Respect symmetric algorithm policy during decryption and throw UnacceptableAlgorithmException if policy is violated

pgpainless-core/src/main/java/org/pgpainless/decryption_verification/DecryptionBuilderInterface.java

@@ -249,6 +249,7 @@ public interface DecryptionBuilderInterface {
          * @return the decryption stream
          * @throws IOException in case of an I/O error
          * @throws PGPException if something is malformed
+         * @throws org.pgpainless.exception.UnacceptableAlgorithmException if the message uses weak/unacceptable algorithms
          */
         DecryptionStream build() throws IOException, PGPException;
 

pgpainless-core/src/main/java/org/pgpainless/decryption_verification/DecryptionStreamFactory.java

@@ -52,10 +52,12 @@ import org.bouncycastle.openpgp.operator.KeyFingerPrintCalculator;
 import org.bouncycastle.openpgp.operator.PBEDataDecryptorFactory;
 import org.bouncycastle.openpgp.operator.PGPContentVerifierBuilderProvider;
 import org.bouncycastle.openpgp.operator.PublicKeyDataDecryptorFactory;
+import org.pgpainless.PGPainless;
 import org.pgpainless.algorithm.CompressionAlgorithm;
 import org.pgpainless.algorithm.StreamEncoding;
 import org.pgpainless.algorithm.SymmetricKeyAlgorithm;
 import org.pgpainless.exception.MessageNotIntegrityProtectedException;
+import org.pgpainless.exception.UnacceptableAlgorithmException;
 import org.pgpainless.implementation.ImplementationFactory;
 import org.pgpainless.key.OpenPgpV4Fingerprint;
 import org.pgpainless.key.SubkeyIdentifier;
@@ -218,9 +220,7 @@ public final class DecryptionStreamFactory {
                             .getPBEDataDecryptorFactory(decryptionPassphrase);
                     SymmetricKeyAlgorithm symmetricKeyAlgorithm = SymmetricKeyAlgorithm.fromId(
                             pbeEncryptedData.getSymmetricAlgorithm(passphraseDecryptor));
-                    if (symmetricKeyAlgorithm == SymmetricKeyAlgorithm.NULL) {
+                    throwIfAlgorithmIsRejected(symmetricKeyAlgorithm);
-                        throw new PGPException("Data is not encrypted.");
-                    }
                     resultBuilder.setSymmetricKeyAlgorithm(symmetricKeyAlgorithm);
 
                     try {
@@ -281,19 +281,25 @@ public final class DecryptionStreamFactory {
         SymmetricKeyAlgorithm symmetricKeyAlgorithm = SymmetricKeyAlgorithm
                 .fromId(encryptedSessionKey.getSymmetricAlgorithm(dataDecryptor));
         if (symmetricKeyAlgorithm == SymmetricKeyAlgorithm.NULL) {
-            throw new PGPException("Data is not encrypted.");
+            LOGGER.log(LEVEL, "Message is unencrypted");
-        }
+        } else {
-
             LOGGER.log(LEVEL, "Message is encrypted using " + symmetricKeyAlgorithm);
+        }
+        throwIfAlgorithmIsRejected(symmetricKeyAlgorithm);
         resultBuilder.setSymmetricKeyAlgorithm(symmetricKeyAlgorithm);
 
-        if (encryptedSessionKey.isIntegrityProtected()) {
         IntegrityProtectedInputStream integrityProtected =
                 new IntegrityProtectedInputStream(encryptedSessionKey.getDataStream(dataDecryptor), encryptedSessionKey);
         integrityProtectedStreams.add(integrityProtected);
         return integrityProtected;
     }
-        return encryptedSessionKey.getDataStream(dataDecryptor);
+
+    private void throwIfAlgorithmIsRejected(SymmetricKeyAlgorithm algorithm) throws UnacceptableAlgorithmException {
+        if (!PGPainless.getPolicy().getSymmetricKeyDecryptionAlgoritmPolicy().isAcceptable(algorithm)) {
+            throw new UnacceptableAlgorithmException("Data is "
+                    + (algorithm == SymmetricKeyAlgorithm.NULL ? "unencrypted" : "encrypted with symmetric algorithm " + algorithm) + " which is not acceptable as per PGPainless' policy.\n" +
+                    "To mark this algorithm as acceptable, use PGPainless.getPolicy().setSymmetricKeyDecryptionAlgorithmPolicy().");
+        }
     }
 
     private void initOnePassSignatures(@Nonnull PGPOnePassSignatureList onePassSignatureList) throws PGPException {

pgpainless-core/src/main/java/org/pgpainless/exception/UnacceptableAlgorithmException.java

