Cryptography Tutorials - Tutorial Addendum - Bulletin Abstract - SHA1 Algorithm

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 31 December 18:00   

    



    



    

(Continued from antecedent part...)

    



    

Task 3. Advancing processing Functions. SHA1 requires 80 processing functions authentic as:

    

 

    

f(t;B,C,D) = (B AND C) OR ((NOT B) AND D) ( 0 <= t <= 19)

    

f(t;B,C,D) = B XOR C XOR D (20 <= t <= 39)

    

f(t;B,C,D) = (B AND C) OR (B AND D) OR (C AND D) (40 <= t <= 59)

    

f(t;B,C,D) = B XOR C XOR D (60 <= t <= 79)

    



    



    

Task 4. Advancing Processing Constants. SHA1 requires 80 processing connected words authentic as:

    

 

    

K(t) = 0x5A827999 ( 0 <= t <= 19)

    

K(t) = 0x6ED9EBA1 (20 <= t <= 39)

    

K(t) = 0x8F1BBCDC (40 <= t <= 59)

    

K(t) = 0xCA62C1D6 (60 <= t <= 79)

    



    



    

Task 5. Initializing Buffers. SHA1 algorithm requires 5 chat buffers with the afterward antecedent values:

    

 

    

H0 = 0x67452301

    

H1 = 0xEFCDAB89

    

H2 = 0x98BADCFE

    

H3 = 0x10325476

    

H4 = 0xC3D2E1F0

    



    



    

Task 6. Processing Bulletin in 512-bit Blocks.

    

This is the capital assignment of SHA1 algorithm, which

    

loops through the bedlam and added bulletin in blocks of 512 $.25 each. For anniversary ascribe block,

    

a amount of operations are performed. This assignment can be

    

described in the afterward bogus cipher hardly adapted from the RFC 3174 s adjustment 1:

    

 

    

Input and predefined functions:

    

M[1, 2, ..., N]: Blocks of the bedlam and added message

    

f(0;B,C,D), f(1,B,C,D), ..., f(79,B,C,D): Authentic as above

    

K(0), K(1), ..., K(79): Authentic as above

    

H0, H1, H2, H3, H4, H5: Chat buffers with antecedent values

    

Algorithm:

    

For bend on k = 1 to N

    

(W(0),W(1),...,W(15)) = M[k] /* Bisect M[k] into 16 words */

    

For t = 16 to 79 do:

    

W(t) = (W(t-3) XOR W(t-8) XOR W(t-14) XOR W(t-16)) <<< 1

    

A = H0, B = H1, C = H2, D = H3, E = H4

    

For t = 0 to 79 do:

    

Acting = A<<<5 + f(t;B,C,D) + E + W(t) + K(t)

    

E = D, D = C, C = B<<<30, B = A, A = TEMP

    

End of for loop

    

H0 = H0 + A, H1 = H1 + B, H2 = H2 + C, H3 = H3 + D, H4 = H4 + E

    

End of for loop

    



    

Output:

    

H0, H1, H2, H3, H4, H5: Chat buffers with final bulletin digest

    



    



    

Step 5. Output. The capacity in H0, H1, H2, H3, H4, H5 are alternate in arrangement

    

the bulletin digest.

    



    

SHA1 Accomplishing in Java

    



    

Sun provides SHA1 algorithm in Java beneath their JCE (Java Cryptography Extension) package,

    

which is included in JDK 1.5.

    



    

Sun s accomplishing of SHA1 can be accessed through a all-encompassing chic alleged MessageDigest.

    

Here are the capital methods of MessageDigest class:

    



        

  • getInstance("SHA1") - Allotment a bulletin abstract item represents a specific accomplishing

        

    of SHA1 algorithm from the absence provider, Sun.

        



  •     

  • getProvider() - Allotment the provider name of the accepted object.

        



  •     

  • update(bytes) - Updates the ascribe bulletin by appending a byte arrangement at the end.

        



  •     

  • digest() - Performs SHA1 algorithm on the accepted ascribe bulletin and allotment the bulletin digest

        

    as a byte array. This adjustment aswell resets the ascribe bulletin to an abandoned byte string.

        



  •     

  • reset() - Resets the ascribe bulletin to an abandoned byte string.

        



  •     



    

(Continued on next part...)

    



    



    

 


Tags: functions, requires, processing, message, blocks, defined, notes, string, tutorial, tutorials

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