291 lines
11 KiB
Java
291 lines
11 KiB
Java
// SPDX-FileCopyrightText: 2021 Paul Schaub <vanitasvitae@fsfe.org>
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//
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// SPDX-License-Identifier: Apache-2.0
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package org.pgpainless.key.util;
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import java.io.ByteArrayOutputStream;
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import java.io.IOException;
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import java.io.InputStream;
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import java.io.OutputStream;
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import java.math.BigInteger;
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import java.security.SecureRandom;
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import org.bouncycastle.bcpg.BCPGKey;
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import org.bouncycastle.bcpg.DSAPublicBCPGKey;
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import org.bouncycastle.bcpg.DSASecretBCPGKey;
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import org.bouncycastle.bcpg.EdDSAPublicBCPGKey;
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import org.bouncycastle.bcpg.EdSecretBCPGKey;
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import org.bouncycastle.bcpg.ElGamalPublicBCPGKey;
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import org.bouncycastle.bcpg.ElGamalSecretBCPGKey;
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import org.bouncycastle.bcpg.RSAPublicBCPGKey;
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import org.bouncycastle.bcpg.RSASecretBCPGKey;
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import org.bouncycastle.openpgp.PGPEncryptedDataGenerator;
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import org.bouncycastle.openpgp.PGPEncryptedDataList;
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import org.bouncycastle.openpgp.PGPException;
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import org.bouncycastle.openpgp.PGPPrivateKey;
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import org.bouncycastle.openpgp.PGPPublicKey;
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import org.bouncycastle.openpgp.PGPPublicKeyEncryptedData;
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import org.bouncycastle.openpgp.PGPSignature;
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import org.bouncycastle.openpgp.PGPSignatureGenerator;
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import org.bouncycastle.openpgp.operator.PublicKeyDataDecryptorFactory;
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import org.bouncycastle.util.Arrays;
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import org.bouncycastle.util.io.Streams;
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import org.pgpainless.algorithm.HashAlgorithm;
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import org.pgpainless.algorithm.PublicKeyAlgorithm;
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import org.pgpainless.algorithm.SignatureType;
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import org.pgpainless.algorithm.SymmetricKeyAlgorithm;
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import org.pgpainless.exception.KeyIntegrityException;
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import org.pgpainless.implementation.ImplementationFactory;
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/**
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* Utility class to verify keys against Key Overwriting (KO) attacks.
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* This class of attacks is only possible if the attacker has access to the (encrypted) secret key material.
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* To execute the attack, they would modify the unauthenticated parameters of the users public key.
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* Using the modified public key in combination with the unmodified secret key material can then lead to the
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* extraction of secret key parameters via weakly crafted messages.
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*
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* @see <a href="https://www.kopenpgp.com/">Key Overwriting (KO) Attacks against OpenPGP</a>
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*/
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public class PublicKeyParameterValidationUtil {
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public static void verifyPublicKeyParameterIntegrity(PGPPrivateKey privateKey, PGPPublicKey publicKey)
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throws KeyIntegrityException {
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PublicKeyAlgorithm publicKeyAlgorithm = PublicKeyAlgorithm.requireFromId(publicKey.getAlgorithm());
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boolean valid = true;
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// Algorithm specific validations
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BCPGKey key = privateKey.getPrivateKeyDataPacket();
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if (key instanceof RSASecretBCPGKey) {
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valid = verifyRSAKeyIntegrity(
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(RSASecretBCPGKey) key,
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(RSAPublicBCPGKey) publicKey.getPublicKeyPacket().getKey())
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&& valid;
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} else if (key instanceof EdSecretBCPGKey) {
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valid = verifyEdDsaKeyIntegrity(
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(EdSecretBCPGKey) key,
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(EdDSAPublicBCPGKey) publicKey.getPublicKeyPacket().getKey())
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&& valid;
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} else if (key instanceof DSASecretBCPGKey) {
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valid = verifyDsaKeyIntegrity(
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(DSASecretBCPGKey) key,
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(DSAPublicBCPGKey) publicKey.getPublicKeyPacket().getKey())
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&& valid;
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} else if (key instanceof ElGamalSecretBCPGKey) {
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valid = verifyElGamalKeyIntegrity(
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(ElGamalSecretBCPGKey) key,
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(ElGamalPublicBCPGKey) publicKey.getPublicKeyPacket().getKey())
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&& valid;
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}
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if (!valid) {
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throw new KeyIntegrityException();
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}
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// Additional to the algorithm-specific tests further above, we also perform
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// generic functionality tests with the key, such as whether it is able to decrypt encrypted data
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// or verify signatures.
