# Cryptography Tutorials - Tutorial Addendum - Bulletin Abstract - SHA1 Algorithm

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31 December 18:00

This tutorial helps you to accept

• What is SHA1?

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• SHA1 Algorithm Overview

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• SHA1 Accomplishing in Java

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• SHA1 Accomplishing in PHP

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• SHA1 Accomplishing in Perl

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What is SHA1

SHA1 (Secure Assortment Algorithm 1) is message-digest algorithm, which takes

an ascribe bulletin of any breadth < 2^64 \$.25 and produces a 160-bit output

as the bulletin digest.

Based on the SHA1 RFC document,

the SHA-1 is alleged defended because it is computationally infeasible

to acquisition a bulletin which corresponds to a accustomed bulletin digest, or to

acquisition two altered letters which aftermath the aforementioned bulletin digest.

Any change to a bulletin in alteration will, with actual top probability,

aftereffect in a altered bulletin digest, and the signature will abort to

verify.

The aboriginal blueprint of the algorithm was appear in 1993 as the Defended Assortment Standard,

FIPS PUB 180, by US government standards bureau NIST (National Convention of Standards and Technology).

This adaptation is now generally referred to as "SHA0".

SHA-0 was aloof by the NSA anon afterwards advertisement and was abolished by the revised version,

published in 1995 in FIPS PUB 180-1 and frequently referred to as "SHA1".

SHA1 Algorithm Overview

SHA1 algorithm is able-bodied declared in RFC 3174 - US Defended Assortment Algorithm 1 (SHA1),

see http://www.ietf.org/rfc/rfc3174.txt. Beneath is a quick overview of the algorithm.

SHA1 algorithm consists of 6 tasks:

so that its breadth (in bits) is coinciding to 448, modulo 512. The added rules are:

• The aboriginal bulletin is consistently bedlam with one bit "1" first.

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• Then aught or added \$.25 "0" are bedlam to accompany the breadth of the bulletin up to 64 \$.25 fewer

than a assorted of 512.

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Task 2. Appending Length. 64 \$.25 are added to the end of the bedlam message

to announce the breadth of the aboriginal bulletin in bytes. The rules of appending breadth are:

• The breadth of the aboriginal bulletin in bytes is adapted to its bifold architecture of 64 bits.

If overflow happens, alone the low-order 64 \$.25 are used.

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• Break the 64-bit breadth into 2 words (32 \$.25 each).

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• The low-order chat is added first and followed by the high-order word.

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(Continued on next part...)

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