diff --git a/external-sop/src/main/java/sop/external/ExternalSOP.java b/external-sop/src/main/java/sop/external/ExternalSOP.java
index 432a16d..add37c5 100644
--- a/external-sop/src/main/java/sop/external/ExternalSOP.java
+++ b/external-sop/src/main/java/sop/external/ExternalSOP.java
@@ -179,14 +179,17 @@ public class ExternalSOP implements SOP {
      * @throws IOException in case of an IO error
      */
     private static void mapExitCodeOrException(@Nonnull Process process) throws InterruptedException, IOException {
+        // wait for process termination
         int exitCode = process.waitFor();
 
         if (exitCode == 0) {
+            // we're good, bye
             return;
         }
 
+        // Read error message
         InputStream errIn = process.getErrorStream();
-        String errorMessage = readFully(errIn);
+        String errorMessage = readString(errIn);
 
         switch (exitCode) {
             case SOPGPException.NoSignature.EXIT_CODE:
@@ -285,7 +288,7 @@ public class ExternalSOP implements SOP {
      * @return string
      * @throws IOException in case of an IO error
      */
-    public static String readFully(@Nonnull InputStream inputStream) throws IOException {
+    public static String readString(@Nonnull InputStream inputStream) throws IOException {
         ByteArrayOutputStream bOut = new ByteArrayOutputStream();
         byte[] buf = new byte[4096];
         int r;
@@ -297,13 +300,16 @@ public class ExternalSOP implements SOP {
 
     /**
      * Execute the given command on the given {@link Runtime} with the given list of environment variables.
+     * This command does not transform any input data, and instead is purely a producer.
      *
      * @param runtime runtime
      * @param commandList command
      * @param envList environment variables
      * @return ready to read the result from
      */
-    public static Ready ready(@Nonnull Runtime runtime, @Nonnull List<String> commandList, @Nonnull List<String> envList) {
+    public static Ready executeProducingOperation(@Nonnull Runtime runtime,
+                                                  @Nonnull List<String> commandList,
+                                                  @Nonnull List<String> envList) {
         String[] command = commandList.toArray(new String[0]);
         String[] env = envList.toArray(new String[0]);
 
@@ -322,6 +328,7 @@ public class ExternalSOP implements SOP {
 
                     outputStream.flush();
                     outputStream.close();
+
                     ExternalSOP.finish(process);
                 }
             };
@@ -333,6 +340,7 @@ public class ExternalSOP implements SOP {
     /**
      * Execute the given command on the given runtime using the given environment variables.
      * The given input stream provides input for the process.
+     * This command is a transformation, meaning it is given input data and transforms it into output data.
      *
      * @param runtime runtime
      * @param commandList command
@@ -340,7 +348,7 @@ public class ExternalSOP implements SOP {
      * @param standardIn stream of input data for the process
      * @return ready to read the result from
      */
-    public static Ready ready(@Nonnull Runtime runtime, @Nonnull List<String> commandList, @Nonnull List<String> envList, @Nonnull InputStream standardIn) {
+    public static Ready executeTransformingOperation(@Nonnull Runtime runtime, @Nonnull List<String> commandList, @Nonnull List<String> envList, @Nonnull InputStream standardIn) {
         String[] command = commandList.toArray(new String[0]);
         String[] env = envList.toArray(new String[0]);
         try {
@@ -362,7 +370,10 @@ public class ExternalSOP implements SOP {
                         processOut.flush();
                         processOut.close();
                     } catch (IOException e) {
-                        // ignore
+                        // Perhaps the stream is already closed, in which case we ignore the exception.
+                        if (!"Stream closed".equals(e.getMessage())) {
+                            throw e;
+                        }
                     }
 
                     while ((r = processIn.read(buf)) > 0) {
diff --git a/external-sop/src/main/java/sop/external/operation/ArmorExternal.java b/external-sop/src/main/java/sop/external/operation/ArmorExternal.java
index bf9ddcd..cb53573 100644
--- a/external-sop/src/main/java/sop/external/operation/ArmorExternal.java
+++ b/external-sop/src/main/java/sop/external/operation/ArmorExternal.java
@@ -38,6 +38,6 @@ public class ArmorExternal implements Armor {
 
