DS1991 MultiKey iButton
Three password-protected 384-bit subkeys in one button.
One token, three walls. The DS1991 carries three independent 384-bit subkeys, each with its own 64-bit password and its own 64-bit public ID field, so three different systems — or three departments, or a landlord and two tenants — can share one physical key, each behind its own password (see the security note below). A 512-bit scratchpad buffers writes, and the whole 1152-bit array is battery-backed NV RAM with over 10 years of retention (per the original manufacturer's datasheet; confirm for the supplied version).
Ordering information
| MOQ | Confirmed by model and order when quoting |
|---|---|
| Preparation time | Availability and lead time are confirmed by model and order when quoting |
| Packing | Confirm pack quantity, protection and labelling for the selected model. |
| Samples | Sample quantity, fees and shipping are confirmed for the selected model. |
| Payment | Agree payment terms and the payee in the quotation and invoice. |
| Shipping | Confirm the shipping method, cost and timing for your destination and order. |
| Customization | State ROM, colour, marking and packing needs; feasibility and cost require confirmation. |
Three isolated key zones in one button
The DS1991 is organised into three separate password-protected subkeys. Where a DS1992 gives you one flat memory that anyone who can touch the key can read, the DS1991 gives three separate areas with their own passwords — a typical fit when one credential must serve several independent operators. Be honest about the era, though: its password scheme dates from the early 1990s and a published dictionary attack (CVE-2001-1436) means it should not be specified as the security layer of a new design. Order it to keep an installed base running; for new systems that need cryptographic authentication, evaluate the DS1961S with its SHA-1 challenge–response instead, on a controller that implements it.
Key features
- Original DS1991 reference: 1,152 bits of nonvolatile user memory in three 384-bit blocks.
- Each original subkey has separate 64-bit password and ID fields; a scratchpad supports checked data transfer.
- For an existing installation, provide the memory layout and password workflow; test both reading and writing before ordering.
How the password protection behaves
Specifications
| Chip / compatibility | DS1991 · model TM1991L-F5 · family code 02h |
|---|---|
| Memory | 1152-bit secure NV RAM = 3 subkeys × 384 bits, each with a 64-bit password and 64-bit ID field, + 512-bit scratchpad |
| Operating temperature | −40 to +70 °C · over 10 years data retention (per the original manufacturer's datasheet; confirm for the supplied version) |
| Package | F5 can — stainless-steel shell with a moulded polymer grommet; the original manufacturer's datasheet describes it as dust-, damp-, shock- and corrosion-resistant (confirm for the supplied version) |
| Protocol | 1-Wire® |
| Mounting | Read/write needs a 1-Wire master plus software that implements the subkey commands — an ordinary key-copier cannot write it |
| Options | Legacy support for installed systems that use the DS1991 three-zone structure. Supply version, quantity tiers, laser marking and pre-programming are confirmed with your quote; test a sample on your own system before ordering. |
Inside the stainless can
Typical construction of this can format: a stainless-steel shell, an insulating grommet separating lid from base, and the chip bonded inside. Lid = data contact, base = ground return. Wall thickness, grommet material and other construction details: confirm for the supplied version.
Which memory iButton do you need?
The whole memory range side by side, grouped by storage technology — capacities and family codes per the Analog Devices datasheets.
| Model | Family code | Capacity | Memory technology | Pick it for |
|---|---|---|---|---|
| DS1971 | 14h | 256 bit + 64-bit OTP | EEPROM — battery-free | Asset tag: a locked ID beside rewritable data |
| DS1972 | 2Dh | 1 Kbit (128 B) | EEPROM — battery-free | Per-page write-protect or EPROM-emulation modes |
| DS1973 | 23h | 4 Kbit (512 B) | EEPROM — battery-free | Battery-free rewritable memory (4 Kbit); production travellers |
| DS1982 | 09h | 1 Kbit (128 B) | EPROM — add-only; written data is not erasable (per datasheet) | Add-only records such as checkpoints and certificates |
| DS1985 | 0Bh | 16 Kbit (2 KB) | EPROM — add-only; written data is not erasable (per datasheet) | Append-only service history (16 Kbit) |
| DS1992 / DS1993 | 08h / 06h | 1 Kbit / 4 Kbit | NV RAM — battery-backed, high write endurance (per datasheet) | Data that changes constantly on the key |
| DS1996 | 0Ch | 64 Kbit (8 KB) | NV RAM — battery-backed, high write endurance (per datasheet) | Portable database — 64 Kbit NV RAM |
| DS1994 | 04h | 4 Kbit + RTC | NV RAM + clock, timer, counter, alarms | Time- or usage-limited access with the expiry held in the key |
| DS1904L | 24h | No user memory | Real-time clock only | Give a microcontroller a real-time timebase |
| DS1991 | 02h | 1152 bit = 3 × 384 bit | Secure NV RAM — three password zones | Legacy multi-tenant systems (not for new secure designs) |
| DS1961S | 33h | 1 Kbit + 64-bit secret | EEPROM + SHA-1 challenge–response | Authentication: proves it knows a secret (assess cloning risk for your own system) |
Typical applications
Frequently asked questions
Is the DS1991 secure enough for a new access-control design?
No — and we would rather say so than sell you the wrong part. Its three-password scheme dates from the early 1990s and a published dictionary attack (CVE-2001-1436) can recover the subkey passwords, after which all protected data is readable. Use it to keep an existing installation running (confirm the supplied version with us first), and specify the DS1961S with SHA-1 challenge–response for anything new that must resist cloning.
What is the DS1991 still genuinely good for?
Compartmentalisation, not cryptography. Per the original manufacturer's datasheet it splits itself into three independent 384-bit zones with separate passwords and separate public ID fields (confirm for the supplied version), so one physical token can serve three unrelated operators who must not read each other's data. Where that structure is what the installed system expects — and the threat model is casual rather than determined — it still does the job. Ask us to confirm supply for installed systems.
Where is a three-zone key like the DS1991 used?
Typical uses of a three-zone key are the following three, mostly in existing installations; for a new design, read the security answer above first. Smart water and utility meters, where the meter reader's token must carry an operator credential the household cannot read. Authorisation keys for precision instruments and test equipment, where a calibration level or licence tier lives in one zone and the service history in another. And high-value industrial equipment management, where the machine builder, the owner and the maintenance contractor each hold rights to their own zone on the same physical key. In every case the reason is the three-way partition, not the strength of the password. Confirm the supplied version with us and test a sample on your own system before ordering.
What equipment do I need to read and write it, and how does it arrive?
You need a 1-Wire master (a USB adapter or your own controller) plus software that implements the DS1991 subkey command set — reading a protected zone means presenting that zone's 64-bit password with the read command. An ordinary door-key duplicator cannot do this: it only handles the 64-bit ROM ID of simple parts and has no notion of subkeys or passwords, which is exactly why this part resists casual copying. Confirm the supplied version and its initial state with us before ordering, and check a sample on your own system: you write your own data and set your own passwords on arrival.
Related products
DS1992 / DS1993 Memory iButton
1 Kb and 4 Kb NV RAM tokens for carrying data on the key.
DS1996 64 Kb Memory iButton
The large-memory token — 64 Kb of rewritable NV RAM.
DS1961S SHA-1 Authentication iButton
1 Kb EEPROM with on-chip SHA-1 challenge–response.
DS1971 EEPROM iButton
256-bit EEPROM — non-volatile without a battery.