DS1961S-F3 Maxim Integrated Products, DS1961S-F3 Datasheet - Page 24

• Manufacturer Part Number: DS1961S-F3
• Description: IBUTTON EEPROM 1KBit SHA-1 2CAN
• Manufacturer: Maxim Integrated Products
• Series: iButton®r

Specifications of DS1961S-F3

• Rohs Information: IButton RoHS Compliance Plan
• Memory Size: 128B
• Memory Type: EEPROM
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

SHA-1 COMPUTATION ALGORITHM
This description of the SHA computation is adapted from the Secure Hash Standard SHA-1 document
that can be downloaded from the NIST website (www.itl.nist.gov/fipspubs/fip180-1.htm). The algorithm
takes as its input data sixteen 32-bit words M t (0 £ t £ 15), as shown in Tables 1, 3A, 3B, and 4 for the
compute next secret, copy scratchpad, and read authenticated page command, respectively. The SHA
computation involves a sequence of eighty 32-bit words called W t (0 £ t £ 79), a sequence of eighty 32-
bit words called K t (0 £ t £ 79), a Boolean function f t (B, C, D) (0 £ t £ 79) with B, C, and D being 32-bit
words, and three more 32-bit words called A, E, and TMP. The operations required for the SHA
computation are arithmetic addition without carry (“+”), logical inversion or 1’s complement (“\”),
EXCLUSIVE OR (“Å”), logical AND (“Ù”), logical OR (“Ú”), assignment (“:=”), and circular shifting
within a 32-bit word. The expression “S n (X)” represents a circular shift of X by n positions to the left,
with X being a 32-bit word.
The function f t is defined as follows:
f t (B,C,D) = (B Ù C) Ú ((B\) Ù D)
The sequence W t (0 £ t £ 79) is defined as follows:
W t := M t
The sequence K t (0 £ t £ 79) is defined as follows:
K t
The variables A, B, C, D, E are initialized as follows:
A
B
C
D
E
The 160-bit MAC is the concatenation of A, B, C, D, and E after looping through the following set of
computations for t = 0 to 79 (discarding any carry-out):
TMP :=
E
D
C
B
A
:=
:=
:=
:=
:=
:=
:=
:=
:=
:=
:=
S 1 (W t-3 Å W t-8 Å W t-14 Å W t-16 )
B Å C Å D
(B Ù C) Ú (B Ù D) Ú (C Ù D)
B Å C Å D
5A827999h
6ED9EBA1h (20 £ t £ 39)
8F1BBCDCh (40 £ t £ 59)
CA62C1D6h (60 £ t £ 79)
67452301h
EFCDAB89h
98BADCFEh
10325476h
C3D2E1F0h
S 5 (A) + f t (B,C,D) + W t + K t + E
D
C
S 30 (B)
A
TMP
(0 £ t £ 19)
24 of 36
(0 £ t £ 19)
(20 £ t £ 39)
(40 £ t £ 59)
(60 £ t £ 79)
(0 £ t £ 15)
(16 £ t £ 79)