     @Override
     public Ready data(InputStream data) throws SOPGPException.BadData, IOException {
-        return ExternalSOP.ready(Runtime.getRuntime(), commandList, envList, data);
+        return ExternalSOP.executeTransformingOperation(Runtime.getRuntime(), commandList, envList, data);
     }
 }
diff --git a/external-sop/src/main/java/sop/external/operation/DearmorExternal.java b/external-sop/src/main/java/sop/external/operation/DearmorExternal.java
index 2406131..7fa1fdc 100644
--- a/external-sop/src/main/java/sop/external/operation/DearmorExternal.java
+++ b/external-sop/src/main/java/sop/external/operation/DearmorExternal.java
@@ -31,6 +31,6 @@ public class DearmorExternal implements Dearmor {
 
     @Override
     public Ready data(InputStream data) throws SOPGPException.BadData, IOException {
-        return ExternalSOP.ready(Runtime.getRuntime(), commandList, envList, data);
+        return ExternalSOP.executeTransformingOperation(Runtime.getRuntime(), commandList, envList, data);
     }
 }
diff --git a/external-sop/src/main/java/sop/external/operation/DecryptExternal.java b/external-sop/src/main/java/sop/external/operation/DecryptExternal.java
index 84da064..0b91d5b 100644
--- a/external-sop/src/main/java/sop/external/operation/DecryptExternal.java
+++ b/external-sop/src/main/java/sop/external/operation/DecryptExternal.java
@@ -66,7 +66,7 @@ public class DecryptExternal implements Decrypt {
             throws SOPGPException.BadData, SOPGPException.UnsupportedAsymmetricAlgo, IOException {
         String envVar = "VERIFY_WITH_" + verifyWithCounter++;
         commandList.add("--verify-with=@ENV:" + envVar);
-        envList.add(envVar + "=" + ExternalSOP.readFully(cert));
+        envList.add(envVar + "=" + ExternalSOP.readString(cert));
         return this;
     }
 
@@ -93,7 +93,7 @@ public class DecryptExternal implements Decrypt {
             throws SOPGPException.BadData, SOPGPException.UnsupportedAsymmetricAlgo, IOException {
         String envVar = "KEY_" + keyCounter++;
         commandList.add("@ENV:" + envVar);
-        envList.add(envVar + "=" + ExternalSOP.readFully(key));
+        envList.add(envVar + "=" + ExternalSOP.readString(key));
         return this;
     }
 
@@ -151,7 +151,7 @@ public class DecryptExternal implements Decrypt {
                     ExternalSOP.finish(process);
 
                     FileInputStream sessionKeyOutIn = new FileInputStream(sessionKeyOut);
-                    String line = ExternalSOP.readFully(sessionKeyOutIn);
+                    String line = ExternalSOP.readString(sessionKeyOutIn);
                     SessionKey sessionKey = SessionKey.fromString(line.trim());
                     sessionKeyOutIn.close();
                     sessionKeyOut.delete();
diff --git a/external-sop/src/main/java/sop/external/operation/DetachedSignExternal.java b/external-sop/src/main/java/sop/external/operation/DetachedSignExternal.java
index 1f9aa81..3e369f1 100644
--- a/external-sop/src/main/java/sop/external/operation/DetachedSignExternal.java
+++ b/external-sop/src/main/java/sop/external/operation/DetachedSignExternal.java
@@ -52,7 +52,7 @@ public class DetachedSignExternal implements DetachedSign {
     public DetachedSign key(InputStream key) throws SOPGPException.KeyCannotSign, SOPGPException.BadData, SOPGPException.UnsupportedAsymmetricAlgo, IOException {
         String envVar = "KEY_" + keyCounter++;
         commandList.add("@ENV:" + envVar);
-        envList.add(envVar + "=" + ExternalSOP.readFully(key));
+        envList.add(envVar + "=" + ExternalSOP.readString(key));
         return this;
     }
 
