Caesar

Shift (Caesar) Cipher Key9

Fischers Fritz fischt frische Fische

orblqnaj oarci orblqc oarblqn orblqn

Security for simple substitution ciphers:

According to the unicity distance of English, 27.6 letters of ciphertext are required to crack a mixed alphabet simple substitution. In practice, typically about 50 letters are needed, although some messages can be broken with fewer if unusual patterns are found. In other cases, the plaintext can be contrived to have a nearly flat frequency distribution, and much longer plaintexts will then be required by the user.

Source:http://en.wikipedia.org/wiki/Substitution_cipher

More information about cryptography you can get here:
https://www.khanacademy.org/computing/computer-science/cryptography