Don't try to erase secrets from memory.

1. The things we're really trying to protect - contact identities,
message contents, etc - can't be erased from memory because they're
encapsulated inside objects we don't control.

2. Long-term secrets can't be protected by erasing them from memory
because they're stored in the database and the database key has to be
held in memory whenever the app's running.

3. If the runtime uses a compacting garbage collector then we have no
way to ensure an object is erased from memory.

4. Trying to erase secrets from memory makes the code more complex.

Conclusion: Let's not try to protect secrets from an attacker who can
read arbitrary memory locations.

briar-core/src/org/briarproject/db/H2Database.java

@@ -81,34 +81,18 @@ class H2Database extends JdbcDatabase {
 		}
 	}
 
+	@Override
 	protected Connection createConnection() throws SQLException {
 		byte[] key = config.getEncryptionKey();
 		if(key == null) throw new IllegalStateException();
-		char[] password = encodePassword(key);
 		Properties props = new Properties();
 		props.setProperty("user", "user");
-		props.put("password", password);
-		try {
-			return DriverManager.getConnection(url, props);
-		} finally {
-			for(int i = 0; i < password.length; i++) password[i] = 0;
-		}
-	}
-
-	private char[] encodePassword(byte[] key) {
-		// The database password is the hex-encoded key
-		char[] hex = StringUtils.toHexChars(key);
-		// Separate the database password from the user password with a space
-		char[] user = "password".toCharArray();
-		char[] combined = new char[hex.length + 1 + user.length];
-		System.arraycopy(hex, 0, combined, 0, hex.length);
-		combined[hex.length] = ' ';
-		System.arraycopy(user, 0, combined, hex.length + 1, user.length);
-		// Erase the hex-encoded key
-		for(int i = 0; i < hex.length; i++) hex[i] = 0;
-		return combined;
+		// Separate the file password from the user password with a space
+		props.put("password", StringUtils.toHexString(key) + " password");
+		return DriverManager.getConnection(url, props);
 	}
 
+	@Override
 	protected void flushBuffersToDisk(Statement s) throws SQLException {
 		// FIXME: Remove this after implementing BTPv2?
 		s.execute("CHECKPOINT SYNC");