Multi iButton. DS1425 Datasheet
• Provides a unique 64–bit serial number and three 384
bit fields of password protected RAM
• Intelligent response generator included
• No external power required
www.DataSheet4U.co•mUses inexpensive 1–WireTM protocol
• Universally portable across platforms
Authorization iButtons are sophisticated microelectron-
ics, sealed into miniature stainless steel cans, creating a
low cost, portable medium for storing and controlling
access to sensitive information.
iButtons are used with port adapters as a hardware
based protection system for software. iButtons help
protect the right to copy software by actually protecting
the right to execute it. Software can now be locked to a
user, a machine, or an application with a complete audit
trail and guaranteed uniqueness.
The DS1425 provides a 64–bit unique ID number, and
three 384 bit fields of password protected RAM. The
DS1425 is used to provide nested levels of protection,
or to protect multiple applications.
Hardware communication with the iButtons is con-
ducted via a 1–Wire interface. The conversion from a
PC I/O port to the 1–Wire interface is the responsibility
of the port adapter.
Software applications communicate with the iButton
using Dallas’ Access System, which is contained in any
of the port adapter Developer’s kits. The Access Sys-
tem provides easy to use commands which are
embedded into the application in order to utilize the
iButton resources during run time.
Each Dallas iButton is uniquely serialized with a 64–bit
code that is laser–etched in the silicon. This unique ID
provides a basic level of security, is traceable in the field,
and makes it possible to identify the specific iButton in a
field of many.
The serial number is divided into three parts (see Figure
1). The 8–bit family code tells the Access System (and
consequently the developer) what type of iButton is
being used. The next 48 bits are lasered sequentially
with no two numbers the same. The last 8 bits contain a
Cyclic Redundancy Check (CRC) value that has been
calculated across the family code and the 48–bit serial
number. The CRC ensures that iButton communication
is error free.
High levels of security are achieved by storing applica-
tion code and/or data necessary for execution in the
Each 384–bit secure data area is prefaced by a 64–bit
identification field and an unreadable 64–bit password.
Note that this password is user selected and pro-
grammed. This means no one, including Dallas Semi-
conductor, can access that data.
If the DS1425 is presented with a valid password from
the host application, the contents of the secure data will
be returned. However, if the DS1425 is presented with
an invalid password, the on–board intelligent response
generator will return what seems to be a normal
response, but is not. The false response will be unique
to the false access.
By using seemingly random data in both the password
and secure data fields, and by generating many false
accesses for each valid access, even sophisticated
attackers are defeated.
DS1425 MULTI iButton ORGANIZATION Figure 1
8-BIT CRC CODE
48-BIT SERIAL NUMBER
FAMILY CODE 82H
Secure Data 0
Secure Data 1
Secure Data 2