refactor SASL choice into factory; remove unused TagWriter

19 files changed, 288 insertions, 231 deletions

diff --git a/src/main/java/eu/siacs/conversations/crypto/axolotl/AxolotlService.java b/src/main/java/eu/siacs/conversations/crypto/axolotl/AxolotlService.java
index faef2e098..3d4f23360 100644
--- a/src/main/java/eu/siacs/conversations/crypto/axolotl/AxolotlService.java
+++ b/src/main/java/eu/siacs/conversations/crypto/axolotl/AxolotlService.java
@@ -1,5 +1,7 @@
 package eu.siacs.conversations.crypto.axolotl;
 
+import static eu.siacs.conversations.utils.Random.SECURE_RANDOM;
+
 import android.os.Bundle;
 import android.security.KeyChain;
 import android.util.Log;
@@ -499,7 +501,7 @@ public class AxolotlService implements OnAdvancedStreamFeaturesLoaded {
             PrivateKey x509PrivateKey = KeyChain.getPrivateKey(mXmppConnectionService, account.getPrivateKeyAlias());
             X509Certificate[] chain = KeyChain.getCertificateChain(mXmppConnectionService, account.getPrivateKeyAlias());
             Signature verifier = Signature.getInstance("sha256WithRSA");
-            verifier.initSign(x509PrivateKey, mXmppConnectionService.getRNG());
+            verifier.initSign(x509PrivateKey, SECURE_RANDOM);
             verifier.update(axolotlPublicKey.serialize());
             byte[] signature = verifier.sign();
             IqPacket packet = mXmppConnectionService.getIqGenerator().publishVerification(signature, chain, getOwnDeviceId());
diff --git a/src/main/java/eu/siacs/conversations/crypto/sasl/Anonymous.java b/src/main/java/eu/siacs/conversations/crypto/sasl/Anonymous.java
index a9abb2bf8..22cf80e65 100644
--- a/src/main/java/eu/siacs/conversations/crypto/sasl/Anonymous.java
+++ b/src/main/java/eu/siacs/conversations/crypto/sasl/Anonymous.java
@@ -1,16 +1,13 @@
 package eu.siacs.conversations.crypto.sasl;
 
-import java.security.SecureRandom;
-
 import eu.siacs.conversations.entities.Account;
-import eu.siacs.conversations.xml.TagWriter;
 
 public class Anonymous extends SaslMechanism {
 
     public static final String MECHANISM = "ANONYMOUS";
 
-    public Anonymous(TagWriter tagWriter, Account account, SecureRandom rng) {
-        super(tagWriter, account, rng);
+    public Anonymous(final Account account) {
+        super(account);
     }
 
     @Override
diff --git a/src/main/java/eu/siacs/conversations/crypto/sasl/DigestMd5.java b/src/main/java/eu/siacs/conversations/crypto/sasl/DigestMd5.java
index 74d4463d5..7229299ef 100644
--- a/src/main/java/eu/siacs/conversations/crypto/sasl/DigestMd5.java
+++ b/src/main/java/eu/siacs/conversations/crypto/sasl/DigestMd5.java
@@ -5,18 +5,17 @@ import android.util.Base64;
 import java.nio.charset.Charset;
 import java.security.MessageDigest;
 import java.security.NoSuchAlgorithmException;
-import java.security.SecureRandom;
 
 import eu.siacs.conversations.entities.Account;
 import eu.siacs.conversations.utils.CryptoHelper;
-import eu.siacs.conversations.xml.TagWriter;
 
 public class DigestMd5 extends SaslMechanism {
 
     public static final String MECHANISM = "DIGEST-MD5";
+    private State state = State.INITIAL;
 
-    public DigestMd5(final TagWriter tagWriter, final Account account, final SecureRandom rng) {
-        super(tagWriter, account, rng);
+    public DigestMd5(final Account account) {
+        super(account);
     }
 
     @Override
@@ -29,8 +28,6 @@ public class DigestMd5 extends SaslMechanism {
         return MECHANISM;
     }
 