@@ -0,0 +1,28 @@
+/*
+ * 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.exception;
+
+import org.bouncycastle.openpgp.PGPException;
+
+/**
+ * Exception that gets thrown if unacceptable algorithms are encountered.
+ */
+public class UnacceptableAlgorithmException extends PGPException {
+
+    public UnacceptableAlgorithmException(String message) {
+        super(message);
+    }
+}

pgpainless-core/src/main/java/org/pgpainless/policy/Policy.java

@@ -37,7 +37,7 @@ public final class Policy {
     private SymmetricKeyAlgorithmPolicy symmetricKeyEncryptionAlgorithmPolicy =
             SymmetricKeyAlgorithmPolicy.defaultSymmetricKeyEncryptionAlgorithmPolicy();
     private SymmetricKeyAlgorithmPolicy symmetricKeyDecryptionAlgorithmPolicy =
-            SymmetricKeyAlgorithmPolicy.defaultSymmetricKeyEncryptionAlgorithmPolicy();
+            SymmetricKeyAlgorithmPolicy.defaultSymmetricKeyDecryptionAlgorithmPolicy();
     private final NotationRegistry notationRegistry = new NotationRegistry();
 
     private Policy() {
@@ -190,6 +190,7 @@ public final class Policy {
          */
         public static SymmetricKeyAlgorithmPolicy defaultSymmetricKeyEncryptionAlgorithmPolicy() {
             return new SymmetricKeyAlgorithmPolicy(SymmetricKeyAlgorithm.AES_256, Arrays.asList(
+                    // Reject: Unencrypted, IDEA, TripleDES, CAST5
                     SymmetricKeyAlgorithm.BLOWFISH,
                     SymmetricKeyAlgorithm.AES_128,
                     SymmetricKeyAlgorithm.AES_192,
@@ -201,9 +202,14 @@ public final class Policy {
             ));
         }
 
+        /**
+         * The default symmetric decryption algorithm policy of PGPainless.
+         *
+         * @return default symmetric decryption algorithm policy
+         */
         public static SymmetricKeyAlgorithmPolicy defaultSymmetricKeyDecryptionAlgorithmPolicy() {
             return new SymmetricKeyAlgorithmPolicy(SymmetricKeyAlgorithm.AES_256, Arrays.asList(
-                    SymmetricKeyAlgorithm.IDEA,
+                    // Reject: Unencrypted, IDEA, TripleDES
                     SymmetricKeyAlgorithm.CAST5,
                     SymmetricKeyAlgorithm.BLOWFISH,
                     SymmetricKeyAlgorithm.AES_128,

pgpainless-core/src/test/java/org/pgpainless/decryption_verification/RejectWeakSymmetricAlgorithmDuringDecryption.java

