diff --git a/java/android/OlmLibSdk/olm-sdk/src/main/java/org/matrix/olm/OlmAccount.java b/java/android/OlmLibSdk/olm-sdk/src/main/java/org/matrix/olm/OlmAccount.java
index 5c1ad3c..1e41fa1 100644
--- a/java/android/OlmLibSdk/olm-sdk/src/main/java/org/matrix/olm/OlmAccount.java
+++ b/java/android/OlmLibSdk/olm-sdk/src/main/java/org/matrix/olm/OlmAccount.java
@@ -118,7 +118,7 @@ public class OlmAccount extends CommonSerializeUtils implements Serializable {
         } else {
             aErrorMsg.setLength(0);
             try {
-                pickleRetValue = serializeDataWithKeyJni(aKey.getBytes("UTF-8"), aErrorMsg);
+                pickleRetValue = new String(serializeDataWithKeyJni(aKey.getBytes("UTF-8"), aErrorMsg), "UTF-8");
             } catch (Exception e) {
                 Log.e(LOG_TAG, "## serializeDataWithKey() failed " + e.getMessage());
                 aErrorMsg.append(e.getMessage());
@@ -127,7 +127,7 @@ public class OlmAccount extends CommonSerializeUtils implements Serializable {
 
         return pickleRetValue;
     }
-    private native String serializeDataWithKeyJni(byte[] aKey, StringBuffer aErrorMsg);
+    private native byte[] serializeDataWithKeyJni(byte[] aKey, StringBuffer aErrorMsg);
 
 
     /**
@@ -164,6 +164,7 @@ public class OlmAccount extends CommonSerializeUtils implements Serializable {
 
         return retCode;
     }
+    
     private native String initWithSerializedDataJni(byte[] aSerializedDataBuffer, byte[] aKeyBuffer);
 
     /**
@@ -363,25 +364,34 @@ public class OlmAccount extends CommonSerializeUtils implements Serializable {
      * @return the signed message if operation succeed, null otherwise
      */
     public String signMessage(String aMessage) {
-        if (null == aMessage) {
-            return null;
+        String result = null;
+
+        if (null != aMessage) {
+            byte[] utf8String = null;
+
+            try {
+                utf8String = aMessage.getBytes("UTF-8");
+            } catch (Exception e) {
+                Log.e(LOG_TAG, "## signMessage(): failed =" + e.getMessage());
+            }
+
+            if (null != utf8String) {
+                byte[] signedMessage = signMessageJni(utf8String);
+
+                if (null != signedMessage) {
+                    try {
+                        result = new String(signedMessage, "UTF-8");
+                    } catch (Exception e) {
+                        Log.e(LOG_TAG, "## signMessage(): failed =" + e.getMessage());
+                    }
+                }
+            }
         }
 
-        byte[] utf8String = null;
-
-        try {
-            utf8String = aMessage.getBytes("UTF-8");
-        } catch (Exception e) {
-            Log.d(LOG_TAG,"## signMessage(): failed ="+e.getMessage());
-        }
-
-        if (null == utf8String) {
-            return null;
-        }
-
-        return signMessageJni(utf8String);
+        return result;
     }
-    private native String signMessageJni(byte[] aMessage);
+
+    private native byte[] signMessageJni(byte[] aMessage);
 
     /**
      * Return true the object resources have been released.<br>
diff --git a/java/android/OlmLibSdk/olm-sdk/src/main/java/org/matrix/olm/OlmInboundGroupSession.java b/java/android/OlmLibSdk/olm-sdk/src/main/java/org/matrix/olm/OlmInboundGroupSession.java
index 7ec5b2f..bfd50fb 100644
--- a/java/android/OlmLibSdk/olm-sdk/src/main/java/org/matrix/olm/OlmInboundGroupSession.java
+++ b/java/android/OlmLibSdk/olm-sdk/src/main/java/org/matrix/olm/OlmInboundGroupSession.java
@@ -144,10 +144,16 @@ public class OlmInboundGroupSession extends CommonSerializeUtils implements Seri
      * @return the session ID if operation succeed, null otherwise
      */
     public String sessionIdentifier() {
-        return sessionIdentifierJni();
-    }
-    private native String sessionIdentifierJni();
+        try {
+            return new String(sessionIdentifierJni(), "UTF-8");
+        } catch (Exception e) {
+            Log.e(LOG_TAG, "## sessionIdentifier() failed " + e.getMessage());
+        }
 
+        return null;
+    }
+
+    private native byte[] sessionIdentifierJni();
 
     /**
      * Decrypt the message passed in parameter.<br>
@@ -161,9 +167,14 @@ public class OlmInboundGroupSession extends CommonSerializeUtils implements Seri
 
         StringBuffer errorMsg = new StringBuffer();
         try {
-            result.mDecryptedMessage = decryptMessageJni(aEncryptedMsg.getBytes("UTF-8"), result, errorMsg);
+            byte[] decryptedMessageBuffer = decryptMessageJni(aEncryptedMsg.getBytes("UTF-8"), result, errorMsg);
+
+            if (null != decryptedMessageBuffer) {
+                result.mDecryptedMessage = new String(decryptedMessageBuffer, "UTF-8");
+            }
         } catch (Exception e) {
             Log.e(LOG_TAG, "## decryptMessage() failed " + e.getMessage());
+            errorMsg.append(e.getMessage());
         }
 
         // check if there is an error while decrypting
@@ -174,7 +185,7 @@ public class OlmInboundGroupSession extends CommonSerializeUtils implements Seri
         return result;
     }
 
-    private native String decryptMessageJni(byte[] aEncryptedMsg, DecryptMessageResult aDecryptMessageResult, StringBuffer aErrorMsg);
+    private native byte[] decryptMessageJni(byte[] aEncryptedMsg, DecryptMessageResult aDecryptMessageResult, StringBuffer aErrorMsg);
 
     /**
      * Kick off the serialization mechanism.
@@ -226,9 +237,10 @@ public class OlmInboundGroupSession extends CommonSerializeUtils implements Seri
         } else {
             aErrorMsg.setLength(0);
             try {
-                pickleRetValue = serializeDataWithKeyJni(aKey.getBytes("UTF-8"), aErrorMsg);
+                pickleRetValue = new String(serializeDataWithKeyJni(aKey.getBytes("UTF-8"), aErrorMsg), "UTF-8");
             } catch (Exception e) {
                 Log.e(LOG_TAG, "## serializeDataWithKey() failed " + e.getMessage());
+                aErrorMsg.append(e.getMessage());
             }
         }
 
