**Cryptography Tutorials - Herong's Tutorial Examples** - Version 5.40, by Dr. Herong Yang

What is OFB (Output FeedBack) Operation Mode?

This section describes what is OFB (Output FeedBack) Operation Mode - each plaintext block is XORed with the current output block to be the ciphertext block. The current output block is the encrypted version of the previous output block.

OFB (Output FeedBack) operation mode can be described with notations defined earlier as the following formula and diagram:

C[i] = P[i] XOR O[i] O[i] = Ek(O[i-1]) O[1] = E(IV) IV | -----| -----| Ek() / Ek() / Ek() |--O[1] |--O[2] |--O[3] | | | P[1]--XOR P[2]--XOR P[3]--XOR | | | C[1] C[2] C[3]

As you can see from the formula and the diagram, in OFB mode, each block of plaintext is XORed with the current output block to generate the current ciphertext block. The current output block is obtained by applying the encryption process on the previous output block. Note that for the first block, the Initial Vector (IV) is used as the previous output block.

Table of Contents

Introduction to AES (Advanced Encryption Standard)

DES Algorithm - Illustrated with Java Programs

DES Algorithm Java Implementation

DES Algorithm - Java Implementation in JDK JCE

►DES Encryption Operation Modes

DES Encryption Operation Mode Introduction

What is ECB (Electronic CodeBook) Operation Mode?

What is CBC (Cipher Block Chaining) Operation Mode?

What is CFB (Cipher FeedBack) Operation Mode?

►What is OFB (Output FeedBack) Operation Mode?

JCE DES Operation Mode Testing Program

JCE DES Operation Mode Testing Program Result

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"