@@ -0,0 +1,232 @@
+/*
+ * 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.decryption_verification;
+
+import static org.junit.jupiter.api.Assertions.assertThrows;
+import static org.junit.jupiter.api.Assertions.fail;
+
+import java.io.ByteArrayInputStream;
+import java.io.IOException;
+import java.nio.charset.StandardCharsets;
+
+import org.bouncycastle.openpgp.PGPException;
+import org.bouncycastle.openpgp.PGPSecretKeyRing;
+import org.junit.jupiter.api.Test;
+import org.pgpainless.PGPainless;
+import org.pgpainless.exception.UnacceptableAlgorithmException;
+import org.pgpainless.key.protection.SecretKeyRingProtector;
+
+/**
+ * Test PGPainless' default symmetric key algorithm policy for decryption of messages.
+ * The default decryption policy rejects messages encrypted with IDEA and TripleDES, as well as unencrypted messages.
+ */
+public class RejectWeakSymmetricAlgorithmDuringDecryption {
+
+    private static final String key = "-----BEGIN PGP PRIVATE KEY BLOCK-----\n" +
+            "   Comment: Bob's OpenPGP Transferable Secret Key\n" +
+            "\n" +
+            "   lQVYBF2lnPIBDAC5cL9PQoQLTMuhjbYvb4Ncuuo0bfmgPRFywX53jPhoFf4Zg6mv\n" +
+            "   /seOXpgecTdOcVttfzC8ycIKrt3aQTiwOG/ctaR4Bk/t6ayNFfdUNxHWk4WCKzdz\n" +
+            "   /56fW2O0F23qIRd8UUJp5IIlN4RDdRCtdhVQIAuzvp2oVy/LaS2kxQoKvph/5pQ/\n" +
+            "   5whqsyroEWDJoSV0yOb25B/iwk/pLUFoyhDG9bj0kIzDxrEqW+7Ba8nocQlecMF3\n" +
+            "   X5KMN5kp2zraLv9dlBBpWW43XktjcCZgMy20SouraVma8Je/ECwUWYUiAZxLIlMv\n" +
+            "   9CurEOtxUw6N3RdOtLmYZS9uEnn5y1UkF88o8Nku890uk6BrewFzJyLAx5wRZ4F0\n" +
+            "   qV/yq36UWQ0JB/AUGhHVPdFf6pl6eaxBwT5GXvbBUibtf8YI2og5RsgTWtXfU7eb\n" +
+            "   SGXrl5ZMpbA6mbfhd0R8aPxWfmDWiIOhBufhMCvUHh1sApMKVZnvIff9/0Dca3wb\n" +
+            "   vLIwa3T4CyshfT0AEQEAAQAL/RZqbJW2IqQDCnJi4Ozm++gPqBPiX1RhTWSjwxfM\n" +
+            "   cJKUZfzLj414rMKm6Jh1cwwGY9jekROhB9WmwaaKT8HtcIgrZNAlYzANGRCM4TLK\n" +
+            "   3VskxfSwKKna8l+s+mZglqbAjUg3wmFuf9Tj2xcUZYmyRm1DEmcN2ZzpvRtHgX7z\n" +
+            "   Wn1mAKUlSDJZSQks0zjuMNbupcpyJokdlkUg2+wBznBOTKzgMxVNC9b2g5/tMPUs\n" +
+            "   hGGWmF1UH+7AHMTaS6dlmr2ZBIyogdnfUqdNg5sZwsxSNrbglKP4sqe7X61uEAIQ\n" +
+            "   bD7rT3LonLbhkrj3I8wilUD8usIwt5IecoHhd9HziqZjRCc1BUBkboUEoyedbDV4\n" +
+            "   i4qfsFZ6CEWoLuD5pW7dEp0M+WeuHXO164Rc+LnH6i1VQrpb1Okl4qO6ejIpIjBI\n" +