@@ -240,7 +252,7 @@ public class OlmInboundGroupSession extends CommonSerializeUtils implements Seri
      * @param aErrorMsg error message description
      * @return pickled base64 string if operation succeed, null otherwise
      */
-    private native String serializeDataWithKeyJni(byte[] aKey, StringBuffer aErrorMsg);
+    private native byte[] serializeDataWithKeyJni(byte[] aKey, StringBuffer aErrorMsg);
 
 
     /**
diff --git a/java/android/OlmLibSdk/olm-sdk/src/main/java/org/matrix/olm/OlmOutboundGroupSession.java b/java/android/OlmLibSdk/olm-sdk/src/main/java/org/matrix/olm/OlmOutboundGroupSession.java
index bfb2cd1..171891c 100644
--- a/java/android/OlmLibSdk/olm-sdk/src/main/java/org/matrix/olm/OlmOutboundGroupSession.java
+++ b/java/android/OlmLibSdk/olm-sdk/src/main/java/org/matrix/olm/OlmOutboundGroupSession.java
@@ -208,10 +208,16 @@ public class OlmOutboundGroupSession extends CommonSerializeUtils implements Ser
      * @return session identifier if operation succeed, null otherwise.
      */
     public String sessionIdentifier() {
-        return sessionIdentifierJni();
+        try {
+            return new String(sessionIdentifierJni(), "UTF-8");
+        } catch (Exception e) {
+            Log.e(LOG_TAG, "## sessionIdentifier() failed " + e.getMessage());
+        }
+
+        return null;
     }
 
-    private native String sessionIdentifierJni();
+    private native byte[] sessionIdentifierJni();
 
     /**
      * Get the current message index for this session.<br>
@@ -231,9 +237,16 @@ public class OlmOutboundGroupSession extends CommonSerializeUtils implements Ser
      * @return outbound session key
      */
     public String sessionKey() {
-        return sessionKeyJni();
+        try {
+            return new String(sessionKeyJni(), "UTF-8");
+        } catch (Exception e) {
+            Log.e(LOG_TAG, "## sessionKey() failed " + e.getMessage());
+        }
+
+        return null;
     }
-    private native String sessionKeyJni();
+
+    private native byte[] sessionKeyJni();
 
     /**
      * Encrypt some plain-text message.<br>
@@ -246,7 +259,7 @@ public class OlmOutboundGroupSession extends CommonSerializeUtils implements Ser
 
         if(!TextUtils.isEmpty(aClearMsg)) {
             try {
-                retValue = encryptMessageJni(aClearMsg.getBytes("UTF-8"));
+                retValue = new String(encryptMessageJni(aClearMsg.getBytes("UTF-8")), "UTF-8");
             } catch (Exception e) {
                 Log.e(LOG_TAG, "## encryptMessage() failed " + e.getMessage());
             }
@@ -254,7 +267,7 @@ public class OlmOutboundGroupSession extends CommonSerializeUtils implements Ser
 
         return retValue;
     }
-    private native String encryptMessageJni(byte[] aClearMsgBuffer);
+    private native byte[] encryptMessageJni(byte[] aClearMsgBuffer);
 
     /**
      * Return true the object resources have been released.<br>
diff --git a/java/android/OlmLibSdk/olm-sdk/src/main/java/org/matrix/olm/OlmSession.java b/java/android/OlmLibSdk/olm-sdk/src/main/java/org/matrix/olm/OlmSession.java
index 7b9b736..a58036f 100644
--- a/java/android/OlmLibSdk/olm-sdk/src/main/java/org/matrix/olm/OlmSession.java
+++ b/java/android/OlmLibSdk/olm-sdk/src/main/java/org/matrix/olm/OlmSession.java
@@ -302,10 +302,16 @@ public class OlmSession extends CommonSerializeUtils implements Serializable {
      * @return the session ID as a String if operation succeed, null otherwise
      */
     public String sessionIdentifier() {
-        return getSessionIdentifierJni();
+        try {
+            return new String(getSessionIdentifierJni(), "UTF-8");
+        } catch (Exception e) {
+            Log.e(LOG_TAG, "## sessionIdentifier(): " + e.getMessage());
+        }
+
+        return null;
     }
 
-    private native String getSessionIdentifierJni();
+    private native byte[] getSessionIdentifierJni();
 
     /**
      * Checks if the PRE_KEY({@link OlmMessage#MESSAGE_TYPE_PRE_KEY}) message is for this in-bound session.<br>
@@ -383,10 +389,16 @@ public class OlmSession extends CommonSerializeUtils implements Serializable {
      * @return the decrypted message if operation succeed, null otherwise
      */
     public String decryptMessage(OlmMessage aEncryptedMsg) {
-        return decryptMessageJni(aEncryptedMsg);
+        try {
+            return new String(decryptMessageJni(aEncryptedMsg), "UTF-8");
+        } catch (Exception e) {
+            Log.e(LOG_TAG, "## decryptMessage(): failed " + e.getMessage());
+        }
+
+        return null;
     }
 
-    private native String decryptMessageJni(OlmMessage aEncryptedMsg);
+    private native byte[] decryptMessageJni(OlmMessage aEncryptedMsg);
 
     /**
      * Return true the object resources have been released.<br>
diff --git a/java/android/OlmLibSdk/olm-sdk/src/main/java/org/matrix/olm/OlmUtility.java b/java/android/OlmLibSdk/olm-sdk/src/main/java/org/matrix/olm/OlmUtility.java
index 3d9d99d..287a9d2 100644
--- a/java/android/OlmLibSdk/olm-sdk/src/main/java/org/matrix/olm/OlmUtility.java
+++ b/java/android/OlmLibSdk/olm-sdk/src/main/java/org/matrix/olm/OlmUtility.java
@@ -121,7 +121,7 @@ public class OlmUtility {
 
          if (null != aMessageToHash) {
              try {
-                 hashRetValue = sha256Jni(aMessageToHash.getBytes("UTF-8"));
+                 hashRetValue = new String(sha256Jni(aMessageToHash.getBytes("UTF-8")), "UTF-8");
              } catch (Exception e) {
                  Log.e(LOG_TAG, "## sha256(): failed " + e.getMessage());
              }
@@ -130,7 +130,7 @@ public class OlmUtility {
         return hashRetValue;
     }
 
-    private native String sha256Jni(byte[] aMessage);
+    private native byte[] sha256Jni(byte[] aMessage);
 
