Merge pull request #101 from wongma7/master

Adding support for password generation

11 files changed, 1031 insertions, 1 deletions

diff --git a/app/src/main/java/com/zeapo/pwdstore/PasswordStore.java b/app/src/main/java/com/zeapo/pwdstore/PasswordStore.java
index a99ec34a..5562f0b9 100644
--- a/app/src/main/java/com/zeapo/pwdstore/PasswordStore.java
+++ b/app/src/main/java/com/zeapo/pwdstore/PasswordStore.java
@@ -20,6 +20,7 @@ import android.view.View;
 import com.zeapo.pwdstore.crypto.PgpHandler;
 import com.zeapo.pwdstore.git.GitActivity;
 import com.zeapo.pwdstore.git.GitAsyncTask;
+import com.zeapo.pwdstore.pwgen.PRNGFixes;
 import com.zeapo.pwdstore.utils.PasswordItem;
 import com.zeapo.pwdstore.utils.PasswordRecyclerAdapter;
 import com.zeapo.pwdstore.utils.PasswordRepository;
@@ -49,6 +50,7 @@ public class PasswordStore extends AppCompatActivity {
         setContentView(R.layout.activity_pwdstore);
         settings = PreferenceManager.getDefaultSharedPreferences(this.getApplicationContext());
         activity = this;
+        PRNGFixes.apply();
     }
 
     @Override
diff --git a/app/src/main/java/com/zeapo/pwdstore/crypto/PgpHandler.java b/app/src/main/java/com/zeapo/pwdstore/crypto/PgpHandler.java
index 28aea81e..9c0bc877 100644
--- a/app/src/main/java/com/zeapo/pwdstore/crypto/PgpHandler.java
+++ b/app/src/main/java/com/zeapo/pwdstore/crypto/PgpHandler.java
@@ -1,6 +1,7 @@
 package com.zeapo.pwdstore.crypto;
 
 import android.app.Activity;
+import android.app.DialogFragment;
 import android.app.PendingIntent;
 import android.content.ClipData;
 import android.content.ClipboardManager;
@@ -28,6 +29,7 @@ import android.widget.Toast;
 import com.google.common.primitives.Longs;
 import com.zeapo.pwdstore.R;
 import com.zeapo.pwdstore.UserPreference;
+import com.zeapo.pwdstore.pwgenDialogFragment;
 import com.zeapo.pwdstore.utils.PasswordRepository;
 
 import org.apache.commons.io.FileUtils;
@@ -174,6 +176,9 @@ public class PgpHandler extends AppCompatActivity implements OpenPgpServiceConne
             case R.id.crypto_get_key_ids:
                 getKeyIds(new Intent());
                 break;
+            case R.id.generate_password:
+                DialogFragment df = new pwgenDialogFragment();
+                df.show(getFragmentManager(), "generator");
             default:
                 // should not happen
 
diff --git a/app/src/main/java/com/zeapo/pwdstore/pwgen/PRNGFixes.java b/app/src/main/java/com/zeapo/pwdstore/pwgen/PRNGFixes.java
new file mode 100644
index 00000000..201e821d
--- /dev/null
+++ b/app/src/main/java/com/zeapo/pwdstore/pwgen/PRNGFixes.java
@@ -0,0 +1,336 @@
+package com.zeapo.pwdstore.pwgen;
+
+/*
+ * This software is provided 'as-is', without any express or implied
+ * warranty.  In no event will Google be held liable for any damages
+ * arising from the use of this software.
+ *
+ * Permission is granted to anyone to use this software for any purpose,
+ * including commercial applications, and to alter it and redistribute it
+ * freely, as long as the origin is not misrepresented.
+ */
+
+import android.os.Build;
+import android.os.Process;
+import android.util.Log;
+
+import java.io.ByteArrayOutputStream;
+import java.io.DataInputStream;
+import java.io.DataOutputStream;
+import java.io.File;
+import java.io.FileInputStream;
+import java.io.FileOutputStream;
+import java.io.IOException;
+import java.io.OutputStream;
+import java.io.UnsupportedEncodingException;
+import java.security.NoSuchAlgorithmException;
+import java.security.Provider;
+import java.security.SecureRandom;
+import java.security.SecureRandomSpi;
+import java.security.Security;
+
+/**
+ * Fixes for the output of the default PRNG having low entropy.
+ *
+ * The fixes need to be applied via {@link #apply()} before any use of Java
+ * Cryptography Architecture primitives. A good place to invoke them is in the
+ * application's {@code onCreate}.
+ */
+public final class PRNGFixes {
+
+    private static final int VERSION_CODE_JELLY_BEAN = 16;
+    private static final int VERSION_CODE_JELLY_BEAN_MR2 = 18;
+    private static final byte[] BUILD_FINGERPRINT_AND_DEVICE_SERIAL =
+            getBuildFingerprintAndDeviceSerial();
+
+    /** Hidden constructor to prevent instantiation. */
+    private PRNGFixes() {}
+
+    /**
+     * Applies all fixes.
+     *
+     * @throws SecurityException if a fix is needed but could not be applied.
+     */
+    public static void apply() {
+        applyOpenSSLFix();
+        installLinuxPRNGSecureRandom();
+    }
+
+    /**
+     * Applies the fix for OpenSSL PRNG having low entropy. Does nothing if the
+     * fix is not needed.
+     *
+     * @throws SecurityException if the fix is needed but could not be applied.