+            "   1t3GshtUu/mwGBBxs60KBX5g77mFQ9lLCRj8lSYqOsHRKBhUp4qM869VA+fD0BRP\n" +
+            "   fqPT0I9IH4Oa/A3jYJcg622GwQYA1LhnP208Waf6PkQSJ6kyr8ymY1yVh9VBE/g6\n" +
+            "   fRDYA+pkqKnw9wfH2Qho3ysAA+OmVOX8Hldg+Pc0Zs0e5pCavb0En8iFLvTA0Q2E\n" +
+            "   LR5rLue9uD7aFuKFU/VdcddY9Ww/vo4k5p/tVGp7F8RYCFn9rSjIWbfvvZi1q5Tx\n" +
+            "   +akoZbga+4qQ4WYzB/obdX6SCmi6BndcQ1QdjCCQU6gpYx0MddVERbIp9+2SXDyL\n" +
+            "   hpxjSyz+RGsZi/9UAshT4txP4+MZBgDfK3ZqtW+h2/eMRxkANqOJpxSjMyLO/FXN\n" +
+            "   WxzTDYeWtHNYiAlOwlQZEPOydZFty9IVzzNFQCIUCGjQ/nNyhw7adSgUk3+BXEx/\n" +
+            "   MyJPYY0BYuhLxLYcrfQ9nrhaVKxRJj25SVHj2ASsiwGJRZW4CC3uw40OYxfKEvNC\n" +
+            "   mer/VxM3kg8qqGf9KUzJ1dVdAvjyx2Hz6jY2qWCyRQ6IMjWHyd43C4r3jxooYKUC\n" +
+            "   YnstRQyb/gCSKahveSEjo07CiXMr88UGALwzEr3npFAsPW3osGaFLj49y1oRe11E\n" +
+            "   he9gCHFm+fuzbXrWmdPjYU5/ZdqdojzDqfu4ThfnipknpVUM1o6MQqkjM896FHm8\n" +
+            "   zbKVFSMhEP6DPHSCexMFrrSgN03PdwHTO6iBaIBBFqmGY01tmJ03SxvSpiBPON9P\n" +
+            "   NVvy/6UZFedTq8A07OUAxO62YUSNtT5pmK2vzs3SAZJmbFbMh+NN204TRI72GlqT\n" +
+            "   t5hcfkuv8hrmwPS/ZR6q312mKQ6w/1pqO9qitCFCb2IgQmFiYmFnZSA8Ym9iQG9w\n" +
+            "   ZW5wZ3AuZXhhbXBsZT6JAc4EEwEKADgCGwMFCwkIBwIGFQoJCAsCBBYCAwECHgEC\n" +
+            "   F4AWIQTRpm4aI7GCyZgPeIz7/MgqAV5zMAUCXaWe+gAKCRD7/MgqAV5zMG9sC/9U\n" +
+            "   2T3RrqEbw533FPNfEflhEVRIZ8gDXKM8hU6cqqEzCmzZT6xYTe6sv4y+PJBGXJFX\n" +
+            "   yhj0g6FDkSyboM5litOcTupURObVqMgA/Y4UKERznm4fzzH9qek85c4ljtLyNufe\n" +
+            "   doL2pp3vkGtn7eD0QFRaLLmnxPKQ/TlZKdLE1G3u8Uot8QHicaR6GnAdc5UXQJE3\n" +
+            "   BiV7jZuDyWmZ1cUNwJkKL6oRtp+ZNDOQCrLNLecKHcgCqrpjSQG5oouba1I1Q6Vl\n" +
+            "   sP44dhA1nkmLHtxlTOzpeHj4jnk1FaXmyasurrrI5CgU/L2Oi39DGKTH/A/cywDN\n" +
+            "   4ZplIQ9zR8enkbXquUZvFDe+Xz+6xRXtb5MwQyWODB3nHw85HocLwRoIN9WdQEI+\n" +
+            "   L8a/56AuOwhs8llkSuiITjR7r9SgKJC2WlAHl7E8lhJ3VDW3ELC56KH308d6mwOG\n" +
+            "   ZRAqIAKzM1T5FGjMBhq7ZV0eqdEntBh3EcOIfj2M8rg1MzJv+0mHZOIjByawikad\n" +
+            "   BVgEXaWc8gEMANYwv1xsYyunXYK0X1vY/rP1NNPvhLyLIE7NpK90YNBj+xS1ldGD\n" +
+            "   bUdZqZeef2xJe8gMQg05DoD1DF3GipZ0Ies65beh+d5hegb7N4pzh0LzrBrVNHar\n" +
+            "   29b5ExdI7i4iYD5TO6Vr/qTUOiAN/byqELEzAb+L+b2DVz/RoCm4PIp1DU9ewcc2\n" +
+            "   WB38Ofqut3nLYA5tqJ9XvAiEQme+qAVcM3ZFcaMt4I4dXhDZZNg+D9LiTWcxdUPB\n" +