 
     /**
diff --git a/java/android/OlmLibSdk/olm-sdk/src/main/jni/olm_account.cpp b/java/android/OlmLibSdk/olm-sdk/src/main/jni/olm_account.cpp
index 87ed86a..06709e7 100644
--- a/java/android/OlmLibSdk/olm-sdk/src/main/jni/olm_account.cpp
+++ b/java/android/OlmLibSdk/olm-sdk/src/main/jni/olm_account.cpp
@@ -405,10 +405,10 @@ JNIEXPORT jint OLM_ACCOUNT_FUNC_DEF(markOneTimeKeysAsPublishedJni)(JNIEnv *env,
  * @param aMessage message to sign
  * @return the signed message, null otherwise
 **/
-JNIEXPORT jstring OLM_ACCOUNT_FUNC_DEF(signMessageJni)(JNIEnv *env, jobject thiz, jbyteArray aMessage)
+JNIEXPORT jbyteArray OLM_ACCOUNT_FUNC_DEF(signMessageJni)(JNIEnv *env, jobject thiz, jbyteArray aMessage)
 {
     OlmAccount* accountPtr = NULL;
-    jstring signedMsgRetValue = NULL;
+    jbyteArray signedMsgRetValueBuffer = NULL;
 
     if (!aMessage)
     {
@@ -425,7 +425,8 @@ JNIEXPORT jstring OLM_ACCOUNT_FUNC_DEF(signMessageJni)(JNIEnv *env, jobject thiz
 
         // signature memory allocation
         size_t signatureLength = olm_account_signature_length(accountPtr);
-        void* signedMsgPtr = malloc((signatureLength+1)*sizeof(uint8_t));
+        size_t bufferLen = signatureLength + 1;
+        void* signedMsgPtr = malloc(bufferLen * sizeof(uint8_t));
 
         if (!signedMsgPtr)
         {
@@ -448,9 +449,12 @@ JNIEXPORT jstring OLM_ACCOUNT_FUNC_DEF(signMessageJni)(JNIEnv *env, jobject thiz
             {
                 // info: signatureLength is always equal to resultSign
                 (static_cast<char*>(signedMsgPtr))[signatureLength] = static_cast<char>('\0');
-                // convert to jstring
-                signedMsgRetValue = env->NewStringUTF((const char*)signedMsgPtr); // UTF8
+
                 LOGD("## signMessageJni(): success - retCode=%lu signatureLength=%lu", static_cast<long unsigned int>(resultSign), static_cast<long unsigned int>(signatureLength));
+     	
+                signedMsgRetValueBuffer = env->NewByteArray(signatureLength);
+                env->SetByteArrayRegion(signedMsgRetValueBuffer, 0 , signatureLength, (jbyte*)signedMsgPtr);
+
             }
 
             free(signedMsgPtr);
@@ -463,7 +467,7 @@ JNIEXPORT jstring OLM_ACCOUNT_FUNC_DEF(signMessageJni)(JNIEnv *env, jobject thiz
         }
     }
 
-    return signedMsgRetValue;
+    return signedMsgRetValueBuffer;
 }
 
 /**
@@ -472,9 +476,9 @@ JNIEXPORT jstring OLM_ACCOUNT_FUNC_DEF(signMessageJni)(JNIEnv *env, jobject thiz
 * @param[out] aErrorMsg error message set if operation failed
 * @return a base64 string if operation succeed, null otherwise
 **/
-JNIEXPORT jstring OLM_ACCOUNT_FUNC_DEF(serializeDataWithKeyJni)(JNIEnv *env, jobject thiz, jbyteArray aKeyBuffer, jobject aErrorMsg)
+JNIEXPORT jbyteArray OLM_ACCOUNT_FUNC_DEF(serializeDataWithKeyJni)(JNIEnv *env, jobject thiz, jbyteArray aKeyBuffer, jobject aErrorMsg)
 {
-    jstring pickledDataRetValue = 0;
+    jbyteArray pickledDataRetValue = 0;
     jclass errorMsgJClass = 0;
     jmethodID errorMsgMethodId = 0;
     jstring errorJstring = 0;
@@ -541,8 +545,11 @@ JNIEXPORT jstring OLM_ACCOUNT_FUNC_DEF(serializeDataWithKeyJni)(JNIEnv *env, job
             {
                 // build success output
                 (static_cast<char*>(pickledPtr))[pickledLength] = static_cast<char>('\0');
-                pickledDataRetValue = env->NewStringUTF((const char*)pickledPtr);
+
                 LOGD(" ## serializeDataWithKeyJni(): success - result=%lu pickled=%s", static_cast<long unsigned int>(result), static_cast<char*>(pickledPtr));
+
+                pickledDataRetValue = env->NewByteArray(pickledLength+1);
+                env->SetByteArrayRegion(pickledDataRetValue, 0 , pickledLength+1, (jbyte*)pickledPtr);
             }
 
             free(pickledPtr);
diff --git a/java/android/OlmLibSdk/olm-sdk/src/main/jni/olm_account.h b/java/android/OlmLibSdk/olm-sdk/src/main/jni/olm_account.h
index 88ef215..c866dbc 100644
--- a/java/android/OlmLibSdk/olm-sdk/src/main/jni/olm_account.h
+++ b/java/android/OlmLibSdk/olm-sdk/src/main/jni/olm_account.h
@@ -44,10 +44,10 @@ JNIEXPORT jint OLM_ACCOUNT_FUNC_DEF(removeOneTimeKeysForSessionJni)(JNIEnv *env,
 JNIEXPORT jint OLM_ACCOUNT_FUNC_DEF(markOneTimeKeysAsPublishedJni)(JNIEnv *env, jobject thiz);
 
 // signing
-JNIEXPORT jstring OLM_ACCOUNT_FUNC_DEF(signMessageJni)(JNIEnv *env, jobject thiz, jbyteArray aMessage);
+JNIEXPORT jbyteArray OLM_ACCOUNT_FUNC_DEF(signMessageJni)(JNIEnv *env, jobject thiz, jbyteArray aMessage);
 
 // serialization
-JNIEXPORT jstring OLM_ACCOUNT_FUNC_DEF(serializeDataWithKeyJni)(JNIEnv *env, jobject thiz, jbyteArray aKeyBuffer, jobject aErrorMsg);
+JNIEXPORT jbyteArray OLM_ACCOUNT_FUNC_DEF(serializeDataWithKeyJni)(JNIEnv *env, jobject thiz, jbyteArray aKeyBuffer, jobject aErrorMsg);
 JNIEXPORT jstring OLM_ACCOUNT_FUNC_DEF(initWithSerializedDataJni)(JNIEnv *env, jobject thiz, jbyteArray aSerializedDataBuffer, jbyteArray aKeyBuffer);
 
