rewrote scram cache implementation

src/main/java/eu/siacs/conversations/crypto/sasl/ScramMechanism.java

@@ -4,6 +4,10 @@ import android.annotation.TargetApi;
 import android.os.Build;
 import android.util.Base64;
 
+import com.google.common.base.Objects;
+import com.google.common.cache.Cache;
+import com.google.common.cache.CacheBuilder;
+
 import org.bouncycastle.crypto.Digest;
 import org.bouncycastle.crypto.macs.HMac;
 import org.bouncycastle.crypto.params.KeyParameter;
@@ -11,6 +15,7 @@ import org.bouncycastle.crypto.params.KeyParameter;
 import java.nio.charset.Charset;
 import java.security.InvalidKeyException;
 import java.security.SecureRandom;
+import java.util.concurrent.ExecutionException;
 
 import eu.siacs.conversations.entities.Account;
 import eu.siacs.conversations.utils.CryptoHelper;
@@ -27,17 +32,46 @@ abstract class ScramMechanism extends SaslMechanism {
 
     protected abstract Digest getDigest();
 
-    private KeyPair getKeyPair(final String password, final String salt, final int iterations) {
+    private static final Cache<CacheKey, KeyPair> CACHE = CacheBuilder.newBuilder().maximumSize(10).build();
-        try {
+
+    private static class CacheKey {
+        final String algorithm;
+        final String password;
+        final String salt;
+        final int iterations;
+
+        private CacheKey(String algorithm, String password, String salt, int iterations) {
+            this.algorithm = algorithm;
+            this.password = password;
+            this.salt = salt;
+            this.iterations = iterations;
+        }
+
+        @Override
+        public boolean equals(Object o) {
+            if (this == o) return true;
+            if (o == null || getClass() != o.getClass()) return false;
+            CacheKey cacheKey = (CacheKey) o;
+            return iterations == cacheKey.iterations &&
+                    Objects.equal(algorithm, cacheKey.algorithm) &&
+                    Objects.equal(password, cacheKey.password) &&
+                    Objects.equal(salt, cacheKey.salt);
+        }
+
+        @Override
+        public int hashCode() {
+            return Objects.hashCode(algorithm, password, salt, iterations);
+        }
+    }
+
+    private KeyPair getKeyPair(final String password, final String salt, final int iterations) throws ExecutionException {
+        return CACHE.get(new CacheKey(getHMAC().getAlgorithmName(), password, salt, iterations), () -> {
             final byte[] saltedPassword, serverKey, clientKey;
             saltedPassword = hi(password.getBytes(), Base64.decode(salt, Base64.DEFAULT), iterations);
             serverKey = hmac(saltedPassword, SERVER_KEY_BYTES);
             clientKey = hmac(saltedPassword, CLIENT_KEY_BYTES);
-
             return new KeyPair(clientKey, serverKey);
-        } catch (final InvalidKeyException | NumberFormatException e) {
+        });
-            return null;
-        }
     }
 
     private final String clientNonce;
@@ -162,8 +196,10 @@ abstract class ScramMechanism extends SaslMechanism {
                 final byte[] authMessage = (clientFirstMessageBare + ',' + new String(serverFirstMessage) + ','
                         + clientFinalMessageWithoutProof).getBytes();
 
-                final KeyPair keys = getKeyPair(CryptoHelper.saslPrep(account.getPassword()), salt, iterationCount);
+                final KeyPair keys;
-                if (keys == null) {
+                try {
+                    keys = getKeyPair(CryptoHelper.saslPrep(account.getPassword()), salt, iterationCount);
+                } catch (ExecutionException e) {
                     throw new AuthenticationException("Invalid keys generated");
                 }
                 final byte[] clientSignature;