+            "   leu8iwDRjAgyAhPzpFp+nWoqWA81uIiULWD1Fj+IVoY3ZvgivoYOiEFBJ9lbb4te\n" +
+            "   g9m5UT/AaVDTWuHzbspVlbiVe+qyB77C2daWzNyx6UYBPLOo4r0t0c91kbNE5lgj\n" +
+            "   Z7xz6los0N1U8vq91EFSeQJoSQ62XWavYmlCLmdNT6BNfgh4icLsT7Vr1QMX9jzn\n" +
+            "   JtTPxdXytSdHvpSpULsqJ016l0dtmONcK3z9mj5N5z0k1tg1AH970TGYOe2aUcSx\n" +
+            "   IRDMXDOPyzEfjwARAQABAAv9F2CwsjS+Sjh1M1vegJbZjei4gF1HHpEM0K0PSXsp\n" +
+            "   SfVvpR4AoSJ4He6CXSMWg0ot8XKtDuZoV9jnJaES5UL9pMAD7JwIOqZm/DYVJM5h\n" +
+            "   OASCh1c356/wSbFbzRHPtUdZO9Q30WFNJM5pHbCJPjtNoRmRGkf71RxtvHBzy7np\n" +
+            "   Ga+W6U/NVKHw0i0CYwMI0YlKDakYW3Pm+QL+gHZFvngGweTod0f9l2VLLAmeQR/c\n" +
+            "   +EZs7lNumhuZ8mXcwhUc9JQIhOkpO+wreDysEFkAcsKbkQP3UDUsA1gFx9pbMzT0\n" +
+            "   tr1oZq2a4QBtxShHzP/ph7KLpN+6qtjks3xB/yjTgaGmtrwM8tSe0wD1RwXS+/1o\n" +
+            "   BHpXTnQ7TfeOGUAu4KCoOQLv6ELpKWbRBLWuiPwMdbGpvVFALO8+kvKAg9/r+/ny\n" +
+            "   zM2GQHY+J3Jh5JxPiJnHfXNZjIKLbFbIPdSKNyJBuazXW8xIa//mEHMI5OcvsZBK\n" +
+            "   clAIp7LXzjEjKXIwHwDcTn9pBgDpdOKTHOtJ3JUKx0rWVsDH6wq6iKV/FTVSY5jl\n" +
+            "   zN+puOEsskF1Lfxn9JsJihAVO3yNsp6RvkKtyNlFazaCVKtDAmkjoh60XNxcNRqr\n" +
+            "   gCnwdpbgdHP6v/hvZY54ZaJjz6L2e8unNEkYLxDt8cmAyGPgH2XgL7giHIp9jrsQ\n" +
+            "   aS381gnYwNX6wE1aEikgtY91nqJjwPlibF9avSyYQoMtEqM/1UjTjB2KdD/MitK5\n" +
+            "   fP0VpvuXpNYZedmyq4UOMwdkiNMGAOrfmOeT0olgLrTMT5H97Cn3Yxbk13uXHNu/\n" +
+            "   ZUZZNe8s+QtuLfUlKAJtLEUutN33TlWQY522FV0m17S+b80xJib3yZVJteVurrh5\n" +
+            "   HSWHAM+zghQAvCesg5CLXa2dNMkTCmZKgCBvfDLZuZbjFwnwCI6u/NhOY9egKuUf\n" +
+            "   SA/je/RXaT8m5VxLYMxwqQXKApzD87fv0tLPlVIEvjEsaf992tFEFSNPcG1l/jpd\n" +
+            "   5AVXw6kKuf85UkJtYR1x2MkQDrqY1QX/XMw00kt8y9kMZUre19aCArcmor+hDhRJ\n" +
+            "   E3Gt4QJrD9z/bICESw4b4z2DbgD/Xz9IXsA/r9cKiM1h5QMtXvuhyfVeM01enhxM\n" +
+            "   GbOH3gjqqGNKysx0UODGEwr6AV9hAd8RWXMchJLaExK9J5SRawSg671ObAU24SdY\n" +
+            "   vMQ9Z4kAQ2+1ReUZzf3ogSMRZtMT+d18gT6L90/y+APZIaoArLPhebIAGq39HLmJ\n" +
+            "   26x3z0WAgrpA1kNsjXEXkoiZGPLKIGoe3hqJAbYEGAEKACAWIQTRpm4aI7GCyZgP\n" +
+            "   eIz7/MgqAV5zMAUCXaWc8gIbDAAKCRD7/MgqAV5zMOn/C/9ugt+HZIwX308zI+QX\n" +
+            "   c5vDLReuzmJ3ieE0DMO/uNSC+K1XEioSIZP91HeZJ2kbT9nn9fuReuoff0T0Dief\n" +