+     */
+    private static void applyOpenSSLFix() throws SecurityException {
+        if ((Build.VERSION.SDK_INT < VERSION_CODE_JELLY_BEAN)
+                || (Build.VERSION.SDK_INT > VERSION_CODE_JELLY_BEAN_MR2)) {
+            // No need to apply the fix
+            return;
+        }
+
+        try {
+            // Mix in the device- and invocation-specific seed.
+            Class.forName("org.apache.harmony.xnet.provider.jsse.NativeCrypto")
+                    .getMethod("RAND_seed", byte[].class)
+                    .invoke(null, generateSeed());
+
+            // Mix output of Linux PRNG into OpenSSL's PRNG
+            int bytesRead = (Integer) Class.forName(
+                    "org.apache.harmony.xnet.provider.jsse.NativeCrypto")
+                    .getMethod("RAND_load_file", String.class, long.class)
+                    .invoke(null, "/dev/urandom", 1024);
+            if (bytesRead != 1024) {
+                throw new IOException(
+                        "Unexpected number of bytes read from Linux PRNG: "
+                                + bytesRead);
+            }
+        } catch (Exception e) {
+            throw new SecurityException("Failed to seed OpenSSL PRNG", e);
+        }
+    }
+
+    /**
+     * Installs a Linux PRNG-backed {@code SecureRandom} implementation as the
+     * default. Does nothing if the implementation is already the default or if
+     * there is not need to install the implementation.
+     *
+     * @throws SecurityException if the fix is needed but could not be applied.
+     */
+    private static void installLinuxPRNGSecureRandom()
+            throws SecurityException {
+        if (Build.VERSION.SDK_INT > VERSION_CODE_JELLY_BEAN_MR2) {
+            // No need to apply the fix
+            return;
+        }
+
+        // Install a Linux PRNG-based SecureRandom implementation as the
+        // default, if not yet installed.
+        Provider[] secureRandomProviders =
+                Security.getProviders("SecureRandom.SHA1PRNG");
+        if ((secureRandomProviders == null)
+                || (secureRandomProviders.length < 1)
+                || (!LinuxPRNGSecureRandomProvider.class.equals(
+                secureRandomProviders[0].getClass()))) {
+            Security.insertProviderAt(new LinuxPRNGSecureRandomProvider(), 1);
+        }
+
+        // Assert that new SecureRandom() and
+        // SecureRandom.getInstance("SHA1PRNG") return a SecureRandom backed
+        // by the Linux PRNG-based SecureRandom implementation.
+        SecureRandom rng1 = new SecureRandom();
+        if (!LinuxPRNGSecureRandomProvider.class.equals(
+                rng1.getProvider().getClass())) {
+            throw new SecurityException(
+                    "new SecureRandom() backed by wrong Provider: "
+                            + rng1.getProvider().getClass());
+        }
+
+        SecureRandom rng2;
+        try {
+            rng2 = SecureRandom.getInstance("SHA1PRNG");
+        } catch (NoSuchAlgorithmException e) {
+            throw new SecurityException("SHA1PRNG not available", e);
+        }
+        if (!LinuxPRNGSecureRandomProvider.class.equals(
+                rng2.getProvider().getClass())) {
+            throw new SecurityException(
+                    "SecureRandom.getInstance(\"SHA1PRNG\") backed by wrong"
+                            + " Provider: " + rng2.getProvider().getClass());
+        }
+    }
+
+    /**
+     * {@code Provider} of {@code SecureRandom} engines which pass through
+     * all requests to the Linux PRNG.
+     */
+    private static class LinuxPRNGSecureRandomProvider extends Provider {
+
+        public LinuxPRNGSecureRandomProvider() {
+            super("LinuxPRNG",
+                    1.0,
+                    "A Linux-specific random number provider that uses"
+                            + " /dev/urandom");
+            // Although /dev/urandom is not a SHA-1 PRNG, some apps
+            // explicitly request a SHA1PRNG SecureRandom and we thus need to
+            // prevent them from getting the default implementation whose output
+            // may have low entropy.
+            put("SecureRandom.SHA1PRNG", LinuxPRNGSecureRandom.class.getName());
+            put("SecureRandom.SHA1PRNG ImplementedIn", "Software");
+        }
+    }
+
+    /**
+     * {@link SecureRandomSpi} which passes all requests to the Linux PRNG
+     * ({@code /dev/urandom}).
+     */
+    public static class LinuxPRNGSecureRandom extends SecureRandomSpi {
+
+        /*
+         * IMPLEMENTATION NOTE: Requests to generate bytes and to mix in a seed
+         * are passed through to the Linux PRNG (/dev/urandom). Instances of
+         * this class seed themselves by mixing in the current time, PID, UID,
+         * build fingerprint, and hardware serial number (where available) into
+         * Linux PRNG.
+         *
+         * Concurrency: Read requests to the underlying Linux PRNG are
+         * serialized (on sLock) to ensure that multiple threads do not get
+         * duplicated PRNG output.
+         */
+
+        private static final File URANDOM_FILE = new File("/dev/urandom");
+
+        private static final Object sLock = new Object();
+
+        /**
+         * Input stream for reading from Linux PRNG or {@code null} if not yet
+         * opened.
+         *
+         * @GuardedBy("sLock")
+         */
+        private static DataInputStream sUrandomIn;
+
+        /**
+         * Output stream for writing to Linux PRNG or {@code null} if not yet
+         * opened.
+         *
+         * @GuardedBy("sLock")
+         */
+        private static OutputStream sUrandomOut;
+
+        /**
+         * Whether this engine instance has been seeded. This is needed because
+         * each instance needs to seed itself if the client does not explicitly
+         * seed it.
