1 files changed, 4 insertions, 2 deletions
diff --git a/src/main/java/eu/siacs/conversations/crypto/sasl/ScramSha1.java b/src/main/java/eu/siacs/conversations/crypto/sasl/ScramSha1.java
index c95a62df..3a05446c 100644
--- a/src/main/java/eu/siacs/conversations/crypto/sasl/ScramSha1.java
+++ b/src/main/java/eu/siacs/conversations/crypto/sasl/ScramSha1.java
@@ -21,7 +21,6 @@ public class ScramSha1 extends SaslMechanism {
 	// TODO: When channel binding (SCRAM-SHA1-PLUS) is supported in future, generalize this to indicate support and/or usage.
 	final private static String GS2_HEADER = "n,,";
 	private String clientFirstMessageBare;
-	private byte[] serverFirstMessage;
 	final private String clientNonce;
 	private byte[] serverSignature = null;
 	private static HMac HMAC;
@@ -101,7 +100,10 @@ public class ScramSha1 extends SaslMechanism {
 	public String getResponse(final String challenge) throws AuthenticationException {
 		switch (state) {
 			case AUTH_TEXT_SENT:
-				serverFirstMessage = Base64.decode(challenge, Base64.DEFAULT);
+				if (challenge == null) {
+					throw new AuthenticationException("challenge can not be null");
+				}
+				byte[] serverFirstMessage = Base64.decode(challenge, Base64.DEFAULT);
 				final Tokenizer tokenizer = new Tokenizer(serverFirstMessage);
 				String nonce = "";
 				int iterationCount = -1;