WIP Add SegwitAddress as a subclass of AbstractAddress (parent of Address too).

Note the class names a subject to change, e.g.
AbstractAddress > Address
Address > LegacyAddress

Uses Bech32 code from sipa/bech32#40.

Author: Andreas Schildbach

core/src/main/java/org/bitcoinj/core/AbstractAddress.java

@@ -0,0 +1,58 @@
+/*
+ * Copyright 2018 Andreas Schildbach
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.bitcoinj.core;
+
+import javax.annotation.Nullable;
+
+import org.bitcoinj.script.Script.ScriptType;
+
+public abstract class AbstractAddress extends VersionedChecksummedBytes {
+    public AbstractAddress(NetworkParameters params, byte[] bytes) {
+        super(params, bytes);
+    }
+
+    /**
+     * Construct an address from its textual representation.
+     * 
+     * @param params
+     *            The expected NetworkParameters or null if you don't want validation.
+     * @param str
+     *            The textual form of the address, such as "17kzeh4N8g49GFvdDzSf8PjaPfyoD1MndL".
+     * @throws AddressFormatException
+     *             if the given string doesn't parse or the checksum is invalid
+     * @throws WrongNetworkException
+     *             if the given string is valid but for a different chain (eg testnet vs mainnet)
+     */
+    public static AbstractAddress fromString(@Nullable NetworkParameters params, String str)
+            throws AddressFormatException {
+        try {
+            return Address.fromBase58(params, str);
+        } catch (WrongNetworkException x) {
+            throw x;
+        } catch (AddressFormatException x) {
+            try {
+                return SegwitAddress.fromBech32(params, str);
+            } catch (WrongNetworkException x2) {
+                throw x;
+            } catch (AddressFormatException x2) {
+                throw new AddressFormatException(str);
+            }
+        }
+    }
+
+    public abstract ScriptType getScriptType();
+}

core/src/main/java/org/bitcoinj/core/Address.java

@@ -26,6 +26,7 @@
 
 import org.bitcoinj.params.Networks;
 import org.bitcoinj.script.Script;
+import org.bitcoinj.script.Script.ScriptType;
 
 import com.google.common.base.Objects;
 
@@ -40,7 +41,7 @@
  * should be interpreted. Whilst almost all addresses today are hashes of public keys, another (currently unsupported
  * type) can contain a hash of a script instead.</p>
  */
-public class Address extends VersionedChecksummedBytes {
+public class Address extends AbstractAddress {
     /**
      * An address is a RIPEMD160 hash of a public key, therefore is always 160 bits or 20 bytes.
      */
@@ -114,19 +115,27 @@ else if (version == params.getP2SHHeader())
         }
     }
 
-    @Override
-    protected int getVersion() {
-        return p2sh ? params.getP2SHHeader() : params.getAddressHeader();
+    /**
+     * Returns the base58-encoded textual representation, including version and checksum bytes.
+     */
+    public String toBase58() {
+        return toBase58(p2sh ? params.getP2SHHeader() : params.getAddressHeader(), bytes);
     }
 
     /** The (big endian) 20 byte hash that is the core of a Bitcoin address. */
     public byte[] getHash160() {
         return bytes;
     }
 
+    @Override
+    public ScriptType getScriptType() {
+        return p2sh ? ScriptType.P2SH : ScriptType.P2PKH;
+    }
+
     /**
      * Returns true if this address is a Pay-To-Script-Hash (P2SH) address.
      * See also https://github.com/bitcoin/bips/blob/master/bip-0013.mediawiki: Address Format for pay-to-script-hash
+     * @deprecated Use {@link #getScriptType()}
      */
     public boolean isP2SHAddress() {
         return p2sh;
@@ -162,6 +171,11 @@ public int hashCode() {
         return Objects.hashCode(super.hashCode(), p2sh);
     }
 
