	MCSoft Security Solutions

Product Overview

Software

MCCrypt Pro

Ciphermodes

MCSoft MCCrypt Pro

Blockcipher operational modes

Block Cipher are transforming a defined block length of data into another defined block length under the use of a cryptographic function. This function is controlled by a key given by the user. The n-Bit input block of data is projected through an one-to-one transformation of n-Bit integer's onto a permutation of n-Bit integer's to a n-Bit output block. How the cipher is applied on these blocks will define through the block cipher operational modes. In the simplest case, like in the ECB mode, every block will be encrypted independently without additional functions (Whitening). This has the big disadvantage, that if the same block of data is encrypted twice by using the same key, it will produce also in both cases the same output data block. This would be an very useful information for the attacker of a Cipher. That's the reason for developing other differently secure operational modes.

ECB - Electronic Codebook

Every Block is treated independently.
Does not hide patterns or Plaintext repetitions
Error propagation: expansion within 1 block
Limited number of applications

CBC - Cipher Block Chaining

Ciphertext depends on all previous plaintext blocks
Hides patterns and Plaintext repetitions
Error propagation: expansion in 1 block, copied into next block
Standard Mode for Blockcipher before the AES Selection Process

OFB - Output Feed Back

Synchronous Stream Cipher
No linking between subsequent blocks
No error propagation: errors are only copied

CFB - Cyphertext Feed Back

Self-synchronizing Stream Cipher
Ciphertext depends on all previous plaintext blocks
Error propagation: error copied and propagated over 1 block

CTR - Counter Mode

Every Block is treated independently
Hides patterns and Plaintext repetitions
Error propagation: expansion within 1 block
Mode allows Random Data Access
Security is comparable with CBC-Mode

CCM - Counter Mode with CBC-MAC

Every Block is treated independently
Hides patterns and Plaintext repetitions
Error propagation: expansion within 1 block
Mode allows Random Data Access
Mode includes efficient authenticated encryption
Security is comparable with OCB-Mode
New, for AES developed standard Mode

OCB - Offset Code Book

Developed by Phillip Rogaway, Mihir Bellare, John Black, Ted Krovetz
Every Block is treated independently
Hides patterns and Plaintext repetitions
Error propagation: expansion within 1 block
Mode includes efficient authenticated encryption
Most secure mode: If this method is broken, then the algorithm is broken
New, for AES developed mode, but it is patented

COA - Counter with Offsetcode Authenticated Encryption Mode

Every Block is treated independently
Hides patterns and Plaintext repetitions
Error propagation: expansion within 1 block
Mode allows Random Data Access
Mode includes efficient authenticated encryption
Security is conform with OCB-Mode
Tweakable Mode
New, for AES developed Modus