+         */
+        private boolean mSeeded;
+
+        @Override
+        protected void engineSetSeed(byte[] bytes) {
+            try {
+                OutputStream out;
+                synchronized (sLock) {
+                    out = getUrandomOutputStream();
+                }
+                out.write(bytes);
+                out.flush();
+            } catch (IOException e) {
+                // On a small fraction of devices /dev/urandom is not writable.
+                // Log and ignore.
+                Log.w(PRNGFixes.class.getSimpleName(),
+                        "Failed to mix seed into " + URANDOM_FILE);
+            } finally {
+                mSeeded = true;
+            }
+        }
+
+        @Override
+        protected void engineNextBytes(byte[] bytes) {
+            if (!mSeeded) {
+                // Mix in the device- and invocation-specific seed.
+                engineSetSeed(generateSeed());
+            }
+
+            try {
+                DataInputStream in;
+                synchronized (sLock) {
+                    in = getUrandomInputStream();
+                }
+                synchronized (in) {
+                    in.readFully(bytes);
+                }
+            } catch (IOException e) {
+                throw new SecurityException(
+                        "Failed to read from " + URANDOM_FILE, e);
+            }
+        }
+
+        @Override
+        protected byte[] engineGenerateSeed(int size) {
+            byte[] seed = new byte[size];
+            engineNextBytes(seed);
+            return seed;
+        }
+
+        private DataInputStream getUrandomInputStream() {
+            synchronized (sLock) {
+                if (sUrandomIn == null) {
+                    // NOTE: Consider inserting a BufferedInputStream between
+                    // DataInputStream and FileInputStream if you need higher
+                    // PRNG output performance and can live with future PRNG
+                    // output being pulled into this process prematurely.
+                    try {
+                        sUrandomIn = new DataInputStream(
+                                new FileInputStream(URANDOM_FILE));
+                    } catch (IOException e) {
+                        throw new SecurityException("Failed to open "
+                                + URANDOM_FILE + " for reading", e);
+                    }
+                }
+                return sUrandomIn;
+            }
+        }
+
+        private OutputStream getUrandomOutputStream() throws IOException {
+            synchronized (sLock) {
+                if (sUrandomOut == null) {
+                    sUrandomOut = new FileOutputStream(URANDOM_FILE);
+                }
+                return sUrandomOut;
+            }
+        }
+    }
+
+    /**
+     * Generates a device- and invocation-specific seed to be mixed into the
+     * Linux PRNG.
+     */
+    private static byte[] generateSeed() {
+        try {
+            ByteArrayOutputStream seedBuffer = new ByteArrayOutputStream();
+            DataOutputStream seedBufferOut =
+                    new DataOutputStream(seedBuffer);
+            seedBufferOut.writeLong(System.currentTimeMillis());
+            seedBufferOut.writeLong(System.nanoTime());
+            seedBufferOut.writeInt(Process.myPid());
+            seedBufferOut.writeInt(Process.myUid());
+            seedBufferOut.write(BUILD_FINGERPRINT_AND_DEVICE_SERIAL);
+            seedBufferOut.close();
+            return seedBuffer.toByteArray();
+        } catch (IOException e) {
+            throw new SecurityException("Failed to generate seed", e);
+        }
+    }
+
+    /**
+     * Gets the hardware serial number of this device.
+     *
+     * @return serial number or {@code null} if not available.
+     */
+    private static String getDeviceSerialNumber() {
+        // We're using the Reflection API because Build.SERIAL is only available
+        // since API Level 9 (Gingerbread, Android 2.3).
+        try {
+            return (String) Build.class.getField("SERIAL").get(null);
+        } catch (Exception ignored) {
+            return null;
+        }
+    }
+
+    private static byte[] getBuildFingerprintAndDeviceSerial() {
+        StringBuilder result = new StringBuilder();
+        String fingerprint = Build.FINGERPRINT;
+        if (fingerprint != null) {
+            result.append(fingerprint);
+        }
+        String serial = getDeviceSerialNumber();
+        if (serial != null) {
+            result.append(serial);
+        }
+        try {
+            return result.toString().getBytes("UTF-8");
+        } catch (UnsupportedEncodingException e) {
+            throw new RuntimeException("UTF-8 encoding not supported");
+        }
+    }
+}
\ No newline at end of file
diff --git a/app/src/main/java/com/zeapo/pwdstore/pwgen/pw_phonemes.java b/app/src/main/java/com/zeapo/pwdstore/pwgen/pw_phonemes.java
new file mode 100644
index 00000000..1b312232
--- /dev/null
+++ b/app/src/main/java/com/zeapo/pwdstore/pwgen/pw_phonemes.java
@@ -0,0 +1,206 @@
+package com.zeapo.pwdstore.pwgen;
+
+public class pw_phonemes {
+    private static final int CONSONANT  = 0x0001;
+    private static final int VOWEL      = 0x0002;
+    private static final int DIPTHONG   = 0x0004;
+    private static final int NOT_FIRST  = 0x0008;
+
+    private static final element elements[] = {
+            new element("a", VOWEL),