+    @Override
+    public String toString() {
+        return toBase58();
+    }
+
     /**
      * This implementation narrows the return type to <code>Address</code>.
      */

core/src/main/java/org/bitcoinj/core/Bech32.java

@@ -0,0 +1,152 @@
+/* Copyright (c) 2018 Coinomi Ltd
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+package org.bitcoinj.core;
+
+import java.util.Arrays;
+import java.util.Locale;
+
+public class Bech32 {
+    /** The Bech32 character set for encoding. */
+    private static final String CHARSET = "qpzry9x8gf2tvdw0s3jn54khce6mua7l";
+
+    /** The Bech32 character set for decoding. */
+    private static final byte[] CHARSET_REV = {
+            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
+            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
+            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
+            15, -1, 10, 17, 21, 20, 26, 30,  7,  5, -1, -1, -1, -1, -1, -1,
+            -1, 29, -1, 24, 13, 25,  9,  8, 23, -1, 18, 22, 31, 27, 19, -1,
+             1,  0,  3, 16, 11, 28, 12, 14,  6,  4,  2, -1, -1, -1, -1, -1,
+            -1, 29, -1, 24, 13, 25,  9,  8, 23, -1, 18, 22, 31, 27, 19, -1,
+             1,  0,  3, 16, 11, 28, 12, 14,  6,  4,  2, -1, -1, -1, -1, -1
+    };
+
+    public static class Bech32Data {
+        final String hrp;
+        final byte[] values;
+
+        private Bech32Data(final String hrp, final byte[] values) {
+            this.hrp = hrp;
+            this.values = values;
+        }
+    }
+
+    /** Find the polynomial with value coefficients mod the generator as 30-bit. */
+    private static int polymod(final byte[] values) {
+        int c = 1;
+        for (byte v_i: values) {
+            int c0 = (c >>> 25) & 0xff;
+            c = ((c & 0x1ffffff) << 5) ^ (v_i & 0xff);
+            if ((c0 &  1) != 0) c ^= 0x3b6a57b2;
+            if ((c0 &  2) != 0) c ^= 0x26508e6d;
+            if ((c0 &  4) != 0) c ^= 0x1ea119fa;
+            if ((c0 &  8) != 0) c ^= 0x3d4233dd;
+            if ((c0 & 16) != 0) c ^= 0x2a1462b3;
+        }
+        return c;
+    }
+
+    /** Expand a HRP for use in checksum computation. */
+    private static byte[] expandHrp(final String hrp) {
+        int hrpLength = hrp.length();
+        byte ret[] = new byte[hrpLength * 2 + 1];
+        for (int i = 0; i < hrpLength; ++i) {
+            int c = hrp.charAt(i) & 0x7f; // Limit to standard 7-bit ASCII
+            ret[i] = (byte) ((c >>> 5) & 0x07);
+            ret[i + hrpLength + 1] = (byte) (c & 0x1f);
+        }
+        ret[hrpLength] = 0;
+        return ret;
+    }
+
+    /** Verify a checksum. */
+    private static boolean verifyChecksum(final String hrp, final byte[] values) {
+        byte[] hrpExpanded = expandHrp(hrp);
+        byte[] combined = new byte[hrpExpanded.length + values.length];
+        System.arraycopy(hrpExpanded, 0, combined, 0, hrpExpanded.length);
+        System.arraycopy(values, 0, combined, hrpExpanded.length, values.length);
+        return polymod(combined) == 1;
+    }
+
+    /** Create a checksum. */
+    private static byte[] createChecksum(final String hrp, final byte[] values)  {
+        byte[] hrpExpanded = expandHrp(hrp);
+        byte[] enc = new byte[hrpExpanded.length + values.length + 6];
+        System.arraycopy(hrpExpanded, 0, enc, 0, hrpExpanded.length);
+        System.arraycopy(values, 0, enc, hrpExpanded.length, values.length);
+        int mod = polymod(enc) ^ 1;
+        byte[] ret = new byte[6];
+        for (int i = 0; i < 6; ++i) {
+            ret[i] = (byte) ((mod >>> (5 * (5 - i))) & 31);
+        }
+        return ret;
+    }
+
+    /** Encode a Bech32 string. */
+    public static String encode(final Bech32Data bech32) throws AddressFormatException {
+        return encode(bech32.hrp, bech32.values);
+    }
+
+    /** Encode a Bech32 string. */
+    public static String encode(String hrp, final byte[] values) throws AddressFormatException {
+        if (hrp.length() < 1) throw new AddressFormatException("Human-readable part is too short");
+        if (hrp.length() > 83) throw new AddressFormatException("Human-readable part is too long");
+        hrp = hrp.toLowerCase(Locale.ROOT);
+        byte[] checksum = createChecksum(hrp, values);
+        byte[] combined = new byte[values.length + checksum.length];
+        System.arraycopy(values, 0, combined, 0, values.length);
+        System.arraycopy(checksum, 0, combined, values.length, checksum.length);
+        StringBuilder sb = new StringBuilder(hrp.length() + 1 + combined.length);
+        sb.append(hrp);
+        sb.append('1');
+        for (byte b : combined) {
+            sb.append(CHARSET.charAt(b));
+        }
+        return sb.toString();
+    }
+
+    /** Decode a Bech32 string. */
+    public static Bech32Data decode(final String str) throws AddressFormatException {
+        boolean lower = false, upper = false;
+        if (str.length() < 8) throw new AddressFormatException("Input too short");
+        if (str.length() > 90) throw new AddressFormatException("Input too long");
+        for (int i = 0; i < str.length(); ++i) {
+            char c = str.charAt(i);
+            if (c < 33 || c > 126) throw new AddressFormatException("Characters out of range");
+            if (c >= 'a' && c <= 'z') lower = true;
+            if (c >= 'A' && c <= 'Z') upper = true;
+        }
+        if (lower && upper)  throw new AddressFormatException("Cannot mix upper and lower cases");
+        int pos = str.lastIndexOf('1');
+        if (pos < 1) throw new AddressFormatException("Missing human-readable part");
+        if (pos + 7 > str.length()) throw new AddressFormatException("Data part too short");
+        byte[] values = new byte[str.length() - 1 - pos];
+        for (int i = 0; i < str.length() - 1 - pos; ++i) {
+            char c = str.charAt(i + pos + 1);
+            if (CHARSET_REV[c] == -1) throw new AddressFormatException("Characters out of range");
+            values[i] = CHARSET_REV[c];
+        }
+        String hrp = str.substring(0, pos).toLowerCase(Locale.ROOT);
+        if (!verifyChecksum(hrp, values)) throw new AddressFormatException("Invalid checksum");
+        return new Bech32Data(hrp, Arrays.copyOfRange(values, 0, values.length - 6));
+    }
+}

