Use prepend to replace concatenate for getting session data

Author: gefeili

pg/src/main/java/org/bouncycastle/openpgp/operator/bc/BcPublicKeyDataDecryptorFactory.java

@@ -244,7 +244,7 @@ private byte[] getSessionData(byte[] enc, AsymmetricKeyParameter privKey, int pL
         KeyParameter key = new KeyParameter(RFC6637KDFCalculator.createKey(hashAlgorithm, symmetricKeyAlgorithm,
             Arrays.concatenate(pEnc, pgpPrivKey.getPublicKeyPacket().getKey().getEncoded(), secret), "OpenPGP " + algorithmName));
 
-        return Arrays.concatenate(new byte[]{enc[pLen + 1]}, unwrapSessionData(keyEnc, symmetricKeyAlgorithm, key));
+        return Arrays.prepend(unwrapSessionData(keyEnc, symmetricKeyAlgorithm, key), enc[pLen + 1]);
     }
 
     private static byte[] unwrapSessionData(byte[] keyEnc, int symmetricKeyAlgorithm, KeyParameter key)

pg/src/main/java/org/bouncycastle/openpgp/operator/jcajce/JcePublicKeyDataDecryptorFactoryBuilder.java

@@ -305,7 +305,7 @@ private byte[] decryptSessionData(JcaPGPKeyConverter converter, PGPPrivateKey pr
             Key paddedSessionKey = getSessionKey(converter, privKey, agreementAlgorithm, publicKey, symmetricKeyAlgorithm, keyEnc,
                 JcaJcePGPUtil.getHybridValueParameterSpecWithPrepend(pEnc, privKey.getPublicKeyPacket(), algorithmName));
             symmetricKeyAlgorithm = enc[pLen + 1] & 0xff;
-            return Arrays.concatenate(new byte[]{(byte)symmetricKeyAlgorithm}, paddedSessionKey.getEncoded());
+            return Arrays.prepend(paddedSessionKey.getEncoded(), (byte)symmetricKeyAlgorithm);
         }
         catch (Exception e)
         {