 #ifdef __cplusplus
diff --git a/java/android/OlmLibSdk/olm-sdk/src/main/jni/olm_inbound_group_session.cpp b/java/android/OlmLibSdk/olm-sdk/src/main/jni/olm_inbound_group_session.cpp
index 9eba3af..ca47dbb 100644
--- a/java/android/OlmLibSdk/olm-sdk/src/main/jni/olm_inbound_group_session.cpp
+++ b/java/android/OlmLibSdk/olm-sdk/src/main/jni/olm_inbound_group_session.cpp
@@ -137,10 +137,10 @@ JNIEXPORT jint OLM_INBOUND_GROUP_SESSION_FUNC_DEF(initInboundGroupSessionWithSes
 /**
 * Get a base64-encoded identifier for this inbound group session.
 */
-JNIEXPORT jstring OLM_INBOUND_GROUP_SESSION_FUNC_DEF(sessionIdentifierJni)(JNIEnv *env, jobject thiz)
+JNIEXPORT jbyteArray OLM_INBOUND_GROUP_SESSION_FUNC_DEF(sessionIdentifierJni)(JNIEnv *env, jobject thiz)
 {
     OlmInboundGroupSession *sessionPtr = NULL;
-    jstring returnValueStr=0;
+    jbyteArray returnValue = 0;
 
     LOGD("## sessionIdentifierJni(): inbound group session IN");
 
@@ -170,22 +170,26 @@ JNIEXPORT jstring OLM_INBOUND_GROUP_SESSION_FUNC_DEF(sessionIdentifierJni)(JNIEn
             }
             else
             {
-                // update length
+            
                 sessionIdPtr[result] = static_cast<char>('\0');
                 LOGD(" ## sessionIdentifierJni(): success - inbound group session result=%lu sessionId=%s",static_cast<long unsigned int>(result), (char*)sessionIdPtr);
-                returnValueStr = env->NewStringUTF((const char*)sessionIdPtr);
+
+                returnValue = env->NewByteArray(result);
+                env->SetByteArrayRegion(returnValue, 0 , result, (jbyte*)sessionIdPtr);
             }
+
             free(sessionIdPtr);
         }
     }
 
-    return returnValueStr;
+    return returnValue;
 }
 
 
-JNIEXPORT jstring OLM_INBOUND_GROUP_SESSION_FUNC_DEF(decryptMessageJni)(JNIEnv *env, jobject thiz, jbyteArray aEncryptedMsgBuffer, jobject aDecryptionResult, jobject aErrorMsg)
+JNIEXPORT jbyteArray OLM_INBOUND_GROUP_SESSION_FUNC_DEF(decryptMessageJni)(JNIEnv *env, jobject thiz, jbyteArray aEncryptedMsgBuffer, jobject aDecryptionResult, jobject aErrorMsg)
 {
-    jstring decryptedMsgRetValue = 0;
+    jbyteArray decryptedMsgBuffer = 0;
+
     OlmInboundGroupSession *sessionPtr = NULL;
     jbyte *encryptedMsgPtr = NULL;
     jclass indexObjJClass = 0;
@@ -298,17 +302,10 @@ JNIEXPORT jstring OLM_INBOUND_GROUP_SESSION_FUNC_DEF(decryptMessageJni)(JNIEnv *
                     // update index
                     env->SetLongField(aDecryptionResult, indexMsgFieldId, (jlong)messageIndex);
 
-                    // convert to utf8
-                    decryptedMsgRetValue = javaCStringToUtf8(env, plainTextMsgPtr, plaintextLength);
+                    decryptedMsgBuffer = env->NewByteArray(plaintextLength);
+                    env->SetByteArrayRegion(decryptedMsgBuffer, 0 , plaintextLength, (jbyte*)plainTextMsgPtr);
 
-                    if (!decryptedMsgRetValue)
-                    {
-                        LOGE(" ## decryptMessageJni(): UTF-8 Conversion failure - javaCStringToUtf8() returns null");
-                    }
-                    else
-                    {
-                        LOGD(" ## decryptMessageJni(): UTF-8 Conversion - decrypted returnedLg=%lu OK",static_cast<long unsigned int>(plaintextLength));
-                    }
+                    LOGD(" ## decryptMessageJni(): UTF-8 Conversion - decrypted returnedLg=%lu OK",static_cast<long unsigned int>(plaintextLength));
                 }
 
                 if (plainTextMsgPtr)
@@ -330,7 +327,7 @@ JNIEXPORT jstring OLM_INBOUND_GROUP_SESSION_FUNC_DEF(decryptMessageJni)(JNIEnv *
         env->ReleaseByteArrayElements(aEncryptedMsgBuffer, encryptedMsgPtr, JNI_ABORT);
     }
 
-    return decryptedMsgRetValue;
+    return decryptedMsgBuffer;
 }
 
 
@@ -340,9 +337,10 @@ JNIEXPORT jstring OLM_INBOUND_GROUP_SESSION_FUNC_DEF(decryptMessageJni)(JNIEnv *
 * @param[out] aErrorMsg error message set if operation failed
 * @return a base64 string if operation succeed, null otherwise
 **/
-JNIEXPORT jstring OLM_INBOUND_GROUP_SESSION_FUNC_DEF(serializeDataWithKeyJni)(JNIEnv *env, jobject thiz, jbyteArray aKeyBuffer, jobject aErrorMsg)
+JNIEXPORT jbyteArray OLM_INBOUND_GROUP_SESSION_FUNC_DEF(serializeDataWithKeyJni)(JNIEnv *env, jobject thiz, jbyteArray aKeyBuffer, jobject aErrorMsg)
 {
-    jstring pickledDataRetValue = 0;
+    jbyteArray pickledDataRet = 0;
+
     jclass errorMsgJClass = 0;
     jmethodID errorMsgMethodId = 0;
     jbyte* keyPtr = NULL;
@@ -408,10 +406,11 @@ JNIEXPORT jstring OLM_INBOUND_GROUP_SESSION_FUNC_DEF(serializeDataWithKeyJni)(JN
             }
             else
             {
-                // build success output
-                (static_cast<char*>(pickledPtr))[pickledLength] = static_cast<char>('\0');
-                pickledDataRetValue = env->NewStringUTF((const char*)pickledPtr);
+             	(static_cast<char*>(pickledPtr))[pickledLength] = static_cast<char>('\0');
                 LOGD(" ## serializeDataWithKeyJni(): success - result=%lu pickled=%s", static_cast<long unsigned int>(result), static_cast<char*>(pickledPtr));
+
+                pickledDataRet = env->NewByteArray(pickledLength);
+                env->SetByteArrayRegion(pickledDataRet, 0 , pickledLength, (jbyte*)pickledPtr);
             }
 
             free(pickledPtr);
@@ -424,7 +423,7 @@ JNIEXPORT jstring OLM_INBOUND_GROUP_SESSION_FUNC_DEF(serializeDataWithKeyJni)(JN
         env->ReleaseByteArrayElements(aKeyBuffer, keyPtr, JNI_ABORT);
     }
 