-    private State state = State.INITIAL;
-
     @Override
     public String getResponse(final String challenge) throws AuthenticationException {
         switch (state) {
@@ -38,7 +35,8 @@ public class DigestMd5 extends SaslMechanism {
                 state = State.RESPONSE_SENT;
                 final String encodedResponse;
                 try {
-                    final Tokenizer tokenizer = new Tokenizer(Base64.decode(challenge, Base64.DEFAULT));
+                    final Tokenizer tokenizer =
+                            new Tokenizer(Base64.decode(challenge, Base64.DEFAULT));
                     String nonce = "";
                     for (final String token : tokenizer) {
                         final String[] parts = token.split("=", 2);
@@ -50,29 +48,49 @@ public class DigestMd5 extends SaslMechanism {
                     }
                     final String digestUri = "xmpp/" + account.getServer();
                     final String nonceCount = "00000001";
-                    final String x = account.getUsername() + ":" + account.getServer() + ":"
-                            + account.getPassword();
+                    final String x =
+                            account.getUsername()
+                                    + ":"
+                                    + account.getServer()
+                                    + ":"
+                                    + account.getPassword();
                     final MessageDigest md = MessageDigest.getInstance("MD5");
                     final byte[] y = md.digest(x.getBytes(Charset.defaultCharset()));
-                    final String cNonce = CryptoHelper.random(100, rng);
-                    final byte[] a1 = CryptoHelper.concatenateByteArrays(y,
-                            (":" + nonce + ":" + cNonce).getBytes(Charset.defaultCharset()));
+                    final String cNonce = CryptoHelper.random(100);
+                    final byte[] a1 =
+                            CryptoHelper.concatenateByteArrays(
+                                    y,
+                                    (":" + nonce + ":" + cNonce)
+                                            .getBytes(Charset.defaultCharset()));
                     final String a2 = "AUTHENTICATE:" + digestUri;
                     final String ha1 = CryptoHelper.bytesToHex(md.digest(a1));
-                    final String ha2 = CryptoHelper.bytesToHex(md.digest(a2.getBytes(Charset
-                            .defaultCharset())));
-                    final String kd = ha1 + ":" + nonce + ":" + nonceCount + ":" + cNonce
-                            + ":auth:" + ha2;
-                    final String response = CryptoHelper.bytesToHex(md.digest(kd.getBytes(Charset
-                            .defaultCharset())));
-                    final String saslString = "username=\"" + account.getUsername()
-                            + "\",realm=\"" + account.getServer() + "\",nonce=\""
-                            + nonce + "\",cnonce=\"" + cNonce + "\",nc=" + nonceCount
-                            + ",qop=auth,digest-uri=\"" + digestUri + "\",response="
-                            + response + ",charset=utf-8";
-                    encodedResponse = Base64.encodeToString(
-                            saslString.getBytes(Charset.defaultCharset()),
-                            Base64.NO_WRAP);
+                    final String ha2 =
+                            CryptoHelper.bytesToHex(
+                                    md.digest(a2.getBytes(Charset.defaultCharset())));
+                    final String kd =
+                            ha1 + ":" + nonce + ":" + nonceCount + ":" + cNonce + ":auth:" + ha2;
+                    final String response =
+                            CryptoHelper.bytesToHex(
+                                    md.digest(kd.getBytes(Charset.defaultCharset())));
+                    final String saslString =
+                            "username=\""
+                                    + account.getUsername()
+                                    + "\",realm=\""
+                                    + account.getServer()
+                                    + "\",nonce=\""
+                                    + nonce
+                                    + "\",cnonce=\""
+                                    + cNonce
+                                    + "\",nc="
+                                    + nonceCount
+                                    + ",qop=auth,digest-uri=\""
+                                    + digestUri
+                                    + "\",response="
+                                    + response
+                                    + ",charset=utf-8";
+                    encodedResponse =
+                            Base64.encodeToString(
+                                    saslString.getBytes(Charset.defaultCharset()), Base64.NO_WRAP);
                 } catch (final NoSuchAlgorithmException e) {
                     throw new AuthenticationException(e);
                 }
@@ -83,7 +101,7 @@ public class DigestMd5 extends SaslMechanism {
                 break;
             case VALID_SERVER_RESPONSE:
                 if (challenge == null) {
-                    return null; //everything is fine
+                    return null; // everything is fine
                 }
             default:
                 throw new InvalidStateException(state);
diff --git a/src/main/java/eu/siacs/conversations/crypto/sasl/External.java b/src/main/java/eu/siacs/conversations/crypto/sasl/External.java
index 6e0ed4390..06323f039 100644
--- a/src/main/java/eu/siacs/conversations/crypto/sasl/External.java
+++ b/src/main/java/eu/siacs/conversations/crypto/sasl/External.java
@@ -2,17 +2,14 @@ package eu.siacs.conversations.crypto.sasl;
 
 import android.util.Base64;
 
-import java.security.SecureRandom;
-
 import eu.siacs.conversations.entities.Account;
-import eu.siacs.conversations.xml.TagWriter;
 
 public class External extends SaslMechanism {
 
     public static final String MECHANISM = "EXTERNAL";
 
-    public External(TagWriter tagWriter, Account account, SecureRandom rng) {
-        super(tagWriter, account, rng);
+    public External(final Account account) {
+        super(account);
     }
 
     @Override
@@ -27,6 +24,7 @@ public class External extends SaslMechanism {
 
     @Override
     public String getClientFirstMessage() {
-        return Base64.encodeToString(account.getJid().asBareJid().toEscapedString().getBytes(), Base64.NO_WRAP);
+        return Base64.encodeToString(
+                account.getJid().asBareJid().toEscapedString().getBytes(), Base64.NO_WRAP);
     }
 }
diff --git a/src/main/java/eu/siacs/conversations/crypto/sasl/Plain.java b/src/main/java/eu/siacs/conversations/crypto/sasl/Plain.java
index d5cc037e1..875538bec 100644
--- a/src/main/java/eu/siacs/conversations/crypto/sasl/Plain.java
+++ b/src/main/java/eu/siacs/conversations/crypto/sasl/Plain.java
@@ -5,14 +5,18 @@ import android.util.Base64;
 import java.nio.charset.Charset;
 
 import eu.siacs.conversations.entities.Account;
-import eu.siacs.conversations.xml.TagWriter;
 
 public class Plain extends SaslMechanism {
 
     public static final String MECHANISM = "PLAIN";
 
-    public Plain(final TagWriter tagWriter, final Account account) {
-        super(tagWriter, account, null);
+    public Plain(final Account account) {
+        super(account);
+    }
+
+    public static String getMessage(String username, String password) {
+        final String message = '\u0000' + username + '\u0000' + password;
+        return Base64.encodeToString(message.getBytes(Charset.defaultCharset()), Base64.NO_WRAP);
     }
 