+            new element("ae", VOWEL | DIPTHONG),
+            new element("ah", VOWEL | DIPTHONG),
+            new element("ai", VOWEL | DIPTHONG),
+            new element("b",  CONSONANT),
+            new element("c", CONSONANT),
+            new element("ch", CONSONANT | DIPTHONG),
+            new element("d", CONSONANT),
+            new element("e", VOWEL),
+            new element("ee", VOWEL | DIPTHONG),
+            new element("ei", VOWEL | DIPTHONG),
+            new element("f", CONSONANT),
+            new element("g", CONSONANT),
+            new element("gh", CONSONANT | DIPTHONG | NOT_FIRST),
+            new element("h", CONSONANT),
+            new element("i", VOWEL),
+            new element("ie", VOWEL | DIPTHONG),
+            new element("j", CONSONANT),
+            new element("k", CONSONANT),
+            new element("l", CONSONANT),
+            new element("m", CONSONANT),
+            new element("n", CONSONANT),
+            new element("ng", CONSONANT | DIPTHONG | NOT_FIRST),
+            new element("o", VOWEL),
+            new element("oh", VOWEL | DIPTHONG),
+            new element("oo", VOWEL | DIPTHONG),
+            new element("p", CONSONANT),
+            new element("ph", CONSONANT | DIPTHONG),
+            new element("qu", CONSONANT | DIPTHONG),
+            new element("r", CONSONANT),
+            new element("s", CONSONANT),
+            new element("sh", CONSONANT | DIPTHONG),
+            new element("t", CONSONANT),
+            new element("th", CONSONANT | DIPTHONG),
+            new element("u", VOWEL),
+            new element("v", CONSONANT),
+            new element("w", CONSONANT),
+            new element("x", CONSONANT),
+            new element("y", CONSONANT),
+            new element("z", CONSONANT)
+    };
+
+    private static class element {
+        String str;
+        int flags;
+        element(String str, int flags) {
+            this.str = str;
+            this.flags = flags;
+        }
+    }
+
+    private static final int NUM_ELEMENTS = elements.length;
+
+    /**
+     * Generates a human-readable password.
+     *
+     * @param size    length of password to generate
+     * @param pwFlags flag field where set bits indicate conditions the
+     *                generated password must meet
+     *                <table summary="bits of flag field">
+     *                <tr><td>Bit</td><td>Condition</td></tr>
+     *                <tr><td>0</td><td>include at least one number</td></tr>
+     *                <tr><td>1</td><td>include at least one uppercase letter</td></tr>
+     *                <tr><td>2</td><td>include at least one symbol</td></tr>
+     *                <tr><td>3</td><td>don't include ambiguous characters</td></tr>
+     *                </table>
+     * @return the generated password
+     */
+    public static String phonemes(int size, int pwFlags) {
+        String password;
+        int curSize, i, length, flags, featureFlags, prev, shouldBe;
+        boolean first;
+        String str;
+        char cha;
+
+        do {
+            password = "";
+            featureFlags = pwFlags;
+            curSize = 0;
+            prev = 0;
+            first = true;
+
+            shouldBe = randnum.number(2) == 1 ? VOWEL : CONSONANT;
+
+            while (curSize < size) {
+                i = randnum.number(NUM_ELEMENTS);
+                str = elements[i].str;
+                length = str.length();
+                flags = elements[i].flags;
+                // Filter on the basic type of the next element
+                if ((flags & shouldBe) == 0) {
+                    continue;
+                }
+                // Handle the NOT_FIRST flag
+                if (first && (flags & NOT_FIRST) > 0) {
+                    continue;
+                }
+                // Don't allow VOWEL followed a Vowel/Dipthong pair
+                if ((prev & VOWEL) > 0 && (flags & VOWEL) > 0
+                        && (flags & DIPTHONG) > 0) {
+                    continue;
+                }
+                // Don't allow us to overflow the buffer
+                if (length > size - curSize) {
+                    continue;
+                }
+                // OK, we found an element which matches our criteria, let's do
+                // it
+                password += str;
+
+                // Handle UPPERS
+                if ((pwFlags & pwgen.UPPERS) > 0) {
+                    if ((first || (flags & CONSONANT) > 0)
+                            && (randnum.number(10) < 2)) {
+                        int index = password.length() - length;
+                        password = password.substring(0, index)
+                                + str.toUpperCase();
+                        featureFlags &= ~pwgen.UPPERS;
+                    }
+                }
+
+                // Handle the AMBIGUOUS flag
+                if ((pwFlags & pwgen.AMBIGUOUS) > 0) {
+                    for (char ambiguous : pwgen.AMBIGUOUS_STR.toCharArray()) {
+                        if (password.contains(String.valueOf(ambiguous))) {
+                            password = password.substring(0, curSize);
+                            break;
+                        }
+                    }
+                    if (password.length() == curSize)
+                        continue;
+                }
+
+                curSize += length;
+
+                // Time to stop?