-    return pickledDataRetValue;
+    return pickledDataRet;
 }
 
 
diff --git a/java/android/OlmLibSdk/olm-sdk/src/main/jni/olm_inbound_group_session.h b/java/android/OlmLibSdk/olm-sdk/src/main/jni/olm_inbound_group_session.h
index af763f4..7ed6d8b 100644
--- a/java/android/OlmLibSdk/olm-sdk/src/main/jni/olm_inbound_group_session.h
+++ b/java/android/OlmLibSdk/olm-sdk/src/main/jni/olm_inbound_group_session.h
@@ -33,11 +33,11 @@ JNIEXPORT void OLM_INBOUND_GROUP_SESSION_FUNC_DEF(releaseSessionJni)(JNIEnv *env
 JNIEXPORT jlong OLM_INBOUND_GROUP_SESSION_FUNC_DEF(createNewSessionJni)(JNIEnv *env, jobject thiz);
 
 JNIEXPORT jint OLM_INBOUND_GROUP_SESSION_FUNC_DEF(initInboundGroupSessionWithSessionKeyJni)(JNIEnv *env, jobject thiz, jbyteArray aSessionKeyBuffer);
-JNIEXPORT jstring OLM_INBOUND_GROUP_SESSION_FUNC_DEF(sessionIdentifierJni)(JNIEnv *env, jobject thiz);
-JNIEXPORT jstring OLM_INBOUND_GROUP_SESSION_FUNC_DEF(decryptMessageJni)(JNIEnv *env, jobject thiz, jbyteArray aEncryptedMsg, jobject aDecryptIndex, jobject aErrorMsg);
+JNIEXPORT jbyteArray OLM_INBOUND_GROUP_SESSION_FUNC_DEF(sessionIdentifierJni)(JNIEnv *env, jobject thiz);
+JNIEXPORT jbyteArray OLM_INBOUND_GROUP_SESSION_FUNC_DEF(decryptMessageJni)(JNIEnv *env, jobject thiz, jbyteArray aEncryptedMsg, jobject aDecryptIndex, jobject aErrorMsg);
 
 // serialization
-JNIEXPORT jstring OLM_INBOUND_GROUP_SESSION_FUNC_DEF(serializeDataWithKeyJni)(JNIEnv *env, jobject thiz, jbyteArray aKey, jobject aErrorMsg);
+JNIEXPORT jbyteArray OLM_INBOUND_GROUP_SESSION_FUNC_DEF(serializeDataWithKeyJni)(JNIEnv *env, jobject thiz, jbyteArray aKey, jobject aErrorMsg);
 JNIEXPORT jstring OLM_INBOUND_GROUP_SESSION_FUNC_DEF(initWithSerializedDataJni)(JNIEnv *env, jobject thiz, jbyteArray aSerializedData, jbyteArray aKey);
 
 
diff --git a/java/android/OlmLibSdk/olm-sdk/src/main/jni/olm_jni.h b/java/android/OlmLibSdk/olm-sdk/src/main/jni/olm_jni.h
index 7fea2f1..f1d124e 100644
--- a/java/android/OlmLibSdk/olm-sdk/src/main/jni/olm_jni.h
+++ b/java/android/OlmLibSdk/olm-sdk/src/main/jni/olm_jni.h
@@ -74,7 +74,6 @@ jlong getAccountInstanceId(JNIEnv* aJniEnv, jobject aJavaObject);
 jlong getInboundGroupSessionInstanceId(JNIEnv* aJniEnv, jobject aJavaObject);
 jlong getOutboundGroupSessionInstanceId(JNIEnv* aJniEnv, jobject aJavaObject);
 jlong getUtilityInstanceId(JNIEnv* aJniEnv, jobject aJavaObject);
-jstring javaCStringToUtf8(JNIEnv *env, uint8_t *aCStringMsgPtr, size_t aMsgLength);
 
 #ifdef __cplusplus
 }
diff --git a/java/android/OlmLibSdk/olm-sdk/src/main/jni/olm_jni_helper.cpp b/java/android/OlmLibSdk/olm-sdk/src/main/jni/olm_jni_helper.cpp
index c649d32..9205fc0 100644
--- a/java/android/OlmLibSdk/olm-sdk/src/main/jni/olm_jni_helper.cpp
+++ b/java/android/OlmLibSdk/olm-sdk/src/main/jni/olm_jni_helper.cpp
@@ -213,45 +213,3 @@ jlong getUtilityInstanceId(JNIEnv* aJniEnv, jobject aJavaObject)
     jlong instanceId = getInstanceId(aJniEnv, aJavaObject, CLASS_OLM_UTILITY);
     return instanceId;
 }
-
-/**
-* Convert a C string into a UTF-8 format string.
-* The conversion is performed in JAVA side to workaround the issue in  NewStringUTF().
-* The problem is described here: https://github.com/eclipsesource/J2V8/issues/142
-*/
-jstring javaCStringToUtf8(JNIEnv *env, uint8_t *aCStringMsgPtr, size_t aMsgLength)
-{
-    jstring convertedRetValue = 0;
-    jbyteArray tempByteArray = NULL;
-
-    if (!aCStringMsgPtr || !env)
-    {
-        LOGE("## javaCStringToUtf8(): failure - invalid parameters (null)");
-    }
-    else if (!(tempByteArray = env->NewByteArray(aMsgLength)))
-    {
-        LOGE("## javaCStringToUtf8(): failure - return byte array OOM");
-    }
-    else
-    {
-        env->SetByteArrayRegion(tempByteArray, 0, aMsgLength, (const jbyte*)aCStringMsgPtr);
-
-        // UTF-8 conversion from JAVA
-        jstring strEncode = (env)->NewStringUTF("UTF-8");
-        jclass jClass = env->FindClass("java/lang/String");
-        jmethodID cstor = env->GetMethodID(jClass, "<init>", "([BLjava/lang/String;)V");
-
-        if (jClass && strEncode)
-        {
-            convertedRetValue = (jstring) env->NewObject(jClass, cstor, tempByteArray, strEncode);
-            LOGD(" ## javaCStringToUtf8(): succeed");
-            env->DeleteLocalRef(tempByteArray);
-        }
-        else
-        {
-            LOGE(" ## javaCStringToUtf8(): failure - invalid Java references");
-        }
-    }
-
-    return convertedRetValue;
-}
diff --git a/java/android/OlmLibSdk/olm-sdk/src/main/jni/olm_outbound_group_session.cpp b/java/android/OlmLibSdk/olm-sdk/src/main/jni/olm_outbound_group_session.cpp
index 0ccc6e8..211757f 100644
--- a/java/android/OlmLibSdk/olm-sdk/src/main/jni/olm_outbound_group_session.cpp
+++ b/java/android/OlmLibSdk/olm-sdk/src/main/jni/olm_outbound_group_session.cpp
@@ -138,12 +138,13 @@ JNIEXPORT jint OLM_OUTBOUND_GROUP_SESSION_FUNC_DEF(initOutboundGroupSessionJni)(
 /**
 * Get a base64-encoded identifier for this outbound group session.
 */
-JNIEXPORT jstring OLM_OUTBOUND_GROUP_SESSION_FUNC_DEF(sessionIdentifierJni)(JNIEnv *env, jobject thiz)
+JNIEXPORT jbyteArray OLM_OUTBOUND_GROUP_SESSION_FUNC_DEF(sessionIdentifierJni)(JNIEnv *env, jobject thiz)
 {
     LOGD("## sessionIdentifierJni(): outbound group session IN");
-    OlmOutboundGroupSession *sessionPtr = (OlmOutboundGroupSession*)getOutboundGroupSessionInstanceId(env,thiz);
-    jstring returnValueStr=0;
 