+            "   rbwcIQQHFFkrqSp1K3VWmUGp2JrUsXFVdjy/fkBIjTd7c5boWljv/6wAsSfiv2V0\n" +
+            "   JSM8EFU6TYXxswGjFVfc6X97tJNeIrXL+mpSmPPqy2bztcCCHkWS5lNLWQw+R7Vg\n" +
+            "   71Fe6yBSNVrqC2/imYG2J9zlowjx1XU63Wdgqp2Wxt0l8OmsB/W80S1fRF5G4SDH\n" +
+            "   s9HXglXXqPsBRZJYfP+VStm9L5P/sKjCcX6WtZR7yS6G8zj/X767MLK/djANvpPd\n" +
+            "   NVniEke6hM3CNBXYPAMhQBMWhCulcoz+0lxi8L34rMN+Dsbma96psdUrn7uLaB91\n" +
+            "   6we0CTfF8qqm7BsVAgalon/UUiuMY80U3ueoj3okiSTiHIjD/YtpXSPioC8nMng7\n" +
+            "   xqAY9Bwizt4FWgXuLm1a4+So4V9j1TRCXd12Uc2l2RNmgDE=\n" +
+            "   =miES\n" +
+            "   -----END PGP PRIVATE KEY BLOCK-----";
+
+    private static PGPSecretKeyRing secretKeys;
+    static {
+        try {
+            secretKeys = PGPainless.readKeyRing().secretKeyRing(key);
+        } catch (IOException | PGPException e) {
+            fail("Secret key cannot be parsed.");
+        }
+    }
+
+    @Test
+    public void testIDEAAlgorithmIsRejected() {
+        // Encrypted using IDEA
+        String message = "-----BEGIN PGP MESSAGE-----\n" +
+                "Comment: Encrypted using GnuPG 1.4.23.\n" +
+                "\n" +
+                "hQGMA3wvqk35PDeyAQv/RXoqPXyIPEAgTj0GPNR/L3qs3kLP05QnpUvVryoKVLh9\n" +
+                "2XgI5quDsIN35X3eMh31UhYe3x6PuxGQYPJ08PbXPB4Ht3ExWxmvDTc1nWAoi9dH\n" +
+                "KBjHXofo2Fqo+TEF1raOr8zDnHlsds8CDgqKS2SIKN/MzPT8Gd+oFSnh/uOCdWUb\n" +
+                "R1T30p/65e30z93jcsVYB+u5mGAfOWVMNEKZEyfdotkO5F+d2R0JwM8CZHHct3Tz\n" +
+                "Zunbd/JPsdafdieLnE9XbyqbcEP+zD1NmaPUtuXUO/cCFfxKvNRv23T5WASgZ1/f\n" +
+                "Psk/ZQ1nL+21sX6CGds9L/Tp2G5qEyiQEdTc2YywslaSoFQ2ElbqUwhONY3rDU1w\n" +
+                "3sodf3AcXAdjDP9C45vrzQR8JTosorU1LiPtQFCr0JS2V6K9T9Jo/520Z6Z6tuqs\n" +
+                "2HlXRQp+uZ8+6mnIlGK3Wnr9j9twGTt2bUiHQRQPddYbk9dUrhbx4kedziHlhY5o\n" +
+                "J1VEHTQT5PJ5/sDkfbva0j4B3pzBIkFzG8TTQzV6ODfdgF5SyP7oHyBRrfJ4TG3g\n" +
+                "V07ytPWcdM3F8gvrvHIF63yctaDTeIL+izIKuGvxfQ==\n" +
+                "=w0KS\n" +
+                "-----END PGP MESSAGE-----\n";
+
+        assertThrows(UnacceptableAlgorithmException.class, () ->
+                PGPainless.decryptAndOrVerify().onInputStream(new ByteArrayInputStream(message.getBytes(StandardCharsets.UTF_8)))
+                        .decryptWith(SecretKeyRingProtector.unprotectedKeys(), secretKeys)
