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kryptós graphein(cryptography)
to write secrets
substitution ciphers are some of the oldest encryption techniques. most famous being the Caesar Cipher; used by Julius Caesar 2000 years ago. each letter in the plaintext message is replaced by a fixed letter x positions left or right.
the example below is using a left shift of 3.
| PLAIN | A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| CIPHER | X | Y | Z | A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W |
PLAINTEXT: SUSSY LIL BOY
CIPHERTEXT: PRPPV IFI YLV
deciphering is reserve of the previous shift.
symmetric and asymmetric are 2 types of encryption. Caesar Cipher is an example of symmetric encryption, which means the same secret key (in this case "3") encrypts and decrypts the message. where as asymmetric encryption uses a "public key" to encrypt and a related "private key" to decrypt. the public key can be freely shared and publicly known all while not comprising the encryption. example of asymmetric encryption below:
PGP (pretty good privacy) refers to programs using public key cryptography for data encryption and digital signatures. the start of PGP originated by a man named Philip R. Zimmermann in 1991. PGP was birthed as a software application as a way to encrypt files and email communications. the original program is in the grave, but numerous open-source and commercial implementations of the OpenPGP standard (revised from mr zimmermann's pgp model) are widely available.
how it works
couple things to remember is that the public key encrypts & private key decrypts. so you want to send a package to your friend that only he can open. how do you do it? first your friend needs to create a key pair. that key pair will contain a "public" and "private"
what its used for
encryption
digital signatures are used for authentication and integrity. you would then use your private key 2 encrypt. thus since the "private key" is well private, it can be assumed only that person(s) has access to it. we now have non-repudiation meaning the signer cannot deny having signed the message.