SHA-1 in Cryptography - Computer Science Knowledge

SHA-1 or Secure Hash Algorithm 1 is a cryptographic hash function which takes an input and produces a 160-bit (20-byte) hash value. It was designed by the National Security Agency (NSA). It is currently a Federal Information Processing Standard. SHA-1 is now considered insecure since 2005. SHA-1 shouldn’t be used for digital signatures or certificates anymore. Theoretically broken since 2005, it was formally deprecated by the National Institute of Standards and Technology (NIST) in 2011. In 2017, SHA-1 was officially broken by Google’s academics, who managed to produce two files with the same hash.

SHA1 is relatable to MD5 as it is based on MD5. Like MD5, SHA-l processes input data in 512-bit blocks.SHA-l generates a 160-bit message digest. Whereas MD5 generated message digest of 128 bits.

Working of SHA-1:

As we know that SHA1 is modelled after MD5 and most of its steps resemble MD5. So, here we will explain the SHA1 steps briefly.

Step 1: Append Padding Bits….

This step adds the padding to the end of the genuine message in such a manner that the length of the message is 64 bits less of the multiple of 512. Padding is continually inserted although the message already has the desired length. Padding includes a single 1 followed by the essential number of 0 bits.

Step 2: Append Length….

64 bits are appended to the end of the padded message. These bits hold the binary format of 64 bits indicating the length of the original message. The complete message’s length is a multiple of 512.

Step 3: Initialize the buffer…

The buffer includes five (5) registers of 32 bits each indicated by A, B, C, D, and E. This 160-bit buffer can be used to influence temporary and final outcomes of the compression function. These five registers are initialized to the following 32-bit integers (in hexadecimal notation).

A = 67 45 23 01

B = ef cd ab 89

C = 98 ba dc fe

D = 10 32 54 76

E = c3 d2 e1 f0

The registers A, B, C, and D are actually the same as the four registers used in MD5 algorithm.

Step 4: Process message in 512-bit blocks…

The compression function is divided into 20 sequential steps includes four rounds of processing where each round is made up of 20 steps.

The four rounds are structurally same as one another with the only difference that each round need a different Boolean function, which it can define as f1, f2, f3, f4 and one of four multiple additive constants K[i] (0 ≤i ≤79) which is based on the step under consideration.

After processing the final 512-bit message block t (considering that the message is divided into t 512-bit blocks), and it can obtain a 160-bit message digest.

However, in SHA1 there are four rounds and each round consist of 20 steps where each round takes the current 512-bit block, the register abcde and constant K[i] (where i=0 to 79) as the three inputs.

Difference between MD5 and SHA1

The MD5 and SHA1 are the hashing algorithms where MD5 is better than SHA in terms of speed. However, SHA1 is more secure as compared to MD5. The concept behind these hashing algorithms is that these are used to generate a unique digital fingerprint of data or message which is known as a hash or digest.

BASIS FOR COMPARISON	MD5	SHA1
Stands for	Message Digest5	Secure Hash Algorithm
Length of Message Digest	128 bits	160 bits
Discerning of original message would require	2¹²⁸ operations	2¹⁶⁰ operations
For finding two messages generating the same message digest	2⁶⁴ operations would be needed	2⁸⁰ operations are required
Security	Poor	Moderate
Speed	Fast	Slow