+                        .doNotVerify()
+                        .build());
+    }
+
+    @Test
+    public void testTripleDESIsRejected() {
+        // encrypted using TripleDES
+        String message = "-----BEGIN PGP ARMORED FILE-----\n" +
+                "Comment: ASCII Armor added by openpgp-interoperability-test-suite\n" +
+                "\n" +
+                "wcDMA3wvqk35PDeyAQv5AbewMcvRHUUxRiw7BJCrYy4CL9LDEoFWv4LXr5u0+TJ1\n" +
+                "3srTQOSO7FVUZ8ITpAM72M929qpRZa6Ia3vlhuRbU4ZHDbWdVDWM3vZwXyqwSCrU\n" +
+                "I8nVhImEmmRH9VT7Kk8FWl2HuDebRp5uEvDp2j2mFqQL5bw7P6WB0qJG3Q7pkbbq\n" +
+                "xdDH3BAQQH3drp1E5fAFtVWsi7KeCfc3IAsTYnotuy7xMmStlZw/UpJ2hM3/UFlO\n" +
+                "fN2tUmQT6aoSEbdFMQN5DA1R98ik2MNck6Nrt2ffk9VP4MTnSBfcgGUGKO/ot/gF\n" +
+                "0SO0yzzrAMIEn3fQuSUBMC/EJc5X5P+EYXzKUmFHajWMiaCB8K/0GvbIsQGg+pOq\n" +
+                "3BHskMaZxAVBWib9fiGe+hFB41MWEfuwHlgldpTsNQkACfyWjd1gevu2uythHSOt\n" +
+                "j5LwHqnWmSF0rqP89PS394TMdWEnHh09A1oDOqj2A+iXnyj0CekKnucRI7HVbwnN\n" +
+                "XtpKTkP7ernVrcl7EpVP0kMBoQA4TrgQARs97nF5fsigLFt1keqbDSOFsXonkWIg\n" +
+                "WLlG7ee7fRqQPTSP+OLh4Cm8zDIaCNowj0Ua4KwcWZDYERzg\n" +
+                "=j71X\n" +
+                "-----END PGP ARMORED FILE-----\n";
+        assertThrows(UnacceptableAlgorithmException.class, () ->
+                PGPainless.decryptAndOrVerify().onInputStream(new ByteArrayInputStream(message.getBytes(StandardCharsets.UTF_8)))
+                        .decryptWith(SecretKeyRingProtector.unprotectedKeys(), secretKeys)
+                        .doNotVerify()
+                        .build());
+    }
+
+    @Test
+    public void testUnencryptedIsRejected() {
+        // Armored, unencrypted message
+        String message = "-----BEGIN PGP ARMORED FILE-----\n" +
+                "Comment: ASCII Armor added by openpgp-interoperability-test-suite\n" +
+                "\n" +
+                "wcDMA3wvqk35PDeyAQv+IABXuLpmBViXGwaF7gFugOleb1Vj5Q7dWsSDBpB8NYA9\n" +
+                "hPMOfwnJ/XFdnvVGZMiH8mFgj6ZHA6S8mo3uS8/gqEcoyyI3RyvFynyyhk5pyiBl\n" +
+                "b7vA+SpPTTHgIdOsc1tA3gvSnicyIGO4bUDODbzkFyuc8BvE0IoKjr6fGWKYKUb1\n" +
+                "xnNeQOqDxQr19u119ac+HUY9AxrEpP7toBuJtF3hwTED5VglA4xWYehmOfeo3mT/\n" +
+                "atc5Hmkc01GOJb59DbySWiG7CRNYnFewWDfNfuOF+/+O1pC0r0lkxwIbQhRhUYh/\n" +
