Crypto constants

[tarakby]

• declare new cryptographic constants related to sha3 and the supported elliptic curves.
• use the cryptographic constants to replace magic numbers

The purpose is:

• clarify the intention of using magic numbers (especially when the same constant 32 is used multiple times, but it has a different meaning depending on the context)
• make the code base more robust if more hashing algorithms or elliptic curves are used in the future