diff --git a/external-sop/src/main/java/sop/external/operation/DetachedVerifyExternal.java b/external-sop/src/main/java/sop/external/operation/DetachedVerifyExternal.java
index ed658c7..05318d4 100644
--- a/external-sop/src/main/java/sop/external/operation/DetachedVerifyExternal.java
+++ b/external-sop/src/main/java/sop/external/operation/DetachedVerifyExternal.java
@@ -68,12 +68,12 @@ public class DetachedVerifyExternal implements DetachedVerify {
     @Override
     public List<Verification> data(InputStream data) throws IOException, SOPGPException.NoSignature, SOPGPException.BadData {
         commandList.add("@ENV:SIGNATURE");
-        envList.add("SIGNATURE=" + ExternalSOP.readFully(signatures));
+        envList.add("SIGNATURE=" + ExternalSOP.readString(signatures));
 
         for (InputStream cert : certs) {
             String envVar = "CERT_" + certCounter++;
             commandList.add("@ENV:" + envVar);
-            envList.add(envVar + "=" + ExternalSOP.readFully(cert));
+            envList.add(envVar + "=" + ExternalSOP.readString(cert));
         }
 
         String[] command = commandList.toArray(new String[0]);
diff --git a/external-sop/src/main/java/sop/external/operation/EncryptExternal.java b/external-sop/src/main/java/sop/external/operation/EncryptExternal.java
index f45cd12..ca8ddf1 100644
--- a/external-sop/src/main/java/sop/external/operation/EncryptExternal.java
+++ b/external-sop/src/main/java/sop/external/operation/EncryptExternal.java
@@ -53,7 +53,7 @@ public class EncryptExternal implements Encrypt {
             IOException {
         String envVar = "SIGN_WITH_" + SIGN_WITH_COUNTER++;
         commandList.add("--sign-with=@ENV:" + envVar);
-        envList.add(envVar + "=" + ExternalSOP.readFully(key));
+        envList.add(envVar + "=" + ExternalSOP.readString(key));
         return this;
     }
 
@@ -81,13 +81,13 @@ public class EncryptExternal implements Encrypt {
             IOException {
         String envVar = "CERT_" + CERT_COUNTER++;
         commandList.add("@ENV:" + envVar);
-        envList.add(envVar + "=" + ExternalSOP.readFully(cert));
+        envList.add(envVar + "=" + ExternalSOP.readString(cert));
         return this;
     }
 
     @Override
     public Ready plaintext(InputStream plaintext)
             throws IOException, SOPGPException.KeyIsProtected {
-        return ExternalSOP.ready(Runtime.getRuntime(), commandList, envList, plaintext);
+        return ExternalSOP.executeTransformingOperation(Runtime.getRuntime(), commandList, envList, plaintext);
     }
 }
diff --git a/external-sop/src/main/java/sop/external/operation/ExtractCertExternal.java b/external-sop/src/main/java/sop/external/operation/ExtractCertExternal.java
index 549b1ad..5fdcdc1 100644
--- a/external-sop/src/main/java/sop/external/operation/ExtractCertExternal.java
+++ b/external-sop/src/main/java/sop/external/operation/ExtractCertExternal.java
@@ -36,6 +36,6 @@ public class ExtractCertExternal implements ExtractCert {
 
     @Override
     public Ready key(InputStream keyInputStream) throws SOPGPException.BadData {
-        return ExternalSOP.ready(Runtime.getRuntime(), commandList, envList, keyInputStream);
+        return ExternalSOP.executeTransformingOperation(Runtime.getRuntime(), commandList, envList, keyInputStream);
     }
 }
diff --git a/external-sop/src/main/java/sop/external/operation/GenerateKeyExternal.java b/external-sop/src/main/java/sop/external/operation/GenerateKeyExternal.java
index d125fc0..95e86b8 100644
--- a/external-sop/src/main/java/sop/external/operation/GenerateKeyExternal.java
+++ b/external-sop/src/main/java/sop/external/operation/GenerateKeyExternal.java
@@ -54,6 +54,6 @@ public class GenerateKeyExternal implements GenerateKey {
     @Override
     public Ready generate()
             throws SOPGPException.MissingArg, SOPGPException.UnsupportedAsymmetricAlgo {
-        return ExternalSOP.ready(Runtime.getRuntime(), commandList, envList);
+        return ExternalSOP.executeProducingOperation(Runtime.getRuntime(), commandList, envList);
     }
 }
diff --git a/external-sop/src/main/java/sop/external/operation/InlineSignExternal.java b/external-sop/src/main/java/sop/external/operation/InlineSignExternal.java
index 17e5b12..d78dd7b 100644
--- a/external-sop/src/main/java/sop/external/operation/InlineSignExternal.java
+++ b/external-sop/src/main/java/sop/external/operation/InlineSignExternal.java
@@ -43,7 +43,7 @@ public class InlineSignExternal implements InlineSign {
     public InlineSign key(InputStream key) throws SOPGPException.KeyCannotSign, SOPGPException.BadData, SOPGPException.UnsupportedAsymmetricAlgo, IOException {
         String envVar = "KEY_" + keyCounter++;
         commandList.add("@ENV:" + envVar);
-        envList.add(envVar + "=" + ExternalSOP.readFully(key));
+        envList.add(envVar + "=" + ExternalSOP.readString(key));
         return this;
     }
 
