Transactions (Tx)
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• Cryptography also helps one more puzzle – authenticity. 
• To be part of the bitcoin network all you need is access to internet. Every user in the network is identified by a string of characters, known as the bitcoin address.
• To transact with someone in bitcoins you need to know their bitcoin address (i.e. email).
• Your bitcoin address is derived from a public key which is derived from a private key. Private key should be kept secret like your password to an email