DS1961S SHA-1 Authentication iButton
1 Kb EEPROM with on-chip SHA-1 challenge–response.
A plain serial-number key is identified by its ID alone, and an ID can be copied to a compatible blank. The DS1961S works differently: per the original manufacturer's datasheet it holds a 64-bit secret that is never transmitted, and an on-chip 512-bit SHA-1 engine that answers the reader's random challenge with a 160-bit message authentication code. Copying only the ID does not produce the correct MAC, so a controller that verifies the MAC can reject the copy. Writes are protected in a similar way: the copy-scratchpad command only executes if it arrives with a matching MAC. The protection depends on the controller implementing the SHA-1 challenge–response, on how the secret is managed and on 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. |
Challenge–response authentication instead of a bare ID
This is the authentication option in the range. A DS1990A, a TM1990A or a DS1991 can be identified by its ID alone, and an ID can be copied to a compatible blank with a duplicator; the DS1961S is designed differently: the reader does not just ask "what is your ID", it asks "prove you know the secret", and per the original manufacturer's datasheet the secret never leaves the chip. That can raise the effort needed to copy a credential, but it is not an absolute guarantee: the result depends on the controller implementation, on how secrets are generated and stored, and on the supplied version. Consider it when the token opens something worth attacking, such as cash-handling equipment, pharmaceutical stores or high-value asset cabinets. Note that it needs a controller that implements SHA-1 authentication — in a plain ID reader it will behave like an ordinary key. Test a sample on your own system before ordering.
Key features
- Original DS1961S reference: 1 Kbit EEPROM, a 64-bit secret and SHA-1 message authentication.
- Original-device data writes require a matching 160-bit MAC; the secret is not available through normal read commands.
- System protection depends on secret provisioning and host verification. Ask whether source information is available for the quoted lot, and validate the complete authentication workflow on a sample.
Specifications
| Chip / compatibility | DS1961S · family code 33h · shares its die with the DS2432 chip form |
|---|---|
| Memory | 1128-bit 5V EEPROM in total — 1024-bit user array (4 pages × 256 bits) + 64-bit secret + 512-bit SHA-1 engine + 8-byte register page + scratchpad; secret and data pages can be write-protected |
| Protocol | 1-Wire single-line data link to the host, ~14.1 kbit/s standard / 125 kbit/s overdrive · 160-bit MAC challenge–response on read and write (per the original manufacturer's datasheet; confirm for the supplied version) |
| Package | F5 can, Ø16.25 × 5.89 mm |
| Operating temperature | −40 °C … +85 °C · data retention at least 10 years at +85 °C (per the original manufacturer's datasheet; confirm for the supplied version) |
| Options | Secret can be loaded or computed on-chip, then write-protected; the same SHA-1 scheme is used by 1-Wire SHA coprocessors · Colour, marking and other customization options: feasibility, MOQ and cost are confirmed in the quote. |
Product dimensions
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
How does the DS1961S stop a key from being cloned?
By never revealing what makes it valid. Each device holds a 64-bit secret that is never transmitted on the bus. The reader sends a random challenge; the on-chip SHA-1 engine combines that challenge with the secret and the page data and returns a 160-bit MAC. Copying the 64-bit ROM ID onto a blank gets you a device that answers the challenge wrongly, so a controller that verifies the response rejects it. Writes are protected the same way — memory only updates when the command arrives with a matching MAC.
Will a DS1961S work in an ordinary iButton reader?
Physically yes, cryptographically no. It is a standard F5 can on the standard 1-Wire bus, so a 1-Wire reader can normally be expected to see it and read its 64-bit ROM ID (test a sample on your own reader) — but a controller that only compares IDs gains none of the protection and treats it like a plain DS1990A. The security only exists if the host implements the SHA-1 challenge–response, usually with a 1-Wire SHA coprocessor. Confirm your controller supports it before ordering in volume.
What is the difference between the DS1961S and the DS2432?
Per the original manufacturer's datasheets, both are 1 Kbit EEPROM devices with SHA-1 (family code 33h); confirm for the supplied version. The difference is packaging: the DS1961S is the F5 MicroCan iButton, while the DS2432 is the chip form (TSOC or UCSP) for soldering onto a board.
What are typical uses for a SHA-1 iButton?
Hardware and IP authentication, anti-counterfeiting of consumables (print cartridges, medical or industrial disposables, batteries), secure access tokens and tamper-resistant data carriers — anywhere the credential controls something worth attacking.
Related products
DS1991 MultiKey iButton
Three password-protected 384-bit subkeys in one button.
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.
DS1971 EEPROM iButton
256-bit EEPROM — non-volatile without a battery.