+    OlmOutboundGroupSession *sessionPtr = (OlmOutboundGroupSession*)getOutboundGroupSessionInstanceId(env,thiz);
+    jbyteArray returnValue = 0;
+    
     if (!sessionPtr)
     {
         LOGE(" ## sessionIdentifierJni(): failure - invalid outbound group session instance");
@@ -172,8 +173,11 @@ JNIEXPORT jstring OLM_OUTBOUND_GROUP_SESSION_FUNC_DEF(sessionIdentifierJni)(JNIE
             {
                 // update length
                 sessionIdPtr[result] = static_cast<char>('\0');
+
+                returnValue = env->NewByteArray(result);
+                env->SetByteArrayRegion(returnValue, 0 , result, (jbyte*)sessionIdPtr);
+
                 LOGD(" ## sessionIdentifierJni(): success - outbound group session identifier result=%lu sessionId=%s",static_cast<long unsigned int>(result), reinterpret_cast<char*>(sessionIdPtr));
-                returnValueStr = env->NewStringUTF((const char*)sessionIdPtr);
             }
 
             // free alloc
@@ -181,7 +185,7 @@ JNIEXPORT jstring OLM_OUTBOUND_GROUP_SESSION_FUNC_DEF(sessionIdentifierJni)(JNIE
         }
     }
 
-    return returnValueStr;
+    return returnValue;
 }
 
 
@@ -215,11 +219,12 @@ JNIEXPORT jint OLM_OUTBOUND_GROUP_SESSION_FUNC_DEF(messageIndexJni)(JNIEnv *env,
 /**
 * Get the base64-encoded current ratchet key for this session.<br>
 */
-JNIEXPORT jstring OLM_OUTBOUND_GROUP_SESSION_FUNC_DEF(sessionKeyJni)(JNIEnv *env, jobject thiz)
+JNIEXPORT jbyteArray OLM_OUTBOUND_GROUP_SESSION_FUNC_DEF(sessionKeyJni)(JNIEnv *env, jobject thiz)
 {
     LOGD("## sessionKeyJni(): outbound group session IN");
+
     OlmOutboundGroupSession *sessionPtr = (OlmOutboundGroupSession*)getOutboundGroupSessionInstanceId(env,thiz);
-    jstring returnValueStr = 0;
+    jbyteArray returnValue = 0;
 
     if (!sessionPtr)
     {
@@ -250,7 +255,9 @@ JNIEXPORT jstring OLM_OUTBOUND_GROUP_SESSION_FUNC_DEF(sessionKeyJni)(JNIEnv *env
                 // update length
                 sessionKeyPtr[result] = static_cast<char>('\0');
                 LOGD(" ## sessionKeyJni(): success - outbound group session key result=%lu sessionKey=%s",static_cast<long unsigned int>(result), reinterpret_cast<char*>(sessionKeyPtr));
-                returnValueStr = env->NewStringUTF((const char*)sessionKeyPtr);
+
+                returnValue = env->NewByteArray(result);
+                env->SetByteArrayRegion(returnValue, 0 , result, (jbyte*)sessionKeyPtr);
             }
 
             // free alloc
@@ -258,15 +265,15 @@ JNIEXPORT jstring OLM_OUTBOUND_GROUP_SESSION_FUNC_DEF(sessionKeyJni)(JNIEnv *env
         }
     }
 
-    return returnValueStr;
+    return returnValue;
 }
 
-
-JNIEXPORT jstring OLM_OUTBOUND_GROUP_SESSION_FUNC_DEF(encryptMessageJni)(JNIEnv *env, jobject thiz, jbyteArray aClearMsgBuffer)
+JNIEXPORT jbyteArray OLM_OUTBOUND_GROUP_SESSION_FUNC_DEF(encryptMessageJni)(JNIEnv *env, jobject thiz, jbyteArray aClearMsgBuffer)
 {
     LOGD("## encryptMessageJni(): IN");
 
-    jstring encryptedMsgRetValue = 0;
+    jbyteArray encryptedMsgRet = 0;
+
     OlmOutboundGroupSession *sessionPtr = NULL;
     jbyte* clearMsgPtr = NULL;
 
@@ -315,7 +322,9 @@ JNIEXPORT jstring OLM_OUTBOUND_GROUP_SESSION_FUNC_DEF(encryptMessageJni)(JNIEnv
                 encryptedMsgPtr[encryptedLength] = static_cast<char>('\0');
 