+                if (curSize >= size)
+                    break;
+
+                // Handle DIGITS
+                if ((pwFlags & pwgen.DIGITS) > 0) {
+                    if (!first && (randnum.number(10) < 3)) {
+                        String val;
+                        do {
+                            cha = Character.forDigit(randnum.number(10), 10);
+                            val = String.valueOf(cha);
+                        } while ((pwFlags & pwgen.AMBIGUOUS) > 0
+                                && pwgen.AMBIGUOUS_STR.contains(val));
+                        password += val;
+                        curSize++;
+
+                        featureFlags &= ~pwgen.DIGITS;
+
+                        first = true;
+                        prev = 0;
+                        shouldBe = randnum.number(2) == 1 ? VOWEL : CONSONANT;
+                        continue;
+                    }
+                }
+
+                // Handle SYMBOLS
+                if ((pwFlags & pwgen.SYMBOLS) > 0) {
+                    if (!first && (randnum.number(10) < 2)) {
+                        String val;
+                        int num;
+                        do {
+                            num = randnum.number(pwgen.SYMBOLS_STR.length());
+                            cha = pwgen.SYMBOLS_STR.toCharArray()[num];
+                            val = String.valueOf(cha);
+                        } while ((pwFlags & pwgen.AMBIGUOUS) > 0
+                                && pwgen.AMBIGUOUS_STR.contains(val));
+                        password += val;
+                        curSize++;
+
+                        featureFlags &= ~pwgen.SYMBOLS;
+                    }
+                }
+
+                // OK, figure out what the next element should be
+                if (shouldBe == CONSONANT) {
+                    shouldBe = VOWEL;
+                } else {
+                    if ((prev & VOWEL) > 0 || (flags & DIPTHONG) > 0
+                            || (randnum.number(10) > 3)) {
+                        shouldBe = CONSONANT;
+                    } else {
+                        shouldBe = VOWEL;
+                    }
+                }
+                prev = flags;
+                first = false;
+            }
+        } while ((featureFlags & (pwgen.UPPERS | pwgen.DIGITS | pwgen.SYMBOLS))
+                > 0);
+        return password;
+    }
+}
diff --git a/app/src/main/java/com/zeapo/pwdstore/pwgen/pw_rand.java b/app/src/main/java/com/zeapo/pwdstore/pwgen/pw_rand.java
new file mode 100644
index 00000000..1f4acdec
--- /dev/null
+++ b/app/src/main/java/com/zeapo/pwdstore/pwgen/pw_rand.java
@@ -0,0 +1,69 @@
+package com.zeapo.pwdstore.pwgen;
+
+public class pw_rand {
+
+    /**
+     * Generates a completely random password.
+     *
+     * @param size    length of password to generate
+     * @param pwFlags flag field where set bits indicate conditions the
+     *                generated password must meet
+     *                <table summary ="bits of flag field">
+     *                <tr><td>Bit</td><td>Condition</td></tr>
+     *                <tr><td>0</td><td>include at least one number</td></tr>
+     *                <tr><td>1</td><td>include at least one uppercase letter</td></tr>
+     *                <tr><td>2</td><td>include at least one symbol</td></tr>
+     *                <tr><td>3</td><td>don't include ambiguous characters</td></tr>
+     *                <tr><td>4</td><td>don't include vowels</td></tr>
+     *                </table>
+     * @return the generated password
+     */
+    public static String rand(int size, int pwFlags) {
+        String password = "";
+        char cha;
+        int i, featureFlags, num;
+        String val;
+
+        String bank = "";
+        if ((pwFlags & pwgen.DIGITS) > 0) {
+            bank += pwgen.DIGITS_STR;
+        }
+        if ((pwFlags & pwgen.UPPERS) > 0) {
+            bank += pwgen.UPPERS_STR;
+        }
+        bank += pwgen.LOWERS_STR;
+        if ((pwFlags & pwgen.SYMBOLS) > 0) {
+            bank += pwgen.SYMBOLS_STR;
+        }
+        do {
+            featureFlags = pwFlags;
+            i = 0;
+            while (i < size) {
+                num = randnum.number(bank.length());
+                cha = bank.toCharArray()[num];
+                val = String.valueOf(cha);
+                if ((pwFlags & pwgen.AMBIGUOUS) > 0
+                        && pwgen.AMBIGUOUS_STR.contains(val)) {
+                    continue;
+                }
+                if ((pwFlags & pwgen.NO_VOWELS) > 0
+                        && pwgen.VOWELS_STR.contains(val)) {
+                    continue;
+                }
+                password += val;
+                i++;
+                if (pwgen.DIGITS_STR.contains(val)) {
+                    featureFlags &= ~pwgen.DIGITS;
+                }
+                if (pwgen.UPPERS_STR.contains(val)) {
+                    featureFlags &= ~pwgen.UPPERS;
+                }
+                if (pwgen.SYMBOLS_STR.contains(val)) {
+                    featureFlags &= ~pwgen.SYMBOLS;
+                }
+            }
+        } while ((featureFlags & (pwgen.UPPERS | pwgen.DIGITS | pwgen.SYMBOLS))
+                > 0);
+        return password;
+    }
+}
diff --git a/app/src/main/java/com/zeapo/pwdstore/pwgen/pwgen.java b/app/src/main/java/com/zeapo/pwdstore/pwgen/pwgen.java
new file mode 100644
index 00000000..e08573f0
--- /dev/null
+++ b/app/src/main/java/com/zeapo/pwdstore/pwgen/pwgen.java
@@ -0,0 +1,138 @@
+package com.zeapo.pwdstore.pwgen;
+
+import android.content.Context;
+import android.content.SharedPreferences;
+
+import java.util.ArrayList;
+
+public class pwgen {
+    static final int DIGITS     = 0x0001;
+    static final int UPPERS     = 0x0002;
+    static final int SYMBOLS    = 0x0004;
+    static final int AMBIGUOUS  = 0x0008;
+    static final int NO_VOWELS  = 0x0010;
+
+    static final String DIGITS_STR = "0123456789";
+    static final String UPPERS_STR = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
+    static final String LOWERS_STR = "abcdefghijklmnopqrstuvwxyz";
+    static final String SYMBOLS_STR = "!\"#$%&'()*+,-./:;<=>?@[\\]^_`{|}~";
+    static final String AMBIGUOUS_STR = "B8G6I1l0OQDS5Z2";
+    static final String VOWELS_STR = "01aeiouyAEIOUY";
+
+    // No a, c, n, h, H, C, 1, N
+    private static final String pwOptions = "0ABsvy";
+
+    /**
+     * Sets password generation preferences.