core/src/main/java/org/bitcoinj/core/DumpedPrivateKey.java

@@ -71,9 +71,11 @@ private DumpedPrivateKey(NetworkParameters params, byte[] bytes) {
         this(params, encode(keyBytes, compressed));
     }
 
-    @Override
-    protected int getVersion() {
-        return params.getDumpedPrivateKeyHeader();
+    /**
+     * Returns the base58-encoded textual representation, including version and checksum bytes.
+     */
+    public String toBase58() {
+        return toBase58(params.getDumpedPrivateKeyHeader(), bytes);
     }
 
     private static byte[] encode(byte[] keyBytes, boolean compressed) {
@@ -102,4 +104,9 @@ public ECKey getKey() {
     public boolean isPubKeyCompressed() {
         return bytes.length == 33 && bytes[32] == 1;
     }
+
+    @Override
+    public String toString() {
+        return toBase58();
+    }
 }

core/src/main/java/org/bitcoinj/core/NetworkParameters.java

@@ -77,6 +77,7 @@ public abstract class NetworkParameters {
     protected int addressHeader;
     protected int p2shHeader;
     protected int dumpedPrivateKeyHeader;
+    protected String segwitAddressHrp;
     protected int interval;
     protected int targetTimespan;
     protected byte[] alertSigningKey;
@@ -336,6 +337,11 @@ public int getDumpedPrivateKeyHeader() {
         return dumpedPrivateKeyHeader;
     }
 
+    /** Human readable part of bech32 encoded segwit address. */
+    public String getSegwitAddressHrp() {
+        return segwitAddressHrp;
+    }
+
     /**
      * How much time in seconds is supposed to pass between "interval" blocks. If the actual elapsed time is
      * significantly different from this value, the network difficulty formula will produce a different value. Both