt(final byte[] plaintext, final byte[] contextInfo) throws GeneralSecurityException; }




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