     @Override
@@ -29,9 +33,4 @@ public class Plain extends SaslMechanism {
     public String getClientFirstMessage() {
         return getMessage(account.getUsername(), account.getPassword());
     }
-
-    public static String getMessage(String username, String password) {
-        final String message = '\u0000' + username + '\u0000' + password;
-        return Base64.encodeToString(message.getBytes(Charset.defaultCharset()), Base64.NO_WRAP);
-    }
 }
diff --git a/src/main/java/eu/siacs/conversations/crypto/sasl/SaslMechanism.java b/src/main/java/eu/siacs/conversations/crypto/sasl/SaslMechanism.java
index b255b6f42..ce2d5cd6a 100644
--- a/src/main/java/eu/siacs/conversations/crypto/sasl/SaslMechanism.java
+++ b/src/main/java/eu/siacs/conversations/crypto/sasl/SaslMechanism.java
@@ -2,18 +2,38 @@ package eu.siacs.conversations.crypto.sasl;
 
 import com.google.common.base.Strings;
 
-import java.security.SecureRandom;
+import java.util.Collection;
 
 import eu.siacs.conversations.entities.Account;
 import eu.siacs.conversations.xml.Element;
 import eu.siacs.conversations.xml.Namespace;
-import eu.siacs.conversations.xml.TagWriter;
 
 public abstract class SaslMechanism {
 
-    final protected TagWriter tagWriter;
-    final protected Account account;
-    final protected SecureRandom rng;
+    protected final Account account;
+
+    protected SaslMechanism(final Account account) {
+        this.account = account;
+    }
+
+    /**
+     * The priority is used to pin the authentication mechanism. If authentication fails, it MAY be
+     * retried with another mechanism of the same priority, but MUST NOT be tried with a mechanism
+     * of lower priority (to prevent downgrade attacks).
+     *
+     * @return An arbitrary int representing the priority
+     */
+    public abstract int getPriority();
+
+    public abstract String getMechanism();
+
+    public String getClientFirstMessage() {
+        return "";
+    }
+
+    public String getResponse(final String challenge) throws AuthenticationException {
+        return "";
+    }
 
     protected enum State {
         INITIAL,
@@ -22,6 +42,22 @@ public abstract class SaslMechanism {
         VALID_SERVER_RESPONSE,
     }
 
+    public enum Version {
+        SASL,
+        SASL_2;
+
+        public static Version of(final Element element) {
+            switch (Strings.nullToEmpty(element.getNamespace())) {
+                case Namespace.SASL:
+                    return SASL;
+                case Namespace.SASL_2:
+                    return SASL_2;
+                default:
+                    throw new IllegalArgumentException("Unrecognized SASL namespace");
+            }
+        }
+    }
+
     public static class AuthenticationException extends Exception {
         public AuthenticationException(final String message) {
             super(message);
@@ -46,42 +82,32 @@ public abstract class SaslMechanism {
         }
     }
 
-    public SaslMechanism(final TagWriter tagWriter, final Account account, final SecureRandom rng) {
-        this.tagWriter = tagWriter;
-        this.account = account;
-        this.rng = rng;
-    }
+    public static final class Factory {
 
-    /**
-     * The priority is used to pin the authentication mechanism. If authentication fails, it MAY be retried with another
-     * mechanism of the same priority, but MUST NOT be tried with a mechanism of lower priority (to prevent downgrade
-     * attacks).
-     *
-     * @return An arbitrary int representing the priority
-     */
-    public abstract int getPriority();
-
-    public abstract String getMechanism();
+        private final Account account;
 
-    public String getClientFirstMessage() {
-        return "";
-    }
-
-    public String getResponse(final String challenge) throws AuthenticationException {
-        return "";
-    }
-
-    public enum Version {
-        SASL, SASL_2;
+        public Factory(final Account account) {
+            this.account = account;
+        }
 
-        public static Version of(final Element element) {
-            switch ( Strings.nullToEmpty(element.getNamespace())) {
-                case Namespace.SASL:
-                    return SASL;
-                case Namespace.SASL_2:
-                    return SASL_2;
-                default:
-                    throw new IllegalArgumentException("Unrecognized SASL namespace");
+        public SaslMechanism of(final Collection<String> mechanisms) {
+            if (mechanisms.contains(External.MECHANISM) && account.getPrivateKeyAlias() != null) {
+                return new External(account);
+            } else if (mechanisms.contains(ScramSha512.MECHANISM)) {
+                return new ScramSha512(account);
+            } else if (mechanisms.contains(ScramSha256.MECHANISM)) {
+                return new ScramSha256(account);
+            } else if (mechanisms.contains(ScramSha1.MECHANISM)) {
+                return new ScramSha1(account);
+            } else if (mechanisms.contains(Plain.MECHANISM)
+                    && !account.getServer().equals("nimbuzz.com")) {
+                return new Plain(account);
+            } else if (mechanisms.contains(DigestMd5.MECHANISM)) {
+                return new DigestMd5(account);
+            } else if (mechanisms.contains(Anonymous.MECHANISM)) {
+                return new Anonymous(account);
+            } else {
+                return null;
             }
         }
     }
diff --git a/src/main/java/eu/siacs/conversations/crypto/sasl/ScramMechanism.java b/src/main/java/eu/siacs/conversations/crypto/sasl/ScramMechanism.java
index 807056bf8..0fe7434a8 100644
--- a/src/main/java/eu/siacs/conversations/crypto/sasl/ScramMechanism.java
+++ b/src/main/java/eu/siacs/conversations/crypto/sasl/ScramMechanism.java
@@ -12,78 +12,53 @@ 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;
-import eu.siacs.conversations.xml.TagWriter;
 
