| // 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.hybrid.subtle; |
| |
| import com.google.crypto.tink.Aead; |
| import com.google.crypto.tink.HybridEncrypt; |
| import com.google.crypto.tink.aead.subtle.AeadFactory; |
| import com.google.crypto.tink.subtle.Hkdf; |
| import java.math.BigInteger; |
| import java.nio.ByteBuffer; |
| import java.security.GeneralSecurityException; |
| import java.security.interfaces.RSAPublicKey; |
| import javax.crypto.Cipher; |
| |
| /** |
| * Hybrid encryption with RSA-KEM as defined in Shoup's ISO standard proposal as KEM, and AEAD as |
| * DEM and HKDF as KDF. |
| * |
| * <p>Shoup's ISO standard proposal is available at https://www.shoup.net/iso/std6.pdf. |
| */ |
| public final class RsaKemHybridEncrypt implements HybridEncrypt { |
| private final RSAPublicKey recipientPublicKey; |
| private final String hkdfHmacAlgo; |
| private final byte[] hkdfSalt; |
| private final AeadFactory aeadFactory; |
| |
| public RsaKemHybridEncrypt( |
| final RSAPublicKey recipientPublicKey, |
| String hkdfHmacAlgo, |
| final byte[] hkdfSalt, |
| AeadFactory aeadFactory) |
| throws GeneralSecurityException { |
| RsaKem.validateRsaModulus(recipientPublicKey.getModulus()); |
| this.recipientPublicKey = recipientPublicKey; |
| this.hkdfHmacAlgo = hkdfHmacAlgo; |
| this.hkdfSalt = hkdfSalt; |
| this.aeadFactory = aeadFactory; |
| } |
| |
| @Override |
| public byte[] encrypt(final byte[] plaintext, final byte[] contextInfo) |
| throws GeneralSecurityException { |
| // KEM: generate a random shared secret whose bit length is equal to the modulus'. |
| BigInteger mod = recipientPublicKey.getModulus(); |
| byte[] sharedSecret = RsaKem.generateSecret(mod); |
| |
| // KEM: encrypt the shared secret using the public key. |
| Cipher rsaCipher = Cipher.getInstance("RSA/ECB/NoPadding"); |
| rsaCipher.init(Cipher.ENCRYPT_MODE, recipientPublicKey); |
| byte[] token = rsaCipher.doFinal(sharedSecret); |
| |
| // KDF: derive a DEM key from the shared secret, salt, and contextInfo. |
| byte[] demKey = |
| Hkdf.computeHkdf( |
| hkdfHmacAlgo, sharedSecret, hkdfSalt, contextInfo, aeadFactory.getKeySizeInBytes()); |
| |
| Aead aead = aeadFactory.createAead(demKey); |
| byte[] ciphertext = aead.encrypt(plaintext, RsaKem.EMPTY_AAD); |
| return ByteBuffer.allocate(token.length + ciphertext.length).put(token).put(ciphertext).array(); |
| } |
| } |