Start adding support for preferred AEAD algorithms

pgpainless-core/src/main/java/org/pgpainless/algorithm/AEADAlgorithm.java

@@ -0,0 +1,57 @@
+// SPDX-FileCopyrightText: 2022 Paul Schaub <vanitasvitae@fsfe.org>
+//
+// SPDX-License-Identifier: Apache-2.0
+
+package org.pgpainless.algorithm;
+
+import javax.annotation.Nonnull;
+import javax.annotation.Nullable;
+import java.util.HashMap;
+import java.util.Map;
+import java.util.NoSuchElementException;
+
+public enum AEADAlgorithm {
+
+    EAX(1, 16, 16),
+    OCB(2, 15, 16),
+    GCM(3, 12, 16),
+    ;
+
+    private static final Map<Integer, AEADAlgorithm> MAP = new HashMap<>();
+
+    private final int id;
+    private final int ivLen;
+    private final int tagLen;
+
+    AEADAlgorithm(int id, int ivLen, int tagLen) {
+        this.id = id;
+        this.ivLen = ivLen;
+        this.tagLen = tagLen;
+    }
+
+    @Nullable
+    public static AEADAlgorithm fromId(int algorithmId) {
+        return MAP.get(algorithmId);
+    }
+
+    @Nonnull
+    public static AEADAlgorithm requireFromId(int algorithmId) {
+        AEADAlgorithm algorithm = fromId(algorithmId);
+        if (algorithm == null) {
+            throw new NoSuchElementException("No AEAD Algorithm found for id " + algorithmId);
+        }
+        return algorithm;
+    }
+
+    public int getAlgorithmId() {
+        return id;
+    }
+
+    public int getIvLength() {
+        return ivLen;
+    }
+
+    public int getTagLength() {
+        return tagLen;
+    }
+}

pgpainless-core/src/main/java/org/pgpainless/algorithm/AEADCipherSuitePair.java

@@ -0,0 +1,56 @@
+// SPDX-FileCopyrightText: 2022 Paul Schaub <vanitasvitae@fsfe.org>
+//
+// SPDX-License-Identifier: Apache-2.0
+
+package org.pgpainless.algorithm;
+
+import javax.annotation.Nonnull;
+
+public class AEADCipherSuitePair {
+
+    private final AEADAlgorithm aeadAlgorithm;
+    private final SymmetricKeyAlgorithm symmetricKeyAlgorithm;
+
+    public AEADCipherSuitePair(@Nonnull SymmetricKeyAlgorithm symmetric, @Nonnull AEADAlgorithm aead) {
+        this.symmetricKeyAlgorithm = symmetric;
+        this.aeadAlgorithm = aead;
+    }
+
+    public SymmetricKeyAlgorithm getSymmetricKeyAlgorithm() {
+        return symmetricKeyAlgorithm;
+    }
+
+    public AEADAlgorithm getAeadAlgorithm() {
+        return aeadAlgorithm;
+    }
+
+    /**
+     * Mandatory-to-implement combination of AES-128 and OCB
+     *
+     * @return algorithm pair for AES-128 and OCB
+     */
+    public static AEADCipherSuitePair aes128WithOcb() {
+        return new AEADCipherSuitePair(SymmetricKeyAlgorithm.AES_128, AEADAlgorithm.OCB);
+    }
+
+    @Override
+    public int hashCode() {
+        return symmetricKeyAlgorithm.hashCode() * 31 + aeadAlgorithm.hashCode();
+    }
+
+    @Override
+    public boolean equals(Object obj) {
+        if (obj == null) {
+            return false;
+        }
+        if (this == obj) {
+            return true;
+        }
+        if (!(obj instanceof AEADCipherSuitePair)) {
+            return false;
+        }
+        AEADCipherSuitePair other = (AEADCipherSuitePair) obj;
+        return getAeadAlgorithm() == other.getAeadAlgorithm()
+                && getSymmetricKeyAlgorithm() == other.getSymmetricKeyAlgorithm();
+    }
+}