Extract checked base58 encoding from Address to Base58.

core/src/main/java/org/bitcoinj/core/Base58.java

@@ -1,5 +1,6 @@
 /*
  * Copyright 2011 Google Inc.
+ * 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.
@@ -90,6 +91,27 @@ public class Base58 {
         return new String(encoded, outputStart, encoded.length - outputStart);
     }
 
+    /**
+     * Encodes the given version and bytes as a base58 string. A checksum is appended.
+     * 
+     * @param version the version to encode
+     * @param payload the bytes to encode, e.g. pubkey hash
+     * @return the base58-encoded string
+     */
+    public static String encodeChecked(int version, byte[] payload) {
+        if (version < 0 || version > 255)
+            throw new IllegalArgumentException("Version not in range.");
+
+        // A stringified buffer is:
+        // 1 byte version + data bytes + 4 bytes check code (a truncated hash)
+        byte[] addressBytes = new byte[1 + payload.length + 4];
+        addressBytes[0] = (byte) version;
+        System.arraycopy(payload, 0, addressBytes, 1, payload.length);
+        byte[] checksum = Sha256Hash.hashTwice(addressBytes, 0, payload.length + 1);
+        System.arraycopy(checksum, 0, addressBytes, payload.length + 1, 4);
+        return Base58.encode(addressBytes);
+    }
+
     /**
      * Decodes the given base58 string into the original data bytes.
      *
@@ -180,5 +202,4 @@ public class Base58 {
         }
         return (byte) remainder;
     }
-
 }

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

@@ -56,14 +56,7 @@ public class VersionedChecksummedBytes implements Serializable, Cloneable, Compa
      * object, including version and checksum bytes.
      */
     public final String toBase58() {
-        // A stringified buffer is:
-        //   1 byte version + data bytes + 4 bytes check code (a truncated hash)
-        byte[] addressBytes = new byte[1 + bytes.length + 4];
-        addressBytes[0] = (byte) version;
-        System.arraycopy(bytes, 0, addressBytes, 1, bytes.length);
-        byte[] checksum = Sha256Hash.hashTwice(addressBytes, 0, bytes.length + 1);
-        System.arraycopy(checksum, 0, addressBytes, bytes.length + 1, 4);
-        return Base58.encode(addressBytes);
+        return Base58.encodeChecked(version, bytes);
     }
 
     @Override

core/src/test/java/org/bitcoinj/core/Base58Test.java

@@ -44,6 +44,18 @@ public class Base58Test {
         assertEquals("", Base58.encode(new byte[0]));
     }
 
+    @Test
+    public void testEncodeChecked_address() throws Exception {
+        String encoded = Base58.encodeChecked(111, new byte[Address.LENGTH]);
+        assertEquals("mfWxJ45yp2SFn7UciZyNpvDKrzbhyfKrY8", encoded);
+    }
+
+    @Test
+    public void testEncodeChecked_privateKey() throws Exception {
+        String encoded = Base58.encodeChecked(128, new byte[32]);
+        assertEquals("5HpHagT65TZzG1PH3CSu63k8DbpvD8s5ip4nEB3kEsreAbuatmU", encoded);
+    }
+
     @Test
     public void testDecode() throws Exception {
         byte[] testbytes = "Hello World".getBytes();