+                "gGo4TM7jbnHuXJZ/dei/FIVldkJLIR5wrMLw/sO1zvX7EPx2cIxjrvpsfrjm39Tm\n" +
+                "RtOhAsq+0jUB3MhDfBlFxyzmTeSAQuEJ2OnfJ2UdZ1XM/Y4NT4cNjMDu3/44rT1l\n" +
+                "OSfuSPnIrheGdtutAojPTtMJs7kZdXUv5E0zfw4Og7KkH3qsBlTro9Jrvut8LI5K\n" +
+                "5J/U4upauTBO4T9xejh/0iwByxNiAAAAAABOT1QgRU5DUllQVEVE0xQAAQIDBAUG\n" +
+                "BwgJAAECAwQFBgcICQ==\n" +
+                "=qNxx\n" +
+                "-----END PGP ARMORED FILE-----\n";
+
+        assertThrows(UnacceptableAlgorithmException.class, () ->
+                PGPainless.decryptAndOrVerify().onInputStream(new ByteArrayInputStream(message.getBytes(StandardCharsets.UTF_8)))
+                        .decryptWith(SecretKeyRingProtector.unprotectedKeys(), secretKeys)
+                        .doNotVerify()
+                        .build());
+    }
+
+    // Control: In contrast, AES256 is acceptable
+    @Test
+    public void testAES256IsAccepted() throws PGPException, IOException {
+        String message = "-----BEGIN PGP ARMORED FILE-----\n" +
+                "Comment: ASCII Armor added by openpgp-interoperability-test-suite\n" +
+                "\n" +
+                "wcDMA3wvqk35PDeyAQwAklBSfkiq1bdIAoT/CKoyHZcm8vIZ0bmoRio9ES1QDdFn\n" +
+                "ZRI4AhCUOSIyn/65aOe6Jole8HuXTxAOqyGxdfgoWOlfbQuuGnOBVus/jekesFfy\n" +
+                "kRZdzK+W/ID6HT6wOXTH+BdrvM4OmJ9ffi7RzdgEXFR+Ujq6670ivGDgvVv59zo7\n" +
+                "jLlzLuCBNuV6cveev2lX4VWrCf5TtikJA9YrY81SMDvui97X1zGO0hdT22LfO9P4\n" +
+                "3dgjs0bCrlvQYbkqkFPscJ073QBeKBKxRZN1kxZARRNXfR7y1rilVEsPm9zJ+/ut\n" +
+                "+Mn6ASWHMU9WgUYHxUqf4g6hIc2Kn2a0bjUevGxUCBTsB0p1joZiG7F3j1bSkS4R\n" +
+                "gTalxogmOjm3DmPsEx5gsHr48Iyweyotp8/zB3wSVh3EuyQ2AtEwqF+agDsyC0Uw\n" +
+                "RzxjlqrNLJ2lzCatbDBnWN/FUQR7BXrkjynFZDc4wXdHN/VdspVBs40xbSllHE1G\n" +
+                "Y4SilAYywXN/hTvCsUBo0kgBW6nOT4fW8Epx9RbKwgY7TFUF/zKOq5aBXvYavsHl\n" +
+                "4yjtOxfmmp9Fac50SS5i9dzBdnVNllLs+ADQt+LksJnzTW1IINGnIw8=\n" +
+                "=kLfl\n" +
+                "-----END PGP ARMORED FILE-----\n";
+
+        PGPainless.decryptAndOrVerify().onInputStream(new ByteArrayInputStream(message.getBytes(StandardCharsets.UTF_8)))
+                .decryptWith(SecretKeyRingProtector.unprotectedKeys(), secretKeys)
+                .doNotVerify()
+                .build();
+    }
+
+}