My thesis is an overview about cryptography and its importance in our digitalized world. it includes details of: -A breif history about crytpgraphy and cryptosystems and how they evolved through out the years. -Information protection using some cryptographic techniques. -Cryptosystems, crytpo algorithms and their classifications. -Hashing, digital signatures and how these terms are crucial in safeguarding data. -Cryptocurrency and its relation to cryptography. -Post-quantum cryptography, and the reason of its existence.