 abstract class ScramMechanism extends SaslMechanism {
-    // TODO: When channel binding (SCRAM-SHA1-PLUS) is supported in future, generalize this to indicate support and/or usage.
-    private final static String GS2_HEADER = "n,,";
+    // TODO: When channel binding (SCRAM-SHA1-PLUS) is supported in future, generalize this to
+    // indicate support and/or usage.
+    private static final String GS2_HEADER = "n,,";
     private static final byte[] CLIENT_KEY_BYTES = "Client Key".getBytes();
     private static final byte[] SERVER_KEY_BYTES = "Server Key".getBytes();
-
-    protected abstract HMac getHMAC();
-
-    protected abstract Digest getDigest();
-
-    private static final Cache<CacheKey, KeyPair> CACHE = CacheBuilder.newBuilder().maximumSize(10).build();
-
-    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);
-        });
-    }
-
+    private static final Cache<CacheKey, KeyPair> CACHE =
+            CacheBuilder.newBuilder().maximumSize(10).build();
     private final String clientNonce;
     protected State state = State.INITIAL;
     private String clientFirstMessageBare;
     private byte[] serverSignature = null;
 
-    ScramMechanism(final TagWriter tagWriter, final Account account, final SecureRandom rng) {
-        super(tagWriter, account, rng);
+    ScramMechanism(final Account account) {
+        super(account);
 
         // This nonce should be different for each authentication attempt.
-        clientNonce = CryptoHelper.random(100, rng);
+        this.clientNonce = CryptoHelper.random(100);
         clientFirstMessageBare = "";
     }
 
+    protected abstract HMac getHMAC();
+
+    protected abstract Digest getDigest();
+
+    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);
+                });
+    }
+
     private byte[] hmac(final byte[] key, final byte[] input) throws InvalidKeyException {
         final HMac hMac = getHMAC();
         hMac.init(new KeyParameter(key));
@@ -123,8 +98,11 @@ abstract class ScramMechanism extends SaslMechanism {
     @Override
     public String getClientFirstMessage() {
         if (clientFirstMessageBare.isEmpty() && state == State.INITIAL) {
-            clientFirstMessageBare = "n=" + CryptoHelper.saslEscape(CryptoHelper.saslPrep(account.getUsername())) +
-                    ",r=" + this.clientNonce;
+            clientFirstMessageBare =
+                    "n="
+                            + CryptoHelper.saslEscape(CryptoHelper.saslPrep(account.getUsername()))
+                            + ",r="
+                            + this.clientNonce;
             state = State.AUTH_TEXT_SENT;
         }
         return Base64.encodeToString(
@@ -173,7 +151,8 @@ abstract class ScramMechanism extends SaslMechanism {
                                  * MUST cause authentication failure when the attribute is parsed by
                                  * the other end.
                                  */
-                                throw new AuthenticationException("Server sent reserved token: `m'");
+                                throw new AuthenticationException(
+                                        "Server sent reserved token: `m'");
                         }
                     }
                 }
@@ -182,20 +161,33 @@ abstract class ScramMechanism extends SaslMechanism {
                     throw new AuthenticationException("Server did not send iteration count");
                 }
                 if (nonce.isEmpty() || !nonce.startsWith(clientNonce)) {
-                    throw new AuthenticationException("Server nonce does not contain client nonce: " + nonce);
+                    throw new AuthenticationException(
+                            "Server nonce does not contain client nonce: " + nonce);
                 }
                 if (salt.isEmpty()) {
                     throw new AuthenticationException("Server sent empty salt");
                 }
 
-                final String clientFinalMessageWithoutProof = "c=" + Base64.encodeToString(
-                        GS2_HEADER.getBytes(), Base64.NO_WRAP) + ",r=" + nonce;
-                final byte[] authMessage = (clientFirstMessageBare + ',' + new String(serverFirstMessage) + ','
-                        + clientFinalMessageWithoutProof).getBytes();
+                final String clientFinalMessageWithoutProof =
+                        "c="
+                                + Base64.encodeToString(GS2_HEADER.getBytes(), Base64.NO_WRAP)
+                                + ",r="
+                                + nonce;
+                final byte[] authMessage =
+                        (clientFirstMessageBare
+                                        + ','
+                                        + new String(serverFirstMessage)
+                                        + ','
+                                        + clientFinalMessageWithoutProof)
+                                .getBytes();
 
                 final KeyPair keys;
                 try {
-                    keys = getKeyPair(CryptoHelper.saslPrep(account.getPassword()), salt, iterationCount);
+                    keys =
+                            getKeyPair(
+                                    CryptoHelper.saslPrep(account.getPassword()),
+                                    salt,
+                                    iterationCount);
                 } catch (ExecutionException e) {
                     throw new AuthenticationException("Invalid keys generated");
                 }
@@ -213,35 +205,69 @@ abstract class ScramMechanism extends SaslMechanism {
                 final byte[] clientProof = new byte[keys.clientKey.length];
 
                 if (clientSignature.length < keys.clientKey.length) {
-                    throw new AuthenticationException("client signature was shorter than clientKey");
+                    throw new AuthenticationException(
+                            "client signature was shorter than clientKey");
                 }
 
                 for (int i = 0; i < clientProof.length; i++) {
                     clientProof[i] = (byte) (keys.clientKey[i] ^ clientSignature[i]);
                 }
 
