**Cryptography Tutorials - Herong's Tutorial Examples** - Version 5.35, by Dr. Herong Yang

What Is Block Cipher?

This section describes what is block cipher - An encryption scheme in which 'the clear text is broken up into blocks of fixed length, and encrypted one block at a time'.

**Block Cipher** - An encryption scheme in which "the clear text is broken up into blocks
of fixed length, and encrypted one block at a time".

Usually, a block cipher encrypts a block of clear text into a block of cipher text of the same length. In this case, a block cipher can be viewed as a simple substitute cipher with character size equal to the block size.

**ECB Operation Mode** - Blocks of clear text are encrypted independently.
ECB stands for Electronic Code Book. Main properties of this mode:

- Identical clear text blocks are encrypted to identical cipher text blocks.
- Re-ordering clear text blocks results in re-ordering cipher text blocks.
- An encryption error affects only the block where it occurs.

**CBC Operation Mode** - The previous cipher text block is XORed with
the clear text block before applying the encryption mapping. Main properties of
this mode:

- An encryption error affects only the block where is occurs and one next block.

**Product Cipher** - An encryption scheme that "uses multiple ciphers
in which the cipher text of one cipher is used as the clear text of
the next cipher". Usually, substitution ciphers and transposition ciphers are used
alternatively to construct a product cipher.

**Iterated Block Cipher** - A block cipher that "iterates a fixed number of times
of another block cipher, called round function, with a different key, called round key,
for each iteration".

**Feistel Cipher** - An iterate block cipher that uses the following algorithm:

Input: T: 2t bits of clear text k1, k2, ..., kr: r round keys f: a block cipher with bock size of t Output: C: 2t bits of cipher text Algorithm: (L0, R0) = T, dividing T in two t-bit parts (L1, R1) = (R0, L0 ^ f(R0, k1)) (L2, R2) = (R1, L1 ^ f(R1, k2)) ...... C = (Rr, Lr), swapping the two parts

^ is the XOR operation.

**DES Cipher** - A 16-round Feistel cipher with block size of 64 bits.
DES stands for Data Encryption Standard.

Table of Contents

Introduction to AES (Advanced Encryption Standard)

►Introduction to DES Algorithm

DES (Data Encryption Standard) Cipher Algorithm

DES Key Schedule (Round Keys Generation) Algorithm

DES Algorithm - Illustrated with Java Programs

DES Algorithm Java Implementation

DES Algorithm - Java Implementation in JDK JCE

DES Encryption Operation Modes

PHP Implementation of DES - mcrypt

Blowfish - 8-Byte Block Cipher

Secret Key Generation and Management

Cipher - Secret Key Encryption and Decryption

RSA Implementation using java.math.BigInteger Class

Introduction of DSA (Digital Signature Algorithm)

Java Default Implementation of DSA

Private key and Public Key Pair Generation

PKCS#8/X.509 Private/Public Encoding Standards

Cipher - Public Key Encryption and Decryption

OpenSSL Introduction and Installation

OpenSSL Generating and Managing RSA Keys

OpenSSL Generating and Signing CSR

OpenSSL Validating Certificate Path

"keytool" and "keystore" from JDK

"OpenSSL" Signing CSR Generated by "keytool"

Migrating Keys from "keystore" to "OpenSSL" Key Files

Certificate X.509 Standard and DER/PEM Formats

Migrating Keys from "OpenSSL" Key Files to "keystore"

Using Certificates in IE (Internet Explorer)