+     *
+     * @param ctx     context from which to retrieve SharedPreferences from
+     *                preferences file 'pwgen'
+     * @param argv    options for password generation
+     *                <table summary="options for password generation">
+     *                <tr><td>Option</td><td>Description</td></tr>
+     *                <tr><td>0</td><td>don't include numbers</td></tr>
+     *                <tr><td>A</td><td>don't include uppercase letters</td></tr>
+     *                <tr><td>B</td><td>don't include ambiguous charactersl</td></tr>
+     *                <tr><td>s</td><td>generate completely random passwords</td></tr>
+     *                <tr><td>v</td><td>don't include vowels</td></tr>
+     *                <tr><td>y</td><td>include at least one symbol</td></tr>
+     *                </table>
+     * @param numArgv numerical options for password generation: length of
+     *                generated passwords followed by number of passwords to
+     *                generate
+     * @return <code>false</code> if a numerical options is invalid,
+     * <code>true</code> otherwise
+     */
+    public static boolean setPrefs(Context ctx, ArrayList<String> argv
+            , int... numArgv) {
+        SharedPreferences prefs
+                = ctx.getSharedPreferences("pwgen", Context.MODE_PRIVATE);
+        SharedPreferences.Editor editor = prefs.edit();
+
+        for (char option : pwOptions.toCharArray()) {
+            if (argv.contains(String.valueOf(option))) {
+                editor.putBoolean(String.valueOf(option), true);
+                argv.remove(String.valueOf(option));
+            } else {
+                editor.putBoolean(String.valueOf(option), false);
+            }
+        }
+        for (int i = 0; i < numArgv.length && i < 2; i++) {
+            if (numArgv[i] <= 0) {
+                // Invalid password length or number of passwords
+                return false;
+            }
+            String name = i == 0 ? "length" : "num";
+            editor.putInt(name, numArgv[i]);
+        }
+        editor.apply();
+        return true;
+    }
+
+    /**
+     * Generates passwords using the preferences set by
+     * {@link #setPrefs(Context, ArrayList, int...)}.
+     *
+     * @param ctx context from which to retrieve SharedPreferences from
+     *            preferences file 'pwgen'
+     * @return list of generated passwords
+     */
+    public static ArrayList<String> generate(Context ctx) {
+        SharedPreferences prefs
+                = ctx.getSharedPreferences("pwgen", Context.MODE_PRIVATE);
+
+        boolean phonemes = true;
+        int pwgenFlags = DIGITS | UPPERS;
+
+        for (char option : pwOptions.toCharArray()) {
+            if (prefs.getBoolean(String.valueOf(option), false)) {
+                switch(option) {
+                    case '0':
+                        pwgenFlags &= ~DIGITS;
+                        break;
+                    case 'A':
+                        pwgenFlags &= ~UPPERS;
+                        break;
+                    case 'B':
+                        pwgenFlags |= AMBIGUOUS;
+                        break;
+                    case 's':
+                        phonemes = false;
+                        // pwgenFlags = DIGITS | UPPERS;
+                        break;
+                    case 'y':
+                        pwgenFlags |= SYMBOLS;
+                        break;
+                    case 'v':
+                        phonemes = false;
+                        pwgenFlags |= NO_VOWELS; // | DIGITS | UPPERS;
+                        break;
+                }
+            }
+        }
+
+        int length = prefs.getInt("length", 8);
+        if (length < 5) {
+            phonemes = false;
+        }
+        if (length <= 2) {
+            pwgenFlags &= ~UPPERS;
+        }
+        if (length <= 1) {
+            pwgenFlags &= ~DIGITS;
+        }
+
+        ArrayList<String> passwords = new ArrayList<>();
+        int num = prefs.getInt("num", 1);
+        for (int i = 0; i < num; i++) {
+            if (phonemes) {
+                passwords.add(pw_phonemes.phonemes(length, pwgenFlags));
+            } else {
+                passwords.add(pw_rand.rand(length, pwgenFlags));
+            }
+        }
+        return passwords;
+    }
+
+}
+
diff --git a/app/src/main/java/com/zeapo/pwdstore/pwgen/randnum.java b/app/src/main/java/com/zeapo/pwdstore/pwgen/randnum.java
new file mode 100644
index 00000000..83cf4b03
--- /dev/null
+++ b/app/src/main/java/com/zeapo/pwdstore/pwgen/randnum.java
@@ -0,0 +1,26 @@
+package com.zeapo.pwdstore.pwgen;
+
+import java.security.NoSuchAlgorithmException;
+import java.security.SecureRandom;
+
+public class randnum {
+    private static SecureRandom random;
+
+    static {
+        try {
+            random = SecureRandom.getInstance("SHA1PRNG");
+        } catch (NoSuchAlgorithmException e) {
+            throw new SecurityException("SHA1PRNG not available", e);
+        }
+    }
+
+    /**
+     * Generate a random number n, where 0 &lt;= n &lt; maxNum.