-
-                final String clientFinalMessage = clientFinalMessageWithoutProof + ",p=" +
-                        Base64.encodeToString(clientProof, Base64.NO_WRAP);
+                final String clientFinalMessage =
+                        clientFinalMessageWithoutProof
+                                + ",p="
+                                + Base64.encodeToString(clientProof, Base64.NO_WRAP);
                 state = State.RESPONSE_SENT;
                 return Base64.encodeToString(clientFinalMessage.getBytes(), Base64.NO_WRAP);
             case RESPONSE_SENT:
                 try {
-                    final String clientCalculatedServerFinalMessage = "v=" +
-                            Base64.encodeToString(serverSignature, Base64.NO_WRAP);
-                    if (!clientCalculatedServerFinalMessage.equals(new String(Base64.decode(challenge, Base64.DEFAULT)))) {
+                    final String clientCalculatedServerFinalMessage =
+                            "v=" + Base64.encodeToString(serverSignature, Base64.NO_WRAP);
+                    if (!clientCalculatedServerFinalMessage.equals(
+                            new String(Base64.decode(challenge, Base64.DEFAULT)))) {
                         throw new Exception();
                     }
                     state = State.VALID_SERVER_RESPONSE;
                     return "";
                 } catch (Exception e) {
-                    throw new AuthenticationException("Server final message does not match calculated final message");
+                    throw new AuthenticationException(
+                            "Server final message does not match calculated final message");
                 }
             default:
                 throw new InvalidStateException(state);
         }
     }
 
+    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 static class KeyPair {
         final byte[] clientKey;
         final byte[] serverKey;
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 c58dd147c..472c4dea1 100644
--- a/src/main/java/eu/siacs/conversations/crypto/sasl/ScramSha1.java
+++ b/src/main/java/eu/siacs/conversations/crypto/sasl/ScramSha1.java
@@ -4,15 +4,16 @@ import org.bouncycastle.crypto.Digest;
 import org.bouncycastle.crypto.digests.SHA1Digest;
 import org.bouncycastle.crypto.macs.HMac;
 
-import java.security.SecureRandom;
-
 import eu.siacs.conversations.entities.Account;
-import eu.siacs.conversations.xml.TagWriter;
 
 public class ScramSha1 extends ScramMechanism {
 
     public static final String MECHANISM = "SCRAM-SHA-1";
 
+    public ScramSha1(final Account account) {
+        super(account);
+    }
+
     @Override
     protected HMac getHMAC() {
         return new HMac(new SHA1Digest());
@@ -23,10 +24,6 @@ public class ScramSha1 extends ScramMechanism {
         return new SHA1Digest();
     }
 
-    public ScramSha1(final TagWriter tagWriter, final Account account, final SecureRandom rng) {
-        super(tagWriter, account, rng);
-    }
-
     @Override
     public int getPriority() {
         return 20;
diff --git a/src/main/java/eu/siacs/conversations/crypto/sasl/ScramSha256.java b/src/main/java/eu/siacs/conversations/crypto/sasl/ScramSha256.java
index d5dc42b07..f3f6cab57 100644
--- a/src/main/java/eu/siacs/conversations/crypto/sasl/ScramSha256.java
+++ b/src/main/java/eu/siacs/conversations/crypto/sasl/ScramSha256.java
@@ -4,15 +4,16 @@ import org.bouncycastle.crypto.Digest;
 import org.bouncycastle.crypto.digests.SHA256Digest;
 import org.bouncycastle.crypto.macs.HMac;
 
-import java.security.SecureRandom;
-
 import eu.siacs.conversations.entities.Account;
-import eu.siacs.conversations.xml.TagWriter;
 
 public class ScramSha256 extends ScramMechanism {
 
     public static final String MECHANISM = "SCRAM-SHA-256";
 
+    public ScramSha256(final Account account) {
+        super(account);
+    }
+
     @Override
     protected HMac getHMAC() {
         return new HMac(new SHA256Digest());
@@ -23,10 +24,6 @@ public class ScramSha256 extends ScramMechanism {
         return new SHA256Digest();
     }
 
-    public ScramSha256(final TagWriter tagWriter, final Account account, final SecureRandom rng) {
-        super(tagWriter, account, rng);
-    }
-
     @Override
     public int getPriority() {
         return 25;
diff --git a/src/main/java/eu/siacs/conversations/crypto/sasl/ScramSha512.java b/src/main/java/eu/siacs/conversations/crypto/sasl/ScramSha512.java
index dbd30945c..9a2f1a82d 100644
--- a/src/main/java/eu/siacs/conversations/crypto/sasl/ScramSha512.java
+++ b/src/main/java/eu/siacs/conversations/crypto/sasl/ScramSha512.java
@@ -4,15 +4,16 @@ import org.bouncycastle.crypto.Digest;
 import org.bouncycastle.crypto.digests.SHA512Digest;
 import org.bouncycastle.crypto.macs.HMac;
 
-import java.security.SecureRandom;
-
 import eu.siacs.conversations.entities.Account;
-import eu.siacs.conversations.xml.TagWriter;
 
 public class ScramSha512 extends ScramMechanism {
 
     public static final String MECHANISM = "SCRAM-SHA-512";
 
+    public ScramSha512(final Account account) {
+        super(account);
+    }
+
     @Override
     protected HMac getHMAC() {
         return new HMac(new SHA512Digest());
@@ -23,10 +24,6 @@ public class ScramSha512 extends ScramMechanism {
         return new SHA512Digest();
     }
 
