1. One-way Encryption Ideal Properties
A cipher designed only to encrypt, not decrypt.
plaintext
ciphertext
encryption algorithm
also known as the
_______________or ______
Ideal Properties

2. Non-keyed One-way Ciphers
MD5
• Created by Ron Rivest (MIT)
• 128-bit digest
SHA family
• SHA-1 created by NSA , others by NSA
• 160-bit digest for SHA-1
• SHA-2 with larger digests: SHA-256, SHA-384, SHA-512
Note: In 2004 three cryptographers (Eli Biham, Rafi Chen, and Antoine Joux) discover
potential collisions in SHA-0 (and possibly SHA-1). MD5 is also considered somewhat vulnerable.

3. How To Use for Passwords?
User Selects New Password
password
digest
encryption algorithm
store in password file
User Enters Password (in response to challenge)
password
digest
encryption algorithm
compared to digest
from password file

4. ...in Java
Four Steps
Instantiate a java.security.MessageDigest object.
(This is done by calling a static method named getInstance).
2) Fill a byte array from plaintext to be hashed.
3) Call update on the object, passing the byte array.
4) Call digest to retrieve the hash value (as a byte array).
MessageDigest md = MessageDigest.getInstance(“SHA-256”);
byte[] buffer = someMethodToReturnPlaintext();
md.update(buffer);
Note: This can be called as many times as necessary.
byte[] digest = md.digest();