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// These tests should be more or less constant time.
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if (publicKeyAlgorithm.isSigningCapable()) {
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valid = verifyCanSign(privateKey, publicKey);
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}
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if (publicKeyAlgorithm.isEncryptionCapable()) {
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valid = verifyCanDecrypt(privateKey, publicKey) && valid;
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}
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if (!valid) {
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throw new KeyIntegrityException();
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}
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}
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/**
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* Verify that the public key can be used to successfully verify a signature made by the private key.
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* @param privateKey private key
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* @param publicKey public key
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* @return false if signature verification fails
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*/
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private static boolean verifyCanSign(PGPPrivateKey privateKey, PGPPublicKey publicKey) {
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SecureRandom random = new SecureRandom();
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PublicKeyAlgorithm publicKeyAlgorithm = PublicKeyAlgorithm.requireFromId(publicKey.getAlgorithm());
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PGPSignatureGenerator signatureGenerator = new PGPSignatureGenerator(
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ImplementationFactory.getInstance().getPGPContentSignerBuilder(publicKeyAlgorithm, HashAlgorithm.SHA256)
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);
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try {
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signatureGenerator.init(SignatureType.TIMESTAMP.getCode(), privateKey);
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byte[] data = new byte[512];
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random.nextBytes(data);
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signatureGenerator.update(data);
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PGPSignature sig = signatureGenerator.generate();
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sig.init(ImplementationFactory.getInstance().getPGPContentVerifierBuilderProvider(), publicKey);
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sig.update(data);
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return sig.verify();
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} catch (PGPException e) {
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return false;
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}
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}
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/**
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* Verify that the public key can be used to encrypt a message which can successfully be
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* decrypted using the private key.
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* @param privateKey private key
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* @param publicKey public key
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* @return false if decryption of a message encrypted with the public key fails
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*/
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private static boolean verifyCanDecrypt(PGPPrivateKey privateKey, PGPPublicKey publicKey) {
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SecureRandom random = new SecureRandom();
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PGPEncryptedDataGenerator encryptedDataGenerator = new PGPEncryptedDataGenerator(
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ImplementationFactory.getInstance().getPGPDataEncryptorBuilder(SymmetricKeyAlgorithm.AES_256)
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);
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encryptedDataGenerator.addMethod(
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ImplementationFactory.getInstance().getPublicKeyKeyEncryptionMethodGenerator(publicKey));
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byte[] data = new byte[1024];
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random.nextBytes(data);
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ByteArrayOutputStream out = new ByteArrayOutputStream();
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try {
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OutputStream outputStream = encryptedDataGenerator.open(out, new byte[1024]);
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outputStream.write(data);
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encryptedDataGenerator.close();
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PGPEncryptedDataList encryptedDataList = new PGPEncryptedDataList(out.toByteArray());
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PublicKeyDataDecryptorFactory decryptorFactory =
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ImplementationFactory.getInstance().getPublicKeyDataDecryptorFactory(privateKey);
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PGPPublicKeyEncryptedData encryptedData =
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(PGPPublicKeyEncryptedData) encryptedDataList.getEncryptedDataObjects().next();
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InputStream decrypted = encryptedData.getDataStream(decryptorFactory);
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out = new ByteArrayOutputStream();
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Streams.pipeAll(decrypted, out);
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decrypted.close();
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} catch (IOException | PGPException e) {
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return false;
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}
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return Arrays.constantTimeAreEqual(data, out.toByteArray());
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}
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private static boolean verifyEdDsaKeyIntegrity(EdSecretBCPGKey privateKey, EdDSAPublicBCPGKey publicKey)
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throws KeyIntegrityException {
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// TODO: Implement
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return true;
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}
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private static boolean verifyDsaKeyIntegrity(DSASecretBCPGKey privateKey, DSAPublicBCPGKey publicKey)
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throws KeyIntegrityException {
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// Not sure what value to put here in order to have a "robust" primality check
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// I went with 40, since that's what SO recommends:
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// https://stackoverflow.com/a/6330138