                 LOGD(" ## encryptMessageJni(): encrypted returnedLg=%lu plainTextMsgPtr=%s",static_cast<long unsigned int>(encryptedLength), reinterpret_cast<char*>(encryptedMsgPtr));
-                encryptedMsgRetValue = env->NewStringUTF((const char*)encryptedMsgPtr);
+
+                encryptedMsgRet = env->NewByteArray(encryptedLength);
+                env->SetByteArrayRegion(encryptedMsgRet, 0 , encryptedLength, (jbyte*)encryptedMsgPtr);
             }
 
             free(encryptedMsgPtr);
@@ -328,7 +337,7 @@ JNIEXPORT jstring OLM_OUTBOUND_GROUP_SESSION_FUNC_DEF(encryptMessageJni)(JNIEnv
         env->ReleaseByteArrayElements(aClearMsgBuffer, clearMsgPtr, JNI_ABORT);
     }
 
-    return encryptedMsgRetValue;
+    return encryptedMsgRet;
 }
 
 
diff --git a/java/android/OlmLibSdk/olm-sdk/src/main/jni/olm_outbound_group_session.h b/java/android/OlmLibSdk/olm-sdk/src/main/jni/olm_outbound_group_session.h
index 43ec4f7..71ddb3b 100644
--- a/java/android/OlmLibSdk/olm-sdk/src/main/jni/olm_outbound_group_session.h
+++ b/java/android/OlmLibSdk/olm-sdk/src/main/jni/olm_outbound_group_session.h
@@ -33,11 +33,11 @@ JNIEXPORT void OLM_OUTBOUND_GROUP_SESSION_FUNC_DEF(releaseSessionJni)(JNIEnv *en
 JNIEXPORT jlong OLM_OUTBOUND_GROUP_SESSION_FUNC_DEF(createNewSessionJni)(JNIEnv *env, jobject thiz);
 
 JNIEXPORT jint OLM_OUTBOUND_GROUP_SESSION_FUNC_DEF(initOutboundGroupSessionJni)(JNIEnv *env, jobject thiz);
-JNIEXPORT jstring OLM_OUTBOUND_GROUP_SESSION_FUNC_DEF(sessionIdentifierJni)(JNIEnv *env, jobject thiz);
+JNIEXPORT jbyteArray OLM_OUTBOUND_GROUP_SESSION_FUNC_DEF(sessionIdentifierJni)(JNIEnv *env, jobject thiz);
 JNIEXPORT jint OLM_OUTBOUND_GROUP_SESSION_FUNC_DEF(messageIndexJni)(JNIEnv *env, jobject thiz);
-JNIEXPORT jstring OLM_OUTBOUND_GROUP_SESSION_FUNC_DEF(sessionKeyJni)(JNIEnv *env, jobject thiz);
+JNIEXPORT jbyteArray OLM_OUTBOUND_GROUP_SESSION_FUNC_DEF(sessionKeyJni)(JNIEnv *env, jobject thiz);
 
-JNIEXPORT jstring OLM_OUTBOUND_GROUP_SESSION_FUNC_DEF(encryptMessageJni)(JNIEnv *env, jobject thiz, jbyteArray aClearMsgBuffer);
+JNIEXPORT jbyteArray OLM_OUTBOUND_GROUP_SESSION_FUNC_DEF(encryptMessageJni)(JNIEnv *env, jobject thiz, jbyteArray aClearMsgBuffer);
 
 // serialization
 JNIEXPORT jstring OLM_OUTBOUND_GROUP_SESSION_FUNC_DEF(serializeDataWithKeyJni)(JNIEnv *env, jobject thiz, jbyteArray aKey, jobject aErrorMsg);
diff --git a/java/android/OlmLibSdk/olm-sdk/src/main/jni/olm_session.cpp b/java/android/OlmLibSdk/olm-sdk/src/main/jni/olm_session.cpp
index 491795f..5ae68d0 100644
--- a/java/android/OlmLibSdk/olm-sdk/src/main/jni/olm_session.cpp
+++ b/java/android/OlmLibSdk/olm-sdk/src/main/jni/olm_session.cpp
@@ -580,9 +580,10 @@ JNIEXPORT jint OLM_SESSION_FUNC_DEF(encryptMessageJni)(JNIEnv *env, jobject thiz
  * @param aEncryptedMsg message to decrypt
  * @return decrypted message if operation succeed, null otherwise
  */
-JNIEXPORT jstring OLM_SESSION_FUNC_DEF(decryptMessageJni)(JNIEnv *env, jobject thiz, jobject aEncryptedMsg)
+JNIEXPORT jbyteArray OLM_SESSION_FUNC_DEF(decryptMessageJni)(JNIEnv *env, jobject thiz, jobject aEncryptedMsg)
 {
-    jstring decryptedMsgRetValue = 0;
+    jbyteArray decryptedMsgRet = 0;
+
     jclass encryptedMsgJClass = 0;
     jstring encryptedMsgJstring = 0; // <= obtained from encryptedMsgFieldId
     // field IDs
@@ -668,16 +669,10 @@ JNIEXPORT jstring OLM_SESSION_FUNC_DEF(decryptMessageJni)(JNIEnv *env, jobject t
             }
             else
             {
-                decryptedMsgRetValue = javaCStringToUtf8(env, plainTextMsgPtr, plaintextLength);
+                decryptedMsgRet = env->NewByteArray(plaintextLength);
+                env->SetByteArrayRegion(decryptedMsgRet, 0 , plaintextLength, (jbyte*)plainTextMsgPtr);
 
-                if (!decryptedMsgRetValue)
-                {
-                    LOGE(" ## decryptMessageJni(): UTF-8 Conversion failure - javaCStringToUtf8() returns null");
-                }
-                else
-                {
-                    LOGD(" ## decryptMessageJni(): UTF-8 Conversion - decrypted returnedLg=%lu OK",static_cast<long unsigned int>(plaintextLength));
-                }
+                LOGD(" ## decryptMessageJni(): UTF-8 Conversion - decrypted returnedLg=%lu OK",static_cast<long unsigned int>(plaintextLength));
             }
         }
     }
@@ -698,7 +693,7 @@ JNIEXPORT jstring OLM_SESSION_FUNC_DEF(decryptMessageJni)(JNIEnv *env, jobject t
         free(plainTextMsgPtr);
     }
 
-    return decryptedMsgRetValue;
+    return decryptedMsgRet;
 }
 
 
@@ -706,9 +701,9 @@ JNIEXPORT jstring OLM_SESSION_FUNC_DEF(decryptMessageJni)(JNIEnv *env, jobject t
 * Get the session identifier for this session.
 * @return the session identifier if operation succeed, null otherwise
 */
-JNIEXPORT jstring OLM_SESSION_FUNC_DEF(getSessionIdentifierJni)(JNIEnv *env, jobject thiz)
+JNIEXPORT jbyteArray OLM_SESSION_FUNC_DEF(getSessionIdentifierJni)(JNIEnv *env, jobject thiz)
 {
-     jstring returnValueStr=0;
+     jbyteArray returnValue = 0;
 
