diff --git a/pgpainless-core/src/test/java/org/pgpainless/signature/SignatureUtilsTest.java b/pgpainless-core/src/test/java/org/pgpainless/signature/SignatureUtilsTest.java
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+++ b/pgpainless-core/src/test/java/org/pgpainless/signature/SignatureUtilsTest.java
@@ -0,0 +1,100 @@
+/*
+ * 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.signature;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import java.io.IOException;
+import java.util.List;
+
+import org.bouncycastle.openpgp.PGPException;
+import org.bouncycastle.openpgp.PGPSignature;
+import org.junit.jupiter.api.Test;
+import org.pgpainless.key.util.KeyIdUtil;
+
+public class SignatureUtilsTest {
+
+    @Test
+    public void readSignaturesFromCompressedData() throws PGPException, IOException {
+        String compressed = "-----BEGIN PGP MESSAGE-----\n" +
+                "Version: PGPainless\n" +
+                "\n" +
+                "owHrKGVhEOZiYGNlSoxcsJtBkVMg3OzZZKnz5jxiiiz+aTG+h46kcR9zinOECZ/o\n" +
+                "YmTYsKve/opb3v/o8J0qq1/MFFBhP9jfEq+/avK6qPMrlh70Zfinu96c+cncX9GK\n" +
+                "B4ui3fUfbUo8tFrVTIRn7kROq69H77hd6cCw9susVdls1as1gNYunnp5V8Qp+wX3\n" +
+                "+jUnwoRB1p4SfPk412lb/cSmShb211fOX07h0JxVH1JXsc/vi2mi5ieG/2Xxb5tk\n" +
+                "LE+r7WwruxSaeXLuLsOmXTPZD0/VtvlqO89RYjsA\n" +
+                "=yZ18\n" +
+                "-----END PGP MESSAGE-----";
+        List<PGPSignature> signatures = SignatureUtils.readSignatures(compressed);
+        assertEquals(2, signatures.size());
+        assertEquals(KeyIdUtil.fromLongKeyId("5736E6931ACF370C"), signatures.get(0).getKeyID());
+        assertEquals(KeyIdUtil.fromLongKeyId("F49AAA6B067BAB28"), signatures.get(1).getKeyID());
+    }
+
+    @Test
+    public void noIssuerResultsInKeyId0() throws PGPException, IOException {
+        String sig = "-----BEGIN PGP SIGNATURE-----\n" +
+                "\n" +
+                "wsEaBAABCABOBYJhVBVcRxQAAAAAAB4AIHNhbHRAbm90YXRpb25zLnNlcXVvaWEt\n" +
+                "cGdwLm9yZ+goUZDURlALH597rQCp41yYHOF90OfPRrp6TSZAA/nQAAAeOQwAni7j\n" +
+                "R4YEXpcDfqwjOPIvq5i7VWBR5EdESvR1fJHD99y4TyllezSpQcmZSGrkIcFRgTxR\n" +
+                "CwJ6oOsY4QILFF5N330Bs7HQfTbdgpx29ELo+8PuizRvhRVlQack/GPoRON/QQDz\n" +
+                "EBjZwiiPHgyw3CeQahHqSPgUT5JvW5yOOs31AhDlgen0qRHKtRwaI+5M5Y9nHR6z\n" +
+                "H2o5xapE4Vz647sPkl269Sd4kl/qkInoyKf1x1U6bu6g9Onr1fafM1HLiGkJl0Sk\n" +
+                "YNHCHdnBbyZBJt3ijCokOAGe7DIHvz5rv9iO/WDdC5Tw9XJlrFTI4xAv0EXJCSZm\n" +
+                "9eVJbaOEmnjqwaZNf4tS+j6+Blp/1p0YMd/10Fh6cmLYyM2mDBB60pE/Y3ARS1lP\n" +
+                "fta43BXTAWu6h+ZT2gncbBv+yAxmMEMY2iBk11dCLrSFWGEcitrOigCLMrPdCKCl\n" +