@@ -63,6 +63,6 @@ public class InlineSignExternal implements InlineSign {
 
     @Override
     public Ready data(InputStream data) throws IOException, SOPGPException.KeyIsProtected, SOPGPException.ExpectedText {
-        return ExternalSOP.ready(Runtime.getRuntime(), commandList, envList, data);
+        return ExternalSOP.executeTransformingOperation(Runtime.getRuntime(), commandList, envList, data);
     }
 }
diff --git a/external-sop/src/main/java/sop/external/operation/InlineVerifyExternal.java b/external-sop/src/main/java/sop/external/operation/InlineVerifyExternal.java
index 5fbdde6..8010367 100644
--- a/external-sop/src/main/java/sop/external/operation/InlineVerifyExternal.java
+++ b/external-sop/src/main/java/sop/external/operation/InlineVerifyExternal.java
@@ -57,7 +57,7 @@ public class InlineVerifyExternal implements InlineVerify {
     public InlineVerify cert(InputStream cert) throws SOPGPException.BadData, IOException {
         String envVar = "CERT_" + certCounter++;
         commandList.add("@ENV:" + envVar);
-        envList.add(envVar + "=" + ExternalSOP.readFully(cert));
+        envList.add(envVar + "=" + ExternalSOP.readString(cert));
         return this;
     }
 
diff --git a/external-sop/src/test/java/sop/external/ExternalDetachedSignVerifyRoundTripTest.java b/external-sop/src/test/java/sop/external/ExternalDetachedSignVerifyRoundTripTest.java
index cf04bd5..aaebe39 100644
--- a/external-sop/src/test/java/sop/external/ExternalDetachedSignVerifyRoundTripTest.java
+++ b/external-sop/src/test/java/sop/external/ExternalDetachedSignVerifyRoundTripTest.java
@@ -230,6 +230,7 @@ public class ExternalDetachedSignVerifyRoundTripTest extends AbstractExternalSOP
 
     @Test
     public void verifyMissingCertCausesMissingArg() {
+        ignoreIf("sqop", Is.leq, "0.27.3");
         ignoreIf("PGPainless-SOP", Is.geq, "0.0.0"); // PGPainless uses picocli which throws
         // UNSUPPORTED_OPTION for missing arg
         byte[] message = TestData.PLAINTEXT.getBytes(StandardCharsets.UTF_8);
diff --git a/external-sop/src/test/java/sop/external/ExternalEncryptDecryptRoundTripTest.java b/external-sop/src/test/java/sop/external/ExternalEncryptDecryptRoundTripTest.java
index 3011a03..2d6077e 100644
--- a/external-sop/src/test/java/sop/external/ExternalEncryptDecryptRoundTripTest.java
+++ b/external-sop/src/test/java/sop/external/ExternalEncryptDecryptRoundTripTest.java
@@ -281,6 +281,7 @@ public class ExternalEncryptDecryptRoundTripTest extends AbstractExternalSOPTest
 
     @Test
     public void missingArgsTest() throws IOException {
+        ignoreIf("sqop", Is.leq, "0.27.3");
         byte[] message = TestData.PLAINTEXT.getBytes(StandardCharsets.UTF_8);
 
         assertThrows(SOPGPException.MissingArg.class, () -> getSop().encrypt()