+     *
+     * @param maxNum the bound on the random number to be returned
+     * @return the generated random number
+     */
+    public static int number(int maxNum) {
+        return random.nextInt(maxNum);
+    }
+}
diff --git a/app/src/main/java/com/zeapo/pwdstore/pwgenDialogFragment.java b/app/src/main/java/com/zeapo/pwdstore/pwgenDialogFragment.java
new file mode 100644
index 00000000..af905b5d
--- /dev/null
+++ b/app/src/main/java/com/zeapo/pwdstore/pwgenDialogFragment.java
@@ -0,0 +1,124 @@
+package com.zeapo.pwdstore;
+
+import android.app.Dialog;
+import android.app.DialogFragment;
+import android.content.Context;
+import android.content.DialogInterface;
+import android.content.SharedPreferences;
+import android.os.Bundle;
+import android.support.v7.app.AlertDialog;
+import android.view.LayoutInflater;
+import android.view.View;
+import android.widget.Button;
+import android.widget.CheckBox;
+import android.widget.TextView;
+
+import com.zeapo.pwdstore.pwgen.pwgen;
+
+import java.util.ArrayList;
+
+
+/**
+ * A placeholder fragment containing a simple view.
+ */
+public class pwgenDialogFragment extends DialogFragment {
+
+    public pwgenDialogFragment() {
+    }
+
+
+    @Override
+    public Dialog onCreateDialog(Bundle savedInstanceState) {
+        AlertDialog.Builder builder = new AlertDialog.Builder(getActivity());
+        LayoutInflater inflater = getActivity().getLayoutInflater();
+        final View view = inflater.inflate(R.layout.fragment_pwgen, null);
+        builder.setView(view);
+
+        SharedPreferences prefs
+                = getActivity().getApplicationContext().getSharedPreferences("pwgen", Context.MODE_PRIVATE);
+
+        CheckBox checkBox = (CheckBox) view.findViewById(R.id.numerals);
+        checkBox.setChecked(!prefs.getBoolean("0", false));
+
+        checkBox = (CheckBox) view.findViewById(R.id.symbols);
+        checkBox.setChecked(prefs.getBoolean("y", false));
+
+        checkBox = (CheckBox) view.findViewById(R.id.uppercase);
+        checkBox.setChecked(!prefs.getBoolean("A", false));
+
+        checkBox = (CheckBox) view.findViewById(R.id.ambiguous);
+        checkBox.setChecked(!prefs.getBoolean("B", false));
+
+        checkBox = (CheckBox) view.findViewById(R.id.pronounceable);
+        checkBox.setChecked(!prefs.getBoolean("s", true));
+
+        TextView textView = (TextView) view.findViewById(R.id.lengthNumber);
+        textView.setText(Integer.toString(prefs.getInt("length", 20)));
+
+        builder.setPositiveButton(getResources().getString(R.string.dialog_ok), new DialogInterface.OnClickListener() {
+            @Override
+            public void onClick(DialogInterface dialog, int which) {
+                TextView edit = (TextView) pwgenDialogFragment.this.getActivity().findViewById(R.id.crypto_password_edit);
+                TextView generate = (TextView) pwgenDialogFragment.this.getDialog().findViewById(R.id.passwordText);
+                edit.append(generate.getText());
+            }
+        });
+
+        builder.setNegativeButton(getResources().getString(R.string.dialog_cancel), new DialogInterface.OnClickListener() {
+            @Override
+            public void onClick(DialogInterface dialog, int which) {
+
+            }
+        });
+
+        builder.setNeutralButton(getResources().getString(R.string.pwgen_generate), null);
+
+        final AlertDialog ad = builder.setTitle("Generate Password").create();
+        ad.setOnShowListener(new DialogInterface.OnShowListener() {
+            @Override
+            public void onShow(DialogInterface dialog) {
+                setPreferences();
+                TextView textView = (TextView) view.findViewById(R.id.passwordText);
+                textView.setText(pwgen.generate(getActivity().getApplicationContext()).get(0));
+
+                Button b = ad.getButton(AlertDialog.BUTTON_NEUTRAL);
+                b.setOnClickListener(new View.OnClickListener() {
+                    @Override
+                    public void onClick(View v) {
+                        setPreferences();
+                        TextView textView = (TextView) getDialog().findViewById(R.id.passwordText);
+                        textView.setText(pwgen.generate(getActivity().getApplicationContext()).get(0));
+                    }
+                });
+            }
+        });
+        return ad;
+    }
+
+    private boolean setPreferences () {
+        ArrayList<String> preferences = new ArrayList<>();
+        if (!((CheckBox) getDialog().findViewById(R.id.numerals)).isChecked()) {
+            preferences.add("0");
+        }
+        if (((CheckBox) getDialog().findViewById(R.id.symbols)).isChecked()) {
+            preferences.add("y");
+        }
+        if (!((CheckBox) getDialog().findViewById(R.id.uppercase)).isChecked()) {
+            preferences.add("A");
+        }
+        if (!((CheckBox) getDialog().findViewById(R.id.ambiguous)).isChecked()) {
+            preferences.add("B");
+        }
+        if (!((CheckBox) getDialog().findViewById(R.id.pronounceable)).isChecked()) {
+            preferences.add("s");
+        }
+        TextView textView = (TextView) getDialog().findViewById(R.id.lengthNumber);
+        try {
+            int length = Integer.valueOf(textView.getText().toString());
+            return pwgen.setPrefs(getActivity().getApplicationContext(), preferences, length);
+        } catch(NumberFormatException e) {
+            return pwgen.setPrefs(getActivity().getApplicationContext(), preferences);
+        }
+    }
+}
+
diff --git a/app/src/main/res/layout/encrypt_layout.xml b/app/src/main/res/layout/encrypt_layout.xml
index 5fc93b3c..dcb6bf88 100644
--- a/app/src/main/res/layout/encrypt_layout.xml
+++ b/app/src/main/res/layout/encrypt_layout.xml
@@ -64,7 +64,15 @@
                     android:id="@+id/crypto_password_edit"
                     android:layout_width="fill_parent"
                     android:layout_height="wrap_content"
-                    android:typeface="monospace"/>
