Security 1 : Asymmetric, symmetric, hash, digital signature, email encryption

Symmetric : shared code
Asymmetric: pair key - public & private

Hash : SHA or MD5 ==> algorithm to make a data into short form, use to verify if data altered or not along the way. Example : email + hash = 010101100 (this is called fingerprint)

Digital signature ==> fingerprint + private key encryption

you sent : email + digital signature (for now we ignore the email encryption)

recipient has your pub key!
recipient also has the hash!
==> first it will hash the email and it will get the fingerprint 010101100
==> second it will decrypt the dig signature with the pub key and it will get the fingerprint
==> A. comparing the fingerprint step 1 and 2 above, if not equal then email was altered!!
B. also if the pub key failed to decrypt at step 2, then it means the private key wrong, which could means it was not sent by the real person (bcoz private key is only had by the real)

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Now, about email encryption:
the encryption is done by the pub key, and is called RSA method.

Sender has the pub key of recipient and encrypt the email with it.
Recipient will use his priv key to decrypt it.

Note : Even if someone else has recipient pub key, it does not mean he can reverse back the data. Only one who has private key can decrypt it.
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