Andrey Komarov @andrey_komarov Пошутите что-нибудь сами Serious Cryptography SHA-1 The SHA-1 standard arose from a failure in the original hash function. In 1993, NIST standardized the NSA’s SHA- 0 ha

Andrey Komarov
@andrey_komarov
Пошутите что-нибудь сами
Serious Cryptography
SHA-1
The SHA-1 standard arose from a failure in the original
hash function. In 1993, NIST standardized the NSA’s SHA-
0 hash algorithm, but in 1995 the NSA released SHA-1 to fix an
unidentified security issue in SHA-0. The reason for the tweak
became clear when in 1998 two researchers discovered how to find
collisions for SHA-0 in abou
260
operations instead of
780
expected for 160-bit hash functions such as SHA-0 and $НА-1.
Later attacks reduced the complexity to around 233 operations,
leading to actual collisions in less than an hour for SHA-0.
SHA-1 Internals
SHA-1 combines
le-Damgard hash function with a Davies—
Meyer
yased on a specially crafted block
cipher,
metimes call
HACAL.
That is, SHA-1 works iterat-
ing the following operation ove
512-bit message blocks
H=E(M,
Here, the use of a plus sign rather than (XOR) is inten-
tional. and are viewed as arrays of 32-bit integers, and
each two words at a same position are added together: the first 32-
bit word of with the first 32-bit word of and so The
initial value of is constant for any message, then is modified as
per the above equation, and the final value of after processing all
blocks is returned as the hash of the message.
Once the block cipher is run using the message block as a key
and the current 160-bit chaining value as a plaintext block, the 160-