img source - https://www.talend.com/blog/2016/07/19/practical-cryptography-with-apache-cxf-jose/

Nowdays

 Cryptography is very popular now  however, unfortunately  not everyone is using it. Every day we hear about data leaks or identity theft  caused by insufficient security. 

 Cryptography should be treated as a safe that we keep at home and we hide in it the most valuable things,  without it our stuff can be stolen by anyone who has access to our home. The same happens ithout encryption, our security may be  compromised by anyone who has access to the data.

  Thanks to the cryptography our bitcoins are safe but let's get back to the beginning :)

Steganography

 The name steganography comes from greek words steganos - covered and  graphein - write.  This is a method of hiding content in messages that are not secret( Everyone sees the same content but the person who knows the used  method can read the hidden message).  

 One of the best known steganographic methods is the use of invisible ink  that you can produce yourself by simply squeezing the lemon juice and using it for writing.  More complex steganography methods are invented all the time such as LTC SegWit riddle.

Cryptography  

 The name  cryptography also comes from greek words kryptos - hidden and graphein - write.  Unlike steganography, cryptography is used to hide the message, but not the fact that it exists.

  The first cryptographic methods were substituting methods.  An example of this would be the most famous ancient cipher algorithm - Caesar cipher.  In the Caesar's cipher each letter is replaced by  a letter some fixed number of positions down the alphabet.  For example, the word Caesar transforms into Fdhvdu(shift left - 3 letters)  to decrypt this message, reverse the process.

  Such a cipher has one main disadvantage. Anyone who knows the constant shift number will see how to decipher the message. To make it safer the number should be periodically changed.  However, such changes are a problem for the addressee because he would have to knowa valid "shift nuber" as well.  

 This problem is known in cryptography as a key distribution problem and it was solved in 1976 with the Whitfield Diffie  invention - asymmetric cryptography also known as public key cryptography,  which relies on the so-called one-way function.  

 The result of this function is difficult to reverse,  we can compare this to the mixing of colors. It is easy to mix colors  but it is hard to extract basic colors from mixed color.

  Bitcoin uses public key cryptography, in a nutshell, a bitcoin address is a public key(not exactly). When someone wants to send bitcoins on some address he states "I give my bitcoins to the person who knows private key corresponding to this address".

  If you want to know more about cryptography, check out this website https://www.khanacademy.org/computing/computer-science/cryptography