+                "7zv9ar9WsNOibOEaso+MF7oAw+97o1nRXPHg/5FzcmosqKU3VJZU8QZfETO7\n" +
+                "=YWPw\n" +
+                "-----END PGP SIGNATURE-----";
+        PGPSignature signature = SignatureUtils.readSignatures(sig).get(0);
+        assertEquals(0, SignatureUtils.determineIssuerKeyId(signature));
+    }
+
+    @Test
+    public void skipInvalidSignatures() throws PGPException, IOException {
+        // Sig version 23 (invalid), sig version 4
+        String sigs = "-----BEGIN PGP SIGNATURE-----\n" +
+                "\n" +
+                "wsE7FwABCgBvBYJhVBVECRD7/MgqAV5zMEcUAAAAAAAeACBzYWx0QG5vdGF0aW9u\n" +
+                "cy5zZXF1b2lhLXBncC5vcmfYpOWFSlKZpeZQTVMyX5UaWW+12r4Xb0EAFS4gOWJ/\n" +
+                "mhYhBNGmbhojsYLJmA94jPv8yCoBXnMwAABpyQwAorVkBMS2DTb5rYFPjWjoIo1A\n" +
+                "3SiYkgPzddqc8ZvTu3zlEXpoGzKQLrXW3AGCuXCeEst+kPV6j33zZiPFSdcn0Ddg\n" +
+                "QUWlxhmsVJ/ePujwfVyPLJISE/g1486qMERSnOKKyL7u62uwCggRzZMYKOC12PFO\n" +
+                "+9OsISkPs+BqsV7jd6L2NJCBZ0VFCP2kE4vMty0VltIa3nfr1PgWPH3ekBPt3a0p\n" +
+                "OF/aSckV0gy4t7JqT9nxU5oWwxef1TQuQ8yh96gBSFUcS58ov+tBuMIjphpKexxU\n" +
+                "HlOTDVRG8+qUiScGFrc1aavepd9x60aHLBSwyGt4/ZhPvRp3fljyGqSapSUmCeFJ\n" +
+                "FN+p7Ne35GO/lrr6Aao3HH1xVGF4+Jn7N8CgN/dsKWa+gSrnKZbYo0Sa7hx6yRtm\n" +
+                "a45VSoRmjEjP+cL+lvDBTqvv3anufZ5OCIzt2sUFJfWF6bOPjc+1X294qYNpVX6j\n" +
+                "xFWiAQt5XvispaNnuHE5tnlI7pLJ66zCU/Kl4WgywsE7BAABCgBvBYJhVBVECRD7\n" +
+                "/MgqAV5zMEcUAAAAAAAeACBzYWx0QG5vdGF0aW9ucy5zZXF1b2lhLXBncC5vcmfY\n" +
+                "pOWFSlKZpeZQTVMyX5UaWW+12r4Xb0EAFS4gOWJ/mhYhBNGmbhojsYLJmA94jPv8\n" +
+                "yCoBXnMwAABpyQwAorVkBMS2DTb5rYFPjWjoIo1A3SiYkgPzddqc8ZvTu3zlEXpo\n" +
+                "GzKQLrXW3AGCuXCeEst+kPV6j33zZiPFSdcn0DdgQUWlxhmsVJ/ePujwfVyPLJIS\n" +
+                "E/g1486qMERSnOKKyL7u62uwCggRzZMYKOC12PFO+9OsISkPs+BqsV7jd6L2NJCB\n" +
+                "Z0VFCP2kE4vMty0VltIa3nfr1PgWPH3ekBPt3a0pOF/aSckV0gy4t7JqT9nxU5oW\n" +
+                "wxef1TQuQ8yh96gBSFUcS58ov+tBuMIjphpKexxUHlOTDVRG8+qUiScGFrc1aave\n" +
+                "pd9x60aHLBSwyGt4/ZhPvRp3fljyGqSapSUmCeFJFN+p7Ne35GO/lrr6Aao3HH1x\n" +
+                "VGF4+Jn7N8CgN/dsKWa+gSrnKZbYo0Sa7hx6yRtma45VSoRmjEjP+cL+lvDBTqvv\n" +
+                "3anufZ5OCIzt2sUFJfWF6bOPjc+1X294qYNpVX6jxFWiAQt5XvispaNnuHE5tnlI\n" +
+                "7pLJ66zCU/Kl4Wgy\n" +
+                "=fvS+\n" +
+                "-----END PGP SIGNATURE-----\n";
+        List<PGPSignature> signatures = SignatureUtils.readSignatures(sigs);
+        assertEquals(1, signatures.size()); // first sig gets skipped
+    }
+}