-    public ScramSha512(final TagWriter tagWriter, final Account account, final SecureRandom rng) {
-        super(tagWriter, account, rng);
-    }
-
     @Override
     public int getPriority() {
         return 30;
diff --git a/src/main/java/eu/siacs/conversations/crypto/sasl/Tokenizer.java b/src/main/java/eu/siacs/conversations/crypto/sasl/Tokenizer.java
index f9ba24f09..3038fb060 100644
--- a/src/main/java/eu/siacs/conversations/crypto/sasl/Tokenizer.java
+++ b/src/main/java/eu/siacs/conversations/crypto/sasl/Tokenizer.java
@@ -6,9 +6,7 @@ import java.util.Iterator;
 import java.util.List;
 import java.util.NoSuchElementException;
 
-/**
- * A tokenizer for GS2 header strings
- */
+/** A tokenizer for GS2 header strings */
 public final class Tokenizer implements Iterator<String>, Iterable<String> {
     private final List<String> parts;
     private int index;
@@ -50,18 +48,19 @@ public final class Tokenizer implements Iterator<String>, Iterable<String> {
     }
 
     /**
-     * Removes the last object returned by {@code next} from the collection.
-     * This method can only be called once between each call to {@code next}.
+     * Removes the last object returned by {@code next} from the collection. This method can only be
+     * called once between each call to {@code next}.
      *
      * @throws UnsupportedOperationException if removing is not supported by the collection being
-     *                                       iterated.
-     * @throws IllegalStateException         if {@code next} has not been called, or {@code remove} has
-     *                                       already been called after the last call to {@code next}.
+     *     iterated.
+     * @throws IllegalStateException if {@code next} has not been called, or {@code remove} has
+     *     already been called after the last call to {@code next}.
      */
     @Override
     public void remove() {
         if (index <= 0) {
-            throw new IllegalStateException("You can't delete an element before first next() method call");
+            throw new IllegalStateException(
+                    "You can't delete an element before first next() method call");
         }
         parts.remove(--index);
     }
diff --git a/src/main/java/eu/siacs/conversations/http/HttpConnectionManager.java b/src/main/java/eu/siacs/conversations/http/HttpConnectionManager.java
index 566ce1e6a..27f5c3fc7 100644
--- a/src/main/java/eu/siacs/conversations/http/HttpConnectionManager.java
+++ b/src/main/java/eu/siacs/conversations/http/HttpConnectionManager.java
@@ -1,5 +1,7 @@
 package eu.siacs.conversations.http;
 
+import static eu.siacs.conversations.utils.Random.SECURE_RANDOM;
+
 import android.os.Build;
 import android.util.Log;
 
@@ -147,7 +149,7 @@ public class HttpConnectionManager extends AbstractConnectionManager {
             trustManager = mXmppConnectionService.getMemorizingTrustManager().getNonInteractive();
         }
         try {
-            final SSLSocketFactory sf = new TLSSocketFactory(new X509TrustManager[]{trustManager}, mXmppConnectionService.getRNG());
+            final SSLSocketFactory sf = new TLSSocketFactory(new X509TrustManager[]{trustManager}, SECURE_RANDOM);
             builder.sslSocketFactory(sf, trustManager);
             builder.hostnameVerifier(new StrictHostnameVerifier());
         } catch (final KeyManagementException | NoSuchAlgorithmException ignored) {
diff --git a/src/main/java/eu/siacs/conversations/http/HttpUploadConnection.java b/src/main/java/eu/siacs/conversations/http/HttpUploadConnection.java
index 3e478dd0f..e2366dd48 100644
--- a/src/main/java/eu/siacs/conversations/http/HttpUploadConnection.java
+++ b/src/main/java/eu/siacs/conversations/http/HttpUploadConnection.java
@@ -1,5 +1,7 @@
 package eu.siacs.conversations.http;
 
+import static eu.siacs.conversations.utils.Random.SECURE_RANDOM;
+
 import android.util.Log;
 
 import androidx.annotation.NonNull;
@@ -124,7 +126,7 @@ public class HttpUploadConnection implements Transferable, AbstractConnectionMan
                 || message.getEncryption() == Message.ENCRYPTION_AXOLOTL
                 || message.getEncryption() == Message.ENCRYPTION_OTR) {
             this.key = new byte[44];
-            mXmppConnectionService.getRNG().nextBytes(this.key);
+            SECURE_RANDOM.nextBytes(this.key);
             this.file.setKeyAndIv(this.key);
         }
         this.file.setExpectedSize(originalFileSize + (file.getKey() != null ? 16 : 0));
diff --git a/src/main/java/eu/siacs/conversations/services/MessageArchiveService.java b/src/main/java/eu/siacs/conversations/services/MessageArchiveService.java
index 79cad9520..e74af3773 100644
--- a/src/main/java/eu/siacs/conversations/services/MessageArchiveService.java
+++ b/src/main/java/eu/siacs/conversations/services/MessageArchiveService.java
@@ -1,5 +1,7 @@
 package eu.siacs.conversations.services;
 