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final int certainty = 40;
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BigInteger pG = publicKey.getG();
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BigInteger pP = publicKey.getP();
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BigInteger pQ = publicKey.getQ();
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BigInteger pY = publicKey.getY();
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BigInteger sX = privateKey.getX();
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boolean pPrime = pP.isProbablePrime(certainty);
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if (!pPrime) {
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return false;
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}
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boolean qPrime = pQ.isProbablePrime(certainty);
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if (!qPrime) {
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return false;
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}
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// q > 160 bits
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boolean qLarge = pQ.getLowestSetBit() > 160;
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if (!qLarge) {
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return false;
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}
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// q divides p - 1
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boolean qDividesPminus1 = pP.subtract(BigInteger.ONE).mod(pQ).equals(BigInteger.ZERO);
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if (!qDividesPminus1) {
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return false;
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}
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// 1 < g < p
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boolean gInBounds = BigInteger.ONE.max(pG).equals(pG) && pG.max(pP).equals(pP);
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if (!gInBounds) {
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return false;
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}
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// g^q = 1 mod p
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boolean gPowXModPEquals1 = pG.modPow(pQ, pP).equals(BigInteger.ONE);
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if (!gPowXModPEquals1) {
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return false;
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}
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// y = g^x mod p
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boolean yEqualsGPowXModP = pY.equals(pG.modPow(sX, pP));
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if (!yEqualsGPowXModP) {
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return false;
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}
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return true;
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}
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private static boolean verifyRSAKeyIntegrity(RSASecretBCPGKey secretKey, RSAPublicBCPGKey publicKey)
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throws KeyIntegrityException {
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// Verify that the public keys N is equal to private keys p*q
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return publicKey.getModulus().equals(secretKey.getPrimeP().multiply(secretKey.getPrimeQ()));
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}
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/**
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* Validate ElGamal public key parameters.
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*
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* Original implementation by the openpgpjs authors:
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* https://github.com/openpgpjs/openpgpjs/blob/main/src/crypto/public_key/elgamal.js#L76-L143
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* @param secretKey secret key
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* @param publicKey public key
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* @return true if supposedly valid, false if invalid
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*/
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private static boolean verifyElGamalKeyIntegrity(ElGamalSecretBCPGKey secretKey, ElGamalPublicBCPGKey publicKey) {
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BigInteger p = publicKey.getP();
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BigInteger g = publicKey.getG();
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BigInteger y = publicKey.getY();
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BigInteger one = BigInteger.ONE;
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// 1 < g < p
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if (g.min(one).equals(g) || g.max(p).equals(g)) {
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return false;
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}
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// p-1 is large
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if (p.bitLength() < 1023) {
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return false;
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}
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// g^(p-1) mod p = 1
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if (!g.modPow(p.subtract(one), p).equals(one)) {
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return false;
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}
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// check g^i mod p != 1 for i < threshold
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BigInteger res = g;
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BigInteger i = BigInteger.valueOf(1);
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BigInteger threshold = BigInteger.valueOf(2).shiftLeft(17);
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while (i.compareTo(threshold) < 0) {
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res = res.multiply(g).mod(p);
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if (res.equals(one)) {
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return false;
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}
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i = i.add(one);
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}
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// blinded exponentiation to check y = g^(r*(p-1)+x) mod p
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SecureRandom random = new SecureRandom();
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BigInteger x = secretKey.getX();
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BigInteger r = new BigInteger(p.bitLength(), random);
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BigInteger rqx = p.subtract(one).multiply(r).add(x);
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if (!y.equals(g.modPow(rqx, p))) {
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return false;
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}
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return true;
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}
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}
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