+                    android:typeface="monospace"
+                    android:layout_weight="1"/>
+                <ImageButton
+                    android:layout_height="wrap_content"
+                    android:layout_width="wrap_content"
+                    android:src="@drawable/ic_action_new"
+                    android:background="@drawable/blue_rectangle"
+                    android:id="@+id/generate_password"
+                    android:onClick="handleClick"/>
             </LinearLayout>
 
             <TextView
diff --git a/app/src/main/res/layout/fragment_pwgen.xml b/app/src/main/res/layout/fragment_pwgen.xml
new file mode 100644
index 00000000..072a78a9
--- /dev/null
+++ b/app/src/main/res/layout/fragment_pwgen.xml
@@ -0,0 +1,108 @@
+<ScrollView
+    android:layout_height="match_parent"
+    android:layout_width="match_parent"
+    xmlns:android="http://schemas.android.com/apk/res/android">
+
+    <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
+                  xmlns:tools="http://schemas.android.com/tools"
+                  android:layout_width="match_parent"
+                  android:layout_height="match_parent"
+                  android:orientation="vertical"
+                  android:paddingBottom="@dimen/activity_vertical_margin"
+                  android:paddingLeft="@dimen/activity_horizontal_margin"
+                  android:paddingRight="@dimen/activity_horizontal_margin"
+                  android:paddingTop="@dimen/activity_vertical_margin"
+                  tools:context=".MainActivityFragment">
+
+        <EditText
+            android:id="@+id/passwordText"
+            android:layout_width="match_parent"
+            android:layout_height="wrap_content"
+            android:layout_marginBottom="8dp"
+            android:editable="false"
+            android:textIsSelectable="true"
+            android:inputType="textVisiblePassword"/>
+
+        <LinearLayout
+            android:layout_width="match_parent"
+            android:layout_height="match_parent"
+            android:orientation="horizontal"
+            android:weightSum="2">
+
+            <LinearLayout
+                android:layout_width="match_parent"
+                android:layout_height="match_parent"
+                android:layout_weight="1"
+                android:orientation="vertical">
+
+                <TextView
+                    android:id="@+id/include"
+                    android:layout_width="wrap_content"
+                    android:layout_height="wrap_content"
+                    android:text="@string/pwgen_include"
+                    android:textAppearance="?android:attr/textAppearanceSmall"
+                    android:layout_marginBottom="8dp"/>
+
+                <CheckBox
+                    android:id="@+id/numerals"
+                    android:layout_width="wrap_content"
+                    android:layout_height="wrap_content"
+                    android:text="@string/pwgen_numerals"/>
+
+
+                <CheckBox
+                    android:id="@+id/symbols"
+                    android:layout_width="wrap_content"
+                    android:layout_height="wrap_content"
+                    android:text="@string/pwgen_symbols"/>
+
+                <CheckBox
+                    android:id="@+id/uppercase"
+                    android:layout_width="wrap_content"
+                    android:layout_height="wrap_content"
+                    android:text="@string/pwgen_uppercase"/>
+
+                <CheckBox
+                    android:id="@+id/ambiguous"
+                    android:layout_width="wrap_content"
+                    android:layout_height="wrap_content"
+                    android:text="@string/pwgen_ambiguous"/>
+
+            </LinearLayout>
+
+            <LinearLayout
+                android:layout_width="match_parent"
+                android:layout_height="match_parent"
+                android:layout_weight="1"
+                android:orientation="vertical">
+
+                <TextView
+                    android:id="@+id/length"
+                    android:layout_width="wrap_content"
+                    android:layout_height="wrap_content"
+                    android:text="Length"
+                    android:textAppearance="?android:attr/textAppearanceSmall"
+                    android:layout_marginBottom="8dp"
+                    />
+
+                <EditText
+                    android:id="@+id/lengthNumber"
+                    android:layout_width="match_parent"
+                    android:layout_height="wrap_content"
+                    android:layout_marginBottom="8dp"
+                    android:ems="10"
+                    android:inputType="number"
+                    />
+
+                <CheckBox
+                    android:id="@+id/pronounceable"
+                    android:layout_width="wrap_content"
+                    android:layout_height="wrap_content"
+                    android:text="Pronounceable"/>
+
+            </LinearLayout>
+
+
+        </LinearLayout>
+    </LinearLayout>
+</ScrollView>
\ No newline at end of file
diff --git a/app/src/main/res/values/strings.xml b/app/src/main/res/values/strings.xml
index a8db99ff..a9b03151 100644
--- a/app/src/main/res/values/strings.xml
+++ b/app/src/main/res/values/strings.xml
@@ -114,6 +114,14 @@
     <string name="pref_recursive_filter">Recursive filtering</string>
     <string name="pref_recursive_filter_hint">Recursively find passwords of the current directory.</string>
 
+    <!-- pwgen fragment -->
+    <string name="pwgen_generate">Generate</string>
+    <string name="pwgen_include">Include</string>
+    <string name="pwgen_numerals">Numerals</string>
+    <string name="pwgen_symbols">Symbols</string>
+    <string name="pwgen_uppercase">Uppercase</string>
+    <string name="pwgen_ambiguous">Ambiguous</string>
+
     <!-- Misc -->
     <string name="dialog_ok">OK</string>
     <string name="dialog_yes">Yes</string>