+import static eu.siacs.conversations.utils.Random.SECURE_RANDOM;
+
 import android.util.Log;
 
 import org.jetbrains.annotations.NotNull;
@@ -502,7 +504,7 @@ public class MessageArchiveService implements OnAdvancedStreamFeaturesLoaded {
                 this.start = start.getTimestamp();
             }
             this.end = end;
-            this.queryId = new BigInteger(50, mXmppConnectionService.getRNG()).toString(32);
+            this.queryId = new BigInteger(50, SECURE_RANDOM).toString(32);
             this.version = version;
         }
 
diff --git a/src/main/java/eu/siacs/conversations/services/XmppConnectionService.java b/src/main/java/eu/siacs/conversations/services/XmppConnectionService.java
index ba2c8514e..586b717ff 100644
--- a/src/main/java/eu/siacs/conversations/services/XmppConnectionService.java
+++ b/src/main/java/eu/siacs/conversations/services/XmppConnectionService.java
@@ -1,6 +1,7 @@
 package eu.siacs.conversations.services;
 
 import static eu.siacs.conversations.utils.Compatibility.s;
+import static eu.siacs.conversations.utils.Random.SECURE_RANDOM;
 
 import android.Manifest;
 import android.annotation.SuppressLint;
@@ -379,7 +380,6 @@ public class XmppConnectionService extends Service {
         }
     };
     private final AtomicLong mLastExpiryRun = new AtomicLong(0);
-    private SecureRandom mRandom;
     private final LruCache<Pair<String, String>, ServiceDiscoveryResult> discoCache = new LruCache<>(20);
     private final OnStatusChanged statusListener = new OnStatusChanged() {
 
@@ -451,7 +451,7 @@ public class XmppConnectionService extends Service {
                     Log.d(Config.LOGTAG, account.getJid().asBareJid() + ": went into offline state during low ping mode. reconnecting now");
                     reconnectAccount(account, true, false);
                 } else {
-                    int timeToReconnect = mRandom.nextInt(10) + 2;
+                    final int timeToReconnect = SECURE_RANDOM.nextInt(10) + 2;
                     scheduleWakeUpCall(timeToReconnect, account.getUuid().hashCode());
                 }
             } else if (account.getStatus() == Account.State.REGISTRATION_SUCCESSFUL) {
@@ -1143,7 +1143,6 @@ public class XmppConnectionService extends Service {
             Log.e(Config.LOGTAG, "unable to initialize security provider", throwable);
         }
         Resolver.init(this);
-        this.mRandom = new SecureRandom();
         updateMemorizingTrustmanager();
         final int maxMemory = (int) (Runtime.getRuntime().maxMemory() / 1024);
         final int cacheSize = maxMemory / 8;
@@ -3269,7 +3268,7 @@ public class XmppConnectionService extends Service {
                     }
                     return false;
                 }
-                final Jid jid = Jid.of(CryptoHelper.pronounceable(getRNG()), server, null);
+                final Jid jid = Jid.of(CryptoHelper.pronounceable(), server, null);
                 final Conversation conversation = findOrCreateConversation(account, jid, true, false, true);
                 joinMuc(conversation, new OnConferenceJoined() {
                     @Override
@@ -4366,10 +4365,6 @@ public class XmppConnectionService extends Service {
         }
     }
 
-    public SecureRandom getRNG() {
-        return this.mRandom;
-    }
-
     public MemorizingTrustManager getMemorizingTrustManager() {
         return this.mMemorizingTrustManager;
     }
diff --git a/src/main/java/eu/siacs/conversations/ui/CreatePublicChannelDialog.java b/src/main/java/eu/siacs/conversations/ui/CreatePublicChannelDialog.java
index 3c23b06eb..8f5e2e6d2 100644
--- a/src/main/java/eu/siacs/conversations/ui/CreatePublicChannelDialog.java
+++ b/src/main/java/eu/siacs/conversations/ui/CreatePublicChannelDialog.java
@@ -43,7 +43,6 @@ public class CreatePublicChannelDialog extends DialogFragment implements OnBacke
     private boolean jidWasModified = false;
     private boolean nameEntered = false;
     private boolean skipTetxWatcher = false;
-    private static final SecureRandom RANDOM = new SecureRandom();
 
     public static CreatePublicChannelDialog newInstance(List<String> accounts) {
         CreatePublicChannelDialog dialog = new CreatePublicChannelDialog();
@@ -158,7 +157,7 @@ public class CreatePublicChannelDialog extends DialogFragment implements OnBacke
             try {
                 return Jid.of(localpart, domain, null).toEscapedString();
             } catch (IllegalArgumentException e) {
-                return Jid.of(CryptoHelper.pronounceable(RANDOM), domain, null).toEscapedString();
+                return Jid.of(CryptoHelper.pronounceable(), domain, null).toEscapedString();
             }
         }
     }
diff --git a/src/main/java/eu/siacs/conversations/utils/CryptoHelper.java b/src/main/java/eu/siacs/conversations/utils/CryptoHelper.java
index a92d48825..85ea2bb86 100644
--- a/src/main/java/eu/siacs/conversations/utils/CryptoHelper.java
+++ b/src/main/java/eu/siacs/conversations/utils/CryptoHelper.java
@@ -1,5 +1,7 @@
 package eu.siacs.conversations.utils;
 
+import static eu.siacs.conversations.utils.Random.SECURE_RANDOM;
+
 import android.os.Bundle;
 import android.util.Base64;
 import android.util.Pair;
@@ -59,12 +61,12 @@ public final class CryptoHelper {
         return builder.toString();
     }
 
-    public static String pronounceable(SecureRandom random) {
-        final int rand = random.nextInt(4);
+    public static String pronounceable() {
+        final int rand = SECURE_RANDOM.nextInt(4);
         char[] output = new char[rand * 2 + (5 - rand)];
-        boolean vowel = random.nextBoolean();
+        boolean vowel = SECURE_RANDOM.nextBoolean();
         for (int i = 0; i < output.length; ++i) {
-            output[i] = vowel ? VOWELS[random.nextInt(VOWELS.length)] : CONSONANTS[random.nextInt(CONSONANTS.length)];
+            output[i] = vowel ? VOWELS[SECURE_RANDOM.nextInt(VOWELS.length)] : CONSONANTS[SECURE_RANDOM.nextInt(CONSONANTS.length)];
             vowel = !vowel;
         }
         return String.valueOf(output);
@@ -117,9 +119,9 @@ public final class CryptoHelper {
         return Normalizer.normalize(s, Normalizer.Form.NFKC);
     }
 