      LOGD("## getSessionIdentifierJni(): IN ");
 
@@ -744,13 +739,16 @@ JNIEXPORT jstring OLM_SESSION_FUNC_DEF(getSessionIdentifierJni)(JNIEnv *env, job
                  (static_cast<char*>(sessionIdPtr))[result] = static_cast<char>('\0');
 
                  LOGD("## getSessionIdentifierJni(): success - result=%lu sessionId=%s",static_cast<long unsigned int>(result), (char*)sessionIdPtr);
-                 returnValueStr = env->NewStringUTF((const char*)sessionIdPtr);
+
+                 returnValue = env->NewByteArray(result);
+                 env->SetByteArrayRegion(returnValue, 0 , result, (jbyte*)sessionIdPtr);
              }
+
              free(sessionIdPtr);
          }
      }
 
-     return returnValueStr;
+     return returnValue;
 }
 
 
diff --git a/java/android/OlmLibSdk/olm-sdk/src/main/jni/olm_session.h b/java/android/OlmLibSdk/olm-sdk/src/main/jni/olm_session.h
index b18ac86..924b439 100644
--- a/java/android/OlmLibSdk/olm-sdk/src/main/jni/olm_session.h
+++ b/java/android/OlmLibSdk/olm-sdk/src/main/jni/olm_session.h
@@ -45,9 +45,9 @@ JNIEXPORT jint OLM_SESSION_FUNC_DEF(matchesInboundSessionFromIdKeyJni)(JNIEnv *e
 
 // encrypt/decrypt
 JNIEXPORT jint OLM_SESSION_FUNC_DEF(encryptMessageJni)(JNIEnv *env, jobject thiz, jbyteArray aClearMsg, jobject aEncryptedMsg);
-JNIEXPORT jstring OLM_SESSION_FUNC_DEF(decryptMessageJni)(JNIEnv *env, jobject thiz, jobject aEncryptedMsg);
+JNIEXPORT jbyteArray OLM_SESSION_FUNC_DEF(decryptMessageJni)(JNIEnv *env, jobject thiz, jobject aEncryptedMsg);
 
-JNIEXPORT jstring OLM_SESSION_FUNC_DEF(getSessionIdentifierJni)(JNIEnv *env, jobject thiz);
+JNIEXPORT jbyteArray OLM_SESSION_FUNC_DEF(getSessionIdentifierJni)(JNIEnv *env, jobject thiz);
 
 // serialization
 JNIEXPORT jstring OLM_SESSION_FUNC_DEF(serializeDataWithKeyJni)(JNIEnv *env, jobject thiz, jbyteArray aKey, jobject aErrorMsg);
diff --git a/java/android/OlmLibSdk/olm-sdk/src/main/jni/olm_utility.cpp b/java/android/OlmLibSdk/olm-sdk/src/main/jni/olm_utility.cpp
index 584e83e..f4a0c80 100644
--- a/java/android/OlmLibSdk/olm-sdk/src/main/jni/olm_utility.cpp
+++ b/java/android/OlmLibSdk/olm-sdk/src/main/jni/olm_utility.cpp
@@ -166,9 +166,10 @@ JNIEXPORT jstring OLM_UTILITY_FUNC_DEF(verifyEd25519SignatureJni)(JNIEnv *env, j
 * @param aMessage
 * @return digest of the message if operation succeed, null otherwise
 **/
-JNIEXPORT jstring OLM_UTILITY_FUNC_DEF(sha256Jni)(JNIEnv *env, jobject thiz, jbyteArray aMessageToHashBuffer)
+JNIEXPORT jbyteArray OLM_UTILITY_FUNC_DEF(sha256Jni)(JNIEnv *env, jobject thiz, jbyteArray aMessageToHashBuffer)
 {
-    jstring sha256RetValue = 0;
+    jbyteArray sha256Ret = 0;
+
     OlmUtility* utilityPtr = NULL;
     jbyte* messagePtr = NULL;
 
@@ -212,9 +213,10 @@ JNIEXPORT jstring OLM_UTILITY_FUNC_DEF(sha256Jni)(JNIEnv *env, jobject thiz, jby
             {
                 // update length
                 (static_cast<char*>(hashValuePtr))[result] = static_cast<char>('\0');
-
                 LOGD("## sha256Jni(): success - result=%lu hashValue=%s",static_cast<long unsigned int>(result), (char*)hashValuePtr);
-                sha256RetValue = env->NewStringUTF((const char*)hashValuePtr);
+
+                 sha256Ret = env->NewByteArray(result);
+                 env->SetByteArrayRegion(sha256Ret, 0 , result, (jbyte*)hashValuePtr);
             }
 
             free(hashValuePtr);
@@ -226,5 +228,5 @@ JNIEXPORT jstring OLM_UTILITY_FUNC_DEF(sha256Jni)(JNIEnv *env, jobject thiz, jby
         env->ReleaseByteArrayElements(aMessageToHashBuffer, messagePtr, JNI_ABORT);
     }
 
-    return sha256RetValue;
+    return sha256Ret;
 }
\ No newline at end of file
diff --git a/java/android/OlmLibSdk/olm-sdk/src/main/jni/olm_utility.h b/java/android/OlmLibSdk/olm-sdk/src/main/jni/olm_utility.h
index 7c3601d..16d9e7a 100644
--- a/java/android/OlmLibSdk/olm-sdk/src/main/jni/olm_utility.h
+++ b/java/android/OlmLibSdk/olm-sdk/src/main/jni/olm_utility.h
@@ -30,7 +30,7 @@ extern "C" {
 JNIEXPORT jlong   OLM_UTILITY_FUNC_DEF(initUtilityJni)(JNIEnv *env, jobject thiz);
 JNIEXPORT void    OLM_UTILITY_FUNC_DEF(releaseUtilityJni)(JNIEnv *env, jobject thiz);
 JNIEXPORT jstring OLM_UTILITY_FUNC_DEF(verifyEd25519SignatureJni)(JNIEnv *env, jobject thiz, jbyteArray aSignature, jbyteArray aKey, jbyteArray aMessage);
-JNIEXPORT jstring OLM_UTILITY_FUNC_DEF(sha256Jni)(JNIEnv *env, jobject thiz, jbyteArray aMessageToHash);
+JNIEXPORT jbyteArray OLM_UTILITY_FUNC_DEF(sha256Jni)(JNIEnv *env, jobject thiz, jbyteArray aMessageToHash);
 #ifdef __cplusplus
 }
 #endif