Add examples for encryption and decryption of messages

pgpainless-core/src/test/java/org/pgpainless/example/Encrypt.java

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+/*
+ * Copyright 2021 Paul Schaub.
+ *
+ * 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 org.pgpainless.example;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import java.io.ByteArrayInputStream;
+import java.io.ByteArrayOutputStream;
+import java.io.IOException;
+import java.nio.charset.StandardCharsets;
+import java.security.InvalidAlgorithmParameterException;
+import java.security.NoSuchAlgorithmException;
+
+import org.bouncycastle.openpgp.PGPException;
+import org.bouncycastle.openpgp.PGPPublicKeyRing;
+import org.bouncycastle.openpgp.PGPSecretKeyRing;
+import org.bouncycastle.util.io.Streams;
+import org.junit.jupiter.api.Test;
+import org.pgpainless.PGPainless;
+import org.pgpainless.algorithm.DocumentSignatureType;
+import org.pgpainless.decryption_verification.DecryptionStream;
+import org.pgpainless.decryption_verification.OpenPgpMetadata;
+import org.pgpainless.encryption_signing.EncryptionOptions;
+import org.pgpainless.encryption_signing.EncryptionStream;
+import org.pgpainless.encryption_signing.ProducerOptions;
+import org.pgpainless.encryption_signing.SigningOptions;
+import org.pgpainless.key.protection.SecretKeyRingProtector;
+import org.pgpainless.key.util.KeyRingUtils;
+import org.pgpainless.util.Passphrase;
+
+public class Encrypt {
+
+    /**
+     * In this example, Alice is sending a signed and encrypted message to Bob.
+     * She signs the message using her key and then encrypts the message to both bobs certificate and her own.
+     *
+     * Bob subsequently decrypts the message using his key and verifies that the message was signed by Alice using
+     * her certificate.
+     */
+    @Test
+    public void encryptAndSignMessage() throws PGPException, InvalidAlgorithmParameterException, NoSuchAlgorithmException, IOException {
+        // Prepare keys
+        PGPSecretKeyRing keyAlice = PGPainless.generateKeyRing()
+                .modernKeyRing("alice@pgpainless.org", null);
+        PGPPublicKeyRing certificateAlice = KeyRingUtils.publicKeyRingFrom(keyAlice);
+        SecretKeyRingProtector protectorAlice = SecretKeyRingProtector.unprotectedKeys();
+
+        PGPSecretKeyRing keyBob = PGPainless.generateKeyRing()
+                .modernKeyRing("bob@pgpainless.org", null);
+        PGPPublicKeyRing certificateBob = KeyRingUtils.publicKeyRingFrom(keyBob);
+        SecretKeyRingProtector protectorBob = SecretKeyRingProtector.unprotectedKeys();
+
+        // plaintext message to encrypt
+        String message = "Hello, World!\n";
+        ByteArrayOutputStream ciphertext = new ByteArrayOutputStream();
+        // Encrypt and sign
+        EncryptionStream encryptor = PGPainless.encryptAndOrSign()
+                .onOutputStream(ciphertext)
+                .withOptions(ProducerOptions.signAndEncrypt(
+                        // we want to encrypt communication (affects key selection based on key flags)
+                        EncryptionOptions.encryptCommunications()
+                                .addRecipient(certificateBob)
+                                .addRecipient(certificateAlice),
+                        new SigningOptions()
+                                .addInlineSignature(protectorAlice, keyAlice, DocumentSignatureType.CANONICAL_TEXT_DOCUMENT)
+                        ).setAsciiArmor(true)
+                );
+
+        // Pipe data trough and CLOSE the stream (important)
+        Streams.pipeAll(new ByteArrayInputStream(message.getBytes(StandardCharsets.UTF_8)), encryptor);
+        encryptor.close();
+        String encryptedMessage = ciphertext.toString();
+
+        // Decrypt and verify signatures
+        DecryptionStream decryptor = PGPainless.decryptAndOrVerify()
+                .onInputStream(new ByteArrayInputStream(encryptedMessage.getBytes(StandardCharsets.UTF_8)))
+                .decryptWith(protectorBob, keyBob)
+                .verifyWith(certificateAlice)
+                .ignoreMissingPublicKeys()
+                .build();
+
+        ByteArrayOutputStream plaintext = new ByteArrayOutputStream();
+
+        Streams.pipeAll(decryptor, plaintext);
+        decryptor.close();
+
+        // Check the metadata to see how the message was encrypted/signed
+        OpenPgpMetadata metadata = decryptor.getResult();
+        assertTrue(metadata.isEncrypted());
+        assertTrue(metadata.containsVerifiedSignatureFrom(certificateAlice));
+        assertEquals(message, plaintext.toString());
+    }
+
+    /**
+     * This example demonstrates how to encrypt and decrypt a message using a passphrase.
+     * This method can be combined with public key based encryption and signing.
+     *
+     * @throws PGPException
+     * @throws IOException
+     */
+    @Test
+    public void encryptUsingPassphrase() throws PGPException, IOException {
+        String message = "Hello, World!";
+        ByteArrayOutputStream ciphertext = new ByteArrayOutputStream();
+        // Encrypt
+        EncryptionStream encryptor = PGPainless.encryptAndOrSign()
+                .onOutputStream(ciphertext)
+                .withOptions(ProducerOptions
+                        .encrypt(EncryptionOptions.encryptCommunications()
+                                .addPassphrase(Passphrase.fromPassword("p4ssphr4s3"))
+                        ).setAsciiArmor(true)
+                );
+
+        Streams.pipeAll(new ByteArrayInputStream(message.getBytes(StandardCharsets.UTF_8)), encryptor);
+        encryptor.close();
+
+        String asciiCiphertext = ciphertext.toString();
+
+        // Decrypt
+        DecryptionStream decryptor = PGPainless.decryptAndOrVerify()
+                .onInputStream(new ByteArrayInputStream(asciiCiphertext.getBytes(StandardCharsets.UTF_8)))
+                .decryptWith(Passphrase.fromPassword("p4ssphr4s3"))
+                .doNotVerify()
+                .build();
+
+        ByteArrayOutputStream plaintext = new ByteArrayOutputStream();
+        Streams.pipeAll(decryptor, plaintext);
+
+        decryptor.close();
+
+        assertEquals(message, plaintext.toString());
+    }
+}