-    public static String random(int length, SecureRandom random) {
+    public static String random(final int length) {
         final byte[] bytes = new byte[length];
-        random.nextBytes(bytes);
+        SECURE_RANDOM.nextBytes(bytes);
         return Base64.encodeToString(bytes, Base64.NO_PADDING | Base64.NO_WRAP | Base64.URL_SAFE);
     }
 
diff --git a/src/main/java/eu/siacs/conversations/utils/Random.java b/src/main/java/eu/siacs/conversations/utils/Random.java
new file mode 100644
index 000000000..792c1fce1
--- /dev/null
+++ b/src/main/java/eu/siacs/conversations/utils/Random.java
@@ -0,0 +1,13 @@
+package eu.siacs.conversations.utils;
+
+import java.security.SecureRandom;
+
+public final class Random {
+
+    public static final SecureRandom SECURE_RANDOM = new SecureRandom();
+
+    private Random() {
+
+    }
+
+}
diff --git a/src/main/java/eu/siacs/conversations/xmpp/XmppConnection.java b/src/main/java/eu/siacs/conversations/xmpp/XmppConnection.java
index 70bc347b3..a1336e22c 100644
--- a/src/main/java/eu/siacs/conversations/xmpp/XmppConnection.java
+++ b/src/main/java/eu/siacs/conversations/xmpp/XmppConnection.java
@@ -1,5 +1,7 @@
 package eu.siacs.conversations.xmpp;
 
+import static eu.siacs.conversations.utils.Random.SECURE_RANDOM;
+
 import android.content.Context;
 import android.graphics.Bitmap;
 import android.graphics.BitmapFactory;
@@ -521,7 +523,7 @@ public class XmppConnection implements Runnable {
                             ? trustManager.getInteractive(domain)
                             : trustManager.getNonInteractive(domain)
                 },
-                mXmppConnectionService.getRNG());
+                SECURE_RANDOM);
         return sc.getSocketFactory();
     }
 
@@ -1216,23 +1218,11 @@ public class XmppConnection implements Runnable {
     }
 
     private void authenticate(final SaslMechanism.Version version) throws IOException {
-        final List<String> mechanisms = extractMechanisms(streamFeatures.findChild("mechanisms"));
-        if (mechanisms.contains(External.MECHANISM) && account.getPrivateKeyAlias() != null) {
-            saslMechanism = new External(tagWriter, account, mXmppConnectionService.getRNG());
-        } else if (mechanisms.contains(ScramSha512.MECHANISM)) {
-            saslMechanism = new ScramSha512(tagWriter, account, mXmppConnectionService.getRNG());
-        } else if (mechanisms.contains(ScramSha256.MECHANISM)) {
-            saslMechanism = new ScramSha256(tagWriter, account, mXmppConnectionService.getRNG());
-        } else if (mechanisms.contains(ScramSha1.MECHANISM)) {
-            saslMechanism = new ScramSha1(tagWriter, account, mXmppConnectionService.getRNG());
-        } else if (mechanisms.contains(Plain.MECHANISM)
-                && !account.getJid().getDomain().toEscapedString().equals("nimbuzz.com")) {
-            saslMechanism = new Plain(tagWriter, account);
-        } else if (mechanisms.contains(DigestMd5.MECHANISM)) {
-            saslMechanism = new DigestMd5(tagWriter, account, mXmppConnectionService.getRNG());
-        } else if (mechanisms.contains(Anonymous.MECHANISM)) {
-            saslMechanism = new Anonymous(tagWriter, account, mXmppConnectionService.getRNG());
-        }
+        final Element element = streamFeatures.findChild("mechanisms");
+        final Collection<String> mechanisms = Collections2.transform(element.getChildren(), c -> c == null ? null : c.getContent());
+        final SaslMechanism.Factory factory = new SaslMechanism.Factory(account);
+        this.saslMechanism = factory.of(mechanisms);
+
         if (saslMechanism == null) {
             Log.d(
                     Config.LOGTAG,
@@ -1317,12 +1307,8 @@ public class XmppConnection implements Runnable {
         return bind;
     }
 
-    private static List<String> extractMechanisms(final Element stream) {
-        final ArrayList<String> mechanisms = new ArrayList<>(stream.getChildren().size());
-        for (final Element child : stream.getChildren()) {
-            mechanisms.add(child.getContent());
-        }
-        return mechanisms;
+    private static Collection<String> extractMechanisms(final Element stream) {
+        return Collections2.transform(stream.getChildren(), c -> c == null ? null : c.getContent());
     }
 
     private void register() {
@@ -1963,8 +1949,8 @@ public class XmppConnection implements Runnable {
         return nextRandomId(false);
     }
 
-    private String nextRandomId(boolean s) {
-        return CryptoHelper.random(s ? 3 : 9, mXmppConnectionService.getRNG());
+    private String nextRandomId(final boolean s) {
+        return CryptoHelper.random(s ? 3 : 9);
     }
 
     public String sendIqPacket(final IqPacket packet, final OnIqPacketReceived callback) {