How does SHA 1

SHA - Secure Hash Algorithm (SHA-1 / SHA-2 / SHA-3)

The Secure Hash Algorithm, SHA for short, and all its versions are cryptographic hash functions. SHA was developed by the US secret service NSA on behalf of the US standardization agency NIST.
SHA was presented to the public together with the DSA signature process in 1991. Although NSA developments are always viewed with suspicion, SHA turned out to be a good cryptographic hash function.

SHA is used in all common web applications and network protocols. PGP, SSL, IPsec and S / MIME. And of course with different signature processes. For example, to sign certificates.

The original SHA is referred to as SHA-1 to distinguish it from its successors, SHA-2 and SHA-3. SHA-3 is not intended to replace SHA-2, but is an alternative. Should SHA-2 ever be broken, one can move on to SHA-3.

MD4 - Message Digest 4

MD4 was developed by RSA co-inventor Ron Rivest. Most of the cryptographic hash functions are further developments of MD4. It has some weaknesses, which is why it is not too secure and should no longer be used for cryptographic applications.

MD5 - Message Digest 5

Due to the weaknesses of MD4, Ron Rivest released a revised version called MD5 in 1991, which temporarily made it the most widely used cryptographic hash function. However, MD5 should no longer be used because it is possible to calculate collisions within a few hours even with a normal PC. But, for non-cryptographic applications, MD5 is still acceptable.

SHA-1 - Secure Hash Algorithm Version 1

SHA-1 is a further development of MD4 and was the most important cryptographic hash function in the 1990s. It was used for a long time with many encrypted connections and certificates.

SHA-1 has not been considered safe since 2004. SHA-1 is vulnerable to collision attacks. These attacks have been practicable since 2009. SHA-1 is particularly critical with SSL certificates. Theoretically, an attacker could create fake server certificates that browsers would consider valid. It is advisable to switch to a more modern hash method such as SHA-2 and SHA-3.

SHA-2 - Secure Hash Algorithm Version 2

Even before the weaknesses of SHA-1 became known, NIST standardized four new SHA versions in 2000: SHA-224, SHA-256, SHA-384 and SHA-512. The number in the name expresses the length of the hash value.
The new hash functions differ from SHA-1 not only in their length, but also in a number of functional differences.
The algorithms of the SHA-2 standard are supported on all common operating systems and can therefore replace SHA-1.
Often only SHA-256 and SHA-512 are mentioned. But there are also SHA-224 and SHA-384. This is because SHA-224 is the same process as SHA-256, with 32 bits being cut off at the end of the output. Same with SHA-384. Functionally, this is SHA-512, with the output of which 128 bits are cut off at the end.

SHA-3 - Secure Hash Algorithm Version 3

SHA-3 is based on the Keccak hashing algorithm and was specified by NIST in 2015 as the successor to SHA-2 as FIPS 202. With SHA-3-224, SHA-3-256, SHA-3-384 and SHA-3-512 there are four variants with different lengths. The functions SHAKE128 and SHAKE256 allow outputs of any length.
SHA-3 is not intended to replace SHA-2, but is an alternative. If SHA-2 should ever be broken, one can move on to SHA-3.

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