(SOA-)Security-Basics - part 2

Here comes part 2 of "digital signature, certificates and digital identities". This is about hashing.

Hashing works, but only in one direction

Cryptographic hashing means, creating a checksum out of plain text. This checksum has to offer the following attributes:

1. The method is irreversible, which means, that you cannot calculate the plain text from the checksum
2. Different plain texts may not create the same hash value (the method must be collison-free)

Hashing - an example

There is the plain text "Hello World". This plain text is now hashed with the algorithm SHA1 and encoded with BASE64 for readability:

SHA1(Hello world) = pTVD5kns67A2N4yRuZ3vROStrxM=

Because the method has to be collision-free another plain text would create another hash value.
SHA1(Hello WorlD) = IYE/IEl7riYyhCez2P3l4xn9qrE=

The irreversibility is also ensured:
SHA1(Hello world) creates: = pTVD5kns67A2N4yRuZ3vROStrxM=, but
SHA1(Hello mars, how is the weather today on the red planet?) creates: = ZAmG0snPZ5zWTWdcwYCvJdZeApY=,
which also is a 28 character hash value encoded in Base64.

So what is the advantage of hashing?

- From a plain text an ambiguous checksum is created
- Every manipulation on the plain text causes another hash value to be created

==>
Thus, for every transmission of a message, its integrity is secured!


Part 3 will follow...